Popular Science Monthly/Volume 15/June 1879/Whales and their Neighbors
|WHALES AND THEIR NEIGHBORS.|
THE medical student, who, in answer to an examiner anxious to ascertain the exact amount of the lad's knowledge concerning fishes, replied that "he knew them all from the limpet to the whale," must indeed be credited with a larger share of candor than of zoölogical science. The limpet is a shell "fish" by courtesy at the best, but the whale, public opinion notwithstanding, is not a fish in any sense of the term. The most that can be said of the whale in this respect is that it is fish-like; and, admitting that appearances in zoölogical study are as deceptive as in ordinary existence, it behooves us to be cautious in accepting outward resemblances as indicative of real and veritable affinity. A popular lesson in natural history, then, teaches us that a whale is a quadruped—that is, apart from the mere etymology of the word, it belongs to the quadruped class. It possesses but two legs, or rather "arms," it is true, and these members do not resemble limbs. But it is a quadruped notwithstanding its deficiencies in this respect; and it agrees in all the characters which are found to distinguish the class to which man himself belongs, that of the Mammalia. These characters it may be advantageous very briefly to detail, by way of preliminary to the general study of whales and their nearest relations. Thus, firstly, they are warm-blooded animals, a statement which must be taken as meaning that their blood is of a temperature considerably higher than that of the medium in which they live. The fish, on the other hand, is a cold-blooded creature. Its temperature is only slightly higher than that of the surrounding water, and in this respect it agrees with all invertebrate animals and with the frogs and reptiles of its own sub-kingdom. Next in order may be noticed the agreement of the whale with the quadruped in the matter of body-covering. The covering of the latter consists of hairs. Although the body of the whale can not be described, by any stretch of the imagination, as having hair, the presence of a few bristles around the mouth extremity sufficiently indicates the nature of its outer garment; while, before birth, the body-covering in some whales is tolerably plentiful, but is soon shed, leaving the hide thick, shining, and hairless. The microscopist might inform us that the blood of the whale presents the same characters as that of other mammals, and possesses red corpuscles or colored bodies, which, unlike those of the fish, reptile, and bird, have no central particle or "nucleus." And while the heart of the fish is a comparatively simple engine of propulsion, consisting of two contractile chambers or cavities, the whale's heart will be found like that of man and other quadrupeds in all essential details of its structure. It is thus a four-chambered organ doing double duty, in that it sends blood not only through the system, but also to the lungs for purification.
The mention of lungs as the breathing organs of whales at once introduces us to a new field of inquiry concerning the habits and life of the aquatic monsters. A popular notion exists that of necessity a water-living animal must be a water-breather. The idea of fish existence and of the manner in which fishes breathe evidently reigns paramount in the present case. That an animal may be completely aquatic in its habits, and yet breathe air directly from the atmosphere, and after a like procedure to that witnessed in human respiration, is a notable fact. A water-newt, despite its aquatic habits, ascends periodically to the surface of the water to breathe; and seals, walruses, and whales agree in that they are truly lung-breathers, and possess gills at no period of their existence. True, a gill differs from a lung only in that it is capable of exposing the blood circulating through it to the air which is entangled or mechanically suspended in the water. Atmospheric air containing the vitalizing oxygen for the renewal and purification of the blood is the great desideratum on the part of all animals, high and low alike. And the gill and lung, therefore, differ simply in the manner and method in which the blood in each is brought in contact with the air, and not in the essential details of their work. The whales are known to "blow," and the act of "blowing" is simply the act of breathing—to be more particularly noticed hereafter. Thus, a whale or seal would be drowned as certainly as an ordinary quadruped would be asphyxiated, were its periodical access to the atmosphere prevented; and the curious fact may here be mentioned that there are also certain abnormal living fishes—notably the climbing perch and ophiocephali of India—which, to use the words of a writer, are as easily drowned as dogs when denied access to the air. There is little need to particularize any of the remaining characters which demonstrate the whale's relationship to mammals, and its difference in structural points from the fishes. The young whale is thus not merely born alive, but is nourished by means of the milk-secretion of the parent, and this last evidence of direct connection with higher animals might of itself be deemed a crucial test of the place and rank of the whales in the animal series.
