[CHAP, iv.] ITS UNITY. 145 



that all the genera, and likewise most of the families, together 

 with some of the subordinal or even ordinal groups of mammals 

 are likewise perfectly different. Were it not also for the compara- 

 tively recent union between South and North America, to which 

 allusion has been made in the preceding chapter, we should 

 likewise find just as well marked a distinction between the 

 mammalian fauna of these two countries ; and, as a matter of" 

 fact, when we go back to the middle portion of the Tertiary 

 epoch, we find such a distinction actually existing. Again, were 

 it not for the intermediate connecting Austro-Malayan region, 

 which forms, as we have said, a kind of zoological No-man's-land, 

 there would be an equally stringent line of division between the 

 Notogasic realm and Asia. If, on the other hand, we take the 

 different regions of Arctogsea, we find not only a certain number 

 of species of mammals common to two or more regions, but 

 when we pass back into the Tertiary epoch, the whole faunas of 

 several of such regions merge more or less completely into one 

 another, instead of becoming more distinct than they are at the 

 present day. The lion and the leopard, for instance, are common 

 to India and Ethiopian Africa, and during the Plistocene epoch 

 ranged over a considerable portion of Europe ; while the range of 

 the tiger includes not only India and Ceylon, but likewise a 

 considerable portion of Central Asia and China. The caracal 

 and the hunting-leopard are also common to India and Africa ; 

 the British fox ranges not only over Europe and a large portion of 

 Asia north of the Himalaya, but likewise over a part of North 

 America; and the common otter is found alike in India and 

 Europe. Still more numerous are the species of mammals com- 

 mon to Europe, Northern Asia, and North America. 



Recapitulating some of the details given in the introductory 

 chapter, it may be observed that by Messrs Sclater and Wallace 

 the area here included in the Arctogaeic realm was divided into 

 the Nearctic, Palaearctic, and Oriental regions. Professor Newton, 

 who was subsequently followed by Dr Heilprin, proposed to 

 brigade the first two of these together under the name of the 

 Holarctic region. At a still later date Dr Blanford 1 , who as 



1 Appendix, No. 8, p. 76. 

 L. IO 



