192 Animal Life and Intelligence. 



folk the offspring inherits one-fourth from each parent, 

 one-sixteenth from each grandparent, leaving one-fourth 

 to be contributed by more remote ancestors. There is no 

 doubt, however, that among domesticated animals rever- 

 sion occurs to characters which have been lost for many 

 generations. But we should probably have to go a very 

 long way back in the ancestry of wild ducks for any marked 

 diminution in wing-power. It must be remembered that, 

 in the case of the artificial selection of domesticated 

 animals, man has been working against and not with the 

 stream of ancestral tendency. Eeversion in their case is 

 towards a standard which was long maintained and had 

 become normal before man's interference. Eeversion in 

 domesticated ducks should therefore be towards the greater 

 wing-power of their normal ancestry before domestication, 

 not in the direction of lessened wing-power and diminished 

 wing- structure. The whole question of reversion is full of 

 interest, and needs further investigation. 



In the dwindling of disused structures, Mr. Eomanes 

 has suggested " failure of heredity " as an efficient cause. 

 I find it difficult, however, to distinguish this failure of 

 heredity from the effects of disuse. To what other cause 

 is the failure of heredity due? If natural selection has 

 intervened to hasten this failure, this can only be because 

 the failure is advantageous, since it permits the growth-force 

 to be applied more advantageously elsewhere. And this 

 involves a different principle. Even so it is difficult to 

 exclude the possibility (to put it no stronger) that the 

 diversion of growth-force from a less useful to a more 

 useful organ is in part due to the use of the one and the 

 disuse of the other. But of disuse Mr. Eomanes says, 

 "There is the gravest possible doubt lying against the 

 supposition that any really inherited decrease is due to 

 the inherited effects of disuse." We may fairly ask Mr. 

 Eomanes, therefore, to explain to what cause the failure of 

 heredity is due. In any case. Professor Weismann and 

 his school are not likely to accept this failure of heredity 

 as an efficient factor in the process. Nor is Professor 



