170 SEXUAL SELECTION: BIRDS. [Part IL 



pigeon has likewise produced a vast number of distinct 

 breeds and sub-breeds, and in these, with rare exceptions, 

 the two sexes are identically alike. Therefore, if other 

 species of Gallus and Columba were domesticated and va- 

 ried, it would not be rash to predict that the same general 

 rules of sexual similarity and dissimilarity, depending on 

 the form of transmission, would, in both cases, hold good. 

 In a similar manner the same form of transmission has 

 generally prevailed throughout the same natural groups, 

 although marked exceptions to this rule occur. Within 

 the same family, or even genus, the sexes may be identi- 

 cally alike or very diiferent in color. Instances have 

 already been given relating to the same genus, as with 

 sparrows, fly-catchers, thrushes, and grouse. In the fam- 

 ily of pheasants the males and females of abnost all the 

 species are wonderfully dissimilar, but are quite similar 

 in the eared pheasant or Crossojytilon auritum. In two 

 species of Chloehaga, a genus of geese, the males cannot 

 be distinguished from the females, except by size ; while in 

 two others the sexes are so unlike that they might easily 

 be mistaken for distinct species." 



The laws of inheritance can alone account for the fol- 

 lowing cases, in which the female, by acquiring at a late 

 period of life certain characters proper to the male, ulti- 

 mately comes to resemble him in a more or less complete 

 manner. Here protection can hardly have come int6 play. 

 Mr. Blyth informs me tliat the females of Oriolus melan- 

 ocephahis and of some allied species, when sufficiently 

 mature to breed, differ considei'ably in plumage from the 

 adult males ; but after the second or third moults they 

 differ only in their beaks having a slight greenish tinge. 

 In the dwarf bitterns (Ardetta), according to the same 

 authority, " the male acquires his final livery at the first 

 moult, the female not before the third or fourth moult; in 

 ^» The 'Ibis,' vol. vi. 1864, p. 122. 



