INTRODUCTION. 49 



element, as their whole organization shows. For we find 

 the exterior of the body covered with feathers the remark- 

 ahle property of which is lightness nicely adapted for 

 sustaining them in the air. The lungs occupy the abdom- 

 inal as well as thoracic cavity, there being no diaphragm, 

 and thus, extending the almost entire length of the trunk, 

 form as it were so many bladders, which being filled with 

 air, give the body the same specific gravity with this fluid 

 consequently placing the animal in the most perfect rela- 

 tion for moving and living in this element. The skele- 

 ton likewise receives air, thus rendering the body still 

 lighter and so with every other part, each being adapted 

 the one to the other, and the whole specially to the atmos- 

 phere, the fundamental element of this variety of organi- 

 zation for a bird can no more live under water, than a 

 fish can in the air. 



The class mammalia, divided into the carnivorous and 

 herbivorous animals, have organizations formed with spe- 

 cial reference to food the one of these living on flesh 

 the other on grass, fruits and grain, and the structure in 

 each, as most distinctly seen in that of the teeth, stomach 

 and alimentary tubes, corresponds to the particular kind 

 of food on which they respectively subsist and so fixed is 

 this relation between the kind of food and the organization 

 adapted to it, that to change the food of the one class for 

 that of the other, would be death to both. 



The same may be said in reference to climate. The polar 

 bear could no more live under the equator, than the ourang- 

 outang could under the north pole each having its organ- 

 ization made with special reference to temperature. 



Now, in all these instances we find the variety of or- 

 ganization depends upon fixed relations established more 

 particularly with one of the fundamental elements than 

 another which particular relationship constitutes so many 

 special laws for each variety violation of which in each 

 case is destructive to organization, and that just in propor- 

 tion to the offence. But these special laws by no means 

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