THE CRAYFISH 115 



definite order? Place the animal on the table, does it 

 walk equally well out of water? While the animal is in the 

 water frighten it by thrusting a pencil at it; notice how it 

 swims, what parts are used and how? What advantage 

 comes from swimming in this direction? 



2. Defense. With a pencil make motions at an animal 

 to see how it defends itself. Allow it to grasp the pencil 

 to show the strength of the grasp. 



3. Respiration. While the animal is at rest in the water 

 place a little colored liquid near the bases of the legs. Where 

 is this liquid drawn into the animal and where does it re- 

 appear? Try dropping the colored liquid at various places 

 along the edge of the carapace. What causes the movement 

 of the liquid? What purpose do the currents serve? How 

 is it that a crayfish, while breathing by gills, can live for 

 some time out of water? 



4. Sensitiveness. Note the range of motion of the eyes. 

 Could an enemy approach the animal from any direction 

 without being seen? What are the advantages and what 

 the disadvantages of having the eyes on movable stalks? 

 In what ways are the eyes protected? Touch one of the 

 eyes and see what happens. 



Test the sense of touch at various places on the body; 

 where is it most sensitive? Are all parts of the appendages 

 equally sensitive? Touch some of the hairs at different 

 places on the body; are they sensitive? 



5. Feeding. Small pieces of meat may be placed near 

 the animal to determine how it reacts, and also to show in 

 what way the food is grasped and how it is passed to the 

 mouth. If possible note the action of the different mouth 

 parts. If this sort of a test is made you should also deter- 

 mine whether the animal prefers fresh or decaying meat. 



