GROWTH AND REPRODUCTION 53 



acquired by a parent can be transmitted to the 

 offspring, and neither the brawn of the blacksmith 

 nor the practiced brain of the thinker can benefit 

 the child by way of inheritance. This is a con- 

 tention which it is probably difficult for most per- 

 sons, unversed in questions of heredity, to accept. 

 It is a position which seems at first sight opposed 

 to experience and probability. But if an attempt 

 be made to give an unimpeachable example of in- 

 heritance of acquired characters, it will be found 

 singularly unsatisfactory and unconvincing. The 

 effects of use or disuse show no clear signs of being 

 transmitted. The same is true of the effects of 

 education. And if we turn to the study of mutila- 

 tions, we find no encouragement there. A religious 

 practice of the Jews has given us an example of a 

 mutilation of singular antiquity. More than a 

 hundred generations have been subject to circum- 

 cision, and yet no inherited influence is visible to-day. 

 Many examples of alleged transmission have, indeed, 

 been offered, but it seems as if none of them were 

 good enough to be considered decisive evidence. 

 For example, by exposing a certain variety of 

 salamander to the action of cold, there is induced a 

 retardation in the delivery of the salamander larvae ; 

 and this peculiarity is observed also in these larvae 

 when they have matured, and in their descendants 

 also, despite the fact that there has been no exposure 

 to cold. But Weismann would say to such a case 

 that the temperature which affected the original 



