546 GEOLOGICAL SURVEY OF THE TERRITORIES. 



size southward, though his law of increase in the length of certain pe- 

 rii)heral parts westward also obtains in the Lepidoptera. The increase 

 of size westward, as seen in the table on p. 541, is of course equivalent lo 

 the well-known southward increase of size in insects ; though in a few 

 species the Coloradian and Oalifornian examples are larger than Flori- 

 dan or Texan insects of the same species. 



The Esquimaux of the Pacific coast show the effect of the difference of 

 climate, being much taller and larger than the stunted Greenland and 

 Labrador Esquimaux. Mr. W. H. Dall, in his "Alaska," remarks that 

 "the average height of the Orarians [Innuit, Aleutians, and Tuski], 

 except among the stunted tribes of the extreme north, will average as 

 great as that of their Indian neighbors." Even the Avhite inhabitants who 

 have moved to California from the Eastern States are said to find the 

 climate more favorable to health than in the Atlantic States. Cultivated 

 fruits are well known to grow larger and more luxuriantly in the Pacific 

 States than in the Atlantic, whence they have been brought. 



As regards the causes of these climatic changes, I find I have, with- 

 out having previously read Mr. Allen's valuable chapter on this subject 

 {loc. cit., 239), written the foregoing remarks on the relation of the climatic 

 variation of these insects to this temperature and humidity of the region 

 they inhabit, which agree with his views. Of the insects above mentioned, 

 Phisia HochenwartM and Agrotis Islandiea are the clearest examples (1) 

 of the increase of size westward and southward; (2) increase in length of 

 peripheral parts westward; (3) brighter, deeper colors westward; {4iAgro- 

 Us Islandiea) of brighter, more reddish colors in Pacific-coast specimens 

 than in those from the more elevated portions of the Eocky Mountains, near 

 the snow-line, where the winters are arctic, i. e., cold and dry, those from 

 the Alpine summitsof the interior being bleached. This law should not 

 be confounded with that established by the ornithologists, which refers 

 to the bleached appearance of individuals from the dry, hot plateau of 

 the interior, or middle zoological province of Korth America. These 

 facts in the geographical distribution of insects, though they can hardly 

 be called laws until confirmed by a greater number of data drawn trom 

 all orders of insects, yet illustrate, to my mind, how far climatic 

 variation goes as a factor in producing primary differences in faunas 

 within the same zone of temperature. Varietal, and, in some cases, spe- 

 cific, differences may have arisen in Asia and Europe and in America, 

 from the climatic causes above stated ; but these must have been largely 

 Inoperative in causing, for example, the present wide distribution of the 

 circumpolar species. Here continuity of land, geological and not climatic 

 causes, alone came in as a factor. And so, on the other hand, in account- 

 ing for the species and types of genera, distinguishing faunas in zones 

 of similar temperature, geological causes have been the main factor 

 in their production. For example, we cannot explain the similarity 

 between the insect-fauna of the Pacific States and Colorado, and that 

 of Eastern Europe and Central Asia without supposing the original 

 migration of those identical generic forms from a Mesozoic and Tertiary 

 continent in the arctic region, and their preservation through similar 

 climatic and physical causes in their present areas. 



In an essay on the geographical distribution of the FhalwnidcG of 

 California,* I divided the phalsenid fauna into four groups. To the 

 second of these groups, embracing species of genera found in Southern 

 and Eastern Europe and Western Asia and Asia Minor, can be added 

 the following species (which live in part both in Colorado and California) : 



^American Naturalist, vii, 453, 1873. Proceedings Bost. Soc. N. H., Jan., 1874, xvi, 13. 



