CETACEA—WHALES AND DOLPHINS
Order VI. CETACEA.[[221]]
Aquatic Mammalia of fish-like form; tail expanded into horizontal flukes; a fatty dorsal "fin" present in most species; anterior limbs converted into fin-like paddles; posterior limbs only represented by skeletal rudiments. Hairy covering reduced to a few isolated hairs in the neighbourhood of the muzzle. Nostrils represented by the single or double blow-hole, nearly always situated far back upon the skull. Bones of loose texture and much impregnated with oil. The skull has a greatly-developed facial portion; supra-occipital bones meeting the frontal by overgrowing, or growing in between the parietals; bones surrounding the organ of hearing loosely attached to the skull, the tympanics of peculiar cowrie-shell form. Coronoid process of mandible absent, or very feebly developed. Teeth, when present, few or numerous, always of simple conical form, with at most traces of additional cusps (Inia); if absent their place taken by whalebone. Cervical vertebrae of short antero-posterior diameter, often more or less completely welded together into a single mass. Articulations between dorsal and other vertebrae feeble. Scapula peculiarly flattened; acromion strongly developed as a rule, but arising from a slightly-marked spine; coracoid process generally strongly developed. Phalanges of digits always more numerous than in other mammals. Clavicles absent. Stomach complex, consisting of at least four and often more chambers. Lungs simple and non-lobulated. Diaphragm obliquely set and very
muscular. Brain much expanded transversely and well convoluted. Testes abdominal. Teats two, inguinal in position. Placenta diffuse and non-deciduate.
The Whales and Dolphins, which constitute this order, form an assemblage which is easily characterised by reason of the fact that their affinities to other groups of Mammalia are so doubtful that they furnish matter rather for speculation than for authoritative statement. Some hold that they resemble in certain points the Ungulata; while others again see in them the culminating term of a series which commences with such a form as the Otter, and of which the Seals and Sea-lions are intermediate stages. A third opinion is that the Whales have arisen from some low mammalian stock, too primitive to be assigned to any existing order of mammals. Palaeontology, as will be seen later, throws no light whatever upon their origin. This matter has already been referred to (see p. [120]) in considering the position of the Cetacea.
The Whales include the most gigantic of all the orders of vertebrated animals. No creature living or extinct is so large as the Sibbald's Rorqual, which attains to a length of some 85 feet, or perhaps even rather more. On the other hand we have what are by comparison minute forms. Apart from the possibly problematical Delphinus minutus, stated to be only 2 feet in length, we have as a minimum 3 or 4 feet. The size of the Cetacea has been subjected to much exaggeration. The first duty of a Whale, observed the late Sir William Flower, is to be large; and Natural Historians, in the recent as well as in the remote past, have not hesitated to put very round numbers upon the dimensions of the larger members of the order. We may perhaps pass over Pliny's "fish called balaena or whirlpool, which is so long and broad as to take up more in length and breadth than two acres of ground," and a number of analogous exaggerations, which gradually dwindled down to the dimensions just stated of the great Rorqual. M. Pouchet has made the ingenious suggestion that the statements of the ancients may have been nearer the truth than observations of to-day would have us believe; he pointed out justly that in former times Whales were not so relentlessly pursued as during the last century; the inference being that they may have lived to a greater age, and attained a more colossal bulk. The more modern exaggerations in the
dimensions of the bigger Whales are probably due to the fact that measurements have been taken, not in a straight line from snout to tail, but along the bulging sides of the Cetacean, rendered even more convex than in nature by decomposition, and by pressure due to the immense tonnage of the creature.
The Cetacea are the most perfectly aquatic of all mammals; they never leave the waters which they inhabit. It is true that legends have represented them as pasturing upon the shore—Aelian spoke of Dolphins basking in the sun's rays upon the sand; and the "Devil Fish" of California, Rhachianectes (see p. [357]) has given rise to improbable stories—but they are apparently only legends. Indeed a stranded Whale cannot live long, for it is unable to breathe, the comparatively feeble breast being crushed by its own weight. In accordance with the purely aquatic habit, we find a modification of the outward form of the body (and as we shall see later of many of the internal organs), which renders the Cetacea externally unlike all other mammals. The form is fish-like, the fore-limbs are paddles, the tail is expanded into two horizontal flukes, which serve to propel the creature through the water.
Fig. 180.—Killer. Orca gladiator. × 1⁄40 (After True.)