230 Heredity. 



fied for clinging to the female, and we can understand 

 that natural selection will perpetuate modifications of 

 this kind, for the males which adhere most firmly to the 

 females will leave the greatest number of descendants, 

 who will inherit their peculiarity; but the same rule 

 would hold good if certain females were so modified as 

 to afford a good surface for the male to cling to, as we 

 may see from the fact that in a few forms the females 

 are thus modified. 



Fritz Muller has described certain species of amphipod 

 Crustacea, of the genus Melitu, in which the female does 

 have special hook-like processes for the male to cling to, 

 and cases of this kind are sufficiently numerous to show 

 that when a useful female modification does appear it 

 becomes hereditary. In all cases where the sexes are 

 separated and different from each other, the female un- 

 doubtedly might be benefited by peculiar organs as fre- 

 quently as the male. How then are we to account for 

 the remarkable fact that the cases of male modification 

 of this kind are so very much more numerous than the 

 instances of female modification? 



Darwin concludes that we must believe that the male 

 is more variable than the female, and we shall subse- 

 quently see that this is so, and the reason for it. Still 

 the /emale does vary, and vary greatly, and unless there 

 is some reason why female variations should be less apt 

 than male variations to become hereditary, the great pre- 

 ponderance of special male modifications is incompre- 

 hensible. 



The Male more Eager than the Female. 



Darwin attributes this to the greater eagerness of 

 the male. He says (Sexual Selection, Vol. I. p. 263): 

 "Throughout the animal kingdom, when the sexes 



