and varieties, a matter of necessity. Thus all human beings belong only to one species, which may, however, be divided into five races, and these again into an infinity of varieties. The differences between a race and a variety are, that the latter is a subdivision of the former, and that in the former the modifications are more profound, the changes not being confined to the surface, but extending to the frame-work of the body; whereas, to constitute a variety, nothing more is necessary than the superficial influence of heat and light on the skin, and its appendages the hairs. The Negro and the Abyssinian are precisely similar in colour, yet they are by no means of the same race, as their different features will distinctly prove; the Abyssinian approaching as much in cast of countenance to the European, as the negro does to the higher orders of the ape. The same may be noticed among sheep, but this is sufficient for the present. The changes induced by climate, result from the working of a power inherent in most animals and vegetables, by which they are suited within certain limits, for bearing up against removal from their ordinary localities, and assuming a different cast, as the place of their exile may differ in degree from that which they have left. This gradual adaptation to circumstances by an accommodating power is termed, in philosophical language, acclimation. (68.) _Adaptation of the Sheep to Climate._--No animal varies more than the sheep, and none so speedily adapts itself to climate; it would almost appear that nature, convinced of its great utility, had bestowed upon it a constitution so pliant, as to enable it to accommodate itself to any point in a wide scale of temperature; for though its natural situation as a wool-bearing animal, like that of man appears to be the wine countries, yet with him, it has spread to every quarter of the globe, becoming impressed at every change with some peculiarity, alterable only by a change of situation, and varying, we might almost affirm, with the weather; for, where the temperature is equable, there does the animal preserve unchanged an atmospheric stamp, and defies our efforts to alter the breed; while under a fluctuating sky we can model it at will, though in this case, continued exertions are required to secure them for any length of time in an undeviating course.