MAMMALS AND LIZARDS 
quadrupedal except occasionally and during his young 
stages ; the whales are clearly not so; neither are the 
manatees and dugongs ; the bats, it is true, do shuffle 
along on their ‘“ wings ”’ as well as by the aid of their 
hind limbs ; but it would be straining the proper use 
of the term to describe them as “ quadrupeds.” But 
when quadrupedal, as in the vast majority of mammals, 
the fore and hind limbs lie beneath and actually support 
the body more directly than in the other quadrupedal 
group, the Reptiles. In the latter it will be noticed 
that the body is, as it were, slung between the legs like the 
body of an eighteenth-century coach between its wheels ; 
in the mammals the legs support the body as its legs 
do a chair. We may, however, legitimately say that the 
mammalia are much more generally quadrupedal than 
are the reptiles, of which (see below) so many are entirely 
or partially legless. The next point is one which abso- 
lutely distinguishes all mammals from al] other verte- 
brates (and, of course, invertebrates). This feature is 
the covering of hair. To this statement there are no 
real exceptions, but several apparent exceptions, which 
we must note. The apparent exceptions, again, are of - 
animals which really do not enter into the subject matter 
of this volume. A very little observation will convince 
any one that the almost naked rhinoceros has some 
vestiges of a hairy covering. But the whales, again, 
which contradict so many generalizations about the 
class mammalia, are rather more deceptive. Their 
covering of hair is reduced to a few hairs in the neigh- 
bourhood of the mouth. If these were to go it would be 
most difficult to state definitely, from external characters 
only, that a whale was not an aquatic reptile like the 
Ichthyosaurus. There are, moreover, a series of excep- 
tions on the other side. Some of the feathers of flightless 
birds, such as the APteryx, have to the naked eye every 
appearance of hairs. Their microscopic character, and 
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