90 HEREDITY [CH. 



The problem in heredity which has probably 

 given rise to more controversy than any other is that 

 alluded to more than once previously, of the inherit- 

 ance or non-inheritance of acquired characters, that 

 is, characters produced in the individual during its 

 life by the action of some sort of stimulus. Some 

 aspects of the question have already been considered, 

 and from what has been shown of the very definite 

 nature of the inheritance of germinal (inborn) cha- 

 racters, it will be understood why students of heredity 

 are increasingly disposed, a priori, to disbelieve in 

 the transmission of acquirements ; for if these were 

 transmitted to any considerable extent, this fact 

 must interfere, one would suppose, with the orderly 

 appearance in the offspring of the characters repre- 

 sented in the germ-cells of the parents. But at the 

 present time no treatment of heredity could be re- 

 garded as complete without some mention of the evi- 

 dence which has been adduced in favour of the 

 transmission of such characters. Unfortunately, the 

 evidence is almost always capable of interpretation 

 in more than one sense. The supporters of the belief 

 in transmission rely largely on indirect evidence, 

 especially on the difficulty of imagining any cause 

 of evolution in certain directions if the eflfects of 

 acquirement are excluded. A vast literature has 

 grown up around this question, of which only 

 illustrative examples can be given. In animals which 



