BIRDS. 513 



country with their voices during the spring. * It is a safer con- 

 clusion 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 their 

 constant 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 ; those, 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 occurring 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 selec- 

 tion. But I will take a more favorable 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 while accom- 

 panying her young. Hence, there is not the least a priori 

 improbability in the development of her tail having been 

 checked through natural selection. But the females of 

 various pheasants, which apparently are exposed on their 

 open nests to as much danger as the peahen, have tails of 

 considerable length. The females as well as the males of 

 the Menura 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 menura could 

 manage her tail during incubation; but it is now knoT\Ti f 

 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 king- 

 fisher {Tanysiptera sylvia) have the middle tail-feathers 

 greatly lengthened, and the female makes her nest in a 



*Daines Barrington, however, thought it probable (" Phil. Trans- 

 act.," 1773, p. 164) that few female birds sing, because the talent 

 would have 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. 



f Mr. Kamsay, in "Proc. Zoolog. Soc.," 1868, p. 50, 



