Among the general characters of the Sirenia is a long, compact, cylindrical body (without back fin), narrowing towards the tail, which terminates either Whale-like, in forked flukes, or Beaver-like, in a great, flat, fibrous expansion, in either case set horizontally. The fore-limbs are encased, flat, and flipper-like, exceedingly flexible, and more completely formed than in Whales. The extinct and fossil Halitherium alone is known to have possessed rudiments of hind-limbs, though pelvic bones are present in all. Ears are wanting, and the eyes are very small, whilst two valvular nostrils are situate over a full prominent muzzle, which is provided with a copious supply of peculiar short bristles, while the inside angles of the mouth are hairy. Their dark skin is Elephant-like, tough, rough, sparsely hairy, or smoothish and Whale-like. The two mammæ are on the breast close to the armpits. One genus (Rhytina) was toothless, but the others had ample dentition. Moreover, in all the front of the upper and lower jaws is provided with curious, rough, horny pads or plates. The larynx differs from that of the Cetacea and resembles that of Land Mammals. The midriff, or diaphragm, is most unusually lengthened backwards. The apex of the heart is cleft, giving the appearance of a double organ, and the blood-vessels almost everywhere in the body and limbs split into rete mirabile. The stomach has two main digestive chambers, and to the first is added a pair of small divergent horn-shaped appendages, besides a remarkable finger-shaped gland. Unlike Whales or Elephants their small brain has few convolutions. All the bones are dense and heavy, and are the most solid among Mammals. Manatus is unique among the living Mammalia in having but six neck vertebræ, and, as in the other Sirenia, they are all separate. The ribs are uncommonly thick. The skull is relatively much smaller than in the Cetacea, is low set, somewhat elongated, and truncated at each extremity. The side bones (parietals) meet above, the occiput is small, the orbits well defined, and the nasal passages are directed forwards; the lower jaw has a high vertical limb (or ramus) behind, and in the Dugong the upper and lower jaw-bones are strangely bent down. The Sirenia are animals of slow habit, and are most inoffensive. They feed solely on aquatic vegetation. As being the most Whale-like in size and shape of tail, we shall first introduce to notice the Rhytina.
STELLER’S RHYTINA,[254] the Morskaia Korava of the Russians, and alone representative of the genus, is a creature now extinct, but which was living and in tolerable abundance a hundred and fifty years ago. When the Russian, Behring—after whom the Strait is named—first visited that region and the neighbourhood of Kamstchatka, there existed a huge animal, of which, under the name of Manatee, or Northern Sea Cow (Vacca marina), the naturalist Steller, who accompanied him, gave a classical account. It had a small oblong head, a full bristly snout, a dark-coloured body, protected by a rugged, gnarled, warty, hairless skin. The fore limbs were quite short and stumpy, hairy at their ends, and they had no finger-bones beyond the wrist. The tail was black, ending in a horizontal, stiff, half-moon-shaped, narrow fin-blade, fringed with a fibrous whalebone-like material. It had no teeth, but horny, almost bony plates, corresponding to the horny gum-pads of the Dugong and Manatee, served the purpose of mastication. According to Steller, it attained a length of from twenty to twenty-eight feet.
Though stupid, voiceless, animals, they were of a very affectionate disposition, and were readily tamed, even allowing themselves to be handled. Their conjugal affection was strikingly developed. A male, who in vain attempted to relieve his partner, stuck by her, in spite of repeated blows, and when she died he returned to the spot for some days, as if he expected to see her again. They were very voracious, and fed on seaweeds, with their heads under water; and every now and then they raised their noses to breathe, and made a snorting noise. They appeared in families, each consisting of a male, female, one half grown, and a cub born in autumn; and sometimes these families united into great herds. As they were very good eating (far preferable to salt junk), Steller recommended them as articles of diet to the sailors; and so faithfully was his advice observed by natives and seamen, that within twenty-seven years of his first visit the last Rhytina was killed, namely, in 1768. They were hunted with a boat-hook attached to a long rope, which, when the animal was struck, was passed to a company of men on shore, who, with considerable difficulty, managed to land the huge Sea Cow. This animal appears to have had an extremely limited range, having never been met with anywhere but in the small Behring Island, off the coast of Kamstchatka. Their sudden extinction is a most noteworthy fact, and but for Steller’s admirable account nothing whatsoever would have been known of the habits, internal structure, or outward appearance of this singular Sirenian. Though the adults were toothless, yet by some it is supposed from analogy that in early life functionless teeth may have existed, though these never appeared above the gums. The Rhytina, in its forked tail, somewhat down-bent jaws, and other points, resembled the Dugong; while in skull characters and skin it was like the Manatee; and though somewhat whale-shaped, it was a true Sirenian.
