i 



I, diagram of side view of the main vessels of the circulatory system of a fish ; 11^ 

 similar diagram of a frog ; III, front view of the human circulatory system, with the 

 lymphatics. 



L, Hver ; G, gills ; Lu, lungs ; D, part of the digestive tract ; K, kidney ; A, auricle ; 

 V, ventricle ; C, typical group of capillaries in the body tissues. 



In the color scheme red represents aerated blood, as seen in the arteries of the 

 body ; blue, the blood carried in the veins of the body. The structures colored dark 

 yellow are the lymph vessels. 



171 



