MODERN VIEWS ON EVOLUTION 181 



been cut off, sometimes produce young ones which have 

 a natural defect of the same part It is taken for granted 

 that these appearances are connected together in the 

 relation of cause and effect, and therefore afford a proof 

 that acquired peculiarities are hereditary.' The author 

 argues that cases of this kind are accidental, and he 

 points out that such defect of parts is apt to occur in 

 every species ; in man as well as in animals. He 

 points to the vast experiment due to 'our caprice' in 

 mutilating the ears and tails of domestic animals, and 

 to the effects of surgical operations upon man. What 

 remarkable results would be witnessed if such changes 

 were hereditary ! 



Professor Weismann was first led to the same con- 

 clusion as Dr. Prichard by constructing a theory of 

 heredity which seemed to him to explain the facts and 

 observations better than any which had been previously 

 proposed. But the theory did not include any mechanism 

 by which the transmission of acquired characters could 

 take place. Professor Weismann, believing that his 

 theory was in the main right, began to inquire for the 

 evidence on which the belief in such transmission is 

 based, and as soon as he commenced his inquiries the 

 evidence broke down in every direction. 



With Prichard it was otherwise, for the existing 

 theories seem to have been against him. Thus he 

 argues that his opponents ' seem to have derived their 

 opinion rather from some conjectural theory of genera- 

 tion, than from any facts which have appeared well 

 established ' ; and he goes on to contend that we know 

 so little ' that we are not authorized to reason from any 

 hypothesis on this subject '. 



He next deals with the statement 'that after any mutila- 

 tion or other artificial change has been repeated through 

 many generations, a sort of habit may be acquired, by 

 which the new state becomes as it were natural, and may 

 thus modify the race '. To this he replies that the evidence 

 of such habit could only be obtained by diminishing the 

 mutilation in progressive generations and comparing the 

 result ; whereas in all such cases the violence committed 



