136 PROCEEDINGS OF THE ACADEMY OF [1899. 



snow-fields consists almost entirely of species which are either black 

 or very dark colored, although closely related species living amid 

 different surroundings may be brightly decorated. That this is true 

 in certain cases, as of the snow-inhabiting Canipodese of the Alps, 

 Deesoria glacialis and Degeeria nivalis, is well known to zoologists, 

 but the all but universality of the fact is not fully appreciatedy 

 except among entomologists who have studied Alpine and boreal 

 forms. As long ago as 1834 Frobel and Heer pointed out the 

 existence of this relation between the pigmentation of insects and a 

 snowy environment. They have compiled ('34, II, 97) tables 

 showing the increase of dark pigments among the representatives 

 of many species and genera of Coleoptera, Lepidoptera, Diptera, 

 Arachnida, etc., as they extend to and beyond the snow line on the 

 Alps or toward the north on the European continent. 



A related fact is that insects which mature and become active 

 during the winter in this latitude are likely to be black, or at least 

 dark colored, although closely related species which are active at 

 other seasons are much paler or brighter. This may be abundantly 

 verified in the minute Diptera and Campodea which frequent sunny 

 spots on the snows of late winter and early spring in the neighbor- 

 hood of Philadelphia, or by reference to a paper by Fitch ('51), 

 on the w^inter insects of New York, in w^hich about twenty species 

 of Campodea, Neuroptera and Diptera are described, every one 

 of which is whoUy or chiefly some shade of black. .Associated with 

 the " snow -worm " on the Malaspina Glacier was found a small 

 Podurian, Achorutes 7iivicola, also black; and in the neighborhood 

 of the glacier were collected a number of moths, flies and spiders, 

 which have been described respectively by Skinner, Johnson ('98) 

 and Banks ('98). So far as the colors of these have been noted, 

 they are confirmatory of the general fact stated above. 



It seems probable that the same causes which have stimulated 

 the formation of pigment in the Oligochieta also favor its production 

 in the Tracheata, and that some factor in a snowy environment lays 

 the brand of melanism upon all of the constituents of its inverte- 

 brate fauna. But an analysis of the physical and vital conditions 

 makes it evident that any one or several of five or six factors may 

 be the effective cause, and until some of these can be eliminated 

 by the conditions of experimentation it is almost idle to speculate. 

 Apparently the most important physiological result to the organ- 



