Andrew Pritchard.

A history of Infusoria, including the Desmidiaceæ and Diatomaceæ. British and foreign online

. (page 55 of 158)
Online LibraryAndrew PritchardA history of Infusoria, including the Desmidiaceæ and Diatomaceæ. British and foreign → online text (page 55 of 158)
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essence of the testis. It is the force which governs the act of propagation bj
spantaneooB fission : and, if Ehrenberg be correct, in viewing the interstitial
«»piiseles as geim-cells (to which opinion Professor Owen inclines), these
essential parts of ova may receive the essential matter of the sperm from the
nudens, which is discharged along with them in the breaking np of the
monad, which Ehrenberg regards as equivalent to an act of oviposition ; and
impregnated germ-cells may thus be prepared to diffuse through space, and
carry the species of Polygastric animalcules to a distance from the scene of
life of the parent " (p. 67, Ed. 1849.)

lieberkiihn (A. N. H, xviii. 1856, p. 321) makes the nucleolus of import-
ance in founding specific characters. He says, that, excepting the eye-point,
the nucleolus is properly the only part which distinguishes Ophryoglena
JIavicans from Burtaria flava, — " lliis body," he proceeds to say, ** is shaped
Hke a grain of barley, and is marked at each end with a few sharply-defined
streaks or Airrows ; its length is somewhat more than yj^ of a millimetre,
its thickness in the middle about y^ of a millimetre. Its substance has a
stronger refractive power than that of the rest of the body, but far less than
the fiit-like globules. Under the highest magnifying power, no structure
could be distinguished, and it withstands for a considerable time the action
of water. The nucleolus is situated on the middle of the nucleus, which is
about one-fifth of the entire length of the animalcule, and its breadth in the
middle about one-third of its length .... It is of ovate form ; its substance
displays no recognizable structure.

'' The nucleolus has very different characters in all the specimens of Bw-
garia jlava I have hitherto observed. It was always so small that it was
difficult to find it, and never became visible until the Infusorium was com-
pressed, while in Ophryoglena ilava it may usually be seen through the
int^nments. Its form is globular, and it presents no structure. It gene-
rally adheres firmly to the surface of the ovate nucleus."

The same lesson concerning the utility of the nucleus and nucleolus in
distinguishing genera and species, might be gathered from the descriptions
of Stein and otiiers, which show clearly enough that these organs have a
determinate figure and relation in several genera, as, for example, in Spiro^
chona and Panrnieeium.

The figure of the nucleus and the relation of the nucleolus to it, in Pro^
rodan teres and in Nassula deganSy are deserving attention. In the former
species the nucleus is represented as gjLobular, with a nucleolus surmounting
it (XXVin. 9) ; in the latter, the nucleus is stoutly clavate, and terminated
by a small oblong nucleolus at its narrower extremity. These well-marked
peculiarities in the two examples named, coupled with the views of lieber-
kiihn just cited, and the conclusions of Stein and Balbiani concerning the
physiological relations of the two organs in question, will challenge for them
much more attention than they have hitherto received.

M. Balbiani has lately contributed to the French Academy two most im-
portant papera, in which he has endeavoured to demonstrate a sexual repro-
duction of the Ciliata, the nucleus representing the female, and the nucleolus
the male, element. In his first essay he illustrates his hypothesis by reference
to Paramecium Bvrsaria (A. N, H. 1868, i. p. 436), and thus writes :—

" For several generations the Paramecia multiply by spontaneous scission,
each of the two new individuals obtaining half the primitive nucleus ....



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6BKBSAL HISTOBt OF THB OrVUBOSIA.

But under the influenoe of conditioiifi of which we are still ignorant^ die
spedee propagates itself in a very different manner, and in the nudst of phe-
nomena far more complex than those which preside over the mnltipliioatioii
by fissiparity. In this new mode we shall see the actual anatomical signifi-
cation of the nucleus and nucleolus^ the function of which, if we except the
division of the former of these two organs in the act of spontaneous diyiaiony
has hitherto been perfectly passive. It is, in iact, at their expense that ihe
male and female rejntKliiotive elements which characterize this mode of
propagation are formed.

