SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS. I l l
in sulphuric acid, and not coloured blue. by iodine and sulphuric acid, and which consequently is not cellulose; in the
mantle of Pliallusia it is only sparingly present, but in Cynthia
and the new Chilian Ascidian it is much more abundant, and
alone constitutes the corneous epidermis of their mantle.
3. The membrane of the cells in the mantle of Phallusia
does not consist of cellulose; it is coloured brown by iodine
and sulphuric acid ; is soluble in caustic potass, and behaves
exactly like an animal membrane, as do the nuclei and vessels.
4. In the mantle of Phallusia cells abound in a homogeneous,
interstitial substance composed of cellulose ; it is only at the
inner margin of the mantle that fibres composed of cellulose,
with nuclei amongst them, make their appearance. In
Cynthia, &c, there are scarcely any traces of cells, whilst the
nuclei and cellulosefibresabound.
5. A tesselated epithelinm, containing no cellulose, covers
the inner surface of the mantle of the three Aseidians examined
by me ; the outer surface of the mantle of Phallusia appears to
possess a similar epithelium.
6. There are two essential points of difference between the
modes in which cellulose occurs in the Aseidians and in the
vegetable kingdom—1. In Phallusia the cellulose constitutes
the intercellular substance, but does not, as in plants, form an
integral part of the cell-wall itself; 2. In Cynthia and other
species the cellulose forms free fibres, a form in which it is
never observed in the vegetable kingdom.
7. The substance of the mantle in the Aseidians is not disintegrated by boiling with caustic potass or by maceration with
chlorate of potass and nitric acid, like the vegetable cellular
tissue into its elementary parts ; there is in it none of the
intercellular substance universally present in vegetable tissues,
and by which the cells are connected, but which intercellular
material is never composed of cellulose, as it resists sulphuric acid, but is soluble in caustic potass, as well as by
maceration.
On
UNICELLULAR
PLANTS and
ANIMALS.
By
C.
TH.
V.
SIEBOLD. From Siebold and Kolliker's Zeitsch. f. w.
Zool. Bd. 1, p. 270.
IN the first part of my work on the ' Comparative Anatomy
of the Invertebrata,' published in 1845, I have arranged the
Protozoa {Infusoria and Rhizopoda) as unicellular animals;
thus separating them from a series of minute organisms, described by Ehrenberg as Polygastric Infusoria, viz. the Clos-
112 SIEBOLD ON UNICELLULAK PLANTS AND ANIMALS.
terina, Bacillaria, and Volvocina, which I referred to the
vegetable kingdom. The limits of that work did not allow
me to adduce more than the most important reasons by which
I had been induced to come to this conclusion. I could well
foresee that in the publication of these views I should be
placed in direct opposition to Ehrenberg's authority; an
authority so generally recognised. Ehrenberg had already
reproachfully said that I should have been more careful in
protecting science against new opinions respecting the organization of microscopic organisms, which are easily introduced, but not so readily dissipated. I can assert, however,
that having for years entertained doubts as to the correctness
of Ehrenberg's views as to the organization of the lowest
animals, I have not ventured to oppose so great an authority,
unless prepared by the assiduous study of the lower organisms, and that the deeper did I enter into this inquiry the
deeper did my doubts, with respect to Ehrenberg's views,
become rooted.
How very much disinclined I have been from the first to disseminate lightly and incautiously, erroneous views in science,
is shown by the way in which I acted with respect to an error
I had fallen into, in the year 1836, and with which I was charged
by Ehrenberg in 1848, meaning me, when he says, without mentioning my name, " the author of the new genus of an inch-long
double animal (Syngamus tracliealis), which, after the publication of his correct anatomy of it, it was necessary for some
one else to remark is nothing but a pair of strongyli in the
act of conjunction, as he himself acknowledges."—Wiegmann's Archiv, 1837. This error, the moment I knew it, I
recanted ; so that it was not quite a year before the scientific
world. On the other hand, how obstinately does not Ehrenberg adhere to the chain of delusions and errors in which he
has more and more closely involved himself from year to year.
