254 PRESIDENTIAL ADDRESS. 



were found in the progeny of a number of individuals, the 

 ^presumption would be that there was a race tendency to 

 these determinate variations. The investigation would be 

 laborious, and perhaps in the end not altogether convincing. 

 In all cases the variations must be restricted within the 

 limits of the organization of the species ; and what exactly 

 these limits are it is not easy to determine. 



The question is rendered more complex by the correlation 

 of variations. That when an organ such as the beak in- 

 creases or decreases in length, adjoining and related parts 

 such as the tongue and the orifice of the nostrils tend to 

 vary conformably, is a comparatively simple case of corre- 

 lation. That if the legs of pigeons be feathered the two 

 outer toes are partially connected by skin, involves a corre- 

 lation less simple. That in several breeds of the pigeon 

 the length of the beak and the size of the feet are correlated, 

 and that young pigeons of all breeds, which, when mature, 

 have white, yellow, silver-blue, or dun-coloured plumage, 

 come out of the egg almost naked — in these and sundry 

 other well-known cases the nexus of correlation is by no 

 means obvious. The whole question of co-adaptation which 

 has recently come to the fore in discussions on Weismannism, 

 is one of great difficulty. The development of the long neck 

 of the giraffe and the gigantic horns of the extinct Irish 

 reindeer must have involved numerous admirably co-ordi- 

 nated modifications of structure. These have been brought 

 forward by Mr. Herbert Spencer as presumptive evidence 

 •in favour of the inherited effects of use and disuse. Mr. 

 -Piatt Ball, in his recent \Niork, in criticising this position, 

 has stated that Mr. Spencer's arguments were " so poorlj' 

 founded as to be rejected by a far greater authority [Darwin] 

 on such subjects." But Darwin himself said : " Although 

 natural selection would thus tend to give to the male elk 



