446 ARGUMENTS FOR AND AGAINST cn.vp. xxn. 



other large islands, to acqiiire teri-estrial habits, venturing first 

 a few yards inland, and then forther and farther until they 

 began to oceup}^ 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 to 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 con- 

 tinent was by no means unfitted to sustain such mammalia, 

 for these, when once introduced b}' man, have run wild and 

 become naturalized in many parts. The following answers 

 may perhaps be off'ered to the above criticisms of some of 

 Mx. Darwin's theoretical views. 



First, as to the bats and seals : they are what zoologists 

 call abei'rant and highly specialized t3q)es, and therefore 

 precisel}" those which might be expected to disjilay a fixity 

 and want of pliancy in their organization, or the smallest pos- 

 sible aptitude for deviating in new directions towai'ds 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. 



