186 
SEXUAL SELECTION: BIRDS. 
Part II. 
Althoiigli many young birds belonging to various 
orders thus give us a glimpse of the plumage of their 
remote progenitors, yet there are many other birds, both 
dull-coloured and bright-coloured, in which the young 
closely resemble their parents. With such species the 
young of the different species cannot resemble each other 
more closely than do the parents ; nor can they present 
striking resemblances to allied forms in their adult 
state. They give us but little insight into the plumage 
of their progenitors, excepting in so far that when the 
young and the old are coloured in the same general 
manner throughout a whole group of species, it is pro- 
bable that their progenitors were similarly coloured. 
We may now consider the classes of cases or rules 
under which the differences and resemblances, between 
the plumage of the young and the old, of both sexes or 
of one sex alone, may be grouped. Eules of this kind 
were first enounced by Cuvier; but with the progress 
of knowledge they require some modification and ampli- 
fication. This I have attempted to do, as far as the 
extreme complexity of the subject permits, from infor- 
mation derived from various sources; but a full essay 
on this subject by some competent ornithologist is 
much needed. In order to ascertain to what extent 
each rule prevails, I have tabulated the facts given in 
four great works, namely, by Macgillivray on the birds 
of Britain, Audubon on those of North America, Jerdon 
on those of India, and Gould on those of Australia. I 
may here premise, firstly, that the several cases or rules 
graduate into each other ; and secondly, that when the 
young are said to resemble their parents, it is not 
meant that they are identically alike, for their colours 
are almost always rather less vivid, and the feathers 
are softer and often of a different shape. 
