CHAP. XIV.] 
THE NEOTROPICAL REGION. 
83 
of interchange of the mammals or land-birds of the two 
countries, no less than by the very fragmentary nature of the 
resemblances that do exist. The northern element consists 
almost wholly of insects ; and is evidently due to the migration 
of arctic and north temperate forms along the ridges and 
plateaus of the Andes ; and most likely occurred when these 
organisms were driven southward at successive cold or Glacial 
periods. 
A curious parallel exists between the past history and actual 
zoological condition of South America and Africa. In both 
we see a very ancient land-area extending into the South 
Temperate zone, isolated at a very early period, and developing 
only a low grade of Mammalian life; chiefly Edentates and 
Kodents on the one, Lemurs and Insectivora in the other. Later 
we find an irruption into both of higher forms, including 
Quadrumana, which soon acquired a large and special develop- 
ment in the tropical portions of each country. Still later we 
have an irruption into both of northern forms, which spread 
widely over the two regions, and having become extinct in the 
land from whence they came, have been long held to be the 
original denizens of their adopted country. Such are the 
various forms of antelopes, the giraffe, the elephant, rhinoceros, 
and lion in Africa ; while in America we have deer and peccaries, 
the tapir, opossums, and the puma. 
On the whole, we cannot but consider that the broad outlines 
of the zoological history of the Neotropical region can be traced 
with some degree of certainty; but, owing to the absence of 
information as to the most important of the geological periods 
— the Miocene and Eocene — we have no clue to the character of 
its early fauna, or to the land connections with other countries, 
which may possibly have occurred in early Tertiary times. 
