In birds the bill especially, but also the claws and tail, is larger in the south. In passing from New England southward to Florida the bill in slender-billed forms becomes larger, longer, more attenuated, and more decurved; while in short-billed forms the southern individuals have thicker and larger bills, although the birds themselves are smaller. The remarkable changes and gradations of color in birds in different parts of North America are very instructive, and the important results obtained by American ornithologists form an interesting chapter in zoology. The evidence would convince the most sceptical of the difficulty of distinguishing between Linnæan species. It is not surprising to find in this connection a leading ornithologist exclaiming, “if there really are such things as species.” The differences here noted are mainly from east to west. We may briefly review here a few striking cases selected from Coues’s “Key to North American Birds.” The flicker, or golden-winged woodpecker (_Colaptes auratus_), has a wide distribution in eastern North America. It is replaced in western North America (from the Rocky Mountains to the Pacific) by _C. mexicanus_. In the intermediate regions, Missouri and the Rocky Mountain region, the characters of the two are blended in every conceivable degree in different specimens. “Perhaps it is a hybrid, and perhaps it is a transitional form, and doubtless there are no such things as species in Nature.... In the west you will find specimens _auratus_ on one side of the body, _mexicanus_ on the other.” There is a third form, _C. chrysoides_, with the wings and tail as in _auratus_, and the head as in _mexicanus_, that lives in the valley of the Colorado River, Lower California, and southward.