a northern origin; and the fact that some are circumpolar in their distribution while most of the others (especially among the mammals) have congeneric Old World allies further strengthens the theory of their northern origin. Not only do individuals of the same species increase in size toward the north, but the same is true of the species of the different genera. Again, in the exceptional cases of increase in size southward, the species belong to southern types, or, more correctly, to types having their center of development within or near the intertropical regions, where occur not only the greatest number of the specific representatives of the type, but also the largest.

For more detailed illustration we may take three families of the North American Carnivora-namely, the Canidæ (wolves and foxes), the Felida (lynxes and wild-cats), and the Procyonidæ (raccoons). The first two are to some extent cosmopolitan, while the third is strictly American. The Canidæ have their largest specific representatives the world over, in the temperate or colder latitudes. In North America the family is represented by six species," the smallest of which, speaking generally, are southern and the largest northern. Four of them are among the most widely distributed of North American mammals, two, the gray wolf and the common fox, being circumpolar species; another, the Arctic fox, is also circumpolar, but is confined to high latitudes. The three widest-ranging species-the gray wolf, the common fox, and the gray fox-are those which present the most marked variation in size. Taking the skull as the basis of comparison, it is found that the common wolf is fully onefifth larger in the northern parts of British America and Alaska than it is in northern Mexico, where it finds the southern limit of its habitat. Between the largest northern skull and the largest southern skull there is a difference of about 35 per cent of the mean size! Specimens from the intermediate region show a gradual intergradation between these extremes, although many of the examples from the upper Missouri country are nearly as large as those from the extreme north.

The common fox, though occurring as far north as the wolf, is much more restricted in its southward range, especially along the Atlantic coast, and presents a correspondingly smaller amount of variation in size. The Alaskan animal, however, averages about onetenth larger than the average size of specimens from New England.

a The gray wolf (Canis lupus [=C. occidentalis and allied forms]), the prairie wolf (C. latrans [now treated as a group of a dozen or more closely related species and subspecies]), the Arctic fox (Vulpes lagopus [now separated into several forms]), the common fox (V. alopex [=V. fulvus and numerous related forms]), the kit fox (V. velox [now subdivided into several forms]), and the gray fox (Urocyon virginianus [=U. cinereoargenteus, with a dozen or more subspecies]).

In the gray fox, whose habitat extends from Pennsylvania southward to Yucatan, the average length of the skull decreases from about 5 inches in Pennsylvania to considerably less than 4 in Central America a difference equal to about 30 per cent of the mean size for the species.

The Felidæ, unlike the Canidæ, reach their greatest development, as respects both the number and the size of the species, in the intertropical regions. This family has but a single typical representative-the panther (Felis concolor)-north of Mexico, and this ranges only to about the northern boundary of the United States. The other North American representatives of the family are the lynxes, which, in some of their varieties, range from Alaska to Mexico. They form, however, the most northern as well as the most specialized or “aberrant" type of the family. While they vary greatly in color as well as in the length and texture of the pelage at different localities, they afford a most remarkable exception to all laws of variation in size with locality; for a large series of skulls, representing localities as widely separated as Louisiana, northern Mexico, and California on the one hand and Alaska and the Mackenzie River district on the other, as well as various intermediate localities, reveals no appreciable difference in size throughout this wide area. The true cats, however, as the panther and the ocelots, are found to greatly increase in size southward or toward the metropolis of the family. The panther ranges from the Northern States southward over most of South America. Skulls from the Adirondack region of New York have an average length of about 7 inches, the length increasing to 83 in Louisiana and Texas, from beyond which points there is lack of data. The ocelot (Felis pardalis) finds its northern limit near the Rio Grande of Texas, and ranges thence southward far into South America. The average size of Costa Rican examples is about onefifth greater than that of specimens from the Rio Grande.

The Procyonidæ are chiefly represented in tropical America, a single species-the common raccoon (Procyon lotor)-being found in the United States, and thence northward to Alaska [=British Columbia. Here again the increase in size is southward or toward the metropolis of the family-Pennsylvania specimens averaging about one-tenth smaller than Costa Rican examples.

The common otter (Lutra canadensis) affords another example of increase in size southward among our Carnivora, although belonging to a family essentially northern in its distribution. The otters, however, form a distinct subfamily, which attains its greatest number of species in the warmer regions of the earth, and hence offers not an exception to but a confirmation of the law of increase toward the center of distribution of the group to which it belongs.

Instances of increase in size northward among the Carnivora of North America are so generally the rule that further space need not be taken in recounting examples in detail. It may suffice to state that the badger (Taxidea americana), the marten (Mustela americana), the fisher (M. pennanti), the wolverine (Gulo luscus), and the ermine (Putorius ermineus [= longicauda, cicognanii, noveboracensis, etc.])-all northern types-afford examples of variation in size strictly parallel with that already noticed as occurring in the foxes and wolves.

To refer briefly to other groups, it may be stated that the Cervida (deer family) are mainly rather northern in their distribution; that the largest species occur in the colder zones, and that individuals of the same species increase rapidly in size toward the north. Some of the species in fact afford some of the most striking instances of northward increase in size, among which are the common Virginia deer and its several representatives in the interior of the continent and on the Pacific slope. It is also noteworthy that the most obviously distinctive characteristic of the group-the large, annually deciduous antlers-reaches its greatest development at the northward. Thus all the northern species, as the moose, the elk, and the caribou, have branching antlers of immense size, while the antlers are relatively much smaller in the species inhabiting the middle region of the continent and are reduced to a rudimentary condition--a simple slender sharp spike, or a small and singly forked one-in the tropical species, the antlers declining in size much more rapidly than the general size of the animal. This is true in individuals of the same species as well as of the species collectively.