In vain, hitherto, have other naturalists in Germany, on the
Seine, and on the other side of the Channel, endeavoured to
draw either Ehrenberg or his followers from their erroneous
ways, and to set them on the right path; and I will therefore
direct the attention of the latter to a voice, which, even from
the other side of the Alps, has made itself loudly heard in
opposition. Meneghini, of Pavia, seeking to prove the vegetable nature of the Closteria and Desmidiaceje, thus expresses
himself on the subject of Ehrenberg's errors:—" Cosa se ne
deve dedurre ? Che anche il piu accurato osservatore e
1' uomo de genio possono errare. Ne cib potra mai scemarne
il merito, o rendere men importanti i benefizii ch' egli rese
alia scienza. II danno non ridonderebbe che su coloro, i
SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS. 113
quali, schivi alia fatica dell' osservare, si accontentano della
autorita del maestro et ne abbraciano indifferentemente, cosi
le vere scoperte come gli errori. Grazie al cielo 1' epoca del
autorita e tramontata, e chi ve si aggioga erri pure conpace,
che per questo la scienza non avanzera meno, ed anzi da
quegli errori stessi essa potra trarre vantaggio."*
With respect to my views on the organization of the Protozoa, published in 1845,1 have nothing in the main to recall;
on the contrary, I have since then had the satisfaction of
knowing that recognised naturalists and distinguished microscopists have already sided with me.
It is, moreover, highly gratifying to notice that at present
the study of the lower vegetable forms, which as unicellular
plants correspond to the Protozoa as unicellular animals, is
exciting a very high interest, and that these hitherto much
neglected organisms are now finding investigators among
the most eminent Botanists, by whose labours their position
in the vegetable world will eventually be decided.
As one of the most important of the works that have
appeared of late upon this subject, the following must be
indicated:—Nageli's 'Genera of Unicellular Algae, physiologically and systematically considered.'!
I believe it will not be without interest if I here notice the
more important points in which, according to Nageli's researches, the unicellular Algae are distinguished from the
lower animal forms. As especially worth consideration, I
would adduce the following expression of Nageli's (p. 2): —"It
is to be lamented that of several genera and of many species of
hitherto known unicellular Algae nothing has been observed
respecting their propagation, and that consequently not only
has their systematic position but even their independence as
unicellular plants remained in doubt." I am satisfied that
many of Ehrenberg's Infusoria, were their origin and development, as well as their modes of propagation, fully traced,
would long since have been recognised as vegetable forms;
that is to say, as lower forms of Algae.
For the better appreciation of the exposition given by
Nageli respecting the organization and vital actions in the
unicellular Algae, with reference to the vegetable forms considered as Infusoria by Ehrenberg, it will be necessary to
premise a list of those vegetable organisms which have been
treated by Ehrenberg as Infusoria, and by Nageli as uni* G. Meneghini. Sulla animalita delle Diatomee. Venezia, 1846,
p. 172.
t Gattuugen einzelliger Algen physiologisch und systematise!) laearbeitet von 0. Nageli (Zurich, 1849, mit 8. lith Tafl.).
VOL. I.
i
114 SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS.
cellular Algae. Among the eight orders of unicellular plants
instituted by Nageli, that of the CIIROOCOCCACEJE contains, in
Meyer's genus Merismopcedia, Gonium ylaucum, tranquillum
and pnnciatum, Ehr. The order of the DrATOMACEJS corresponds to the siliceous Bacillaria, Naviculacea, Echinellea,
and Lacernata, Ehr. In Nageli's order of the PALMELLACEJE we find Artkrodesmus and Tassarthra, Ehr., referred to
Scenodesmus, Mey.,as well as the genus Micrasterias, Ehr., to
Pediastrum, Kiitz. Lastly, the order DESMiurACEa; contains
many unicellular Algae, placed by Ehrenberg under the
genera Desmidium, Pentasterias, Euastrum, and Closterium.
For part of these Ehrenberg's definition is retained; but
others of them are raised to the rank of distinct genera. Thus
has Nageli from Closterium trabecula, Ehr., formed the genus
Pleurotcenium, and from Closterium cylindrus, Ehr., the genus
Dysphinctium ; whilst a portion of the Desmidese with Pentasterias have been placed under the genus Phycastrum, Kiitz.
According to Nageli (p. 3), the unicellular Algee occur
either solitary or united into colonies, which readily break up
into single cells ; or thej .may be firmly united by a gelatinous
envelope, though separated from each other by a gelatinous
s ubstance, and without any organic connexion; or they are
placed singly at the extremities of a branched gelatiniform
peduncle. Occasionally, also, the cells are firmly connected
into a parenchyma, as in multicellular plants, in which case
the connexion breaks up into smaller portions, or even into
single cells, either not at all or but very seldom.
