DR. MARTIN BARRY ON THE CORPUSCLES OF THE BLOOD. 
243 
We thus find that in the minutest details, such as those which I have elsewhere de- 
scribed, the germinal spot and vesicle are formed like other nuclei and cells. 
191. I long found it impossible to understand in what way the membrane of the 
ovisac, as I termed it, was formed around the mass of peculiar granules having the 
germinal vesicle in its interior ; and equally difficult to conceive the mode of origin 
of the discus vitellinus, the true yelk, and the membrane of the yelk. It now appears 
to me that all these (as well as the germinal vesicle and spot) originate in a corpuscle 
having the same appearance as a corpuscle of the blood. That part of this corpuscle 
which surrounds the germinal vesicle (see the figures), becomes the source of the pe- 
culiar granules (as I formerly termed them) by which this vesicle is surrounded. 
These peculiar granules — the objects subsequently contained within the ovisac — are 
not originally cells : so that the term granule proves to have been not inappropriate. 
The fact is, they are discs, having the same form and general appearance as discs in 
other situations (only being very red) ; and by a change the same as that we have so 
often seen elsewhere, assume a cell-like appearance, and are reproduced in the same 
manner as other discs. Hence, in advanced states of the ovisac, the quantity of 
these objects becomes very large : and, as we formerly had occasion to observe, they 
arrange themselves into structures, some of which — the retinacula — enter into the 
formation of the mechanism regulating the expulsion of the ovumj;. 
192. But my purpose in referring to these discs so fully in this place, is to be en- 
abled to make the following addition : namely, that they also give origin to the mem- 
brane of the ovisac, the discus vitellinus as well as the true yelk, and the membrane 
of the yelk. And as the discs in question are derived from a corpuscle having the 
same appearance as a corpuscle of the blood, so therefore are all these objects. 
193. Delineations are given of the membrane of the ovisac thus forming. In figs. 
170 and 171- the discs (g), quite red and large where in the neighbourhood of the 
germinal vesicle (c), were undergoing division; the young and paler discs passing 
outwards, increasing in size, dividing in their turn, then enlarging, and coalescing to 
form the membrane ( h ) of the ovisac. Traces of these coalesced discs, as well as a 
tinge of red, are to be discerned even after the ovisac has attained a considerable 
size ; producing the appearance which, when first describing this membrane, I com- 
pared to that of plaits or folds. 
194. I do not think that there is any essential difference between the discus vitel- 
linus and what is called the true yelk : at least it would seem difficult to draw a line 
between the two. Where it is required to provide before-hand a stock of substance 
for foetal u. f e, — as in many of the Ovipara, — the discs g are made to form the yelk in 
f First Series on Embryology, l. c., pars. 14, 23. 
1 It may now be added, that the delicate membrane I described as sometimes seen investing the retinacula, 
and reflected from their branches to the membrana granulosa, seems to be formed by the coalescence of some of 
these discs. 
2 K 
MDCCCXLI. 
