Allen.] 284 [February 4, 



at about the 40th parallel, embracing a comparatively narrow belt 

 along the coast from Northern California to Sitka. Its peculiarities 

 are most strongly developed west of the Cascade Range, north of 

 45°; they also prevail eastward nearly or quite to the main chain 

 of the Rocky Mountains. It may hence be termed the Columbian 

 Region. With an average annual rain-fall of fifty-five to sixty-five 

 inches, the prevalent tendency in color is to dusky and fuscous 

 rather than rufous tints. The district between the Cascade Range 

 and the main chain of the Rocky Mountains presents features that 

 may almost entitle it to rank as a distinct region, as might also 

 the region of maximum rain-fall in the Mississippi Region. The 

 southern half of Florida is also perhaps entitled to recognition as a 

 distinct region, being characterized by excessive humidity and a sub- 

 tropical intensity of color. It may also be necessary to eventually 

 recognize as distinct districts the almost rainless portions of the 

 Campestrian Region. 



In respect to the correlation of intensity of color in animals with 

 the degree of humidity, it would perhaps be more in accordance with 

 cause and effect to express this law of correllation as a decrease of 

 intensity of color with a decrease of humidity, the paleness evidently 

 resulting from exposure and the blanching effect of intense sunlight, 

 and a dry, often intensely heated atmosphere. With the decrease of 

 the aqueous precipitation, the forest growth and the protection af- 

 forded by arborescent vegetation gradually also decreases, as of 

 course does also the protection afforded by clouds, the excessively 

 humid regions being also regions of extreme cloudiness, while the dry 

 regions are comparatively cloudless districts. 



In addition to the tendency to change of color with locality, there 

 is another phase of color variation that requires, in this connection, a 

 passing notice, — namely, Melanism. It is now well known that al- 

 most every species of mammal may be expected to present melanis- 

 tic individuals, instances of its occurrence in the majority of the 

 North American species being now well established. Indeed, the 

 very fact of a melanistic phase of coloration may be looked upon as 

 almost a priori evidence that the individuals presenting it belong to a 

 melanistic race of some species whose normal color is some other tint 

 than black, as Prof. Baird long since remarked in respect to the 

 American squirrels. It has been supposed that the tendency to me- 

 lanism is more prevalent at the northward; but such does not appear 

 to be necessarily the case. Among the Sciuridce, for instance, a 