With regard to the relation of the unicellular Algae to the unicellular animals, and the unicellular condition of multicellular
animals, Nageli (p. 4) thus expresses himself. " The most important difference :—that the vegetable cell-membrane contains
no azote, whilst the animal cell-membrane does—cannot be applied, especially in doubtful cases ; the tenuity of the membrane
not allowing of the investigation. That animals possess the
power of locomotion but plants not, is, in the first place, incorrect, as applied generally, and also here the less admits of
application, because many unicellular Algae exhibit motion, frequently very energetic motion (when swarming), whilst the ova
of multicellular animals are quiescent. The unicellular Alga;
differ from the Infusoria in this, that their membrane and its
appendages are not motile, and that consequently they have a
rigid form, whilst the latter, in some instances, change their
figure, and in others are furnished with motile-cilia. The
presence of starch in the cell-contents is, further, invariably
decisive as to the vegetable nature of a cell. The ova of
multicellular animals, the figure of which is rigid and un-
SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS. 115
changeable, may also be recognised as not belonging to the
unicellular Algae from the want of colouring matter, which is
present in all the latter." I shall have an opportunity further
on of recurring to several of these points, and of entering
more particularly into them.
As respects the chemical relation of the cell-contents of
unicellular Algae, Nageli lays great stress upon the presence
of colouring matter. This colouring matter is distinguished
by him as Chlorophyll,Phycochrom, Erythrophyll, and Diatomin.
The Chlorophyll is of a grass or yellow-green colour, little or
at all affected by diluted acids and alkalies, and frequently turns
brownish-green upon the death of the plant.* The Phycochrom
is verdigris-green or orange, changed into orange by the action
of diluted acid, and into a brown-yellow by that of diluted
alkalies. The Erythrophyll presents a red or purple colour,
not changed by diluted acids, but. becoming green on the
addition of alkalies, and also most usually after death. The
Diatomin is brownish-yellow, not altered by diluted alkalies,
but changed into verdigris-green by diluted hydrochloric
acid, and, for the most part, by death. Together with the
colouring matter, continues Nageli (p. 9), starch grains, or
colourless oil-drops, are frequently formed, with the increase
of which in the persistent cells (dauerzellen) the former
finally disappears.
I must here remark, that we can scarcely expect chemistry
to decide what is animal and what plant, having several times
been deceived in our hopes in this respect. The non-nitrogenous cellulose, which at first sight appears to be an exclusive attribute of the vegetable, also occurs pretty generally
disseminated in the animal kingdom, as we learn from the
researches of C. Schmidt on Cynthia mamittaris, and those of
Kolliker and Lowig on a great number of the most various
of the lower animals. Just as little does Chlorophyll appear to be exclusively characteristic of the vegetable world,
since the green granules and vesicles, which occur imbedded
in the parenchyma of Hydra viridis, of various Turbellariaa
(Hypostornum viride and Typhloplana viridata, Schm.), and
of Infusoria (Euglena viridis, Stentor polymorphus, Bursaria
vernalis, Luxodes bursaria, &c.), are probably closely allied to
Chlorophyll, if not identical with it.
Erythrophyll also
might be said to occur in the lower animals, for instance, in
Leucophrys sanguinea and Astasia hcematodes, in which latter
the red colour frequently passes into green, as does the Erythrophyll of unicellular Algae.
* Vide CohD.
i2
1 1G SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS.
Another more important circumstance connected with the
chemical composition of the cell contents, is also noticed by
Nageli, and which relates to the so called red eye-spot of certain
Infusoria. He saw, for instance (p. 9), in the midst of the
Chlorophyll of certain unicellular Algae, one or several bright
red or orange-coloured oil-drops, upon which he remarks upon
the similarity of these red granules with the red point, which
occurs in several swann-spores, for instance in Ulothrix.
An inspection of Nageli's PI. IV., B. fig. 1-4, will at once
show the identity of the bright red oil-drops in the quadrangular unicellular Algae Polyedriurn tric/onum, tetragonum,
tetraedricum, and lobulatum, Nag., as well as in the interesting
new unicellular Algae, Ophiocytium majus, Nag. (PI. IV., A.
fig. 2), with the points, so often stated to be eyes by Ehrenberg.
These are precisely the same red points, as those which
are met with also in Eadorina, Chlamidomonas, and Vblvox
Infusoria—which I must declare to be unicellular Algae.
Very remarkable is Nageli's statement (p. 9), that the chlorophyll in many unicellular Algae occasionally disappears
altogether, being transformed into a red or orange-coloured
oil, a change not always connected with the death of the cells,
as for instance in Pleurocovcus miniatus, Nag. ; Protococcus
nivalis, Kiitz.; Palmella miniata, Leibl., &c.
