AND DEVELOPMENT OF PVROSOMA. 225 
and yet I could neither observe the smallest trace of the yelk in entire ovisacs in this 
stage, nor, however carefully I opened them, discover any trace of yelk within them. I 
found, furthermore, not only that, by a little pains, I could open the ovisac so as to view 
the germinal vesicle from within (figs. 6 and 7), but that I could evert it, turn it in all 
directions, and even detach it entirely : and when I discovered, by these means, not merely 
that no vitellus surrounds the germinal vesicle in this stage, but that it is enclosed and 
held in place by something which is assuredly not vitellus, I was forced back into my 
original conclusion, that in this stage the vitellus, as such, has disappeared. 
There is, however, one suggestion which deserves careful consideration. It may be 
said, that what I have termed the germinal vesicle (represented separately in figs. G a & 8) 
i in fact the ovum. To meet this objection, I would beg the reader to compare figs. 8 
and 8* ; the former of which represents the body whose nature is in dispute, and the latter 
an ovum which has not reached its full size, the two figures preserving the true relative 
proportions of the originals. It is at once obvious that the circular solid-lookin 
puscle, situated towards the upper end of fig. 8, is identical in all essential respects witli 
the germinal spot of fig. 8*, the only difference being that it is slightly larger, measuring 
TsVoth f an i nc } l3 w hii e the germinal spot of the entire ovum is about y^nr. But if this 
corpuscle represent the germinal spot, then the only structure which corresponds with 
the wall of the germinal vesicle in fig. 8* is the structureless, oval, membranous sac, 
wrinkled on one side, which encloses the germinal spot in fig. 8. This sac, it must be 
admitted, differs a good deal from the germinal vesicle of fig. 8*, not only in size, but in 
form and in contents. In the first place, it is much larger, measuring g^th of an inch in 
s 
length, while the germinal vesicle of fig. 8* is only -§ 
oval and irregular 
Thus 
one side ; and thirdly (and this is the most important difference), it contains a homoge- 
neous yellowish deposit, which is especially accumulated around the germinal spot, but is 
absent under the wrinkled moiety of the vesicle. 
All doubts as to the identification of the body (fig. 8) with the germinal vesicle and 
spot of fig. 8*, however, vanish when a series of ovisacs, intermediate in size between that 
which yielded the ovum, fig. 8*, and that represented in fig. 6, are studied. 
fig. 4, the unquestionable germinal vesicle is oval, and its long diameter amounts 
to 5i- -th of an inch ; while in the ovisac represented in fig. 5, in which the yelk has 
disappeared, the body in dispute is precisely similar to the germinal vesicle of fig. 4, 
except that it is a little more flattened and a little longer (^th). Its contents are 
quite clear, and its wall is but very slightly corrugated. But no one can question the 
identity of this body with that represented in place in fig. 6, and separately magnified m 
%. 6«, which has a long diameter of ^iyth of an inch, whose walls are much wrinkled, 
and which contains a dense yellow deposit. 
I have no hesitation then in regarding the body, fig. 8, which agrees in all essential 
respects with that represented in fig. Qa, as the germinal vesicle of the primitive ovum, 
stripped of its vitellus. , , 
Though devoid of any vitelline investment, however, the germinal vesicle Has Deen 
neither free nor bare, in any ovisac which I have examined. It is always seen to occupy 
inner face of the ovisac, a little behind and to the right of the upper 
ie spot of the 
vol. XXIII. 
2 
