38 A MANUAL OF- ZOOLOGY 



and along the entire length- pf ■ the pyloric stomach is a 

 large, reddish organ, the spleen. Is it continuous? Pos- 

 terior to the opening of the stomach into the intestine, 

 lies a small, flattish, irregular body, the pancreas. Demon- 

 strate. Is there a small intestine? Open the stomach 

 along its' ventral edge until you demonstrate the pyloric 

 opening. Note the contents of the stomach. Wash the 

 stomach clean and examine its mucous lining carefully 

 with the hand lens for the openings of the stomach gland*. 

 Note differences in the lining of the stomach in the differ- ' 

 ent parts. Open the intestine and note the peculiar mem- 

 branous folds in the interior of the posterior portion, the 

 spiral valve. Is the name Justified? What might have 

 been its origin? What the use now? Extending from the 

 dorsal wall of the intestine near the posterior end notice 

 a small diverticulum-like gland, the anal gland. The in- 

 testine opens into a short chamber common to it as well 

 as to the ureters. This is the cloaca. Make a drawing 

 of the digestive apparatus. Show the spiral valve in a 

 separate drawing. 



CIRCULATORY AND RESPIRATORY SYSTEMS— 

 The heart lies in the pericardial cavity in the mid-ventral 

 line, just under the pectoral girdle. The posterior wall of 

 the pericardial cavity has the appearance of a diaphragm. 

 The heavy, thick-walled middle portion of the heart is 

 the ventricle. Anterior and connected to this note the 

 conus arteriosus, which is developed from the ventricle 

 as is indicated from the' striped muscle fibers of, which 

 it Is composed. Posterior and dorsal to the ventricle lies 

 the thin-walled atrium or auricle. Posterior and dorsal 

 to this lies the sinus venosus, which is developed as a 

 part of the vein ending, and has the appearance of a thin 

 membrane. This is determined by the smooth muscle 

 fibers of which it is composed. From the anterior part of 

 the conus arteriosus trace forward the ventral aorta. This 

 gives off an afferent branchial artery to each gill-pouch. 

 They enter the gills from the ventral side. Demonstrate 

 each one by the proper longitudinal cuts at the ventral 

 ends of the gill-clefts. Carefully dissect off the skin from 

 the roof of the mouth and expose the efferent branchial 

 arteries, then trace them until they converge to form the 



