COURTSHIP AND SEX 215 



conditions the same as those under which they were originally 

 produced. 



Cunningham seeks to show that sex-characters may be 

 interpreted as the hereditary outcome of special irritations. 

 The legitimacy of this interpretation depends (i) on the 

 experimental evidence that can be adduced to show the 

 origin of callosities, excrescences, proliferations, etc., as the 

 direct result of stimulation, and (2) on the case that can be 

 made out, on experimental or logical grounds, for believing 

 that somatic modifications may be directly transmitted, in 

 some degree at least. This raises the whole question of the 

 transmission of somatic modifications, which we waive. 

 We simply express our opinion, argued for elsewhere, that 

 the evidence does not warrant an acceptance of Cunningham's 

 theory. 



With special reference to birds, Cunningham emphasises 

 the connection between erecting the decorative feathers 

 during sexual excitement and the exaggerated growth of 

 these feathers. ** 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 source of 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 " (1900, 



P- 109)- 



** The male, when in the beginning he is quite similar 



to the female, erects and moves some part of his plumage 



under the influence of sexual excitement. When he fights 



he erects his neck feathers partly to ward olT the blows of 



his enemy's beak. When he courts he erects or vibrates 



other feathers. Nearly all the feathers of a bird can be 



voluntarily moved or erected. The particular feathers 



