VUl PREFACE 



this great question may be attacked. One of these is by 

 the method of experiment — a method which is being 

 pursued with increasing vigour by more than one school 

 of Biologists ; the other is the careful and thorough exam- 

 ination of living and extinct organisms, particularly in their 

 relations to one another. It is the second of these methods 

 which comes under our notice in the three volumes of the 

 first part of this work dealing with systematic zoology. It 

 is unquestionable that this study does shed light, if only a 

 dim light, on the course of organic evolution and indirectly 

 on the origin of the properties of living matter, and it is 

 most important that the light so obtained should be brought 

 to bear upon the problem. To discover this we must 

 approach the subject with unbiassed minds, for it is one 

 of immense complexity and it is extremely unlikely that 

 any particular solution which commends itself to us 

 will turn out to be final. I would therefore ask for 

 lenient judgment if in some pages of this work I have 

 seemed to take up an unduly critical position with regard 

 to views widely prevalent at the present time on some 

 aspects of organic evolution. That does not mean that I 

 am unsound on the great question itself, but only that 

 I am sceptical as to the value of some hypotheses widely 

 held as to the course of organic evolution. It is true that 

 working hypotheses are necessary in constructive work, but 

 in a subject of the complexity of the present one, they can only 

 be provisional and as such are legitimately open to criticism. 

 It may be urged that I have said too much or too little, that 

 I ought not to have touched upon the matter unless I was 

 prepared to state fully my own views. While allowing 

 that there would be some justice in such a criticism, I do 

 not admit its complete vahdity. In deference to it, how- 

 ever, I have materially altered in proof what I had written 

 in manuscript, but it was not possible to remove all refer- 

 ence to the subject. It was necessary to note the facts in 

 passing. In the final volume on the Principles of Zoology, 

 I return to it and endeavour to justify, in the fuller 

 treatment which is there, the criticisms which are only 



