THE DEVELOPMENT OF THE MOLE. 163 
to decide, but the appearance of the nucleoli in figs. 4 and 5, 
considered in connection with the researches of Griber 
(No. 12) on the nuclei of Protozoa, would suggest that such 
is the case. 
Mature Ovarian Ovum. 
The phenomena of the maturation of the ovum I have not 
had an opportunity of observing in all its phases, but I have 
been fortunate enough to obtain a fully mature ovarian ovum 
(or one almost in a mature condition) which has been repre- 
sented in fig. 8. 
In this latter the ovum lies freely within the zona radiata 
and is separated from it by a considerable space, the circum- 
vitelline space in which, according to v. Beneden, is a fluid, 
the circum-vitelline fluid. The vitelline membrane is here 
distinctly seen on account of the contraction of the substance 
of the vitellus. 
The ovum itself is very dense and contains a number of dark 
granules not observed in less mature ova; it is separated from 
the vitelliue membrane by a narrow space excepting (1) at 
certain points where pseudopodia-like processes of the vitellus 
project across the space and are attached to the vitelline mem- 
brane, and (2) at one spot where no contraction of the ovum 
has occurred. At this latter point the vitellus is more trans- 
parent than elsewhere, and the nucleus may there be seen in 
close approximation to a dark oval body lying immediately 
outside tke vitelline membrane, while a second more trans- 
parent oval body in which is a central dark mass may be seen 
lying in the midst of the circum-vitelline space. These two 
bodies are the polar bodies (p. 4.), the second of which has but 
just been produced ; while the nucleus seen within the ovum 
is the female pronucleus (f. p.). 
It is possible to describe the vitellus as composed of a 
cortical more clear, and a medullary granular portion such as 
Beneden (No. 5) describes in the mature ovarian ovum of the 
Rabbit, but the boundary of these layers is by no means easy 
to define. The light-coloured space in which the nucleus is 
