^^^^ ZOOGENESIS ^^^'^ 



the parents until almost the adult stage is reached, 

 as in the mammals and most birds. In other cases 

 the hazards of life are so very great that very many 

 young must die for each one that survives. 



In the common human tapeworm it has been shown 

 that of the young produced only one in thirty-five 

 millions has any chance of becoming an adult 

 tapeworm. 



In the case of the common eel of our ponds and 

 streams an average female lays from five to ten million 

 eggs, and large females lay from fifteen to twenty 

 millions. Thus the chance that any given egg will 

 hatch and the resulting young will grow into a 

 mature eel which will succeed in returning to the 

 spawning grounds is only one in about ten millions. 



[163] 



