CHARA

GENERAL CHARACTERS

233

established. The steps by which a land mammal may have been modified into a purely aquatic one are indicated by the stages which still survive among the Carnivora in the Otariide and in the true Seals. A further change in the same direction would produce an animal somewhat resembling a Dolphin; and it has been thought that this may have been the route by which the Cetacean form has been developed. There are, however, great difficulties in the way of this view. Thus if the hind limbs had ever been developed into the very efficient aquatic propelling organs they present in the Seals, it is not easy to imagine how they could have become completely atrophied and their function transferred to the tail. So that from this point of view it is more likely that Whales were derived from animals with long tails, which were used in swimming, eventually with such effect that the hind limbs became no longer necessary. The powerful tail, with its lateral cutaneous flanges, of an American species of Otter (Lutra brasiliensis) may give an idea of this member in the primitive Cetaceans. But the structure of the Cetacea is, in so many essential characters, so unlike that of the Carnivora that the probabilities are against these orders being nearly related. Even in the skull of the Zeuglodon, which has been cited as presenting a great resemblance to that of a Seal, quite as many likenesses may be traced to one of the primitive Piglike Ungulates (except in the purely adaptive character of the form of the teeth), while the elongated larynx,1 complex stomach, simple liver, reproductive organs both male and female, and foetal membranes of the existing Cetacea are far more like those of that group than of the Carnivora. Indeed it appears probable that the old popular idea which affixed the name of "Sea-Hog" 2 to the Porpoise contains a larger element of truth than the speculations of many accomplished zoologists of modern times. The fact that Platanista, which, as mentioned above, appears to retain more of the primitive characteristics of the group than any other existing form, and also the somewhat related Inia from South America, are both at the present day exclusively fluviatile, may point to the fresh-water origin of the whole group, in which case their otherwise rather inexplicable absence from the seas of the Cretaceous period would be accounted for.

On the other hand, it should be observed that the teeth of the Zeuglodonts approximate more to a carnivorous than to an ungulate type. It is scarcely necessary to allude to the hypothesis started by some Continental writers to the effect that the Whales are the most primitive type of mammals with which we are acquainted, 1 There is much resemblance in the larynx of the Hippopotamus, but none in that of the Seal, to the same organ in the Cetacea.

* German Meerschwein, whence the French Marsouin. to be derived from "Porc-poisson."

"Porpoise" is said

and that they are the descendants of the Mesozoic reptilian order Ichthyopterygia, from which their hyperphalangism is a direct inheritance. The Ichthyopterygia have been shown, on very strong evidence, to have been derived from land reptiles, and to have gradually acquired their hyperphalangism as an adaptive character suitable to their peculiar mode of life, and there can be but little doubt that a similar adaptation has taken place in the case of the Whales.

Suborder MYSTACOCETI,

the BALENOIDEA, Whalebone, or True Whales.1

Family BALENIDÆ.

Teeth never functionally developed, but always disappearing before the close of intra-uterine life. Palate provided with plates of baleen or “whalebone." Skull symmetrical. Nasal bones forming a roof to the anterior nasal passages, which are directed upwards and forwards. Maxilla produced in front of, but not over, the orbital process of the frontal. Lachrymal bones small and distinct from the jugal. Tympanic bone involuted (Fig. 76), and ankylosed with the periotic, which is attached to the base of the cranium by two strong diverging processes. Olfactory organ distinctly developed. Rami of mandible arched outwards, their anterior ends. meeting at an angle, and connected by fibrous tissue without any true symphysis. All the ribs at their upper extremities articulating only with the transverse processes of the vertebræ; their capitular processes, when present, not articulating directly with the bodies of the vertebræ. Sternum composed of a single piece, and articulating only with a single pair of ribs. No ossified sternal ribs. External openings of nostrils distinct from each other, longitudinal. A short conical cæcum.

These animals have, when in the foetal state, numerous minute calcified teeth lying in the dental groove of both upper and lower jaws. They are best developed about the middle of foetal life, after which period they are absorbed, and no trace of them remains at the time of birth. The baleen or whalebone does not make its appearance until after birth. It consists of a series of flattened horny plates, between three and four hundred in number, on each side of

1 Icel. hvalr; Dan. and Swed. hval; Anglo-Saxon hwal; Germ. wal, walfisch. The meaning apparently is "roller," the word being closely allied to "wheel" (Skeat).

2 These were discovered in the Greenland Whale by Geoffroy St. Hilaire, whose observations were confirmed and extended to other genera by Eschricht. They have been very fully described in Balanoptera rostrata by Julin (Archivs de Biologie, i. 1880).

