174 ACQUIRED CHARACTERS sec. 



This exposition is in direct contradiction to my views. 



But farther on Weismann makes some concession. He 

 says, "But although I hold it improbable that individual 

 variability can depend on a direct action of external influences 

 upon the germ-cells and their contained germ-plasm, because 

 — as follows from sundry facts — the molecular structure 

 of the germ-plasm must be very difficult to change, yet it is 

 by no means to be implied that this structure may not 

 possibly be altered by influences of the same kind continuing 

 for a very long time. Thus it seems to me the possibility is 

 not to be rejected, that influences continued for a long time, 

 that is, for generations, such as temperature, kind of nourish- 

 ment, etc., which may affect the germ- cells as well as any 

 other part of the organism, may produce a change in the 

 constitution of the germ -plasm. But such influences would 

 not then produce individual variations, but would necessarily 

 modify in the same way all the individuals of a species living 

 in a certain district. It is possible, though it cannot be 

 proved, that many climatic varieties have arisen in this 

 manner. Possibly other phenomena of variation must be 

 referred to a variation in the structure of the germ -plasm 

 produced directly by external influences. At present we 

 cannot decide upon this ; but this much may be maintained, 

 that influences which are mostly of variable nature, tending 

 now in one direction, now in another, can hardly produce a 

 change in the structure of the germ -plasm, and this is the 

 reason why the causes of inheritable individual differences 

 must be sought elsewhere than in these varying influences." 



..." 1^0 one has doubted," he says further, in reply to 

 objections made by Yirchow, " that there are a number of 

 congenital deformities, birth-marks, and other individual 

 peculiarities, which are inherited. But these are not acquired 

 characters in the above sense. True, they must once have 

 appeared for the first time, but we cannot say exactly from 



