420 FRANK R. LILLIE 



zygotic determination of sex is not irreversible predestination, 

 but a quantitative overbalance. in the direction of one sex on the 

 other. I refer more especially to the studies of Richard Hertwig 

 ('06), Kuschakewitsch ('14), of Whitman-Riddle on pigeons 

 (Riddle '16), and especially the very convincing demonstration 

 of reversibility of sex in the gypsy moth by Goldschmidt ('16). 

 These studies demonstrate that sex differentiation is controlable 

 within variable limits in certain groups, to which mammals must 

 be added as a result of the present study. To determine the 

 means, limits and subsequent results of such control is now one 

 of the most important tasks of biology. 



LITERATURE CITED 



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