In almost all the genera in which chlorophyll occurs Nageli
found (p. 11) one or more chlrrrophyll-cells, for the most part
in regular number and disposition, and exhibiting the appearance of granules or even of nuclei. Nageli satisfied himself
that these chlorophyll-cells, even from external appearance, are
the same forms as those which occur in the multicellular alga;
containing chlorophyll, such as Zygnema, Spirogyra, Spheroplea, Conferva, &c. Further investigation perfectly assured
him of their identity. These chlorophyll-cells at first contained only clilorophyll (that is, mucus coloured by chlorophyll')
with a delicate membrane. But they seldom remain in this
condition, starch at a subsequent period becoming developed
in them, by which the chlorophyll is wholly or in part displaced. Then there either lie in the chlorophyll-cell one or
several minute starch-grains, or it becomes almost entirely filled
with starch, as happens in the Palmellaceae and Desmidiaceae.
From this it follows that, although the presence of starch,
as Nageli says, is decisive as to the vegetable nature of a cell,
this important means of diagnosis does not always admit of
application, because starch is not found in all stages of the development of those plants which might be confounded with
unicellular animals.
But to return to these chlorophyll-cells—is it not apparent
SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS. 117
that they are the bodies described by Ehrenberg as the testes?
To perceive this it is only necessary to compare the various
figures in Nageli's work with Plates X. and XI. of Ehrenberg's
great work, in which Scenodesmus, Mey., is figured as Arthrodesmus and Tassarthra, and further Pediastrtim, Kiitz., as
Micrasterias. The colourless hollow spaces filled with water,
observed by Nageli (p. 91, 95, Sec.) in the above named, as
well as in many other unicellular Algae, have been regarded as
gastric cells by Ehrenberg, as is obvious at the first glance,
whilst the green granular Chlorophyll contents of these vegetable organisms, according to Ehrenberg, would have to be
regarded as ova. In various Desmidiaceae, for instance in
Pleurotcewium, Cahcylindms, and Closterium, Nageli noticed
several Chlorophyll-cells, frequently arranged in a serial manner. In CTosterium digitus and Monilifervm, as well as in some
other Closteria, he observed in the centre of the cell a clear
nuclear-vesicle with an opaque central nucleolus. It is these
chlorophyll and nuclear cells which Ehrenberg and Eckhardt
would arbitrarily explain sometimes as a polygastric apparatus,
sometimes as the male glandular organs of the Closteria.
The cell-wall in the unicellular Algap, according to Nageli
(p. 12), exhibits in respect to colour, conformation, and substance, the greatest variety. Very frequently it possesses a
considerable thickness, and in this case may be regarded as
laminated, the innermost very delicate layer representing the
true cell-membrane, whilst the external thick layer, more or
less distinctly defined on the outer side, constitutes an envelope for the cell. This enveloping membrane consists of
vegetable gelatine in various stages of condensation. It may
surround each individual cell, or contain 2, 4, 8, &c. together,
or even a whole aggregation of cells, as an entire family or
colony. As forms of Algae furnished with a gelatinous envelope I may adduce Gonium, Schizonenia, JVaunema, and Syncyclia, Ehr.; to which must be added Evdorina, Spkcerosyra,
Clilamidomonas, Pandorina, and Volvox, Ehr. In some cases
the lamination and thickening of the envelope takes place only
on one side, whence it assumes the form of a peduncle, at the
extremity of which the cell is placed, owing to which, when
longitudinal scission of the cells takes place, a branched peduncle is produced. Wit'i reference to this compare the figures
of Synedra, Achnanthes, Echinella, Cocconema, and Gomphonerna, Ehr. Frequently also the cell-membrane exhibits thickenings, which are sometimes placed towards the interior (in
the Diatomaceae), sometimes towards the exterior (in Eitastrum
and C/osteriiirn).
The growth of the unicellular Algae, according to Nageli,
118 SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS.
takes place, either with a general expansion of the cell-membrane or with a unilateral, or point-growth as it is termed.
The propagation of the unicellular Alga: (p. 17) is effected in
very various ways, by division, by conjugation, by free cellformation, and by abscission of segments, with various modifications. Of these various modes of propagation discussed
by Nageli, I will only observe upon those which have reference to the Algae described by Ehrenberg as Infusoria.
