232 



HYDRA 



spermary the sperms are liberated and swim freely in the 

 water. 



The ovaries (Fig. 49, b, and Fig. 50, a, 07>y) are found 

 near the proximal end of the body, and vary in number from 

 one to eight. When ripe an ovary is larger than a spermary, 

 and of a hemispherical form. It begins, like the spermary, 

 as an aggregation of interstitial cells, so that in their earlier 

 stages the sex of the gonads is indeterminate. But while 



Fig. 52. — a, Ovum of Hydra viridis, showing pseudopods, nucleus 

 [gv\ and numerous chromatophores and yolk spheres. 



B, a single yolk sphere. (From Balfour after Kleinenberg. ) 



in the spermary each cell is converted into a sperm, in the 

 ovary one cell soon begins to grow faster than the rest 

 becomes amoeboid in form (Fig. 50, a, 0%), and Fig. 52, a), 

 sending out pseudopods amongst its companions and ingest- 

 ing the fragments into which they become broken up, thus 

 continually increasing in size at their expense. Ultimately 

 the ovary comes to consist of this single amoeboid ovuni^ 

 and of a layer of superficial cells forming a capsule for it. 



