NATURAL SELECTION. 387 



treated by Darwin, Wallace, and other writers, and it 

 is one on which much further research maybe profita- 

 bly expended. It is the science of adaptations, and 

 the name Chorology has been framed for it by Haeckel, 

 but the earlier term Oncology is now generally used. It 

 was not overlooked by biologists prior to Darwin and 

 Wallace, and is stated in general terms by Lamarck in 

 his Philosophic Zoologique, but it was reserved for the 

 two authors just mentioned to create the science. I 

 shall here only refer to a few aspects of the subject. 

 Isolation naturally tends to emphasize any pecu- 

 liarities of structure which may harmonize with the 

 conditions of the environment, by the barrier which it 

 sets up against the entrance and mixture of forms from 

 other localities where the environments are more or 

 less different, and where the characters are correspond- 

 ingly proportionately diverse. Isolation conversely 

 prevents the emigration of forms, and the consequent 

 mixture with the differing forms of other regions. 

 Breeding in and in is produced on a large scale. Geo- 

 graphical isolation is a result of the formation and 

 population of islands, whether this be accomplished 

 by submergence below or by elevation above sea level. 

 A noteworthy illustration of the former case is seen in 

 the West Indian Islands, which represent the elevated 

 regions of a former continent. Here the faunae of the 

 respective islands have been separated from each other 

 since late Pliocene time. We find that while most of 

 the genera of land Vertebrata are generally distributed, 

 each island possesses peculiar species. This is even 

 true of the birds, whose powers of migration are quite 

 sufficient to enable them to pass from island to island. 

 The restriction of land mollusca is still greater, several 

 islands having genera peculiar to them. 



