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INTRODUCTION.
In the preceding part of our work, we have discussed the
geographical distribution of animals from the point of view of
the geographer; taking the different regions of the earth in
succession, and giving as full an account as our space would
permit of their chief forms of animal life. Now, we proceed
from the standpoint of the systematic zoologist ; taking in
succession each of the families with which we deal, and giving
an account of the distribution, both of the entire family and, as
far as practicable, of each of the genera of which it is composed.
As in the former part, our mode of treatment led us to speculate
on the past changes of the earth's surface; so here we shall
endeavour to elucidate the past migrations of animals, and thus,
to some extent, account for their actual distribution.
The tabular headings, showing the range of the family in each
region, will enable the reader to determine at a glance the
general distribution of the group, as soon as he has familiarised
himself, by a study of our general and regional maps, with the
limits of the regions and sub-regions, and the figures (1 to 4)
by which the latter are indicated. Much pains have been taken,
to give the number of the known genera and species in each
family, correctly ; but these numbers must, in most cases, only
be looked upon as approximations ; because, owing to constant
accessions of fresh material on the one hand, and the discovery
that many supposed species are only varieties, on the other, such
statistics are in a continual state of fluctuation. In the number
of genera there is the greatest uncertainty ; as will be seen by
the two sets of numbers sometimes given, which denote the
genera according to different modern authorities.
Vol. II.—12