But, granting that in the whales we meet with true quadrupeds, it may be well to indicate the chief points in which they differ from their mammalian brethren at large. It may be admitted, at the outset, that they present us with a very distinct modification of the quadruped type. Their adaptation to a water-life is so complete, in truth, that it has destroyed to a large extent the outward and visible signs of their relationship with mammals. The body is thoroughly fish-like and tapers toward the tail, where we meet with a tail-fin, which, however, is set right across the body, and not vertically as in the fishes. This latter difference, indeed, is a very prominent feature in whale-structure. The limbs, as already remarked, are represented by the two fore-limbs alone. No trace of hinder-extremities is to be perceived externally, and the anatomical investigation of the skeleton reveals at the best the merest rudiments of haunch-bones and of hind-limbs in certain whales, of which the well-known Greenland whale may be cited as an example. A distinct character of the whales has been found by naturalists of all periods in the "blowholes" or apertures through which the whale is popularly supposed to "spout." Thus we find on the upper surface of the head of a Greenland whale a couple of these "blowholes," or "spiracles," as they are also called. These apertures exist on the front of the snout in the sperm whales, while in the porpoises, dolphins, and their neighbors the blowhole is single, of crescentic shape, and placed on the top of the head. It requires but little exercise of anatomical skill to identify the "blowholes" of the whales with the nostrils of other animals; and it becomes an interesting matter to trace the adaptation of the nostrils to the aquatic life and breathing habits of these animals.
There are natural history text-books still extant in which a very familiar error regarding the "blowing" of the whales is propagated—an error which, like many other delusions of popular kind, has become so fossilized, so to speak, that it is difficult to convince believers of its falsity. A manual of natural history, of no ancient date, lies before me as I write, and when I turn to the section which treats of the whales, I find an illustration of a Greenland whale, which is represented as lying high and dry on the beach, but which, despite its stranded state, appears in the act of vigorously puffing streams of water from the blowholes on the top of its head. To say the least of it, such an illustration is simply fictitious, and might safely be discarded as of purely inventive kind, were it only from the fact of its supposing a whale to be provided with some mysterious reservoir of water from which it could eject copious streams, even when removed from the sea. The common notion regarding the "blowing" of the whale appears to be that which credits the animal with inhaling large quantities of water into its mouth, presumably in the act of nutrition. This water was then said to escape into the nostrils and to be ejected therefrom in the act of blowing. The behavior of a whale in the open sea at first sight favors this apparently simple explanation. Careering along in the full exercise of its mighty powers, the huge body is seen to dive and to reappear some distance off at the surface, discharging from its nostrils a shower of water and spray. The observation is correct enough as it stands, but the interpretation of the phenomena is erroneous. Apart from the anatomical difficulties in the way of explaining how water from the mouth could escape in such large quantities, and so persistently into the nostrils, there is not merely an utter want of purpose in this view of the act of "spouting," but we have also to consider that this act would materially interfere with the breathing of the animal. Hence a more rational explanation of what is implied in the "blowing" of the whales rests on the simple assertion that the water and spray do not in reality proceed from the blowhole, but consist of water forced upward into the air by the expiratory effort of the animal. The whale begins the expiratory or "breathing-out" action of its lungs just before reaching the surface of the water, and the warm expired air therefore carries up with it the water lying above the head and blowholes of the ascending animal. That this view is correct is rendered highly probable, not merely by the observation of the breathing of young whales and porpoises kept in confinement, but also by the fact that the last portion of the "blow" consists of a white silvery spray or vapor, formed by the rapid condensation of the warm air from the lungs as it comes in contact with the colder atmosphere. The water received into the mouth escapes at the sides of the mouth, and does not enter the nostrils at all.
The furnishings of the mouth of the whales include sundry remarkable structures peculiar to a certain family circle of these animals. Such are the "whalebone"-plates, furnishing a substance familiarly spoken of by everybody, but exemplifying at the same time a kind of material regarding the origin of which a tacit ignorance, sanctioned by the stolid indifference of many years' standing, commonly prevails. Whalebone, or "baleen," is a commodity occurring in one group of these animals only, this group being that of the whalebone whales (Balænidæ), of which the Greenland or Right whale (Balæna mysticetus) is the most noteworthy example. From this whale the whalebone of commerce is derived; other and nearly related species—such as the Rorquals and Furrowed whales—possessing the whalebone-plates in a comparatively rudimentary state. The baleen occurs in the mouth of these whales, and is disposed in a curious fashion. It exists in the form of flat plates of triangular shape, each plate being fixed by its base in the palate. The inner side, or that next the center of the mouth, is strongly fringed by frayed-out whalebone fibers, the outer edge of each plate being straight. A double row of these triangular plates of baleen depends in the form of two great fringes from the palate of the whale; and it would appear that each baleen-plate is in reality a compound structure, being composed of several smaller plates closely united. The largest plates lie to the outer side of the series, and in a full-grown whale may measure from eight to fourteen feet in length, and as many as 250 or 300 plates may exist on each side of the palate.
