External and Internal Factors in Evolution 309 



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 great- 

 est 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 in- 

 dividuals of the same species, is often strikingly apparent." 



