Chap. XV Birds — Length of Female's Tail. 451 



a safer conclusion that, as vocal and instrumental organs are of 

 special service only to the males during tlieir courtship, these 

 organs were developed through sexual selection and their con- 

 stant use in that sex alone —the successive variations and the 

 effects of use having been from the first more or less limited in 

 transmission to the male offspring. 



Many analogous cases could be adduced ; these for instance of 

 the plumes on the head being 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 occuring 

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

 such a difference between the sexes by the female having been 

 benefited by possessing a slightly shorter crest than the male, 

 and its consequent diminution 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 incubation and whilst accompany- 

 ing her young. Hence there is not the least a priori improba- 

 bility in the development of her tail having been checked 

 through 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 considerable length. 

 TJie females as well as the males of the Menura superbu have 

 .ong tails, and they build a domed nest, which is a great 

 anomaly in so large a bird. Naturalists have wondered how the 

 female Menura could manage her tail during incubation : but it 

 is now known 8 that she " enters the nest head first, ' and then 

 " turns round with her tail sometimes over her back, but more 

 " often bent round by her side. Thus in time the tail becomes 

 " quite askew, and is a tolerable guide to the length of time the 

 " bird has been sitting." Both sexes of an Australian kingfisher 

 (Tanysiptera sylvia) have the middle tail-feathers greatly length- 

 ened, and the female makes her nest in a hole ; and as I am 

 informed by Mr. R. B. Sharpe these feathers become much 

 crumpled during incubation. 



In these two latter cases the great length of the tail-feathers 

 must be in some degree inconvenient to the female ; and as in both 

 species the tail-feathers of the female are somewhat shorter than 

 those of the male, it might be argued that their full development 

 had been prevented through natural selection. But if the 

 development of the tail of the peahen had been checked only 

 when it became inconveniently or dangerously great, she would 

 tiave retained a much longer tail than she actually possesses ' 

 8 Mr. Ramsay, in ' Proc. Zoolog. Soc' 1868, p. 50. 



