MIGRATION OF TERRESTRIAL VERTEBRATES 311 



a detailed history of all these exchanges of faunas. 

 As regards some of the continents, particularly the 

 two Asiatic nuclei of the North and South, the 

 documents for this history are either utterly lacking, 

 as ill the case of the Siberian one, or else restricted 

 to the most recent fauna, as happens with China 

 and the Hindu expanse. The history of the develop- 

 ment of the Tertiary fauna on the Asiatic continent 

 constitutes, at the present moment, the most funda- 

 mental gap in our knowledge. It is patent to us 

 that a certain number of groups of Mammals, which 

 suddenly appeared on the continent of Europe in 

 the first half of Tertiary times, such as the Palceo- 

 theridce, the Anoplotheridce, the Canidce, the Mus- 

 telidce, the Suidce, the Tragulidce, the Cervulidce, etc. 

 are Asiatic immigrants ; but it is, for the moment, 

 totally impossible to prove it. 



It is, fortunately, otherwise as regards the migra- 

 tions occurring between a few other regions. 

 Among the best known of these migrations may be 

 pointed out the exchange of faunas happening on 

 several occasions between Europe and North 

 America. 



The first North American migration brings to 

 Cernay, in Europe, at the beginning of the Plio- 

 cene, several families of Creodonts (Proviverridce, 

 Arctocyonidce, Mesonychidce), as well as the Condy- 

 larthra, neighbours of the famous Phenacodus, to 

 whom was too hastily attributed the part of 

 ancestor of all the other Ungulates. 



A second migration, still more clearly defined, 

 that of the Sparnacian epoch, passes over into 

 England and France some other Creodonts, such 



