t he
uni vers i ty of cuh i cag o
30
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av
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T H E S T R U C T U R E A N D D E V E LO P M E N T O F
T H E N E P H R I D I A 0F A R E N I C O LA
C R I ST AT A S T I M P S O N
A
S U BM I
TT ED TO
D
IS S E R T
AT
IO N
T
O G DE N G R A D U A T E
S C I E N C E I N C A N D I D A C Y F O R T H E DE G R E E O F
D O C TO R O F P H I L O S O P H Y
T H E
F AC U L
(D E
Y O F T H E
PART M E N T
O F
BY
zo é L o c v
“
.
A
RAL PH
"
f
IL LIE
“
C H IC A G O
I
0
9 5
)
SC H
OO
L
“
I
O
u
i
ngen
i
t
h
e
l
M
t
(
a
.
d
z ool og i s ch e n
.
S ta ti on
z
uN
e apel
.
1 7 Bd
.
3
.
.
H e ft
.
ct
ure and D e ve l opme nt of the N e phri di a
T he S tru
i mpson
at
a St
of A re ni col a cri st
.
By
R
W i th
S
al ph
L illie
an d
P l a te s
1
.
I
.
nt
rod
.
—
on e
uctory
T
e x tfi g
ure
.
.
nep hri d ia ofA rm i cola were first suggeste d to me as a su b
j ce t of anato mical a n d em b ry ological investigation b y D r C O
W H I T M A N d uring the season of 1 8 9 6 at the Marine B iologi cal Lab o
T he work then beg un was sub seq uentl y
o ry
ra t
of W oo d s H ole
i n t e rrupt e d for a time ; and the greater part of th e w ork d escribe d
—
in the follo win g pap e r w a s completed d uri n g the y ears 1 8 9 8 1 901
Biolo g ical Laborator y a n d in the H ull Z o ologic a l
a t the Marine
Lab oratory of the U nivers ity of C hicago
I tak e pleasure in expressi n g my b est than k s to D r WH I T M A N
for h i s continued interest a n d c ri ticism My thanks are al s o d u
e to
D r C M C H I L D of th e U n iv e rsity of C hicago for much help fu
l
in formation especiall y with reference to the early development ; a nd
to m y brother Pro fessor F R L I L L I E of the same U niversity for
co n s tan t a n d valuable a ssistance
T he nephri d ia of s eve ral species of the genus A ren icola h a ve
b een at various time s fi g ured and brie fly d escri b e d in systematic or
anatomical treati s es ; a n d in several instances have b een ma d e th e
su bj ect ofs p ecial investigation C L A P A R E D E ( 1 8 6 8 ) a n d F A U V E L ( 1 8 99)
have given b rie f d escriptions of the nephri d ia of A Grubci a n d
A eca u
a re s pectivel y
The great e r number of such studies h ave
da t
b e e n ma d e on A m a ri na ; inve s tigations on the nephri d ia of t hi s
C U N N I N GH AM
form have b e e n ma d e by C O S M O V I C I
and more recentl y b x; G mxxxx x &
BE N I I A M ( 1 89 1
KYL E
T he
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R a lp h
342
s
.
L i ll i e
who in their two important pap e rs o n the
anatomy a n d affinities of the A re n i col i d a e have ad d ed m a t e ri a lly to
our knowle d ge of these organs The secon d paper of the s e a utho rs
s
1
9
0
contain
a
comparat
i
ve
account
the
anatomy
r
e
ti
n
0
o
f
l
a
o
s
(
)
and vascular suppl y of the nephri d ia of five species of th e g e n
at
a S timpson , A
vi z :
A m a ri n a Linn A cris t
C lap a red ci L e v i n s e n
A Gm bzi C l a p a rcd e a n d A eca u
a Johnston ;
da t
the auth or s h a ve
also given a summary of our present knowledge of th e a n a tomv
and histology of the adult nephri d ia and have added a bri e f a c c ou nt
of the con d ition of the organs in earlier developmental s ta e s
o
s
g
fa r a s this has as yet been ascertained
r knowledge ofthe larval d evelopment ofA ren i cola h a s h o w e
Ou
,
ve r until recentl y b een too limited to admit of a detailed s t u
d y of
the mo d e of origin of the nephridia a n d of the condition o f these
or g ans at d i fferent periods in the li fe history B E N I I A M ( 1 8 9 3 ) a nd
G AM B L E
1 900) have contri b uted a fe w ob s e r
A S I I W O R I I I ( 1 8 98
vat
i on s on the nephridia of certain post l a rval s tages
Thei r ob s e r
va t
i on s were m a d e on relati v ely fe w specimens which in a l l c ases
were well a d vance d in d evelopment A ccor d ingly w e hav e h a d as
yet no detailed account of the o rigin growth a n d histologic a l d i fi e
re n t
i a ti on ofthe nephri d ia in A rm i cola O n e reason for this de fi ci e n cy
s eems hitherto to have been the d i ffi culty of obtaini n g th e m a te ri a l
I n my own s t udies , however ins tea d o f
for such an investigation
d epen d ing upon the slow a n d precarious method s of di ggi n g a n d
tow net coll e ctin g I ha ve found it more practicable to re a r th e
larvae artificial l y ; in this manner it has b een found poss i b l e to
s e cure all the m aterial necessary for a detaile d examination of th e
larval d evelopment from the ea rl y free swim mi ng period up to a
stage at which the a d ult characteristic s are es s entiall y comp l e te
The a i m of the pre s ent stud y has b een to co mplete so fa r a s
possi b le our knowledge of the origin a n d histological d i ffer e nti a ti on
o what extent the peculi a r i t
of the nephri d ia and to d etermine t
ies
gh the con d i ti o n s
of the adult nephridium gain an explanation thro u
The relatio n s of the nephri d ia to the b od y
of lar val development
segmentation and to the septa and the m anner of developm e n t o f
the d i fferent portions ofthe organ
nephrosto me glandular p o rti o n
or by di fferenti a tion fr o m
a n d terminal vesicle ( whether separatel y
matters that have rec e i v e d
a single embryonic rudiment )
a re
e s pecial attention
There has also been added a bri e f acc o u n t
of the
anatomy and histolo g y of the adult nephri d ium dr a w
ASHWOR T II
1
9
8
8
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-
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,
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,
,
,
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,
S tructure
.
a nd
D e ve l op me nt of th e N e p h ri d i a
especi a l attention to a fe w peculiarities that
pparently escaped observation
n ng
a
343
.
h a ve
hithert o
.
2
.
T e ch n i qu
e
.
The a d ult nephridia are best prepare d for histological s tudy b y
id for 1 5 to 3 0 min utes and then trans
fi xing in H E R M A N N S fl u
fe rring im me d iately to M E RKE L S flui d ( WH I T M A N S mo d ification with
s 1 % chro mic acid a n d
platinic chloride ), where they
e qual p a rt
or one to thre e hour s
They are then wa s hed
a re allo we d to remain f
The treat
i n distille d water and trans ferre d to a lcohol as usual
m e n t with M E R K E L s flui d prevents excessive blacke n ing ; the fixation
l and the cilia are well pres e rv e d The
i s apparentl y v ery fai th fu
m
u
m
in
thickness
T
he
reduced
os
iu
ma
y
be
s ections were mo s tly
,
urther removed from the sections by leavin g the sli d es over
s till f
re of alcohol and hy d rogen peroxi d e ( us uall y com
n ight in a mixt u
po s e d of about one par t commercial H 2 02 to three parts strong a l
co hol mixed imm ediately be fore u s ing) The ti s s ue s are by this
t re atment almost entirely free d of the osmium and le ft in a suitabl e
co n d itio n f
The most s a ti s factory stain wa s foun d to be
or staining
H E I D E N T TA I N S iron hae matoxylin with a counter stain of erythrosin
F or s tudy with oi l immersi on o bj ectives the best m oun ti n g me d i um
p rove d to be thicken e d ce d ar—
oil ( immersion oil ) This m e d i um har
d ens slowly but has the a d va n tage of pro d uci n g a p e r fectly homo
n
u
e
e
o
a
n
s
d
s
f
r
tran
parent
lacquer
at
permanence
and
o
almost
o
f
e
g
g
the same re fractive in d ex a s that of th e oil in which the lens is
im mersed V ery clear and sharp images are thus obtained with the
highest powers
’
,
i
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’
,
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’
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,
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’
-
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,
-
,
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.
T he larvae were fi xed by a great variety of methods of which
only a fe w proved satis factory Treatment with 1 % osmic aci d for
—
2 to 5 minutes
followed by M E R KE L s fluid for 1
3 hours gave
fair preparations in ma n y instanc e s
T he b est fi xat i ve for general
—
purposes prove d to b e H E R M A N N S fluid ( 2 5 mi n ute s ) , followe d by
M E R K E L s fluid ( 1 —3 hours )
In mo s t in s tanc e s there fore the lar
w
fi
vae ere xed by the H E R M A N N M E R K E L m e tho d , a n d th e s ections
m
u
o
s
tly
5
in thickness ) w ere s tained chi e fly with iron haematoxylin
(
e
r
m
s
i
d
and ythro in as ab ove descri b e d and ou n ted n ce ar oil V e ry
clear a n d sharply d i f
fe rentiate d preparations w ere thus obtai n e d
The ti s sues were rem a rk a bly w ell pre ser ve d delicate structures
l it
a d 2 1 S tati u N ap l B d 1 7
th il ug
Th
,
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’
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’
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,
o
n
en
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00
.
on z
e
e
.
.
.
Ra l p h
344
S
.
L i ll i e
s uch as cilia retaining in favo rable preparations , almost th e n orm:
appearance
Young larvae of the s warming s tage were best pr e p ar e d b
fixati on in H E R M A N N s fluid for two minutes fo l lowed by M E R K E L s fl u
i
for one hour I t is nece s sary to im b e d s u
ch l a rvae as soon a s p o s s ihl
a fter fixation ; otherwise the y olk b ecom e s s o brittle a s to re n d er
practically impossi b le to secure unbroken sections I fimb e d d e d an
ou
t imme d iately a fter fi xation no s uch d i fficulty is expe ri e n c e d
T he succeedin g d escriptions are b ased upon the e xam i n a ti on 1
a very large num b er of preparations a n d a ll possibility o f d e cel
tion arising fro m imperfect prepara tions , abnormalities of s tructure i
indi vi d ual larvae or failure to observe critical stages h a s it
hoped b een avoided
,
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=
’
’
,
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:
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,
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,
,
,
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,
3
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,
u
Ge n e ra l
a cco n t of
th e l a rva l D
h
e ve l op m e n t wi t
R e fe re n ce to S e g me n ta l S tru
ct
ure s
A rem cola
E
s p e ci d
.
S ti mp s on the species upon which th e e n til
follo wing study has been ma d e is foun d in several localiti e s i n ti
neigh b orhoo d of Wood s H ole
most a b undantly at N orth F a
mouth where the extensi v e sa nd fl a ts furnish i d eal con d it i o n s f
its development The animal s are fou n d b urrowing at a de p th of
to 1 8 i n ches in the sand which is deepl y sat urate d with d e ca y i i
or g anic matter ; and in the s umme r m onths are in nearly a l l i :
—
stances well develope d and of large size ( 6 1 2 inch e s i n l e n g tl
For the larval stages it has pro ved neces s ary to rel y up o n ma te n z
reared in the l a b oratory for it has b een foun d impo s s i b le i n an
other way to obtain the requisite quan tity of yo un g larva e I h a
frequently s earched the san d with a lens in the hop e o f fi n d i l
youn g A re n i col a e but alway s witho ut s ucces s ; the larvae h ow e vc
le n d themselves so readil y to ar tificial r e ari n g that n o d i ffi c ul ty h
been experie n ce d in s ecuring in this manner an ab un d anc e of 8 13 6 1
mens of all stages
The ge n eral characteristics ofthe ad ult A cri s ta ta are su ffi c i e n t
known from the de s criptions ofS T I M P S O N V E R R I L L G A M B L E
As
The y o ung free swimming larv ae have b e
W O RT H , and others
b rie fl y d e s cri b e d b y WI L S O N ( Johns H opkins S tud ies 1 8 8 3 ) an d 0 11 1 1
1
Z
B
a
m
u
l
V
ol
I
n
the
pre
ent
paper
I
sh
ll
ive
e
ly
l
s
r
e
(
g
short account of the general charac teri s tic s of the larval s ta g e
omitting details that do not immediatel y b ear on the problem s a n d
'
at
a,
cri s t
,
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-
t
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,
S tructure
mco n s ideration
an d
D e ve l o p me n t of th e N e p h ri d i a
3 45
.
has given an a cc urate acco unt of the
My own descriptions
e a rl y development within the egg membrane
e w i l l have re f
erence to the metamorphosis and larval development
S u
h
a ra ct
c
e
m
to
a
period
at
w
ich
ost
the
definitive
external
o
f
h
p
S ri s t
i cs are complete
"
f
V ery little care is nee d ed in order to pres erve the l a r v a e for
fi w e e k s or even months in a healthy condition
and cap able of
a g rowth and d evelopment Th e egg strin g s are placed in clean s e a
i i w a te r in large flat well lighted di shes covere d by s heets of glass
i to pre v ent excess of evaporation , and contain i n g a fe w pieces of
u U l va for aeration I tis advisable to change the s e a water at inter
v als of a w eek or ten day s ; otherwise the dishes require very little
The organic debris p resent d erived from minute A lgae
a ttenti on
particle s of decay ing U lva and the bodies of dead lar vae seem to
ffi cient food for the de velopment of a
fur n ish the lar vae wi th s u
fairl y large proportion of their n umber
U nder these con d itions
l a rvae ha v e been kept in the laboratory for perio d s of 1 4 to 1 5
8 : w eeks
apparently in a perfectly he althy condition and exhibiting
a l l the normal activities
D e velopment seems however , to progress
m ore s lowl y than under the natural conditions for the largest speci
m e n s re are d never exceed e d a length of 1 5 mm , a lthough e xhi b iti n g
in other re s p e cts an a lmost per fect agre e me n t with the a d ult in
a ppearance , a n atomic a l structure
and
behavior
The
oo
d
suppl
y
is
f
,
i n all probability in s ufficient for rapi d gro wth ; this is indicated b y
f
a
i
f
the ct that
kept in s e a water to which carmine powder has
b een a d ded the larvae usually exhibit a grea tly increased rate of
r
I t would no d ou b t be pos
g owth especially in the early s tages
si ble , by th e employment of s uita ble methods of feeding to rear
them to more a d vanced stages than the abo v e
The l a r v a e lea ve the egg strings in from two to three day s after
o viposition i n the form of slightly elongated m a ggot like free swim
ming organisms ( about
mm in le n gth ) which exhibit a mo s t
v
ronounced
positi
e phototaxi s combined with n egative geotaxis A s
p
a result of the s e ten d encies they swi m rapidly to the ligh t s ide of
the dish and there gather in enormous num b ers at the s urface of
the water A t thi s stage a lar va pos s esses in a d d ition to the peri
stomium ( which is without setae ) three setigero us trunk s o mites in
each of which are two paire d sets of setae corre s ponding to the
notopo d ial and neu ropo d ial s etae of the a d ult The notopo d ial setae
o f each si d e are generall y two in number
spoon shaped a n d s pear
C H IL D
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1
9
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0
(
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R a l p h S L i ll i e
34 6
.
shape d respectively and are elongate d a n d alrea d y capab le o f a
very consi d era ble degree of protrusion and retraction The n e uro
podial setae consi s t ofa single s hort b ook on each si d e of the v e n
tral sur face of each s eti g erou s somite A s growth procee d s a d d iti o n al
hooke d setae appear ventrally to those already lai d down ; a t th e
swarming stag e ho w ever a s ingle hook only is as a r ule pr e s e nt
on either si d e in each s omite I n the third s etigerous somite t he
setae in the maj ority of larvae are as yet incompletely forme d ; a s
elongation proceeds , howe ver they enlarge and acquire th e s a m e
characteri stics as those of the pr e ce d ing somite Locomotion in th e
swar ming stage is e ffecte d by means of the two ciliary ring s pro to
troch a n d p a ra troch ; these a re connecte d by a median ventral b a n d
The conti nued activity of the cilia p ro
outer cili a
of shorter a n d s t
pel s the larvae at a uni form rate in a forward d irection tow a rd
"
—
the source of light O n the prostomi um are tw o s imple ey e S p o t s
each of which consists of a c omp a ct cl ump of p i g ment or excre to ry
granules on the s urface of th e b rain Larg e clear c e ll s appare n tl y
re oc cupy a large portion of the prostomi um
of a glandular nat u
ound at the posterior extre m it y
a n d similar b ut s m a ller cells are f
These cel l s pro b a bl y furnish in p a rt at least the g l uti
ofthe b o d y
nous material by the aid of which the larvae later form the ro ug h
tubes in which they live su b sequentl y to the termination of t he
swarming perio d I n fixe d and staine d preparations the cells h a v e
a clear and reticulate appearance ( F igs 7 and 8 , Plate
th e y
d i mini s h a n d d i sappear shortly a fter the b eginn ing of the cra wl i n g
a n d b urro wing per i od
The swarming s tage apparen tly serves simply for the d i s s e mi
nation of the individuals ofthe n e w generation , and differentiation o f
internal organs remains very incomplete until after its terminatio n
T he i n t e s ti n e at this perio d still con s ists largely of yolk and i ts
lumen is as y et very incompletel y for me d Ther e i s howe ver a
partial s ub d ivision into o esophagus s tomach and rectum
a s ub
division which becomes well d efin e d shortly a fter the b eginn i n g o f
the crawling stage and persists thro ug h part of th e larval peri o d
and into adult li fe Mouth a n d anus have not y et appeared ; th e
anterior part of the intesti ne however wh i ch later forms an e v er
sible prob oscis exhibits alrea d y a relatively high d egree of d i ffe
a peculiarity in evi d ent correspon d en ce wit h
i a ti on ( Fig 7 )
re n t
the early appearance of i ts activity a n d the important par t whic h
it plays in larva l li fe T he b r a i n oesophageal ring a n d ventral
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Structure
an d
D e vel op me nt of th e Ne p h ri d i a
34 7
.
ner ve cord are continuous with one a nother and are well define d
in the ectoderm of the anterior region of the bo d y Posteri orly the
ventral cord is less distinctly delimited fro m the rest of the ecto
derm , passing gradually into the un d i fferentiated tissue ofthe growing
—
zone Nu mero us longitudinal m u s c l e fi b r e s are cl osel y applied to
the inner surface of the body wall , a n d fibres derive d fro m this
—
layer are a l re a d v attached to the inner ends of the seta sacs No
circular fibres however have as yet appeared ; these arise later
in development and apparently in an entirely di fferent manner
from the lon g itu d inal fibrils i e the y appear in the e ctoder m while
ric ( see below)
th e longitu d inal fi b res are s omatople u
The free swi mming stage l a sts for a perio d who s e exact dura
tion in the ca s e of an individual larva is d i fficult ofdetermination
but i s p roba b l y from one to two d ays at normal summer temperat ure
A t its clo s e the larvae u n dergo the chan g e which has been des
c ri b e d as a m e t a m o r p h o s i s ;
they lose th eir cilia s ink to the
b ottom a n d a d opt a crawling and b ur rowi ng and partiall y tub i cul ous
mode of li fe which lasts for the remain d er of thei r exi s tenc e This
change takes place at about the time of f
ormation of the fourth
setigerous somite The larva represente d i n longitudinal section i n
fi gu
re 8 ( Pl a te
is undergoing the t rans formation ; it h a s alrea d y
l os t mos t of its cilia ; the mouth O peni n g has broken through and
the procto d ae um is i n process of formation ; the int estinal v olk is
e vidently undergoing a b sorption
and the l umen h a s b ecome mo re
di s tinct
T he intestinal lumen quickl y become s spacious and continuous
fro m end to end of the body ; and in larva e of 6 or 7 somites the
r
olk
has
la
gely disapp e ared a n d the intestine ha s begun its func
y
ti ona l activit y The probosci s b i ts continual eversion and retraction
,
y
fills the inte s tine with the surroun d ing d ébris , playing at the s ame
ti me an important part as a burro wing organ , in which form of
a ctivity it i s assisted by the action of the setae and the mu s cl e s of
the body wall From now on , the ha bits remain uni form a n d seem
in all essential respects identica l with those of the adult A ren i cola
T he material introduced by the proboscis i n to the inte s tine is pa s s ed
thro ugh the latter , and the containe d organic matter furnishe s the
s ole foo d s upply of the developing lar vae
With the assumption of the definiti ve li fe ha b its is a s sociat e d a
change i n the reac t
io n s towar d s light a n d toward s the contact of
s olid b odie s
The larvae become n e g a t i v e l y heliotro p ic exhi b iti n g
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R a l p h S L i ll i e
34 8
.