the palate, with a bare interval along the middle line. These plates are placed transversely to the long axis of the palate, with very short intervals between them. Each plate or blade is somewhat triangular in form, with the base attached to the palate and the apex hanging downwards. The outer edge of the blade is hard and smooth; but the inner edge and apex fray out into long bristly fibres, so that the roof of the Whale's mouth looks as if covered with hair, as described by Aristotle. At the inner edge of each principal blade are two or three much smaller or subsidiary blades. The principal blades are longest near the middle of the series, and gradually diminish towards the front and back of the mouth. The horny plates grow from a dense fibrous and highly vascular matrix, covering the palatal surface of the maxillæ, and sending out lamellar processes, one of which penetrates the base of each blade. Moreover, the free edge of these processes is covered with very long vascular thread-like papillæ, one of which forms the central axis of each of the hair-like epidermic fibres of which the blade is mainly composed. A transverse section of fresh whalebone shows that it is made up of numbers of these soft vascular papillæ, circular in outline, each surrounded by concentrically arranged epidermic cells, and the whole bound together by other epidermic cells, that constitute the smooth cortical (so-called " enamel ") surface of the blade, which, disintegrating at the free edge, allows the individual fibres to become loose and assume the hair-like appearance before spoken of. These fibres differ from hairs in not being formed in depressed follicles in the enderon, but rather resemble the fibres composing the horn of the Rhinoceros. The whalebone in fact consists of nothing more than modified papillæ of the buccal mucous membrane, with an excessive and cornified epithelial development. The blades are supported and bound together for a certain distance from their base by a mass of less hardened epithelium, secreted by the surface of the palatal membrane or matrix of the whalebone in the intervals of the lamellar processes. This is the "intermediate substance" of Hunter, the "gum" of the whalers. Baleen varies much in colour in different species. In some it is almost jet black, in others slatecolour, horn-colour, yellow, or even creamy-white. In some the blades are variegated with longitudinal strips of different hues. Baleen differs also greatly in other respects, being short, thick, coarse, and stiff in some, and greatly elongated and highly elastic in those species in which it has attained its fullest development. Its function is to strain the water from the small marine molluscs, crustaceans, or fish upon which the Whales subsist. In feeding the immense mouth is filled with water containing shoals of these small creatures, and then, on the Whale closing the jaws and raising the tongue, so as to diminish the cavity of the mouth, the water streams out through the narrow intervals between the hairy fringe of the

whalebone blades, and escapes through the lips, leaving the living prey to be swallowed.1

Our knowledge of the different structural modifications attained by members of this important group of mammals, though largely increased of late years, is still imperfect. Formerly they were all divided into Right Whales (Balana) and Rorquals or Fin-Whales (Balaenoptera), the latter distinguished by their smaller heads, elongated and slender form, free cervical vertebræ, tetradactylous manus, and the presence of very conspicuous longitudinal furrows or folds in the skin of the throat and chest, and of a small adipose dorsal fin. Recent discoveries have, however, brought to light several forms holding a somewhat intermediate position, and presenting combinations of characters not found in either of the longer known sections. According to our present knowledge the group naturally divided into five very distinct genera, of which the leading characters are given below.

Balana.2-Skin of throat smooth, not furrowed. No dorsal fin. Cervical vertebræ united into a single mass. Pectoral limb short, broad, and pentadactylous. Head very large. Baleen very long and narrow, highly elastic, and black. Scapula high, with a distinct coracoid and acromion process. Tympanic (Fig. 78) deep and angular, its inflation comparatively slight, and the involuted portion not figshaped, and frequently without a well-marked depression at the anterior extremity of the superior border of the inner surface for the Eustachian canal.

The Greenland, or more properly Arctic, Right Whale (Balana mysticetus) attains, when full grown, a length of from 45 to 50 feet. Its usual vertebral formula is C 7, D 12, L 14, C 22. The external form is shown in Fig. 76 from a careful drawing by

1 For the structure of whalebone see Hunter, "Observations on the Structure and Economy of Whales," Phil. Trans. 1787; Eschricht and Reinhardt, On the Greenland Right Whale, English translation by the Ray Society, 1866, pp. 67-78; and Sir W. Turner, in Trans. Roy. Soc. Edin. 1870.

2 Linn. Syst. Nat. 12th ed. vol. i. p. 105 (1766).

Mr. Robert Gray. In this species all the peculiarities which distinguish the head and mouth of the Whales from those of other mammals have attained their greatest development. The head is of enormous size, exceeding one-third of the whole length of the creature. The cavity of the mouth is actually larger than that of the body, thorax and abdomen together. The upper jaw is very narrow, but greatly arched from before backwards, to increase the height of the cavity and allow for the great length of the baleen blades; the rami of the mandible are widely separated posteriorly, and have a still further outward sweep before they meet at the symphysis in front, giving the floor of the mouth the shape of an immense spoon. The baleen blades attain the number of 380 or more on each side, those in the middle of the series having a length of 10 or sometimes 12 feet. They are black in colour, fine and highly elastic in texture, and fray out at the inner edge and ends into long, delicate, soft, almost silky, but very tough, hairs. The remarkable development of the mouth and the structures in connection with it, which distinguishes the Right Whale among all its allies, is entirely in relation to the nature of its food. It is by this apparatus that the animal is enabled to avail itself of the minute but highly nutritious crustaceans and pteropods which swarm in immense shoals in the seas it frequents. The large mouth enables it to take in at one time a sufficient quantity of water filled with these small organisms, and the length and delicate structure of the baleen provide an efficient strainer or hair-sieve by which the water can be drained off. If the baleen were rigid, and only as long as is the aperture between the upper and lower jaws when the mouth is shut, a space would be left beneath it when the jaws were separated, through which the water and the minute particles of food would escape together. But instead of this the long, slender, brush-like, elastic ends of the whalebone blades fold back when the mouth is closed, the front ones passing below the hinder ones in a channel lying between the tongue and the lower jaw. When the mouth is opened, their elasticity causes them to straighten out like a bow unbent, so that at whatever distance the jaws are separated the strainer remains in perfect action, filling the whole of the interval. The mechanical perfection of the arrangement is completed by the great development of the lower lip, which rises stiffly above the jaw-bone and prevents the long, slender, flexible ends of the baleen from being carried outwards by the rush of water from the mouth, when its cavity is being diminished by the closure of the jaws and raising of the tongue.

If, as appears highly probable, the "bowhead" of the Okhotsk Sea and Behring Strait belongs to this species, its range is circumpolar. Though found in the seas on both sides of Greenland, and