222 COMPARATIVE ANATOMY 



A living Hydra adheres pretty firmly by its proximal end — 

 often called the foot, or, better, the basal disc — to the object to 

 which it is attached. It is not permanently fixed, however, but 



Fig- 47- 



On the left hand a specimen of Hydra/usca^ fully extended ; 

 tt, testes ; ov, ovum with horny case. On the right hand a 

 specimen of Hydra viridis, half extended ; b^ a bud. 



can detach itself and move slowly from place to place, either 

 creeping along by means of its tentacles, or by a series of 

 movements resembling those of the looping caterpillar. In the 

 latter case, the body is extended as far as possible and bent 



Digitized by Microsoft® 



