We now come to the most thoroughly aquatic of the Fissipedia, the sub-family of Otters, animals which, although quite capable of active and unembarrassed movement on land, are yet thoroughly at home only in the water. In accordance with this mode of life, the toes are webbed, and provided with very short claws, and the tail is long, tapering, and flattened, so as to serve the precise purpose of the corresponding appendage in a fish. The length of the head and body is about two feet, that of the tail, one foot five inches. The fur is of a soft brown colour, becoming lighter on the under side of the throat and the breast, and consists of long, coarse, shining hairs, with a short under-fur of fine texture, well calculated to preserve equality of temperature as the animal resorts alternately to land or water. The skull is greatly elongated, and flattened from above downwards; the facial part of it is small, as compared with the brain-containing or cranial part. The region of the skull between the eyes is very narrow, and its floor is wide and thin. In all these points, save the first mentioned, the skull of the Otter approaches that of the Seal. As to the teeth, there is one premolar less on each side of the lower jaw than in the Martens,[188] and both molars and premolars have sharp-pointed cusps, quite like those of the other _Mustelidæ_. [Illustration: SIDE VIEW OF SKULL OF COMMON OTTER. (_After Coues._)] The habits of the Otter are so entirely aquatic, that in the good old times it was thought to be a sort of cross between a beast and a fish, just as the Bat was thought to be intermediate between a beast and a bird. So deeply rooted was this opinion that the Otter’s flesh was considered quite fishy enough to be eaten by devout Catholics on fast days. To this Izaak Walton alludes in a well-known passage in his “Complete Angler.” “_Piscator._ ‘I pray, honest huntsman, let me ask you a pleasant question: do you hunt a beast or a fish?’ “_Huntsman._ ‘Sir, it is not in my power to resolve you; I leave it to be resolved by the College of Carthusians, who have made vows never to eat flesh. But I have heard the question hath been debated among many great clerks, and they seem to differ about it, yet most agree that her tail is fish; and if her body be fish too, then I may say that a fish will walk upon land.’” The movements of the Otters in water are marvellous. They swim about in families, performing the most astonishing pranks, from mere exuberance of spirits and excess of energy. Nothing can give a better idea of their activity, than the description of them in that most delightful of natural history books and fairy tales, “Water Babies.”