568 MERISTIC VARIATION. [part I. 



doubt whether the variations here detailed are such as go to the 

 building of Specific Differences (a doubt which, it must be granted, 

 does fairly attach to some part of the evidence), yet the existence 

 of sudden and discontinuous Variation, the existence, that is to 

 say, of new forms having from their first beginning more or less of 

 the kind of perfection that we associate with normality, is a fact 

 that disposes, once and for all, of the attempt to interpret all per- 

 fection and definiteness of form as the work of Selection. The 

 study of Variation leads us into the presence of whole classes of 

 phenomena that are plainly incapable of such interpretation. 



The existence of Discontinuity in Variation is therefore a final 

 proof that the accepted hypothesis is inadequate. If the evidence 

 went no further than this the result would be of use, though its 

 use would be rather to destroy than to build up. But besides this 

 negative result there is a positive result too, and the same Discon- 

 tinuity which in the old structure had no place, may be made the 

 framework round which a new structure may be built. 



For if distinct and "perfect" varieties may come into existence 

 discontinuous!)', may not the Discontinuity of Species have had a 

 similar origin ? If we accept the postulate of Common Descent 

 this expectation is hard to resist. In accepting that postulate it 

 was admitted that the definiteness and Discontinuity of Species 

 depends upon the greater permanence or stability of certain terms 

 in the series of Descent. The evidence of Variation suggests that 

 this greater stability depends primarily not on a relation between 

 organism and environment, not, that is to say, on Adaptation, but 

 on the Discontinuity of Variation. It suggests in brief that the 

 Discontinuity of Species results from the Discontinuity of Variation. 



This suggestion is in a word the one clear and positive indica- 

 tion borne on the face of the facts. Though as yet it is but an 

 indication, there is scarcely a problem in the comparison of 

 structures where it may not be applied with profit. 



The magnitude and Discontinuity of Variation depends on 

 many elements. So far as Meristic Variation is concerned, this 

 Discontinuity is primarily associated with and results from the fact 

 that the bodies of living things are mostly made up of repeated 

 parts — of organs or groups of organs, that is to say, which exhibit 

 the property of "unity," or, as it is generally called, "individuality." 

 Upon this phenomenon depends the fact that Meristic Variation in 

 number of parts is often integral, and thus discontinuous. 



The second factor that most contributes to the Discontinuity of 

 Variation is Symmetry, manifesting its control in the first place 

 directly, leading often to a result that we recognize as definite and 

 perfect because it is symmetrical. 



But besides this direct control that we associate with Symmetry, 

 other erfects greatly contributing to the magnitude of Variation 



