VI PREFACE. 



into the phenomena presented by oceanic islands he 

 showed that these islands had never been connected 

 with the continents, as had been almost invariably 

 assumed by previous writers, and, consequently, that 

 their entire fauna and flora must have originated from 

 such species as could, in the course of ages, have reached 

 the islands by natural means of dispersal. Hence the 

 importance of studying what are the means of dispersal 

 of the various groups, and why it is that, with the two 

 absolute exceptions of mammals and amphibia, none of 

 the larger groups of animals or plants are invariably 

 absent from this class of islands. As a corollary from his 

 investigation he was led to conclude that the great 

 oceans were, broadly speaking, permanent features of 

 the earth's surface, and that it was scientifically in- 

 admissible to bridge them over in various directions and 

 at various geological epochs in order to provide a 

 short and easy road for the passage of beetles or 

 snakes, snails or frogs, and thus save us the trouble of 

 solving the problem of their a ctual distribution by less 

 obvious and also by less heroic means. 



Having myself devoted some time and research with 

 the object of showing that almost every anomaly in the 

 distribution of animals and plants may be explained 

 by a careful consideration of the various means of 

 dispersal which organisms possess, combined with the 

 climatic and geographical changes which are known to 

 have occurred during later geological times, and taking 

 into account the known distribution of the several 

 groups at remiote epochs as proved by the discovery of 



