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THE EVOLUTION OF SEX. 



has been sacrificed in reproduction. '-The death is an 

 altogether inevitable consequence of the reproduction." 



Nor is this sacrifice confined to the incipient multicellular 

 organisms. Thus in some species of the annelid Folygoj-dius, 

 the mature females break up and die in liberating their ova. 

 This is approached, but suggestively avoided, in a genus of 

 capitellid sea-worms {Clitomastus). The whole organism is 



A figure of cell division suggesting the Internal disruptions and re- 

 arrangements of the nucleus {a) and protoplasm. — From Rauber. 



not sacrificed, but only an abdominal portion of the body. 

 This is in fact one of the keynotes to reproductive differentia- 

 tion, — the sacrifice is lessened, and the fatality thus warded off. 

 But again, we find in some threadworms or nematodes {e.g., 

 Ascaris dadyluris) that the young live at the expense of the 

 mother, until she is reduced to a mere husk. In fresh-water 

 Polyzoa, Kraepelin notes that the ciliated embryo leaves the 