The Rodentia (the squirrels, marmots, spermophiles, mice, and their affines) offer the same illustrations in respect to the law of increase in size as the species already mentioned, the size sometimes increasing to the southward, but more generally to the northward, since the greater number of the species belong decidedly to northern types. There is no more striking instance known among mammals of variation in size with locality than that afforded by the flying squirrels, in which the northern race is more than one-half larger than the southern; yet the two extremes are found to pass so gradually the one into the other that it is hardly possible to define even a southern and a northern geographical race except on the almost wholly arbitrary ground of difference in size. The species, moreover, is one of the most widely distributed, ranging from the Arctic regions (the northern limit of forests) to Central America.

Among birds the local differences in size are almost as strongly marked as among mammals and, in the main, follow the same general law. A decided increase in size southward, however, or toward

the warmer latitudes, occurs more rarely than in mammals, although several well-marked instances are known. The increase is generally northward and is often very strongly marked. The greatest difference between northern and southern races occurs, as in mammals, in the species whose breeding stations embrace a wide range of latitude. In species which breed from northern New England to Florida the southern forms are not only smaller, but are also quite different in color and in other features. This is eminently the case in the common quail (Ortyx virginianus), the meadow lark (Sturnella magna), the purple grackle (Quiscalus purpureus), the red-winged blackbird (Agelaus phoniceus), the golden-winged woodpecker (Colaptes auratus), the towhee (Pipilo erythrophthalmus), the Carolina dove (Zenadura carolinensis), and in numerous other species, and is quite appreciable in the blue jay (Cyanurus cristatus), the crow (Corvus americanus), in most of the woodpeckers, in the titmice, numerous sparrows, and several thrushes and warblers, the variation often amounting to from 10 to 15 per cent of the average size of the species."

As a general rule certain parts of the organisms vary more than does general size, there being a marked tendency to enlargement of peripheral parts under high temperature or toward the Tropics; hence southward in North America. This is more readily seen in birds. than in mammals, in consequence mainly of their peculiar type of structure. In mammals it is manifested occasionally in the size of the ears and feet and in the horns of bovines, but especially and more generally in the pelage. At the northward, in individuals of the same species, the hairs are longer and softer, the under fur more abundant, and the ears and the soles of the feet better clothed. This is not only true of individuals of the same species, but of northern species collectively, as compared with their nearest southern allies. Southern individuals retain permanently in many cases the sparsely clothed ears and the naked soles that characterize northern individuals only in summer, as is notably the case among the different squirrels and spermophiles.

In mammals which have the external ear largely developed, as the wolves, foxes, some of the deer, and especially the hares, the larger size of this organ in southern as compared with northern individuals of the same species is often strikingly apparent. It is more especially marked, however, in species inhabiting extensive open plains and semidesert regions. The little wood hare, or gray "rabbit" (Lepus

a The modern equivalents of several of the technical names in this paragraph are as follows: Ortyr [=Colinus] virginianus; Quiscalus purpureus [=quiscula]; Zenadura carolinensis [=Zenaidura macroura]; Cyanurus [=Cyanocitta cristata; Corvus americanus [=brachyrhynchos].-Author's note, 1906.

sylvaticus), affords a case in point. This species is represented in some of its varieties across the whole breadth of the continent and from the northern border of the United States southward to Central America, but in different regions by different geographical races or subspecies. In addition to certain differences of color and general size, the ears vary still more strongly. In the form inhabiting the Great Plains, commonly known as the little sagebrush hare (L. sylvaticus nuttalli), the ears are considerably longer than in the eastern variety and increase in size from the north southward, reaching their greatest development in western Arizona and the desert region farther westward and southward, where the variety of the plains proper passes into still another variety characterized mainly by the large size of its ears, which are in this race nearly twice the size they attain in the eastern variety. In the large long-eared "jackass hares of the plains the ear likewise increases in size to the southward. In Lepus callotis, for example, which ranges from Wyoming southward far into Mexico, the ear is about one-fourth to one-third larger in the southern examples than in the northern. The little brown hare of the Pacific coast (L. trowbridgei) presents a similar increase in the size of the ear southward, as does to a less extent the prairie hare (L. campestris). Not only are all of the long-eared species of American hares confined to the open plains of the arid interior of the continent, but over this same region is the tendency to an enlargement of the ear southward stronger than elsewhere. It is also of interest in this connection that the largest-eared hares of the Old World occur over similar open, half-desert regions, as do also the largest-eared foxes. On our western plains the deer are represented by a largeeared species. Among the domestic races of cattle those of the warm temperate and intertropical regions have much larger and longer horns than those of northern countries, as is shown by a comparison of the Texan, Mexican, and South American breeds with the northern stock, or those of the south of Europe with the more northern races. In the wild species of the Old World the southern or subtropical are remarkable for the large size of their horns. The horns of the American pronghorn (Antilocapra americana) are also much larger at southern than at northern localities. Naturalists

a The group here referred to as Lepus sylvaticus has in recent years been divided into some twenty-five or more forms, mostly with the rank of subspecies.-Author's note, 1906.

b Lepus callotis, as now recognized, does not occur north of Mexico; in place of this name may be substituted Lepus texianus and its subspecies.-Author's note, 1906.

The deer tribe, in which the antlers increase in size toward the north, offer an apparent exception to the rule of increase in size of peripheral parts toward the Tropics. The antlers of the deer, however, are merely seasonal appendages,