THE YELLOW PERCH 313 



pelvic, fms. The fins are supported by fin rays of two sorts, 

 the one hard, unsegmented, and unbranched (Fig. 160) ; the 

 other soft, segmented, and branched. 



The Digestive System. The mouth is large. Teeth are 

 borne not only on the jaws but also on the roof of the mouth 

 (Fig. 160). On the ventral surface of the mouth is a rather 

 large, fleshy tongue. Behind the tongue is the pharynx, with 

 gill slits on both sides, which allow water from the mouth 

 to pass into the gill chamber. From the pharynx a short 

 esophagus leads to the stomach. Several pyloric cseca open 

 into the intestine, increasing its absorbing and secreting sur- 

 face. The intestine ends ventrally at the anal opening an- 

 terior to the anal fin. The liver-secretion, called bile, is 

 stored in a gall bladder attached to the posterior surface of 

 the liver, and finds its way into the alimentary canal through 

 the bile duct. Close to the alimentary canal, but not open- 

 ing into it, is a bright-red organ called the spleen, the func- 

 tion of which is not positively known. 



The Circulatory System. The heart is placed in a large 

 pericardial cavity, the posterior wall of which forms a thin 

 membrane separating the heart from the other organs of 

 the body cavity. Two divisions of the heart may be clearly 

 distinguished, an auricle and a ventricle (Fig. 160). The 

 blood, driven from the heart by the contraction of the ven- 

 tricle, is forced through an artery (the aorta) with a bul- 

 bous base (bulbus aortae) to the gills, where it gives off its 

 carbon dioxide and takes on oxygen. After leaving the gills 

 the blood is collected into a dorsal artery, which carries 

 it through the body, giving off branches to the various 

 organs. In the capillaries of the different organs it gives 

 up its oxygen, collects waste products, and makes its way 

 through the veins to the auricle, whence it enters the ven- 

 tricle to repeat its circulation. Valves in the heart and in 

 the course of the venous circulation prevent the backward 



