THE HYDRA. 



29 



may be found entirely dislodged from the tentacle, and 

 showing, beside the long stinging filament, a flask-shaped 

 base, with minute retrorse spines at the neck of the flask 

 whence the filament springs. 



4. The sexual reproductive elements are developed in 

 low elevations upon the sides of the body. These are of 

 two kinds : 



(a) Spermariet, conical, pointed elevations near the 

 anterior end of the body, just behind the tentacles, of 



HYDRA (X 6) : m, mouth; sp, spermaries ; ov, ovary; b, bud. 



variable number. In the transparent apex of a ripe sper- 

 mary, the sperms may be seen swimming actively about or 

 breaking out into the surrounding water. 



(6) Ovaries, rounded, obtuse elevations nearer the 

 foot, rather larger than spermaries when ripe, usually 

 fewer in number, and each containing but a single ovum. 



Both spermaries and ovaries are developed from the 

 ectoderm, as might be inferred from their position and 

 from their transparency. 



