STAGES OF VITAL MOTION. 19 



tists to ascribe specific rank to insular forms differing in details utterly 

 inadequate for the diagnosis of widely distributed continental types. 

 Multiplicity of species does not signify that the land-snails of the iso- 

 lated valleys of the Hawaiian Islands are in a state of more rapid evolu- 

 tion than other mollusca, but that the characters of these segregated 

 groups are so uniform that systematists can readily define and distin- 

 guish them. Many very small species are known, but they are extremely 

 few in comparison with those of larger distribution, and with suggestive 

 frequency they present indications of approaching extinction.* 



The Significance of Mutations. 



The uniformity of such narrowly segregated groups is the same as 

 that of many of our varieties of domesticated plants and animals, the 

 history of which is also brief. We have, moreover, with these the oppor- 

 tunity of observing the further symptoms of the process of decline. 



As though to compensate for the want of access to the normal num- 

 ber of variations, those which occur become more and more striking, 

 and may even be more different from the parent form than the wild 

 species of the same genus are from each other. They have been said, 

 in other words, to * answer the definition of species. ' Professor De Vries 

 has courageously accepted the results of this reasoning and has equipped 

 his new Oenotheras with specific names and introduced them to the sci- 

 entific world as new members of the vegetable kingdom in regular stand- 

 ing, while the description of many other 'De Vriesian species/ is 

 threatened by some of our too-progressive naturalists. 



The inadequacy of natural or other forms of selection as an explana- 

 tion of evolution has become more and more appreciated, and has 

 decreased confidence in the Darwinian idea that species originate by 

 imperceptible gradations, impelled by natural selection. Professor De 

 Vries and his followers argue accordingly that species must originate by 

 definite and abrupt changes, and have set out to search the biological 

 field for instances to support this theory. But if the present interpreta- 

 tion of evolutionary facts and factors be correct the forms described as 

 'mutations' are not true evolutionary species, either actual or potential. 

 Mutations more fertile than the parent type have not been reported. 

 They do not arise through normal evolution, but are symptoms of 

 debility due to the absence of evolutionary opportunities; they are not 

 parts of an ascending series, but are obviously declining toward extinc- 

 tion. This difference of interpretation well shows the antithesis of static 



* Degeneration and extinction as the result of inbreeding has not been 

 suflBciently considered as an explanation of the dying-out of insular animals 

 protected from competition and other dangers of continental forms. There are, 

 for example, human remains on many Pacific islands uninhabited at the time 

 of their discovery by Europeans. 



