82 GENERAL BIOLOGY 



settles down, fastens itself to some body and grows into a 

 polyp or hydranth, which by budding produces a new 

 hydroid colony. 



The life cycle of this animal is, therefore, somewhat com- 

 plicated and involves an alternation of generations. A 

 hydroid, we have seen, by asexual budding produces a 

 medusa, and this through sex cells gives rise to a hydroid 

 colony. There is, therefore, an alternation of the asexual 

 and the sexual methods of reproduction. 



