CHAP. XVI.] SUMMARY AND CONCLUSION. 153 



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 

 afiinities 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 Eegions. 



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 ths objections, 



