INDIRECT EQUILIBRATION. 449 



other hypotheses. While the production of neuters among 

 bees and ants, is inexplicable as a result of direct adaptation, 

 natural selection affords a feasible solution of it. The various 

 differences that accompany difference of sex, sometimes 

 slight, sometimes very great, are similarly accounted for. 

 As before suggested (§ 79), natural selection appears capa- 

 ble of producing and maintaining the right proportion of 

 the sexes in each species ; and it requires but to contemplate 

 the bearings of the argument, to see that the formation of 

 different sexes may itself have been determined in the same 

 way. 



To convey here an adequate idea of Mr Darwin's doctrine, 

 in the immense range of its applications, is of course impos- 

 sible. The few illustrations just given, serving but dimly to 

 indicate the many classes of phenomena interpreted by it, 

 are set down simply to remind the reader what Mr Darwin's 

 hypothesis is, and what are the else insoluble problems which 

 it solves for us. 



§ 166. But now, though it seems to me that we are thus 

 supplied with a key to phenomena which are multitudinous 

 and varied beyond all conception ; it also seems to me that 

 there is a moiety of the phenomena which this key will not 

 unlock. Mr Darwin himself recognizes use and disuse of 

 parts, as causes of modifications in organisms ; and does this, 

 indeed, to a greater extent than do some who accept his 

 general conclusion. But I conceive that he does not re- 

 cognize them to a sufficient extent. While he conclusively 

 shows that the inheritance of changes of structure, caused by 

 changes of function, is utterly insufficient to explain a great 

 mass — probably the greater mass — of morphological pheno- 

 mena ; I think he leaves unconsidered a mass of morphological 

 phenomena that are explicable as results of functionally- 

 acquired modifications, transmitted and increased, and which 

 are not explicable as results of natural selection. 



By induction, as well as by inference from the hypothesis 



on 



