Address to the British Association 197 



New World's animals are derived from the same source as 

 those of the Old, whence they have descended. . . . Nature 

 is in a state of perpetual flux.' In his chapter on the De- 

 feneration of Animals ^ he sums up saying : ' After comparing 

 all the animals, and arranging them all in their own group, 

 we shall find that the two hundred kinds described here may 

 be reduced to a small number of original forms, whence it 

 may be all the rest have issued.' 



As to the modes and causes of the origin of new forms, he 

 entertained four connected opinions : — 



(1) He attributed much modifying efficacy to migrations; 



(2) Also to the direct action of external conditions ; 



(3) He believed largely in the origin of new forms by 

 degradation; and 



(4) He regarded each animal as the manifestation of an 

 individuating force, lying, as it were, at the root of the 

 changes manifested by it. 



The view that migration (with isolation) is a necessary 

 antecedent to the origin of new species, is one which has 

 been advocated by a modern naturalist, Moritz Wagner,^ who 

 does not hesitate to affirm 3 that the formation of a really 

 new species 'will only succeed Avhen a few individuals, 

 having crossed the barriers of their station, are able to 

 separate themselves for a long time from the old stock.' 



In support of his view the author brings forward a multi- 

 tude of interesting facts, one of the most significant of which 

 appears to me to be the following. It concerns Beetles of 

 Tropical America of the genus Tetracha. In Venezuela (as 



the Llama, the American Apes, Agoutis, and Ant-eaters might be examples 

 of such forms ; but the Opossums, Sloths, and Tapirs he took to be original 

 species. (See vol. xiv. pp. 272, 273. ) 



1 Vol. xiv. p. 358. 



2 In a paper read before the Royal Academy of Sciences at Munich on 

 March 2, 1868. This has been translated by Mr. James L. Laird, and pub- 

 lished by Edward Stanford in 1873. 



3 Op. cit., p. 29. 



