Chap. XIY. 
GKADATION OF CHAKACTERS. 
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 . — Cases 
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 peacock, 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 