The nature of these curious organs forms an appropriate subject of inquiry. It is exceedingly rare in nature to find an animal provided with organs or structures which have no affinity with organs in other and related animals. On the contrary, the principle of likeness or "homology" teaches us that the most unwonted and curious structures in animal existence are for the most part modifications of common organs, or at any rate of parts which are represented under varying forms and guises in other animals. By aid of such a principle we discover that the fore-limb of a horse, the wing of a bird, and the paddle of a whale are essentially similar in fundamental structure, and in turn agree in all necessary details with the arm of man. Through the deductions of this science of tracing likenesses and correspondences between the organs of different animals, the zoölogist has been taught that the "air-bladder" or "sound" of the fish is the forerunner of the lung of higher animals–an inference proved by the fact that in some fishes, such as the curious Lepidosirens or "mud-fishes" of Africa and South America, the air-bladder actually becomes lung-like, not merely in form but in function also. By means of this useful guide to the mysteries of animal structure, we note that the bony box in which the body of the tortoise or turtle is contained is formed by no new elements or parts, but consists chiefly of the greatly modified backbone and of the ribs and scales of these animals. To what conclusion, then, does this same principle lead us respecting the nature of the baleen-plates in the mouth of the Greenland whale and its allies? To a sufficiently certain, but at the same time startling thought, is the reply of the comparative anatomist.
If we examine the structure of the human mouth, or that of animals allied to man, we find that cavity to be lined by a delicate layer named epithelium. This epithelium consists really of a modification of the upper layer of the skin, and we see this modification familiarly in the difference between the skin of the face and the layer which is infolded to form the covering of the lips and the lining membrane of the mouth. No tissue is more familiar to the student of physiology than epithelium, composed as it is of epithelial cells or microscopic elements, which in one form or another are found in almost every important tissue of the body. The epithelium is a delicate tissue, as usually seen in man and vertebrate animals; but in some instances it becomes hardened by the development of horny matter, and may then appear as a tissue of tolerably solid consistence. In the mouth of a cow or sheep, the epithelium of part of the upper jaw is found hardened and callous, and there forms a horny pad against which the front teeth of the lower jaw may bite in the act of mastication. It is exactly this epithelial layer, then, which becomes enormously developed in the whalebone whales to form the baleen-plates just described. That this is actually the case is ascertained by the development of the baleen-plates, as well as by their situation and relations to the gum and palate. And the recital becomes the more astonishing when we consider that, from cells of microscopic size in other animals, structures of enormous extent may be developed in the whales. The baleen-plates possess a highly important office. They constitute a kind of huge strainer or sieve, the possession of which enables the whale to obtain its food in a convenient fashion. Whether or not Biblical scholars and commentators agree in regarding the "great fish" which wrought calamity to the prophet Jonah as a special creation, and as an entirely different animal from the whale of to-day, the plain fact remains that a whale has a gullet of relatively small size when compared with the bulk of the animal. Fortunately, however, the faith of rational mankind is not pinned to literal interpretation of the untoward incident chronicled in Jonah, and, whale or no whale, it is curious to learn that the largest of animals may in a manner be said to feed on some of the most diminutive of its fellows. In the far north, and in the surface-waters of the Arctic seas, myriads of minute organisms, closely allied to our whelks, and like mollusks, are found. Such are the "Sea-butterflies," or Pteropoda of the naturalist: little delicate creatures which paddle their way through the yielding waters by aid of the wing-like appendages springing from the sides of the head and neck. These organisms are drawn into the mouth of the Greenland whale in veritable shoals, and as the literal flood of waters streams out of the sides of the mouth, the "sea butterflies" are strained off therefrom, the savory morsels being retained by the fringed edges of the baleen-plates, and thereafter duly swallowed as food.