THE DUGONG,[255] typical of the genus Halicore, is a living form, ordinarily from ten to twelve feet long, though very old males are said occasionally to reach as much as eighteen to twenty feet. Its distribution is rather widespread, namely, from the Red Sea and East African coasts to the west coast of Australia; and they are even yet not unfrequently met with within these limits, on the coasts of Mauritius, Ceylon, and the Indian Archipelago, though in numbers fast becoming thinned. Outwardly they differ from the Rhytina in being smoother-skinned, and in having the fore-limbs longer, and the tail semi-lunar, but deeper or less fluked, and not marginally split. Their colour is slaty-brown or bluish-black above, and whitish below. The early traveller, Leguat, speaks of droves of several hundreds grazing like Sheep on the seaweeds a few fathoms deep in the clear waters of the Mascarene Islands. Usually this tropical animal frequents the shallow smooth waters of the bays, inlets, and river estuaries where marine vegetation (fucus and seaweeds) is in abundance, and there it leisurely feeds, being lethargic in disposition, but an immense eater. When they have not been much chased they are not shy or timid, and even allow the natives to handle them; on which occasions the admiring spectators generally manage to abstract the smaller and fatter cubs as dainties, for they are considered uncommon good food. So highly prized are they, that the Malay king considers it a royal “fish,” and he claims all taken in his dominions. The flesh of the young, when cooked in a variety of ways, is certainly wholesome—by some compared to veal, and by others to beef or pork—but the older animals are tougher. The Moreton Bay colonists call them “Sea Pig.” They yield a clear oil of the best quality, which is free from all objectionable smell, and it is strongly recommended as a remedial agent in lieu of cod-liver oil. Hence an Australian Dugong fishery has been established; but its equipped boats’ crews are fast sweeping off the once plentiful numbers. The stories of their being found ashore, browsing on land herbage, are not supported by fact; indeed, the inadequate strength of their fore-limbs, the absence of hind extremities, and their unwieldy bodies, prevent them from travelling on land. This is borne out by the statements of the natives of Sumatra to Sir Stamford Raffles, as well as other travellers. The Red Sea Arabs told Dr. Rüppell that they had feeble voices, a fact that other Australian observers have corroborated, although the roaring of Seals has been mistaken for them. In the spring months the males do battle for partners, and the young are born towards the end of the year. Like the Rhytina, the Dugong shows intense maternal affection, for if the young be taken, the mother suffers herself to be speared in following her offspring. In its strange bristly-clad muzzle the Dugong resembles its congeners, but its skull and dentition are singular. Thus, the fore or premaxillary region of the upper jaw is elongated, sharply crooked downwards, and overlaps the very deep lower jaw, which is similarly down-bent. The two opposed surfaces bear the horny tuberculated plates which rub and grind the vegetable food. The dental formula ordinarily is—Incisors, 1–1 0–0; canines, 0–0 0–0; molars, 3–3 3–3 = 14. The pair of incisor tusks are lodged in the down-bent upper jaw, and protrude in the male, but in the female they are diminutive, and retained within the bone. Behind them there is a considerable space devoid of canine, and then come three slightly laterally compressed ovoid molars without enamel. The molars, however, may occasionally be five in number, the fore ones dropping out, and others behind taking their places, but not succeeding vertically. In some instances the males have an additional lateral small incisor. Thus as many as twenty-four teeth may be developed, but these are never in use at one and the same time. This peculiar dentition, and the successive displacement of the anterior molars, foreshadows what is regularly found in the Elephants and Mastodons.
MANATEES.
THE MANATEE, or Lamantin of the French, inhabits the African and American Continents. In Africa it ranges along the west coast, and ascends the Senegal, Niger, Congo, and other rivers, where it not only frequents the lagoons, but even has been captured in Lake Tchad. This animal is known as M. senegalensis. In America two forms are supposed to exist—one, the M. latirostris, of Florida, is said to have closer resemblance to the African form than to its fellow-countryman; the other, M. americanus, is found in Surinam, Guiana, Jamaica, the Amazon and its tributaries, and, indeed, in the various rivers, bays, and inlets of the tropical American coast. These creatures, like the foregoing, browse upon the aquatic vegetation of the shallow lagoons and river banks, apparently, however, having a preference for fresh-water plants. Their habits and mode of feeding are, in a measure, similar to those of the Dugong and the Rhytina. The full-grown Manatee is from ten to twelve feet in length. Its long body terminates in a thin, wide, shovel-shaped, fibrous, horizontal tail, proportionally broader, but resembling somewhat that of the Beaver. The fore-limbs, or flippers, have diminutive flat nails. The skin of the body can be compared only to that of the Elephant, not in colour alone, but also in its coarse, wrinkly texture, and widely-scattered, delicate, but long hairs. Its deep-set, minute eye is surrounded by skin wrinkles. As in the preceding genera, the muzzle is peculiar—a kind of half-moon-shaped swelling above, with deep crossing wrinkles set with short stiff bristles. Beneath this there projects a mass of hard gum, covered with a roughened horny plate. The lower jaw also has a gum plate, underhung by a bristle-clad lower lip. The nostrils are two semi-lunar, valve-like slits, at the apex of the muzzle. When the mouth is opened, the marginal inner cheeks are seen to be hair-covered, and the hard, horny palate