Zoology. : 437 
examination with sufficient care. Their error here evidently arises 
from their having considered the superficial part of the viscid matter 
which retains the granulations mingled in its own substance as an en- 
veloping membrane. This matter is in fact merely lodged in the inter- 
stices of the granulations which it agglutinates, and which it separates 
so regularly that it appears at first sight to form a wall at the periphery 
of the vitellus, the outline of which appears more distinctly delineated 
in proportion as its transparence contrasts with the opacity of the granu- 
dations which it bounds. But, I repeat, this is an illusion which an 
attentive analysis corrects, and on this point I have sufficiently repeated 
my observations to have a well-founded conviction. 
The vitellus is not then, as has been supposed, a vesicle or cell filled 
with granules, but simply a granular homogeneous sphere, the whole 
of the grains of which are kept agglutinated by a diaphanous interstitial 
matter, the retraction of which matter gives the whole mass the some- 
what geometric regularity which it assumes. 
Soon (a few hours are sufficient for the accomplishment of this 
phenomenon) the vitelline sphere divides it into two nearly equal parts, 
each of which, immediately rendered spherical in form by the cen- 
tripetal retraction of the viscosity which retains its granulations in union, 
presents the same aspect and the same composition as the whole from 
which it emanates. 
This primary division is scarcely accomplished before the two secon- 
dary granular spheres which are thus formed by a primary division of 
the vitellus become in their turn the seat of a similar division, and the 
same phenomenon being repeated during a certain time upon each new 
segment, the vitellus is finally resolved into a considerable number of 
granular spheres of a progressively diminishing volume, but always of 
the same nature. However Reichert, who has made some special re- 
searches upon the division of the vitellus of the Batrachia, believes he 
has observed that each segment is a true cell possessing an enveloping 
membrane and granular contents. According to him, the phenome- 
non of the division of the yolk would then have a totally different 
signification to that which ‘we have given, and would essentially be 
nothing more than an illusion produced by the liberation of the pre- 
existing vesicles which were inclosed one within another. The vitellus, 
in his view, would at first represent a mother-cell, the wall of which, 
when ultimately absorbed, would expose to view two inclosed vesicles 
which form its contents; these two vesicles having thus become free 
would be dissolved in their turn, and each of them would allow two 
other vesicles to escape, which would produce an appearance of a divi- 
sion of the yolk into four segments, and so on, until the completion of 
this illusory division arrived. But although this hypothesis appears to 
Seconp Serizs, Vol. I, No. 3.—May, 1846. 56 
ei 
SE REN 
