i 34 SEXUAL SELECTION : BIRDS. Part IL 



development of a perfect ocellus does not require a 

 long course of variation and selection. 



With birds and many other animals it seems, from 

 the comparison of allied species, to folloNv, that cir- 

 cular spots are often generated by the breaking up 

 and contraction of stripes. In the Tragopan pheasant 

 faint white lines in the female represent the beautiful 

 white spots in the male ; *^ and something of the 

 same kind may be observed in the two sexes of the 

 Argus pheasant. However this may be, appearances 

 strongly favour the belief that, on the one hand, a dark 

 spot is often formed by the colouring-matter being 

 drawn towards a central point from a surrounding 

 zone, which is thus rendered lighter. And, on the other 

 hand, that a white spot is often formed by the colour 

 being driven away from a central point, so that it accu- 

 mulates in a surrounding darker zone. In either case 

 an ocellus is the result. The colouring matter seems 

 to be a nearly constant quantity, but is redistributed, 

 either centripetally or centrifugally. The feathers of 

 the common guinea-fowl offer a good instance of white 

 spots surrounded by darker zones; and wherever the 

 white spots are large and stand near each other, tlie 

 surrounding dark zones become confluent. In the same 

 wing-feather of the Argus pheasant dark spots may 

 be seen surrounded by a pale zone, and white spots 

 bv a dark zone. Thus the formation of an ocellus 

 in its simplest state appears to be a simple affair. 

 By what further steps the more comj^lex ocelli, which 



wonderful amount of variation in the coloration and shape of the wings 

 of this butterfly, in his ' Rhopalocera Africse Australis,' jj. 1 86. See 

 also an interesting paper by the Eev, H. H. Higgins, on the origin 

 of the ocelli in the Lepidoptera in the ' Quarterly Journal of Science,' 

 July, 18G8, p. 325. 



■*6 Jerdon, ' Birds of India,' vol. iii. p. 517. 



