The Conjugation of a Triploid C h i l o d o n .
By
Mary Stuart MacDougall,
Agnes Scott College and The Marine Biological Laboratory.
With 16 Text-figures.
THE finding of a triploid C h i l o d o n in the cultures of
C h i l o d o n u n c i n a t u s which had been exposed to the action
of ultra-violet rays has been previously reported, MacDougall
(1929). The present paper deals with the conjugation of this
organism.
C h i l o d o n u n c i n a t u s has been described many times.
A brief description is included here for comparison only. It is
a holotrichous ciliate, belonging to the family Chlamydodontidae. The ventral surface is very flat, and the dorsal surface
curved, Text-figs. 1 and 2. The arrangement of the cilia,
which are confined to the ventral surface, is characteristic. At
the anterior end, on the left side, there is a zone along which
a band of stronger cilia lead from a lateral angle to the mouth.
From this zone, five rows of cilia take their origin, pass around
the anterior end, and down the right side, the outermost row
extending only about half-way down, the others ending at
different points near the posterior end. On the left-hand side
(right in the figure) four rows take their origin at the zone before
mentioned. Two of these are short, extending about one-fourth
the length of the body, and two extend to the posterior region.
Two additional rows originate about one-fourth of the way from
the posterior margin, and extend caudad.
The macronucleus is in the posterior region, is granular, and
contains an endosome. This endosome contains .a kinetic
element designated by Calkins (1919) as an endobasal body.
The micronucleus is very close to the macronucleus, and is
posterior to it. It also contains an endobasal body.
216
MARY STUART MACDOUGALL
The oral basket, or ' Reusenapparat' is in the anterior region.
Typically it contains ten trichites. The identity of the trichites
is lost about half-way its length, where they seem to fuse,
forming a tube. The basket is characteristically drawn out into
a filament curved like a ' twice wound horn '.
TEXT-FIGS. 1 AKD 2.
y
Fig. 1.—Chilodon u n c i n a t u
ventral view.
Fig. 2—Side view.
The triploid C h i l o d o n , Text-fig. 3, differs from C h i l o d o n
u n c i n a t u s chiefly in the posterior portion. The ciliated
margin in this region is wider, and the rows of cilia encircle it
completely. The nuclei are nearer the centre of the body, and
there seems to be twelve trichites in the pharyngeal basket.
Although C h i l o d o n u n c i n a t u s usually has ten trichites in
its oral apparatus, the writer has seen individuals with twelve.
Details of the conjugation of C h i l o d o n u n c i n a t u s have
been described by Enriques (1908) and MacDougall (1925).
The behaviour of the pharyngeal basket during conjugation has
also been fully described.
CONJUGATION OF CHILODON
217
A comparison of the details of the conjugation of the triploid
organism with the diploid and tetraploid forms show very little
difference. The behaviour of the odd number of chromosomes,
TEXT-FIG. 3.
The Triploid Chilodon.
however, seems interesting enough to warrant the present
investigation.
F i r s t M a t u r a t i o n Division.—In the early stage of
maturation the endobasal body in the micronucleus divides,
then a spireme in the form of a ' parachute ' (Calkins, 1919)
appears, Text-fig. 4. The spireme breaks up into strings of
granules, Text-fig. 5, which later condense into six chromosomes, Text-fig. 6. The metaphase follows, the chromosomes
having split, Text-fig. 7, six to go to each pole of the spindle.
A pairing of the chromosomes, preparatory to the resting stage,
has been observed in C h i l o d o n u n c i n a t u s in the diploid
and tetraploid forms. This phenomenon was also observed in
the triploid form, Text-fig. 8.
218
MARY STUART MACDOUGALL
TEXT-FIG. 4.
lhe Parichute Stage
JLEXT FIC >
.*?*
The micronucleus drawn out into strings of granules.
TKXT-FIG. 6.
Six chromosomes on spindle.
CONJUGATION OF CHILODON
219
TEXT-FIG. 7.
