156 



MICROSCOPY FOR BEGINNERS. 



tracted it resembles a minute globule of green or brown 

 jelly, with the shortened arms at the summit like very 

 small drops or projections. It is very active so far as 

 the arms are concerned, for the body is always adherent 

 to some submerged object. The arms or tentacles are 

 usually stretched out to their fullest extent, then often 

 exceeding the body in length, waving and twisting about 

 in search of prey. The figure (Fig. 130) shows several 



Pig. 130. Hydras adherent to Lerana rootlets. 



Hydras nearly the natural size adherent to Lemna root- 

 lets. The body is like a narrow bag, the hollow part 

 of the little sack being the stomach, and communicating 

 directly with the external water, in which the Hydra 

 lives, by means of the mouth, around which are arranged 

 the arms or tentacles. These tentacles are themselves 

 hollow, and communicate with the hollow of the stomach. 



