io LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



yellowish, very irregular body, lying in the mesentery which extends between 

 the liver, the small intestine, and the stomach. The first part of the small 

 intestine, called the duodenum, will be found to bend abruptly forward 

 toward the liver, and in the mesentery between this bent portion of the 

 small intestine and the stomach is located some yellowish branching material 

 which constitutes the pancreas. Between the lobes of the liver lies the round 

 green gall bladder. 



The following mesenteries should be carefully identified, and each organ 

 picked up with a forceps as you read the description, and its relation to the body 

 wall and other organs noted. The entire alimentary canal is suspended from the 

 median 'dorsal line of the coelome by an extensive mesentery, the dorsal mesentery, 

 in which run the blood vessels, lymphatics, nerves, etc., that supply the digestive 

 system. Pick up the stomach and intestine with a forceps and see how they are 

 attached to the dorsal median line by this mesentery, a very delicate and trans- 

 parent membrane. The part of the mesentery which supports the esophagus 

 is called the meso-esophageum; the stomach, mesogastrium, or mesogaster; the 

 small intestine, mesenterium, or mesentery proper; and the large intestine, 

 mesorectum. The small red body located in the mesorectum is the spleen, an 

 organ associated with the lymphatic system. Pick up the urinary bladder -with 

 a forceps, and find its attachments to the ventral median line by the median 

 ligament of the bladder, already noted; to the large intestine by the rectovesical 

 ligament; and to the lateral body wall on each side by the lateral ligaments of the 

 bladder. The liver is connected to the dorsal wall of the coelome by the dorsal 

 mesentery of the liver or mesohepar; to the pericardial sac by the coronary liga- 

 ment; to the digestive tract mainly by the hepato-gastro-duodenal ligament in 

 which the pancreas is located; and to the ventral wall in the median line by the 

 suspensory ligament, previously noticed and cut. The student will perceive 

 that the ligaments of the bladder, and the suspensory and hepato-gastro-duodenal 

 ligaments are remnants of an originally more extensive ventral mesentery, which 

 connected the alimentary canal and all structures ventral to it to the ventral 

 body wall. 



The mesenteries constitute an ingenious device which permits the viscera 

 to adjust themselves to movements of the body and to carry out their own move- 

 ments freely, and yet at the same time holds them in place with reference to each 

 other and to the body wall. 



4. Reproductive system. This system consists of a pair of reproductive 

 glands, or gonads, in which the sexual elements are produced, and a pair of ducts 

 which convey these elements to the exterior. 



The female gonads, or ovaries, are, in the mature female, the most conspicuous 

 organs in the body. Each is a large, lobed mass composed mainly of numerous 

 black and white eggs, or ova. Each is suspended from the dorsal wall by a 