** When the period arrives at which the Partvnuda are to propagate with
concourse of the sexes, they are seen assembling upon certain parts of the
vessel, either towards tiie bottom, or on the walls. The copulation is always
preceded by certain preliminaries which are very curious to observe, but upon
which we cannot dwell here. Soon they are found coupled in pairs, adbermt
laterally and as it were locked together, with the similar extremities turned
in the same direction, and the two mouths closely applied to each other. In
this state the two conjugated individuals continue moving with agility in the
liquid, and turning constantly round their axis. There is nothing, before the
copulation, to announce the considerable changes which are about to take
place in the nucleus, and the nucleolus Which accompanies it. It is daring
the copulation itself, of which the durati<m is prolonged for five or six days or
more, that their transformation into sexual reproductive apparatus takes plaee.

** The nucleolus has undergone a considerable increase in siie, and hts
become converted into a sort of capsule of an oval form, of which the surCiee
presents longitudinal and parallel lioes or streaks. Nearly always, it soon
divides in the directi<m of its greater axis, into two, or more frequently into
four, parts, which continue increasing independently of each other, and in a
very irregular manner, and form so many secondary sacs or capsules. At a
period which is still near that of division, these latter appear to be composed
of an extremely fine membrane, enveloping a bundle of small, curved bacilla,
extending from one extremity of the sac to the other, inflated towards the
middle, narrowed towards the extremities. It is these which, when seen
through the enveloping membrane, give the capsule the striated appearance
which is characteristic of it, and which even exists in the nucleolus at ahnoet
all the other periods of the life of the Infusorium. It also contains a perfectly
colourless and homogeneous fluid.

** At the same time the nucleus has also changed its form and aspect; it
has become rounded and widened ; its substance has become softer and lost
its refractive power, and towards its margins it presents notdies, which,
penetrating more and more deeply into its mass, isdLate one or more frig-
ments, in which a sufficient magnifying power enables us to see a certain
number of small transparent spheres with an obscure eentral point. In other
cases the nucleus, whilst still almost entire, presents this aspect, and thei
appears as if stuffed with these little rounded bodies, the analogy of 'wbach to
ovules cannot be doubted in the least. The evolution of the nucleus and
nucleolus being identical and progressing at the same rate in the two ooiqiled
individuals, it follows, if from this moment we regard the former as an ovaiy,
and the second as a testicle or seminal capsule, not only that eadi oi them
possesses the attributes of both sexes, but that they fecundate each other,
and serve at the same time as male and female. As regards this feeundatkn
itself, everything seems to prove that it takes place by means of an exchange,
made by the two coupled individuals, of one or more of their seminal capsolee,
which pass, through the apertures of the mouths closely applied against eaeh
other, from the body of one Paramecium into that of the other ; for, verj



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OF THE PBOTOZOA.-— CIIJATA. 331

often, although we may not be able to perceive this passage itself, we may
at least detect the moment when one of the capsules already engaged in one
of the mouths, is on the point of clearing this aperture. Does the exchange
which causes fecundation take place with all the capsules in a single copula-
tion, or in so many successive copulations with different individuals ? This
is a questiim the solution of which is not easy, and which, to keep within the
fidd of our observations, we shall not attempt to solve at present.

*^ However this may be, each capsule, after its transmission, still continues
to increase in size in tiie body of the individual which has received it ; for we
have never found any which had attained the limit of their development in
individnals which were still coupled. They then frequently attahi a volume
greater than that of the nucleus itself; but there is never more than one that
arriveB at maturity at the same time. When, having arrived at this state,
it is examined after being pressed out of the body of the animalcule to free
it from the granulations which mask it more or less while there, it appears
under tiie foarm of a large ovoid body, the surfiEice of which presents a multi-
tude of parallel strisB directed longitudinally, and due to the arrangement in
series of the corpuscles contained in the interior. Compression, carried so fax
•8 to cause its rupture, distinctly shows it to be formed by a membrane of
extreme tenuity, and contents, enclosing an innumerable quantity of small
fusiform civpuscles, of which ih^ extremities are completely lost to sight in
eooaeqaence of their extreme fineness. As soon as they are free, these Httle
bodies show themselves to be animated by a vacillatory and translatory move-
menty which soon causes their dispersicm in the eircumambi^it fluid. These
are the spermatosoids of P. Bwnaria, Iodine, alcohol, and acetic add instantly
stop their movements ; they are insoluble in the last-mentioned reagent when
conoentzated, although this dissolves all the other elements of the body, with
the exoeptum of the green granules.

