Page:Geological Evidences of the Antiquity of Man.djvu/466

446 other large islands, to acquire terrestrial habits, venturing first a few yards inland, and then farther and farther until they began to occupy some of those "places left vacant in the economy of nature." During these excursions, we might suppose some varieties, which had the skin of the webbed intervals of their toes less developed, to succeed best in walking on the land, and in the course of several generations they might exchange their present gait or manner of shuffling along and jumping by aid of the tail and their fin-like extremities, for feet better adapted for running.

It is said that one of the bats in the island of Palma (one of the Canaries) is of a peculiar species, and that some of the Cheiroptera of the Pacific islands (or Oceanica) are even of peculiar genera. If so, we seem, on organic as well as on geological grounds, to be precluded from arguing that there has not been time for great divergence of character. We seem also entitled to ask why the bats and rodents of Australia, which are spread so widely among the marsupials over that continent, have never, under the influence of the principle of progression, been developed into the higher or placental type, since we have now ascertained that that continent was by no means unfitted to sustain such mammalia, for these, when once introduced by man, have run wild and become naturalised in many parts. The following answers may perhaps be offered to the above criticisms of some of Mr. Darwin's theoretical views.

First, as to the bats and seals: they are what zoologists call aberrant and highly specialised types, and therefore precisely those which might be expected to display a fixity and want of pliancy in their organisation, or the smallest possible aptitude for deviating in new directions towards new structures, and the acquisition of such altered habits as a change from aquatic to terrestrial or from volant to non-volant modes of living would imply.