An interesting speculation yet remains, however, regarding the origin and first development of these peculiar whalebone-structures. Advocates of the doctrine which assumes that animal forms and their belongings arise by gradual modifications of preëxistent animals may be reasonably asked to explain the origin of the baleen-plates of the whales. Let us briefly hear what Mr. Darwin, as the spokesman of the party, has to say in reply to such an inquiry. Quoting a remark of an opponent regarding the whalebone, Mr. Darwin says, if the baleen "'had once attained such a size and development as to be at all useful, then its preservation and augmentation within serviceable limits would be promoted by natural selection alone. But how to obtain the beginning of such useful development?' In answer," continues Mr. Darwin (in his own words), "it may be asked, why should not the early progenitors of the whales with baleen have possessed a mouth constructed something like the lamellated beak of a duck. Ducks, like whales, subsist by sifting the mud and water; and the family (of ducks) has sometimes been called Criblatores, or sifters." Mr. Darwin's reference to the duck's bill is peculiarly happy. The edges of the beak in these birds are fringed with a beautiful series of horny plates named lamellæ, which serve as a straining apparatus as the birds grope for their food amid the mud of ponds and rivers. These plates are richly supplied with nervous filaments, and doubtless also some as organs of touch. Mr. Darwin is careful to add that he hopes he may not "be misconstrued into saying that the progenitors of whales did actually possess mouths lamellated like the beak of a duck. I only wish to show," he continues, "that this is not incredible, and that the immense plates of baleen in the Greenland whale might have been developed from such lamellæ by finely graduated steps, each of service to its possessor."
In these last words, which we have italicized, lies the strength of Mr. Darwin's hypothesis. Nature will preserve and develop useful structures alone, and will leave the useless and unneeded to perish and decay. This, indeed, is the keynote of natural selection. Mr. Darwin next proceeds to examine in detail the plates and lamellæ in the bill of a shoveler duck. He describes the horny plates, one hundred and eighty-eight in number, which "arise from the palate, and are attached by flexible membrane to the sides of the mandible." He further notes that these plates "in several respects resemble the plates of baleen in the mouth of a whale." If the head of a shoveler duck were made as long as the head of a species of whale in which the baleen-plates are only nine inches long, the duck's lamellæ would be six inches in length. The head of the shoveler is about one eighteenth of the length of the head of such a whale, so that the difference in size between the duck's lamellæ and the imperfect baleen-plates of this whale is not markedly disproportionate, after all. After the examination of the beaks of various species of swimming-birds, Mr. Darwin arrives at the conclusion that "a member of the duck family with a beak constructed like that of the common goose, and adapted solely for grazing, or even a member with a beak having less well-developed lamellæ, might be converted by small changes into a species like the Egyptian goose (which partly grazes and partly sifts mud)—this into one like the common duck—and, lastly, into one like the shoveler, provided with a beak almost exclusively adapted for sifting the water; for this bird could hardly use any part of its beak, except the hooked tip for seizing or tearing solid food. The beak of a goose, as I may add," says Mr. Darwin, "might also be converted by small changes into one provided with prominent recurved teeth, like those of the Merganser (a member of the same family), serving for the widely different purpose of securing live fish."
Mr. Darwin next endeavors to apply the moral of this interesting sketch of probable modification of the bills of ducks to the case of the whales. If the stages of modification in these animals are hypothetically so clear, may not the case of the whalebone-bearing whales be susceptible of like explanation? A certain whale (Hyperoödon) belonging to a small group known popularly as the "beaked whales," from the possession of a prominent beak or snout, has no true teeth, but bears rough, unequal knobs of horny nature in its palate. Here, therefore, is a beginning for the work of selection and development. Granted that these horny processes were useful to the animal in the prehension and tearing of food, then their subsequent development into more efficient organs is a warrantable inference if the order of living nature teaches us aright. From rudimentary knobs, a further stage of development would lead to an increase in which they may have attained the size of the lamellæ of an Egyptian goose, which, as already remarked, are adapted both for sifting mud and for seizing food. A stage beyond, and we reach the shoveler's condition, "in which the lamellæ would be two thirds of the length of the plates of baleen," in a species of whalebone whale (Balænoptera) possessing a slight development of these organs. And from this point, the further gradations leading onward to the enormous developments seen in the Greenland whale itself, are easily enough traced. Hypothetically, therefore, the path of development is clear enough. Even if it be remarked that the matter is entirely one of theory, not likely to be ever partly verified, far less proved at all, we may retort that any other explanation of the development of the organs of living beings, and of living beings themselves, must also be theoretical in its nature and as insusceptible of direct proof as are Mr. Darwin's ideas. But the thoughtful mind must select a side, and choose between probabilities; and it is not too much to say that toward the side of the idea which advocates gradual modification and selection as the rule of life and nature, every unbiased student of natural science will by sheer force of circumstances be led to turn.
