DARWIN. 71 



fluenced Darwin, and led him to comprehend how species 

 might be modified. 



We see Darwin, then, possessed of the idea that species 

 are mutable, informed as to past and recent changes in 

 the animal, plant, and physical world, seeking for causes 

 which should suffice to produce modification of species 

 by a continuous law. The next step in his progress was 

 attention to domestic animals and cultivated plants. As 

 he wrote in 1864 to Haeckel, one of his most brilliant 

 followers : " In South America three classes of facts were 

 brought strongly before my mind. Firstly, the manner 

 in which closely-allied species replace species in going 

 southward. Secondly, the close affinity of the species 

 inhabiting the islands near South America to those proper 

 to the continent. This struck me profoundly, especially 

 the difference of the species in the adjoining islets in the 

 Galapagos Archipelago. Thirdly, the relation of the 

 living Edentata and Rodentia to the extinct species. 

 I shall never forget my astonishment when I dug out a 

 gigantic piece of armour like that of the living armadillo. 



"Having reflected much on the foregoing facts, it 

 seemed to me probable that allied species were descended 

 from a common ancestor. But during several years I 

 could not conceive how each form could have been modi- 

 fied so as to become admirably adapted to its place in 

 nature. I began, therefore, to study domesticated ani- 

 mals and cultivated plants, 1 and after a time perceived 



1 In this study Darwin came into communication, as early as 1839, 

 with the Hon. and Rev. W. Herbert, afterwards Dean of Manchester, 

 and received from him a personal account of his experiments on 

 hybrids. It was Herbert who, as early as 1822, in the fourth 



