56 PROBLEMS OF EVOLUTION 



But the reduction is not very great, and it must be remembered 

 that the huge weight of the Aylesbury duck, for instance, as 

 compared with the wild duck, is due to a general increase in 

 size, and that in this increase the breast muscles, i.e. the muscles 

 of flight, have shared, the breast bone from which they spring 

 being much larger than in the wild ancestors of the breed. Selec- 

 tion for bulk has brought about an increase in spite of disuse. 1 



Weismann attributes to disuse effects which seem to me to 

 be due to a different cause. "We know," he says, "that, as 

 a matter of fact, the olfactory organ of a frog completely 

 degenerates when the olfactory nerve is divided ; and that 

 great degeneration of the eye may be brought about by the 

 artificial destruction of the optic centre in the brain." 2 This 

 shows that the olfactory organ and the eye cannot be healthy 

 when severed from the lobes of the brain in association with 

 which they work. This is quite different from mere disuse. 

 He himself in the same essay 3 points out that the flight muscles 

 of the domestic goose have not undergone any marked de- 

 generation. 



Vestiges I will now discuss the question of the rudimentary or, as they 

 are better named, vestigial organs. Examples are easy to find. 

 Man is still possessed of muscles for moving his ears forward, 

 though he has altogether lost the use of them. The apteryx, 

 or kiwi, the New Zealand bird that has lost the power of flight, 

 has still beneath its feathers the chief wing bones, reduced to 

 minute dimensions. The python has tiny hind legs bearing 

 claws that just appear through the skin. The slow-worm has 

 a remnant of a shoulder girdle and in the embryo there are 

 short stumps representing the forelimbs. The blind cray-fish 

 have eye-stalks and some vestiges of eyes though their sight 

 has gone. 



Take the apteryx with its much reduced wings as a typical 

 example of such phenomena. Suppose the reduction in the size 

 of the wing to be due to disuse. Then, in the early stages when 

 disuse was incomplete, the process of reduction would be very 



1 See Darwin, Animals and Plants under Domestication, vol. i. p. 84. 



2 Essays, vol. i. p. 87. 3 Loc. cit., p. 91. 



