ASPECTS OF KINETIC EVOLUTION 237 



species. Teratism occurs whenever there is any accidental 

 deviation from normal developmental processes, whenever con- 

 ditions change beyond the practicable limits of normal adjust- 

 ment, and whenever the specific network of descent is abnor- 

 mally narrowed. Thus there are many kinds of teratisms, and 

 manj^ gradations between them and the other more normal kinds 

 of variations. 



Mutations are abnormal or teratic neisms which appear 

 abruptly in inbred or narrowly segregated groups, and which 

 require isolation in order to be preserved. Even when in- 

 duced by changes of environment, mutations are to be reckoned 

 as aberrations rather than as accommodations. 



This classification makes no claim to final completeness, since 

 still other kinds of intraspecific differences may be discovered. 

 No doubt the schedule will appear to some as already too 

 extensive and complex, but it will be evident that none of 

 the alleged kinds of differences can be left out of account with- 

 out misinterpreting one or more of the other groups of phe- 

 nomena. To overlook the facts of heterism would make hope- 

 less confusion under artism, topism and neotopism. To fail to 

 distinguish between neism and teratism is to mistake degenera- 

 tive mutations for examples of progressive evolution. 



Characters, in the morphological sense, cannot be classified 

 and catalogued as heterisms, artisms, or teratisms. There is an 

 intimate and even interchangeable relation between these differ- 

 ent kinds of differences. An individual may be larger than 

 others of its species, either as an inheritance or as a new vari- 

 ation, or because the conditions are favorable, or even because 

 they are new. Finally its greater size may be abnormal, or of 

 the nature of a monstrosity. The same character may thus 

 have great diversity of evolutionary significance. 



DIFFERENCES OF GROWTH-STAGES. 



Under this class of intraspecific differences it is proposed to 

 include all the general forms and growth-stages in which the 

 members of a species normally appear in any part of their life 

 history. Only in the lowest and most primitive groups do all 

 the separate, individual organisms belonging to the same 



