CONCLUSIONS. 363 
themselves to live more among sea-weed, ice, and rocks than their 
direct ancestors, the long tail must have been inconvenient, so 
that individuals with a shorter tail must have survived the others, 
and finally a species arose with a tolerably short tail: our sea-otter. 
To make up for this loss of tail, the hind-feet had become more 
webbed, and were gradually stretched more backwards, and, mod- 
ified in this way, they were valuable swimming organs. The change 
was great enough for zoologists to create a new genus for this 
animal, which is called Hxhydra Cvuv. 
Some of the Jong-tailed ancestors of sea-otters took to a still 
more aquatic, or better pelagic life, migrated more towards the 
north, accustomed themselves to the icy regions, to swim greater 
distances and to remain longer under water. The consequences of 
this change in the manner of living were that all little adapted to 
this new life became extinct, and that all which were better privi- 
leged survived them, so that at last a group of animals arose of which 
we may safely admit that they had the following characters: The head 
and fore-feet resembled still more those of seals, the hind-legs were still 
more able swimming organs, and less fit for terrestrial locomotion , they 
were smaller than the fore-legs, because they were not always used 
in swimming, as the best manner of swimming must have been by 
means of vertical undulations; the long tail surpassed half of the total 
length, and served as a rudder and as propelling organ; the ears were 
still smaller, the dentition was still a normal carnivorous one (i ;, 
c +, m 7), especially the molars were sharp and pointed, and on the 
skull were found peculiar modifications which are so distinctly visible 
on that of Pinnipeds. The animals must have resembled our common | 
seals, having, however, small external ears, and a tail, surpassing 
one half of the total length. It is difficult to believe that these ani- 
mals, which I will call Propimnipedia, moved on land; probably 
they came from time to time aland or on the ice to rest with the 
fore-part of the body on it, leaving, however, most certainly the long 
tail in the water. These Propinnipedia gave origin to two groups of 
animals, which are marked below with A and B. 
A. — This group, by their having lived almost constantly far 
from land, and having come only very seldom near the shore to 
rest, supporting themselves on the chest or breast, clinging with 
the nails of the fore-legs to the beach, rock, or ice, changed in 
such a way, that zoologists can hardly reckon them any longer 
among Pinnipeds, but generally consider them as a link between 
Pinnipeds and Whales. Professor D’Arcy W. THompson (Sludes 
