LOGICAL POSITION OF THE ARGUMENT 241 



and so on. But these cuticular structures are non-cellulai", non- 

 living parts of the external investment of the body ; they are 

 made and re-made (after moulting), by the underlying living 

 skin. How then can they be interpreted in terms of modifica- 

 tion-inheritance ? The matter becomes even more difficult 

 when we consider cases in which the adaptiveness is in the colour 

 or markings of these inert cuticular parts. Weismann has 

 argued that, since there are some adaptive characters which can- 

 not be interpreted in terms of modification-inheritance, this 

 hypothetical factor need not be assumed in attempting to in- 

 terpret the origin of other adaptations, similar to the former, 

 except that the factor in question is not by the nature of the 

 case apparently excluded from having any connection with 

 them. 



But it cannot be said that this application of the " law of par- 

 simony " is altogether successful. It may recoil on those who 

 use it. It might be argued that there are some adaptive charac- 

 ters which cannot be readily interpreted in terms of natural 

 selection (as is implied in the appeal of some Neo-Darwinians 

 to " intra-selection/' " germinal selection," and so on), and that 

 therefore natural selection cannot be regarded as a generally 

 acting factor. Moreover, the Neo-Lamarckian is at liberty to 

 reply, that he does not regard the modification-inheritance 

 theory as applicable to all possible cases. 



Antecedent Probabilities. — If we turn to the antecedent 

 probabilities of the two beliefs, we find that the assumptions of 

 either side are equally improbable to the other, according to 

 their respective points of view. Thus, the supporters of the 

 negative answer may say that they cannot conceive how a par- 

 ticular local modification of the body can so affect the germ-cells 

 that, when these develop into offspring, the acquired character 

 shall re-appear. The supporters of the affirmative answer may 

 say that they find it impossible to believe in the selectionist in- 

 terpretation of many of the adaptive characters which make up 



16 



