THE DEVELOPMENT OF THE CAPE CEPHALODISCUS. 193 
however, assume various irregular shapes, as if it were of an 
amoeboid nature, though there were no prolongations into the 
surrounding yolk mass. It is never of the elongate or semi- 
lunar form figured by Schepotieff for his species. A con- 
spicuous, deeply staining nucleolus is always present, and, in- 
some preparations, was observed to have a series of rounded 
vacuole-like spots, arranged around its border ; in other case& 
there appeared to be a single large vacuole, seemingly con- 
firming the view that the vacuoles are of a changing nature. 
That the nucleolus takes a part in the functional activity of 
the egg at this stage is indicated by these different appear- 
ances, and also by the fact that in some cases it was observed 
drawn out in a tapering manner quite to the periphery of the 
germinal vesicle, and, iu one case, a small detached part of it 
was observed lying in the germinal vesicle not far from it. 
Stages in the formation of the yolk granules are well illus- 
trated. These granules are very numerous, of an oval or 
rounded shape, with well-defined borders, and stain deeply 
with eosin. Scattered throughout them appeared a number 
of minute bodies (PL 13, fig. 1, y. ?^.), which readily stained 
with hematoxylin. The transformation of the homogeneous 
substance of the ovum into yolk granules does not appear to 
begin in the immediate neighbourhood of the nucleus, as in 
some other cases, for, in several instances, the nucleus with 
its nucleolus was observed in a homogeneous matrix in the 
form of a crescent at the periphery of a large mass of yolk 
granules. In others, the homogeneous part assumed the form 
of a portion slightly constricted off from the main mass of 
the egg. The boundary between the homogeneous and the 
granular part of the egg in these cases was well defined, and 
in it occurred a layer of the deeply staining bodies above 
mentioned, which may be termed yolk nuclei, though a 
variety of objects seem to be included under this term. So 
definite was the demarcation that it was at first supposed 
that there were here two cells, the semilunar homogeneous 
cell with its nucleus being a nourishing cell, assisting in 
building up the relatively enormous yolk mass. The fact that 
