INTRODUCTION. 
V 
The animal kingdom adorns the external parts of 
the earth with sentient beings. These have volun- 
tary motion, respire air, are impelled to action by 
the cravings of want, by love, and by pain. They 
keep within proper bounds, by preying on them, 
the numbers both of animals and vegetables. 
The latter of these kingdoms was subdivided by 
Linnaeus into six classes, viz. mammiferous animals, 
which he called mammalia, birds, | amphibious 
animals, fishes, insects, and worms. 
The class of animals denominated mammalia 
comprehends all those that nourish their young by 
means of lactiferous glands, or teats, and that have, 
flowing in their veins, a warm and red blood. It 
includes the whales, an order that, from external 
shape and habits of life, has usually been arranged 
among the fishes. It is true that these animals 
inhabit exclusively the water, an element in which 
none of the quadrupeds can long subsist, and are 
furnished like the fish with fins, still, however, in 
every essential characteristic, they exhibit an alli- 
ance to the quadrupeds. They have warm blood, 
produce their young alive, and nourish them with 
milk furnished*from teats. In their internal struc- 
ture they are likewise in a great measure allied to 
the quadrupeds, having similar lungs, and two 
auricles, and two ventricles to the heart. 
Upon comparing the various animals of the 
globe with each other, we shall find that quadru- 
