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LIFE, IN ITS HIGHER FORMS. 



upon the air, would be comparatively powerless as a means 

 of locomotion, if that limb were in the condition which it 

 presents when the cook puts the bird on the spit. The 

 breadth of the oar and its hold upon the element through 

 which it is to move are, therefore, increased by a most ad- 

 mirable contrivance. The quill-feathers, inserted along one 

 edge of the arm, and radiating outwards and backwards, 

 like a fan, answer the purpose proposed. Just look at the 

 quill-feather from a bird's wing. With how small an ex- 

 penditure of material is a broad surface obtained ! How 

 slight and apparently feeble is the structure, when examined 

 fibre by fibre; and yet how firmly and compactly it bincfg 

 together, and how strongly the expanded web resists the 

 air ! Breadth, strength, and lightness were the requisites, 

 and, incompatible as they might have appeared, they are 

 here exquisitely combined. 



Even such instruments as these, however, would not 

 avail to lift the animal from the earth, and to bear it with 

 ease and rapidity through the thin air, were its body of the 

 same density as that of a quadruped. It must, therefore, 

 be made buoyant, and this buoyancy is secured by several 

 concurrent ordinances. In the first place, the whole of the 

 muscles are abundantly supplied with blood, which passes 

 through a heart of four chambers, with a rapidity far greater 

 than that which obtains in terrestrial animals. Secondly, 

 to supply the oxygen which is required for the vitalising of 

 this swiftly circulating blood, a peculiar system of respira- 

 tion is required. The lungs are very large — spongy masses 

 of blood-vessels lying along each side of the back-bone, and 

 bound down to it : through these the bronchi, or divisions 

 of the windpipe, pass ; and, opening into the general cavity 