a marked tendency to become oriente d with the anterior e n d d i r c e
ted away from the source of illu mination and thus eventu a ll y , a t
a result of the continued crawling movements to gather in r e g i o n s
remote from the source of light The other marke d pecul i a rity
whi ch now first makes i ts a ppearance is a tendency to bri n g a s
large a portion a s po s si b le of the body sur face into contact w i tl
solid b odies ( positi ve stereotropism or thigmotaxis) Lar vae fr e e d
from adhering soli d particle s , a n d placed in a v e s sel cont a i n in g
loose finely divi d e d d ébris of an y kind inv a riably exhi b it re s tl e s :
squir ming a n d crawling move me n ts which continue until th e b o dy
is once more in contact on all sides with soli d particles W h e r
these particles consist of loose s an d grains diatom shells or s i m i lar
ligh t fi n e l y divi d e d material the result is that the ani mal s o o n b e
comes enclosed i n a rough t u b e fo rme d by the adhesion of s ucl
particles to one a n other a nd to the b o d y surfac e by mean s o f th e
abundant secretion furnished by the ecto d er mal glan d s I n th e
manner are forme d the rough tubes in which the remain d er o f th e
larval period is passed When the larva is freed from such a tube
the re s tless squirming movements are resume d , and continu e u n til
anothe r tube has b een forme d Ten d encie s such a s these whe n com
b i n e d with the characteristic negative heliotropism , will un d e r n at
u
ral con d itions plainly favor burrowing mo v ements of the kin d o b s e r
B oth forms of reaction apparently persist until adult li fe , a n d
ve d
through them the characteristic behavior of the ani mal is l a rg e l y
determined
A fter the close of the swarmi n g perio d a n d th e assumpti on 0 1
the burrowing hab it of li fe growth a n d elongation proceed ste a di l y
and uni forml y until the full number of somites have be e n for me d
E lo n gation i s due as in othe r A nnelid a to the acti vity of a p os te
rior growing z one which occupies a position imme d iately anter i o
—
to the original s i tua ti on ofthe p a ra troch ( Figs 7 1 0 Plates 2 2 a n d 2 3
—
2 9 3 3 Plates 2 3 and
The large clear meso d ermal and e cto d e r
mal cells of th i s region contain large n ucleolate d nuclei frequ e n tl y
foun d in process of mitosis , and continuall y give rise anteriorl y t(
new cells which con s titute the ba s is of the ne wly forming somit e s
A s each somite appears it is d i vided of
f fro m the on e next succ e e d
ing by a mesodermal s eptum ; the growi n g zone thus retains n u
altered its d i s tinctive characters and occ upi e s a constant position re l a
ti ve l y to the posterior end
T he short regi on posterior to the growing zone ( post me s o d erm a l
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S tructure
a nd
D e vel op me n t of th e N e p h ri d i a
3 49
.
region or pygidium ) retains i ts characteristi c peculiariti es in an
almost unaltere d for m throughout th e whole of the development
—
2
2
1
3
Plates
and
Its
ecto
Plates
2
2
2
3
7
a
n
d
3
Fi
3
9
s
0
;
( g
,
dermal cells are s mal l and vacuolate d and contain a gra nular yellow
or brownish pigment evidently ofan e xcretory nature , which seems
to a ccu mulate in this region a s the animal grows older
possibly
b ecause of its isol a tion from the rest of the larval body and its
lack of vascular supply A sharp li n e ofd emarcation exi s ts b etwe e n
the ectoderm of this region and that ofthe gro wing z on e imme d iatel y
anterior to it T he portion of the intestine contained in this regi on
correspon d s to the proctodaeum , an d is separated by a val v e from
the entoder mal portion immediat e ly in front ( Fig 3 3 Plate
In
its ventral wall is inserted a bunch of strong sti fi cilia
Whil e the posterior por tion of the larval body is undergoing
ferentiati on of the more anterior somites
e longation in this manner d i f
i s in progress In yo u
ng lar vae ( with fewer than nineteen somites ),
each somite possesses at its earliest appearance
in addition to
its se ction of the i n testine and the ne wly formed muscle fi b re s of
—
the body wall
the rudiments of dorsal and v entral setae ; a n d
i s separated fro m its neighbors b y complete mesoblastic septal par
titi cus ( F igs 9 1 0; 2 9 3 0, 3 1
A s growth pro cee d s , the
s e pt a b e co m e incomplete dorsally
ie s
a n d the adj acent bo d y cavi t
become contin uo us with one another A t th e same ti me the setae
b e come fully for me d a n d functional ; a n d the supra and s ub inte s tinal
b lood ve s sel s originally simple spaces b etwee n the opposed and
thin n ed out walls of the early meso b lastic somites ( Figs 8
be
come well define d and of uni f
or m d iameter throughout
The s t o m a c h as desc ribed abo ve i s at a n early stage ( s e e
Figs 7 , 8 Plate 2 2) a lready sha rply distinct from the oesophag us
Throughout the perio d n ow under con sideration ( from 8 to 1 8 ao
mites), the oesophagus und e rgoes a continual backward prolongation
i n a manner pre sently to be de s cribed an d its region of j unc tion
with the stomach is thus gradually shift e d b a ck w ard from the second
F
i
8
( g ) to the seventh somite , its definitive position I n histological
s t ru
cture , the walls of the oesophagus consist chie fly of a si n gle
laye r of densely ciliated cubical epitheli a l cells The s to mach is of
g reater diameter than the oesophagu s , and its walls which are much
thicker v e ntrally than dor s ally are composed of very characteri s ti c
l a rge uni formly s tained cells of ho mogeneous appearance A lon g i ts
v entral wall extends a ciliat e d groove continuous anteriorl y with
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Ra l p h S Li ll i e
350
.
the ciliated cells of the oesophagus a n d posteriorl y with th o s e 0
the rectu m Poste riorly the sto mach merge s gra d ually in e a rlie
s tages into the u
n d i fferentiated po s terior portion of th e int e s ti n e
later its po s terior l i mit b eco me s d efined th o ugh nev e r w i th a b s ol utc
precision ; this li mit is in the t e nth or eleventh so mit e , wh e r e th c
s to mach pa s ses w itho u
t a b rupt tran s ition into the po s terior n a rro w e
portion of the intestine This latter region ( re ctum l is in i ts a n t e ri o
porti on co mpletely lined by ciliated cells continuo us w ith th os e 0
th e s to m ach ; further b ackward th e cilia b eco me r e s trict e d to
longitudinal groove along the v entral w all ; a n d as th e gro w i n g
region is n e are d
the cilia finally d i s appear a n d the wa ll b e co m e
composed of large clear cells fe w in numb er in cro s s section a n
containing large nuclei ( Figs 2 1 2 4 3 0, Plat e
B oth s to m ach and oesophagus a re suspended to the dorsal b o d y
w all by a m esent e ry in which ru n s the supra i n te s tinal b lood v e s s el
The su b intestin a l ve s sel runs along the ventral surfa ce of th e i n te
s tine ,
and presents a characteri s tic appe a rance from the l a rgt
granular chloragogen cells which invest it Posteriorl y thes e c ell:
merge graduall y into the un d i f
ferentiated m eso d erm cells o f tie
growing zone ( see Figs 9 1 0 1 6 1 7 etc 3 0 Plates 2 2 and
For the greater part of the above period the s e p t a fo r m i n
c omplete transverse part
itions extending o b liquel y b ackwar d fr or
the ventro lateral regions of the corre s ponding so mites to th e s ub
intestinal b lood vessel E ach septum from the th ird to th e te n t ]
incl usive di ffe rs from the rest in b eing a s s ociated w ith the d e vel o p
m ent of a pair of nephridia w hich arise on either side i n th e
m e s o b l a s t at the time of formation of the septum and in continuit y
w ith the posterior fa ce of the latter
E ach n e p h r i d i u m wh i cl
thus arises soon acquires the for m of a minute intracell ular tub ul
in the anterior region of th e somite , opening through the s e p tur
into the b ody cavity b ey on d by an ap e rt ure through whi ch c i li
proj ect The two earliest formed p ron e p h ri d i a those of somit e s I
and V persist for a short ti me onl y and d egenerate at a com p a ra
The re maining s i x p a i r
ti v e l y early period in the d evelop m ent
h
f
m
d
t
e de
in
so
ites
VI
to
inclusive
are
directl
y
trans
or
e
into
m
X
I
)
(
T h e so mite s b ehind the eleventh n e v e
fi n i ti ve adult nephridia
give rise to such p ron e p h ri d i a s o fa r as my o b servation h a s e x
te n ded I t i s possi ble that p ron e p h ri d i a ma y occ a s ion a ll y app e a r i :
t h ese s o mites a s might b e exp e cted from the fa ct tha tc e rta i n s p e ci e
g A eca ud a ta ) in w h ich n ephridia are normall y p re s e n
e xist ( e
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S tructure
and
D e ve lop me n t o f th e Ne p h ri d i a
35 1
.
these somites ; but of the nu merous larvae that I have examine d
so that its occurrence is at
ot one has pre s ented this condition
The p ron e p h ri d i a ofsomites IV and V on the
n v rate exceptional
app e ar with per fect con s tancy as normal featur e s of the
on t
ra ry
a rl y developme n t
In oth er re s pects th e development ofthe po s t n ep h ridial s omites
h e nineteenth so mite i s reached ) in exactly the
I ke s place ( until t
mann er as that of the more anterior s o mites as alrea d y
a me
e s cribed The res ult is the formation of a ch a e ti g e rous ante rior
The primi
O d y region which inclu d es the first eighteen somites
as a b o v e explai n ed d o rsall y incomplete so that th e
ve s epta a re
nicate freel y w ith one another throughout the
O d y cavities co mmu
h e time of attainment ofthe nineteenth
re a t
e r pa rt ofthis re g ion B y t
o und however that the four most an terior so mite s
s mite it i s f
rom the others b y muscular partition s w h ich
a ve b e come separated f
ave arisen at the poste rior b o undaries of the first thir d and fourth
o mites
Th e s e s tructures are the fore ru n ner s of the th ree
i a p h ra g ms of the adult ; t h e y d o n o t r e p r e s e n t t h e p r i m i t i v e
c p ta o f th i s r e g i o n
but are formed independently of these in a
Ta n ner pre s ently to b e d e s cri b ed
The body cavity from the poste
io r b oundary of som i te IV to the anterior bo u
ndary ofso mite XIX
e n ti re l y without septa
and remain s in thi s condition througho ut
fe
formin g the s pacious undivi d ed coelom characteri s tic of the
1
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re n i col i d a e
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With the appearance ofsomite XIX a marke d change takes place
{I t
h e character of the s e g m e n t a t i o n
The septum b etween s o
I it
es X
VII I and XI Xrema ins compl e te for ming a membranous partition
h i ch per s i s ts throughout li fe and divi d es the anterior ch a e ti g e rou
s
o d y region f
rom the region formed b ehind this limit The somites
ow formed are narrower and s horter tha n those of the anterior
agion ( s e e Plate 2 4
Fig
they are furthermore e n tirel y desti
It
e of setae
and are separated from one another b y co mpl e te
ep t
A t th e beginning of the time of formation of this r e gion
a
s somites are not con s picuously narrower or s horter than those of
re ant e rior region
A s growth proceeds howev e r the characteri s tic
i fi e re n ce s betwee n the two regions b e co me more evide n t , a n d are
e ll marked by the time the total n u
mb er of som i tes has reac h ed
re nei g h b orhood of thi rt
y W ith a further increa s e in the n um b er
ts omi te s the dividing line b eco me s b etter define d until fi n all y in
I rva e of 2
mm length the d i s tinction b etween the two regions
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Ra l p h s L i ll i e
35 2
.
as d istinct as in the adul t The posterior achaetous re g i o n u n d er
goes relatively little furth er d i fferentiation and its somite s e x hi bit
throughout li fe an almost complete resemblance to one anoth er T he
addition of n e w so mites continue s in the u s ual m anner unti l the
definitive num b er h a s b een atta ined after which th e g rowi n g z one
loses its distinctive character s a n d b eco m es indi s ting ui s ha b le a s s u ch
The disappearance of the growing zone and th e ces s at i o n 01
somite formation take place with gre a t re g ularity at a st a g e 01
ab out 5 8 so mites The final nu mb er of achaetous somite s i s th at
found to b e approxi matel y consta n t ; it ma y b e accuratel y dete rm i n ed
b y coun ting the sept a i n lon gitudinal s ections ofS pecimen s in w hich
the growing z o n e has disappeare d In such larvae the nu m b e r is
‘
found to range fro m 3 8 to 4 0 and appears n ever to exceed o r fal
b elow thi s The total nu mb er of s o m i t e s formed in this s p e c i e s :
A rem cola s eems thus approxi m at e l y co n s t a nt ( from 5 6 to
in a d u
k
s peci m e n s
however , the n u mb er a ctua l l y fo und i s genera ll y c on
s p i cu
ou
s l y smaller t h an the a b ove ; the d eficie n c y i s re a d ily a c co u
n
ted for as d ue to a los s of a portion of the po s t e rior regi o n by
a utoto my which i s of fr e quent occ urrence in this section ofth e b o d y
A lth ou g h the po s terior region increases in ab s olute s iz e w i tl
the growth of the a n imal , it undergoes little further di fferenti a ti on
and remains throughout li fe in a pri mitive uni formly s e g mente d a n d
achaetous con d itio n The presence of both dors a l and v e n tra i
the regular repetition from end to end of co mpl e te
n i e s e nt
e ri e s ,
s e pta the simple uni form struct ure of the intestine a n d the re g ul a r
m etam eric rep e titi on of the circu m inte s tinal b loo d ve s sels a re ot h e r
characteri s tic fe ature s of this region all of them of a deci d e d l y
A l l of these features appear early in the d e v e
primitive kin d
l op me n t of the region a n d persis t throughout li fe
With the anterior ch a e ti g e rous region the case is very differ e n t
and very extensive further alt e rations are necessary b e fore th e d e fi
Fig 3 0 Plate 2 3 represents 2
i v e s tructure is finall y a ttaine d
nit
sagittal section of a lar va at a stage of about 8 somites T h t
it will b e o b s e rve d , is expre s se d in a relativ e l y
me tam er is m
s i mple manner : the v entral ectoderm is thickene d at segmental i n t e r
vals and the sept a all of which are incomplete d orsal ly ( e x ce p
those j ust for ming ) e xtend from a region a little in front of th t
constriction upwar d s and o bliqu e ly b ackw a rds to the su b intesti n a
b lood vessel Th e firs t sept um is in s erted into th e oe s op h a g uu
immediately b ehind the pro b oscis and into the b o d y wall al m o s t a
is
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O
u
o n
:
*
9
I
I
p
O
O
0
0
o
C
O
O
3
S tructure
D e ve l opme nt of th e N e p h ri d i a
an d
35 3
.
th e p l ane of insertion of the retractor mu s cles ofthe pro b oscis The
h e second somite a n d j oins
o esophagus extend s b ackward through t
the stomach near the anterior limit of the third somite ; it is evi
as may b e s e e n by comparing i ts
d e n tl y un d ergoing e l o n g a tion
extens i on at thi s stage with that found in the earli er stage s re p re
This backward prolongation is further
s ent e d i n Fi g ures 7 and 8
indicated in the fact th at the septa which in earlier stages occ upied
planes approxi mately perpendicular to the long axis ( Plates 2 2 a n d
hav e a cquired a pronounced slant upw ar d s a n d
2 3 Fi g s 7 , 8
backwards I t i s to b e care fully noted that at thi s stage the second
s e ptum is ins e rte d al most at the a nterio r b o un d ary of the s tomach ,
while the thir d and fo urth s epta , whose line of insertion i n to the
bo dy wall correspo n ds with that of the later formed diaphrag ms , are
attach e d to the v entral b lood ve ssel at points fa r behind the anterior
b oundary of th e stomach
A s the oe s ophagus elongates th e s tomach is a s it were pushed
b ackwards a n d the a b ove mentioned b a ckward mp e of the septa
b ecomes more marke d ( Plate 2 4 Fig
This b a ckward growth
h as the further re sult that when the s econd a n d thir d di a phragms
are formed ( in a manner s h o rtly to b e d e scri b e d ) each becomes
i n s e rt e d into the oesophagus at a position well in advance of the
a lth o u
s to ma ch
gh as j u s t shown this organ origin a l l y exten d s fa r
in adv a nce of the region finally occupied by the oesoph a gus The
stomach seem s d uring the s e changes of po s ition to undergo an e x
t e nsive h isto l ytic disintegration and reorgani z ation to for m the tissue
h e oesophagus
of t
a fa ct which m ust also b e take n into conside
ration i n accounting for the changes in the position of septa and
d iaphragms
T hese hi s tolytic changes w ill s hortly b e described
The most anterior septum oc cupies from the first a po s ition
i mme di ately b ehin d the line of in s ertion ofthe pro b o s cidial retractor
muscles ( Plate 2 4 , Fig
A s growth proceed s
the relations of
these two originall y independent structures b ecome closer and at
th e sta ge represented in Fig 3 6
in w h ich twelve somites have
b een laid down
the two have become inti matel y associated with one
another , although still d istinguishab le on close examination This
a sso ci a tion of proboscidial m u
scles and first septum b ecomes in later
s t a g e s more complete
and both e v entually enter into th e for ma tion
h e muscular first diaphragm
of t
T h e poste rior peritoneal wall of
t
h e a dult diaphragm may be regarded as repre s enting the original
fi rst s e ptum
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I
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F
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Ra lp h
35 4
S
.
L i ll i e
T he ventral portion of the se cond s eptu m which li k e all tl
other sept a b ehind the first , is inti mat e l y related to the s ub i n te s tin
1
ve s sel carries b lood v es s els ( which are alre a d y lai d do w n in ti
larva of Plate 2 4 F i g 3 6 ) from th e su b inte s tinal ve s sel to th e v e nt:
bo d y wall ofthe second s o mite These bloo d ve s sels mark th roug ho
li fe the original position of the s econd s ept um ; this s tr uct ur e 11
thus nothing to do with the formation of the s econ d d iap h r a g m
The second and thir d diaphragms which in the a d ul t fo r m t
posterior b oun da ries of s omites 3 a n d 4 respecti v el y , a re fo rm
i n d e p e n d a n tly of the pri mitive septa
and repres e nt enti r e ly d i t
rent structures from these
as shown by their method o f fo r n
tion , histological compo s ition and relations to intern al org a n s 1
s e c o n d d i a p h r a g m b egins its appearance at the ti me of fo r m ati
of the e l e venth or twel f
th somite ; and in most instances c o m p le
i ts extension across the b od y cavity d u
ring the ti me of fo r m a t i
of the next two so mites
Plate 2 4 Fig 3 6 represents th e a p p e a ra r
in sagittal s ection of a la rva of 1 3 somites showing the a p p e a ra r
of the newly f
or med d i a phragm under a low power It w i ll
o b ser ved that its line of insertion i n to the ventral b o d y w a ll c o
ci d es with that ofthe primitive septu m The latter st ruct ure p e rs i
for some time a fter th e diaphrag m is forme d and can b e s e e n
its origin a l position stretching diagonally upwards and b a ck w a i
to th e su bintestinal v es s el at the anterior bor d er of the s tom a
The diaphragm on the other h a n d extends in a perfe ctl y tra n s v e i
d ir e ction co mpletel y across the b od y-cavity a n d is inse rte d into 1;
oe s oph a gu s i n a posi tion a s hort d istance in front of the s to ma c h
T h e fo rmat i on ofthe d iaphrag m takes place through the int e
action of s e veral d i ffe re n t and par tl y i n depe n dent p rocesses A t i
first appearanc e ( in a l a rva of 1 2 s omites ) it has the form o f
p urely me mbranous partition i n s e rted into th e ventro lateral re g i
m and e x te
of the b ody wall o n a lev e l with the pri mit i v e sept u
ding transvers e l y to the oe s ophagus w hich it j oin s at a re g i
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l a te r l a i d d own i n t
p os t d i a p h ra g ma l s e p ta ; a n d a s wi ll b e s h o wn l a te r th e d i s tri b uti o n o f
a l bl oo d v e s s e l s i n th e a d u
l t a n d e s p e ci a ll y th e i r p e cul i a r re la ti on s
s e g me nt
i
on i n 1
rma t
h
r
f
o
i
th e n e p h ro s to ma ta
o
f
e
h
t
h
f
a
c
t
a re e x p l a i n e d th ro u
e
t
g
p ri mi ti ve s e p ta wh e re the y a pp e a r a s s p a ce s b e twe e n th e two l a me llae ( P l a te
F i g 9 ; P l a te 2 4 F i g s 3 2
S in ce th e n e p h ri d i a a re from th e fi rs t i n i t
ma te con n e ctio n w i th th e s e p ta th e p o s i ti on ofth e n e p h ro s to mi a l bl o o d ve s s
ll y d e a l t w
th u
s b e come s re a d i l y i n te l l i g i bl e
T h e s e re l a ti o n s wi ll b e more fu
i n th e d i vi s i o n tre a ti n g of th e d e v e l op me n t o f th e n e p h ri d i a
1
B l oo d
l
-
ve s s e s
ia
of e s s e nt
ll y
l
s i mi a r re l a ti o n s
a re
-
,
,
-
,
,
.
,
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,
-
,
.
.
R a lp h s L i ll i e
35 6
.
