160 
ZOOLOGICAL GEOGRAPHY. 
[PAST III, 
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 Palsearctic 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 have thus come to resemble each 
other more than they once did, while the Oriental retains 
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 Palsearctic 
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, i'he 
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. 
