THE YELLOW PERCH 307 



pelvic fins. The fins are supported by Jin-rays of two sorts, 

 the one hard, unsegmented, and unbranched (Fig. 153,1); the 

 other soft, segmented, and branched (Fig. 153, 2). 



The Digestive System. The mouth is large. Teeth are borne 

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

 (Fig. 153, 6, 7, 9). On the ventral surface of the mouth is a 

 rather large, fleshy tongue (Fig. 153, 8). Behind the tongue 

 is the pharynx (Fig. 153, 10), with gill-slits on both sides, 

 which allow water from the mouth to pass into the gill-cham- 

 ber. From the pharynx a short oesophagus leads to the stomach 

 (Fig. 153, 14). Several pyloric cceca (Fig. 153, 15) open into 

 the intestine (Fig. 153, 16), increasing its absorbing and secret- 

 ing surface. The intestine ends ventrally at the anal opening 

 anterior to the anal fin (Fig. 153, 4). The liver-secretion, 

 called bile, is stored in a gall-bladder (Fig. 153, 12) attached 

 to the posterior surface of the liver (Fig. 153, 11), and finds 

 its way into the alimentary canal through the bile-duct (Fig. 

 153, 13). Close to the alimentary canal, but not opening into 

 it, is a bright red organ called the spleen (Fig. 153, 20), the 

 function of which is not positively known. 



The Circulatory, Respiratory, and Excretory Systems. 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 to the heart 

 may be clearly distinguished, an auricle (Fig. 153, 21) and a 

 ventricle (Fig. 153, 22). The blood, driven from the heart by 

 the contraction of the ventricle, is forced through an artery 

 (the aorta] with a bulbous base (bulbus aorta;, Fig. 153, 23) to 

 the gills, where it is aerated. After aeration the blood is 

 collected into a dorsal artery, which carries it through the 

 bodjr, giving off branches to the various organs. In the 

 capillaries of the different organs it gives up its oxygen, col- 

 lects waste products, and makes its way through the veins 

 to the auricle, whence it enters the ventricle to repeat its 



