264 GEO. W. TANNREUTHER. 



ovary are taken up by the amoeboid egg and become changed 

 into the yolk or pseudo-cells of the egg. Fig. 6 represents a 

 cross-section of several pseudopodia into which the nuclei of the 

 interstitial cells of the ovary are passing. The transformation of 

 these interstitial cells into yolk is shown in Fig. 7, a—e. The 

 chromatin becomes very granular and forms a band around the 

 inner border of the nuclear membrane. The nucleolus becomes 

 imbedded in this band of granular chromatin and the nucleus has 

 the appearance of a hollow sphere with its wall thickened on one 

 side. After the yolk or pseudo-cells are formed they divide 

 amitotically. 



According to Kleinenberg, the interstitial cells of the ovary 

 surrounding the egg break down and act as food for the develop- 

 ing egg. Brauer says the interstitial cells, after breaking down, 

 enter the egg and give rise to the pseudo-cells. 



After the amoeboid egg becomes filled with yolk, the pseu- 

 dopodia are drawn in and the egg becomes nearly spherical (PI. 

 XL, Fig. 33, a), and is surrounded by a single layer of ectodermal 

 cells except at its base. The egg nucleus during the contraction 

 of the pseudopodia becomes very faint and is difficult to recognize. 

 According to Brauer, the nucleus becomes entirely invisible. 



Abortive ova are often found in sexually reproducing hydra. 

 They consist of a small mass of yolk cells surrounded by a thin 

 egg membrane, and are devoid of a nucleus. The ovary begins 

 as in the normal cases, but instead of one of the nuclei persisting 

 in the multinucleate cytoplasmic cell mass, they all break down, 

 leaving the common mass of cytoplasm without a nucleus. No 

 pseudopodia are formed. This condition would be represented 

 in PI. VIII., Fig. 3, if no nuclei were present in the cytoplasm 

 between the enlarged interstitial cells and the mesoglea. Some 

 of the nuclei of the interstitial cells enter the cytoplasm as in the 

 normal egg and form the yolk. The common mass of cytoplasm 

 with its contained yolk now becomes spherical. The abortive 

 ova do not break through the ectoderm, but are gradually 

 absorbed. 



Maturation. 



Immediately after the pseudopodia are drawn in, the polar 

 bodies are formed (PI. XL, Fig. 33, a, pb). When formed they 



