DISTRIBUTION AND MIGRATION O^ UNE:ATA GROUP. I3 



is no criterion at all, although it has been shown in the discussion of the 

 sixth criterion that continuity and directness of individual variation or 

 modification may be of value in the determination of highways of dispersal. 

 The eighth criterion assumes, if I understand it correctly, a knowledge of 

 the center of origin and highways of dispersal previous to the beginning of 

 the study of the data to determine that center of origin. It certainly is 

 impossible to apply this to the genus Leptinotarsa , although it does assist 

 very directly in the solution by criterion No. 6. 



The ninth criterion, "direction indicated by biogeographical affinities," 

 seems to be a loose reiteration of the ideas expressed in No. 3, as applied 

 to a somewhat broader area. It is, however, a criterion of no value from 

 the standpoint of this group of animals. 



The tenth criterion, "direction of annual migration in birds" (Palmen) 

 has no bearing upon the present case. 



To sum up the evidence derived from the application of these criteria, it 

 appears that 1,2, and 3 point conclusively to southern Mexico as a center 

 of origin; 4 is shown to be of no value, and 5 is based, seemingly, upon 

 wrong conceptions and data. The important criterion, 6, points unmis- 

 takably to the same area as Nos. 1,2, and 3, while from criteria 7, 8, 9, and 

 10 we derive nothing of value. Our evidence clearly indicates that southern 

 Mexico is the center of origin or adaptive radiation of the genus Leptinotarsa. 

 There is nothing to even suggest an origin in South America, and we may 

 well surmise that like results will be obtained concerning other groups of 

 animals when adequately studied. 



The following criteria are adequate for determining the center of origin 

 or adaptive radiation without the introduction of any of doubtful value: 



(i) Location of greatest differentiation of a type. (Adams.) 



(2) Continuity and convergence of lines of dispersal. (Adams.) 



(3) Location of synthetic or closely related forms. (Allen.) 



(4) In some cases, location of dominance or great abundance of individ- 

 uals. (Adams.) 



These criteria cover fully all cases and are not open to the very serious 

 objections that may be advanced against the others. 



The distribution and dissemination of these beetles can be best considered 

 by groups of species, as we shall then be able to follow closely one line of 

 species differentiation at a time and examine the effect of the different environ- 

 mental complexes in controlling and directing distribution and dissemination. 



