INTRODUCTION. 
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of birds., by bringing forth their young alive ; 
like us., they are placed above the class of fishes, 
by breathing through their lungs ; like us, they 
are placed above the class of insects, by having 
red blood circulating through their veins ; and, 
lastly, like us, they are different from almost all 
the other classes of animated nature, being either 
wholly or partly covered with hair. Thus nearly 
are we represented in point of conformation to the 
class of animals immediately below us ; and this 
shows what little reason we have to be proud of 
our persons alone, to the perfection of which qua- 
drupeds make such very near approaches. 
? Quadrupeds, although they are thus strongly 
marked, and in general divided from the various 
kinds around them, yet some of them are often of 
so equivocal a nature, that it has been asserted, it 
is hard to tell whether they ought to be ranked 
in the quadruped class, or degraded to those below 
them. If, for instance, we were to marshal the 
whole group of animals around man, placing the 
most perfect next him, and those most equivocal 
near the classes they most approach, we should, it 
is said, find it difficult, after the principal had 
taken their stations near him, where to place many 
that lie at the out-skirts of this phalanx. The 
hat makes a near approach to the aerial tribe, and 
might, by some, be reckoned among the birds. 
The porcupine has also some pretensions to that 
class, being covered with quills, and showing that 
birds are not the only part of nature that are fur~ 
