VERTEBRATA. 



147 



its passage through the gills it rids itself of one kind of 

 waste (carbon dioxide) and absorbs oxygen from the water. 

 This exchange is accompanied by a change of color to bright 

 red. The other waste is gotten rid of in the kidneys. In 



FIG. 69. Diagram of the arterial arches and their modificaitons in vari- 

 ous vertebrates. A, fish ; B, batrachia ; C, snake ; D, bird ; E, mammal. 

 a, ventral aorta ; c, internal carotid ; d, dorsal aorta ; e, external carotid ; 

 p, pulmonary artery ; s, subclavian. Drawn by Dr. F. D. Lambert. 



the capillaries of the body it gives np its oxygen and 

 nourishment to the surrounding parts, and becomes loaded 

 anew with carbon dioxide and other waste, changing color 

 again to the dark red. From this account it will be seen 



