ii ABDOMIXAL VISCERA 23 



the dorsal wall of the abdomen, and called the large 

 intestine or rectum. It is continued into a short tube, the 

 cloaca (cl), which passes backwards, between the back- 

 bone above and the pubis below, to open externally by 

 the vent. Thus the mouth-cavity, pharynx, gullet, 

 stomach, small intestine, rectum, and cloaca form a 

 continuous tube, opening externally at each end, by 

 mouth and vent respectively, and, for the greater part 

 of its extent, contained within the body-cavity. The 

 whole tube is known as the enteric or alimentary canal. 



Attached to the mesentery, close to the anterior end 

 of the rectum, is a rounded body of a deep-red colour, 

 the spleen (Figs. 3 and 7, spl). Quite at the posterior 

 end of the abdominal cavity a very thin-walled and 

 transparent sac (u. bl) will be seen, connected with the 

 ventral side of the cloaca, and varying much in size 

 according to its state of distension. This is the urinary 

 bladder, which communicates by an aperture (Fig. 7, bl} 

 with the cloaca, and when distended will be seen to be 

 bilobed and of considerable size. 



If your specimen should be an adult female, and the 

 time of year approaching the breeding season, you will 

 already have observed, as the most prominent organs in 

 the body, two large, lobed structures of a dark colour, 

 protruding one on either side, and partly obscuring the 

 view of the other organs. Each (Fig. 4, /. ovy) contains 

 a great number of small globular bodies, half black and 

 half white, and is suspended to the roof of the body- 

 cavity by a sheet of peritoneum. These bodies are the 

 ovaries, or organs for the manufacture of the eggs ; the 

 rounded bodies of which they are largely composed are 

 the eggs themselves. To each ovary is attached a 

 yellow structure, produced into a number of streamer- 

 like lobes (cp. ad) ; this is the fat-body, which serves as a 

 storehouse of reserve nutriment. 



