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 

 and 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 



