Modification and Variation. 315 



the organism are in a certain degree variable [i.e. modifi- 

 able], and capable of being determined by the strength and 

 nature of the influences that affect them, and this capacity 

 to respond conformably to functional stimulus must be 

 regarded as the means which make possible the mainten- 

 ance of a harmonious co-adaptation of parts in the course 

 of the phyletic metamorphosis of a species. ... As the 

 primary variations in the phyletic metamorphosis occurred 

 little by little, the secondary adaptations would as a rule 

 be able to keep pace with them." 



So far Professor Weismann. According to his concep- 

 tion variations of germinal origin occur from time to time. 

 By its innate plasticity the several parts of an organism 

 implicated by their association with the varying part are 

 modified in individual life in such a way that their modifi- 

 cations co-operate with the germinal variation in producing 

 an adaptation of double origin, partly congenital, partly 

 acquired. The organism then waits, so to speak, for a 

 further congenital variation, when a like process of adapta- 

 tion again occurs ; and thus race progress is effected by a 

 series of successive variational steps, assisted by a series 

 of co-operating individual modifications. 



If now it could be shown that, although on selectionist 

 principles there is no transmission of modifications due to 

 individual plasticity, yet these modifications afford the 

 conditions under which variations of like nature are 

 afforded an opportunity of occurring and of making them- 

 selves felt in race progress, a farther step would be taken 

 towards a reconciliation of opposing views, Such, it 

 appears to me, may well be the case.* 



* In an article entitled " A New Factor in Evolution," published in the 

 American Naturalist for June and July, 1896, Prof. Mark Baldwin has 

 given expression to views of like nature to those which are here developed. 

 And Prof. Henry F. Osborn, in a paper read before the New York Academy 

 of Sciences, propounded a somewhat similar theory, but with, he tells me, 

 less stress upon the action of natural selection. 



