iv weismann on variability 173 



Inheritance of Injuries and Diseases 



Weismann expresses himself concerning acquired characters 

 as follows : ^ " Acquired characters are universally understood 

 to be those which arise in consequence of the action of 

 external forces upon the organism, in contrast to those which 

 proceed from the constitution of the germ." To which it 

 might be objected, according to my views, that the germ also 

 may acquire characters and transmit them by inheritance, and 

 that it is, moreover, always affected by the condition of the body. 

 How far Weismann admits this will be discussed in the sequel. 

 Characters acquired during individual life Weismann describes 

 as transient, because, according to his view, they cannot be 

 transmitted by inheritance, " for it is obviously a consequence 

 of the theory of the continuity of the germ -plasm, that 

 characters can only be inherited when their rudiments are con- 

 tained in the germ-plasm, but that modifications which occur 

 in the developed body in consequence of external influences 

 must be limited to the organism in which they arise. The 

 latter must therefore be the case with mutilations, and with 

 the effects of exercise, or of the disuse of any part of the body. 

 "If then this is true, there is not only an end of all 

 Lamarckism, i.e. of the view which derives the modification of 

 species from the direct influence of the conditions of life, 

 especially from the increased or diminished use of particular 

 parts, but it becomes necessary to discover a new basis for 

 one factor of selection, namely, variability. For variability 

 has hitherto been attributed to the variable influences w^hich 

 act upon the organism without intermission. But if all the 

 influences which might make bodies individually different 

 have only a transient and not an inheritable effect, the 

 individual variations which form the material for selection to 

 work upon cannot arise in this way." 



^ Biolog. CentralUatt, loc. cit. 



