, ( xcvii ) 
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 
Clirysoplmmis plilaeas, 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 AYeismann 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. AVe 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 
PROG. ENT. SOC. LOND., V. 1910. G 
