anic world in a state of rapid change and development
proportioned to the comparatively rapid changes in the earth's surface.

We have now finished the series of preliminary studies of the biological
conditions and physical changes which have affected the modification and
dispersal of organisms, and have thus brought about their actual
distribution on {126} the surface of the earth. These studies will, it is
believed, place us in a condition to solve most of the problems presented
by the distribution of animals and plants, whenever the necessary facts,
both as to their distribution and their affinities, are sufficiently well
known; and we now proceed to apply the principles we have established to
the interpretation of the phenomena presented by some of the more important
and best known of the islands of our globe, limiting ourselves to these for
reasons which have been already sufficiently explained in our preface.

* * * * *

PART II

_INSULAR FAUNAS AND FLORAS_

{241}

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 presented 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 {242} case of
continents, and their peculiar spec