554 THE DESCENT OF MAN 



la tlie Tragopan pheasant faint white lines in the female rep- 

 resent 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 favor the belief that, on the one hand, a dark spot 

 is often formed by the coloring matter being drawn toward 

 a central point from a surrounding zone, which latter is thus 

 rendered lighter; and, on the other hand, that a white spot 

 is often formed by the color being driven away from a cen- 

 tral point, so that it accumulates in a surrounding darker 

 zone. In either case an ocellus is the result. The color- 

 ing 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, the 

 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 by a 

 dark zone. Thus the formation of an ocellus in its most 

 elementary state appears to be a simple affair. By what 

 further steps the more complex ocelli, which are sur- 

 rounded by many successive zones of color, have been 

 generated, I will not pretend to say. But the zoned 

 feathers of the mongrels from differently colored fowls, 

 and the extraordinary variability of the ocelli on many 

 Lepidoptera, lead us to conclude that their formation is 

 not a complex process, but depends on some slight and 

 graduated change in the nature of the adjoining tissues. 



Gradation of Secondary Sexual Characters. — Cases of 

 gradation are important, as showing us that highly com- 

 plex ornaments may be acquired by small successive steps. 

 In order to discover the actual steps by which the male 

 of a,ny existing bird has acquired his magnificent colors or 



« Jerdon, "Birds of India," voL iil. p. 51T. 



