As we shall presently see, the brooks of the chalk downs of Wiltshire, and of the regular mixture of rock and level ground, which are characteristic of Derbyshire, have also their own separate individualities. We shall, however, find many allusions to them in the course of the work, and we will therefore suppose ourselves to be approaching the bank of any brook that is but little disturbed by man. What will be likely to happen to us will be told in the following chapters. CHAPTER II. Life-history of the water-rat--No science can stand alone--What is a water-rat?--The voles of the land and water--Their remarkable teeth--The rodents and their incisor teeth--The tooth and the chisel--The skate "iron"--Chewing the cud--Teeth of the elephant--Feet of the water-vole--A false accusation--Water-voles in gardens--Winter stores--Cats and water-voles--Subterranean pioneering--Mental character of the water-vole--Standing fire--Its mode of eating. Plop! A water-rat has taken alarm, and has leaped into the brook. A common animal enough, but none the less worthy of notice because it is common. Indeed, it is in many respects a very remarkable creature, and we may think ourselves fortunate that we have the opportunity of studying its habits and structure. There is much more in the animal than meets the eye, and we cannot examine its life-history without at the same time touching upon that of several other creatures. No science stands alone, neither does any animal, however insignificant it may appear to be; and we shall find that before we have done with the water-rat, we shall have had something to say of comparative anatomy, ornithology, ichthyology, entomology and botany, beside treating of the connection which exists between man and the lower animals, and the reciprocal influence of civilisation and animal life. In the first place, let us define our animal. What is a water-rat, and where is its place in zoological systems of the present day? Its name in science is _Arvicola amphibius_. This title tells its own story. Though popularly called a rat, the animal has no right to the name, although, like the true rat, it is a rodent, and much resembles the rat in size and in the length and colour of its fur. The likeness, however, extends no further. The rats are long-nosed and sharp-snouted animals, whereas the water-rat has a short, blunt nose. Then, the ears of the rats are large and stand out boldly from the head, while those of the water-rat are small, short, and rounded. Again, the tail of the rat is long and slender, while that of the water-rat is comparatively short. Place the two animals side by side, and you will wonder how anyone could mistake the one for the other. The teeth, too, are quite different.