Vili PREFACE. 
distribution of an organic type, and to be more clearly influenced 
by the. various known. or inferred changes in the organic and 
physical environment. 
This systematic review of the distribution of families and 
genera, now forms the last part of my book—Geographical 
Zoology; but it was nearly the first written, and the copious 
materials collected for it enabled me to determine the zoo- 
geographical divisions of the earth (regions and sub-regions) to 
be adopted. I next drew up tables of the families and genera 
found in each region and sub-region ; and this afforded a basis 
for the geographical treatment of the subject—Zoological Geo- 
oraphy—the most novel, and perhaps the most useful and 
generally interesting part of my work. While this was in progress 
I found it necessary to make a careful summary of the distribu- 
tion of extinct Mammalia. This was a difficult task, owing 
to the great uncertainty that prevails as to the affinities of many 
of the fossils, and my want. of practical acquaintance with 
Paleontology ; but having carefully examined and combined 
the works of the best authors, I have given what I believe is 
the first connected sketch of the relation of extinct Mammalia 
to the distribution of living groups, and have arrived at some 
very interesting and suggestive results. 
It will be observed that man is altogether omitted from 
the series of the animal kingdom as here given, and some ex- 
planation of this omission may perhaps be required. If the 
genus Homo had been here treated like all other genera, nothing 
more than the bare statement—“ universally distributed ”— 
could have been given;—and this would inevitably have pro- 
voked the criticism that it conveyed no information. If, on the 
other hand, I had given an outline of the distribution of the 
varieties or races of man, I should have departed from the plan 
of my work for no sufficient reason. Anthropology is a science 
