164 SEXUAL selection: birds. Part II. 



sion that as vocal and instrumental organs are of special 

 service only to the males during their courtship, these 

 organs were developed through sexual selection and 

 continued use in this sex alone — the successive varia^ 

 tions and the effects of use having been from the first 

 limited in their transmission in a greater or less degree 

 to the male offspring. 



Many analogous cases could be advanced ; for in- 

 stance the plumes on the head, which are generally 

 longer in the male than in the female, sometimes of 

 equal length in both sexes, and occasionally absent in 

 the female, — these several cases sometimes occurring 

 in the same group of birds. It would be difficult to 

 account for a difference of this kind between the sexes 

 on the principle of the female liaving been benefited by 

 possessing a slightly shorter crest than the male, and its 

 consequent aiminution or complete suppression through 

 natural selection. But I will take a more favourable 

 case, namely, the length of the tail. The long train 

 of the peacock would have been not only inconvenient 

 but dangerous to the peahen during the period of incu- 

 bation and whilst accompanying her yonng. Hence 

 there is not the least a 'priori improbability in the 

 development of lier tail having been checked througli 

 natural selection. But the females of various phea- 

 sants, which apparently are exposed on their open nests 

 to as much danger as the peahen, have tails of con- 

 siderable lens^th. The females as well as the males 

 of the M67iura superha have long tails, and they build 

 a domed nest, which is a great anomaly in so large a 

 bird. Naturalists have wondered how the female Me- 

 nura could manage her tail during incubation ; but it 



been dangerous to them during incubation. He adds, that a similar 

 view may possibly account for the inferiority of the female to the male 

 in plumage. 



