DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
539 
fracting power. The ovum Plate XXIIX. fig. 1/9', from the ovary, presented an ap- 
pearance which differed only in degree from that just referred to ; and I do not re- 
collect to have met with the twin cells in stages such as those represented in Plate 
XXIV. figs. 191. 193, Plate XXV. figs. 196. 199, without finding them invested by 
minute dark objects, of apparently the same nature. 
35lJf, The greatest size to which the germinal vesicle distends I do not know. In 
the ovum Plate XXV. fig. 198. it had a diameter of ; that is, I believe, double what 
it had been seen to measure before fecundation in this animal -f*. In another instance 
(Plate XXIV. fig. 193.) it was as large as I am disposed to think that this vesicle 
sometimes attains a still greater size ; and indeed that its membrane may continue 
until after the disappearance of the last of the membranes e ; for states of the ovum 
are met with, in which it is not easy to determine whether the membrane surround- 
ing the central sphere of cells (Plate XXV. fig. 204.) is that of the enlarged germinal 
vesicle, or the last of the membranes e in a very attenuated state. In those figures 
where neither c nor e is affixed to the representation of a membrane in this situation, 
it may therefore be inferred that I have felt uncertainty in this respect. 
352. It has been already shown that the germinal vesicle — or original parent cell — 
disappearing, twin cells succeed it (Plate XXVI. figs. 206. 20/. 208.). I have now to 
add, that each of these twin cells gives origin to two others, making four (fig. 209.) ; 
that each of these four, in its turn a parent cell, gives origin to two, by which the 
number is increased to eight (figs. 213 A. 213 B.) ; and that this mode of augmenta- 
tion continues, until the germ consists of a mulberry-like object, the cells of which 
are so numerous as not to admit of being counted (Plate XXVII. figs. 230. 231.). 
Together with a doubling of the number of the cells, there occurs a diminution of their 
size. This will be easily seen on reference to the figures, these being for the most part 
on the same scale. 
353. Nor does the mode of propagation continue the same with reference to number 
only. The process inherited from the germinal vesicle by its twin offspring, reap- 
pears in the descendants of these. Every cell, whatever its minuteness, if its interior 
can be discerned, is found filled with the foundations of new cells into which its nucleus 
has been resolved. These foundations of new cells at an early period (in the exist- 
ence of a parent cell) are arranged in concentric layers around a pellucid point (Plate 
XXVII. fig. 230.) ; subsequently they are larger (fig. 231.) ; at a later period, when 
the outer layer has partially liquefied and presents its remains as minute cells (Plate 
XXVI. fig. 210.), the inner cells have increased in size ; and at a period still more ad- 
vanced, each cell presents two (fig. 222.) destined to succeed the parent cell, the 
others having disappeared by liquefaction. It is very possible, however, that though 
the same in kind, the process may, with a diminution in the size, lessen in degree. 
The number of concentric layers, for instance, arising in such minute cells as those 
f The Rabbit. 
3 z 2 