<' It is usually from the fifth to the sixth day following the copulation, that
the first germs are seen to make their appearance, in the form of small rounded
bodies, formed of a membrane which is rendered very evident by acetic add,
and gr^rish, pale, homogeneous, or ahnost imperceptibly granular contents,
in which ndther nudeus nor contractile vedde is yet to be distinguished.
These cngans do not appear until afterwards. The observations of Stein
and F. Cohn have shown how these embryos quit the body of the mother in
the form of AaneUx furnished with knobbed tentades — ^true suckers, by
means of which they remain for some time still adherent to the mother,
diving tiifiir nourishment from her substance ; but their investigations did
not re'rael to them the ultimate fate of these young animalcules. I have
been able to follow them for a condderable time after they detached them-
setves from the body of the mother, and have convinced myself that, after
losing their suckers, becoming surrounded with vibratile cilia, and obtaining
a moaUi which first shows itself in the form of a longitudinal furrow, they
definitdy acquired the form of the mother, becoming penetrated in the same
way by the green granulaticms characteristic of this Paramedum, without
undergoing any more important metamorphoses."

At the time this first record of his observations was read, M. Balbiani stated
that he had collected them from the investigation of six or seven spedes, but
since that period he has pursued his observations in several other species, and
completed some old <mes previoudy interrupted from want of materials
(A. N. H. 1858, ii. p. 439). In his latest paper, he enunciates the remark-
aUe statement that he has been led to regard, in a great number of cases,
what nearly all authors have conddered to be a spontaneous dividon in a
kmgitodinal direction, as a sexual union of two individuals. " Very often,



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OEKSRiU:. H18T0RT OF THE INFUSORIA.

in h/cst, I have been able to ascertain that this state coincided with cer-
tain remarkable changes which took place in the internal organs of these
animals."

The following is the general summary of the results M. Balbiani has
arrived at : — ** I. The corpuscle which, in the InAisoria, has been described
under the name of nucleolus, and which I have shown to be the male genital
gland, has hitherto only been indicated in a few rare species. In connexion
with this, I have examined a great number of individuals belonging to numer-
ous and varied forms, and I have convinced myself that, far from constituting
an exception, the presence of one or even several nucleoles was a nearly con-
stant fact in the different types of this class ; but frequently the simple or
multiple nucleole which they contain is so intimately confounded willi the
substance of the nucleus, that it only becomes apparent when it is separated
therefrom accidentally by the action of reagents, or spontaneously at certain
determinate periods in the life of these creatures, principally at the time of
their sexual propagation. I have counted fourteen species in which this
organ was very evident to me, and in which I have also been able to follow
its evolution, to a greater or less extent, at the breeding-season, at the same
time that I was an eye-witness of the other actions which concur in assuring
the reproduction of these animalcules by fecundated germs.

« As regards the number and situation of the testicular organ of the Infu-
soria, I have met with the following varieties. It is simple, rounded, and
lodged in more or less deep depressions of the nucleus in Paramecium Aurelia
and P. eaudatum, and also in a third species, nearly allied to P. Bursaria, but
smaller and destitute of green granules. The genus Bursaria {B, leueas,
Jla/va, and vemalis) also presents a simple nucleole situated in the vicinity of the
nucleus. The same ihmgo(xxii8mChilo<ionCucullulu8, But with regard to the
latter, I must remark that I do not regard as the analogue of the nucleole of the
preceding species the corpusde to which M. von Siebold has given this name,
and which is placed in the interior of the granular mass of the nucleus, in
the centre of a broad transparent zone. The true nucleole or testicle of
ChUodon appears in the form of a small, rounded, brilliant grain, provided
with a proper membrane, and situated quite to one side and towards the
middle of the nucleus. It is very easily perceived in lai^ specimens by
employing the action of reagents. As regards the nucleus and its intemfJ
parts, I make no difficulty in regarding them as representing all the elements
of an ovum, of which the nucleole of tiie celebrated German naturalist would
be nothing but the germinal spot. Hie disappearance of the clear zone and
of its central corpuscle in the animals which have just copulated, especially
appears to me to militate in favour of this view.

