246 THE DOCTRINE OF DESCENT. 



diluvial fauna of South America collected by Lund, 

 Castlenau, and Weddell, from the Brazilian caves, and 

 the alluvium of the Pampas, among the 1 18 species cited, 

 actually includes, in addition to those already mentioned, 

 as being of probably Old-World pedigree, no less than 

 35 species of Edentata, and these animals of consider- 

 able bulk. Not reckoning the 36 rodents and bats, and 

 the smaller fauna in general, they constitute nearly half 

 of the larger diluvial animals of South America. The 

 assemblage of Edentata previously settled in these 

 regions thus held their own against the invasion from 

 the north. 



It is comprehensible that the same external causes 

 which led the march of the children of the north con- 

 stantly further, may likewise have invited the members 

 of the antarctic fauna to extend themselves northwards. 

 As we even now encounter the incongruous forms of 

 the sloth, the armadillo, and the ant-eater in Guatemala 

 and Mexico, in the midst of a fauna in great part con- 

 sisting of races still represented in Europe, we also find, 

 even in diluvial eras, gigantic sloths and armadillos 

 ranging far into the north. Megalonyx Jeffersoni, and 

 Mylodon Harlemi, sentries of South American origin 

 thrown out as far as Kentucky and Missouri, are a 

 phenomenon as heterogeneous in the land of the bison 

 and the deer, as is the mastodon in the Andes of New 

 Granada and Bolivia. Over the whole enormous extent 

 of both portions of the New Continent, the mixture 

 and interpenetration of two mammalian groups of com- 

 pletely diverse families, constitutes the most conspicuous 

 feature of its fauna ; and it is significant that each 

 group increases in the abundance of its representatives 



