1877.] The Geographical Distribution of Animals. 161 
now one of the most prominent features in the distribution of 
animal as well as of vegetable forms. 
It is not necessary to go into any further details here, as we 
have already, in our discussion of the origin of the fauna of the 
several regions, pointed out what changes most probably occurred 
in each case. These details are, however, to a great extent 
speculative, and they must remain so till we obtain as much 
knowledge of the extinct faunas and past geological history of 
the southern lands as we have those of Europe and North 
America. But the broad conclusions at which we have now ar- 
rived seem to rest on a sufficiently extensive basis of facts, and 
they lead us to a clearer conception of the mutual relations and 
comparative importance of the several regions than could be ob- 
tained at an earlier stage of our inquiries. 
If our views of the origin of the several regions are correct, it 
is clear that no mere binary division into north and south, or 
into east and west can be altogether satisfactory, since at the 
dawn of the Tertiary period we still find our six regions, or 
what may be termed the rudiments of them, already established. 
The north and south division truly represents the fact that the 
great northern continents are the seat and birthplace of all the 
higher forms of life, while the southern continents have derived 
the greater part, if not the whole of their vertebrate fauna from 
the north ; but it implies the erroneous conclusion that the chief 
southern lands, Australia and South America, are more closely 
related to each other than to the northern continent. The fact, 
however, is that the fauna of each has been derived, independ- 
ently, and perhaps at very different times, from the north, with 
which they therefore have a true genetic relation, while any in- 
tercommunion between themselves has been comparatively recent 
and superficial, and has in no way modified the great features of 
animal life in each. The east and west division represents — 
according to our views —a more fundamental diversity, since 
We find the northern continent itself so divided in the earliest 
Eocene and even in Cretaceous times, while we have the strong- 
est proof that South America was peopled from the Nearctic, 
and Australia and Africa from the Palearctic region ; hence, 
the eastern and western hemispheres are the two great branches 
of the tree of life of our globe. But this division, taken by 
Itself, would obscure the facts, firstly, of the close relation and 
Parallelism of the Nearctic and Palwaretic regions, not only now, 
but as far back as we can clearly trace them in the past; and 
VOL. XI. — xo, 3. 11 
