Delphinida.—This family includes the Dolphins, Porpoises, and Narwhal, and is characterized by usually possessing teeth in both jaws : the teeth being numerous, and conical in shape. 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. 214.—The common Dolphin (Jielphinus delphis).

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 ddphis, fig. 214) 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 (Phocana 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 North Sea, and is commonly seen off our coasts. Another British species is the Grampus (Phocana orca), 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 (Globicephaltts or Phoaena 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.

 

Dolphin Birth

Closely allied to the true Dolphins are two curious Cetaceans, belonging to different genera, but both inhabiting fresh waters. One of these is the Gangetic Dolphin (Platanista Gangetica), 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 Delphinida. The other 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. In its essential characters it differs little from its marine brethren, and it attains a length of from seven (female) to fourteen feet (male). The last of the Ddphinida 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 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 incisors. Of these two upper incisors, that of the right side is generally rudimentary, and is concealed from view. The left upper incisor, 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 incisors 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. - Manual of Zoology  by HENRY ALLEYNE NICHOLSON edited by Stanley L. Klos.