RESEMBLANCES AMONG ANIMALS. Ill 



tible with either of the other hypotheses ; namely, the 

 relation of protective colouring and mimicry to the 

 sexual differences of animals. It will be clear to every 

 one that if two animals, which as regards " external 

 conditions " and " hereditary descent," are exactly 

 alike, yet differ remarkably in colouration, one resem- 

 bling a protected species and the other not, the resem- 

 blance that exists in one only can hardly be imputed 

 to the influence of external conditions or as the effect 

 of heredity. And if, further, it can be proved that 

 the one requires protection more than the other, and 

 that in several cases it is that one which mimics the 

 protected species, while the one that least requires 

 protection never does so, it will afford very strong 

 corroborative evidence that there is a real connexion 

 between the necessity for protection and the pheno- 

 menon of mimicry. Now the sexes of insects offer 

 us a test of the nature here indicated, and appear to 

 furnish one of the most conclusive arguments in favour 

 of the theory that the phenomena termed " mimicry " 

 are produced by natural selection. 



The comparative importance of the sexes varies 

 much in different classes of animals. In the higher 

 vertebrates, where the number of young produced at a 

 birth is small and the same individuals breed many 

 years in succession, the preservation of both sexes is 

 almost equally important. In all the numerous cases 

 in which the male protects the female and her offspring, 

 or helps to supply them with food, his importance in 

 the economy of nature is proportionately increased, 



