178 SEXUAL SELECTION: BIRDS. [Part II. 



ders thus give us a glimpse of the plumage of their remote . 

 progenitors, yet they are many other birds, both dull- 

 colored and bright-colored, in which the young closely re- 

 semble 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 resem- 

 blances to allied forms in their adult state. They give us 

 but little insight into the plumage of their progenitors, ex- 

 cepting in so far that, when the young and the old are 

 colored in the same general manner throughout a whole 

 group of species, it is probable that their progenitors were 

 similarly colored. 



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. Rules of this kind were first 

 enounced by Cuvier ; but with the progress of knowledge 

 they require some modification and amplification. This I 

 have attempted to do, as far as the extreme complexity 

 of the subject permits, from information 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 tabu- 

 lated the facts given in four great works, namely, Macgilli- 

 vray 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 

 colors are almost always rather less vivid, and the feathers 

 are softer and often of a different shape. 



