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we have already seen that this effect is not purely a matter of 

 influence upon the individual. The apparent fact of accumu- 

 lation from generation to generation shows that behind the 

 individual change there must be some element of heredity. 

 Where is this to be sought 1 Weismann is ready with an 

 explanation which is consonant with his general theory, and 

 which, at any rate, has the merit of accounting for the facts. 

 The modifying influence, he points out, though specially 

 effective at a certain stage in the ontogeny, is not entirely 

 inoperative at other periods. The phenomenon of seasonal 

 dimorphism, as exemplified in the Ligurian race of 

 Chrysophanus phlaeas, seems to suggest that the suscept- 

 ible constituent, whatever it may be, has passed through a 

 preparatory change under the influence of the climate of that 

 region, and so has been brought up to a point where it needs 

 only the finishing touch of the active influence at the specially 

 susceptible ontogenetic stage to push it over into the fully 

 modified condition. This finishing touch is absent during the 

 life-history of the early spring brood, but is supplied by the 

 heightened temperature at which the summer brood pupates ; 

 hence the difference in aspect between the two emergences. 

 But where does this store, so to speak, of partly-prepared 

 material reside 1 Weismann answers, " in the germ-plasm." 

 The constituent in question, or the antecedents thereof, exists 

 within the germ-plasm in a condition which allows of gradual 

 modification by heat, cold, or whatever the influence may be. 

 But inasmuch as it has not reached the specially susceptible 

 stage, the modification may become only slightly manifest, or 

 may even find no visible expression at all. Still it is there; 

 and inasmuch as it belongs to the germ-plasm, it forms 

 necessarily a part of the inheritance of the next generation, 

 and as such may be capable of still further advance in the 

 same direction ; this advance being of course limited by the 

 potency of the external influence and by the time during 

 which it has worked. We have here no reflection of somatic 

 change upon the germ-plasm, such as would be supposed to 

 take place under Darwin's pangenesis and similar theories, 

 but a common action upon the antecedents of the final 

 coloration, whether these antecedents are to be found in the 



