4.66 The Descent of Man. Pabt H 



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 wheu the joung are said to resemble 

 their parents, it is not meant that they are identically alike, 

 for their colours are almost always less vivid, and the feathers 

 sire softer and uften of a different shape. 



RULES OR CLASSES OF 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. 



IV. When the adult male resembles the adult female, the 

 young of both sexes in their first plumage resemble the adults, 

 as with the kingfisher, many parrots, crows, hedge-warblers. 



V. When the adults of both sexes have a distinct winter and 

 summer plumage, whether or not the male differs from the 

 female, the young resemble the adults of both sexes in their 

 winter dress, or much more rarely in their summer dress, or 

 they resemble the females alone. Or the young may have an 

 intermediate character ; or again they may differ greatly from 

 the adults in both their seasonal plumages. 



VI. In some few cases the young in their first plumage differ 

 from each other according to sex ; the young males resembling 

 more or less closely the adult males, and the young females 

 more or less closely the adult females. 



Class T. — In this class, the young of both sexes more or less 

 closely resemble the adult female, whilst the adult male differs 

 from the adult female, often in the most conspicuous manner. 

 Innumerable instances in all Orders could be given; it wi'l 

 suffice to call to mind the common pheasant, duck, and house- 

 sparrow. The cases under this class graduate into others. 

 Thus the two sexes when adult may differ so slightly, and the 

 young so slightly from the adults, that it is doubtful whether 



