THEORY OF SEX-DIMORPHISM 77 



in function or in environment. We have 

 considered the pros and cons at some length 

 elsewhere, and it appears to us that the 

 seriously discussible evidence on the affirma- 

 tive side is riot sufficient to warrant an 

 acceptance of Cunningham's position, at any 

 rate without the considerable degree of 

 restatement which the Lamarckian theory 

 requires though again it is to be admitted 

 that this re-statement is in progress and on 

 various sides, as from Semon to Bergson. 



A PHYSIOLOGICAL THEORY. Professors 

 Hesse and Doflein have made the interesting 

 suggestion that, as reproduction is commonly 

 of much less organic strain to males, they have 

 so far a surplus of plasmic material and vital 

 energy at their disposal, which may account 

 for their frequently greater variability, for 

 certain characteristics of habit and tem- 

 perament, and for exuberant growths of 

 various special kinds. 



To the objection that the male is often 

 much smaller than the female, and that his 

 nutritive income is proportionally less, the 

 answer is that the decisive fact is one of 

 ratio, e.g. between the amount of material 

 used in reproduction and the weight of the 

 body in the two sexes, or between the size 

 of the reproductive organs and the size of the 

 body in the two sexes. 



In cases where the sexes expend approxi- 

 mately equal amounts of material in repro- 

 duction, almost no sex differences occur. 

 Thus in many fishes, such as the herring, 

 the ovaries and testes are about the same 

 size, and enormous quantities of milt are shed 