The t h i r d di a p h r a g m does not appear until a so m ew h a t l at
stage
typicall y at the ti me of formation of the si x t e e n th
seventeenth somite I ts manner offormation is in all respe ct s s i mi l
to that of th e seco n d d iaphragm I ts ventral in s ertion c o i n ci d
with th at of the fourth pri mitive s e ptum ; and the latter , a s i n t
ma y persist in its origi nal pos i ti o n 1
ca s e of the third septum ,
some time a fter the diaphragm has become co mplete
A t thi s stage ( 1 7 somites ) the o esophageal ins e rtion of th e th i
diaphrag m is i mme d iately anterior to the stomach The o e s o p h a g
has thus e videntl y undergone an elongation of about the l e n g th
one somite since th e time of formation of the s econd d i a p h ra g
I n later stages a sectio n of considerable length intervenes b e t w s
the oesophageal insertion of the third d iaphragm a n d the a n t e r i
b oundary o f the sto mach E vid e ntl y there fore there is in p rog rt
a b ackw ard prolongation of the o e s o ph agus The man n er i n w h i
this prolo n gation takes plac e is peculiar : it takes place in p :
pro b ably by a process of s i mple b ackw a r d grow th ; b ut it s ee m s
h e chie fl y due to an ext e n s ive histolytic trans fo rmat i on of t
anterior r e g ion of the primitive sto mach The nature o f tl
trans forma tio n ma y b e determined in p a rt from the examinati o n
In a I a r
l ongitudinal sections of larvae of slightly later s tages
ormed ; a n d i n t
of 2 3 so mites b oth diap h ra g m s are completely f
fi fth somite a sho rt distance b ehind the third di aphrag m the C h a n g
allude d to are a pparently in active progress The oe s opha g u s
here al most occluded by what ap pear s to b e a st rong con s tri c ti l
lar fi b res situated at the p oi n t
m us cle of d e e pl y st a ining circ u
j unction of o e s opha gus and stoma ch The anterior stomach re g h
see m s to b e un d ergoing a proc e ss of dissolution p reparatory to i
tran s formation i nto oesophageal tissue The ty pica l unaltered sto m a
cells are lightl y staini n g a n d ho mo g en e o us in appe a ra n c e ; tb
are n on ciliated
except in a groo v e along the me di a n v e n tl
ain i
wall ( Pl a te 2 3 , Figs 1 6 , 1 7 , 3 0)
e w de ep l y s t
a n d contai n a f
granules A s the region of con s tr i ction is neared , howev e r th
app e arance undergo e s a ma rked alteration ; th e y b eco me g re a t
narrowed and elon g ated and d rawn out at their inn e r ends a p p a re n l
i n to lon g tapering flag ella S till farther fo rward the cells a
vacuolate d and l a rgely b rok e n d o wn O n pa s sin g still farth e r f(
ward the vacuolation beco mes les s m arked ; and fi n a lly the v a cr
lated cell s pass b y a grad ual transition into the ordinary C ll b i t
ciliated cells of the oesophagus
.
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i
S tructure
an d
D e ve lop men t of th e N e p h ri d i a
35 7
.
E verything thus points to the conclusio n that a disintegration
h e anterio r stomach c e lls are in
a n d subsequent reorganization of t
rog
ess
In
earlier
stages
the
region
f
t
r
a
n
s
o
r
m
a
ti
o
n
is
f
ound
o
f
r
p
farther and farther forwa rd s , and alway s at the j unc t
io n of ceso
l phag ne and sto mach
It t h us moves gradually b ackwards a s deve
J I O me nt proc ee ds , and the proce s s oftrans f
ormation
apparently
ceases
p
onl y whe n the definiti v e limit s of the two regions ha v e b ecome
tifi n a l ly esta b lished
In later larval stages and in the adult , the
; o e sophagus j oins the stomach near the line of separation ofthe sixth
l a n d s eventh somites immediatel y behin d the oesophageal p ouches
T h e se latter organs there fore d o not arise until oesophagus and
s t om ach h ave attained thei r definitive limits
S ome space has bee n devote d to a description of the ab ove
h i s tolyti c chan g es in or d er to make clear the manner in which the
fi n al relations of th e diaphragms b ecome establis h ed
A t the b ody
w a ll , the line of in s ertion of e a ch diap h ragm corresponds to that of
a
m to wh ich it corresponds
and
3
At
th e ori ginal s eptu
th e i n t e s t i n al inse rtion however no s uch correspondence can exist
T h e whole anterior region of the alimentary canal has undergone
complete alteration from its earlier condition ; and the sections of
a
o e s o p h a g u s b ounded b y successive diaphragms can there f
ore in no
way corres po n d to the original s e gmental d ivisions In A ren i cola
the alim enta ry can al fa ils indee d to exhi b it metamerism in its anterior
p o rtion s becomi n g d i fferentiated as a whole witho ut re ference to
s e g mental limits In the b o d y w a l l , on the other h an d th e
meta merism
as indicated by the positio n of the s e tae , e xternal
body rings , b ranchiae and n e p hrO p ore s
corresponds closely with
that ori g inally laid down in earl y developm e nt These facts have
a n import a nt bearing on the
u
s
e
tion
the
possibility
rigorou
ly
o
f
o
f
s
q
m arking ofi se g mental limits in the adult stages of m e tam e ric
a nim a ls
This can b e done o n ly i n the case of certain struct ures
in A rem cola : th e anterior part of the intestine shows n o indications
of m e ta merism
I t will be su fficient for the purpose ofthis paper to give merely
a b ri e f out l ine of the remainder of the larval d evelopment
since its
d etail s are of interest in the present paper only in so fa r a s th e y
co n ce rn the characteristics of the nephridia w h ich will shortly b e
d ealt with at leng th
A s growth proceeds
the division between
cha e t
i g e rou
s and a chaetous b od y -sections b ecomes well d e fi n e d
and
wi t h the compl e tio n ofthe diaphragms a n d the definite esta b li s h me n t
.
l
,
"
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-
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,
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'
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,
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-
,
Ra l p h s L i ll i e
358
.
the limits of th e intestinal regions th e m a i n ch a ra cte ri s ti
the adult b o d y are complete T he activity of the g ro w i n g
ceases when the l a rva has attained a le n gth of from 2 to
at which stage the outward appearance and internal org a n i z
are essentially identical with those of the ad ult
furthe r d e v
ment consisti n g c h ie fly in an increase in size and in th e com p ]
I n such larvae th e
of histological di f
ferentiation
b lood vessels is su b stantially a s in the adult and
conn ecti ng the gastric and su b intesti n al ve s sel s at
mity of the sto m
ach , are already d i fferentiated
th
contractile The gills have appeared in the 7
—
so mites ( VIII XV I I I ) a s thin walled evagin a tions
b od y wall containing loo p ed b l oo d ve s sels The otocys ts ar
the sides of th e prostomiu m The six nephridia are vi s i b l e
th
the transparent b ody wall a s sac like s tr uct ures in the 5
th
1 0 setigerous so mites ( V I —XI )
The d o rs a l s e t a e and th e
rows of b ook s ha v e the us ual c h aracters b ut hav e incre a se d
—
i
in num b er as co m pare d w th earlier stages Larvae o f 1 0 1
length ha ve u n d e rgone little further alteration except in r
to size and d egree of histological di fferentiation The g i ll s
"
”
b eco me more branc h ed the hearts more co n spicuous and
d efined the num b er of setae has increased and the external
rings have appeared A t this stage in fact , th e a d ult org a n i z a ti o
is ess e ntially complet e
of
,
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,
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-
-
-
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-
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,
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,
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,
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4
.
A n a tom y
and
h i s tol ogy
of
th e
ad
ul t nep h ri d i um
.
The s i x pairs of n ephridia of the adult A remcola mi s ta ta a re
th
ih
T he s e
situated in the 5 to the 1 o setigerous somites i n clusi ve
somites correspond however a s seen from a comp ari son of early
larval stages , to b o d y somite s VI to XI , the first somite ( peristomiu m )
being without setae , and in the adult n ot sharply demarcated e x te r
nally from th e second Internally however its posterior li mit i s
marked by the first diaphragm whose position corre s ponds cl os e ly
with that of the original first septum B etwee n th e firs t a nd se co n d
diaphragms intervenes a region composed of two somites ; thes e a re
in early stages perfec tly distinct fro m one another ; in adult life
however , the b i se g me ntal co mposition ofthis region is less evi d e n t;
it is however , clearly in d icated by the presence of two s e g me n ta l
tu fts of notopodial setae , a s well as by certain peculiarities of th e
’
.
,
,
.
,
,
.
,
S tructure
and
D e ve l op me nt of th e N e p h ri d i a
ul a r s y stem ( s e e G AM B L E
35 9
.
Fig
T
he
g
a e con d diaphragm thus constitutes in real ity the po s teri or boundary
while the third diaphragm si milarly delimits somite IV
3 f s omite I I I
h
e species
l
h
i
s d isposition of the diaphragms is cha racteristic ofa l l t
ir
a r b een e xa mined ,
and
has
its
origin
o f A rm i cola that h ave t h us f
r
d esc ri
a in a manner that has already b een su f
ficiently
a t
i n A cris t
i
p
The first ch a e ti g e rous somite is there fore strictly spca
b e d above
k
th e s e c o n d body somite and not the third a s G A M BL E
i
ng
I e
ferences
I t is highl y improbab le that di f
A e W O R rH suppose
E
ferent species ofAr en a"
n this respect should prevail among the di f
i
D i
a
at
cri s t
st udy of the larval stage s proves
cola ; at all events in A
b
e y on d a doubt th at the composition of the anterior region is as
E
a b o ve descri b ed
“
T he po s ition of the first n ephridium in A cri s ta ta ( b ody somite
th
V I , or 5 ch a e ti g e rou
s somite ) agrees with that of the maj ority of
o th er specie s hitherto investigated
A ma ri n a however , the first
In
n
th
m occupies somite V ( 4 ch a e ti g e rous ) and its nephro s tom e
n e p hri d i u
e
n
orates
h
third
diaphragm
and
ope
s
into
the
b
ody
avity
e
f
t
r
c
e
p
It i s n oteworthy as G AM B L E
A S H W O R I H have emphasized ,
b e y ond
th a t this nephridiu m is ty picall y smaller than the other s and ftc
n
u
u
n
m
e
tl
y
uch
red
ced
or
eve
absent
S
ince
the
larvae
A
t
a
t
a
f
c
fl
s
o
q
Bn
s
s
s
r
n
o
e
h
r
i
i
i
d
a
s
os
e
b
oth
omites
V
and
I
V
it
is
evident
that
the
n
p
p
p
,
d
present con d ition has bee n reach ed through the disappearance of
i
certain more a nteriorly situated nephri dia ; a nd the process of re
duction is appare n tly still i n progress in A ma ri na The forma
tion of the anterior diaphrag ms is po s s ib ly i n part responsible for
th e disappearance of the nephridia of this reg ion , sinc e the nephridia
a re thus cut of
f from the genital region an d d eprived ofone of their
most characteristic functions t h at of conve y ing the genital products
to the e xte ri e r
In a n a t o m i c a l s t r u c t u r e the nephridia ofA cri s ta ta are very
similar to those of A ma ri na T he large con s picuous nephrostom e
with its fringe d dors a l lip trans vers ed by the nephrosto mial b lood
vessel , the spacious a n d uncoi l e d g l a n d ul a r region , and the large
contractile terminal vesicle a re characters apparently possessed in
common b y all s pecie s of the genus T he nephrostomial blood
vessel , a fter leaving the posterior m a rgin of the d orsal lip passe s
along the b ody of th e nephridiu m and is associate d i n b ody so mites
V II to X with th e formation of the gonads T hese organs have the
ch aracteristic f
orm of s t ran d s of cellular tissue traversed by the
H i tth i l u g
a d Z l S t ti u N ap l B d 1 7
LS
A S H W O RT H
a sc
1 9 00,
,
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,
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,
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’
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-
,
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-
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'
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a
,
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,
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’ ‘
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i
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-
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o
n
cn
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oo
.
a
on z
e
e
‘
.
.
.
‘
R alp h
360
s
.
L i ll i e
blood v essel and for med b y a proli feration ofthe peritone a l c ov e
The p o s i ti or
of the latter , in a man n er lat e r to be descri b ed
the anterior margi n of the nephrostome correspon d s to th e b o un t
b etween two s ucces s ive somites ; in earl y larval life the n e p h ro s t
actually per forate s the sept um a n d O pens in the ty pi ca l m a l
into the bo d y cavity b eyond I n a d ult li fe n o sept a a re p re
i n the nephridial re g ion ; the s e structures are however r epr e s e
by the segment a l b lood vessels which pas s b etween the s ub i n te s
vessel and the lateral longitudinal vessels These ve s s els wi th w
the n ephrostomial b lood vessels are directly continuous a r e c
nally formed in the inters egmental septa as alread y d e s cri b e d ;
i n this sen s e each nephrosto me may be considered to op e n t h r o n g
li fe into the next anterior so mite The ext e r na l openin g O f
ne p hridium is at the po s terior extr e m i ty of the somite , d o r s a l
a little posterior to th e row of v e ntral hooked setae
I n its natural position each nephridium is situated i mm e d i a
withi n the dorsal inser tion of the trans v erse muscular b a n d s
—
which i t is partial l y isolated from the gene ral body cavit y
W
these mu s cl e s are cut a n d turned back the nephridia ar e fr
e xposed to view ( Plate 2 2 Fig
E ach is then s e e n as an elon g :
tub ular or gan with brown walls , terminated po s teriorl y at the l l
a n d anteriorl y by th e 12
of the setae by the cont ractile vesicle
characteristic nephrostome conspic uo us fro m the br i ght
a nd
processes of its dorsal lip A slip of transverse mu s cle i s a tta c
to the ante rior portion of the dor s al lip and in li fe b in d s the n e p i
om e do wn in s u
ch a m anner that its O pening is d irected i n w a
st
Fi g ure 3 r e pr e s e n ts a nephridium seen in i ts nat ural posi ti on fr
a b ove a fter the r e moval of a l l the transverse m usculature , e x e
a por tion of the attach e d slip
The n e p h r o s t o m e is of peculiar a n d co mpl e x structur e
presents certain peculiarities th a t appar e ntl y have not h i thert o b
observe d in th e other spec i e s of A ren i cola Figure 2 , which re )
h e fir s t n e phr i d iu m of th e ri g ht 8
s ents an e nl a rg e d view of t
shows the app e aranc e of th e nephrostome a fte r its attachment s h
b een remove d and i ts aperture has b een free l y ex p osed to v
a n d s p rea d ope n
It will b e ob s e rve d th a t a wel l define d lin t
divi s ion sep arates the li g ht colore d n on pi g m e n ted n e ph ro s to m e f
the deep b row n gland ular portion ofth e organ a di vi s ion corr e s ]
d i n g to a marked d i f
ference in th e histolog i cal character o f
lin i n g epithelium of the two r e gions
-
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-
-
,
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S tructure
a nd
D e ve l op me nt o f th e N e p hri d i a
361
.
The limits of the nephrostome as such are thus s h arply defined
lt In early stages on the other hand n o sharp line of
i n the adu
d e marcation can be drawn
T he ab ove di fference of struct ure must
n o t there f
ore , a s so me suppose , he held to indicate that the two
r e g ions repre s ent g e netically distinct structures which h a ve secon
d a ri l y entered into intimate association
I t will be shown beyond
t h at the two porti ons develop in direct continuity with one another
a s portion s of an origi n ally single em b ryonic rudiment
T he d o r s a l l i p i s bordered by a series of b right re d vascular
: c iliated
proces s e s T he s e are flatte n ed and somewhat le a f shape d
s tructures
partiall y subdivided b y s e con dary fi ng e r like processes
a n d arranged i n a s ingle row f
rom e n d to end of the dorsal lip
and is u s uall y
I l he dorsal lip i s somewhat the longer of the two
s
r
A
m
i
l
a
eo
[ o m ewhat fol d e d i n th e livi ng
so that the one rowe d
a rrangement is
not obvious on ca s ual ex amination Whe n th e
n e phrosto m e i s slightly stretched , however ( as in Fig
the pro
c e s ses are rea d ily seen to have the a b ove- d escri b ed arrange m ent
,
W i th their broad faces O pposed like the leaves of a book
A t the
a n terior a n d posterior limit s of the lip the y dimini s h i n size a n d
th e n u
mber of s u b divi s ions becomes less
E ach process may be
d e s c ri b ed a s palmate in shap e ; at its s omewhat narrowe d b a se it
i s a tta ch e d to th e b order of the dorsal lip ; in st ruc ture it is ess e n
ti a l l y a hollow thin -walled flattened vesicle
lined inte rnall y b y a
c o n necti v e ti s s ue b asement membrane a n d covered b y a columnar
c i liated epithelium which passe s without t ran s ition into the e i t
h
e
p
l iu
m lining the interior of the n e phro s tome
T he r e lation of the proces s es to the n e p h r o s t o m i a l v e s s e l is
i n reality very simple , and may b e rea d ily un d erstood by a re fe rence
to the te xtfi g u
re ( p
which represents in a somewhat s implifi e d
fo rm a cross section of th e entire anterior region of the nephridi um
T h e m a in portion of the ve s sel
n s along the outer mar g in
ru
o f the dorsal l i
m
i
mediately
b
low
the
insertion
the
processe
e
o
f
s
p
a n d its interior communicate s directl y with that of the processes
whose bright red color i s thus due to the containe d b loo d No
d istincti on however
can be seen b e t
ween the wall of the b l ood
vessel and the internal connective tissue lining or ba s ement me m
r
b
a
n
f
e
o
the processes the two bein g directl y continuous with one
l
a n ot
h e r a n d in real ity di f
f
ering
onl
y
in
their
relations
to
the
n
e phro
P
st
omi a l epithelium
This epitheliu m is i n timately related to that
o
f
w
art
the
blood
vessel
hich enters the interior of the processe s
p
.
,
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,
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-
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a“
.
Ra l p h
3 64
S
L i ll i e
.
pu b lished drawings of nephridia of young specimens of A m a
re s pectively 3 0 and 4 4 mm in lengt h ( Figs 1 6
i n w h i ch
dorsal proces s es are just b eginni n g their formation in a m a n n e r
corresponds su b stan tially with the above description I n A cri s
it is pro b ab le that the y ari s e at a correspon d i ng stage a n d in
It is in teresting to note that i n certain oth e r S p e ci
s ame manner
) a n d A eca ud a t
a
notabl y A Grubs"
the processes whil e e v i d e n
beari n g the sam e relation to th e nephro s tomial b lood ves s e l
fe w er in n umb er and si mpler in structure remaining appa r e n tly
a les s di fferentiated con d itio n thro ugho ut li fe ( G A M B L E
A S H W OB
.
.
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,
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,
,
-
,
,
1 9 00)
indic a tions ther e fore point to the conclusio n that the p ro ce
represent s i mp l y an ela b orate a n d regular s y s tem of fol d s O f
m
n ephro s to mi a l epitheli u
The correctness of this view i s furt
i n dicated b y the identity i n s tr ucture of the cili a te d cell s O f
processes and of th e other portions of the n e phrostome
B y the formation of the proce s ses of the dorsal lip the c i li
s urface of the n e phro s to me i s enormousl y extended and its e ffi ci e
as an org a n for re m o ving s u s p e n d e d s o l i d p a r t i c l e s fro m
coelo mic fluid is correspon d ingl y increa s ed The cilia whi ch co
the processes are in cessan tly and vigorou s l y active ( a c o n diti
presumably fa v ored b y the ab un d ant va s c ular su p ply ) an d te n d
s weep all su
spende d solid particles into the interior of th e n e p h
m
diu
In living A re n i col a e it is found that the interior O f the
n e phro s to m e a n d the inter s tices bet ween the proce s ses are oc c u ied
p
by a m as s of loosel y granular su b sta nce e vidently colle cte d i n th i :
wa y
O n m ic ro s co p ical ex a min a tion the m ass is fo und to co us i s
large l y of b roke n d own c e lls containing excretory granules s i m i l a l
to th ose fo und in the c h lor a g o g en cells coating the ventral b l oo d
v e s sel
It appears p ro b ab l e in fa ct that the chlora goge n c ells
un d e rgo a conti n u a l proce s s of d i s integrat i on a n d that th e s ol i t
ex cr e t ory product s thu s set fre e i n the co e l om are swept int o tht
i n terio r of th e n e phri d ia by the nephrostomi a l cilia a n d so con v e y e t
to the exterio r The broken d own chlorag ogen cells are p o s s i b l y
replaced b y wan d eri n g cells or , m ore specificall y e xcre top h ore s
which are chemotropic a ll y attract e d to the ventr a l b lood ve s s e l a n t
w h ile there e xtract fro m the bloo d the excretory matters ; the l at te
b e ing d epo s ited in a soli d form in the interior of the cell s a n t
eventu a lly set free in the coelo m to be remove d to the exteri o r b y
the nephri d ia U rea and other sol uble waste products seem , on 1311 1
A ll
.
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,
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,
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-
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,
,
-
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,
-
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S tructure
and
D e ve l opme n t of th e N e p hri d i a
365
.
hand , to b e e xcreted by the glan d ular epithelium of the
im e p h ri d i a
Further evidence of the excretory function of th e
ffi
A t present it is s u
et
c h l ora g og e n cells will be presented later
n o i e nt
to note that an important part of the e xcretory function is
iz a p p are n tl y performed i n the abo v e manner ; and it seems possible
"t h a t the increased ciliary sur face pro vide d b y the vascular nephros
t o mi a l proce s ses has proved advanta geous in facilitati n g the removal
rom the coelomic fluid a nd has there
o f soli d e xcretory particles f
fo re been acquired in relation to this function ( co mpare R O S A ,
"o th e r
.
.
