THE FISH 153 



as before? Look up next to the arch for a blood vessel. 

 Is it an artery or a veinf How is the blood purified in the 

 gill? Study the filaments under the low power of the mi- 

 croscope and also under the high power. Make drawings 

 of each. 



Draw entire gill (X2). 



Look on the under side of the operculum for a red spot. 

 What do you think it is? Observe it closely, noting its 

 position, shape, color, etc. (This is not present in all fishes). 

 Do you think it is a rudimentary gill? 

 Draw a fish from the left side ( X J^ ) . 

 The Systems of the Visceral Cavity. — (i) Hold the 

 fish in the left hand with the tail towards you and thrust 

 the point of one blade of the scissors through the body wall 

 between the ventral and the anal fins just in front of the 

 anus (near the anal fin), and cut forward to the ventral 

 fins. Look carefully at the organs within ; cut upward 

 toward the dorsal region of the fish as far as the abdominal 

 cavity extends being especially careful not to cut anything 

 but the body wall, as the air bladder lies in this part of 

 the body. Now cut forward to a point a little above the pec- 

 toral fin. Turn the flaps forward or cut them off, and note 

 the silvery membrane, the peritoneum, lining these flaps. 



In the front part of the body cavity is a reddish or brown- 

 ish mass, the liver. Find the hepatic vein passing forward 

 from the liver through the thin partition in front. How 

 many lobes to the liver? Turn it aside and find under it 

 a greenish or yellowish sac, the gall sac. This sac contains 

 a secretion of the liver called bile. With a needle find how 

 the gall sac is connected with the liver. Can you find an 

 opening of the gall sac into the stomach? Into the intes- 



