vi Preface. 



grown much beyond the bulk of the original lectures, 

 I have thought it desirable to publish the whole in 

 the form of three separate works. Of these the first 

 or that which deals with the purely historical side 

 of biological science may be allowed to stand over 

 for an indefinite time. The second is the one which 

 is now brought out, and which, as its sub-title signifies, 

 is devoted to the general theory of organic evolution 

 as this was left by the stupendous labours of Darwin. 

 As soon as the translations shall have been completed, 

 the third portion will follow (probably in the Autumn 

 season), under the sub-title, " Post-Darwinian Ques- 

 tions." 



As the present volume is thus intended to be merely 

 a systematic exposition of what may be termed the 

 Darwinism of Darwin, and as on this account it is 

 likely to prove of more service to general readers than 

 to professed naturalists, I have been everywhere care- 

 ful to avoid assuming even the most elementary know- 

 ledge of natural science on the part of those to whom 

 the exposition is addressed. The case, however, will 

 be different as regards the next volume, where I shall 

 have to deal with the important questions touching 

 Heredity, Utility, Isolation, &C., which have been 

 raised since the death of Mr. Darwin, and which are 

 now being debated with such salutary vehemence by 

 the best naturalists of our time. 



My obligations to the Senatus of the University 

 of Edinburgh, and to the Board of Management of 

 the Royal Institution, have already been virtually 



