BIRDS— LENGTH OP FEMALE'S TAIL. 445 



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 oc- 

 casionally 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 bene- 

 fited by possessing a slightly shorter crest than the male, and 

 its consequent diminution or complete suppression through natu- 

 ral selection. 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 whilst accompanying her young. 

 Hence there is not the least §, priori improbability in the de- 

 velopment of her tail having been checked through natural selec- 

 tion. 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 superba have long lails, and they build a 

 domed nest, which is a great anomaly in so large a bird. Natu- 

 ralists have wondered how the female Menura could manage her 

 tail during incubation; but it is now known' 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 lengthened, 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 develop- 

 ment 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 

 have retained a much longer tail than she actually possesses; 

 for her tail is not nearly so long, relatively to the size of her 

 body, as that of many female pheasants, nor longer than that 

 of the female turkey. It must also be borne in mind, that in 

 accordance with this view as soon as the tail of the peahen be- 



'^ Mr. Eamsa;,, in 'Proc. Zoolog. Soc' 1S6S, p. 50. 



