The best-known species of this family is the great Cachalot or Spermaceti Whale (Physeter macrocephalus, fig. 384). This animal is of enormous size, averaging from fifty to seventy feet in length, but the females are a good deal smaller than the males. The head is disproportionately large, as in the Balaenidae, forming more than one-third of the entire length of the body. The snout forms a broad truncated muzzle, and the nostrils are placed near the front margin of this. The Sperm Whales live together in troops or "schools," and they are found in various seas, especially within the tropics. They are largely sought after, chiefly for the substance known as "spermaceti;" but besides this they yield oil and the singular body called "ambergris." The spermaceti is a fatty substance, which has the power of concreting when exposed to the air, being in life a clear white oily liquid. It is not only diffused through the entire blubber, but is also contained in special cavities of the head. The sperm-oil yielded by the blubber is exceedingly pure, and is free from the unpleasant odour of ordinary whale-oil. The ambergris is a peculiar substance which is found in masses in the intestine, and is probably of the nature of a biliary calculus, since it is said to be composed of a substance very nearly allied to cholesterine. It is used both as a perfume itself, and to mix with other perfumes.

Fig. 384.   Spermaceti Whale (Physeter macrocephalus).

Fig. 384. - Spermaceti Whale (Physeter macrocephalus).

Fam. 3. Delphinidae. - This family includes the Dolphins, Porpoises, and Narwhal, and is characterised by usually possessing teeth in both jaws: the teeth being numerous, and conical in shape (fig. 385). The nostrils, as in the last family, are united, but they are placed further back, upon the top of the head. The single blow-hole or nostril is transverse and mostly crescentic or lunate in shape. The head is by no means so disproportionately large as in the former families, usually forming about one-seventh of the entire length of the body.

Fig. 385.   Side view of the skull of Delphinus tursio. (After Cuvier.)

Fig. 385. - Side-view of the skull of Delphinus tursio. (After Cuvier.)

The most noticeable members of this family are the true Dolphins, the Porpoises, and the Narwhal.

The Dolphins have an elongated snout, separated from the head by a transverse depression. The common Dolphin (Delphinus delphis, fig. 386) is the best-known species. It averages from six to eight feet in length, and has the habit of swimming in flocks, often accompanying ships for many miles. The female, like most of the Cetacea, is uniparous. The Dolphin occurs commonly in all European seas, and is especially abundant in the Mediterranean.

The common Porpoise (Phocaena communis) is the commonest and smallest of all the Cetacea, rarely exceeding four feet in length. The head is blunt, and is not produced into a projecting muzzle. The Porpoise frequents the Atlantic, Pacific, Mediterranean, and Arctic Oceans, and the North Sea, and is commonly seen off our coasts. Another British species is the Grampus (Orca gladiator), but this is much larger, attaining a length of from eighteen to twenty feet. Nearly allied to the Grampus is the so-called "Caing" Whale, or, as it is sometimes termed, the Bottle-nosed Whale (Globicephalus melas or Phocaena globiceps). This species occurs not uncommonly round the Orkney and Shetland Islands, and attains a length of as much as twenty-four feet. It is gregarious in its habits, and is often killed for the sake of its oil.

Fig. 386.   The common Dolphin (Delphinus delphis).

Fig. 386. - The common Dolphin (Delphinus delphis).

Closely allied to the true Dolphins are some curious Cetaceans, belonging to three genera, but all inhabiting fresh waters. One of these is the Gan-getic Dolphin (Platanista Gangelica), which inhabits the Ganges, especially near its mouth. This singular animal is characterised by the great length of its slender muzzle, and by the small size of the eyes. It attains the length of seven feet, and the blow-hole is a longitudinal fissure, and therefore quite unlike that of the typical Delphinidae. Closely allied to this, or identical with it, is the Platanista Indi of the Indus ; while the Orcella fiuminalis inhabits the Irawaddy. Another fresh-water form is the Inia Boliviensis, which inhabits the rivers of Bolivia, and is found at a distance of more than two thousand miles from the sea. Lastly, the Pontoporia Blainvillii is a small Dolphin which inhabits the rivers of the Argentine Republic and of Patagonia.