Metapha e
TEXT-FIG. 8.
Pairing of the chromosomes preparatory to the resting stage.
The S e c o n d M a t u r a t i o n Division.—This is the
reduction "division. After telophase of the first maturation
division, the daughter nuclei go into a resting stage. Sometimes
both of these nuclei divide, and sometimes only one. The endobasal body divides, as in the first maturation division, and a
2-20
MARY STUART MACDOUGALL
spireme is formed, Text-fig. 9. No granule stage was found in
the second maturation division, probably due to the fact that
the material was not very abundant. Six chromosomes appear,
three of which go to each pole of the spindle, Text-fig. 10. The
TEXT-FIG. 9.
Beginning of the second maturation division. Spireme stage.
TEXT-FIG. 10.
V
./
Ss
^.
The reduction division.
reduction division is thus accomplished. Preparatory to the
resting stage, which follows, two chromosomes pair, and one
remains unpaired, Text-fig. 11.
In the previous studies of the diploid and tetraploid forms of
C h i l o d o n u n c i n a t u s , the endobasal body could not be
found after the spindle was formed. In the triploid organism,
the endobasal body was found to be present at each end of the
CONJUGATION OF CHILODON
221
spindle in all of the stages. Failure to find them in the other
material was probably a matter of technique.
The T h i r d M a t u r a t i o n Division.—Following the
resting stage of the second maturation division, Text-fig. 12,
the pronuclei move into the region of the protoplasmic bridge,
TEXT-FIG. 11.
Pairing of the chromosomes preparatory to the resting stage of the
second maturation division.
TEXT-FIG. 12.
#1 © S)\J 0*1
Resting stage of the second maturation division.
Text-fig. 13. As in the other maturation divisions, the endobasal body divides, and a spireme is formed. The spireme is very
dense. Three short rows of granules appear, Text-fig. 14, and
these condense into three chromosomes. The manner of division
of these chromosomes has not been accurately determined. Xo
clear figures have been found in the material which show a split
in the chromosomes. After division of the chromosomes the
222
MARY STUART MACDOUGALL
spindle pulls out, and three chromosomes are seen at each end,
Text-fig. 15. The interchange of nuclei then takes place. It
will be noted in both Text-figs. 15 and 16 that two of the
chromosomes are paired, and one remains unpaired. Extended
observations have yielded no light as to the significance of this
TEXT-FIG.
13.
"^a..,.*-*^
Division of the endobasal body. Third maturation division.
TEXT-FIG.
14.
Granule stage. Third maturation division.
pairing preceding the resting stage. When the migrating and
stationary nuclei touch, the membranes disappear at the point
of contact, and the two sets of chromosomes come to lie side by
side, Text-fig. 16. After fusion of the nuclei there is a resting
stage, at which time the animals separate.
Only the important stages of conjugation have been included
here. All the other details are identical with those of the diploid
and tetraploid forms of C h i l o d o n u n c i n a t u s .
Eeorganization of the exconjugant is exactly similar to that
described for the forms referred to above. •
CONJUGATION OF CHILODON
TEXT-FIG.
223
15.
Interchange of Nuclei.
TEXT-FIG.
16.
Late stage of the interchange of nuclei.
LlTEEATUKB ClTBD.
Calkins, Gary N. (1926).—'The Biology of the Protozoa'. New York,
Lea and Febiger.
Enriques, P. (1908).—"Die Conjugation und sexuelle Diiferenzierung der
Infusorien", 'Archiv fur Protistenkunde', Bd. 12, pp. 213-74.
MacDougall, Mary Stuart (1925).—"Cytological observations on Gymnostomatous ciliates, with a description of the maturation phenomena in
diploid and tetraploid forms of Chilodon imcinatus", 'Quart. Journ.
Micro. Sci.', vol. 69, Part III.
(1929).—"Modifications of Chilodon uncinatus produced by ultraviolet light", 'Journ. Exp. Zool.', v. 54, no. 1.