to be very conspicuous above and below. This remarkable muzzle and mouth are specially adapted to the animal’s mode of feeding. Steller long ago remarked that the Rhytina’s muzzle was exceedingly prehensile; but in a live Manatee exhibited at the London Zoological Gardens, Professor Garrod observed and has recorded the remarkable manner and use of this lip-structure. In grasping its food, the bristly-clad outer angles of the upper lip at first diverge, and then approximate like a pair of pincers, holding the object firmly, which is then drawn inwards by a backward movement of the lips. The horny pads again on the closing of the mouth further bruise the vegetable matter. In 1866, the Zoological Society sent Mr. Clarence Bartlett to Surinam, to bring home a young Manatee. This suckling, christened “Patcheley,” had been obtained when quite a baby by the Indians, and duly transferred to a lakelet, where he had his freedom. Although fishy in form and fondness for the water, he had nevertheless to receive daily a good quantum of Cow’s milk from a bottle. He soon got fond of the “black Jack,” as well as of his keeper. Mr. Bartlett, as wet nurse, had a difficulty in training his charge. Loosely attired, he waded about and coaxed his pet to the water’s edge, where, after a stolen suck or two, he permitted himself to be raised partly on his knees, and then sucked away might and main till the bottle was dry. His appetite satisfied, he seemed in high glee, tumbled and rolled about a while, then got quieter, retired to the pool, and slept lazily near the surface. At times his disposition was more rollicking, and Master Patcheley would overturn his nurse into the mud, where the two spluttered and floundered for possession of the bottle. Clusius recounts how a pet “Mato” was kept by a Spanish Governor for twenty-six years; it came at call to the side of the lake to be fed, and would even allow boys to mount on its back while it harmlessly swam about. For long the pursuit of the Manatee has been a favourite amusement with the natives. One instance is related of Indians on the Mosquito shore spearing it from canoes, when the animal darted off as he felt the weapon, dragging the canoe after it round and round the bight until exhausted. Mr. Alfred R. Wallace says the natives of the Amazon capture them alive, in strong nets, at the mouth of the streams, and afterwards kill them by thrusting wooden plugs up their nostrils. The Manatee has no milk-teeth, though when young there are two rudimentary incisors in each jaw, which afterwards become covered in. Canines are entirely absent, and the molars vary in number from nine to eleven in the upper and lower jaw on each side. Those in the upper series are three-rooted, in the lower series two-rooted; all the molars are broad, square-crowned, and with transverse ridging or cusp structure like that of the Hippopotamus or partly like that of Mastodon. The molar series are never simultaneously in place and use, those in front dropping out and making room for those behind.
FOSSIL SIRENIA.—The HALITHERIUM is the name given to certain fossil remains which have been found in the Miocene strata of Germany and various other parts of Europe. These remains show that there may have been several species, but all are truly of a Sirenian character. The fossil remains were intermediate, though possibly most closely allied to the Manatee, some of them being slightly larger than this animal. The dentition is unusually interesting, inasmuch as there appear to have been vertical successors; anteriorly there are simple, cylindrical premolars, and posteriorly larger, complex molars, while the somewhat bent-down upper jaw bore tusk-like appendages. But the most peculiar and interesting point in connection with the Halitheria, is that they were provided with rudiments of a hind limb, a thigh-bone some few inches in length having been found by the late Professor Kaup, though curiously enough no further vestige of it has since turned up. Judging from the almost complete skeletons obtained, and from comparison with what we know of other Sirenia, the Halitherium must have closely resembled the living Manatee, and possibly have lived in the lagoons and brackish waters of mid-Europe and elsewhere, for in the Eocene and Miocene times these regions, now high and dry, formed watery areas in communication with the ocean.
Besides the foregoing, within the last few years our knowledge of Sirenoids has been considerably augmented by the discovery of other fossil remains indicating several new genera. Prorastomus is founded by Owen on a skull from West Indian (doubtful) Tertiary strata. Crassitherium is applied by Van Beneden to vertebræ, and part of a skull from deposits near Antwerp. Felsinotherium, (with but 5–5 5–5 molar teeth) is a form described by Capellini, from Pliocene beds in Bologna. Pachyacanthus, found in strata in the neighbourhood of Vienna, Brandt supposed a Cetacean, but Van Beneden regards it as a Sirenian. The Rhytiodus, of Lartet, is based on some fossil teeth bearing resemblances to those of the Dugong. Lastly comes (in the cast of a brain), the still more remarkable Eotherium of Owen, from the nummulitic Eocene of Egypt. Some of these fossils are of intense interest, for example, Prorastomus, the Tapir-like dentition of which is—Incisors, 3–3 3–3; canines, 1–1 1–1; premolars, 5–5 5–5; molars, 3–3 3–3 = 48. Very interesting also are Pachyacanthus, with possibly but six neck vertebræ, like the Manatee; and Halitherium, with its hind limb bones, and which also, along with Felsinotherium, foreshadows the molar pattern of Hippopotamus. Thus, taking these facts into consideration, together with many other structural peculiarities, Elephant-like and otherwise, and notwithstanding that the Sirenia are aquatic and Whale-like, their structural relationship with the Proboscidea and Ungulata is not so far-fetched as at first sight might seem. But the gap is not yet bridged, and until that is done the order Sirenia must be retained.
JAMES MURIE.