PREFACE. 



The present paper was read in the first general 

 meeting of the International Congress of Zoologists at 

 Leyden on September 16, 1895. Several points, which 

 for reasons of brevity were omitted when the paper 

 was read, have been re-embodied in the text, and an 

 Appendix has been added where a number of topics 

 receive fuller treatment than could well be accorded 

 to them in a lecture. The address was first printed in 

 The Monist for January, 1896, and afterwards in a 

 German pamphlet. 



The basal idea of the essay the existence of Ger- 

 minal Selection was propounded by me some time 

 since, 1 but it is here for the first time fully set forth 

 and tentatively shown to be the necessary complement 

 of the process of selection. Knowing this factor, we 

 remove, it seems to me, the patent contradiction of 

 the assumption that the general fitness of organisms, 

 or the adaptations necessary to their existence, are 

 produced by accidental variations a contradiction 

 which formed a serious stumbling-block to the theory 

 of selection. Though still assuming that the primary 

 variations are "accidental," I yet hope to have demon- 

 strated that an interior mechanism exists which com- 

 pels them to go on increasing in a definite direction, 

 the moment selection intervenes. Definitely directed 



1 Ncue Gedanken zur Vererbungsfrage, cine Antwort an 

 Herbert Spencer. Jena. 1895. 



3 



