CHAPTKR VIII 



HYDRA AND CGELENTERATES IN GENERAL 

 i. HYDRA 



(Hydra fusca Linnaeus) 



Hydra fusca is a simple Metazoon abundant in fresh water 

 ponds and streams. If a quantity of aquatic vegetation is gat h 

 ered and placed in glass dishes full of water, these little fresh-water 

 polyps will be found clinging to the plants and the sides and bot- 

 tom of the dish. They are easily seen with the naked ryr. bring 

 from 2 to 20 mm. in length, and may be likened to a short ihirk 

 thread frazzled at the unattached, distal end. The great varia- 

 tion in length is due to the fact that both body and trnlarlrs air 

 capable of remarkable expansion and contraction because of the 

 presence of specialized muscle fibrils in many of the cells. 



TABLE IV 



THE NAMES AND CHARACTERISTICS OF THE PRINCIPAL SPECIES OF HYDRA (105) 



116 



