Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 5: Supplementary Volume
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit36060/16/
8 OVUM. 
gous to transverse fission. Stein, on the 
other hand, has been convinced by a very at¬ 
tentive observation of the different stages of 
this process, that it is of an opposite character, 
and that, previous to the development of the 
young progeny, two of the Gregarinæ have 
become fused, or united into one. As the 
two are about to unite, they gradually change 
their form from that of elongated planaria- 
like animalcules, to that nearly of hemispheres, 
closely pressed together; then a complete 
fusion or union occurs, and the whole of the 
granules of both having become amalgamated 
in one sphere, the development of the internal 
progeny takes place gradually from the mass. 
This progeny consists in a vast multitude 
of minute bodies, shaped like the Navicellæ 
(among the Diatomaceæ), but different from 
these bodies, and very probably constituting 
the reproductive germs or embryos of Gre¬ 
garinæ. The development of this Navi- 
cella-like progeny into the Gregarina does 
not appear as yet to have been traced ; as in 
this animal, like many other parasites, the 
progeny is required to migrate during its de¬ 
velopment from one stage to another, and the 
little bodies are passed out of the alimentary 
canal of the insect before undergoing farther 
changes. 
The views and observations of Stein, how¬ 
ever, should they be confirmed by others, 
would prove the very remarkable fact, that 
the phenomenon of conjugation, or fusion of 
two unicellular individuals, hitherto supposed 
to be confined to some of the simpler plants, 
as Closterium, Spirogyra and Zygnema, &c., 
may occur also in animals of a similar simple 
structure. 
These observations on the Gregarina are 
not altogether of an isolated kind. In a 
recent interesting notice of this subject by V. 
Siebold*, he has called attention to the ob¬ 
servation of Kölliker on the conjugation or 
fusion of two individuals of Actinophrys f, a 
spherical infusorian animalcule analogous to 
the Amoeba or Rhizopoda, by its slowly con¬ 
tractile, amorphous texture, and its long, ra¬ 
diating, contractile processes. Kölliker ob¬ 
served two individuals of this animalcule to 
approach each other, adhere, and gradually to 
fuse into one, which soon assumed the same 
globular form, with the radiated contractile 
processes, as each of the two that formed it, 
and differing only from them by the increase 
success by various observers, as Y. Siebold (Beitrag. 
Z. Naturgesch. Wirbellos. Thiere, 1839, p. 63.). 
Heule (Müller’s Archiv, 1845, p. 369.), and Stein in 
the same, 1848, p. 182. Kölliker (Zeitscli. f. Wiss. 
Zool. 1848 and 1849), and as many as eighty dif¬ 
ferent species of them have now been discovered. _ 
* Zeitsch. f. Wissensch. Zool. March, 1851, 
p. 62. 
f Op. cit. 1849, p. 207. In this very interesting 
memoir Kölliker has proved the animal nature of 
the Actinophrys by his observations on its contrac¬ 
tility, and on the manner in which the particles of 
solid matters, vegetable and animal, are involved in 
its substance for the purpose of digestion, and their 
remains again rejected when that process is com¬ 
pleted. 
of size which it sustained. This very curious 
observation has been confirmed by Stein, in 
an allied genus Podophyra, both of the sessile 
and pediculated kind ; and V. Siebold has ob¬ 
served the same phenomenon in a species of 
Acineta belonging to the same family of 
Infusoria. Cohn, also, has repeated and con¬ 
firmed Kölliker’s observations in the Acti¬ 
nophrys sol, and has made a farther discovery 
of great interest in connection with the pro¬ 
cess of conjugation in these animals, having 
observed after the union, both in the Acineta 
and Actinophrys, the development, at certain 
periods, between the united individuals, of a 
spherical body of considerable size, vesicular 
form, and containing within it a nuclear forma¬ 
tion of variable magnitude. 
Although the farther development of this 
body has not yet been traced, it seems not 
improbable to V. Siebold that it may be 
analogous to the reproductive capsule or 
sporo-cyst of the conjugating Closterium or 
Zygnema*, from which bodies it seems to be 
certain that a number of reproductive spores 
are produced. 
Since the foregoing was written, indeed, 
renewed researches by Stein f have come 
under my notice which are confirmatory of 
the view previously stated as to the repro¬ 
ductive process in Gregarina, and explain in 
a great degree the apparently incomplete 
observations of Pineau j and others as to the 
varying conditions of Vorticella, and also 
extend our knowledge of the production of 
germs of the Infusoria. Stein observed the 
Vorticella microstoma to lose its pedicle, 
become free, assume the globular form, and 
at last to be enclosed in a cyst produced by- 
exudation from its own body. After a time 
the band-like nucleus of the encysted Vorti¬ 
cella is divided into a number of small discoid 
bodies, not by a regular or progressive process 
of cell-cleavage, but at once and directly. 
These minute bodies gradually increase in 
size at the expense of the granular and fluid 
substance surrounding them in the cyst, and 
ultimately escape in the form exactly of Monas 
colpoda (of Ehrenberg). These very soon fix 
themselves ; and a fine pedicle is developed at 
the place of attachment. In other instances 
the Vorticella-cyst was observed to send 
forth long contractile processes from its sur¬ 
face, and then assumed very much the form 
and appearance of an Acineta or Actinophrys; 
and in this case a new Vorticella was formed 
in the interior in the manner of a bud. The 
Vorticella, therefore, it would appear, is ca¬ 
pable of reproduction in two modes,—by the 
development of embryoes from the divided 
nucleus, which Stein on this account proposes 
to call nucleus germinativus (the testis of 
Ehrenberg); and by gemmation from an 
intermediate Acineta form. The first form 
Stein would regard as the equivalent of sex- 
* See the Article Vegetable Ovum for an ac¬ 
count of this process in the lower forms of plants. 
f Zeitsch. fur Wissensch. Zool. Feb. 1852. 
J Ann. des Seien. Nat. 1845 and 1848.
        

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