142 ACQUIRED CHARACTERS SEC. 



in particular islands, such as those Wallace mentions, and 

 many others known to me, are certainly not to be considered 

 as due to selection, but in part at least are to be recognised as 

 stages of evolution in a definite direction, which I shall not 

 discuss here in detail. Thus Wallace himself, joint-discoverer 

 with Darwin of the principle of utility, says : " But this 

 hypothetical explanation of the form and veining of the wings 

 in the Celebes butterflies does not apply to other cases of 

 local modification. Why the species of the western islands 

 are smaller than those in the islands lying farther to the east, 

 why those of Amboina surpass those of Dschilolo and New 

 Guinea in size, why the tailed species of India begin to lose 

 these appendages in the islands, and on the shores of the 

 Pacific no longer show a trace of them, and why in three 

 different cases the females of the Amboinese species are less 

 gaily coloured than the corresponding females of the sur- 

 rounding islands these are questions we cannot yet attempt 

 to answer.". 



These are, therefore, characters whose utility in any case 

 cannot be proved, in which the determining influence of selec- 

 tion cannot be recognised are certainly acquired and inherited 

 characters. 



I can increase the number of these examples by many 

 others taken from this same group the butterflies ; cases in 

 which the variations determining the origin of species are so 

 small, so obviously in constant progress towards definite 

 directions of evolution, that their explanation by selection is 

 in fact absolutely excluded. 



IMPORTANCE OF THE STIMULATION OF THE NERVOUS SYSTEM IN 

 RELATION TO ADAPTATION AND THE ORIGIN OF SPECIES 



The reader will perhaps wonder that I did not assign a special 

 role from the beginning to the action of the nervous system 



