SPERMARY AND OVARY 



235 



sperm ary the sperms are liberated and swim freely in the 

 water. 



The ovaries (Fig. 50, B, and Fig. 51, A, ovy) 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. 53. 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. 51, A, ov, and Fig. 53, 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 only of this single amoeboid 

 ovum, and of a layer of superficial cells forming a capsule 

 for it. As the ovum grows yolk-spheres (Fig. 53), small 