The whalebone whales have no teeth, although the sperm whale possesses teeth in the lower jaw; but thereby—that is, as regards the teeth of whales at large—hangs a tale of some importance, and to which our attention may be briefly directed. Among the paradoxes of living nature, no circumstances present more curious features than those relating to the so-called "rudimentary organs" of animals and plants; the subject of these organs, and the lessons they are well calculated to teach, having been recently treated at some length in these pages. Now, the whales furnish several notable examples of the anomalies which apparently beset the pathways of development in animals. The adult whalebone whale is toothless, as has just been remarked; and this fact becomes more than usually interesting when taken in connection with another, namely, that the young whale before birth possesses teeth, which are shed or absorbed, and in consequence disappear before it is born. These teeth never "cut the gum," and the upper jaw of the sperm whale presents us with a like phenomenon for consideration. Nor are the whales peculiar in this respect. The upper jaw of ruminant animals has no front teeth—as may be seen by looking at the mouth of a cow or sheep—yet the calf may possess rudimentary teeth in this situation, these teeth also disappearing before birth. Now, what meaning, it may be asked, are we to attach to such phases of development? Will any considerations regarding the necessity for preserving the "symmetry," or "type," of the animal form aid us here; or will the old and overstrained argument from design enable us to comprehend why nature should provide a whale or a calf with teeth for which there is no conceivable use? The only satisfying explanation which may be given of such anomalies may be couched in Darwin's own words. The embryonic teeth of the whales have a reference "to a former state of things." They have been retained by the power of inheritance. They are the ignoble remnants and descendants of teeth which once were powerful enough, and of organs with which the mighty tenants of the seas and oceans of the past may have waged war on their neighbors. Again, the laws and ideas of development stand out in bold relief as supplying the key to the enigma. Adopt the theory that "things are now just as they always were," and what can we say of rudimentary teeth, save that Nature is a blunderer at best, and that she exhibits a lavish waste of power in supplying animals with useless structures? But choose the hypothesis of development, and we may see in the embryo-teeth the representatives of teeth which in the ancestors of our whales served all the purposes of such organs. Admit that, through disuse, they have become abortive and useless; and we may then, with some degree of satisfaction, explain their true nature. To use Darwin's simile, such rudiments are like letters in a word which have become obsolete in pronunciation, but which are retained in the spelling, and serve as a clew to the derivation of the word.