‘
e
,
1 9 03 )
The v e n t r a l l i p o f t h e n e p h r o s t o m e di ffers from the dor s al
as in apparently all other
l i p in b e ing entire and non vascular
a
i
c
o
l
pecies
It presents a curious and hitherto undescri b ed
A
ren
o
f
s
1
f
h e shape o a large
thin walled hollow vesicle
i t m odification in t
2
4
Plate
Figs
which
occupies
its
median
portion
and
is
pro
2
2
1
)
(
,
l o nged a t either end i n to a tubular re g ion of narrower calibre form
o
o
f
n
the
remainder
f
the
margin
the
ventr
a
l
lip
The
entire
i
Li
g
e
a
f
v
nt
r
al
m
rgin
between
th
e
anterior
and
post
e
rior
limits
the
o
i
d ors al lip i s thus i n reality a thin walled tub e
with a central
dilatation constituting the v e sicle in question T he greater part of
h
t
e
f
i
t
w
o
s
all
the
vesicle
and
tubular
prolongation
is
or
ed
o
f
m
f
g
of a c i l i a t e d epithelium conti nuous with that lining t
h e i nterior of
th e nephrostome ( s e e p
In cros s section th e epitheliu m of
th e ventral lip is foun d to curve out ward as the margin i s reache d ,
a n d to pa s s wi thou t demarc a tion into the e ithelium co vering the
p
o ute r surface of the tubular region s This e pithelium e xtends around
the g reater par t of the circu mference ofthe vesicle and the marginal
tu b ul e ; it ceases abruptly , however at a well defined line an the
o uter sur face ( F ig s 2 6 ) a n d the remainder of the circum ference
i s formed of a thin
tra nslucent membrane which at its j unction
wit h the wall of the nephrosto me beco mes continuous with the
peritoneal cov e ring of the ne p h ridium Near its line of j unc tion
with the nephro s tomi a l wall th e membrane may s how a fe w blood
ve s sels d erived from the general nephridial net work but to war d s
its junction with the epithelium such vessel s are generall y wanting
T he interior of the vesicle is ty pically co mpletel y shut of
f from
direct co mmunicatio n with the body cavity O ccasio n all y ho w e v er
a fe w ova may b e seen within ; these ma v hav e gain e d acces s to
its interio r as ob g on i a and have there undergon e further growth
a n d maturation
The thin walle d membranous portion ma y pos s i bl y
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R alp h
3 66
S
.
L i lli e
e xhibit occasional interruptions in its contin uity which m i g h t a d
o
o f the passage of minute b odies such as the earl y ofi g o n i a i n t
interio r of the vesicle Leucocyte s appear alway s to b e p r es
there to a greater or less degree D efinite O penings b ow e
placing its interior in free co mmunication with th e bo d y ca vity
not exist The cavity in fact appears simpl y to repre s ent a n e n l a r
l y mph s p ace It i s lined by a thin lay er of connecti v e t i s s
containing minute bloo d vessels and occasional n uclei a n d d i m
co n tin uou s with the me mbranous portion of the wall of th e v e si
T he remainder of the ventral lip b e low th e tu b ular m argi n
like all the non marginal portion ofthe nephrosto mial wall co mp o
l i n ing
of ( 1 ) an internal lay e r of cu b ical ciliated epithelium
interior of the n e p hrosto me ; and ( 2) an external connect i v e ti s
lay er b earing blood vessels and continuous with the p e ri to m
h e outer s ur fa ce of the entire organ
c overi n g t
T he manner in which the ventral lip acquires its cha ra cte r
structure is at pres e nt some what uncertai n T he vesicl e a n d m a rg
t ube make their appe a ranc e at a r e latively late period of d e v e
—
the l a r g e
ment and are not pre s ent i n larvae of 1 0 1 5 mm
have so fa r reare d The pro b able manner of t h eir forma ti o n
however be in fe rred from a co mpari s o n of the adult a n d 1a
nephrostomes I n larvae of the above dimensions th e n e p h ro s t
is formed of a singl e lay er of cu b ic a l ciliate d c e lls cover e d e x tl
ally by a thin peritoneal layer ( Plate 2 5 Figs 4 3 4 4 4 8 etc )
pos s e s ses an e n tire margin along whos e d orsal portion r un s
nephrosto mial vessel ( Fig s 4 2
T he ventral lip is s h orter t1
the dorsal lip b ut in other respect s possesses a similar s truct
i
f
m
m
Fig
The
or
ation
a
tubular
ar
in
had
t
s
ori
in
n
i
o
f
g
g
(
proba b ility primarily i n an increase in the extent of th e cili a
surface I n the adult organ the original border of the n e p h ros t
i s undo u
b tedly represente d by the line of s eparation b et w e en
epitheli a l and me mb rano us portions of the tu b ular margin ( Pl a t e
Fig
T h e m e mb ranous portion appa rentl y represents th e o ri g
peritoneal layer which is here no lo n ger ( as o riginall y ) in i mm e d
contact with the o uter wal l of the nephrostome b ut has b e c "
s epa rate d
from the latter b y the for matio n of a marginal l y r
or m The manner in which the p r e s
s pace of v e ry definite f
conditions arose was thus very probab ly somewhat as foll o w s :
T he epi theli um of the ventral lip underwent a process of e x te n s
in an outwar d direction ; i f the area of the epithelium i n cre a
.
l
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,
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,
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l
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S tructure
an d
D e ve l op me nt o f th e N e p h ri di a
367
.
rapidly than that of the associated peritone um on its outer
the for mer would soon exceed the latter in e xtent and as a
d e
lt would tend at first to curve outward a n d eventually with the
: su
to beco me s eparated from the peritone a l lay er
a n ti n u
e d g ro wth
m arginal space would thus b e for med between the epithelium and
Th is space
3 e peritoneum which was originally i n cont a ct with it
later acquire the definite characteristics presented b y the
a ight
This space inde e d
J h ular marginal space of the a d ult nephrosto me
i -re s e n ts man
f
o
the
characteristics
that
we
should
expect
to
find
y
: J ere s uch its m ode of f
o rmatio n I n cross section its epithelial
wal l is much more e xtensi ve than i ts me mb ranou s wall ; its e p ith e
um is conti nuo us with that of the interior of the nephrostome ; its
rt
e ri or is close d on all sides to ward the body cavit y ; and it is lined
( e ternall y by a thi n layer of connective tissue
continuous with th a t
i b ich i s ev e ry where present bet ween the periton e al epitheli u
m an d
ter en d s of the epithelial cel l s of the neph ridi um Whether
l e ou
tit
h e con d itions of its formation were of the m echanical kin d
l rr not t
there see ms little doub t that it represents e s s e ntiall y
above im a gine d
r l arg e and well defined l y mph space betwe e n the per i toneum and
g
t e r sur face of the nephrosto mial epithelium
j he o u
T h e b o d y o ft h e n e p h r i d i u m is of a deep b rown color ; it is
l
s p a cio u
s an d u
n coiled
as in all other S pecies ofA ren i cola and taper s
l
t
l
i
h
s
d
i
t
r
n
r
towar
s
posterior
termination
wh
it
j
oi
s
the
la
ge
s
e
e
g
g
y
cont ractile terminal vesicle The brown colo r of th e se reg ions l i ke
th a t of the external integ ument i s d ue to the n umerous excreto ry
gr a n ul e s co n tai ned i n their walls The walls of the terminal vesicle
a re thinner than those ofthe t u
b ular r e gion and are typicall y fol d ed
in s uch a manner a s to present a so m e what morula—
like appearanc e
—
as
represented in Plate 2 2 F i g s 1 4 This a ppearance is a n
inci d ental res ult of the net work like arra n gement ofthe muscle fi b re s
w hich occ up y th e position of the interspac e s b e tween the elevatio n s
O f the s u
r face E ach inter m uscular area thus tends in the con
tracted co n d ition of the v e sicle to proj ect bey o n d th e g eneral s u
rface
i n the manner represented
be and terminal
B oth nep hridial t u
v e sicle are richly supplied with b loo d vessels
a
re
,
,
,
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"
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,
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,
2
.
"
-
,
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,
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-
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-
-
,
,
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-
.
H i s tol og y
.
The lips of the nephrostome a n d its interior are lin e d by a
s i ngle lay e r of colu mn a r ciliat e d ce ll s w h i ch s ho w b ut s lig ht d i f
fer
en ce s of s tructure i n t
h e di f
O ver the sur face ofthe
fe rent reg i ons
.
Ra lph
368
S
.
Li l li e
dorsal processes the e p i t h e l i u m is fold e d ( Text fi g ure on p 362
a nd
is composed of cell s of a more columnar shape th a n t
coveri n g the ve n tral lip which a re more cubical in a p p e a r
2
2
n
l
P
ate
Fig
6
The
di
f
f
ere
ce
i
ha
e
is
however
n
s
(
)
p
and is due in all pro b a b ility to the di fferent con d iti o n s of p
a n d te n sion t
o which the cell s are exp o sed in the di f
fe re n t r
th e epithelial cells of th e processes
being appar e ntly s u
to lateral press ure as indicate d by the foldi n g
are for th i s
m ore colu mnar ; while the cells of the smooth un fol d e d e
of the ventral vesicle
are apparentl y s ubj ected to th e t
tension characteristic of distended vesicles a n d are th us
assume a more cu b ical shape In all essential respect s
th e c e ll s are i d entica l in structure
The y are large and
approximately the s a me s i z e in d i fferent regions and do n
concr e tions E ach is bordere d by numerous stron g c i lia
which has a well d e fi n e d d eeply s taini n g b a s al gr a n ule )
protopla s m exhibits in staine d p reparations th e fi b ri l l a r
characteristic of ci lia te d cells A s GAM B L E
A S H WO R
point e d out ( 1 9 00 p 5 1 5 ) th e cells a re much larg e r th a n
the c ub ical epitheliu m of the e arly nephrostomes The r e la ti v
of the two may b e seen b y comparing Plate 2 2 Fig 6 and P l a
Fig 4 7 which are draw n to the s ame sc a le It will b e
however that the n uclei of the e a rly n ephrosto m e are of a l m ost
cl e i ofthe a d ult structure a n d o c cupy
e xactl y the sam e s ize a s the n u
a correspondingly large porti on of th e cell
I n thei r cil i a ti o n
chara ct e r of the protoplas m a n d general shape ho we ver the c e l l :
are closely si milar
The c ubic a l epitheli um of the funnel pa s s es over into the e x cre
tory epitheliu m of the gland ular regio n by a somewhat a b rup
tran s ition a lthough a fe w of the cubical cells i mm ediatel y a dj o i n ing
the excretory epitheliu m proper may contain gran ul e s in their i n te ri o
and in o ther respec ts exhibit a partially inte rm e d i a te structur e
T h e large excretory cells of the g l a n d u l a r p o r t i o
n Of ti
p
orm a single layered excretory epitheli um lini n g th
n ephridiu m f
int e rior of the organ a n d generall y thrown i nto a well marked s y s te n
folds
E xternal to the epith e li um is a thin con n e cti w
of int e rnal
tis s ue layer b earing n umerous b lood vessels ; externall y the W h O l t
organ is covered b y the peritoneum
I n s tructure the cells agree clos e l y with those of A eca uda tl
as described by GAM B L E
Like most cells o f a i
A sH W O R T H
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S tructure
and
D e ve l op me nt o f the N e phri d i a
3 69
.
xcretory function they are much vacuolated and contain numerous
1
deeply s taining granules The n u c l e u s i s situated in the middle
1
region of the cell usually somewhat nearer the base than the outer
'
1 border
It is large , generall y rounded i n shape b ut frequen t l y of
irregular o utline and contains a chromatin network ofthe appearan ce
repres ente d in Pl a te 2 2 , Fig 5 together with a conspicuous deeply
i s ta i ni n g n ucleolus whi ch in nearly every instance is seen to contain
E
T he vacuolation ofthe nucleolus is character
a w ell d e fi n e d vacuole
l r i st
i c of the excretory cells , a n d also as will be pointed out later ,
n
e
o
f
6 O f t
r
n
large
nuclei
the
g
owi
g
zon
and
the
gla
dular cells
o
f
he
T he pec u
liarity seems to be
O f the ventral wall of the sto mach
nusual me tabolic activity It is noteworth y that in
0 a s s ociated with u
s
f
u
o
e
cretor
y
cel
s
position
the
n
cleus
always
closely
corre
l
h
e
t
x
th e
nds
with
that
i
of the z one of deeply staining e xcretory g ranules
o
p
T he d i fferent region s ofthe cell show very constant and character
ro m Fig 5 which represents a
a s may be s een f
i s ti c p e culiarities
s
A
t
rtion
the
excretor
epithelium
seen
in
cross
ection
its
f
o
o
y
p
L b a s e each cell shows typically a denser structure than at the more
ratio n s
ripheral
portions
and
in
fixed
and
stained
prepa
seems
6
e
p
eltwork of prev a ilingly longit ud inal fi b rils
c omposed chiefl y of a f
appearance which seems characteristic of cili a ted cells
an
T ypicall y th e b a s al part of the cell i s almost free of granules
the
T owards the mi d d le region where the nucleus is s itu a te d
m
rotoplas
b
e comes more vacuolated and is i n most instances largely
p
filled w i th minute round g ra n u l e s which stain an intense b lack
w ith iron haematoxylin
B esi d es these deeply staining granules
there are other s ( which in some cells may prepondera te : see F i g 5 )
which stain less d eepl y a n d see m to have a greater a ffinity for the
a cid sta in s such a s ery t
hrosin T he restriction ofthe deepl y staining
f
ranules
to
the
middle
region
the
cell
is
very
constant
though
not
o
g
a b solutel y so
and give s rise in cross section to the appearance
re pres e nted i n the te xt fi g u
re ( p
The nu mb er of gran ules
h o wever shows great variability
some cells being almost fre e of
them while others are so dee ply laden a s to present an almost uni
formly blac k appearance
T he extreme outer portion of the cell is
usually b ut not always , fre e of black granules , and is co mp os e d
o f a finely granula r
much v acuolated protoplasm which fr e qu e ntly
contain nu merous lightly staining roun d ed b odies apparent l y ofthe
s am e nature as the erythrophilous granules j ust described a s present
i n th e middle region of the cell
These bodies range i n si z e from
e
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'
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R al p h S L i ll i e
370
.
minute g ranules to large rounded masses of hal fth e d i a m e te r o
cell ; they are of very variable occurrence at times v e ry m m
and at other tim es al most entirely absent They app a re ntly
sent the final s tage of the excretory products imm e d i a tel y b
their extrusion into the lu men ofthe nephridium Fre q uentl y b
ound i n the l um e n i m me d i
of precisely si milar appearance are f
witho ut the cell wall and apparentl y s till a d hering to the l :
S uch bodies have evidently recently been extruded T h e in d ica
are therefore that the b lack gra n ules do not repre s e nt the
stage of the excretory pro d ucts ; but that the latter und e rg o a fu
chemical tran s formation in the outer portion ofthe cell s b e fore h
cast out into the l umen
The outer ro unded margin of the cell usuall y proj ect s into
lu men of the nephridi um and b e ars flagella
The n umb o
flag ella is not however constantly o n e to each cell a s s o met
h e ld ; a single cell may frequently be a r a t uft compose d O f s e
flagella The proj ection of the cell b o d y into th e l um e n i
general less pro minent i n c e ll s that contain relativ e ly fe w e x e r
granule s
The t e r m i n a l v e s i c l e is also lined internally b y ex cr e to ry
of the same ge n e ral character as the above
B etwee n th e l
of the epithelial c e lls a n d the i n vesting co n necti ve tissu e
l a ye l
situated a strong network of m uscle fibres who s e str a n d s d
the sur face ofthe vesicle in to the he mispherical elevate d a reas a
d esc ri b e d
In other respects the histological structure of th e v e
is s i mil a r to that of the t ub ular region The muscul a r n e tworl
d e rive d i n a ma n n e r to b e later descri b ed , fro m the l on gi tud
fibres of the b o d y wall and is continuous with these
A comp a rison of the e xcretor y cell s of the a d ult n e p h ri u
with those of earlier s t a ges show s various poi n ts of a gre e m ent
Fig 6 Plate 2 2 show s a longitudinal s e cti o n th r
d isagreeme n t
the wal l of the nephridi um of a larva of 5 6 mm T h e cel l
will b e o b serve d a re much shorter and b roa d e r th a n tho s e o f
a d ul t nephri dium a n d contain fe wer gr a n ule s which furtherm o r e
to show the d e fi ni te n e s s of distri b utio n found in a d ult in d ivi d
I n the g eneral c h aracte ristics of the protoplas m its vacuolati on
its greater d en s ity at the b ase of th e c e ll th e larv a l excretory
ag ree with the a d ult ; and the n uclei a re ofalmost pre cisely s i r
s ize and appearance
even to the presence in ea ch of a con s p i c
nucleo l us which al most alway s contains a well define d vacuol e
,
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R al ph s L i ll i e
37 2
.
boundary is sharply defined ; anteriorly it passes b y a gra d u al tl
sitiou i n to the more fully di fferentiate d region in front T h e p ygil
r e gion thus takes no part in the formation of so mites b ut i s can
pas s ivel y b ackwar d s as the body elongat e s a n d preserve s unch
ged its pec uliar ch aracte rs throughout th e whole d evelopm e n t
T h e h i s t o l o g i c a l structure of the growing z one m a y b e s ee l
a re ference to the figures ab ove m entione d C ros s s ectio n s sl
that the ectode rm of the extreme posterior region of th e b e d
the young larvae is greatly thickene d , and of al most uni fo rm
meter i n all portions of its circum ference ( Figs 1 4 2 1 a n d
Plate
Fi gure 1 4 is a s e ction pa s sing through the posteri o r re;
—
6 so mites The section is slightl y o b liqu e ; d ors
of a larva of 5
it cuts through th e ante rior portion ofthe p a ra troch a l regio n a n dlt
gh the reg ion ofcom mencin g d i ffere n tiation at th e p o s h
tra l l y thro u
b order of so mite V The e ctoder m of the growing zon e i s s e e
be co mposed of a s ingle lay e r of larg e c ub i cal cell s c o n tai
large clear nuclei each of which us ually exhi b its a w e ll d e i
n ucleolus O n pa s sing forwar d from this z one the d orsal a n d l a
re g ions of the ecto d erm a re s ee n gra d uall y to become thi n n e r
defined th e num b e r of n uc l e
cel l li mits b eco m e les s sharply
cros s section beco mes fewer and the nuclei themse l ve s b e com e s m
more d eeply s tained , gr a d ually ass umi n g the usual c h :
and
The ventral ectoder m al so b e cc
te ri s t
i cs of the tissue nuclei
thinner anteriorl y although to a l e ss extent than th e d o rsa l
latera l r e g ions ; and the ventral nerve cord appe a r s a s a fi b r
d if
fe rentiation of th e inner en d s of its cells
The re g ion of lar g e cells with the large clear n ucl e i th us
ferentiate d em b ry onic r e g i o n of
d e n tl y corresponds to the un d i f
gro wing z one fro m which cells are d i vided ofi ante riorl y ; in 0
word s to the t e l o b l a s t i c region D efinite in divi d ualize d te l ob I
however are not present in A renicola at thi s stag e The n ur
of c e ll s in c ros s s ection is not constant and the c e lls s how n o
position to b ecome arranged in rows but si mpl y form an un d
i a te d z o n e which passes by a gradua l tra n sition into th e n
re n t
di ffe rentiated ectoderm in advance Po s teriorl y the ecto d ermal
of the growing zone are
as already me n tioned sh a rply d eli m
fro m the s mall radially arranged pigmente d cells of the a djoi r
p ygidial region ( Plate 2 4 Fig 3 2 ,
The thinning out which the ectoderm shows on p a s s i n g forw
fro m the growin g z one is in all probability due in large part 1
.
,
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,
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,
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-
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,
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-
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,
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'
,
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,
,
,
,
,
-
.
