Introductory. 9 



possible, the whole theory of organic evolution as I 

 believe that it will eventually stand. My endeavour, 

 therefore, will be to exhibit the general structure of 

 this theory in what I take to be its strictly logical 

 form, rather than to encumber any of its parts by a 

 lengthy citation of facts. Following this method, I 

 shall in each case give only what I consider the main 

 facts for and against the positions which have to be 

 argued ; and in most cases I shall arrange the facts 

 in two divisions, namely, first those of largest gener- 

 ality, and next a few of the most special character 

 that can be found. 



As explained in the Preface, the present instalment 

 of the treatise is concerned with the theory of evolu- 

 tion, from the appearance of the Origin of Species in 

 1859, to the death of its author in 1882; while the 

 second part will be devoted to the sundry post- 

 Darwinian questions which have arisen in the sub- 

 sequent decade. To the possible criticism that a 

 disproportionate amount of space will thus be allotted 

 to a consideration of these post-Darwinian questions, 

 I may furnish in advance the following reply. 



In the first place, besides the works of Darwin 

 himself, there are a number of others which have 

 already and very admirably expounded the evidences, 

 both of organic evolution as a fact, and of natural 

 selection as a cause. Therefore, in the present 

 treatise it seemed needless to go beyond the ground 

 which was covered by my original lectures, namely, a 

 condensed and connected, while at the same time 

 a critical statement of the main evidences, and the 

 main objections, which have thus far been published 

 with reference to the distinctively Darwinian theory. 



