26 LABORATORY WORK. 



Where is the thin membrane (mesentery) supporting the 

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

 vessels iii 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. In 

 the male the testes are usually white; in the female the 

 ovaries yellow or pink. Both vary in size according to 

 the season. Are 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- 

 kulneys)\ Can you trace the kidney duct? 



Continue the median ventral incision forward between 

 the pectoral fins nearly to the isthmus, taking care as 

 before not to cut the underlying parts. Cut away the 

 thin partition (false diaphragm) just in front of the liver., 

 This will lay open the pericardial cavity (part of the 

 coelom). 



In the pericardial cavity lies the heart. It consists of 

 a triangular ventricle below (in the normal position of the 

 fish) and a more dorsal auricle. In front the ventricle 

 gives off a blood-vessel, which at first has a conical enlarge- 

 ment (arterial bulb), and then is continued forward as the 

 ventral aorta. Behind the heart is a blood-cavity (venous 

 sinus) extending across the body-cavity in front of the 

 false diaphragm. How are the hepatic veins (p. 25) 

 related to this? 



Follow the ventral aorto forward through the muscu- 



