400 THE STUDY OF ANIMAL LIFE CHAP. 



of the same species all those that are due to age and sex, 

 and all those that can be shown to be modifications, the 

 remainder consists of inborn or germinal variations. 

 endogenous not exogenous in origin. We are sure 

 that many variations, both large and small, are trans- 

 missible from the organisms that first show them to their 

 descendants or to a certain proportion of their descen- 

 dants. In regard to the transmissibility of modifications, 

 however, the absence of convincing evidence has forced 

 most naturalists into a position of scepticism. This 

 scepticism is not strictly modern we find expressions of 

 it on the part of Kant, His, Pfliiger, Prichard, and others. 

 A few sentences from Galton (1875), whose far-sighted- 

 ness has been insufficiently recognised, may be quoted : 



" The inheritance of characters acquired during the Iifetim6 of 

 the parents includes much questionable evidence, usually difficult 

 of verification. We might almost reserve our belief that the 

 structural cells can react on the sexual elements at all, and we 

 may be confident that at the most they do so in a very faint degree 

 in other words, that acquired modifications are barely, if at all, 

 inherited in the correct sense of that word." 



But Weismann brought the discussion to a climax by 

 altogether denying the transmissibility of acquired 

 characters. Weismann's reasons for maintaining that no 

 acquired characters are transmissible are twofold, first, 

 because the evidence in favour of such transmission is in 

 the main anecdotal and is never cogent ; second because 

 the " germ-plasm," early set apart in the develop- 

 ment of the body, is from the nature of the case likely 

 to remain but little affected by the vicissitudes which 

 beset the body. Weismann was quite clear that bodily 

 modifications, due to peculiarities of function and 

 environment, might be very important for the individual. 

 What seemed to him unlikely was that their influence 

 could spread through the body so as to affect the repro- 

 ductive cells in a specific and representative way. Unless 

 they do so, they cannot be transmitted, and evidence of 

 this transmission is conspicuous by its absence. 



The precise point of the discussion as to the trans- 