<< n. I have met with a multiple testicle in many spedee belonging to the
groups of the OxytrUMncB and of the Euplotes or PUesconiaSy inclu<&ig the
highest types of this class. In the genus Oxytrieha the two nuclei, which
are elongated in the direction of the greater axis of the body, are each aooom-
panied by a small, rounded, testicular body, very distinct horn, the correspond-
ing nucleus. There are also two, placed one to the right and the other to
the left of the long nucleus, which is curved into the form of a horse-shoe,
in Euplotes Charon and E. viridis. In the genera Stylonychia (S, MytUuSj
pustyiata, and laneeolata) and Urostyla {U, grandis) the nucleoles, to the
number of four or five, are distributed in two groups in the vicinity of the
nuclei, of which the anterior is accompanied by two, and the posterior also
by two or sometimes three, of these littie organs. They are remarkable from
their distinctly-rounded outline, their great refractive power, and their
homogeneous structure. In Spirostomum amhiyuum, each of the g^rains of



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or THB FBOTOSOl.-— CILIATA. 333

the long moniliform oord which here replaces the oval nndeiiB of the other
^>ecies, gives lodgment, in a deep depression of its surface, to a small rounded
corpuscle, which corresponds widi the nucleole of the preceding species ; this
brings the number of testides in this animal to fortj-five or fifty. I have
only been able to perceive them in individuals which have been copulating
fbr a certain time, and by employing dilute acetic add. It is very probable
that an analogous arrangement will be found in the other types, in which the
nudeus is formed of grains placed in a single row, like a necklace, such as
StetUoTf Kondylottomumy TraeheUus monUiger, &c.

'* m. The evdution of the male genital apparatus of the Infusoria, as just
characterized, in the other spedes of the genus Parameeittm does not differ
trom that presented to us by P. Bursaria, In the Oxytriekina each of these
organs remains entire, becomes enlarged, and exhibits in its interior, applied
against its wall, a thick granular body, furnished with a tubular appendage,
which projects into the cavity of the capsule, and fq)pears to be open at its
free extremity. This tube, which seems to be an excretory duct, often
appeared to be filled with capillary filaments of extreme fineness, arranged
paialld to the axis of the duct in question, in which they were fixed hy a
portion of their length, whilst the remainder, escaping by the orifice of the
tube, radiated in all directions in the interior of the capsule. Subsequently
the granular body and its duct disappear, and the filaments, becoming free»
collect into a bundle, which fills the whole of the formative sac. Altiiough
I have never seen them execute any movements, I do not hesitate in cond-
dering them as the spermatic filaments of these animals.

*' IV. It is with equal certainty that we may call the mneleu$ the female
genital organ of the Infusoria, in oppodtion to the perfectly hypothetical
assertion of Ehrenberg, who regards it as the testicle. Its evolution likewise
only commences at ^e time of reproduction, and often during the sexual
union itself. In P, AwreUa and P. caudatum, towards the end of the copulation,
its suifEU^ is traversed in all directions by numerous furrows, which, penetrat-
ing deeper and deeper into its mass, finally divide it into a great number of
unequal and irregularly-rounded fragments, having a dear centre more or
less surrounded by granules. I diould compare l£ese with the first rudi-
ment of a vitdlus, and the transparent central portion to a more or
less developed germinal vedde. The fragments thus formed are soon dis-
persed in the surrounding parenchyma. Here a very small number of them,
almost always four, never more and very rarely less, complete their evolution,
and soon acquire the appearance of complete and wdl-devdoped ova. In
this state they present themselves in the form of small brilliant bodies, per-
fectiy equal in volume, dightiy oval, and of a bluish-grey appearance. We
may very dearly fKatingnigh in them a findy-granular viteSlus, surrounded
by its proper membrane, which separates from it more or less after a few
moments' exposure to water. The germinal vedde and spot are also vidble
with a distinctness truly surprising, conddering that we have to do here with
the smallest of living organisms. I have met with these ova still endosed in
the body of the animal on the seventh day after the copulation : they no
longer exhibited either germinal vedcle or spot ; and their volume had dightiy
increased. In the allied spedes, P. Bursaria, the reniform nudeus becomes
unrolled before breaking up, and in this state resembles the ribbon-shaped
nudeus of the VortieeU(B. About twenty or twenty-five of the fragments
produced from it continue their devdopment and become so many perfect
ova. In the nudeus of Chilodon Cuetdltdus, also, we observe, after tie copu-
lation, the disappearance of the transparent zone with its central obscure
spot. In the genera Styhwyehia and Urostyla the ova are four in number.



