cy above alluded to will not
counterbalance the exceptions caused by our naturalizations, admits at
least of some doubt. In the attempt to form an estimate on this subject,
we must be careful not to underrate, or almost overlook, as some appear
to have done, the influence of man in checking the diffusion of plants,
and restricting their distribution to narrower limits.

CHAPTER XXXVIII.

LAWS WHICH REGULATE THE GEOGRAPHICAL DISTRIBUTION OF
SPECIES--_continued_.

Geographical distribution of animals--Buffon on specific
distinctness of quadrupeds of Old and New World--Doctrine of
"natural barriers"--Different regions of indigenous
mammalia--Europe--Africa--India, and Indian
Archipelago--Australia--North and South America--Quadrupeds in
islands--Range of the Cetacea--Dispersion of quadrupeds--Their
powers of swimming--Migratory instincts--Drifting of animals on
ice-floes--On floating islands of drift-timber--Migrations of
Cetacea--Habitations of birds--Their migrations and facilities of
diffusion--Distribution of reptiles, and their power of
dissemination.

_Geographical distribution of animals._--Although in speculating on
"philosophical possibilities," said Buffon, "the same temperature might
have been expected, all other circumstances being equal, to produce the
same beings in different parts of the globe, both in the animal and
vegetable kingdoms, yet it is an undoubted fact, that when America was
discovered, its indigenous quadrupeds were all dissimilar to those
previously known in the Old World. The elephant, the rhinoceros, the
hippopotamus, the camelopard, the camel, the dromedary, the buffalo, the
horse, the ass, the lion, the tiger, the apes, the baboons, and a number
of other mammalia, were nowhere to be met with on the new continent;
while in the old, the American species, of the same great class, were
nowhere to be seen--the tapir, the lama, the pecari, the jaguar, the
couguar, the agouti, the paca, the coati, and the sloth."

These phenomena, although few in number relatively to the whole animate
creation, were so striking and so positive in their nature, that the
great French naturalist caught sight at once of a general law in the
geographical distribution of organic beings, namely, the limitation of
groups of distinct species to regions separated from the rest of the
globe by certain natural barriers. It was, therefore, in a truly
philosophical spir