25G A BOOK OF INSECTS 



the female may be seen standing just behind him, and 

 with her head applied to the base of the wings, evidently 

 eager to get the full benefit of every note produced." 



The males of many insects, especially butterflies, are 

 often more strikingly coloured — more " beautiful " in the 

 commonly accepted sense of the word — than the females. 

 The male chalk-hill blue butterfly {Polyommatus corydon) 

 has exquisite azure wings, those of the female being dark 

 brown ; the male orange-tip butterfly {Euchloe cardamines) 

 is adorned with conspicuous orange spots which are absent 

 from the wings of his mate ; while among exotic insects we 

 find still more striking examples of masculine splendour 

 yoked to feminine dowdiness. The cause and significance 

 of such sex- difference remains a vexed question among 

 naturalists. Some believe that the male is more showy 

 than his mate because his stock of surplus vitality is greater 

 than hers. In the language of science : " The small and 

 active sperm- cell, with a more abundant vitality than the 

 passive egg-cell, dissipates energy while the egg-cell stores 

 it up. " O thers, who follow Darwin, believe that the colours 

 and ornaments of male animals are the outcome of sexual 

 selection ; that the females, through countless generations, 

 have consistently chosen the most ornate from among their 

 suitors, and have thus transmitted their qualities to pos- 

 terity. The reason why the female is slow to acquire the 

 characters which she appreciates in the opposite sex is ex- 

 plained on the ground that her need for protection is more 

 urgent. As a rule, she is less alert than the male, and when 

 engaged in egg-laying is exposed to risks from which he 

 is exempt. Thus, while the female occasionally partici- 

 pates in the growing adornment of her species, such a 

 tendency is usually checked by natural selection, which in 

 each generation preserves the best-protected individuals 

 for the office of parentage. The male's greater wariness 



