SPERMARY AND OVARY 231 



of cutting the living animal into pieces, each of which was 

 found to grow into a perfect individual. 



As in Vaucheria and Nitella, the sexual organs or gonads 

 are of two kinds, spermaries and ovaries. Both are found 

 in the same individual, Hydra being, like the plants just 

 mentioned, hermaphrodite or monoecious. 



The spermaries (Fig. 51, B, and Fig. 52, A, spy) are white 

 conical elevations situated near the distal end of the body : 

 as a rule not more than one or two are present at the same 

 time, but there may be as many as twenty. They are per- 

 fectly colourless, even in the green and brown species being 

 obviously formed of ectoderm alone. 



In the immature condition the spermary consists of a little 

 heap of interstitial cells covered by an investment of some- 

 what flattened cells formed by a modification of the ordinary 

 large cells of the ectoderm. When mature each of the small 

 internal cells becomes converted into a sperm (Fig. 52, G), 

 consisting of a small ovoid head formed from the nucleus of 

 the cell, and of a long vibratile tail formed from its proto- 

 plasm. By the rupture of the investing cells or wall of the 

 spermary the sperms are liberated and swim freely in the 

 water. 



The ovaries (Fig. 51, B, and Fig. 52, 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 

 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. 52, A, ov, and Fig. 53, A), 

 sending out pseudopods amongst its companions and ab- 



