If we descend by degrees from great to small, from strong to weak, we find that Nature has uniformly maintained a balance throughout her works; attentive only to the preservation of each species, she creates a profusion of individuals, and supports by numbers those she has formed of a diminutive size, and left unprovided with arms, courage, or resources; she has not only enabled these inferior species to resist and maintain their ground by their own numbers, but has added a kind of supplement to each, by multiplying the neighbouring species. The rat (_fig. 74._), the mouse (_fig. 76._), the field mouse (_fig. 77._), the water-rat (_fig. 75._), the short-tailed field mouse (_fig. 78._), the dormouse, the shrew mouse, with several others, which I shall not mention here, because they do not belong to our climate, form so many distinct and separate species, but yet so little varied, that should any one chance to fail, its absence would be hardly perceptible. It is this great number of approximate species that first gave naturalists the idea of genera, an idea which can only be employed when we view objects in the gross, but which vanishes when we apply it to reality, or when we consider Nature minutely. Men began by appropriating different names to objects which appeared to them distinctly different, and at the same time, they gave general denominations to such as seemed to resemble each other. Among unenlightened nations, and in the infancy of languages, there are hardly any but general names, or vague or ill-formed expressions for objects of the same order, though in themselves highly different. Thus the oak, beech, linden, fir, yew, pine, had at first no name but that of tree; afterwards the oak, beech, and linden, were called oak, when they came to be distinguished from the fir, pine, and yew, which in like manner would be called fir. Particular names could proceed only from a minute examination of each species, and of course those names would be increased in proportion as the works of Nature were more studied and better understood; the more they studied her, the more generic and specific names would be introduced. To represent Nature, therefore, by general denominations, or genera, is to refer us back to the dark and infant state of human knowledge. Ignorance produced genera, but science will ever continue to create proper names; and we shall not be afraid of increasing the number whenever we have occasion to delineate different species.