S tructure
and
D e ve lop me n t o f th e N e p h ri di a
37 3
.
body wall by the contained coelomic flui d whose
i o pres s ure must n e ce s sa rily exceed that of the sea wat e r
( m ot
The extension of the b ody wall
t h e rw i s e collapse would result)
th e region immediately an terior to the g ro wing zone is c e rtainly not
s
t
i
m
rely
to
a
process
cell
ultiplicat
on
or
simple
grow
h
Thi
f
o
1
u
e p
ac t that the w all beco mes thin n er and the nuclei
s h own by the f
o r e S parsely di s tri b uted at the s a m e ti m e as the superficial exte n t
m o re as e s indicating clearly that the m a terial which is b eing a d de d
t: th e g ro wing zone i s undergoi n g a re arran g ement a n d exten s ion
f a k ind simi l ar to that which wo uld result from mechanical stret
L i n g T h e expansive force which in this manner str e tches the newl y
o rm e d body wall and thus cau s e s this reg i on to extend b oth tra ns
—
1
2
2
2
Figs
1
is
4
9
1
n
s
e
e
9
and
longitudi
all
y
Plates
e
l
r
s
e
(
y
u a l l pro b a b i l i ty th e o s motic pre s sure of the coelo mic fluid The
or mation of a so a p b u b ble
b ro c e s s ma y b e compare d rough l y to the f
w h e r e th e thick layer of flui d added at th e rim of the pip e bo wl
re
po
n ding to the growing zone ) i s th i nned out a n d e xte n ded in
r
s
o
c
[
re acting on th e walls fro m within
b o th direction s by the pre s s u
rth e r detai l ; it i s pro b a b ly
T h e a n a l og y need n ot b e pursued in fu
al thou g h i n the g row th of the larval
o a certai n degre e
a c c urate t
b o d y wal l material i s undou b te d l y a d d ed a t other region s than at
th e growin g zone
T h e analogy fail s for e xampl e to e xplain wh y
th e ve ntra l bo d y wall r e mains thi cker tha n the d o rs al a n d l a t e ral
The a b ove peculiarities of the e cto d e rm a t a n d i mme d i a t e ly
e g l o ns
h e g rowing zone are how e ver ren d e re d p a rtly int e ll i gi ble
i n front of t
b y this comparison
T he s p ace b et wee n ento d e r m a n d ecto d erm at th e growi n g zone
i s fil le d with a ma s s of un d i f
ferentiat e d meso d erm ; more a n ter i orl y
fe re n ti a t e d a n d s ho ws the usu a l d ivision
th e me sod e r m b eco mes d i f
i n to somite s
A t the ext reme posterior narro w reg i on b et ween the
e nto d e rm a n d the ventral ecto d e r m are f
oun d un d i fferentiate d cells
Fig s 1 0 3 0
o f a ch aracteristic e mb ryonic a p pea rance ( P l ate 2 3
T h e s e cells are ty p i ca ll y l a rger and clearer than tho s e s it u
ate d
m or e a nteriorl y
and a re frequently fo un d i n proc e s s of mi to s is ;
h e y p osses s large clear nuclei each of which t y pi call y co n tains a
c on s p i cuou s vacuolated nucleolu s
T h ey undou bte d ly co rrespond to
th e t
e l ob l a s t
s or m eso b l a stic pole c e ll s w h i ch ter minate the mes o
d e r m ban d s in s o many other S pecies
I n A re n icola howeve r their
nu
mbe r is not co n s ta n t nor are th e y sharpl y d e fine d from the m eso
b l as t ce l l s immediatel y i n fro n t
The extreme p o s terior me s o d e rm
e
x te n s i on of the
-
,
-
-
.
-
.
L
,
-
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-
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,
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-
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-
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,
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,
,
Ral ph
374
S
.
Li ll i e
might ind eed be more accurately d e scribed as consi s tin g ofa a
nuo ns mass of undi fferentiated protop l a s m contai n ing large in
f anterio rly to form
from w h ich smaller nuclei are d i vided of
nuclei of the di fferentiati n g mesoderm The terminal c ells cal
thus strictly S peaking b e regarded as po s sessing an i n d i vid u al
which persists through development D e s cri b ed obj ecti v e ly th e l
d i ti on s are simply as follows : the extreme posterio r mesobh
region contains large clear nuclei in proce s s ofactive m ultiplicai
the nuclei that r e m a i n in this po s ition retain thei r e mb ryl
character while those which are given off anteriorly be c o me smi
and more chromatic ( to d escri b e simpl y the change in a p p e s rar
and form the nuclei of the newly di fferentiating tissue s
demarcations a re in fact di fficult or i mpossible to ob s e r
early mesoderm of A ren icola ; the term m e s e n c h y m e i s
perhaps more accurate in that it does not imply a defini t e e
arrangement of the cells
a condition which is never foun d ill
growing zone of this s pecies
T h e undi f
ferentiate d portio n of the m esoderm i s of v e ry lill
e xtent ( Plate 2 2 and 2 3 Figs 9 , 1 0, 2 9
almost im m e d i a te]
front of the teloblastic region the mesenchyme cells b eco m e arra
to for m the primitive septu m b ou n ding the newly formi n g so "
while the cells applied to the body wall in the same r e g i on
fine muscle fi b ri l s in their i nterior
the precursors of th e I t
tu
d i n a l muscles of the b ody wall ( Plate 2 3 Figs 1 3 1 4 , 2 1 ,
The limit s of th e somites are thus d efined very earl y ; when
—
for me d th e y are very short ( Plate 2 2 2 4 Figs 9 1 0 2 9 ,
1
soon elongate a n d attain the normal proportions a s h o rt di ets
in advance of the growing z one
The ectoderm and mesoderm of the growing zon e th us a
in th e possession of large undi fferentiated cells contai n in g 1
nucl e olate d nuclei which form the posterior terminatio n of
growi n g region and represent the telo b las tic or un di ffe re n ti
em b ryonic region of the elongati n g em b ryo The fact that th e
d if
m b er and arrange me nt
of thi s region are indefinite in n u
ft
markedly in this respect from the s h a rply individualized te l ob
1 8 8 7 ) an d L u
m bri cus ( WI L S O N 1 8 8 9)
of C l ep s i n e ( WH I T M A N
is
i n an y d egree incon s is tent wit h their b eing descri b ed as te l ob l a
Whether the terminal growi n g region is constituted of o n e ce l
The d i s ti n l
of s e v e r a l cells see ms indeed to b e i mmaterial
characteristic of telo b la s tic growth is the presence of a t e r n
,
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,
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-
-
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,
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‘
,
,
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re
ctu
S tru
and
D e ve l op me n t o f th e N e p h ri d i a
375
.
growing re gion , which retains i ts e mbryoni c char a cter
f
o the di f
i
ed
dev
lopme
erent
at
n t and gives ri s e anteriorly t
h
u
t
e
o
r ou
g
h e devel opi n g org a nism ; and on th is crite rion the devel op
ce oft
sa u
ru
ctures in A ren icola is
e n t of b oth ect odermal and m e sodermal s t
other han d does n ot
telobl
stic
T
he
entoderm
on
the
i
a
c
l
a
l
y
p
elongat
by
telobl
pro
as ti c growth and it does not
l
e
t
r
e
n
a
y
pp
exhibit a metameric structure in the s am e sense as
e rl y speak i ng
Its th in walled posterior portion is
o t
he ectod e rm an d mesod e rm
t at th e l ine s of inserti on ofthe primiti v e septa
re q uently d rawn ou
Figs 1 0 3 0
and in this
i s re pre s ented in P l a t e s 2 3 and 2 4
h e e a rly metamerism ; but this apparent meta
tan n e r p a rt a k e s of t
rely i nci d ental and imposed u p o n the orga n
I e ri s m s ee ms to be p u
I t is
mm w ithout a n d th e re fore not inherent in its structure
h y that i n o th e r sp e cies that show te l oblas tic growth the
:ot
e w ort
i ca ll y
te l ob l a s t
o develop
Thi s fact seems
at
e s ti ne neve r s ee ms t
afford s upp ort to thos e authors ( such a s H AT S C H E K M E YE R ,
:o
late ani
BE RG H
G O O D RI C H ) who believe that metameri s m in ann u
mal s is p ri ma ri l y m e s o b l a s ti c and that the other m etameri c
ly s t
e ms of orga n s h ave beco m e implicated in a purely secondar y
nanne n
T h e l a rg e mesodermal and ectod e rmal cells ofthe growing z one
I re
f
e
v
u
u
o
r
t
ab
e
des
ribed
thro
ho
t
the
entire
period
se
n
a
c
s
o
p
,
g
wmi te -forma tion
The ectod e rmal cells a re e vid e ntl y the lineal
l e s ce n d e n ts of the cell s d es cri b ed b y C H I L D ( 1 9 00) a s d e ri ved from
"
”
h e d i vi s ion of the
st
e mce l l s
i e of the two sy m m e trical
l e ri va t
i v e s of the s oma tob l a s t
of the s econd quartette of ecto
n e re s )
whi ch form th e po s terior portion of the s omatic plate
I b ese c ells at the com me n ce ment of the concrescence ofthe s omati c
”
s la t
e form a transvers e b a n d of seven cells l y in g j us t anterior to
:h e
w
s
and
ext
e
d
in
in
the
am
e
direction
ith
it
The
e
ar
r
h
n
s
c
a
t
o
g
p
3 ell s a re large and thick a n d grow rapidly a f
ter d ivision It see ms
p e rf
e ctly clear t h at we have h e re what i s kno w n a s the growing
:i p
i e that portio n of th e body j us t anterior to the p a ra troch
wh i ch continually gives ri s e to the n e w segment s a n d leads to the
el ong ation of the larva
T h e final r e s u
lts of concresc e nce will be
firs t, to u n it e th e end s of the p a ra troch a n d then th e en d s of th e
"
C H I L D d i d n ot
se co nd ro w of cell s
the growing tip ( p
f
o llow the concrescence to its co mpleti on ; b u
rom the po s ition and
tf
re l a t
ions of th e larg e ecto d e rm al cells of the larval growing regio n
t
he re ca n b e n o doubt that the s e are the direct descendents of the
H i tth il u g
a d 2 1 S tati u N ap l B d 1 7
d i fi e re n ti a te d
‘
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,
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,
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,
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,
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.
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,
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,
‘
.
.
’
‘
,
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,
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,
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o
n
en
.
.
00
.
on z
e
e
.
.
.
R a l p h s Li l li e
37 6
.
T he
abo ve b and of cells ( s e e C H I LD loc cit F igs 1 1 2
retai n their large size throughout larv a l developmen t s h owi ng
change in character from the early larval stages ( th re e so
until the completion of the defi n itive number of so m i t e s
The large termi nal meso b las t cell s of th e larva are si mila
be regarded as th e descen d ents of the two te l ob l a s ts of the
mesoder m ( C H I L D loc cit p
e mb r y onic
T h e embry
m esobl a st b ands take up a ventro lateral position b e tween
entoder m and the ventral ecto d er m ofthe posterior re g i on ( F ig 1
A t this stage e a ch band is terminated by a singl e larg e to
”
visi ble di fferen tiati on in the de s c e nd
A ccording to C H I L D
the m eso b last s is very slow The cells retain th ei r e m
"
appearance till a late s tage ( p
The origi n al conditi o n i
each m e s o b last ban d is terminated po s teri orly by a si n gl e te l
cell doe s not apparently persist long for in the larval s
telo b lastic region of th e meso blast alway s contains s e v e ra l
embryonic nuclei a s a b ove d e s cribed which exhibit n o co
n um b er or arrangement Their position however b e tw e en
posterior attach ment ofth e inte s tine and the ventral ecto d e rm co
po n ds accuratel y with their positio n i n later em b ry o n ic s tages
B etween the l a test s ta g e s desc ri b e d b y t
described by C H I L D
author and the ear l iest I have exa mi n e d intervenes a p e ri od wh
has not y et been st udied with re ference to the char a ct e r of
m e sobla s t There can however b e no doubt that exami n a tion we
d i s clo s e a d irect continuity between the te l obl a s ts O f the l a
e mbry onic s tages a n d th e posterior undi fferentiated m e s o d erm 06
of the larval g rowin
zone
g
,
.
.
.
,
,
,
.
,
.
.
.
-
.
.
.
,
,
,
,
,
.
.
.
,
.
n
b
F
o
r
m
at
i
o
( )
of
the S o mites
.
The first larval nephrid i u m a ppears in somite IV an d b e co
reco g nizab le soon a fter the forma tion of th e earl y sep tum w
s e p arate s thi s somite fro m the on e i mmediately a n terior to i t Yo
l a r vae that have j u
st terminated the swarming stag e ( e g P l a t e
F i g 8 ) thus generall y exhibit this nephridi u
m in th e e a rly at:
o f its f
or mation in the m e s oder m of the posterior region S i n ce
of the n eph ridia arise i n exactl y the sa m e m an n er , a de s cri p t
io
the cha n ges t a king pl a ce in the po s t e rior meso d er m of su ch a l a
will appl y to all of the ea rl y nephridial somites The m e s o d
of the n on nephridial so mites undergoes closel y similar ch a n g e s
‘
.
.
.
.
.
.
-
l
S tructure
a nd
D e ve l opme n t o f th e N e p h ri d i a
37 7
.
mesoblas tic somite s of the whol e larval body being indee d
m e d in a n essentially unvaryi ng manner
A s the lar va advances in devel opment the nephri dia ofthe more
es increase in s ize and undergo a more complet e
e ri or somit
i a ti on a t the s a me ti me as the others arise in the gro wi n g
e re n t
H ori z ontal secti on s p a ssing through the nephridial region
i on
ortunate preparat i ons s how the entir e series
ch larvae may i n f
s u
fe r e nti ated rudi ments of the regi on
h e e a rly un di f
rom t
n e p hridi a, f
-d e fi
n e d n e phri dia of th e
to the well
o i n i n g the gro wing z one
r e anterio r somites Fig 2 9 Plate 2 3 represent s such a prepara
O n th e right
n
i n the case of a l arv a of about ele ven somites
no t
h e secti on passe s s l ightl y vent rad to th e ventral hoo k ed setae
3 s h ows th e larval n ep hrid ia from the first ( in somit e I V) to th e
th
u
o
5
f
f
u
f
i
n
di
erentiated
r
diment
the
e
fi
t
h
e
d
r
n
i b ( s omi te I X
(
);
m ) is j ust visible a t the angle between the n ewly
" n e p h ridi u
In Figs 1 6 to 2 2 inclusive
m a n d the hodyw a l l
: ming sep tu
l ate
h a ve b e e n represented cross sections of the succes s ive
a n d the post mes oder ma l region
a rv a i n
m
s
a
l
i
o
f
i
o
t
e
d
s
h
r
i
a
l
p
e I X i s in proce s s of f
ormation The di fferent stages in
: I i ch s omi t
early development of a n eph ridi um can thus be stud ied to
3
v a ntag e in singl e larvae of thi s a n d si milar stages T he develop
en t of t
h e n e phridia is however so intimately b ound u
ith
that
w
p
th e s o mi te s that it will b e n ecessary firs t of all to con s ider th e
te r p rocess in detail
T h e firs t changes
prepara tory to somite for mation that take
ferentiate d me s ode rm al reg i o n consist in
we i n th e posterior un d i f
m ul ti pli ca ti on and subsequent rearrange ment of the mesodermal
l s which at first are tightl y packed together at the posterior angle
—
—
w ee n th e intest ine and the b ody wall ( Plates 2 2 2 4 Figs 7
10
t
The manner in which this rearrangement is a ccompli s hed
be seen from the above drawin g s e s pecia l ly the sagittal
ly
i on s ( Plat e 2 3 Figs 1 0 and
:t
and
th e horizontal s e ctions
Fig 9 a n d Plate 2 4 Fig
The closely packed po s terior
at
e 22
ghl y defi n ed
s od e rm is here seen to be bounded ant e riorly b y a ro u
p a rti tion whos e cel ls are directly continuou s with the
n s v e rs e
: s e n ch y
ully for me d adj oin
e cells lining the cavi ty of the m o re f
s
9
a
t
o
m
ite
V
I
i
omite
I
I
Fig
Thi
s
p
r
ition
th
e
re
f
ore
F
V
I
s
;
g
(
ront of the one
) re s ents the posterio r wall of the s omite n e xt in f
u
u
r
ess
o
r
ma
t
ion
defines
the
po
s
ition
o
f
the
t
re
inter
f
f
a
n
d
f
oc
o
p
l
f
m
i
c
sep
m
o
which
structure
it
in
f
act
or
s
the
anter
or
m
n
f
t
a
t
u
g
th e
.
’
,
.
,
.
.
,
.
.
.
,
-
e
.
.
.
.
-
,
,
,
-
.
,
,
,
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,
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,
,
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.
l
m
,
,
.
.
,
,
,
25
*
,
R al p h S L i ll i e
37 8
.
as will be ho wn beyond A s the number of m e s e nch
cell s behind this partition incre ases
h e m ultipli ca
chiefly by t
h e large polar nuclei
an irreg ul a r hollow S p a ce appl
of t
between the cells i n the ne i ghborhood ofthe partitio n a n d grad n:
enlarges app a ren tly in part by the absorption of fl ui d from
a dj oining coelomic cavi ties The space s o for med re p res ents
early coelomic cavity of the somite which i s in proce s s O fformati
it be co mes pro g ressi vely better d efine d as growth pro c e ed s vi
the lay e r of meso b last for ming its w a lls becom e s irreg ul a rly appii
to the s urface of a djoining s truct
w a ll of the next somite in front ,
b ody wall inte rn a lly to the wall of
the den s ely p a cke d m e soderm of the growing region
partiti o n forme d by the apposition of th e s e me s ob l a s
po s t e rior w a ll of th e somite in front represen ts the earl
ormi n g intersegmental sept um and thu
of the newl y f
anteri or boun d ary of the n ewly forming so mite The e ar l y
n
thus consist s ess e ntially of the O pp osed walls ofthis incipi e nt su
and of th e s o mite in front Its characteri s tics and relati on s to
n e ph ridia will sho rtly b e co n s id e red in detail
The b ilaterality of the early mesoderm is n ot very d e ci dl
pronounce d A v entral mesente ry is apparentl y not fo rm e d in
anteri or region of th e bod y a n d the coelomic cavities of th e
sides are there fore fro m the first contin uo us b elo w th e i n te si
the right a n d l e ft cos l l
D orsally however ( Plate 2 3 Fig
cavities r e main di s tinct a n d the adj oi n in g wal ls ( which s o on a s s
a me mb rano us cha racter ) b eco me applied to one anoth e r ab ove
intestine forming a b ila min a r me mb ra n e who s e la mell a e a re
the condition s of their formatio n necessari l y conti n uou s w ith
and W i t h
m es oderm coveri n g the intestinal and b o d y wall s
lamellae of the pri mitive septa Th i s me mb rane con s tit ute s
dorsal mesent e ry which per s ists thro ughout li fe and s uspe n d s
i nte s tine to th e dorsal bo d y wa ll
B e fore co n si d ering in greater detail the charac teristics o f
primitive septa th e formation of the d orsal and v e ntra l b l t
since these structures appe a r
v e s s e l s may be b rie fl y d escri b ed
early and apparen tly p l a y an i mportant p a rt in the nutritio n 0 1
gro wing region The dorsal bloo d ve s sel is earl y forme d a s a s
b etween the O pposed lamellae of the d orsal m e s en ter y ( P l a t
Fi g s 1 3 2 0 a n d
It does not , however a p pear to beco m e
l amella ,
s
l
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,
,
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,
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l
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,
,
R al ph s L i ll i e
330
.
at th e z on e wh e re le a st resis tance i s o ffered to th e p a s s a ge of1
b etween the two vessels and thus represen ts no s h a rp l y define
persistent channel The b ranching b lood sinu s wh i ch in later
e nvelopes t
h e stomach region s ee ms to b e for med i n e s s e nt
iallr
same manner
T h e primiti ve s e pta are formed
as ab ove des c ribe d , by
apposition of the a djoining walls of two successi v e meschli
s omites
T h e walls of th e se earl y s omites are
h o w ever no
formed of a reg u
l a r epitheli al layer ofwell
appearance con s ist of a continuous syncytial layer ofp
taini n g numero us nuclei ( Plate 2 3 Fig s 1 3 1 4 , 2 3
a pplied to the s u
rface of adj oinin g structures Ea ch 11
for p u
rposes of de s cripti on b e regarded as b elongin g to
cell b ut definite cell wall s at t h is stage at leas t a r
disting ui sha ble
T h e str u
cture of a s e p t u m at i ts e a rliest d i s ti n g ui s h a b
ma y b e b est seen i n Fig s 9 and 1 0 Plate 2 2 a n d 2 3 a n d Fig
Pl a te 2 3 A t this pe rio d of i ts formation th e s e pt um fo r m s an
gular n ucl e ate d partitio n s e parating the ca vity ofthe n e w ly for
s o mite f
ro m that of the s omite next in ad vance A t t h i s stag
b ilaminar str ucture can wi th certai n ty b e d i scer n e d in i t a nt
constitu e nt cells , which re s emb le in all re s p e c ts th e o the r m e s od
cells of thi s region seem to b e en ti rel y undi fferentiate d a n d si
to one another A s growth proce e ds howev e r , the coel o m i c ca
incr e ase in size and in transverse dia meter in the mann e r d ose
on page 3 7 4 ; the s epta a re th u
s s ubj ected to a stretch i n g pa
and increas e rapid ly in s upe rficial extent b eco ming a t the
ti me thinner a n d b e tt e r d e fined D uring th is process th e op
faces of the cells of the two s eptal layers ( which are n o w 11 1
d i s ting u
i s hab le fro m each other) a s sume a more me mb ra n ou s ch ar
b ecomi n g at the s ame tim e mo re deeply s taining and a p p a re n
a d e nser con s is tenc y ( Plate 2 4 , Fig
A s the septu m c e n t
to extend it acq uires more a n d more of the ch a racter o f a
mem b rane and the nuclei of its con s tit uent cells are mov e d f:
an d f
arth er apart Finally the sept um acq uires the a p p e a ra n
a thin , sharply defin e d m e m b ra nous partition exten d ing a e r o s
b o d y cavity and to wh ose s urface the original nuclei ( e a ch o f i
is still surro unded b y a s mall qu a ntity ofundi fferentiate d p rotO p
—
are appli e d at infreq uent inter vals ( Plates 2 2 2 4 F i g s 9 , 2 9
A t the j unction of the septu m w ith the b ody w a ll and w i t
,
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S ti u
ct
u
re
an d
’
D e v e l op men t o f th e N e p h ri di a
38 1
.
blood vessel the two closely appl ied lamellae are usu
rom each o ther w here they p as s
e n to be slightly separated f
i nt
In the lar va re p re
inu
i ty with the peritoneal m e mbrane
i l l sectio n in Fig 9 the interlam ella r s pace is continued for
m
ht di s tan ce outw ard from the lu en of the su b intestinal
ve s s el ;
thi s S pace repre s ents in a ll pro b a b ility the b eginning
s e g menta l blood v ess e l which lat e r passes to the b ody wall
I v e rs e s the dors a l li p of the nephros to m e
The septu m is seen
figure ( a n d also in Fig 1 0 2 9 3 1 , 3 3 Plate s 2 3 and 2 4 )
inuous at its lateral margin with the lips of the
ome co n t
t
h
e
b ody wall its cells b e co me
A t its insertion into
st
ome
h e b o d y cavity
lou
s w ith tho s e li n i n g t
he line along which th e septum is ins erted into the b o d y wall
wo succe s si v e
i l l v con s idered to mark the b onn d a rv between t
This line occupies in A ren i cola a constant and de finite
s
n with re feren ce to the other segmental s tructures of th e
pi n g l a r va D uri ng the formation of the me s o b la s tic s o mites
undergoe s a di vi sion into seg me n tal re g ions
ad v wall a l s o
ue ta me ri c structure of the ecto d er m is mo s t cons picuou s ly
ed
b y the s e t a e wh i ch a ppear at an early stage in the
ll s
b etw een the succes s i ve s epta The seta sacs which give
th e s e str uct ures a ppear l a te ra l l v in the e ctoderm in a position
2
v b ehin d the middle of the inter s epta l re ion
i
3
F
Plate
( g
g
entral e ctod e r m in the neigh b orhoo d of the nerve cord a lso
exhi b its a me ta meric s tructur e b eco ming s li g htly th inn e r or
e ted at segme ntal inter va ls
The septa are inserted v entrall y
a transve rse line pas s ing i mmediately in front of th e con
n ( Plate 2 3
Fig
Thi s line therefore i f the above cri te
tseg me ntal li mit s is accepted marks th e b oundary b etw e en
sive s omite s
Later in de velopmen t when the septu m h a s
ea red a s s uch th e po s ition of th e line of de marcation corre s
cl os e l v with that of the nephrostom e a n d i t
s a s s ociat e d b ranch
s e gmen ta l b loo d vessel
both of which s tructure s a s a lre a dy
a rise in inti ma te co n nection with the pri mitive inter s eg m enta l
i
st
i na l
-
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5
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,
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,
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,
,
-
,
eptum when firs t for me d con s titutes a complete partition
n the bod y ca vitie s of a dj a ce nt somites
S oo n a fter i ts forma
e d ors a lly as alread y menti o ned
owe ve r, it b e co m e s inco mpl e t
and for the remainder of its exi s t e nce it i s fou n d only in
nt
h e b o d y ca vi tv as an incomplete m e mb ranou s
ra l p orti on of t
he
i
s
,
,
-
.
