HISTORY OF MARINE MAMMALS—ABEL. 479 
2. THE SEA-COWS. 
The sea-cows, or sirenians, are awkward, stupid creatures, which 
can scarcely move on land, but are excellent swimmers. In spite of 
their whale-like form, they must be associated with the ungulates, 
from which at first sight they seem very different. Their food con- 
sists exclusively of aquatic plants, and it is for this reason that they 
live only on the seacoast or in rivers. 
The arms and hands, as in the whales, take the form of flippers. 
As in the whales also, locomotion is due solely to the action of the 
caudal fin, and the hind limbs are aborted. 
A sea-cow leaves the water no more willingly than a whale. Their 
arms, however, are capable of supporting the body while the animals 
are grazing on the fields of seaweed (Tangwilder), and on this ac- 
count they are still movable at the elbow, which is no longer the case 
in whales. 
Within historical times a sea-cow, known as Steller’s sea-cow, 
Rhytina (or Hydrodamalis), has been completely exterminated. 
Steller discovered this helpless animal, which was from 8 to 10 meters 
(26 to 32} feet) long, in 1741 in Bering Island. About twenty-seven 
years later it was annihilated. 
At present only two genera of sea-cows live in the tropics. One 
of them, the dugong (falicore), is distributed from the Red Sea 
along the coast of India to the Solomon Islands. The other genus, 
the manatee (J/anatus, or Trichechus) (fig. 6), lives on the east coast 
of South America (ranging northward to Florida). The dugong 
lives exclusively in the ocean, but the manatee ascends rivers. The 
African manatee has been met with in the Kibali River more than 
2,000 kilometers (1,243 miles) from the mouth of the Congo. The 
American manatee has withdrawn in part to the upper courses of 
the Orinoco and the Amazon. 
3. THE PINNIPEDS. 
The seals are at once distinguishable from the whales and sea-cows 
from the fact that they possess well-developed hind limbs. The tail, 
on the contrary, is aborted and does not end in a fin. 
The manner of progression in the water is entirely different in the 
representatives of the three families of pinnipeds (sea-lions, walruses, 
and seals). The seal (fig. 7) swims by powerful back strokes of its 
hind limbs, which are formed like fins, and after a stroke are laid 
against one another and, as it were, folded together. This mode of 
swimming has a great advantage, because the surface exposed to the 
water, and hence the resistance of the water, is thereby greatly re- 
duced. The arms of the seal serve only for steering, as in the whales. 