In the course of these remarks allusion has been made to more than one species of whale, and it may, therefore, form a study of some interest if we endeavor, shortly, to gain an idea of the general relationship and degrees of affinity of the various members of this curious family-circle. The whale order includes several of the divisions to which the zoölogist applies the name of "families," indicating, by this latter term, a close affinity in form, structure, and habits between the members of each group. First in importance among these families comes that of the whalebone whales (Balænidæ). Here we find family characters in a head disproportionately large when compared with the body as a whole, while the muzzle is sloping, and of rounded conformation. Teeth are absent, as we have seen; whalebone-plates fringe the palate; and the "blowhole" is single, and exists on the top of the head. Such are the family characters in which the Greenland or Right whale and the still larger Rorqual participate along with the "finner" whales and "humpbacked" whales. There is no back fin in the Greenland whale, but the Rorquals and their neighbors possess this appendage. It need hardly be said that, commercially, the former animal is of most importance; while the Rorquals are famed as the largest of the whales. Specimens of the Rorqual have been captured exceeding a hundred feet in length. One specimen, measuring ninety-five feet in length, weighed 245 tons. Next in importance to the Greenland whale and its relatives may be mentioned the family Physeteridæ, of which the sperm whale is the representative form. Here, the head reaches literally enormous proportions, and may make up fully one third of the body. A blunt, square muzzle; a lower jaw armed with teeth; an absence of baleen-plates, and a front blowhole—such are the characters of the sperm whale, which gives sperm-oil to the merchant, and spermaceti and ambergris to the man of drugs. A whole host of "small fry" present themselves as near relations of the whales, in the shape of the dolphins, porpoises, grampus, "bottle-noses," and other animals, including the famous narwhal, or sea-unicorn, possessing the longest tooth in the world in the shape of a spiral ivory pole, of some eight or ten feet in length. Here also the Beluga catodon, or "white whale," finds a zoölogical home, this latter form being the species of which more than one specimen has been recently exhibited in London. The beluga, being a member of the dolphin family, is a "whale" by courtesy only. Like the other members of this group, its blowhole is single and crescentic in shape, and both jaws are well provided with teeth. But the beluga, unlike the dolphins and porpoises, has no back fin, and its muzzle is blunt. This animal, however, is still certainly "very like a whale" in its general shape and aspect. Its creamy, white skin is certainly a peculiar feature; but the broad, horizontal tail-fin is well exemplified in this northern stranger, while the breathing habits of its group may also be studied superficially but satisfactorily on the specimen in question. The beluga inhabits the North American coast, at the mouths of the rivers on the Labrador and Hudson's Bay coast, while it is known to penetrate even to the Arctic regions. These whales are plentiful in the Gulf of St. Lawrence in spring and summer, and appear to migrate to the west coast of Greenland in October and November. The Esquimaux regard the beluga as their special prize, and contrive, with the aptitude for design which the necessities of savage existence teach, to utilize wellnigh every portion of its frame, even to the manufacture of a kind of animal-glass from its dried and transparent internal membranes.
But little space remains in which to treat of certain near relations and somewhat interesting allies of the whales. Such are the Manatees, or "sea-cows," and the Dugongs, collectively named Sirenia, in the category of zoölogists. The origin of this latter name is attended with some degree of interest. It has been bestowed on these animals from their habit of assuming an upright or semi-erect posture in the water; their appearance in this position, and especially when viewed from a distance by the imaginative nautical mind, having doubtless laid a foundation, in fact, for the tales of "sirens" and "mermaids" anxious to lure sailors to destruction by their amatory numbers. Any one who has watched the countenance of a seal from a short distance must have been struck with the close resemblance to the human face which the countenance of these animals presents. Such a likeness is seen even to a greater degree in the sea-cows, which also possess the habit of folding their "flippers," or swimming-paddles, across their chests, and, it is said, of holding the young to the breast in the act of nutrition by aid of the paddle-like fore-limbs. If I mistake not, Captain Sowerby mentions, in an account of his voyages, that the surgeon of the ship on one occasion came to him in a state of excitement to announce that he had seen a man swimming in the water close at hand; the supposed human being proving to be a manatee, which had been, doubtless, merely exercising a natural curiosity regarding the ship and its tenants.
These animals are near relatives of the whales, but differ from them, not merely in habits, but in bodily structure and conformation. They live an estuarine existence, rarely venturing out to sea. The manatees occur in the shallow waters and at the mouths of the great rivers of the Atlantic coasts of America and Africa. The dugongs inhabit the shores of the Indian Ocean, and are common on certain parts of the Australian coasts. There are only two living genera—the manatees and dugongs—of these animals; a third, the Rhytina Stelleri, having, like the famous Dodo, become extinct through its wholesale slaughter by man, in 1768, just twenty-seven years after it was first discovered by the voyager Behring on a small island lying off the Kamtchatkan coast. The Rhytina was a great unwieldy animal of some twenty-seven feet in length, and about twenty feet in circumference. It fell a ready prey to Behring and his crew, who were located on the island for several months; the work of extermination being duly completed by subsequent voyagers who visited the island. The manatees are no strangers to London, since in 1875 one of these animals was to be seen disporting itself in the seal-tank in the gardens of the Zoölogical Society at Regent's Park. This specimen, a female of immature age, was brought from the Demerara coast, and was the first living specimen which had been brought to England, although attempts had been made in 1866 to procure these animals for the gardens at Regent's Park, one specimen, indeed, dying just before reaching Southampton. A member of the Manatee group, obtained from Trinidad, was recently exhibited in London, and the public, interested in the curious in zoölogy, were thus enabled to interview a living member of the Siren group, while comparative anatomists, in their turn, have been afforded a rich treat from the fate which awaits rare and common specimens having, as we write, overtaken the illustrious visitor in question.
