212 CALIFORNIA ACADEMY OF SCIENCES. 



have any validity (see ante, pp. 99-102) they do not so 

 much belong to the class of useful markings as to the 

 division of beautiful colors. 



Darwin devotes a large portion of his work on the 

 Descent of Man to a consideration of sexual selection in 

 birds. He there tabulates the rules or classes of cases 

 under which birds may be grouped according to the 

 constancy or variability of the style of coloration with 

 sex, age or season, this purpose being to show how 

 heredity acts with regard to the transmission of sexual 

 characters. His classification, which is an amplification 

 of Cuvier's, is as follows: 



"I. When the adult male is more beautiful or con- 

 spicuous 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 occasion- 

 ally 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 



