102 



GENERAL PRINCIPLES OF ZOOLOGY 



body. Since the branches of the main trunk formed by the 'gill-veins' 

 lead again into a capillary region they must, like the main stem, be called 

 arteries. 



Arterial and Venous Blood. During its course through the body 

 the blood twice changes its chemical character and correspondingly its 

 color. The blood which flows from the body capillary region has given up 



FIG. 66. Scheme of circulation in a fish. a', ascending (Ventral) oarta; a~, descend- 

 ing (dorsal) aorta; c, carotid; da, intestinal arteries; dc, intestinal capillaries; dv, 

 intestinal veins; h, auricle; k, ventricle; ka, afferent gill-arteries; kc, gill-capillaries; kv, 

 efferent gill-arteries; Ic, liver-capillaries; sc, body-capillaries; vc, cardinal veins; i<h, 

 hepatic vein, vj, jugular vein. 



its oxygen to the tissues, receiving in exchange carbon dioxide, and has be- 

 come dark red. This character is maintained until, in the gill-capillaries, it 

 again becomes oxygenated, giving up the carbon dioxide and becoming 

 bright red. Since the different character of the blood was first known in 



