RESEMBLANCES AMONG ANIMALS. 111 
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 “‘ éxternal 
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, 
