CHAr. XVI.] 
SUMMARY AND CONCLUSION. 
163 
found useful to zoologists ; for it really involves a fundamental 
problem in the theory of evolution. The question we have to 
answer, is, firstly — whether the distribution of plants is, like that 
of animals, mainly and primarily dependent on the past revolu- 
tions of the earth's surface ; or, whether other, and altogether dis- 
tinct causes, have had a preponderating influence in determining 
the range and limits of vegetable forms ; and, secondly — whether 
those revolutions have been, in their general outlines, correctly 
interpreted by means of a study of the distribution and 
affinities of the higher animals. The first question is one for 
botanists alone to answer ; but, on the second point, the author 
ventures to hope for an affirmative reply, from such of his 
readers as will weigh carefully the facts and arguments he has 
adduced. 
The remaining part of this volume, will consist, of a systematic 
review of the distribution of each family of animals, and an 
application of the principles already established to elucidate the 
chief phenomena they present. The present chapter must, 
therefore, be considered as the conclusion of the argumentative 
and theoretical part of the present work ; but it must be read 
in connection with the various discussions in Parts II. and III., 
in which the conclusions to be drawn from the several groups of 
facts have been successively given ; — and especially in connec- 
tion with the general observations at the end of each of the six 
chapters on the Zoological Regions. 
The hypothetical view, as to the more recent of the great 
Geographical changes of the Earth's surface, here set forth, 
is not the result of any preconceived theory, but has grown out 
of a careful study of the facts accumulated, and has led to a 
considerable modification of the author's previous views. It 
may be described, as an application of the general theory of 
Evolution, to solve the problem of the distribution of animals ; 
but it also furnishes some independent support to that theory, 
both by showing what a great variety of curious facts are ex- 
plained by its means, and by answering some of the objections, 
M 2 
