HIGH SCHOOL ZOOLOGY. 



45 



vessels, the walls of which are so thin that 

 the blood while flowing through them is 

 enabled to effect exchanges with the sur- 

 rounding medium. Thus in the gill-capil- 

 laries it readily gives up the carbonic acid, 

 which it has accumulated in the tissues, 

 and combines anew with the oxygen in the 

 water, and, while flowing through the 

 capillaries of the rest of the body, gives up 

 to the tissues the food they require, and 

 receives from them the accumulated refuse 

 which has to be removed through the inter- 

 vention of the glandular cells of the liver 

 and kidney, with which tlie hepatic and 

 renal capillaries enter into intimate con- 

 nection. (Fig. 18). 



In the catfish the heart is situated be- 

 tween the floor of the hinder part of tho 

 mouth-cavity, and the ventral part of the 

 pectoral girdle. A strong partition 

 stretches from the hinder border of the 

 girdle up towards the back bone, and 

 bounds the coelom anteriorly ; it is per- 

 forated by the cesophagus and several 

 veins. In front of this partition is the pericardial sac, which 

 contains the heart, and between tlie partition and the pericard- 

 ium is the venous sinus, to which the various veins converire 

 before they enter the heart. The venous stream is received 

 from the sinus into the atrium, or auricle, a thin-walled 

 chamber, which (when the heart is inspected from below) is 

 largely concealed by the ventricle, a thick-walled inuscular 

 chamber, which drives the blood through the gills to the body. 

 Connected with the ventricle by a narrow neck is the bulb-like 

 beginning of the great trunk artery, which lies below the copu- 



Fi^"-. 18.— Dia!,'ram of the 

 Circulation in a Teleost. 



(After Glaus). 

 Ba, bulhus arteriosus; 

 Ab, liranchial vessels ; V, 

 ventricle ; Ao, aorta ; Lk, 

 capillaries of liver; N, kid- 

 ney ; D, intestine. 



