342 WILSON. [Vol. IX. 



is growing larger and becoming stored with yolk that it is 

 surrounded by the cells in question, the purpose of which it 

 would seem is to bring food to the young egg. Since none of 

 the surrounding mesoderm cells are ever seen to break through 

 the follicle, it must be that the food is passed through the 

 follicular membrane in a liquid shape and is then absorbed by 

 the egg. Fiedler's description (5) of the manner in which 

 nutrition is brought to the growing egg of Spongilla, differs 

 from the above account in some respects. In Spongilla special 

 " Nahrzellen " congregate round the egg during its growth, and 

 penetrate between the follicular cells, supplying the egg with 

 food. The " Nahrzellen " do not fuse with the egg, and it 

 would seem that the food must be transferred by osmosis. As 

 in Tedanione, the nourishing cells disappear when segmenta- 

 tion begins. 



The very small ovarian egg is filled with the extremely fine 

 granular yolk which is found in the body of any mesoderm cell 

 at all noticeable for its size. But as the egg increases in size, 

 yolk of a different character makes its appearance, consisting 

 of small spheres thickly packed. In eggs of about one half the 

 adult size. Fig. 103, these small spheres may be found filling 

 the entire peripheral region, but leaving round the nucleus an 

 area containing only fine granules. With continued increase in 

 size the whole egg becomes filled with yolk spheres, which 

 themselves increase considerably in size, as may be seen on 

 comparing Fig. 103 with Fig. 104, the egg in the latter figure 

 being of full size. 



The nucleus of the young egg cell contains a single nucleolus 

 which occupies a more or less central position, Fig. 102. By 

 the time the egg has reached a size equal to one half that of 

 the ripe egg, the single nucleolus has given place to two, which 

 are invariably placed on opposite sides of the nucleus and 

 adhere to the inner surface of the nuclear membrane. Fig. 103. 

 In eggs which have reached the adult size it is the rule to find 

 either one nucleolus peripherally placed, as in Fig. 104, or the 

 nucleus contains no nucleolus at all, as in Fig. 105. It some- 

 times happens that an egg of full size is found with two nucle- 

 oli, but this is rare. From this evidence it would seem that 