The manatees and dugongs possess bodies which, as regards their shape, may be described each as a great barrel "long drawn out." No hinder limbs are developed, this latter peculiarity distinguishing them from the seals, and relating them to the whales. The hide is very tough, sparsely covered with hair, and most nearly resembles that of the hippopotamus. The "flippers," or paddle-like limbs, are placed far forward on the body, and on the edge of the paddle rudimentary nails are developed; while concealed beneath the skin of the paddle we find the complete skeleton of an arm or fore-limb. The tail is broad, horizontally flattened, like that of the whales, and forms an effective propeller. These animals are vegetable feeders, the Zoölogical Society's specimen having exhibited a strong partiality for lettuce and vegetable-marrow. In a state of nature the sea-cows crop the marine vegetation which fringes their native shores. The remaining outward features of interest in these creatures may be summed up by saying that no back fins are developed; that the eyes are very small and inconspicuous; and that, although the anterior nostrils are never used as "blowholes," they can be closed at will like the nostrils of the seals—a faculty of needful kind in aquatic animals. To the technical anatomist, the sea-cows present strong points of resemblance to some of the hoofed quadrupeds. The anatomical examination of these animals has shown that their peculiarities are not limited to their outward appearance and habits. It is not generally known, for example, that the neck of the vast majority of mammals consists of seven vertebræ or segments of the spine. Man thus possesses this number in common with the giraffe, the elongation of whose neck is produced not by introduction of new vertebræ, but by the great development of the normal number, seven. The manatees, however, present a very remarkable exception to this most general of rules, in that they possess only six vertebræ in their necks. The only other exceptions to the rule of seven, as the normal number of neck-vertebræ in quadrupeds, are found in one species of sloth which has six vertebræ like the manatee, and in another kind of sloth which possesses nine. Then, also, the manatees possess a heart of very curious conformation, its apex or tip being widely cleft or divided—a feature much more plainly marked in these animals than in the elephants and seals, whose hearts, anatomically speaking, are also divided. The manatees possess well-developed molars or grinding teeth, but have no front teeth in the adult state. Like the whalebone whale, however, the young manatee has front teeth, these again disappearing before birth, and presenting us once more with examples of rudimentary organs which possess a reference "to a former state of things."
What evidence is at hand respecting the remote ancestors of the whales and their neighbors? is a question which may form a fitting conclusion to these brief details of the family history of the group. The geological evidence shows us that the whales are comparatively "recent" forms, speaking geologically, and dealing—notwithstanding the word "recent"—with very remote and immense periods of time. Among the oldest fossil whales we find one form in particular (Zeuglodon) which had teeth of larger kind than are possessed by any living whale, this creature being by some authorities regarded as linking the whales with the seals. The fossil remains of Zeuglodon and its neighbors first occur in Eocene rocks—that is, in the oldest formations of the Tertiary series, and in rocks of relatively "recent" nature. These remarkable creatures were as gigantic as their living representatives. One species is known to have attained a length of seventy feet. Their remains are of such frequent occurrence in the "Jackson Beds" of the United States, that Professor Dana remarks: "The large vertebræ, some of them a foot and a half long and a foot in diameter, were formerly so abundant over the country in Alabama, that they were used for making walls, or were burned to rid the fields of them." The teeth of this curious monster of the vasty Eocene deep were of two kinds, and included front teeth of conical shape, and grinders or molars; the latter exhibiting a striking peculiarity in that they were formed each of two halves, or teeth united by their crowns, but separated at their roots. Zeuglodon appears to connect the whales and their neighbors with the seals and walruses, and thus in one sense may be said to constitute, if not a "missing link," at least an intermediate form of anomalous kind, when viewed relatively to the existing cetaceans. According to the geological evidence at hand, we may assume that the modifications which have produced the existing whales and their neighbors are of comparatively recent date, and that their adaptation to an aquatic life is a thing but of yesterday when compared with the duration of previous æons in the history of our globe.