The Probert Encyclopaedia of Nature

CETACEA

Cetacea is an order of marine animals, surpassing in size all others in existence. They are true mammals, since they suckle their young, have warm blood, and respire by means of lungs, for which purpose they come to the surface of the water to take in fresh supplies of air.

The body is fish-like in form, but ends in a bilobate tail, which is placed horizontally, not, as in the fishes, vertically. The posterior limbs are wanting - though not unfrequently stumps are present in individuals - and the anterior are converted into broad paddles or flippers, consisting of a continuous sheath of the thick integument, within which are present representatives of all the bones usually found in the fore-limb of mammals. The fish-like aspect is further increased by the presence of a dorsal fin, but this is a simple fold of integument, and does not contain bony spines.

The right whale and its allies have no teeth in the adult state, their place being taken by the triangular plates of baleen or whalebone which are developed on transverse ridges of the palate, but the foetal whales possess minute teeth, which are very soon lost. The nostrils open directly upwards on the top of the head, and are closed by valvular folds of integument which are under the control of the animal. When it comes to the surface to breathe it expels the air violently (popularly known as 'blowing' or 'spouting'), and the vapour it contains becomes condensed into a cloud, which resembles a column of water and spray. The blood-vessels in these animals break up into extensive plexuses or net-works, in which a large amount of oxygenated blood is delayed, and they are thus enabled to remain a considerable time under water. Injury to these dilated vessels leads to profuse hemorrhage, and hence the whale is killed by the comparatively trifling wound of the harpoon.

The Cetacea (which are grouped broadly as Mysticeti or toothless whales; and Odontoceti, Denticeti, or toothed whales) are commonly divided into five families: (1) Balaenidce, or whalebone whales, divided into two sections: smooth whales, with smooth skin and no dorsal fin, and furrowed whales, with furrowed skin and a dorsal fin; (2) Physeteridae, Catodontidae, sperm-whales or cachalots, the palates of which have no baleen-plates, and which are furnished with teeth, developed in the lower jaw only; (3) Delphinidae, a family possessing teeth in both jaws, and including the dolphins, porpoises, and narwhal; (4) Rhynchoceti, a family allied to the sperm-whales, but having only a pair or two pairs of teeth in the lower jaw, a pointed snout or beak, a single blow-hole, etc; (5) Zeuglodontidae, an extinct family, distinguished from all the tooth-bearing whales by the possession of molar teeth implanted by two distinct fangs, etc. The last family is exclusively confined to the Eocene, Miocene, and Pliocene periods. The Sirenia, or manatees and dugongs, have sometimes been classified among the Cetacea, but they must be regarded as forming a separate order.
Research Cetacea