82 THE GERM-PLASM THEORY 



doubtless are, the result of changes in the environ- 

 ment. Such changes in the nutritive stream may 

 affect some of these determinants favourably and 

 some unfavourably. Thus in that internecine 

 strife in which they are engaged, some will be 

 assisted to gain the mastery, whilst others have 

 impediments placed in their way. Such very briefly 

 is the theory of germinal selection ; and any one 

 who considers carefully what it means will see 

 that, through it, Weismann once more comes back 

 to that influence of external conditions upon the 

 germ which he set out, if not to deny, at least to 

 minimize. For if the vital units make up the germ, 

 and the vital units can be affected by the nutritive 

 stream, and this again may be altered by external 

 conditions, is it not clear that external conditions 

 alter the character of the germ, which is precisely 

 what Lamarck and Darwin claimed ? Let us 

 look at one example of this. Polyommatus fhltzas, 

 the " fire-butterfly," presents two forms, a north- 

 ern and a southern, with different colourings. 

 Now the colouring of the southern form can be 

 induced in the northern, by the action of a higher 

 temperature, showing 



" that the direct influence of higher temperature 

 affects the quality of the nutritive fluids in the 

 germ-plasm, and thereby at the same time the 

 determinants of one or more kinds of wing-scales 

 are caused to vary in all the ids in the same direc- 

 tion, in such a fashion that they give rise to black 

 scales instead of the former red-gold ones. It is 

 thus certain that there are external influences 



