358 F. W. HEAD LEY [may 



know the cause of any particular variation. Darwin, as may be seen 

 by reference to the opening paragraph of the fifth chapter of the 

 " Origin of Species," meant no more than this when he attributed vari- 

 ations to chance. He did not renounce the attempt to find law and 

 system running through animal variability. For in his " Animals and 

 Plants under Domestication," he writes at length upon the " laws of 

 variation," upon " correlated variability," and on the " continuity of 

 variation." He spoke of variations as " spontaneous," meaning that he 

 could not trace them to a definite cause. But he strove to discover 

 the laws which these spontaneous variations obeyed. Obscure as the 

 subject is he has not left it in complete obscurity. The object of this 

 paper is, if possible, to throw some further light upon it. 



Even though we should be unable to discover any regulating prin- 

 ciple, it is difficult — for me impossible — to allow free play to chance 

 after tracing the development of a chick through its regular stages. 

 Are we to suppose that the organism, roughly but truly, recapitulates 

 its phylogeny, goes through a series of definite phases and at the end 

 of the prescribed course is at liberty to break out into wild haphazard 

 developments ? Law and order so perfect surely never ended in 

 chaos. Nevertheless, even if variations were chaotic with no guide but 

 mere chance, if any animal might produce any kind of new organ, and 

 if any existing organ might be moulded to any new form, even then, 

 given an unlimited number of individuals in a species, mere chance 

 might produce a sufficient number of representatives of some new type 

 to form a new species. But the great results achieved by breeders of 

 cattle, horses, pigeons, and other animals have been attained in many 

 cases with quite small numbers. When breeding for some particular 

 point, they have been generally able to find two animals among the 

 few at their disposal in which this was prominent. The smallness of 

 their resources and the greatness of their achievements put it out of the 

 question that they have worked with nothing but chance to help them. 

 If it were a question merely of more or less, then we might call in the 

 doctrine of chances as expounded by Prof. Weldon. But how is the 

 hood of the nun pigeon a question of more or less ? In the wild 

 rock dove or in the common dovecot pigeon there is no such growth 

 of feathers in a rudimentary form. Game-fowls occasionally have as 

 many as five spurs. In some breeds particular feathers show particular 

 markings. In these cases we have new departures, not a gradual 

 increase or decrease of an existing organ. Turning to wild animals we 

 find problems of the same kind. There was a time when stags had 

 no horns. The first development of these cannot be put down to 

 deviations on either side of a mean in accordance with the 

 law of chance. Before the horns originated, obviously there was no 

 room for the working of the principle. When once they have come 

 into existence, then their further development can be accounted for on 

 the principle which Prof. Weldon has explained. Take a feather as. 