The last of the Delphinidae is the extraordinary Narwhal or Sea-unicorn (Monodon monoceros). The Narwhal is an inhabitant of the arctic seas, and attains a length of as much as fifteen feet, counting in the body alone. The dentition, however, is what constitutes the great peculiarity of the Narwhal. The lower jaw is altogether destitute of teeth, and the upper jaw in the females also exhibits no teeth externally, as a general rule at any rate, though there are two rudimentary canines (often looked upon as incisors) which do not cut the gum. In the males, the lower jaw is likewise edentulous, but the upper jaw is furnished with two molar teeth concealed in the gum, and with two canines. Of these two upper canines, that of the right side is generally rudimentary, and is concealed from view. The left upper canine, on the other hand, is developed from a permanent pulp, and grows to an enormous size, continuing to increase in length throughout the life of the animal. It forms a tusk of from eight to ten feet in length, and it has its entire surface spirally twisted. As an abnormality, both the upper canines may be developed in this way so as to form projecting tusks; and it is stated that the tusk is occasionally present in the female. The function of this extraordinary tooth is doubtless offensive.

Fam. 4. Rhynchoceti. - This family is allied to the Cachalots or Sperm Whales, and includes the so-called "Ziphioid Whales." They are distinguished by the possession of a pointed snout (the "beak" or "rostrum"), single blow-hole, small dorsal fin, and dentition. The upper jaw is greatly extended and is edentulous, any teeth which may be present not cutting the gum. The lower jaw, on the other hand, possesses usually a single pair of teeth, sometimes two pairs, which are sometimes tusk-like, but which in other cases are concealed by the gum, and are always most conspicuous in the males.

The rostrum of these Cetaceans is of great density, and has often been preserved in a fossil state, usually presenting itself as a bony cylinder or elongated cone, generally more or less water-worn. The most important living genera are Hyperoodon and Ziphius, of which the former is found in the North Atlantic, and the latter in the Mediterranean and South Atlantic. The genera Berardius and Mesoplodon belong to the New Zealand province, species of the latter having been obtained at the Cape of Good Hope and on the coasts of Britain and France.

Fam. 5. Zeuglodontidae. - The members of this family differ from all existing Odontoceti in the possession of molar teeth implanted by two distinct fangs. Incisor teeth are likewise present, and the animal is diphyodont. The Zeuglodonts are entirely extinct, and they are exclusively confined to the Eocene, Miocene, and Pliocene periods. The chief genera are Zeuglodon and Squalodon.

Zeuglodon (fig. 387) is distinguished by its elongated snout, conical incisors, and molar teeth with triangular serrated crowns, implanted in the jaw by two roots. Each molar looks as if it were composed of two separate teeth united on one side by their crowns; and it is this peculiarity which is expressed by the generic name. The species of Zeuglodon are Eocene and Miocene. The species of Squalodon are Miocene and Pliocene.

Fig. 387.   Zeuglodon cetoides. A, Molar tooth, natural size ; B, Vertebra, reduced. From the Middle Eocene of North America. (After Lyell.)

Fig. 387. - Zeuglodon cetoides. A, Molar tooth, natural size ; B, Vertebra, reduced. From the Middle Eocene of North America. (After Lyell.)

As regards the distribution of the Cetacea in time, no member of the order has yet been detected in any Secondary deposit. The Zeuglodonts, as just remarked, extend from the Eocene to the Pliocene, Zeuglodon itself being the oldest Cetacean at present known. The Ziphioid Whales begin in the Pliocene, as do the Catodontidae.; but the Delphinidae are known to occur in the Miocene. The Balaenidae are not known to have existed earlier than the Pliocene.