,
-
Ra lp h
332
s
.
Li lli e
partit i on exten d ing from the ventral blood vessel to th e v e
lateral b ody wall I t usually b ecom es i n complete at th e s e
third so mite in a dvance of th e growi n g region ( Plate s
—
apparently as a result of
Figs 8 1 0 2 9
eventual disruption of its dor s al portions The
lead to thi s result seem to d epend in part upon
increa s e in the transverse di a meter of this regi
associated as ab ove d e s cri b ed w ith an increase in
b o d y-wall A further re ference to Plate 2 3
represent sec tions through successive s omites of a single
show th at the increase i n trans v erse di a meter i s d epen d
upon the extensio n of the thin walled dorsal and lateral
the b ody wall It see ms there fore pro b a b le as ab ove
that the septa first b eco me inco mplete in the dor s al re g i
in conse quence of the undue stretchi n g to wh i c h the y
s ubj ected wh ich has cause d here a thi nnin g
r uptio n and disappearance of the septa O n the other h
ventral portions per s i st for a v ery con s iderable perio d , a n d p lay
import a nt part in later development i n connec tio n with th e n e p hri
and nephrosto mial b lood ves s els
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I i lt
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-
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m
c
F
o
r
a
t
i
o
n
( )
of
the N ephri d ia
.
I shal l now proceed to a descriptio n of the h i s t o g e n e t i c p
cesses b y which the neph ridi a are di fferentiated outofthe o ri g inally
u ni for m so ma topleuric layer of the me s o b last I n the regio n imme
d i a te l y adj oini n g the pole cel l s t his l a yer a s descri b ed a b o ve, i s
compose d of a conti n uous n ucle a ted protoplas m witho ut c e l l -hm
dari cs a n d witho ut visi b le d i fferentiation ; at a slightly more a n terior
positio n howe ver where the so matople ure passes i n to c o n tinuity
w ith the newly for ming sept um the d i ffere n tiatio n ofthe long i tudi nal
m u s cl e fi b re s of the b ody wall is alrea d y in progress Th ese
str ucture s make their first appearance at a very early pe riod i n
that portion of the meso b last which is in i mme d iate conta ct w ith
the ectoder m of the b ody wall ( Plate 2 3 , Figs 1 3 1 4 2 1
T he
fi b res fir s t b eco me vi s i b le in two ventro lateral areas on eith e r s ide
which is j us t b eginning i ts ap p e a r a n ce
of the ve n tral nerve cord
a n d at a slightl y later period they app e ar al s o i n t
wo d ors o
lateral areas on either side of the dorsal mesentery A l on g the
line of i n sertion of th e dor s al setae muscle fi b re s do not a t fir st
appear
.
-
,
,
,
,
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,
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ct
ure
S tru
a nd
D e ve l op me n t of th e N e p hri d i a
38 3
.
ea rli est a ppearance the fi bres have in cross section the
d
a
row
deepl
y
s
aining
ots
at
the
b
oundary
b
etween
t
o
f
e
f
r
n
ce
o
a
a
p
21
A t a s lightly
= 0d e rm and m e soder m ( Plate 2 3 F i gs 1 3
2 3 ) the dots have b eco me larger and b ett e r
: e r st
a ge ( Fi gs 1 5
l in e d , a n d have assumed the ty pical appearance of t riangular
d
ne
s
h
ped
str
ctures
which
stain
ver
y
eeply
in
the
erythro
i
:d
u
a
e
s
,
g
In the vent ro
1 p roject i nto the protopl a sm of the meso b last cells
e r a l region the me s o b l a st nuclei have b ecome arrange d i n a single
h e appearance
e r, a n d i n cross s e ctio n the meso b last h a s assu med t
of a row of nucleate d cells
i c h i s very typical for this stage
by
cell
walls
a n d contai n ing in their interior deeply
le
t
r
a
e
d
a
p
Fig s 1 3 1 5 1 9
[ m ing lon g itudi n al mu s cle fi b rils ( Plate 2 3
i s evi d en t th a t the longitudi n al muscle fi b re s are originally laid
which may there fore with pro
e r i or o f th ese cells
7 n in the int
termed
m
y
o
b
l
a
s
t
cells
T
h
e
cells
h
owever
it
is
to
b
e
e t
e
h
y
ze d
present no constant and regular arrangement and are n ot
A t this s t a ge the longitudinal
rom on e another
h rp l y defi n ed f
L s cl e s a re t
hus compose d of fi b ri l l a e appli e d to the b ody w a ll and
ferentiated protoplas m
e rna l ly by a nucleate d la y er of u n di f
e re d i n t
r cO l a s m)
T
h
e
condition
recalls
that
which
exi
s
ts
throughout
p
a in ce rt a in other S ecies
u
partic
larl
y
the
Nemathel
inth
s
The
m
e
p
ms ve rs e m uscles on the other h an d are not visi b le until a much
age ; they appear externally to the longitu d inal m uscle s a n d
e r st
‘
m
o
d
ntly
n
relation
to
the
inner
la
y
er
f
the
ecto
er
al
cells
i
t
e
a
p
o do with their
e a b ove myobla s ts a t all eve n ts hav e nothing t
ion
rmat
gh the region immediatel y b ehind
C ros s s ections passing thro u
e e arly septu m S how the a b o ve descri b e d appearances i n a chara c
i o man n er ( Fi g s 1 3 , 1 5
Longitudinal section s ( Plate s 2 2 a n d
ri s t
1, F igs 9 1 0 and
assing
through
the
ventro
lateral
regions
S
ho
w
p
at t
h e meso b la s tic lay er is thicke s t and b est define d a t the j unction
se p t
um and b od y wall It is i n this reg i on that the e mb ry onic
ld ime n t
first beco me d i s tinguish a b le fro m th e
s of the nephridia
s t of t
It must b e e mph a si z ed ho wever th at
h e mesobla s tic layer
ar
e i s a t first no setting aside of spec i al ne p hridial cells ; nothing
”
I n a ra b l e to the septal n e p h rob l a s t
b
f
u
s
b
or
nnel
cell
descri
ed
v
s
p
A t th e
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,
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,
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"
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,
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,
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-
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,
,
'
-
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,
.
“
1
E
D
.
M E YE
R
0
1
1
9
i
)
(
g ve s
p e a r tha t a n
a
s
umma ry
of
-
th e e v i d e n ce
i ch i t wo ul d a p
e ct
o d e rma l o ri g i n i s
r
la r b ody mus cul a ture of a n n e l i d s
th e ci cu
.
on
th e rue
l
,
thi s
p oi n t
,
fro m
i f n ot i n va ri a bl e ,
R a lp h
384
S
L i lli e
.
WI LS O N and B E R G H and more re c e n tl y v
The nephridia simply b ecome gradually d i ffe re nti at
orm and ho m ogenous mesobl a s t w h i ch in
of an originally uni f
stages pre s ents no definite cell b o undaries T he d i ffe rentiatl
the nephridium sta rts from the angle between s e pt um and
wall ; b ut at first no visi b le d i fferences exist b e tw e e n the h i
b las tic mesoderm a n d th e adj oining myoblastic or s e p t a l mess
The first signs ofthe appearance of the n e p h r i d i um are u
us ually at the second s eptu m in advance of th e g rowing l
Yo ung larvae of five s omites thus as a rule exhibit th e firsth
nephri d ium in the earliest stages of its formation
section represented in Fig 9 Plate 2 2 shows th
d
2 nephridium in somite V
A t this st a ge th e ru
has the form of a somewhat triangular mass of
ou
s anter i orly with the f
ourth s eptum Fig
ti n u
a s imilar stage in the formation of the fourth neph
similarly represents the r udi ment of the sixth T h e contin u
ity
the septum at the j unction of th e latter with the bod y wall ii
di
haps the m ost characteri s tic feat ure ofthe earl y nephridial r u
The histologic a l di fferentiation of the nephridial cells c:
st udied to b etter adv a ntage in trans v erse s e ctions In P la
Fig 1 3 which represents a s ectio n th rough th e fo urth septal
—
of a larva of 5
6 somites
the somatopleuric cells of the v
lateral region are entirely alike wi th nothing to disti n gu
is
future nephridial regio n fro m th e other portions of th e mes
T h e protopl a sm is homogenous a n d non granular
th e n u
cl
similar to one another in s ize a n d appearance and cell wal
indisting uishable A t this s t a ge in fact no essential di fference
b etween the cells of this interse g m ental region a n d tho s e
i n terseg mental region of so mites II a n d III where no n e p h ri d
In F i g 1 5 whi ch represents a l
formed ( Plate 2 3 Fig
through the b eginning of so mite VI in a larva ofa b o ut eight 8 1
one of the cells of the right side is distinguished from the
by th e presence of a small s pace bordered b y d eeply st
p rotoplas m which has ma d e its appearance in the i mme d iat
nit
f
o
the
nucleus
T
is
min
u
te
space
is
the
fi
r
st
in
d
ic
a
ion
h
t
y
appea rance of the n ephridial lum e n w hich it is of inter e s t t1
always s e e ms to arise in th e neigh b orhood of the n ucleu s I r
respects the cell which S how s this peculiarity is entirel y s i m
the adj oini n g pure l y myoblastic cells e v e n t o t h e p o s s e
V E JD
O V S KY ,
'
-
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.
.
,
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-
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,
,
‘
,
-
l
,
-
,
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,
,
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,
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,
,
e
,
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,
,
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,
S tructure
D e ve l op me n t of th e N e p h ri d i a
an d
m us c l e fi b r e s i n i t s i n t e r i o r
385
.
Fig 2 3 , Plate 2 3 shows a
i l a t conditi on
T he nephridium is thus di fferentiated out of a
ti on of the ori g inal mesobl ast which in its early sta ges posse s ses
S ame prope rt
i es and undergoes the same t
rans formations as th e
B I porti ons of the l a yer
At a s lightly later stage the neph ridial cells become more re a di l v
ting ni s h a b l e fro m th e a dj oini n g purely myoblast cells The lumen
ferentiating organ i n
0 1118 8 m ore di stinct and the bo d y of the di f
us e s in siz e a pparen tly in part at the expense ofth e protoplas m
t
h e adj oining m esoblast cells , which b ecome visibly smaller In
18
h e nephridial rudiment i s soon ob s erv ed to b e more
s ection t
n i n e nt t
han th e adj oining m y oblasti c cells and its bounda ries
: a r b ette r d efine d ( Plate 2 3 ,
Figs 2 3 le ft , 1 9 le ft) Its pro to
be co m es vacuol a te d a nd minute g ra n ules in many c ase s b egin
n
mak e their ap p eara n ce i n its interior ; the lumen beco me s pro
S s i v e l v w i d er a n d better defined and the cil i a beco m e vi sible
t h e s ection repre s ented in Fig 1 9 ( 3 somites from the growing
3 ) t
h e n e phri di um of the le ft side is somew h at more a dv a nce d
1
t
h a t of the right a n d i s b e co ming s h a rpl y defined fro m the
D i n i ng myobl a st cells which ha v e percep t
ibl y d iminishe d in volume
th e next somite of the same l a r v a Fig 1 8
the
b
oun
ries
the
d
a
o
f
(
)
l rri d i u
m a re quite definite , and fl a ttened mesobl a s t cell s a re b e
l in
t
s
i
pplied
to
ur
a
e
to
or
outer
peritone
l
cov
ring
a
s
f
c
f
m
h
e
a
t
e
g
The nephridi um in the somite next in advance
th e organ
1 7 ) is still more highly di f
ferentiate d ; the lumen is more
h e excretory g ran u
les are more numerous A t this
c ion s a nd t
f
m
o
the
organ
has
the
orm
o
f
a
si
ple
t
u
bule
with
an
intr
ellular
a
c
g
e ri orl v through the se p tum into the cavi t
re n openi n g a n t
y of the
oi n i n g so mite
The progre s sive histologi ca l di fferen ti ation of
e a rl y nephridia is w e ll s hown in the series of se ctions rep te
lt
e d in th e s e dra wing s ( Plate 2 3 Fi g s 1 6
A s the nephridium advances in d e velopment the my o b last cells
d uall y dimi n i s h in volume while at the same time the muscle fi b ri l s
E ventu a ll y the n u
th ei r interior increase in size ( Figs 1 6
ia te d protopl a s m or sarcopl a s m i s redu ced to a thin la v er
e re n t
up y i ng the i nter s tices between th e fi b ril s and cont a i n ing here and
—
3
s I n l a t e r s t a g es ( Pla t e 2 Figs 2 5 2 8 )
re a fl a ttene d nucle u
ch more nu merous a n d mo re clo s el y s et
mu s cle fibre s b e co me m u
and the s a rcopl a s m i s red uced to a n incon s picuo us inter
e th e r
i ll a r m a trix in which the fibre s a re i mb edded T he innermos tla v e r
-
.
.
.
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,
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,
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,
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,
-
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,
.
'
,
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,
'
.
.
Ra l ph s Li ll i e
336
.
sarcoplasm seems to become m e mb ranous a n d to contribri
the for mation of the peritoneal lining of the b ody ca v i
diment ca n as a rule be di e tin g
T h e nephridial r u
the septu m has assumed a definite membranous s tructu
Fig
It is t h ere fore di fficult to decide wh e th e r
nephri d iu m is derive d chiefly fro m one or oth er of th e
m is composed or fro mboth From al l
ofwhich the sept u
h o wever it seems clear that neither lamella I s e xc
in its for mation but that b o th contribute i n part ;
septal meso b last also participate s in the process
of the nephridial rudi ment and that of the septal cell s
con t
s with one a n oth e r ; it is o n l y later tha t the b
i n ou
the two b ecome sh a rpl y define d The fa ct ho wever ,
very earl i est a p peara n ce the nephri d i a l lumen commu
the b ody cavity of the prece d ing somit e proves
wall of this somi te enters in part at least in
the early nephrostome It cannot however , be said th a t the net
ormed exclusively fro m the posterior wall of this so
ome is f
st
T he earl y nephridial rudiment is in fact a conti nuOus a n d un di
structur e wi thout regional d eli mitations and it is n ot u n til
later that the nephrosto me b ecome s d istinct fro m th e glan
po rtion of the org a n It is i mpo s s i b le the refore , to s a y that
definite portion of the nephri d iu m i s derived fro m one somite
another portion fro m another so mit e It is even i mpos s ible i n
early stage s to shar p ly de fi ne th e limits of the mesoder m o f 81
sive somit e s s inc e th e di fferentiation of so mites is itsel f 9 gr
proce s s a n d the nephri d ial r udiment is already l a id d o w n l
the seg menta l limits are sharpl y d e fi n ed It is h owe ve r tru e
ferentiate d c on d ition the nephridi um is conti
i n its early undi f
w i th mesoder ma l tissue which later forms p ortions oftwo s ucc
so mites The orga n , however is d i fferentiated a s a wh o l e w
strict reference to segmental limits E ve n ce ll limits a s a]
pointed out are not sharp l y defined until the orga n has a l
acquired m a ny of its most disti n ctive characters T he wh ole
earl y nephridiu m i s , however s trictly m e s o b l a s t i c and the ce t e
plays no part whatever in i ts for mation L a ter in d e ve l op me
will be sho wn the ectoderm app a r e ntly contrib utes to the for i
of the terminal vesicle ; but as orig i na l ly laid do wn in e a rly ( 16
ment the entire organ i s strictl y mesobl a stic
The structure ofthe e a r l y n e p h r i d i u m , as p resent in th e
of
t
he
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,
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-
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R al p h
38 8
s L i ll i e
.
It is noteworthy that at the s tage r e p re s e n te d
Plate 2 4 the two fore most pair of nephri d ia a re i n a l l res
altho ugh the anterior of the two later on com p l e te
an d d isappears while the posterior continue s i ts
for ms th e fi rst d efi nitive nephri di um of the ad ul t
nephri d i um ( in so mi te I V ) has in m
T he ti me of its d isappeara nce i s
a t this stage
larvae it has alrea dy d isapp e are d at a stage of 9
in othe rs it ma y persist in a rec ogni z able form
so mites h ave bee n attaine d The secon d larval
correspon d to the fi rst d e fi n itive n e phri d i um
d e g enerates an d disappear s , b ut not until a con
,
.
.
.
L
ater
D
e v el o p me n t o f th e
N
ep
h ri d
T he later d evelop ment of the nephri d ium consists
an increase in si z e an d an acco mpanying division i n t
cells with d efi nite bo un d aries ; ( 2 ) in a d i fferentiati on
region of the ne phri di um an d appa rently also of a
a djoining septum to for m the nephrosto me , an d in the e stabl
of characteristic relations with the bloo d vessels ; a n d ( 3)
E ach of these p ro c e ss es
for mation of the ter minal vesicle
consi d ere d in or d e r
,
,
.
.
S
ub d i v i s i o n i n t o C e l l s
.
I n nephri d ia of the stage represente d in Fig 3 4 , P l ate l l
d e fi nite cell bo un d aries are vi s i b le altho ugh th e protopl a s m Ill
l
u
typical vac olate d struct ure a n d contains excretory gra n ules
re mains none th e l e ss contin uo us an d un d ivi d e d fro m e n d to "
i ts n u
of the organ ;
clei a re s mall an d as yet d i ffer o n ly aligi
fro m the nei ghboring m eso d erma l an d ecto d er mal n uclei of the b1
wall T h e l umen retains t hi s int racel l ular character for a cousi
able perio d F i g 2 5 , Plate 2 3 represents a c ross section of the
nep h ri d i um ( so mite XI ) of a more a d van ce d larva than tha
Fig 3 4 ; the organ has increase d consi d erably in si z e an d i ts p
plas m together with the large n ucle olate d n uclei shows the s trn l
chara cterist i c of fully d i ffere n tiate d an d functional excretory
A s yet h o wever cel l li mi ts have not appe a re d an d th e l u
m en re n
intracel l ular Fig 3 7 , Pl a te 2 4 represents a longit ud inal s coti c
the correspon d ing neph ri d i um ( s o mite XI ) of a slightly m or e a d v a
larva in which the organ is beginning to s how a s ub d ivisi o n
.
-
,
'
.
.
.
.
,
,
-
,
.
