438 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
nucleolus stains deeply. The primitive ova are first distinguished 
from the rest of the ovarian cells by the increase in the density of the 
cytoplasm and the enlarging of the nucleus. The latter becomes 
very large in proportion to the size of the cell, and acquires a vescicular 
character. The nucleolus is conspicuous, and a network of chromatin 
is scattered throughout the germinal vesicle. 
The primitive ova grow by the absorption of the ovarian cells around 
them. As growth takes place there is a change in the character of 
the cytoplasm. It loses its homogeneous and finely granular nature 
and develops a supply of deuteroplasm in the form of yolk granules. 
These are large and stain very darkly. They first appear around 
the germinal vesicle. As they become more numerous by the continual 
formation of new ones, they are pushed out through the cytoplasm 
toward the periphery. The formation of the yolk spheres goes on 
until the ovum is densely crowded with them except for a narrow 
peripheral zone, in which the protoplasm retains its homogeneous 
nnd finely granular character and forms the ectoplasm of the mature 
egg. Figures 10 to 15 of plate 32 show different stages in the develop¬ 
ment of the ovarian egg and the formation and migration of the yolk 
granules. Some idea of the extent to which the protoplasm becomes 
crowded with spheres of deuteroplasm can be formed from figure 15 
(pi. 32) which is drawn from a nearly mature ovum. In the fully 
developed egg the layer of ectoplasm is narrower than represented 
in this figure. 
The yolk granules first appear around the nucleus of the ovum; 
and it is not improbable that they are, in part at least, the result of 
nuclear activity. During the formation of these bodies, the nucleolus 
shows signs of being in an active condition and it may also be con¬ 
nected with their manufacture. In some stages the nucleolus is dense 
and homogeneous; in others it has one or two clearer globules in its 
interior. These facts seem to show that it is not in a dormant state; 
and it is possible that it may be associated in some way with the 
transformation of the absorbed protoplasm into deuteroplasm. That 
the yolk spheres arise directly through the activity of the cytoplasm, 
independently of any nuclear or nucleolar function, is doubtful at 
least. If this were the case we should expect the yolk bodies to arise 
in other parts of the ovum than around the germinal vesicle. There 
is no evidence from the study of many eggs that this occurs. The 
primitive ovarian cells are all, or nearly all, absorbed and used in the 
