178 SEXUAL SELECTION: BIEDS. Part IL 



great number of breeds and sub-breeds, and in these 

 the sexes generally differ in plumage; so that it has 

 been noticed as a remarkable circumstance when in 

 certain sub-breeds they resemble each other. On the 

 other hand, the domestic pigeon has likewise produced 

 a vast number of distinct breeds and sub-breeds, and 

 in these, with rare exceptions, the two sexes are identi- 

 cally alike. Therefore if other species of Gallus and 

 Columba were domesticated and varied, 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 maner the same form of transmission has gene- 

 rally prevailed throughout the same natural groups, 

 although marked exceptions to this rule occur. Within 

 the same family or even genus, the sexes may be 

 identically alike or very different in colour. Instances 

 have already been given relating to the same genus, 

 as with sparrows, fly-catchers, thrashes and grouse. In 

 the family of pheasants the males and females of almost 

 all the species are wonderfully dissimilar, but are quite 

 similar in the eared pheasant or Crossojptilon auritum. 

 In two sj)ecies of Chloephaga, a genus of geese, the 

 males cannot be distinguished from the females, except 

 by size ; whilst 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 

 following cases, in which the female by acquiring at 

 a late period of life certain characters proper to the 

 male, ultimately comes to resemble him in a more or 

 less complete manner. Here protection can hardly 

 have come into play. Mr. Blyth informs me that 

 the females of Oriolus melanoeephalus and of some 



-3 The 'Ibis,' vol. vi. 1864, p. 122. 



