Hubbard.] *^ [Dec. 16, 



In the ripe egg (Fig. 31) the body in question is found surrounded by 

 the yolk. This egg was in tlie act of giving off tlie second polar globule. 

 The latter is not figured because seen in another section. 



After the egg is matured this body assumes many curious and interest- 

 ing shapes (Figs. 21-26). In Fig. 21 the yo1k nucleus seems to have, 

 broken into large granules, several of them being grouped into a dark 

 mass (yk. nl.). The whole region including the granules is somewhat 

 shaded. 



Afier the egg has segmented into two cells, the appearance is nearly the 

 same as that just described, except the granules are not quite so large and 

 prominent (Fig. 22). To this time the j'olk nucleus has shown a granu- 

 lar structure, but as I have represented in the remaining figures it looses 

 that structure and appears to be homogeneous. 



In the stage represented in Fig. 23 this yolk nucleus has entirely 

 changed its appearance. I did not have the sections to show the inter- 

 mediate stages. At this time the egg has segmented into 32-64 cells. The 

 3'olk nucleus and its vicinity shows four different degrees of shading. The 

 centre of what seems to be the yolk nucleus proper is of a lighter shade 

 than the margin which is quite dark. Outside of this there is a still 

 lighter shade than that within the body. Beyond the last is another still 

 less distinct. 



When the egg has segmented into many cells, perhaps 600 (Fig. 24). 

 the yolk nucleus is larger and shows only one distinct shading. 



Fig. 25 shows the greatest peculiarity of any. Here the blastopore is 

 nearly closed. The body in question is somewliat pear-shaped and has a 

 few small vacuoles scattered through it. It does not have such a dis- 

 tinctly granular structure, but is of a uniformly dark shade. It seems to 

 form a kind of plug to the blastopore. The lower edge of this body is 

 marked by a distinct outline, but the upper edge does not have such an 

 outline. For a considerable region in its vicinity there are different de- 

 grees of shading. Also near the upper side there is a heavy shading which 

 seems to consist of minute granules. 



After the closing of the blastopore (Fig. 25) the yolk nucleus is much 

 reduced in size, the shadings have disappeared and there is seen only a 

 number of granules. The yolk also contains several similar granules 

 scattered through it. Here it seems evident the yolk nucleus has reached 

 the final stage of disintegration. It does not appear in any of the later 

 stages of development. I think that the diflerent appearances this body 

 presents after segmentation of the egg begins are due to the fact that it is 

 in the process of disintegration. The different depths of shading probably 

 indicate the scattering of its substance through the yolk. 



This body seems always to be situated at or nearer the entodermic end 

 of the pole of the egg. Its position is constant during all its stages of 

 growth. It may be utilized in determining whether the axis of the egg has 

 any definite and uniform relation to the axis of the ovary. A compari- 



