446 ARGUMENTS FOR AND AGAINST CHAP. xxn. 



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 walk 

 ing 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 ex 

 tremities, 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 pos 

 sible 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. 



