The group of the Pinnipedia is one in which considerable interest is centred, and this for several reasons. Their history, as handed down by classical lore, has a shade of the mythical, and well shows how fable has become engrafted on fact. Within the last two centuries their pursuit has been brimful of incident and adventure. As articles of commerce, the oil and the furs of certain kinds of the Seal tribe are of immense importance; whilst the mere hides of all, besides the Walrus tusks, are commodities of great value. Indeed, to the natives of the Arctic regions, Seals are indispensable as a means of every-day existence. But to the naturalist the fact of their being Carnivores peculiarly adapted to an aquatic life, and the study of their habits generally, are subjects of intense interest.
Moreover, the gradual, in some instances sudden, diminution of Seal life at the hand of man, points to a possible early period of their extinction, as in the case of the Whales and Manatee tribes, and warns, like the Roman story of the Sybilline books, that if we would read the history of the past, the knowledge must be culled ere the records are swept beyond recall.
The three families of the Pinnipedia are denominated in technical language the Trichechidæ,[205] the Otariidæ,[206] and the Phocidæ.[207] The first has but one living representative, the Walrus, or Morse; the second contains the so-called Sea Lions and Sea Bears, more distinctively known as Eared Seals; in the third family are ranged the ordinary Seals, contra-distinguished as Earless Seals. Sufficiently different among themselves in general aspects and habits, as to be recognised at a glance, the three families, nevertheless, have characteristic features common to all, wherefrom the sub-order has received its name. Their toes are united nearly throughout by a web of membrane, as in a duck’s foot, which converts the paws into broad, fin-like organs (the flippers), well adapted for swimming purposes. This feather-footed, pinnipedal condition is associated with a shortening of the upper segments of the limbs, and such peculiar attachment especially of the hind-legs as to leave little more than the feet free. The body is long, usually ample and fleshy at the neck and shoulders, but narrows taperingly behind towards the rump. The head is either flattish and elongated or more or less rounded, but in all cases relatively small to the bulk of the animal. External ears are absent save in the Otary family, which possess a diminutive, conical, or pear-shaped ear-conch. The eyes are full, and often expressive, though usually on land bearing a drowsy look, from their vision being adapted for a watery medium. Unless as the merest rudiment, there are no eyelashes or eyebrows. The muzzle is dog-like, but with long, stiff, though exceedingly mobile moustaches. In the Walrus, however, chiefly on account of its huge tusks, this part of the face is immensely dilated, fleshy, and covered with great pliable bristles, like knitting-needles in calibre; these latter and tusks being adaptations suited to the animal’s mode of feeding. The skin of the body fits loosely, and there is a thick layer of oily fat beneath, its amount depending on general condition, season, and sex. The hairy covering is of two sorts, a stouter, coarser, and at the roots a much shorter, softer kind. As it appears ordinarily, the hair seems uniform and short, and when wetted it clings close to the skin, so that the surface then is smooth and polished, becoming rougher as it dries. Now, it is the soft under-wool, which is in great abundance in some of the Sea Lions only, that constitutes the fur of commerce.
SKELETON OF OTARIA IN THE ATTITUDE OF WALKING.
(Reduced after Murie.)
In the skeleton it is to the amount of cartilage between the bones, along with the gristly rods attaching the ribs to the back and breast-bones, that the extraordinary mobility of figure on land, and easy motions of swimming in the water, which belong par excellence to the Marine Carnivora, are due. Add to this that the hip-bones are narrow and remarkably compressed, the thigh-bones excessively short, the shank-bones long and tied in behind, while great hind-flippers, like double oars rearwards, drive or steer with sculling sweep. The bones of the fore-limb and its modified foot altogether are strong, and remarkably so in the powerful-swimming Sea Lions. All four feet have excessively long toes, the thumb-bones being longest, the fingers lessening to the little toes; in the hind-foot the three middle toes are shorter than the two outer ones. There are tiny nails on each toe at the bone ends, beyond which is a flat spatula-shaped cartilage, of excessive length in the Otary family. The webbed flat feet are thus altogether very peculiar, and when used the entire sole, even including wrist and ankle-bones, is laid flat on the ground, so that two families of the Pinnipedia are really more plantigrade than the Bears. The Common Seals, or Phocidæ, however, never use the hind-feet on land, and the fore-feet but sparingly, while their nails are more claw-like than in their marine congeners. In none of the Seal tribe, though, are the nails or claws retractile, as previously has been shown ([p. 12]) in the Cat and Lion.
The skull in the three families presents modifications partly adapted to their different habits and modes of life, and partly to their race characters. In none, however, do we find the peculiar scissor-like or cutting teeth ([see p. 13]) of the typical Land Carnivora, but, as in the Bear tribe, the dentition exhibits a diminution in the cutting form of the teeth, and a tendency in some of the creatures to a levelling and conical production of the crown of the molars, while in others these latter show a serrate or saw-like character. For example, in the Walrus all the teeth, save the canines, are short and simple-fanged, the canines themselves, or, as they are more commonly termed in this animal, tusks, being of inordinate length and strength. In the Otariidæ, the canines, though themselves of good size, are small in comparison with those of the Morse tribe, while the incisors and single-rooted molars are more conical and prominent. The dentition of the Phocidæ varies considerably, in some the occasionally double-rooted molars acquiring a tuberculate, in others a saw-like or serrate character, while the incisors are notch-crowned. The bony cavity for the eye is open behind; the facial region is less prominently produced than in some of the feline Carnivora. The region of the brain-pan is relatively full, while the skull, as a whole, is elongated and flat. In youth, the cranium of the Pinnipedia has a predominating brain area, and the entire bony surface is smooth and featureless. As age advances, however, in certain of the genera at least, the relation of parts changes, and the face acquires prominence, while great bony crests arise on the summit and back of the head. The tongue does not possess the spines met with in the Cat tribe, though the surface is roughish. In the Seals, but not in the Walrus, the tip is slightly cleft. The stomach is single-chambered. The intestine is considerably longer than in the Felidæ, averaging fifteen times the length of the body, or thereabouts. The glands of the internal coat in some of the tribe are very extensive, and co-ordinate with the excessively rapid digestion.
UPPER SURFACE OF BRAIN OF OTARIA.
(After Murie.)
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.