Introduced species tend to vary much more than in their native lands. Children born of British, German, or French parentage become in the States slightly taller than their parents; the soldiers of the United States Army during the Civil War of 1861-05 were found, by measurements made on 1,110.000 individuals, to average taller than those of the British Army.
Dr. Bumpus has critically examined and meas ured over 1700 eggs of the English sparrow, one half from England and the other half collected at Providence. R. I. He found that the eggs of the new or American race or breed vary much more than the European, differing in being smaller and of a strikingly different shape, being more rounded, and with a greater amount of colo• variation. His measurements of the European periwinkle (Littorine littorce), 3000 from Eng land, and 3000 from New England, afforded shni lar results. Since its introduction, about 1855, into the Bay of Chaleurs and its rapid spread along the coast to New York. this little mollusk has undergone a transformatio» adapting it to the different conditions of our northeastern eoast. it has become more elongated, lighter in weight, more bulky, and the color-markings are less pronounced. Also large collections, in some eases 1000, from Casco Bay, Wood's Hole, Sea eonnet, Newport. and Bristol, were found to present constant variations at each locality, the curves of variation exhibited on the charts prepared by Or. Bumpus tieing different for eaell st, it is with a European land-snail (Helix nemeralis) introduced within a few years into Lexington, Va. In Europe this is an exceedingly variable species, but already of the t25 Virginian varieties found by Mr. Cockerel], 67 arc new nd unknown in Europe.
hut by far the strongest and clearest evidence of the means by which species arc originated are afforded by Dr. .1. A. Allen in the case of our _American birds and mammals, his results having based on prolonged studies made upon :t vast number of specimens front different localities. Our birds are found in passing from the Atlantic to the Pacific coast to vary in gen eral size, in the size of the peripheral parts (wings, etc.), and in color, thus varying with latitude or longitude. There is all increase in size from the south northward, not only in in dividuals, butt generally, though there are some exceptions. The largest species of each genus and family are northern, as in the cases of the fox and wolf, the latter being one-fifth larger in Alaska than are southern species of their kind. In the case of those birds which breed from New England to Florida, the southern ones are small er and differ in color. Mammals and birds, in their southerly examples, have larger cars and feet, and the cattle have larger horns. The
hares have less furry ears and naked soles; the sage-brush hare has longer ears southward; so with the large long-eared `jack-rabbit.' In birds hill, claws, and tail are larger in southern species and all the largest-billed birds live in the tropics. This, however, is to be observed in sparrows, blackbirds, crows, thrushes, wrens, and war blers, in the quail, meadowlark. and flicker. In Florida, forms with slender bills common to that Stale and to the North have beaks still more slender, longer, and decurved. Those with a short conical bill have thicker and longer bills than their northern relatives, though the birds themselves are smaller. It is so with the tail—the size of the body is the same as in the North, while the tail is proportionately larger and longer.
The color in mammals, as the red changes in going southward from pale yellow or fulvous to rufous. Except three species, all squirrels living north of Mexico have the lower parts of the body white, while those inhabiting tropical Mexico have the lower parts fulvous, deep golden, orange, or even dark brownish-red. In birds the colors are so much stronger and darker in southern forms that they might with their smaller size and larger bills he regarded as distinct species. The blue-jay, cardinal, and other birds have, in the South, a more brilliant and intense hue; some species are mere black and red. In crossing from the Atlantic to the Pacific coast, Allen observes that there are three phases of color. On the Atlantic coast the birds are bright and strongly colored: on the great plains they are pallid. owing to the dryness; and on the humid, heavily wooded Pacific coast the hues are deep-colo•ed or piceous, both in lords and mammals.
The same obtains in the Old World. The marsh-tit of Europe in warm, rainy regions has its browns intensified; in dry, sandy districts the plumage is paler: in the Arctic regions it varies in paleness, and in Kamchatka it is al most white (Dixon). The birds of the Gahipagos Islands differ from their nearest allies of the South American mainland in their larger hills, shorter wings, longer tails, and darker colors.
Besides this each of these islands has its local species or varieties, which do nol pass from one island to the others.
.Many other examples could he given, but enough has been stated to prove that in the past, as well as at present, changes in climate have hail an all-powerful inthience in the origination of species. 'l'o this factor, together with migra tion and geographical isolation, we may attribute a very large proportion of the known species of plant and animal life, and also the raves of man kind.