Chap. XIV. GKADATION OF CHAKACTEES. 135 



are surrounded by many successive zones of colour, 

 have been generated, I will not pretend to say. But 

 bearing in mind the zoned feathers of the mongrel 

 offspring from differently-coloured fowls, and the extra- 

 ordinary variability of the ocelli in many Lepidoptera, 

 the formation of these beautiful ornaments can hardly 

 be a highly complex process, and probably depends on 

 some slight and graduated change in the nature of the 

 tissues. 



Gradation of Secondary Sexual Characters. — Cages 

 of gradation are important for us, as they shew that 

 it is at least possible that highly complex ornaments 

 may have been acquired by small successive steps. 

 In order to discover the actual steps by which the 

 male of any existing bird has acquired his magnifi- 

 cent colours or other ornaments, we ought to behold 

 the long line of his ancient and extinct progenitors ; 

 but this is obviously impossible. We may, however, 

 generally gain a clue by comparing all the species of 

 a group, if it be a large one ; for some of them will 

 probably retain, at least in a partial manner, traces of 

 their former characters. Instead of entering on tedious 

 details respecting various groups, in which striking 

 instances of gradation could be given, it seems the best 

 plan to take some one or two strongly-characterised 

 cases, for instance that of the 23eacock, in order to dis- 

 cover if any light can thus be thrown on the steps by 

 which this bird has become so splendidly decorated. 

 The peacock is chiefly remarkable from the extra- 

 ordinary length of his tail-coverts ; the tail itself not 

 being much elongated. The barbs along nearly the 

 whole length of these feathers stand separate or are 

 decomposed ; but this is the case with the feathers 

 of many species, and with some varieties of the 



