CRAYFISH OR LOBSTER. 71 



Beneath the heart, and projecting from beneath it in 

 front and behind, are the paired reproductive organs. Do 

 those of the two sides connect? Can you find the ducts 

 leading down from them? Where do they end? Still 

 farther in front is the large thin-walled stomach, and on 

 either side of this, and reaching back to the heart, is the 

 liver, reddish in the crayfish, green in the lobster. Tip 

 the stomach backwards and see the oesophagus or tube 

 leading to the stomach from the mouth. Tip it forwards 

 and find the intestine. Can you find the ducts leading 

 from the liver to the intestine? 



Draw the viscera, etc., as far as made out, adding the 

 intestine later. 



Cut away heart, liver, reproductive organs, and trace 

 the intestine to the vent. Is it the same size throughout? 

 Follow the sternal artery from the lower surface of the 

 heart downwards towards the floor, taking care not to 

 cut anything. 



Take out the stomach, being very careful not to injure 

 other structures when cutting the oesophagus. Open the 

 stomach and find the teeth; how many? Try to see how 

 the teeth grind the food. 



In the front part of the body, close to the antennae, find 

 the green glands (paired). Their openings have already 

 been found. They are excretory in function (kidneys). 



Cut away the (white) muscles in the abdomen, being 

 careful as you approach the floor, and expose the hinder 

 part of the central nervous system (ventral cord). How 

 are the enlargements (ganglia) arranged with reference to 

 the somites of the abdomen? Are the nerves given off 

 from the ganglia, or from the cord (commissure) connecting 

 them? Trace the ventral cord forward into the cephalo- 

 thorax, carefully breaking away the hard parts which cover 



