THE COELOM, DIGESTIVE, AND RESPIRATORY SYSTEMS 169 



the pleuro peritoneal cavity, lined by the pleuroperitoneum. The body wall 

 consists of skin, muscle, and peritoneum as can be seen on the cut surface. 

 In the median ventral line on the inside of the abdominal wall runs a large vein, 

 the ventral abdominal vein. 



Examine the viscera. The liver is the large greenish or brownish organ 

 occupying the anterior half of the pleuroperitoneal cavity. Its margins are 

 divided into several scallop-like lobes by shallow indentations. It is united to 

 the median ventral line by a mesentery which should not be disturbed at present. 

 On raising the left side of the liver, the elongated stomach will be seen dorsal to 

 the liver. Along the left side of the stomach is situated the dark-colored spleen. 

 On raising the spleen there will be seen dorsal to it and lying along the left side 

 of the stomach, the left lung, a very long slender tubular structure which termi- 

 nates some distance posterior to the liver. Follow the stomach posteriorly. It 

 is a straight tube, somewhat shorter than the liver, terminating at a constriction, 

 the pylorus. From the pylorus the small intestine begins and makes an abrupt 

 right-angled bend to the right. In this bend rests a white gland, the pancreas, 

 which also extends onto the dorsal surface of the liver. That part of the small 

 intestine in contact with the pancreas is known as the duodenum. On raising 

 the duodenum and looking on its dorsal side the pancreas will be seen to send 

 one tail toward the spleen and another posteriorly along the small intestine. 

 The small intestine proceeds posteriorly somewhat coiled. In the case of females 

 it will be found coiled on the ventral surface of the large ovaries, on the surface 

 of which the eggs will be noted. (The size of the ovaries varies with the sexual 

 state of the animal.) To each side and dorsal to the ovaries is a large, white, 

 much-coiled tube, the oviduct. Trace the intestine, posteriorly pressing the 

 ovaries away from the median line. The small intestine widens near the anus 

 into the short large intestine. It lies in female specimens between the posterior 

 terminations of the two oviducts. At the posterior end of the pleuroperitoneal 

 cavity ventral to the large intestine will be found a sac, generally collapsed and 

 shriveled, the urinary bladder. Note the stalk by which it is attached to the 

 ventral side of the intestine. That part of the intestine to which the urinary 

 bladder is attached (and into which the ducts of the kidneys and gonads also 

 open) is the cloaca. It terminates at the anus. 



The female gonads and ducts have already been noted. The left male 

 gonad will be found dorsal to the intestine and posterior to the spleen. Dorsal 

 to the gonad will be seen the left kidney with its duct attached to its left margin. 



2. The mesenteries. The digestive tract is attached for most of its length 

 to the median dorsal line of the coelom by the dorsal mesentery. This should 

 be noted by pressing other organs away from the median line. It is missing in 

 the pyloric region of the stomach. That portion of the dorsal mesentery support- 

 ing the stomach is the mesogaster. The spleen is inclosed in the mesogaster, 

 that portion of the mesogaster which extends from the spleen to the stomach 



