DARWIN AND PALEONTOLOGY 233 



ness the origin of what naturalists have been des- 

 ignating as species. 



In a lower horizon a cusp of one of the teeth, 

 for example, is adumbrated in shadowy form; in 

 a slightly higher horizon it is visible; in a still 

 higher horizon it is fully grown, and all paleon- 

 tologists have hitherto agreed to honor this final 

 stage by assigning to the animal which bears it 

 a new specific name. In the face of these con- 

 tinuous series of changes revealed by paleontol- 

 ogy the species and genera of Linnaeus break up 

 into the continuous chain of the " mutations of 

 Waagen," and for such progressive changes 

 Deperet has proposed the term " ascending mu- 

 tation." 



No theoretical conflict between the mutations 

 of Waagen and of De Fries. It will be shown 

 presently that a very considerable number, if not 

 all, of these slow origins are of a kind which arise 

 from internal causes (intrinsic causes, Williams) , 

 that is, in heredity. It is evident that if there do 

 exist hereditary predispositions to mutate in def- 

 inite directions, such predispositions may mani- 

 fest themselves very gradually, as in the " muta- 

 tions of Waagen," or under certain circum- 

 stances very suddenly, as in the lesser saltations 

 or "mutations of De Vries." Theoretically, at 

 least, there thus ceases to be any inherent conflict 

 between the hypotheses of " continuity " and 

 " discontinuity " ; the latter may represent an in- 

 tensified or accelerated state of the former. 



