70 AMPHIBIA 



in this scheme. Huxley's division (1868) into XOTOGAEA and 

 ARCTOGAEA (see p. 74) is of fundamental importance. The next 

 improvement was the combination of the Palaearctic and Nearctic 

 " regions " into one, an advance originally due to Professor Newton, 

 carried out by Heilprin (1887) as the Holarctic region. I have, 

 in 1893, substituted for it the more appropriate term Periarctic y 

 meaning the whole mass of land which lies around the indifferent 

 Arctic zone. The want of further co-ordination and subordination 

 required the combination of the African and Oriental or Indian 

 countries into a Palaeotropical region (1893); the Ethiopian or 

 African and the Indian or Oriental regions of Sclater and Wallace 

 thereby assuming their proper subordinate rank of subregions. 



The two primary divisions NOTOGAEA and ARCTOGAEA are 

 fundamental. The four secondary divisions, namely the Aus- 

 tralian and Neotropical, Periarctic and Palaeotropical regions, 

 also stand the test of application to the various classes and main 

 groups of Vertebrata ; but naturally, under the present con- 

 figuration of the world, the Palaeotropical region is nothing but 

 the Southern continuation of the Eastern half of the Periarctic 

 mass of land. This is especially obvious so far as India is con- 

 cerned. There is, however, that broad belt of desert, sand, and 

 salt-steppes, which extends from North-West Africa to Manchuria, 

 and this belt is one of the most important physical features of 

 the Old World. It is complicated by the system of uioimtain- 

 chains which, broadly speaking, centre at the Pamirs, and radiate 

 westwards through the Caucasus and Alps into Spain, eastwards 

 through the Himalayas into China, and north-eastwards to Kamt- 

 schatka ; interrupted by Bering's Sea, it is continued as the back- 

 bone of both Americas to Patagonia. 



The tertiary divisions, the subregions, have no real existence. 

 They depend upon the class, or even order, of animals, which we 

 happen to study. The faunistic distribution of the Urodela is 

 not that of the Anura, and both follow separate lines of dispersal, 

 different from those of the various orders of Reptiles, Birds, and 

 Mammals. This must be so. There is no doubt that the dis- 

 tribution of land and water was totally different in the Coal A_ 

 from what it is now. The face of the globe at the Jurassic Ag 

 can scarcely be compared with the aspect which the world has 

 assumed in the Miocene period. 



This leads to another consideration, often neglected. We 



