192 NATURAL SCIENCE [September 1898 



Iii no family of birds are the males more gorgeous or more 

 different from the females than in the Birds of Paradise. Darwin says 

 in his treatise on Descent of Man and Sexual Selection that, accord- 

 ing to Lesson, these birds are polygamous, but that Mr Wallace doubts 

 it. The sexual selection therefore is to this extent less probable or less 

 severe, but there is no doubt whatever about the difference of habits 

 to which I attribute the difference of plumage between the sexes. 

 In another passage in the same book Darwin writes : " With Birds 

 of Paradise a dozen or more full-plumaged males congregate in a 

 tree to hold a dancing party as it is called by the natives, and here 

 they fly about, raise their wings, elevate their exquisite plumes, and 

 make them vibrate, and the whole tree seems filled with waving 

 plumes." 



It may be objected that the mechanical stimulation which I 

 have adduced as the cause of the hypertrophy of the feathers, will 

 not explain their brilliant colouring or the beauty and symmetry of 

 their markings. To which I would reply that stimulation of the 

 growth probably causes also a more intense production of pigment ; 

 that symmetry of marking is a universal character in organic growth 

 throughout the animal kingdom ; and, thirdly, that very possibly 

 the different qualities of the light to which males and females are 

 exposed have something to do with the dull colours of the female 

 which sits close with her young in obscure retreats, and the bright 

 colours of the male which keeps more in the open. 



I have already referred to the fact that in some species the 

 relative characters of the sexes are reversed, and it is the females 

 which are larger, more pugnacious, and more elaborately adorned 

 than the males. Darwin, of course, attributes this to the reversal 

 of sexual selection, but it seems to me more rational to hold that 

 the differences are not merely selected but called into existence by 

 the habits and conditions. In these cases the male alone performs 

 the duties of incubation and nursing, and the female takes all the 

 initiative in courtship. Here, as in the males in the usual case, 

 the peculiarities of the female only begin to develop when she is 

 approaching maturity, the young of both sexes being similar to the 

 adult male. Species of Turnix in India and Australia are instances 

 of this condition. 



J. T. Cunningham. 



1 Morrab Terrace, 

 Penzance. 



(To be continued.) 



