570 CONCLUSIONS. 
called Propinnipedia, had most probably hind-legs which were 
smaller than the fore-legs, and most certainly a tail which was 
nearly as long as the head, neck and trunk together. They had 
small external ears. Their most successful. manner of swimming 
must have been by means of vertical undulations. It is difficult to 
believe that the Propinnipedia moved on land; probably they came 
only from time to time aland, or on the ice, to rest, leaving, 
however, most probably the long tail in the water. These Propin- 
nipedia divided themselves into two branches. 
All the members of the frs¢ branch got a tendency to bulkiness. 
The head grew longer and larger, consequently the neck grew 
shorter; the jaws grew longer, consequently the teeth began to 
stand widely apart; in consequence of the little mobility of the 
head the nostrils, placed at the top of the nose, became turned 
upwards, or probably got their seat a little more towards the top of 
the head; and in proportion as the animal got a thick layer of bacon, 
the hairs became thinly scattered. Probably it is here better to say: 
in proportion as the animal lost its hairs, it got a thick layer of 
bacon. The warm-blooded mammals are possessed of the hair, be- 
cause hair was to them what feathers are to a bird. The air en- 
closed between the hairs and the feathers is a worse conductor of 
temperature than the hairs or feathers themselves. As soon as the 
manner of living has changed so much that air could no longer 
come between the hairs, the hairs themselves lost their reason of 
existence, hence a thick layer of bacon gradually replaced them. 
Probably this is a better way to explain the presence of bacon and 
the absence of hair, than to say that the hair disappeared because 
the animals obtained a layer of bacon, and could therefore dispense 
with them, or that the layer of bacon checked the development 
of hairs. —In short we may admit that the animals, of which we 
treat at present, were thinly scattered with hairs. The whiskers 
in all probability were still present, and even well developed. 
This branch has wholly become extinct. The fossil remains were 
called Basilosaurus, 
All the members of the second branch did not show a tendency 
to bulkiness, they retained the relatively small head and well de- — 
veloped neck, the head consequently could very well move on the 
trunk. These are the Pinnipedia. : 
Already very early they divided themselves into two sections. 
Al the members of the jist section accustomed themselves to 
crawl more on land, ice, and rocks, and as the long tail must 
