INHERITANCE OF ACQUIRED CHARACTERS 103 



result of intra-uterine under-development, due to in- 

 sufficient nourishment, and is not necessarily due to an 

 inherent defect of the germ. 



(/) Environmental Influences on Germ-Cells. 



There are other cases similar to those just described, 

 where certain environmental influences, acting on the 

 individual, are held to yield decisive evidence of their being 

 inherited. To these belong the variations of certain 

 butterflies due to climatic conditions. For instance, 

 exposure of the Vanessa butterfly during its pupa stage to 

 cold or heat alters the colouring of the developing butter- 

 flies in accordance with the natural variety prevalent in the 

 northern cold or southern warmer region. Not only this, 

 but some of the progeny show a tendency in the same 

 direction. While this seems conclusive evidence against 

 Weismann, he none the less finds that even these cases are 

 not at all so simple as they at the first glance appear. First 

 of all, it is possible that the germ-cells are influenced by en- 

 vironmental changes along with the body harbouring them. 

 Furthermore, the variations resulting from the experiments 

 were not a completely new creation, but only showed a 

 tendency more or less towards the northern or southern 

 coloration of the butterflies. As in some cases it could 

 be shown that the changes induced by cold were nothing 

 but reversions to older phyletic stages of the same species, 

 it is not going too far to conclude that the influence of the 

 temperature did not in reality change the germ- plasm, but 

 only acted as a stimulus for the reappearance of certain sets 

 of older determinants still present in the germ-plasm. We 

 have here, then, the simultaneous influence of the external 

 conditions acting in the same direction on the wing deter- 

 minants of the parent pupa and of its germ-cells. 



The example of malnutrition of the factory worker quoted 

 already in the last paragraph may also be cited here. The 

 effects may be all due to harmful influences acting on the 