.
c tur e
S tr u
an d
D eve l op me n t of th e N e p h ridi a
38 9
.
cross section of a si mila r nephri di um is represente d in
P l ate 2 3 T he ce l ls are large an d few in n umber an d
I l arge nu
cleolate d nuclei A t the n a rrower poste rior region
u
m
m
a
m
u
n
ephri
d
ia
of
this
stage
the
l
en
re
ain
intracell
lar
,
y
y
gh its anterior region ma y be intercell ul ar an d bo un d e d
th o u
A s the cells increase
o r thre e d istinct ce l ls in cross section
l ar
T he d istinction
men beco mes interce ll u
) e r , the entire l u
men seems th us p u
re l y arti fi cial an d a
I t
h e two for ms of l u
DD S gra d ation can be tra ce d
b division into cells tak es place apparentl y in si mple rela
e su
men of the organ A ccor d ingl y
th e inc rease d calibre of the l u
as growth procee d s tha t the l umen beco mes bor d ere d
an d
bical excretory cell s who se n umber in
e l l d e fi n e d layer of c u
re of
ac tion is in general d irectly proportional to the m eas u
Figs 2 7 an d 2 8 P l ate 2 3 show
men
mfe re n ce of the l u
zu
Fig 2 8
m
iv e s tages in the formation of this epitheli u
gh the bo dy of a nephri d i um of al most
nt
s a cross section thro u
P l ate 2 5 Five cells are a lread y
ne stag e as that of Fig 4 2
i n cross s ection an d their inner en d s are be g in n ing to pro
0 the l u
men in the manner characteristic of latter stages
—
46
54
Plate 2 5 an d Fig 6 a Plate 2 2 show still more
ad nephri d i a with a greatly increase d n u
mber of cells in cross
A
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1
,
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,
,
the leng th of the nephri d i um in A re n i cola is l i mite d never
ng that of the so mite to which it belongs , the only way in
t is possible to sec ure the necessary increase in the exte n t
e x cretory s urface is by an increase in the calibre of th e
S ince each n u
cle us is in d irect physiological re l ation to only
( 1 portion of the excretory protoplas m the increase in calibre
a correspon d ing incre a se
i n the n u
mb er of cells in cross
T he ce l ls retain an appro x i mately uniform siz e ( as ma y
co mparing the above fi g u
res) an d increase in n umber
lt
l y by d irect division) as the epithe l i u
m increases in extent
are never seen in th e e x cretory epitheli um ; an d it see ms
at th e ce l ls when they e x cee d a certain li mit of si z e un d ergo
e su
b d ivi s ion prece d e d by an a mitot i c division of the n ucle us
not d irectly observe d the sever a l stages of this process ; the
however , are fre q uently seen in an irregular or constricte d
nd su
b division probably si mply repr e sents the extreme of
con d ition T he for mation of a cell wal l b etween the two
[ 06
,
,
r
,
.
,
,
.
.
.
Ral p h
3 90
s L i ll i e
.
uclei thus forme d woul d co mplete th e process T h e s tru
ct
u
the l a rva l e xcre tory cells va ries b ut slightly a t di ffe r e n t s tage
lt nephri d i um the cel ls have beco me very n umerou
th e a d u
s
greatly compresse d in a lateral d irection , ass umi n g a ma rk ed colnl
s t ru
cture ; in con s e q uence of this , apparently , the d i ffe rent reg
of in d ivi dual cells ma y present more mark e d d i ffer e n ces from
another than are foun d in the broa d cubical c e lls of the ll
n ephri d i u
m
I n essential histological ch a ra cter , how e v er the la
and
a d ult cells see m to d i ffer b ut slightl y from each d
see
p
(
n
.
.
,
.
N
ephrostome an d i ts
A
ss o ci ate d
Blood V
-
e
s s el s
.
I n the for ma tion of the nephrosto me both the ant e ri o r
m a n d a po rtion of the a dj oining s
th e original neph ri di u
m
i
o
a
h
art
Fr
its
earl
est
app
rance
as
above
s
o
n
e
w
h
t
e
,
p
,
possesses an anterior opening into the bo d y cavity of th e 1 1
bu
t at fi rst the margin a l region bor d e ring th i s O p e ni n g in
respect d i fferent fro m th e re main d er of the o rgan Whe n s u
bdil
into cells begins the cells of the a n te rior region at fi rst on
r e se mble the others i n str ucture an d appearance ; as g rowth
ce e d s
however s ub d ivision progre s ses more rapi dl y i n th ese
than in those behin d an d as a re s ult the more anteri orly sit
c ell s beco me s maller an d more c u
bic a l A t the s a m e ti m e the
their d istinctivel y excretory character an d the protopl a s m be
m o re ho mogeneo us in a ppearance while the vacu
oles a n d exc
gran ules disappear ( P l ates 2 4 an d 2 5 F i g s 3 7 3 9 ,
I n Figs 3 7 a n d 3 9 a porti on of the a dj oining s ept um a]
ming the character of a c u
to be ass u
bical epitheli um a n d ti
be contrib uting to the extension of the d orsal lip of the funnel
li mits between sept um an d nephri d i um proper are in fact n ots
d efi ne d in early stages ( Plate 2 4 , Fig
an d until th e f
epitheli um is d e fi nitely forme d , it is i mpossible to s a y whe
two beco m e contin uo us I ts hin d er part however is unq uesti l
fo rme d fro m the a nterior cells of the nephri d i um proper ( F igs 3
while its marginal cells es pecially those of the d ors al l i p
to be forme d in the region of the original sep tum T he clos
tion of the d orsal lip to the septal str uctures , especially th e
vessels ( a relation whi ch p e rsists thro ugho ut life ), is th us e xp
T he anterior po rtion of the n ephri d i um beco mes in this I
c o mpose d of an epi t
heli um of s ma ll c ubical ciliate d ce l l s ( 8 11 1
.
-
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,
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,
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,
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,
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,
S tr uct ur e
D e ve lop me n t
an d
he
of t
Ne p h ridi a
39 1
.
section in Plate 2 5 , Figs 4 3 an d
T he cilia of these cells
some shorter an d more n u
mero u
s ( co mpare Plate 2 4 Figs 3 8 3 9 ;
l ie 2 5
Fi g s 4 2 4 6
while at th e same ti me the n uclei be come
al l e r an d more ro u
n de d an d the n ucleoli characteristic of the
Sre t
s ually d isappear E ventually a well d e fi n e d funnel
ory ce l ls u
i o n is for me d whose cells are sharply d istinct fro m th e excretory
s behin d ( Fi g s 4 6
a ges of the above transfo rmation the inter
ring the earl ier s t
Du
m un d ergoes changes which lea d to the forma tion
n ent
a l s e pt u
The sept um at th e beg inning of th e
h e seg mental blo od vessel
estion e xten d s ob l i q uely forwar d fro m the ventral region
e d in q u
b intestinal bloo d
l i e sto ma ch ( where it is contin uo us with the s u
te l ) to the v en t
ral bo dy wall for ming a thin me mbrane whic h
a n d s l a t e ral ly to a point slightly above the l e vel of the early
I n its latera l porti on its bor d er
h ros tome ( Pl ate 2 5 , Fig
in uous wi th the lip of the early nephrosto me as above
( me s co n t
the an te rior face of th e sept um b e ing d irectl y contin uo us
c ri b e d
3 1 the e pi th e li u
m of the fu
nnel
while the posterior lamel l a
s e s di rectly i n to the peritone u
m covering the ne phri d i um Fi g s 3 7
9 , Plate 2 4 show the rel ations of sep tu
m an d neph ri d i u
m at the
l y pe rio d of d i f
fe rentiation of th e nephrosto me be fore d e fi nite
: l d ves s e l s have ap p eare d
E a ch s e g mental bloo d-vessel appears i n the sept u
m ( see Plate 2 5 ,
z 43
in which portions of th e original sept um yet re main ) origi
I y as a s p a ce between the two la mellae ofthe latter
The vessel
i
i
n
t
s
m
i
s
u
b
l
for
ation
at
the
j
nction
w
th
the
intes
ina
b
o
d
s
t
o
u
l
g
B e l ( Plate 2 2 Fig 9) an d gra d u
ally exten d s outwar d to the bo d y
11 wh ere it j oins the lateral longit u
d inal ves s e l a l so forme d abo ut
I t
i me ( The re l ations of the seg mental vessel to the nephri d i u
m
l i n part sho wn in Pl ate 2 5
Figs 4 2
N e a r its j u
nction
t
l
t
h
s
e
bo
d
y
wall
the
m
ain
ves
el gives otf a branch ( the nephro
i
l l i a l vessel ) which c u
rves bac k a n d passes inwar d an d bac k war d
I I;
th e d orsal lip of the n ephrosto me between the fu
nnel e p i the
m a n d the peritone um to the gl an d ul a r porti on of the n e phri d i um
l g wh ich i t passes as the mai n nephri d ia l vessel
The nephro
mi a l vessel is th us directl y contin uo us with the seg men tal vesse l
l i s forme d in e s s e nti a l l v th e sa me ma nner as this latte r re p re
ti ng in reality a space between the post e rior se p tal l a m ell a
a at t
h
e
nte
d
by
the
peritone
an
d
the
anterior
la
ell
m
m
u
r
e
se
p
)
m with w h i ch it i s
i on where th e lat ter j oi n s th e funnel epit h eli u
as
.
,
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,
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,
-
M
ail
m
an
d 2 001 S ta ti on
.
.
z
u N e ap e l
.
Bd 1 7
.
.
26
R a l ph S
3 92
.
L i ll i e
uous A s the epith e li um increases in extent th e v e s sel acq
its d efi nitive po s ition j us t external to the margin o f th e dorsal
I n thi s w a y are d e fi ne d the li mit s of th e future d or s a l a nd re
lip s the former of which is disting uishe d by the p r e sence 01
bloo d vessel w hich r uns a long its enti re marg in
A t the il
a
f
u
u
)
o
s
f
t
re
posterior
ngle
the
nephro
to
e
the
essel
p
se
m
v
a
s
o
s
o
n
t
(
m a n d gr a d ua l l y exten d s bac k w ards t
b od v of the nephri d i u
o f
the nephri d i al v e s s e l Thi s v e s s e l also represe n ts a s p ac e betw
t
h e peritone u
m an d the nephri d ial epitheli u
m , an d i s fo rmed a
si mple contin ua tion of the nephrosto mi a l vessel A sli g ht petite:
fol d exte n d ing a long the le n gth of the nephri d i um ( Pl a t e 2 3 , Figs"
2 6 ) ma rk s i n e a rly stages the position of the fu
t ure
more a d vance d nephri d i u
m represente d in F i g 2 7 the v e s
beco me well d e fi n e d i l l the anterior pa rt of the nephri d i um
posteriorl y it i s st il l represente d by the peritoneal fol d L a
vessel co mpletes its bac k war d extension a n d for ms , as w ell kl
the ch ief vasc ular s uppl y of the glan d ul ar region a n d tell
vesicle
I t is i mpo s s ible in this place to give a full acco unt of the m
in which all the bloo d vessels of A rm icola arise , an d the
‘
brief acco unt serves si mply to explain th e manner in whic
c
m
chara teristic relations arise between the s eg ental bloo d V e S S t
the nephrosto me We have seen th at th e nephrosto mia l b l ood
is for me d as a portion of the syste m of septal bloo d v e s sels :
th a t i ts a s s ociati on wi th the fun nel d epen d s si mply up o n tll
that this s truc ture its e lf represents in large part si mply a di ffe rs"
1
e
par t of th e s ptum
S h or tly after the appearance of the syste m of septal b l oo
’
sels the me mbrano us portion of the septum disap p e a rs
nephrosto me then un d er g oes a ch ange of position , its d o rsal
assuming th e a ntero posterior d irection of the nephri d ial b l oo
sel an d the apert ure conse q uen tly becoming d irecte d i n
in
cont
.
,
-
.
.
.
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-
,
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.
,
For th e va s c ul a r s uppl y o f th e a d ul t n e phridi um s e e GA M B L E A S H
1 9 00 T h e ir Fig 2 9 s ho ws i n a s i mpl e a n d c l e a r ma n n e r th e e s s e n ti a l v
r e l a tio n s of th e n e phri d i a T h e d e ta il e d di s tri b utio n of th e b lood v e
A crzs ta ta h a s b e e n th e s u
bj e ct of i n v e s tig a tio n a t th e M a ri n e B i
L a b or a tor y th e r e s ult s o f w hi ch a re n ot y e t p ub l i s h e d
2 W ith th e e x c e ti o n of a s ma l l por t
n
h
l
n
m
e
n
t
io
n
e
x
t
e
di
g
fro
t
a
e
r
i
p
o f th e n e phro s to me to th e b od y wa ll a n d b e a ri n g th e e x tr a n e p h ridi a l
th e s e g me n t a l v e s s e l ( s e e Pl a t e 2 2 Fig 6 a cf a l s o GA M B L E & A S H W O R I
Figs 5 3
1
‘
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-
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'
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,
-
-
'
,
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,
.
c tur e
S tru
an d
D e v e l op me n t
of t
he
—
4 9) as
46
N e p h ridi a
3 93
.
Figs 4 4
lt The slip of transverse
i n the a d u
S ale w hich bin d s the nephrosto me d o wn to the bo dy wall has alrea d y
Deare d
at th e stage of Fig 4 4 in a manner n ot satisfactorily
lu
The slip however is associate d with the segmental
oo d
st
il l -ve ss e l a n d is attache d to the ante rior b or d er of the nephro
1 0 n ear t
h e poin t where the nephrosto mial bloo d vessel ta k es it
T h e fact of its attachment to the d orsal lip at the ante rior
of the funnel beco mes th us to some d egree intellig ible
e
T h e ori g in of the g e r m c e l l s , which arise in connection with
M ere
e a rly neph ri d ia l v e sse l s ma y be brie fl y referre d to here
ti on of th e p l ace an d m anner of ori gin of these cel ls will be
h e s permato g enesis an d ovigenesis of A ren i cola have
c i e nt sin c e t
bje ct of s pecial investigation at Woo d s H ole by other
th e s u
I
n t of whose wor k will it is hope d appear before l ong
tors an accou
i
h
—
X
to 5 nephri d ia)
T h e n e phri d ial vessels in so mites V I I
T h e early germ
ass oci a te d with th e for mation of the gona d s
m beco me d isting u
ishable
l s i n connecti on with e a ch n ephri d i u
e r th e a ppearance of the bloo d vessel of the latter an d arise
1 1 aft
a p rol i f
erati on of the peritoneal cells of its wall T hey appear
I: on t
h e ante rior an d fi rs t for m e d portion of the v ess e l
i e in
r e g ion i mme d iately a dj oining the posterior angl e of the funnel
l at their fi rst appe a rance ( Plate 2 3 Fig 2 7 ) have the form of
lar n uclei surro un d e d by a s mall q uantity
m
e wh a t enl a rge d vesic u
m
a
t
t
o
p
l
an
d
otherwise
d
i
ering
sl
i
ghty
fro
m
h
naltere
d
r
o
s
f
f
u
t
e
b
u
p
A
w
it
s gro th procee d s the ge r m c ells increas e in
on e a l cells
i re a very ch ara cteri stic appe aranc e
n b e r a n d in si z e an d ac q u
r
te 2 5
Fig
The n ucle us beco mes greatly en large d an d is
rrou
n d e d by a well d e fi n e d protoplas m of h o mogen e ou
s appearance
5 6 represents the a p p earance of these cells ( cc or spermatogoni a )
t
he secon d nephri d i um of a l arva of a well a d vance d s tage
a l a rge vesic u
lar n uclei whose chro matin is arrange d in scattere d
mps closely ap plie d to the n ucl e ar membrane , alrea dy bear a
so rese mblance to the n u
clei of the large o ogonia or sper mato
l i a of the a d u
lt gona d The germ cells usually ap p ear on their
t
v
c
i
e
f
nephri
d
ia
in
the
or
d
er
the
for
ation
these
organ
e
m
f
o
o
s
p
,
3 i n or d er fro m be f
ore back I have never fo und the m in con
ti on wi th the fi rst or last pair of nephri d ia
which typically d o
lt
b e a r gona d s i n the a d u
T h e later d evelop ment of th e nephros to me consists essentially in
e x tension of its epi t
helial s urface an d in the co mpletion of the
40 2 5 ,
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,
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,
26
*
R a lp h
3 94
S
.
L
i ll i e
charac teristic relati ons of this epitheli um to th e b l ood
explai n e d above the formation of th e s e ri e s o f d o rs a l
cesses , an d also of th e vesicle of th e ventral l i p i s i n
primarily d epen d ent up on the incre a se in epith e l i a l e u
not however been a b le d irectly to st udy the
characteristic struct ures which d o not aris e un ti l a l ate
d evelop ment a n d have not yet beg un their app e a ra n ce in t
a dvan ce d larvae at my d isposal
,
,
,
.
T e r m i n al
V
esicle
.
T he terminal vesicl e
as might have be e n e x p e cte d
si milarity of its ad ult struct ure to that of the g 1
i s forme d as a di fferentiation of the most poste rio r
m
u
ri
itive
nephri
d
i
m
T
here
is
no
ecto
d
er
al
i
n
m
p
from the resemblance in st ructure between the two r
app ear a p r i o r i p ro b able that the vesicle lik e the
of the neph ri d i um is chiefl y if not e n ti re l
A co mplete fu
sion however tak es place at
the ecto d erm a n d the posterior e n d of the
fro m this region of fusion in which the l i mits 0
meso d erm beco me in d istingu
ish a b le that the vesicl e
I n all probability therefore i ts d istal p ortion i s
region which originally was of ectoblastic origin ; it
i mpos s ible to d eci d e the extent to which each ger m
part in i ts format i on I n point of fact the vesicle is
as a whole w i tho ut rega r d to l i mits of germ layers ,
tre me posterior regi on wh ere the nephri d i um an d
beco me in d isting uishably fuse d ( see Plates 2 4 an d
.
,
,
,
,
,
,
,
,
.
-
,
37
Fig 3 4 Plate 2 4 represents the early neph ri d ia of so m ites V 1
The nephri d i um i s fuse d w i th the et
V I in a larva of 1 4 so mite s
d er m sli g h tly beh i n d an d intern a l to th e ventral hoo k e d setae a
point where th e ne phropore afterw a r d s opens A t th e poi nt
fusion ecto d er m an d meso d er m a pp e a r si mp l y to beco me conti nu
with each other witho ut any visible line of d e ma rcation T h e ]
tion of the nephri d i um i mme d iately a dj oi n ing the fusio n re m:
si mil a r to the rest of the orga n until a relatively l a te s t
5
2
4
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7
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4
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mm
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d e v e lop me n t of th e n e p h ridi a o fA nn e l i d a R e fe r e n ce ha s b e e n o mitted “
p a p e r s t h a t h a ve b e e n co n s ult e d r e l a ti ve l y to th e n e p h ri d i a o f othergro
a n i ma l s
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1 4 Bd
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2
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1 891 pp
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b e i H i rud i n e e n ill zz
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re i f
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of N ume ro us Ne p h r i d i a i n the
b e twe e n th e Ex c r e to ry S ystmi
Pl a ty h e l mi n th s i n : " Jo ur n M i c r S c (l l
.
i n th e
an d
—4 1 1
.
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.
397
.
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.
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.
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.
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5
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4
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pp
P I 30 3 1
r e of U roch a e ta a n d D i chogm
O n c e rta i n poi n t s i n th e S t ruct u
furt h e r r e ma r k s on the N e phri d i a of E a rt h wor ms I b i d V ol 1
—
2
1
28
2
Pl
2
3
2
3
5
pp
ct s a n d Ne p h ri d i a i n
O n th e H o molog y b e t we e n Ge n it a l D u
—
9
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4 55
c h a e ta i : P roc R S oc Lo do Vo l
pp
Re s e a rch e s i n to th e E mb r y o l ogy o f th e O ligo ch a e ta 1 On
poi n ts i n the D e ve l op me n t of A ca n th od rzl us m ul tip aras i n : "
540 P 1 30 3 1
M icr S oc ( 2 ) V o l 3 3 1 8 9 2 pp 4 97 —
m o f I /u
B e nh a m , W B L , T h e N e phri d i u
mbrze us a n d i ts B lood
I b id
wit h R e ma r k s on th e N e p h ri d i a i n ot he r C h a e topod a
—
—
2
25
3
2
3
3
4
2
1 8 9 1 pp
9
Pl
Po s t la r v a l S t a g e o f A ren i cola ma ri n a i n : Journ M a r Bi
—
4
3
8
9
Pl y mo uth Vol 1 3 pp 8 5 2 Pl 1
B e rg h , B
fi b e r d i e M e t a morpho s e v on N ep h el i s i n : Z e it
—
2
8 4 3 01 T a f 1 8 1 9
4 1 B d 1 8 8 4 pp
D i e E x k r e tio n s org a n e d e r W ii rme r i n : Ko s mos 1 7 B d 1 88
1 888
.
