The Felidæ, or cats, “reach their greatest development as respects both the number and the size of the species in the intertropical regions. This family has sent 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.” Although they vary greatly in different localities in color and in length and texture of pelage, they do not vary as to the size of their skulls. On the other hand the panther (and the ocelots) greatly increases in size southward, “or toward the metropolis of the family.” Other carnivora that increase in size northward are the badger, the marten, the fisher, the wolverine, and the ermine, which are all northern types. Deer are also larger in the north; in the Virginia deer the annually deciduous antlers of immense size reach their greatest development in the north. The northern race of flying squirrels is one-half larger than the southern, “yet the two extremes are found to pass so gradually one into the other, that it is hardly possible to define even a southern and a northern geographical race.” The species ranges from the arctic regions to Central America. In birds also similar relations exist, but there is less often an increase in size northward. In species whose breeding station covers a wide range of latitude, the northern birds are not only smaller, but have quite different colors, as is markedly the case in the common quail, the meadow-lark, the purple grackle, the red-winged blackbird, the flicker, the towhee bunting, the Carolina dove, and in numerous other species. The same difference is also quite apparent in the blue jay, the crow, in most of the woodpeckers, in the titmice, numerous sparrows, and several warblers and thrushes. The variation often amounts to from ten to fifteen per cent of the average size of the species. Allen also states that certain parts of the animal may vary proportionately more than the general size, there being an apparent tendency for peripheral parts to enlarge toward the warmer regions, _i.e._ toward the south. “In mammals which have the external ears largely developed—as in 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 even more apparent in species inhabiting open plains. The ears of the gray rabbit of the plains of western Arizona are twice the size of those of the Eastern states.