82 INTRODUCTION TO ZOOLOGY. 



3. Notice concenti'ic striae running ai'ound the 

 edge. 



4. Which is the anterior and which the posterior 

 edge of the scale? 



5. Note fine teetli on the posteiior edge of the 

 scale. Draw. 



6. Find a distinct line running along the sides of 

 the body lengthwise. This is the lateral line. 



7. Pull one scale out of the lateral line. Ex- 

 amine carefully. How does it differ from other 

 scales ? 



8. How many scales in the lateral line? 



The Body Cavities. 



1. Find the opening of the intestine, in front of 

 the anal fin. Cut through the body wall carefully 

 from the anal opening to the isthmus. Cut away as 

 much of the body wall on the left side as you can 

 without injuring the internal organs. 



2. Notice the silvery lining of the body cavity. 

 This is the peritoneum. 



3. Find a membranous partition near the front of 

 the body cavity. This is the false diaphragm. The 

 part of the body cavity in the front of it is the peri- 

 cardial cavity. The part behind it is the abdominal 

 cavity. 



4. In the dorsal part of the abdominal cavity, find 

 a thin membrane. This is the air bladder. Does the 

 peritoneum cover it? Does it have any connection 

 with the mouth or stomach? 



The Digestive Organs. 



1. Identify as well as you can the sesophagus, 

 stomach, intestine, liver, spleen. 



2. What is the shape of the stomach? Where does 



