36 Darwin, and after Darwin. 



lighted up to the full blaze of active discussion ^. By 

 far the most important of them are those to which 

 the rest of this treatise will be confined. They are 

 four in number, and it is noteworthy that they are all 

 intimately connected with the great question which 

 Darwin spent the best years of his life in contem- 

 plating, and which has therefore, in one form or 

 another, occupied the whole of the present chapter — 

 the question as to whether natural selection has been 

 the sole cause, or but the chief cause of modification. 

 The four questions above alluded to appertain 

 respectively to Heredity, Utility, Isolation, and Physio- 

 logical Selection. Of these the first two will form 

 the subject-matter of the present volume, while the 

 last two will be dealt with in the final instalment of 

 Darwin, and after Darwin. 



' It is almost needless to say that besides the woAs mentioned in this 

 chapter, many others have been added to the literature of Darwinism 

 since Darwin's death. But as none of these profess to contain much 

 that is original, I have not thought it necessary to consider any of them 

 in this merely general review of the period in question. In subsequent 

 chapters, however, allusions will be made to those among them which 

 I deem of most importance. 



[Since this note was written and printed the following works have 

 been published to which it does not apply : Animal Life and Intelli- 

 gence, by Professor Lloyd Morgan ; The Colours of Animals, by 

 Professor Ponlton ; and Materials for the Study of Variation, by 

 Mr. Bateson. All these works are of high value and importance. 

 Special reference should also be made to Professor Weismann's Essays.] 



