342 WILSON. [Vor 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 
