ix THE DEBT OF SCIENCE TO DARWIN 457 



sented by this latter group of islands brought out so clearly 

 and strongly the insuperable difficulties of the then accepted 

 theory of the independent origin of species, as to keep this 

 great problem ever present to his mind, and, at a later period, 

 led him to devote himself to the patient and laborious in- 

 quiries which were the foundation of his immortal work. He 

 again and again remarks on the singular facts presented 

 by these islands. Why, he asks, were the aboriginal in- 

 habitants of the Galapagos created on American types of 

 organisation, though the two countries differ totally in geolo- 

 gical character and physical conditions ? Why are so many 

 of the species peculiar to the separate islands? He "is 

 astonished at the amount of creative force, if such an expres- 

 sion may be used, displayed in these small, barren, and rocky 

 islands ; and still more so at its diverse, yet analogous action 

 on points so near each other." 



The variations which occur in species, as well as the modi- 

 fications of the same organ in allied species, subjects which 

 had been much neglected by ordinary naturalists, were con- 

 stantly noted and commented on. He remarks on the 

 occasional blindness of the burrowing tucutucu of the Pampas 

 as supporting the view of Lamarck on the gradually acquired 

 blindness of the aspalax; on the hard point of the tail of 

 trigonocephalus, which constantly vibrates and produces a 

 rattling noise by striking against grass and brushwood, as a 

 character varying towards the complete rattle of the rattle- 

 snake ; on the small size of the wild horses in the Falkland 

 islands, as progressing towards a small breed like the Shetland 

 ponies of the North; and on the strange fact of the cattle 

 having increased in size, and having partly separated into two 

 differently coloured breeds. While collecting the remains of 

 the great extinct mammals of the Pampas, he was much im- 

 pressed by the fact that, however huge in size or strange in 

 form, they were all allied to living South American animals, 

 as are those of the cave-deposits of Australia to the marsupials 

 of that country ; and he thereon remarks : " This wonderful 

 relationship in the same continent between the dead and the 

 living will, I do not doubt, hereafter throw more light on the 

 appearance of organic beings on our earth, and their disap- 

 pearance from it, than any other class of facts." 



