RELATION TO ENVIRONMENTAL COMPLEXES. 55 



in a favorable habitat, it would be a remarkable coincidence that these 

 species, which represent steps in an orthogenetic specific differentiation, 

 should occupy habitats which are also steps in habitat differentiation. 



Additional evidence along this line is afforded by other species in this 

 group. Distributed over the South Mesa, the Escarpment, the North Mesa, 

 the Great Plains, and the eastern portion of the United States, is a series of 

 species that show the most perfect continuity, not only in their distribution, 

 but also in their geographical variations. We are also able to follow the 

 migrations of these species over different habitats. The species nmltitcs7iiata , 

 intermedia, and decemlineata present continuity in distribution and specific 

 differentiation over a wide area to an unusual degree. On pages i8 to 49 

 the data of the distribution of these beetles is given and discussed at length, 

 and it seems only too evident that the dissemination and specific differentia- 

 tion of the race in response to environment have gone hand in hand. So 

 continuous is the distribution and the geographical variation in these species 

 that their separation is diJB&cult. In this group, wherein continuity in dis- 

 tribution is indisputable, another process is also at work. At Toluca, Mexico, 

 there exists a species {rubicunda) which arises as an extreme variation 

 from niultitceniata. This species is able to maintain itself as a member of the 

 fauna at Toluca, and, in as far as can be determined from observation, it is 

 far less successful in the struggle for existence than the parent form with 

 which it lives. It has a very restricted distribution, owing to its depend- 

 ence upon a particular environmental complex, in direct response to which 

 it has perhaps arisen. At this same place, as also at others, another form 

 (species) arises as an extreme variation of multitceniata. This is the species 

 melanothorax , which is found in almost every generation of multitcsniata at 

 Toluca, although it is not able there nor at any other point in the habitat of 

 its parent species to become established as a member of the fauna. Evidently 

 it is ill adapted to the environment into which it is born. There are environ- 

 ments, however, to which it is adapted, but to reach these requires a numerical 

 strength sufficient to enable it to spread out ; and a species so ill adapted to the 

 habitat into which it is born that it can not maintain itself will not develop the 

 numerical and physical strength that is necessary to enable it to seek new and 

 more favorable habitations. The theory of ' * segregation in fittest environ- 

 ment ' ' could be of no use in the explanation of the early stages in specific dif- 

 erentiation and dissemination, as it is impossible to see how an " unadaptive 

 mutation ' ' (Davenport) is able to find its proper place in nature. If it is 

 unadapted, as in the case of melanothorax , does not the very fact of its 

 unadapted condition so hamper it in the development of that numerical and 

 physical strength necessary for any extensive movement that dissemination 

 would never occur ? It must always remain an ill-adapted member of the 

 fauna into which it has been born, unless by chance it is carried into some 



