VARIATION IN SPACE AT PRESENT EPOCH 137 



nature, certain species vary very little, while 

 others are subject to a more or less wide poly- 

 morphism, which is sometimes even excessive. 

 It is this maximum of variation observed in a very 

 small number of groups which has always been the 

 chief argument used by the champions of the trans- 

 formist hypothesis in demonstrating the variability 

 of species. We have seen Neumayr apply this 

 consideration successfully to a few types of land 

 Molluscs, the Melanopsis, the Iberus, and theAchatin- 

 ella. Closely analyzed, nearly all living species can 

 be sub-divided into a certain number of forms, or, if 

 you will, of sub-species. Certain nomenclators have 

 unfortunately thought of separating these under 

 distinct names, which no longer permit the natural 

 links with the parent species to be recognized. Of 

 these forms, arranged according to certain definite 

 modes of variation, some are produced on the spot, 

 that is to say, almost everywhere and in the same 

 localities as the typical species; and these are the 

 varieties. The rest are confined to certain regions, 

 and offer still more interest than the first, because 

 we must see in them the result of the special action 

 of the general surroundings ; these are the local 

 or regional races. But it is important not to lose 

 sight of the fact that these groups of forms which 

 constitute, perhaps, the most real and the most 

 striking of all natural classifications are linked 

 to a typical species, more largely conceived and 

 bounded, and acting, so to speak, the part of a 

 centre of radiation to all these forms. Do these 

 great species, termed, not always correctly, Linncean 

 species, pass one into the other by gradation, as 



