484 



HEREDITY AND SEX 



either of the fundamental alternatives of maleness or femaleness 

 in the simple sense already defined. 



It is not inconsistent with this view to suppose that some of 

 the distinctions which eventually become obvious between males 

 and females in any given case are simply physiological reactions 

 due for instance to the stimulus of secretions from the gonads 

 which saturate through the body. It also seems to us that in 

 certain cases the so-called contrasted peculiarities of the two 

 sexes are due to internal physiological conditions which give the 



Fig. 46. — Winged male and wingless female of Pneumora, a kind of 

 grasshopper. (From Darwin.) 



same primordium two different expressions — much less different 

 than they seem. We may conceive of a sort of internal physio- 

 logical " poecilomorphy." 



§ 2. Variety of Possible Factors in Sex Determination 



Variety of Organisms probably implies a Variety of Sex- 

 determining Factors. — As the variety of organisms is very great 

 and their modes of development very diverse, it seems unhkely that 

 there is any one answer to the question, What determines the 

 sex of the offspring ? In some cases we know that a certain kind 

 of egg, e.g. the larger eggs of the Rotifer Hydatina, will develop 



