From the true seals of the family _Phocidæ_ the eared seals, or _Otariidæ_, differ by retaining small external ears, as well as by the fact that the hind-flippers are not permanently turned backwards; this latter feature being also distinctive of the walrus (_Odobænidæ_). In addition to being the most specialised of the aquatic Carnivora, the true seals are also the most widely distributed, inhabiting nearly all seas, and being likewise found in the Caspian Sea and in Lakes Aral and Baikal. Although seals go on land nightly to sleep, and likewise spend a considerable amount of time in the day on the shore or on ice, while the females give birth to their young on land, none of the _Phocidæ_ regularly leave the water for a period of several weeks during the breeding-season, after the fashion of their eared cousins. Neither do any of them yield commercial sealskin, which is a product of certain members of the eared groups. Commercially, they are therefore valued only for their hides and oil, for the sake of which vast numbers are annually slaughtered. Seals are adepts in swimming and diving, and have the power of closing their nostrils and the apertures of their ears while under water, although they are unable to remain beneath the surface for anything like so long as whales and dolphins. The food of the common seal, as well as most other kinds, consists chiefly of fishes, for capturing and holding which their sharply cusped teeth are admirably adapted. Graceful and active as are their movements in water, on land they are comparatively awkward and ungainly; progression being effected by means of the limbs, accompanied by sudden flexures of the body, so that it in some degree partakes of the nature of hopping. To land, seals shoot themselves out of the water by a strong and sudden movement of the hind-limbs. When once on land, they may remain there for days and even weeks together, till compelled by hunger to return to the sea. [Illustration] The senses of the seal are highly developed. The eye, for instance, is full and globular, and thus specially adapted to catch every ray of light when the animal is in the water. It is noteworthy that seals can shed tears under the influence of excitement, and especially when in pain. And the idea of the ancients that these animals are attracted by music and singing appears to be founded on fact. Their usual cry is a sharp bark, but when angered they give vent to dog-like snarlings. Seals always associate in parties, which may comprise hundreds of individuals. The young, which are beautiful little creatures, are tenderly and affectionately nurtured by their parents, who protect them from danger by every means in their power.