In the mode of propagation by scission the entire cell-contents, according to Nageli, become individualised into two
(rarely four) parts. After the formation of these filial cells the
mother-cell ceases to exist. Nageli here adduces, as an example,
the propagation of thePalmellaceze (to which belong several species of Gonium, Ehr.), the Diatomaceae and Desmidjaceae. In
Euastrum, after the scission has taken place, in each filial cell
the one half is perfected entirely anew, whence in the younger
condition this new half is small, almost spherical and colourless. Nageli has shown this mode of propagation in Euastrum
margaritiferum, Ehr. (p. 118, Tab. VII. A, fig. 2, e); whilst
we had previously a description of this interesting process of
division and growth in Staurastrum and Euastrum, by Ralfs
(Ann. Nat. Hist., vol. 14, 1844, PI. VI., VII., and vol. 15,
1845, PI. X., XII.) and Focke (Physiol. Stud., Bremen, 1847,
p. 47, PI. II.).
Propagation by conjugation occurs in the Desmidiaceae, which Nageli (pp. 17, 18, Tab. VII., A. fig. 6 h) thus
describes, in Euastrum rupestre, Nag. :—Two individuals are
placed close together, and push out short processes, which
meet, and by the absorption of the wall constitute a canal, into
which the entire contents of the two cells thus connected
enters, constitutes one mass, and is gradually formed into a
single cell. Nageli adds, however, that in Closterium this
act of conjugation proceeds in a different way, which I can
confirm. In Closterium lunula, according to Morren (Ann.
d. Sc. Nat., torn. V. 1836—Botanique, p. 325, pi. 9) the conjugated individuals appear to grow together exactly in the
way above described; in Closterium rostratum also, two individuals appear to become united by the middle of their body
(Vid. Focke, 1. c. pi. III. fig. 34-36, and Ralfs, Brit. Desmidieae, 1848, pi. X X X . fig. 3 c ) ; whilst Closterium Diance,
lineatum, striolatum, setaceum, &c, behave in a totally different
manner in this process. In these species the middle of the
cell-membrane dehisces with a transverse fissure, and the
entire contents, from two contiguous, opened cells, coalesce
into a single rounded or angular mass. Sometimes (in Closterium
lineatum) it is only the two upper and lower halves which thus
SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS. 119
coalesce, forming two closely approximated compressed globules. Relatively to this mode of conjugation 1 reler to the
representations given in Ehrenberg, pi. V. and VI., as well as
in Ralfs, pi. XXIV. to X X X . It remains to be inquired
whether the green bodies produced by this conjugation, the
covei'ing of which, at first very delicate, gradually becomes
thickened, are to be regarded as spores or as sporangia. I
have not myself been able to observe what proceeds from the
green bodies in course of time. According to Morren (o. c.
p. 329, pi. 10), however, it would appear that in Closterium
lunula the green spores arising from the conjugation grow
into a new Closterium after they have emerged from thenenvelope and, like the spores of Vaucheria, move about freely
in the water. This process, as is truly remarked by Focke
and Nageli, is not in any way one of multiplication, but properly a kind of reduction or diminution. I suppose, therefore, that the green bodies produced by the conjugation are
not in all cases developed into a single Closterium, like spores,
but that, as in the case of other Algae, such as Vaucheria,
(Edogonium, there are two sorts of spore formations, and that
under certain circumstances these green bodies represent a
germ—capsule or sporangium—-in which, by a process of division, several young Closteria come to be perfected. With
this mode of development, probably, is connected the vesicular
body, containing sixteen small Closteria, figured by Ralfs
(pi. XXVIT.) as belonging to Closterium acerosum. According to Jenner (ib. p. 11) the covering of the green bodies in
Closterium, which are regarded by Ralfs as sporangia, swells
whilst a mucus is secreted within it, and minute Closteria arc
formed, which at last, by their increase, rupture the attenuated
vesicular covering. Whether or no that form of gelatinous
vesicle, containing eight young Closteria, which, according to
Focke (op. c. p. 57, pi. III. fig. 27), proceeds, in Closterium
digitus, from a process of envelopment, belongs to this category,
I will leave undecided.
Ehrenberg has proposed {p. c, p. 89) to designate these green
bodies of the Closteria, produced by conjugation, as double
buds, and the entire act of conjugation as a double gemmation.
This designation, however, is quite inapplicable, since in any
form of gemmation it is impossible that the entire contents of
a cell, as is the case here, should germinate into the newformed bud. Ehrenberg, moreover, in the exposition of the
organization and vital processes of the Closteria, perceived their
similarity with those of the Zygnemaceae (Zyqiiema, Spirogyra,
Zygogonium, &c.), which are also propagated by conjugation.
