184 MICHIGAN SURVEY, 1908. 



may be numerous centers of dispersal in wide ranging forms. It should 

 also be again stated that centers of dispersal while not necessarily 

 centers of origin, are likely to become such with age, particularly if 

 favored by diverse environmental conditions. 



It is desirable to understand clearly what is meant by criteria. As 

 understood by the writer, they indicate the kinds or convenient classes 

 of evidence to which we may turn for suggestions and proof as to the 

 origin and dispersal of organisms. Their value is largely relative, so 

 that they vary much in value, and in their application to various groups. 

 In some cases a criterion may have gi*eat weight, while in another 

 taxonomic or ecologic group it may have no value or so little as to be 

 merely suggestive. Each case must 6e tested on its oion merits. The 

 main advantage of criteria is the definite form in which they present 

 the problems and in the deflniteness which it gives to such inquiries 

 as to origin. The number of criteria needs to be greatly increased 

 by the formulation of those restricted to groups of peculiar taxonomic 

 oi- ecologic character. It should be clearly emphasized that it is the 

 convergence of evidence from many criteria which must be the final 

 test in the deterhiination of origins rather than the dependence upon 

 any supposedly absolute criterion. 



The development of criteria has been largely along taxonomic lines, 

 because taxonomy has been based largely upon structural characters 

 rather than upon the convergence of all kinds of affinities and evidence. 

 For this reason ecological criteria have been largely overlooked. With 

 their increase in number, certain origins and dispersals may be estab- 

 lished which otherwise could not be determined. 



It should be understood that the breeding range only is of fundamen- 

 tal value in the use of criteria, in the determination of origins and the 

 centers of dispersal. Of course only natural dispersal is considered 

 when criteria and natural centers are involved. Dispersal as influenced 

 by man has peculiarities of its own which have not yet been carefully 

 formulated. Species introduced by man may thus secure many new 

 centers of dispersal. 



Aside from historical and paleontological evidence the following 

 criteria, may be listed as those which will probably be of value in the 

 study of beetles. They have also furnished the basis for the determina- 

 tion of centers of dispersal and origin of the North American beetle 

 fauna. 



1. Location of great or maximum taxonomic differentiation of a type 

 or types. 



2. Location of synthetic, primitive or closely allied taxonomic forms 

 or groups possessing convergent aflflnities. 



3. Location of maximum size of taxonomic forms or groups. 



4. Continuity and convergence of lines of dispersal. 



5. Direction indicated by seasonal appearance; vernal suggesting 

 boreal or montane origin, and aestival as austral or lowland derivation. 



6. Direction indicated by continiuity and directness of individual 

 variations or modifications along highways of dispersal. 



7. Location where the succession of beetle associations or societies 

 reaches the relative equilibrium of a climax association or formation. 



