12 ELEMENTS OF COMPARATIVE ZOOLOGY. 



In the front part of the cavity is the large reddish or 

 brownish liver ; turn this over to the left and expose the 

 stomach, connected apparently with the front wall of the 

 body-cavity. Pass a probe from the mouth through the 

 oesophagus or gullet into the stomach. From the stomach 

 the intestine passes back to the vent. From what part of 

 the stomach does it arise.* Is it straight? How is it sup- 

 ported in its position ? 



Study the liver more carefully. On its anterior surface 

 see blood-vessels (hepatic veins). Where do they go ? On 

 its posterior surface is the thin-walled green or yellow gall- 

 bladder. Can you trace any connection between liver and 

 intestine ? 



Where is the thin membrane (mesentery) supporting the 

 intestine attached to the body-wall ? Can you find blood- 

 vessels in it ? From where do they seem to come ? 



Pull the intestine to one side, and expose the reproduc- 

 tive organs in the posterior part of the body-cavity. The 

 testes are usually white, the ovaries yellow or pink. Both 

 vary in size according to the season. Are either of these 

 structures paired ? Trace their ducts backwards, and see 

 where they empty. In the dorsal part of the body-cavity 

 look for the air-bladder (lacking in some fishes). Can you 

 find a duct connecting it with the oesophagus ? 



Make a drawing from the side showing the organs studied, 

 and leaving space for additions. Then cut away these parts 

 and find, dorsal to the air-bladder, the long, dark red 

 kidneys. Are they enlarged in front (head-kidneys) ? Can 

 you trace the kidney duct ? 



Continue the median ventral incision forward between 



* In many fishes worm-like blind tubes (pyloric caeca) arise at the 

 junction of stomach and intestine. Their purpose is to increase the 

 surface secreting the digestive fluids. 



