IGO ZOOLOGICAL GEOGRAPHY. [part hi. 



Mammalia it appears to have produced, we can have little doubt 

 that here was the earliest seat of the development of the 

 vertebrate type ; and probably of the higher forms of insects 

 and land-molluscs. Whether the Nearctic region ever formed 

 one mass with it, or only received successive immigrations from 

 it by northern land-connections both in an easterly and westerly 

 direction, we cannot decide ; but the latter seems the most 

 probable supposition. In any case, we must concede the first 

 rank to the Palrearctic and Oriental regions, as representing the 

 most important part of what seems always to have been the 

 Great Continent of the earth, and the source from which all the 

 other regions were supplied with the higher forms of life. These 

 once formed a single great region, which has been since divided 

 into a temperate and a tropical portion, now sufficiently distinct ; 

 while the Nearctic region has, by deterioration of climate, 

 suffered a considerable diminution of productive area, and 

 has in consequence lost a number of its more remarkable forms. 

 The two temperate regions haA^e thus come to resemble each 

 other more than they once did, while the Oriental retain?, 

 more of the zoological aspect of the great northern regions 

 of Miocene times. The Ethiopian, from having been once an 

 insular region, where lower types of vertebrates alone prevailed, 

 has been so overrun with higher types from the old PalfBarctic 

 and Oriental lands that it now rivals, or even surpasses, the 

 Oriental region in its representation of the ancient fauna of 

 the great northern continent. Both of our tropical regions of 

 the Eastern Hemisphere possess faunas which are, to some 

 extent, composite, being made up in different proportions of 

 the productions of the northern and southern continents, — the 

 former prevailing largely in the Oriental, while the latter 

 constitutes an important feature in the Ethiopian fauna. The 

 Neotropical region has probably undergone great fluctuations 

 in early times ; but it was, undoubtedly, for long periods com- 

 pletely isolated, and then developed the Edentate type of 

 Mammals and the Formicaroid type of Passerine birds into 

 a variety of forms, comparable with the diversified Marsupials 

 of Australia, and typical Passeres of the Eastern Hemisphere. 



