74 Practical Zoology. 



are reached, the body wall is stronger and cannot be cut with the 

 tips of the scissors without danger of straining them ; lift with 

 the forceps almost enough to raise the fish; insert nearly the 

 whole length of one blade so as to cut near the joint of the scis- 

 sors between the pelvic fins. Continue the cut to the narrowest 

 part of the isthmus, where it joins the branchiostegal membranes. 



1. Observe that most of the internal organs are in one large 

 cavity, called the body cavity. Its silvery lining is the peritoneum. 



2. Near the anterior end of the opening, about 9pposite the 

 posterior border of the gills, find a transverse partition, the false 

 diaphragm ; back of this is the main body cavity ; in front of the 

 partition is the pericardial cavity, which contains the heart. 



3. Keeping the fish still on its back, turn now to the posterior 

 part of the body cavity. While holding the edge of the body 

 wall, use the scalpel handle to push aside the internal organs. 

 Note how yielding is the membrane on which the internal organs 

 rest. Beyond this membrane is the air bladder. Be careful not 

 to cut into it until directed to do so. 



4. Turn the abdominal wall outward and note the projections 

 made by the ventral ends of the ribs. Begin again at the point 

 of beginning of the first cut, just in front of the anus, and, with 

 scissors, cut the right side of the body wall along the ends of the 

 ribs as above noted. Continue the cut as far as the bony pectoral 

 arch, just back of the gill opening. Repeat this cut on the left 

 side. Look again at the false diaphragm and its relations to sur- 

 rounding organs, as it will probably be torn in following subsequent 

 directions. Now turn the two flaps of the body wall well out and 

 forward, and tack them down so as to hold the fish securely resting 

 on its back. 



5. In the front part of the body cavity is a dull pink or brownish 

 mass, the liver, lying chiefly on the left side of the fish. Raise 

 the hinder edge of the liver, and observe how closely it fits the 

 organs next to it. Press the liver backward, and observe the hepatic 

 veins passing forward from the liver through the thin partition, the 

 false diaphragm, in front. 



