70 STUDIES OF ANIMAL TYPES 



Note the shining membrane lining the abdominal cavity. 

 This is the peritoneum. Note that there is another cavity 

 between the gill covers which is separated from the 

 abdominal cavity by a thin transverse partition^ the false 

 diaphragm. This anterior cavity is the pericardial cavity, 

 and contains the heart. 



The air bladder is the largest organ in the abdominal 

 cavity. How much space does it occupy? Find the 

 pinkish or brownish liver in the anterior part of the abdo- 

 minal cavity. Tear it free and turn anteriorly. A rather 

 large sac, the stomach, will then be seen. Pass a probe 

 down the gullet into the stomach. Note that the stomach 

 ends blindly at its posterior end and that the intestine 

 branches off near the anterior end. Note several long, 

 cylindrical appendages, the pyloric cceca, arising from the 

 intestine a little ways from its origin at the stomach. 

 Trace the intestine among the masses of fat and find 

 that it is coiled in its anterior part and extends to 

 the anus. 



Find the greenish bile sac on the posterior surface of the 

 liver. 



The spermaries of the male are white and in the breeding 

 season appear as long white bodies running toward the 

 anterior part of the abdominal cavity, just under the air 

 bladder. The ovary is an elongated sac lying in a corre- 

 sponding position in the female. 



A small pink or green sac, the urinary bladder, lies just 

 posterior to the oviduct. 



If a fresh fish is being dissected, examine the air bladder. 

 Note its thin walls. Puncture it. What is the result? 

 Determine if there are any blood vessels in the walls of the 

 air bladder. 



