116 LABORATORY STUDIES IN ZOOLOGY 



vertebral relations of the supporting structures of the caudal 

 fin. 



The dorsal ends of the pectoral girdle are attached to the caudal 

 end of the cranium. The arch is suspended ventrally to support 

 the pectoral fins. The pelvic girdle of the perch is composed of 

 two flat plates of bone on the midventral line free from other 

 skeletal parts. 



Abdominal Viscera,— Make an incision through the body wall 

 along the midventral line from a point immediately in front of the 

 anus to the region of the lower jaw. Care should be used that the 

 internal organs be not injured by too deep a cut. Make a dorsal 

 incision at the point of origin of the midventral slit. Remove 

 a portion of the body wall of the left side so as to expose the 

 abdominal cavity. 



Note the glistening membrane, the peritoneum, which lines the 

 cavity and suspends the various visceral organs from the dorsal 

 body walls. A transverse septum forms the anterior wall of the 

 abdominal cavity. In front of this septum is the pericardial 

 cavity, lined with a thin membrane, the pericardium. It contains 

 the heart. 



From the pharynx the alimentary canal continues caudad into 

 the oesophagus. The oesophagus merges into stomach the con- 

 stricted caudal limit of which is the pylorus. Beyond this point the 

 canal is continued as the intestine. In the region of the pylorus 

 there are three finger-like blind pouches arising from the 

 intestine and called pyloric coeca. Note the liver attached by the 

 coronary ligament to the transverse septum. The gall bladder lies 

 on the posterior surface of the liver. The spleen appears as a 

 small dark body between the coils of the intestine. Because 

 of its diffuse nature the pancreas is difficult to find. A descrip- 

 tion of this organ is therefore omitted. In order to view the 

 other viscera to the best advantage it will be necessary to strip 

 off the layers of fat in which they are embedded. 



The reproductive system consists of a pair of gonads. There is 

 no connection between the testes and the kidneys as is the case in 

 the males of most vertebrates, but the testes as well as the 

 ovaries merely taper down to a tube leading to the urogenital 

 opening. 



Along the dorsal wall of the abdominal cavity extends a large 

 gas-filled sac, the swiyn bladder or air bladder. By slitting the 

 wall of the bladder the extent of this sac can be determined. 



