454 THE DESCENT OF MAN. 



and the females of other species show traces of the green and 

 other colors of the males. Nevertheless we have a near approach 

 to close sexual similarity or dissimilarity throughout several 

 groups: and this, from what has just been said of the fluctuating 

 nature of inheritance, is a somewhat surprising circumstance. 

 But that the same laws should largely prevail with allied animals 

 is not surprising. The domestic fowl has produced a great num- 

 ber of breeds and sub-breeds, and in these the sexes generally 

 differ in plumage; so that it has been noticed as an unusual cir- 

 cumstance 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 identically alike. There- 

 fore if other species of Gallus and Columba were domesticated and 

 varied, it would not be rash to predict that similar rules of sex- 

 ual similarity and dissimilarity, depending on the form of trans- 

 mission, would hold good In both cases. In like manner the same 

 form of transmission has generally prevailed under nature 

 throughout the same groups, although marked exceptions to this 

 rule occur. Thus within the same family or even genus, the 

 sexes may be identically alike, or very different in color. In- 

 stances have already been given in the same genus, as with spar- 

 rows, fly-catchers, thrushes and grouse. In the family of pbeas- 

 ants the sexes of almost all the species are wonderfully dissimilar, 

 but are quite alike in the eared pheasant or Crossoptilon auritum. 

 In two species of Chloephaga, a genus of geese, the male 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 acquires, late in life, certain characters 

 proper to the male, and ultimately comes to resemble him more 

 or less completely. Here protection can hardly have come into 

 play. Mr. Blyth informs me that the females of Oriolus melano- 

 cephalus and of some allied species, when sufficiently mature to 

 breed, differ considerably 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 meanwhile she presents an intermediate 

 "garb, which is ultimately exchanged for the same livery as that 

 "of the male." So again the female Falco peregrinus acquires 

 her blue plumage more slowly than the male. Mr. Swinhoe states 

 that with one of the Drongo shrikes (Dicrurus macrocercus) the 



™ The 'Ibis,' vol. vi. 1864, p. 122. 



