CHAPTER VII.
SPECIES AND SPACE.
The geographical distribution of animals presents difficulties .-- These not insurmountable in themselves; harmonize with other difficulties .-- Fresh-water fishes .-- Forms common to Africa and India; to Africa and South America; to China and Australia; to North America and China; to New Zealand and South America; to South America and Tasmania; to South America and Australia .-- Pleurodont lizards .-- Insectivorous mammals .-- Similarity of European and South American frogs--Analogy between European salmon and fishes of New Zealand, &c.

An ancient Antarctic continent probable .-- Other modes of accounting for facts of distribution .-- Independent origin of closely similar forms .-- Conclusion.
The study of the distribution of animals over the earth's surface presents us with many facts having certain not unimportant bearings on the question of specific origin.

Amongst these are instances which, at least at first sight, appear to conflict with the Darwinian theory of "Natural Selection." It is not, however, here contended that such facts do by any means constitute by themselves obstacles which cannot be got over.

Indeed it would be difficult to imagine any obstacles of the kind which could not be surmounted by an indefinite number of terrestrial modifications of surface--submergences and emergences--junctions and separations of continents in all directions and combinations of any desired degree of frequency.

All this being supplemented by the intercalation of armies of enemies, multitudes of ancestors of all kinds, and myriads of connecting forms, whose _raison d'etre_ may be simply their utility or necessity {145} for the support of the theory of "Natural Selection." Nevertheless, when brought in merely to supplement and accentuate considerations and arguments derived from other sources, in that case difficulties connected with the geographical distribution of animals are not without significance, and are worthy of mention even though, by themselves, they constitute but feeble and more or less easily explicable puzzles which could not alone suffice either to sustain or to defeat any theory of specific origination.
Many facts as to the present distribution of animal life over the world are very readily explicable by the hypothesis of slight elevations and depressions of larger and smaller parts of its surface, but there are others the existence of which it is much more difficult so to explain.
The distribution either of animals possessing the power of flight, or of inhabitants of the ocean, is, of course, easily to be accounted for; the difficulty, if there is really any, must mainly be with strictly terrestrial animals of moderate or small powers of locomotion and with inhabitants of fresh water.