104 THE CATFISH. 



Exercise 6. Without displacing any 0} the organs exposed by the dissection, 

 draw them in position, identifying later such as you are not familiar 

 with. 



Note the following as the specimen lies on its back in a dissecting pan : 



a) The peritoneum, a thin, silvery, pigmented lining to the abdominal 



cavity. 



b) The liver, a dark-colored, lobulated organ in the front part of this 



cavity. Note its position in relation to the other organs, and the 

 inequality of the lobes. On its dorsal surface is the gall bladder 

 containing the greenish bile. By gentle compression force the 

 bile into the bile duct, thus demonstrating the location of the 

 latter and its communication with a region of the digestive tract. 

 How is the liver supported in the abdominal cavity ? 



c) Look for the O3sophagus entering the cavity through its anterior 



wall. It soon enlarges into a pouch-like stomach which, in turn, 

 is followed by a short division of the intestine known as the 

 duodenum. At the junction of duodenum and stomach there are, 

 in some species of fish, a number of blind pockets called cosca. 

 Are there any in your specimen ? 



d) Beneath the stomach is a small, dark red gland, the spleen. 



e) Stomach, intestine, and spleen are suspended from the dorsal wall of 



the abdominal cavity by the mesentery, a fold of peritoneum. 

 Intimately connected with the mesentery is usually more or less 

 fatty tissue. Trace the intestine to the anus. Straighten out its 

 folds, by tearing the mesentery, and compare its length with that 

 of the trunk. At what point does the bile duct enter ? Snip off 

 the alimentary canal just ahead of anus and stomach, respectively, 

 and remove it. Remove also the liver. 



f) In the dorsal wall of the oesophagus, a short distance from its 



posterior end, is an opening into a tube leading to the air bladder. 

 Demonstrate the connection by inflation or by a small, flexible, 

 blunt probe. 



g) Note the inflated condition of the air bladder and the propor- 



tionately large amount of room it takes up in the body cavity. 



