MODIFICATION OF PASSIVE PARTS 77 



Weismann's view are mostly based on a misunderstanding ; in 

 regard to the transmission of instinct, we have seen that it wholly 

 faUs in respect of one great category of instincts — ^those which 

 manifest themselves only once in the course of the individual 

 life ; while an explanation alike more rational and more in har- 

 mony with what we know of the process of organic evolution in 

 general is furnished by natural selection. 



But even were we to suppose the impossible, and to grant the 

 accuracy of the Lamarckian theory in certain cases, there would 

 still remain entire categories of cases to which it cannot be 

 applied. These cases are those which concern the modification 

 of purely passive parts of the organism — the colour, the skeleton 

 of the arthropods in its various parts, etc. — and also the modifi- 

 cation of non-passive organs in the sterile members of a species 

 — ^for instance, in worker ants. 



The passive, purely morphological parts of the organism are 

 useful by their mere presence, and not by any active assistance 

 they render to the animal. Their variation cannot, therefore, 

 be explained as a result of use or disuse, since they are by their 

 nature entirely inactive. Such variation must be due solely to 

 natural selection. And if natural selection is thus capable of 

 transforming entire parts of the organism without the co-opera- 

 tion of any other factor, why, as Weismann asks, should we 

 restrict this capacity of natural selection to the purely passive 

 parts ? The active parts of the organism play a role consider- 

 ably more important in the struggle for existence ; and as the 

 conditions of that struggle are governed by the law of natural 

 selection, it is only rational to suppose that law to determine 

 the variation of the active as well as of the passive parts of the 

 organism. 



The degeneration of the wings of the worker ants is an example 

 of a change effected in an active part of the organism in a caste 

 which is sterile, in which, consequently, the transmission of 

 variations resulting from use and disuse is excluded. The wings 



