ALTERNATION OF GENERATIONS 283 



presented by a single life : in other words, it is all those animal 

 forms taken together which proceed from a single egg." Since 

 all the hydranths, blastostyles, and medusae which make up or 

 are derived from a colony of Obelia proceed from a single egg, 

 they comprise one individual; there is only one generation, 

 and consequently there can be no alternation of generations in 

 this or any similar Hydromedusan organism. 



