308 Habit and Instinct. 



were warmly discussed. Meanwhile, a different view of 

 the relation between the organism and its reproductive 

 cells came into prominence. With it the names of Francis 

 Galton in England and August Weismann in Germany are 

 'inseparably connected. Of late years it has gained the 

 approval of many, though by no means all, of our fore- 

 most biologists. This view, again in briefest possible 

 outline, is as follows: the fertilized egg of any many- 

 celled organism gives origin to all the cells of which that 

 organism is composed. In some of these, the reproductive 

 cells, germinal substance is set aside for the future con- 

 tinuance of the race; the rest give rise to all the other 

 cells of the body, those which constitute or give rise to 

 muscle, nerve, bone, glands and so forth. Thus there is 

 a division into germ-substance and body-substance. Germ 

 gives origin to germ, plus body; but the body takes no 

 share, according to Prof. Weismann, in giving origin to — 

 though it ministers to, protects, and may influence — the 

 germinal substance of the reproductive cells. 



The logical development of this theory led Prof. Weis- 

 mann to doubt the inheritance of characters acquired by 

 the bodily substance in the course of individual life, and to 

 examine anew the supposed evidence in its favour. If 

 brain-substance, for example, contributes nothing to the 

 reproductive cells, any modification it acquires during 

 individual life can only reach the germ through some in- 

 direct mode of influence. But does it ? does any modifi- 

 cation of the body-substance so affect the germ-substance 

 as to become hereditary? Prof. Weismann answers this 

 question by asserting that the evidence for the direct trans- 

 mission of acquired characters is wholly insufficient, and 

 by contending that, until satisfactory evidence is forth- 

 coming, transmission must not be accepted as a factor in 

 evolution. 



