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Show 86 DIFFUSION OF PLANTS• [Ch. V. the m· sects, bt' rd s, an d quadrupeds of two regions situat.e d like b 11 ded to No beasts of prey are permitted to those a ove a u • ma k e t l1 e1· r wa y across the intervening arable tracts. Many birds, and hundreds of insects, which would have found som.e palatable food amongst the various herbs and trees of the primeval wilderness, are unable to subsist on the olive, the vine, th wheat and a few trees and grasses favoured by man. In aded ition, t'h erefore, to his direct interventi.O n, man, m• t hI' s case, operates indirectly to impede the _dissemination of ~lants, by intercepting the migrations of ammals, many of whiCh would otherwise have been active in transporting seeds from one pro-vince to another. Whether in the vegetable kingdom the influence of man will tend, after a considerable lapse of ages, to render the geogra· phical range of species in general more extended, as Decandolle seems to anticipate, or whether the compensating agency 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 VI. Geographical Distribution of Animals-Buffon on the specific distinctness of the quadrupeds o£ the old and new world-Different regions of indigenou1 mammalia-Quadrupeds in islands-Range of the Cetacea-Dissemination of quadrupeds-their powers of swimming- Migratory in,.tincts-Drifting of quadrupeds on ice-floes-On floating islands of drift timber-Migrations of Cetacea-Habitations of Birds-Their migrations and facilities of diffusionDistribution of Reptiles and their powers of dissemination. ALTHOUGH in speculating on "philosophical possibilities,'1 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 from those previously known in the old world. The elephant, the rhinoceros, the hippopotamus, the cameleopard, the camel, the dromedary, the buffalo, the horse, the ass, the Hon, the tiger, the apes, the baboons, and a number of other mammalia, where 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. 'rhese phenomena, although few in number relatively to the whole animate creation, were so striking and so positive in their nature, that the 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 spirit that, relying on the clearness of the evidence obtained respecting the larger quadrupeds, he ventured to call in question the identifications announced by some contemporary naturalists, of species of |