He says (p. c, p. 99) that were any one readily disposed to
120 SIEBOLD ON UNICELLULAli PLANTS AND ANIMALS.
look for similarities, it would be easy to speak of vesiculsB
seminales, oviducts, and testes (in Spirogyra); but all is
motionless ; and just as motionless is everything in the Closteria.
All those particulars, which, according to Ehrenberg, would
serve to prove the animality of these organisms, either have no
existence at all or are of no validity. He adduces four principal characters especially (/. c, p. 88), which would exclude
the Closteria from the vegetable kingdom.
1. They have spontaneous motion. The slow, turning, and
at the same time rare movements of the Closteria, present
no character of spontaneity ; these motions are certainly merely
the consequence of an active endosmosis and exosmosis, by
which the water immediately surrounding the Closteria, and
consequently themselves, are put into motion. 2. That they
have an opening at each end. But these openings have not
been seen by any other observer; the sharp-sighted Focke
(o. c, p. 55, 60), even, has been unable to perceive any. That
Eckhardt (o. c, p. 211 ; p. vii., fig. \,rr) should have introduced these openings into his figure of Closteriurn acerosum—
although they have not been observed in that instance, either by
himself or by Ehrenberg—can decide nothing. 3. That they
are furnished with conical, wart-like organs, projecting even from
these two openings, which are in continual motion; but these
organs, also, have not been discovered by any other observer.
According to Ehrenberg, the number of these proboscis-like,
motile organs is easily computed, since their basal portions, in
the form of minute, continually moving papillae, may be distinctly seen and counted in almost all Closteria. These papillae,
however, are nothing else than quivering masses of granules,
in molecular motion, contained in two vesicular spaces. 4.
Lastly, Ehrenberg refers to the transverse division observed in
the Closteria, which, according to him, is to be indisputably
regarded as irreconcilable with the vegetable character. That
Ehrenberg is here altogether in error, will be admitted by
any one who has at all studied the lower vegetable world.
The Closteria, therefore, are not only as rigid as the Zygnemata, but have quite as much right to be regarded as belonging
to the vegetable kingdom. No part of their body possesses
that contractility and expansibility which is an attribute of the
animal body alone. The progressive motion of granules and
fluids, which has been noticed in Clsoterium by Meyen,
Dalrymple, Lobarzewski, Focke, and Ralfs, does not proceed
from any contractile part of the Closteriurn cell, but corresponds much more with the circulation exhibited in other
plant-cells, as in Chora, Vallisneria, and the hairs of the Nettle,
&c. But whether this motion of the fluids depends upon an
SIEBOLD ON UNICELLULAR PLANTS AND ANIMALS. 121
internal ciliary investment, as asserted by Focke (o. a, p. 56),
I may be allowed to doubt, as I have never been able to perceive such cilia in the Closteria; and my friend A. Braun,
whose opinion on such a matter is of the utmost value, has
been equally unsuccessful. Since the Closteria, as well as the
rest of the Desmidiacese, are certainly plants, it follows that
conjugation, or zygosis, as a special kind of propagation, does
not belong to the animal kingdom, unless Kolliker's observation, of the coalescence of two individuals of Actinophrys Sol,
should be regarded as an analogous process. There is nothing
contradictory in the notion that such a conjugation should
exist in Acthwplirys Sol, a protozoon of so simple a kind,
whose structureless body, according to Kolliker's late researches,
consists of a homogeneous, contractile substance, without
mouth, intestine, or other organs. I would, on the other hand,
ask those who, with Ehrenberg, not only regard the Closteria
as animals, but are, besides, under the erroneous impression
that these creatures possess a very complex, motile apparatus,
polygastric digestive organs, male and female sexual organs—
1 would ask them what becomes of this motile apparatus,—of
the various stomachs, ovaries, and testes,—when all these parts,
with the rest of the contents of the two cases which enclose
these so-termed complete animal organisms, have coalesced in
the act of conjugation ?
A third mode of propagation, viz. a free cell-formation, in
which the contents of the mother-cell are employed as a nutritive material, in the formation of the filial cells, and, consequently, in which the death of the mother-cell is involved,
would appear, according to Nageli (p. 17), to be restricted to
the orders of the Protococcaceae and Valoniacese. Whether such
a production of filial cells within a mother-cell does not occur
in certain Palmellacese and Desmidiaceaj, which have been
confounded with Infusoria, I must leave as doubtful.
[To be continued.]