114 GENERAL BIOLOGY 



Open the stomach and observe the character of the lining. 

 Of what use are the teeth that are present in the walls ? How 

 do they operate? If food is present in the stomach try to 

 determine its character. 



5. Excretory System. The openings have been noted 

 as being on the basal joint of the antenna?. The excretory 

 organs themselves, the kidneys or green glands, lie just 

 dorsal to the bases of these antenna? and therefore in the 

 extreme anterior part of the body cavity. 



6. Nervous System. Dissect the muscle and other tissues 

 from the abdomen and expose the nerve cord. Be careful 

 not to break any of the nerves in cleaning away the muscle. 

 Expose the cord to the extreme posterior part of the abdo- 

 men, then trace it forward into the thorax, dissecting as 

 much as is necessary to expose it. In the anterior part of 

 the body the cord will be found to divide into two parts, 

 forming a commissure which passes around the esophagus 

 to the dorsal side. Here the two cords unite again to form 

 the cerebral ganglia or brain. 



Notice the number, position, arrangement of the ganglia, 

 then* size, the distribution of the nerves which come from 

 them, and the termination of the nerves of the brain in the 

 sense organs of the head. Compare this nervous system 

 with that of the earthworm. 



Make an enlarged drawing of the entire system. 



IV. Physiology. 



1. Locomotion. In working on the living animals do 

 not excite or irritate them. Place the crayfish in a pan 

 with sufficient water to cover it and observe it while walk- 

 ing_or crawling. What appendages are used? Can it walk 

 backward as well as forward? Are the legs used in any 



