ix THE DEBT OF SCIENCE TO DARWIN 459 



the cirripedia or barnacles, as well as of a most ingenious 

 explanation of the origin and structure of coral-reefs a 

 series of volumes which were the direct outcome of his 

 voyage, and which gave him an established reputation. Even 

 when the great work at last appeared, few could appreciate 

 the enormous basis of fact and experiment on which it rested, 

 until, during the succeeding twenty years, there appeared 

 that remarkable succession of works which exhibited a sample 

 (and only a sample) of the exhaustless store of materials and 

 the profound maturity of thought on which his early volume 

 was founded. From these various works, aided by some per- 

 sonal intercourse and a correspondence extending over twenty 

 years, the present writer will endeavour to indicate the 

 nature and extent of Darwin's researches. 



Studies of Domestic Animals 



Although, as we have said, Darwin had early arrived at 

 the conclusion that allied species had descended from common 

 ancestors by gradual modification, it long remained to him an 

 inexplicable problem how the necessary degree of modifica- 

 tion could have been effected, and he adds : "It would thus 

 have remained for ever, had I not studied domestic produc- 

 tions, and thus acquired a just idea of the power of selection." 

 These researches, very briefly sketched in the first and parts 

 of the fifth and ninth chapters of the Origin of Species, were 

 published at length (after a delay of nine years, owing to ill 

 health) in two large volumes, with the title Animals and Plants 

 Under Domestication; and no one who has not read these 

 can form an adequate idea of the wide range and thorough 

 character of the investigation on which every statement or 

 suggestion in the former work was founded. 



The copious references to authorities show us that he 

 must have searched through almost the entire literature of 

 agriculture and horticulture, of horse and cattle breeding, of 

 sporting, of dog, cat, pigeon, and fowl fancying, including 

 endless series of reviews, magazines, journals of societies, and 

 newspapers, besides every scientific treatise bearing in any 

 way on the subject, whether published in this country, on the 

 Continent, or in America. The facts thus laboriously gathered 

 were supplemented by personal inquiries among zoologists and 



