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 all 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 



8 



