26 The Mechanism of Evolution in Leptinotarsa 



do not occur in the Antilles, and, as far as is known, are distributed from the 

 northeast corner of South America northward through Central x\merica and 

 into North America as far as southern Canada. It has been difficult to deter- 

 mine what names should be applied to many of the forms found in nature, due 

 to the fact that for most of the species the material existing in museums is 

 meager, often inferior in quality and data, and, moreover, the taxonomic 

 descriptions are based upon dead and often upon only a few badly preserved 

 specimens. Because of post-mortem changes in color, systematic descriptions, 

 especially of the colors, are in the main incorrect for the living animal, and 

 since students of the physiology of evolution are only interested in living 

 organisms, I have given for all species used in this report diagnoses from the 

 living material. 



These species are specific kinds of living substances, each with its specific 

 qualities, which, in each, are genetically reproduced true to type, generation 

 after generation, in experimental cultures and in nature. To prevent confusion 

 and to make clear the exact nature and source of my materials, I have presented 

 in this report as complete a taxonomic description as is at present possible of 

 each of the different species in the lineata group, their juvenile stages, distribu- 

 tion, and ecology, and such discussion of their life-histories, distribution, and 

 other activities as is necessary to an understanding of the work described herein. 



The descriptions are, as far as possible, compiled from the original sources, 

 and I have given the original descriptions as printed and supplement each 

 with a description of the living material that has passed through my hands. 

 Many questions concerning the nomenclature have presented difficulties in the 

 effort to arrive at a just settlement of the complicated taxonomic situation. 

 For example, four species (L. panamensis n. sp., L. guaiemalensis n. sp., L. 

 diversa n. sp., and L. undecimlineata Stal) are distinguished with difficulty 

 as far as museum specimens are concerned, but they are definite, clearly dis- 

 tinguishable organisms when alive, especially when followed through their life- 

 histories, and when crossed their differentiating characters are sharply alter- 

 native in behavior. The most conspicuous differences between the four species 

 are found in the larval stages, and in their habits, distribution, and ecological 

 relationships. Stal (1858) and in 1862 in his Monographic des Chrysomelides 

 de L'Amerique, described L. undecimlineata, and as far as his description is con- 

 cerned it would apply fairly well to the imagines of either of the forms, and as 

 far as the distribution given by him is concerned it would also apply to any one 

 of the four found, but the one which I have designated L. undecimlineata is 

 more probably the one which Stal had, and it is certainly the one which has in 

 later years most often been so designated. Much later, Duges described the 

 larvae and life-history of a form from Guanajuato, Mexico, which he believed to 

 be L. undecimlineata Stal, but his description is of the juvenile stages of the 

 form that is here recorded as L. diversa. Of the two forms, that which has the 

 wider distribution as given by Stal I have called L. undecinnlineata, and this is 

 in accord with the identifications given to many museum specimens. In the 

 Baily Collection in the British Museum there is a specimen labeled, " Coll. 

 Baily," named by Stal " L. 11 lineata," "Type Stal 194"; "Mexico," that is 

 the same form that I have called L. 11 lineata so that there can be little doubt 

 but that the determination is correct. The other I have called L. diversa, 

 although many specimens of this species exist in collections and are labeled 