388
M
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cc
rr e n c e
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o n th e R e l a tio n s h i p
B e d d ard , F
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A p ath y, S t, Ke i ms tre i fe n
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H i ru
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I b id
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N oc h ma l s ii b e r d i e E n t wic k l u
a l org a n e
I b id
1 8 9 9 pp 4 3 5 —4 4 9 T a f 3 0
B ol s l u
r l a s tr u
ctur e d e s orga n e s s e g me n ta i re S l
s , I L , R e c h e rc h e s s u
—
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1
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d i n ée s i n : C e ll ul e T o me
No uve lle s r e c h e rc h es s ur l a s tr uct ur e d e s orga n e s s e g me n t
—
—
7
7
1
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0
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I b id T o me
7
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L e s org a n e s cili ée s d e s H i ru
d i n ée s ( N ep h eles )
I b id 1 8 9 1 p p
Pl 1 2
rn e , A
ct ur e of th e N e p h ri d i a o f the M e d i c i n e
B ou
O n th e s tr u
G
—
rn M icr S c ( 2 ) Vol 2 0 1 8 8 0 pp 2 8 3 3 02 P I 2 4 2 5
i n : " Jo u
di n e a I b id V o l
C o n tri b utio n s to th e A n a to my of th e H ir u
—
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34
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R e vi e w :
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N e phri d i a
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of
Le e ch e s
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i n th e A n a to my
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I b id Vo l 3 6
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D e ve lop me n t
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pp 1 1 —3 3 Pl 2 —5
r E n t wic k l u
B e i trii g e z u
n g s g e s chicht e d e r H i ru
rEm
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rg e r,
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N e ue B e i trii g e z ur E nt wi c k l un g s g e s chichte d e r H i rud i n e e n Z ur E m
b r y ologi e v on H erud o m e d i cma l l s un d A ulos tom a g ul o i n : Z e it VV i s s Z
—
4
5 8 B d 1 8 94 p p 4 0 4 5 9 T a f 2 6 —2 8
W e it e r e B e i trii g e z ur E n t wic k l un g s g e s chic h t e d e r H i rud i n e e n Z ur
—
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—
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l i d e s pol y ch et e s n A ch Z E xp ér T ome 8 8
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pp
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to my
of
Pol y ch a e t e s
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—
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S
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E i si g , H u
g o, M o n ogr a phi e d e r C a p i t l l i d e n d e s G ol fe s von N e a p e l i n : F a u
Flor a Go l f Ne a p e l 1 6 M on og r 1 8 8 7
F auvcl , P i erre L e s s t a d e s po s t l a r v a ir e s d e s A r én icol e s i n : C R A c a d
S c P a r i s T o me 1 2 7 1 8 9 8 pp 7 3 3 —
7 35
F ra i p on t, J , L e g e n r e P oly/g a rd ens i n : F a u
n a F l or a G o l f N e a p e l 1 4 M o n og r
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N e phri d i a o f th e P ol ych a e t a P a rt 1 O n H es i on e T yrrh en a
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Glyce m a n d Gom a d a
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O n th e B o d y c a v iti e s a n d N e phri d i a of th e A c ti n otroch a l a r va
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Gra f, A rn ol d , B e i trii g e z ur Ke n n t n i s d e r E x k re tio n s org a n e v o n N ep h el es
—
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5
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—
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M az i a rs k i , S ta n
R e c h e rc h e s c y tologique s s ur l e s org a n e s s e g mentilrel l
V e r s d e te rr e i n : P ol n A rch B iol M e d W i s s L e m b e rg
pp 1 —8 1 T a f 1 —3
M e s n i l , F , L e s g e n r e s O lymen i d es e t B ra m lzi omal d rm e e t l e s s ta
l a rva ire s d e s A r énico l e s i n : Z A n z 2 1 B d 1 8 98 pp 6 3 0—6 3 8
M e ye r , Bd , S tu
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S ch a cp p i , T h , D a s C h lora gog e n v on Op h eli a ra d i u
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ph y s iologi s ch e S t udi e i n : Je n a Z e it N a turw ( 2) 28 B d 1 8 94 p]
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lip O f n e phro s to me s h o wi n g th e a b r upt tr a n s itio n to th e
portio n of th e s a me X 8 00
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ta n g e n ti a ll y to b o d y wa ll
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thi s s t a ge Ne r ve cor d di ffe r e n ti a te d i n v e n tr a l e ctO
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fe r e n ti a tio n
th e e x tr e me p o s t e rior r e gion i n proc e s s Of d i f
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i s i n proc e s s o f for ma tio n s ho wi n g e a rl y p ron e p h ri d i a o
an d 5
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gh ve n tr a l portio n of i n te r s e gme n t a l
C ro s s s e ctio n thro u
s t a p p e a ri n g s ho w i n g l a
o fa l a r v a i n wh ich s o mit e V II i s j u
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O f a l a r va i n w h ic h
ctio n thro ugh i n te r s e g me n t a l r e gio
or ma tio n s ho wi ng d i s po s itio n a n d h i s to logica l
s o m it e V I I i s i n proc e s s O f f
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T ra n s v e r s e s e ctio n thro ugh g ro w i n g z o n e O f a l a rva i n w h ic h s o mit e
V I i s i n proc e s s O f for ma tio n S e cti on p a s s e s s o me w h a t o b l i que l y fo r
w a r d s fro m a b o v e d o w n
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X 8 00
—
5
6 i n a l a r va i n w hi ch
gh i n t e rs e g me n ta l r e gio n
C ro s s s e ctio n thro u
s o mit e V I I i s j u
s t a p p e a ri n g ; s ho wi n g on th e righ t s i d e th e co mme n ci n g
d if
fe re n t i a tio n O f the t hir d l a r va l n e phridi um ( s o mit e V I ) ; l u
me n j u
st
a pp e a ri n g i n c e ll s ot h e rw i e s i m il a r to th e a dj oi n i n g my o b l a s t c e ll s
E c t d e r m c e ll s w e l l d e fi n e d
O n l e ft s id e i s s ho wn e a rl y co n d itio n
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X 8 00
S i m il a r cro s s s e ctio n thro ug h s o mit e V O f th e s a me l a r v a X 8 00
S i mil a r cros s s e ct i o n thro ugh s omit e V I O f s a me l a r v a X 8 00
S i mil a r cro s s s e cti on through s o mit e V II O f s a me l a rv a O n l e ft s i d e
n e phri d i u
m furth e r a d v a n c e d t ha n o n right M us cl e fi b re s l e s s d e v e lop e d
th a n i n pr e c e di n g s o mit s a n d my o b l a s t c e l ls l a rg e r X 8 00
S i mil a r cro s s s e c tio n thro ug h s o mit e V II I O f th e s a me l a rv a O n th e
l e ft th e s e ctio n p a s s e s more a n te ri orl y th a n on ri g ht a n d th e r e s ho ws
—
7
i n t e r s e gm n t a l r e gio n
8 w it h my o b l a s t s
N e p h ri d a l c e ll n o t y e t
d i s ti n g u
i s h a b l e fro m th e oth e r s S ho ws a l s o e a rl y s e ta s a c s wh ic h s till
r e ta i n co n n e ctio n w ith th e e cto d e r m a n d to w hi ch fl a tt e n e d me s o d e r m
c e ll s a re a ppli e d M us cl e fi b re s l e s s d e v e lop e d th a n i n pr e c e di n g
s o mit e
X 8 00
S e ct i o n thro ugh r e g i o n O f for ma tio n of s o mi te I X O f the s a me l a r va
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r e gio n L a rge we l l d e fi n e d c e l ls O f th e e cto d e r ma l gro wi n g z o ne
Lo n g i t udi n a l m us c l e fi b re s j us t ma k i n g th e ir a pp e a r a n c e X 8 00
C ro s s s e ctio n thro u
gh po s t me s od e r ma l r e g io n O f s a me l a r va s ho wi n g
s ma ll
pig me n t e d v a c uo la t e d r a d i a ll y a rr a n ge d e ctod e r m ce ll s with
th e ir s ma l l d e e pl y s t a i n i n g n u
cl e i A fe w fl a tt e n e d me s od e rm c e ll s
a p pli e d t
S t ro n g cili a o n ve n tra l wa l l
o b o d y wa ll a n d procto d a e u
m
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X 8 00
C ro s s s e ctio n thro u
gh a n t e rior r e gi o n O f s o mit e XI o fa l a r va i n w h ic h
fe r e n ti a
s o mit e X
I I i s i n proc e s s O f for ma t i o n ; s ho wi n g co mme n ci n g di f
ti n O f b i h l a r va l n e ph ri d i u
N e phri d i um s o me wh a t
m { 01 1 d e fi n it i v e )
mo r e a d v a n c e d i n d e v e lop me n t o n th e l e ft s i d e
M y o b l a s t c e l l s we l l
t a pp a r e n tl y u
d e fined bu
n d e rg o i n g r e d u
ctio n L a rge e mb r y o n ic n ucl e i
i l e c to d e r m ; s ma ll e r n u
cl e i i n th e ve n t ra l r e gio n h a ve the ch a r a cte r s
f tis su
fe r e n ti a ti n g
e nu
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I I i s a pp e a ri n g ; s ho wi n g e a rl y me s o b l a s t ; i n t e s ti n e s ur r
by b loo d s i n us co n ti no us w ith d or s a l a n d v e n tr a l b l o o d v e s s e l s
w e l l d e fi n e d e ct o d e rm c e l l s O f the gr o wi n g z o n e
D i fi e re n ti a
th e v e n t ra l n e r v e cord i s i n progr e s s a n d s ma l l e r mor e d e e p l y E
nu
cl e i a re s e e n i n i ts v ici n it y X 8 00
C ro s s s e ctio n thro ugh n e phridi u
m a n d a dj a c e n t b od y wa l l o f 8 0 )
N e p h ri d i
mm l e n gt h a n d ca 4 5 s o mi t e s
O f a l a r v a O f ca
d e fi n iti v e of rig h t s id e ) s till a pp a r e n tl y o n e c e l l i n c ro s s s
s h o wi n g a l s o a p e rito n e a l fold r u
n n i ng a l o n g n e phri d i u
m fro m
i n a po s itio n corr e s po n di n g to the l a t e r n e phri d i a l
b l oo d
N uc l e us l a rge a n d n uc l e o l a t e d P rotop l a s m v a cuol a t e d a n d cor
gr a nul e s ; s t a i n s mor e d e e pl y a t b or d e r O f l umen C ro s s cl
me n
X 8 00
vi s i bl e i n l u
gh n e p h ri d i um a n d a dj a c e n t b od y wa l l o fs o m
C ro s s s e ctio n t hro u
O f a l a r va o f a l a t e r s t a g e th a n th a t o f F ig 2 5 ( ca
mm
a
3
m
d e fi n iti v e O f l e ft s i d e ) h a s b e c o m e
so
it e s) N e phri d i um (
i n to c e l ls a n d l ume n h a s b e co me i n t e rc e l l ul a r ; 3 c e l l s p r e s e n t
s e ctio n a t t h i s r e g i o n
H i s to l ogic a l c h a r a ct e ri s tic s o f c e ll s s a nl
F ig 25
pi e s p o s itio n O f fut ur e n e)
A s i mi l a r m e mb r a n e occ u
b l ood ve s s e l
m a n d a dj a c e n tb od y wal l o f s o m
C ro s s s e ctio n thro ug h n e phridi u
d d e fi n iti ve n e phri d i u
3
m l e ft s id e ) O f a mor e a d va n c e d l a r i
(
th a t O f Fig 2 6 ( ca
ll n umb e r s o mite s ) ; s e cti o n p a s s
mm ; fu
b e hi n d n e p h ro s to me an d s h o ws n e phridi a l b l ood ve s s e l w i t h a
ge r m c el l a pp l i e d to it X 8 00
t
1
m
r
S i i la cro s s s e c tio n throug h midd l e r e gion o f
d e fi n i ti v e
d iu
m ( s o mi t e V I ) of ri g ht s i d e of a l a r va o f l a t e r s t a g e th a n
F ig 2 7
mm ; f u
l l n umb e r s o mit e s ) N e p h ridi um 5 c e ll s i i
s e ctio n ;
hi s to l ogical s tr uct ur e a s a b o v e N e p h ridi a l b l o o d
pr e s e n t i n a n t e rior por tio n Of n e phridi um X 8 00
H ori z o n t a l s e ctio n thro u
g h po s t e rior b o d y re gio n of a l a r v a i n
1 i s b e i n g for me d
s o mit e X
S e ctio n p a s s e s a l o n g l e v e l o f n o
a n d v e n tr a l s e t a e
a n d s h o ws th e e n tir e s e ri e s Of e a r l
n
el
y
-
-
‘
-
.
-
,
,
.
.
Fig
.
25
-
.
.
.
.
.
.
-
.
.
F i g 26
.
.
-
.
.
.
.
t
.
.
.
.
-
Fig
.
27
.
.
-
r
,
.
.
.
-
.
.
r
F ig 2 8
.
.
s
.
.
.
.
.
Fig
.
29
.
.
-
.
,
x
Fig
.
30
.
4 00
.
S a gitt a l s e ctio n thro u
gh po s t e ri or b o d y -r e gion
s o mit e X
1 i s b e i n g for me d
S ho ws e a rly s e pta
Of a l a rv a i n
i n t e s ti n e n e r v
dor s a lly i nco mpl e t e S h o v
.
,
,
S e pt a i n a d va n c e O f s o mit e V III a re
l a rg e t e rmi n a l me s o bl a s t n uc l e us X 8 00
Lo ng it udi n a l s e ctio n t h ro ug h e a rl y r e g i o n of for ma tio n o f no;
i n a l a r va i n which s o mit e X1 i s j u
s t a pp e a ri n g ; s h o wi n g e a r l
y
t
h
t
h
7
m
a n d a s s o ci a t e d n e phridi a l r u
f
6
n
di e n t s O th e
a d
l a rv al 1
d i a ( s o mit e s I X a n d X
) Pol e n uc l e us O f me s od e r m a n d m i to s i s
fe r e n ti a t e d me s o d e r m c e l l s a l s o s e e n
dif
A l s o th e l a rg e e cto c
nu
cl e i O f th e gro wi n g z on e X 8 00
.
-
.
.
F ig 3 1
.
.
-
.
.
.
.
ta
N e a rl y h ori z o n t a l s e ctio n thro ugh the po s te rior re gio n o f a
whi ch s o mit e XV I i s i n proc e s s O f for ma tio n T h e e ctod e rma l
P l a te 2 4
Fig
.
32
.
.
A
re n
i co l a
cri s ta
.
.
la
l
g
R a lp h
4 04
s
.
Lilli e
O f th e b od y wa ll T h e s e r e pr e s e n t th e fi r s t a pp e a r a n c e o f the
l a t ur e O f th e t e rmi n a l ve s ic l e ( co mp a r e Fig s 4 5 5 3
mu
scu
X 800
H ori z o n t a l s e ctio n thro u
gh v e n tr a l r e gio n O fs omit e s VII a n d V III o fa more
a d va n c e d l a r va ( ca
3 mm ; fu
l l n umb e r O fs o mit e s ) s ho wi n g th e o rigin
O f th e s e g me nt
ro m th e v e n tr a l b loo d v e s s e l a n d th e r ela
al ve s se l s f
m O f th e ri g h t s i de
ti o ns O f o n e Of th e v e s s e l s to th e 2m1 n e p h ri d i u
X 2 00
fi b re s
-
.
.
Fig
.
41
.
.
.
.
,
,
,
-
,
.
P l a te 2 5
Fig
.
A
re n i co l a
c ri s ta ta .
Lo n gitudi n a l s e ctio n
l e ft
of
fi n i ti ve n e phridi u
m) a n d a dj a c e n t b od y wa l l of th e l a r va o f F i g 41
1
e
s
a
n
f
t
h
el
portio
p
h
ridi
l
b
lood
s h o wi n g
o
e
n
e
a
s
to w h ich is
v
( )
a pp l i e d a l a rg e g e r m n u
c l e us ; ( 2) th e po s t e rior j un ctio n of th e n e p h ridium
w it h th e e ctod e r m ( corr e s po n di n g to th e e a r ly u
n di f
fe r e n ti a t e d te r minal
v e s icl e ) ; a n d ( 3 ) t
he cu
b ic a l c e l l s of the e a rl y n e p h ro s to me w i t h their
me n h a s e x t e n d e d t h ro u
gh o ut th e e n ti re length
s h ort e r ci l i a
T he l u
O f th e org a n a n d s e e ms to c o mmu
n ic a t e wi th t
h e e x t e rior ; th e e xt
e nd
op e n i ng h o we ve r i s v e ry mi n ut e X 8 00
C ro s s s e ctio n t h rough th e a n t e rior e n d of th e fi rs t l e ft d e fi nit
ive
n e p h ridi u
m ( s o mit e V I) O f a l a r v a O f a b o ut th e s a me s t a ge a s F i g 42
s h o wi n g t
h e e a rl y co n ditio n of th e s e pt a l b l oo d v e s s e l s O fth i s s o mite
th e ir r e l a tio n s to th e n e p h ri d i a a n d to th e b o d y wa l l P o r ti on
a nd
m s ti l l r e ma i n X8 00
oft
h e pri miti v e s e pt u
t
h
4
L on g i tud i n a l s e ct i o n thro ugh th e a n t e rior p a rt of th e
s
m
a
v
a
f
a
w
m
a
a
n
e
o
it
l
r
O
f
o
h
t
or
d
c
d
t
e
I
X
a
a
s
m
s
o
a
e
e
v
(
)
ge
T h e n e phro s to me i s t u
r ne d s o me wh a t i n wa rd and
( l e n gth ca 3
h a s b e e n cu
t in su
ch a wa y a s to s h ow i ts e pit h e li um i n cro s s s e c tion:
i
o
h
a
th e fi g u
r e s ho ws a l s o ts r e l a tio n s t t e n e p h ro s to mi l b l o o d v e s sel
whic h r u
s dor s a l lip a n d i s i n clo s e r e l a tio n to th e tra ns
n s a cro s s i t
v e r s e b a n d O f mu
s cl e
m
wh ic h i s a l s o a tt a c h e d to t h i s l i p and
b i n ds i t do wn to th e v e n tra l b o d y-wa l l
A porti o n of the p ri m itive
m i n w h ich the b lood -v e s s e l a pp e a rs i s s e e n a t s
s e pt u
X 8 00
1
1
n
e
m
h
d
u
h
t
h
po
s
t
rior
d
Of
t
e
phri
i
e
e
e
n
C ro s s s e ctio n t h ro u
( s o mite
g
VI) of a l a r va i n w hi c h the t e rmi n a l v e s icl e i s b e gi n n i n g to d i ffe ren
ti a te ( l e n gth ca
mm ; fu
l l no Of s o mi te s ) T h e t e r mi n a l p ortion
h e e ctod e r m i s t h i n wa l l e d a n d s o me wh a t dil a t e d A band
a dj o i n i n g t
di n a l l a y e r O f the b o d y -wall)
O f mu
s cl e fi b re ( d e ri v e d fro m th e l o ng it u
n ctio n wit h t
h e g la n d u
h e t e r mi n a l ve s ic l e a t i ts j u
lar
e x t e n d s a cro s s t
r e gio n p rop e r G r a n ul e s i n th e e ctod e r m n e a r th e t e r mi n a l v e s icl e
X 800
5 0 Th e s e fi g u
r e s re pre s en t s ucce s s iv e tr an s v e r s e s e ctio n s
p t h ick
thro ug h th e n e p h ro s to me a n d a n t e ri or g l an d ul a r portion Of th e fi rst
m ( s o mit e V I) O f a l a r va O fca 4 mm i n l e n gt h T h e n e p h ro
n e p h ridi u
st
ome h a s b e co me w e l l d e fi n e d a n d i s co mpo s e d O f a s i n g l e l a y e r of
bi c a l cili a t e d c e ll s ; a lon g i ts dor s a l l ip r un s the n e p h r o s to mial
s ma ll c u
b lood -ve s s e l T he co n ti n uity of thi s v e s s e l wi th th e n e p h ri di a l v e s sel
i s s h o wn
T h e re l a tio n O f th e s e gme n t a l b l ood ve s s e l to th e tra ns
v e rs e
mu
to the dor sa l lip i s a l s o s h o wn I
a tt a c h e d
s cle b an d
va cu
o l a te d wan d e ri n g c e l l s
X 8 00
m
n e p h ridi u
thro ugh th e
.
s
l
m
V
2
m
t
I
e
I
o i
de
(
-
.
.
.
.
-
-
.
,
Fig
.
43
.
.
,
.
-
.
-
.
Fig
.
44
.
:
.
.
.
.
.
.
Fig
.
45
.
.
8 %
.
.
.
.
-
.
.
.
Figs
.
4 6-
.
,
.
.
.
.
.
-
.
-
.
-
.
.
,
re
S tr uct u
s
g
.
and
D e ve lopme n t of
the
N e p h ridi a
4 05
.
Th e s e fi g ur e s s i mil a r l y r e pr e s e n t four s ucc e ss i ve s e ctio ns O f th e
te r mi n a l ve s ic l e of th e s a me n e ph rid i um L a r ge d e e pl y s t ai n i ng g ra
nu
l e s a re pre s e n t i n th e w a l l s o f the ve s i c le a n d i n th e a dj a c e n t
e ctod e r m O f t
h e b od y wa ll
X 8 00
C ro s s s e ctio n o f th e t e r mi n a l v e s ic l e a n d a dj a c e n t gl a n d u
lar r e g i on
Of th e 2 m1 n ep h ridi um Of th e l e ft s id e ( s omit e VII ) o f th e s a me l a r va
T h e fl a tt e n e d c e ll s o f th e v e s ic l e wit h t h e i r co n ta i n e d e x cr e to ry g ra
nu
l e s a re s h o wn A l s o th e e a r ly mus cl e -b a n d cro s s in g th e ve s icl e a t
i ts j u
h e gl a n d ul a r r e g io n
n ctio n wit h t
X 8 00
5
5
C ro s s s e ctio n th ro u
h
e
a
n
u
m
h
t
rior
r
gio
Of
p
h
idi
Of
Fig
t
n
r
n
e
e
h
e
e
t
g
i mme di a te l y b e h i n d th e fun n e l s h o wi n g th e n ep h ridi a l bl o o d v es s e l
wi th w e l l d e fi n e d g e r m-c e l l s ( r u
d i me n ta ry o va ry or t e s ti s ) a ppli e d to
it X 8 00
5 1 -5 4
.
.
,
.
g
.
55
.
.
.
.
.
56
.
.
.
,
-
.
-
.
.
,