102 



GENERAL TRIXCirLES OF ZOOLOGY 



1)od\-. Since ihc branches of the main trunlv formed l>y lire 'gill-veins' 

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

 arteries. 



Arterial and Venous Blood. — During its course through the bodv 

 tire lilood twice changes its chemical character and correspondingly its 

 color. The blood which (lows from the iKxh' capillary region has given up 



Flc. 66. — Scheme of ciriiilalion in :\ lisli. ,;'. asccmlir^ (ventral carta; a-, descend- 

 ing tilorsal) aorla: c, laro.i.l; </,i, inieslinal arlcrics; (/(■, intestinal ca|iillarief; liv, 

 intestinal veins; /;, auricle; /,■, \enlriele; kj. afferent gilUarleries; At, gill-capillaries; h', 

 efferent gill-arteries; /f, li\er-ca|iilhn-ies; ic, iHuly-eaiiiUaries; re, cardinal veins; lii, 

 hepatic vcm, ;■/, jugular \ein. 



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 ox}-genated, giving up the earl)on dioxide and ])ecoming 

 bright red. Since the dii'ferent character of the blood was hrsl ktiown in 



