178 
SEXUAL SELECTION: BIKDS. 
Part II. 
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 eases> hold good. In a 
similar manor 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, thrushes 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 Grossojptilon auritum. 
In two species of Chloehaga, 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 melanocepJialm and of some 
28 The ‘ Ibis,’ vol. vi. 1864, p. 122. 
