CHAPTER 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 study of the Distribution 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 smaller 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 
