460 THE DESCENT OF M^\N. 



in their immature plumage; and as the true affinities of all organic 

 beings depend on their descent from a common progenitor, this re- 

 mark strongly confirms the belief that the immature plumage 

 approximately shows us the former or ancestral condition of the 

 species. 



Although many young birds, belonging to various families, 

 thus give us a glimpse of the plumage of their remote progenitors, 

 yet there are many other birds, both dull-colored and bright-col- 

 ored, in which the young closely resemble their parents. In such 

 cases the young of the different species cannot resemble each other 

 more closely than do the parents; nor can they strikingly resemble 

 allied forms when adult. They give us but little insight into the 

 plumage of their progenitors, excepting in so far that, when the 

 young and the old are colored in the same general manner through- 

 out a whole group of species, it is probable that their progenitors 

 were similarly colored. 



We may now consider the classes of cases, under which the dif- 

 ferences and resemblances between the plumage of the young and 

 the old, in both sexes or in 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 pei'mits, from information derived from various sour- 

 ces; but a full essay on this subject by some competent ornith- 

 ologist 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, first, 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 less 

 vivid, and the feathers are softer and often a different shape. 



RULES OR CLASSES OP CASES. 



I. When the adult male is more beautiful or conspicuous than 

 the adult female, the young of both sexes in their first plumage 

 closely resemble the adult female, as with the common fowl and 

 peacock; or, as occasionally occurs, they resemble her much more 

 closely than they do the adult male. 



II. When the adult female is more conspicuous than the adult 

 male, as sometimes though rarely occurs, the young of both sexes 

 in their first plumage resemble the adult male. 



III. When the adult male resembles the adult female, the young 

 of both sexes have a peculiar first plumage of their own, as with 

 the robin. 



