254 COMPARATIVE ANATOMY 



viz. that "the individual animal is the sum of the phenomena 

 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. 



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