CCELENTERATA 



145 



and unite, forming new cells with the power of cell 

 division and cell differentiation (Figs. 54; 55, A). 



Alternation of Generations. — In addition to the form 

 relationship there is a very curious parental relationship 





Fig. 82.— Hydroid showing alternation of generations, h, polyps which have given 

 off medusa buds ; mk, medusa buds; m, separated medusa. (From Hertwig, 

 after Lang.) 



between the hydroid and the jellyfish. The hydroid is 

 colonial. The individuals increase in number on the 

 common stalk by continual budding. Some of these 

 buds break off and become free-swimming jellyfish 

 which assume a sexual character. They produce eggs 

 and sperm which unite, divide, and differentiate to form 