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334 OBineRAL HISTOBT of THB iNFUSORIA.

as in Parameeium eaudatum, but thoy are produced by a difierent mechanism.
Each of the two nuclei divides into two halves, as in the act of spontaneous
division ; and the four fragments thus produced form an equal numb^ of
perfect ova. Lastly, in SpirostorMmi ambiguumf we have seen, in individuals
which have be^i copulatmg for some time, the forty or fifty grains of the
long flexuous cord which traverses the body become rounded and detached
from each other. But we have been unable to discover in these all the
characters of an ovum with the same distinctness as in the preceding species,
no doubt because they had not yet arrived at their complete development.

*^ y. I have not witnessed the deposithn of the ova in these animals. It
is very probaUe that they escaped by the anus, or by some neighbooiing
apertcure. Thus, in the StylonyMcBy I have seen tiiem collect in the posterior
part of the body, which bears the anal orifice, and diminish gradually in num-
ber from the filrst or second day after the copulation. It is a singcdar thing,
that about this period a round pale body b^ns to make its appearance in tibe
centre of the animal ; this becomes constricted about the middle, and recon-
stitutes the douUe nucleus of Stylonychia,

** VI. The Infusoria are destitute of copulatory organs. In most cases tilie
copulation is effected by simple juxtaposition, tibe two mouths estabHshing
the sexual communication (Paramecium, Burearia, Euplotes, Cflulodony Spiro-
itomum). In the Oxytrichina the union is more intimate, and goes so fiir as
to constitute a true soldering of the two individuals for more thtm two-thirds
of their anterior part. Anyone who had not witnessed all the phases of this
singular copulation, would be unable to avoid r^arding this state as a longi-
tu^nal division, proceeding from behind forwards, in a single animaL But,
ev^i if direct observation were wanting, the concomitant dianges of the
internal organs, which are so characteristic, cannot leave the least doubt as
to the actufiJ signification of this act."

Ovules. — In Ehrenberg's organology of Infusoria, ovules or ova assomed a
high importance. The structures he so designated had no distinctive featoreB
assigned them, whereby they could be distinguished frtnn oth^ corpuscles
and granules in the interior ; and, in consequence, their existence could not
be confirmed by other microscopists, who for the most part declared that the
supposed ova were indifferently aUmentary vacuoles, particles of food, fat
globules, or the ordinary granules of the interior. The general o^Hnion became
pronounced against the very existence of ovules and of development by their
means, whilst the deposition of ova, which Ehrenbeig believed he witnessed in
several instances, was explained to be an act of difiuence misconceived. This
explanation, for instance, has been given to his recorded observation and his
figures of the act of oviposition in Colpoda Ouctdhdus, which represented this
animalcule as bursting and giving vent to strings of ova, which first ran
together in a reticulate manner, and then, after a time, became individually
developed into young Colpoda. According to the opposite view, tJie bursting
and extrusion of contents are no other than the phenomena of diffluenoe and
the dispersion of particles of sarcode, whilst the young supposed to originate
from those particles are merely minute Mon^ or monadiform corposdes
found in company with the Colpoda^.

One objection brought against the assumption of ova being ejected from
Protozoa in the exercise of a generative frmction is certainly frivolous — ^riz.
that the empty or broken shells of the ova ought to be met with ; for the shell
of an ef;^y however useful in larger animals as a deface against injury, is no
essential part of an ovum from which a new being can be developed.

Although the existence of ova among the Ciliata has been denied by the
great authorities on Infiisoria — ^by KoUiker, Siebold, Leuckart, Cohn^ Stein,



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OV THB FBOIOSOA.— CIUATA. 885

Van der Hoeven and others, yet it has latterly found two adrooates in Prof.
Perty and Mr. Carta-. The latter writer (A. N. H. 1856, xviii. p. 225) can
addooe littLe direct evidence to support his views, and seems to rest moire
wei^t upon argument from analogy with Amcebcea, AredUma^ A$ta$UE, and
BugUncBj in all which he has satisfied his own mind ol the presence of ovules,
and of their development in the two latter genera. ''The same kind of develop-
meat," he writes, '' of the ovule probaUy takes place in all the Bhixopoda as
in SpangiUa and in AsUuia and Euglma :" hut this is not proviog that Rhi-



Online LibraryAndrew PritchardA history of Infusoria, including the Desmidiaceæ and Diatomaceæ. British and foreign → online text (page 55 of 158)