64° CETACEA. 
dugong from Indian, and ZH. australis from Australian seas, but 
no valid characters by which to distinguish the various forms 
appear to have been adduced. 
Order II.—CETACEA. 
Body fusiform, passing anteriorly into the head without any 
distinct neck, posteriorly tapering off gradually to the base of the 
tail, which is provided with a pair of lateral, pointed expansions 
of skin, forming together a horizontally placed triangular propell- 
ing organ, notched in the middle line behind. Head generally 
large, sometimes more than one-third of the total length ; aperture 
of mouth always wide, bounded by stiff immobile lips. Fore limbs 
modified into flattened ovoid paddles, encased in a continuous 
integument. No external signs of hind limbs. General surface 
of skin smooth and glistening, devoid of hair. A compressed 
median dorsal fin almost always present. Eye small; no nictita- 
ting membrane nor true lachrymal apparatus, Auditory opening 
consisting of a minute aperture in the skin situated a short distance 
behind the eye, without vestige of pinna. Nostrils opening 
separately or by a single crescentic valvular aperture near the 
vertex. Teeth generally present but very variable in number, of 
simple, uniform character, having conical, compressed crowns, 
and single roots, and never preceded by milk teeth. Among the 
Mystacoceti the teeth are absent (see p. 65). No clavicles. Im- 
mediately beneath the skin and intimately connected with it, is a 
thick layer of fat, held together by a dense mesh of areolar tissue 
constituting the blubber, which serves the purpose of the hairy 
covering of other mammals in retaining the heat of the body. 
Cetaceans abound in all seas and in some of the larger rivers of 
Asia, such as the Ganges, Indus, and Irrawaddy, and cf South 
America where the “ Jnia” of the natives of Bolivia ascends the 
Amazon even to its remote sources among the Peruvian Lakes. 
Necessarily from the structure of their limbs they are purely 
aquatic mammals and once stranded, from any cause whatever, 
are absolutely at the mercy of their smallest enemy. For the 
purpose of respiration it is necessary that they should rise fre- 
quently to the surface, and since this necessitates a frequent 
upwardly rising motion and a subsequent plunging downwards 
the tail is therefore expanded horizontally, not vertically as in 
Fishes where no such motion is requisite. For an equally benefi- 
cent reason the respiratory orifice is placed on the highest point, 
or vertex, of the head, with the purpose of enabling the animal to 
breathe without trouble while at the same time exposing the 
smallest possible portion of its body above the surface, where it 
might necessarily expect to meet with its most dangerous foes and 
where its powers of vision, such as they are, would be hopelessly 
