48 



to a single species, at present represented by the American 

 Indian. 



In this rapid review of Mammalian life in America, from its 

 first known appearance in the Trias down to the present time, I 

 have endeavored to state briefly the introduction and succes- 

 sion of the principal forms in each natural group. If time per- 

 mitted, I might attempt the more difficult task of trying to 

 indicate what relations these various groups may possibly bear 

 to each other ; what connection the ancient Mammals of this 

 continent have with the corresponding forms of the Old World; 

 and, most important of all, what real progress Mammalian life 

 has here made since the beginning of the Eocene. As it is, I 

 can only say in summing up, that the Marsupials are clearly 

 the remnants of a very ancient fauna, which occupied this 

 continent millions of years ago, and from which the other 

 Mammals were doubtless all derived, although the direct evi- 

 dence of the transformation is wanting. 



Although the Marsupials are nearly related to the still 

 lower Monotremes, now living in the Australian Region, we 

 have as yet no hint of the path by which these two groups 

 became separated from the inferior vertebrates. Neither have 

 we to-day much light as to the genetic connection existing 

 between Marsupials and the placental Mammalia, although it is 

 possible that the different orders of the latter had their origin 

 each from a separate group of the Marsupials. 



The presence, however, of undoubted Marsupials in our 

 lower and middle Eocene, some of them related to the genus 

 Didelphys, although remotely, is important evidence as to the 

 introduction of these animals into America. Against this, their 

 supposed absence in our Miocene and Pliocene can have but 

 limited weight, when taken in connection with the fact that 

 they flourished in the Post-Tertiary, and are still abundant. 

 The evidence we now have is quite as strongly in favor of a 

 migration of Marsupials from America to the Old World, as the 

 reverse, which has been supposed by some naturalists. Possi- 

 bly, as Huxley has suggested, both countries were peopled with 

 these low mammals from a continent now submerged. 



