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Show 302 ences which are the natural outgrowth of the modifications of food and climate produced during ages of separation. The primary causes of differentiation, however, appear to be of a geological rather than meteorological nature; the climatic causes operating as a factor, which subsequently appeared as a necessary sequence of the termination of the Glacial period. This interesting fauna obviously possesses characteristics which at once attract attention and induce study in determining the great causes which have operated to produce such a remarkable distribution of life. The observations of Dr. A. S. Packard, jr., on the geographioil distribution of the moths of Colorado, have established the fact of the existence of a law of increase in the length of certain peripheral parts for western species. Professor 8. F. Baird and Mr. J. A. Allen have shown that the same law of variation obtains in regard to the birds of North America. Dr. Packard states that the moths of the Pacific coast are generally larger than those of the Rocky Mountains, and almost invariably larger than the same species from New England and Labrador; and he considers the difference in growth to be due to the more genial climate and greater rain- fall of the western coast. While a difference of temperature and relative humidity exercise an influence over the growth and. coloration of insects of sufficient importance to be accepted as a factor affecting their development, this is probably also due in some degree to the prevalence of high winds, which have operated to produce greater development of the wings as a natural result of greater habitual exertion in combating them; and perhaps also to the acquisition of nomadic habits rendered necessary in a comparatively barren region, where vegetation is not as exuberant as in more civilized localities which have been nnder cultivation for a long time. The swarming grasshopper, Caloptenus sprelus, which by its periodic migrations, extending over 20° of latitude, proves so destructive to our agricultural interests, singularly confirms this law. This insect, having been accustomed to sustain long continued flights, has consequently developed more powerful wings than the same species which occurs in the Eastern States, in no respects differing from the western insect except in its habits of more local residence and shorter wings. As regards variation of color, I believe that species from a cold climate, or where there is an unusual absence of sunshine, will be characterized by the predominance of somber- hued types, or will present a bleached appearance when compared with specimens from a warmer climate. In the arctic regions, the short summers seem poorly adapted to the development of vivid colors, and we accordingly find few of the beetles known to occur there which are remarkable for bright colors; the same fact is noticeable in those obtained from the western mountains above the timber- line. A notable exception to this rule, however, is Carabus vietinghovii, Adams, from Hudson Bay; a northern insect, which may well vie with tropical species in brilliancy of color. This insect may be regarded as an example of the effect of a short period of almost constant sunshine, such as prevails during the summer in this part of the circumpolar regions. More complete data regarding variation in color should be collated before the facts can be regarded as establishing any conclusive law of melanism affecting species inhabiting separate zoological zones. Although I have not had an opportunity to institute extensive comparisons between collections from different mouutain- regions, observations made in the West daring several seasons have convinced me that, in general, the animal kingdom existing at great elevations is as dwarfish as the vegetable kingdom. This is especially apparent in the Coleoptera, Hemiptera, Orihoptera, Xeuroptera, and Arachnida, the types of which are usually represented by the smaller species. But this does not appear to be the case with the Lepidoptera, Hymenoptera, and Diptera, which furnish large- sized forms, especially prominent among which are the Papilionidce, Argynnides, Apid&} and Taba-nidai. The Coleoptera show a remarkably uniform distribution over Colorado, Oregon, and the circumpolar regions. So apparent is this, that a species obtained at a great elevation from Colorado may be looked for with almost certainty in these other localities. Further research will probably verify this distribution in other orders. The collection of spiders exhibits a striking resemblance to those found in the barren grounds of the far north, by Captain Back, R. N., whose collections contain four genera; all of which occur above timber- line, and have the same habits of living in the ground and rocky crevices, incumbent in regions of stunted and scant vegetation. Among the grasshoppers obtained by Captain Back, we find Acridium sulphureum, Pal. de Beanvoix. ( Tomonohis 8ulphureu& j Fabr.), which is found in the mountains of Colorado; and although it has not yet been obtained above timber- line, it may be accepted as a true resident of that desolate region. From the Fauna Boreali- Americana, we have Locusla leuco8toma, Kirby ( Caloptenus bivittalus, Uhler), found by Sir John Richardson, latitude ( 55° north, and which is also a western species. Among other mountain Orthoptera, the genus Pezottitix should be regarded as a typical alpine form ; two species having been found at an elevation of 13,000 feet. The Hymenoptera were among the insects earliest observed above timber- line. Fremont records the presence of bumblebees amidst snow and ice on the summit of the |
