Chap. VIII.] SEXUAL SELECTION. 277 



an early age would tend to be inherited equally by both 

 sexes, for the sexes do not differ much in constitution, be- 

 fore the power of reproduction is gained. On the other 

 hand, after this power has been gained and the sexes have 

 come to differ in constitution, the geminules (if I may 

 again use the language of pangenesis) which are cast off 

 from each varying part in the one sex would be much 

 more likely to possess the proper affinities for uniting 

 with the tissues of the same sex, and thus becoming de- 

 veloped, than with those of the opposite sex. 



I was first led to infer that a relation of this kind ex- 

 ists, from the fact that whenever and in whatever manner 

 the adult male has come to differ from the adult female, 

 he differs in the same manner from the young of both 

 sexes. The generality of this fact is quite remarkable : it 

 holds good with almost all mammals, birds, amphibians, 

 and fishes ; also with many crustaceans, spiders, and some 

 few insects, namely, certain orthoptera and libellulaB. In 

 all these cases the variations, through the accumulation of 

 which the male acquired his proper masculine characters, 

 must have occurred at a somewhat late period of life ; 

 otherwise the young males would have been similarly 

 characterized ; and conformably with our rule, they are 

 transmitted to and developed' in the adult males alone. 

 When, on the other hand, the adult male closely resem- 

 bles the young of both sexes (these, with rare exceptions, 

 being alike), lie generally resembles the adult female; 

 and in most of these cases the variations through which 

 the young and old acquired their present characters, prob- 

 ably occurred in conformity with our rule during youth. 

 But there is here room for doubt, as characters are some- 

 times transferred to the offspring at an earlier age than 

 that at which they first appeared in the parents, so that 

 the parents may have varied when adult, and have trans- 

 ferred their characters to their offspring while young. 



