SUMMARY OF THE WORK 327 



supply a definition that takes the matter beyond 

 the range of argument. 



And, inasmuch as the minds of the biologists 

 were now adjusted to the new Darwinian idea 

 that there is a wide range of variation in natural 

 forms, and that natural species are after all only 

 varieties that have separated a little farther, the 

 idea that the classifier might be mistaken in 

 ascribing specific difference to any pair of forms, 

 and that the physiological test of the production 

 of sterile hybrids might afford a final guide, was 

 not without its practical value, and made per- 

 haps not unnatural appeal to the more or less 

 befuddled classifiers themselves. 



And so long as cross-fertilization was effected 

 solely between forms of animal or p]ant life that 

 were found growing wild in the same region, 

 and were obviously not very distantly related, 

 it was hardly possible to present evidence of the 

 fertility of hybrids of true species that would 

 be convincing. 



The more fully the biologist grasped the phil- 

 osophical idea that the word "species" is after 

 all only a convenient formula to apply to a given 

 form rather for convenience of nomenclature 

 than as representing true and permanent dis- 

 tinctions, the more logically might he grasp the 

 dictum that any two forms that can interbreed 



