A curious point in connection with the veins entering the liver is their enormous dilatation. This, by some writers, has been regarded as the means whereby the animal is enabled to remain submerged, the blood being held in these reservoirs instead of passing on towards the heart and lungs to be aërated. But whether this peculiar disposition of the blood-vessels is necessarily connected with diving powers, up to the present time has not been satisfactorily decided. Whatsoever the relation between structure and habit in this respect, it has been observed that the staying-power of the Seal tribe under water increases from youth to age. In the Pinnipedia, the lungs, relatively, are capacious, the animal rising to breathe air at intervals from ten minutes to half an hour or more, when at the surface taking a long and deep inspiration. The nostrils are under the influence of strong fleshy bundles, which firmly compress the orifices when below water. Their sense of smell is well developed, and the larynx simple. The brain in all is not only large, but far surpasses in volume and in amount of convolutions that of the Land Carnivora as a whole. Their docility and intelligence, especially when young, are often remarkable. The voice is plaintive or bellowing, but wanting the great compass and strength of the Felidæ. The nerves supplying the organs of smell, sight, and hearing are large, and the last is most unusually acute. Indeed, it is possibly to hearing more than to the other senses that the Seal tribe are dependent for their safety and living. The facts of sound readily travelling under water, of solid ice being also a good conductor, and of the quietness of the frozen regions, all tend to render this faculty of the highest service, nay, a necessity, to the creatures possessing it. Particularly is the faculty of hearing essential when the Pinniped goes on land, for in the rarer medium of the air its vision is defective, the construction of the lens, &c., being that best fitted for sight under water. [Illustration: TONGUE AND BACK PARTS OF MOUTH OF OTARIA. (_Reduced after Murie._) _to_, Right Tonsil; _u_, Uvula, or Curtain; _T_, Tongue.] I.--THE WALRUS FAMILY (TRICHECHIDÆ).