128 . ANIMALS OF THE PAST 
their feathers have become a sort of cross be- 
tween scales and hairs. Hair and fur belong — 
to mammals only, although these creatures 
show much variety in their outer covering. 
The thoroughly marine whales have discarded 
furs and adopted a smooth and slippery skin,* 
well adapted to movement through the water, 
relying for warmth on a thick undershirt of 
blubber. The earless seals that pass much of 
their time on the ice have just enough hair 
to keep them from absolute contact with it, 
warmth again being provided for by blubber. 
The fur seals, which for several months in the 
year dwell largely on land, have a coat of fur 
and hair, although warmth is mostly furnished, 
or rather kept in, by fat. 
No reptile, therefore, would be covered with 
** The reader is warned that this is a mere figure of speech, Ly 
for, of course, the process of adaptation to surroundings is 
passive, not active, although there is a most unfortunate ten- 
dency among writers on evolution, and particularly on mimicry, 
to speak of it as active. The writer believes that no animal | 
in the first stages of mimicry, consciously mimics or endeav- | 
ors to resemble another animal or any part of its surround- 
ings, but a habit at first accidental may in time become 
more or less conscious. 
