226 DARWINISM AND THE PROBLEMS OF LIFE 



particular direction. And when the same stimulus is 

 said to weaken in one case and strengthen in another, 

 we shall do best to discard an explanation that is 

 unworthy of the name. 



It might still be said : We admit that the chief 

 postulate of the Lamarckian principle has never been 

 proved, but that is because we know so little about the 

 conveyance of stimuli in the body. Still, the principle 

 has one advantage. It unites a large number of cases 

 under a single head. Thus we trace all the cases of 

 falling to terrestrial magnetism without knowing its real 

 nature. 



But it is precisely the element which gives any value 

 to such a concentration the embracing of all falls that 

 we observe under one law that is lacking in the 

 Lamarckian principle, which always leaves gaps that 

 it cannot explain. And apart from the fact that the 

 principle cannot explain the origin and transformation 

 of the organic world as a whole, it proves useless even 

 in small groups of cases, and it has to leave gaps in 

 those where its action seems most probable, such as the 

 co-adaptations. 



There is only one phenomenon in the organic world of 

 which selection does not give an entirely satisfactory 

 explanation. I mean the rudimentary organs. But 

 even here the Lamarckian principle is of no use to us, 

 as it cannot have acted in many of these cases, and so 

 we know that rudimentary organs may be brought about 

 without its aid. There are some in the coat of insects ; 

 I need only recall the degenerated wings of the orgyia, 

 which consist mainly of shell. In this case the inactivity 



