BIRDS 109 



and attitudes of display in so forcible and picturesque a 

 manner that they have become familiar to all who take an 

 interest in natural history. But he regarded them as the 

 most important evidence of the exercise of choice and 

 selection on the part of the females. Their chief significance 

 appears to me to be quite different. The feather is erected 

 by muscular action ; the quill of the feather is a hard, rigid 

 body, implanted in a socket in the living skin ; and the 

 growth of the feather is due to the growth of the living cells 

 which form the papilla at the base of the feather. The 

 habitual erection of feathers is, therefore, a constant irritation 

 of the papilla, and there can be no doubt that the effect of 

 such irritation must be, and is, to cause the feather to grow 

 larger. If it be urged that the feather ceases its growth 

 after a certain time, I would reply that the irritation either 

 acts before growth has ceased, or else produces its effect on 

 the succeeding feather when the first is shed. With regard 

 to the coloration and markings of special plumage I have 

 little to say. I regard them as due partly to the same 

 excessive growth as that which increases the size of the 

 feather, partly to the universal regularity and symmetrical 

 repetition of marks, due to the rhythmical nature of growth 

 processes, and partly perhaps to the action of the light from 

 particular surroundings. 



Darwin has referred to the polygamy of certain birds as 

 associated with the presence of marked unisexual peculiarities 

 in the males, and, as in the case of other animals, considered 

 that the reason of this was that polygamy involved severer 

 competition, because it implied the triumph of a few of the 

 best developed males, and therefore the failure of a large 

 number of the inferior among them. In mammals it has 

 been pointed out that it is not polygamy in itself which is of 

 importance, but the pugnacious habits of polygamous males. 

 In birds the same truth is evident, but the peculiarities of 



