CHAPTEPv XI. 



THE CLASSIFICATION OF ISLANDS. 



Importance of Islands in the study of the Distribution of Organisms — 

 Classification of Islands with reference to Distribution — Continental 

 Islands — Oceanic Islands. 



In the preceding chapters, forming the first part of our work, 

 we have discussed, more or less fully, the general features pre- 

 sented by animal distribution, as well as the various physical 

 and biological changes which have been the most important 

 agents in bringing about the present condition of the organic 

 world. 



We now proceed to apply these principles to the solution of 

 the numerous problems presented by the distribution of animals ; 

 and in order to limit the field of our inquiry, and at the same 

 time to deal only with such facts as may be rendered intelligible 

 and interesting to those readers who have not much acquaintance 

 with the details of natural history, we propose to consider only 

 such phenomena as are presented by the islands of the globe. 



Importance of Islands in the stndy of the Distrihution of 

 Organisms. — Islands possess many advantages for the study of 

 the laws and phenomena of distribution. As compared with 

 continents they have a restricted area and definite boundaries, 

 and in most cases their geographical and biological limits 

 coincide. The number of species and of genera they contain 

 is always much sm_aller than in the case of continents, and their 

 peculiar species and groups are usually well defined and strictly 

 limited in range. Again, their relations with other lands are often 



