HISTORY OF MARINE MAMMALS—ABEL. 481 
and conical. The teeth of the walrus, on the contrary, are blunt and 
small, and some of them fall out early. 
Among the seals belong the harp seal, the monk seal (J/onachus), 
the hood seal, and the elephant seal, the last of which is the giant 
among seals and reaches a length of 9 meters (294 feet). The eared 
seals include the sea-lions and fur seals. The northern fur seal is the 
best known representative. 
The walrus is the only living genus of the family to which it 
belongs. 
4, THE OTTERS. 
Only one genus of otters, Hnhydris (or Lataw), that to which the 
sea-otter belongs, can be included among marine mammals, as all 
other otters are fresh-water animals and only occasionally go to sea. 
The sea-otter has a special interest for us, because its adaptation for 
a life in the sea has not progressed so far that the characters pecul- 
iar to otters have been effaced. If we compare the sea-otter with its 
allies, however, we see that its hind limbs have already become real 
fins, as in the seals, while the fore feet differ but little from those of 
land otters. It follows as a consequence of the larger size of the 
hind flippers that they play a more important role in the locomotion 
of this animal in the water than do the fore legs. 
We have passed step by step from the whales, which are modified 
in a remarkable manner for life in the sea, to the otters, which show 
but few differences from carnivorous land mammals. The thought 
might arise, therefore, that the sea-otters have descended from the 
otters, the seals from the sea-otters, and the whales from the seals; 
or, in other words, that in these several types we see before us the 
various stages through which the development of the whales has 
passed. This is not the case. We have only to observe the different 
modes of locomotion in the water displayed by the whales on the 
one hand and the seals on the other, and to consider that in the 
seals the tail is aborted, and does not bear a fin, while in the whales 
the tail fin is extraordinarily powerful, to be relieved of all doubt 
that there are here two fundamentally different forms of adaptation 
for life in the sea. 
Because these modifications of the seals and whales are entirely 
different, the latter can not possibly be derived from the former. 
The whales must possess ancestors in which the tail was long and 
well developed, so that at an early stage it could assume the labor 
of locomotion in the water. 
Similarly, detailed comparisons show that no close relationship 
exists between the seals and otters, and that the seals must have 
taken their origin from another branch of the carnivore stem. From 
the otters, seals, and whales. which without exception were originally 
