94 ARTHROPODS 



of water at the botton, or they may be preserved in alcohol 

 by placing them in fifty per cent alcohol for a day, and 

 afterward changing the alcohol to seventy-five per cent, 

 and finally ninety-five per cent. If placed in alcohol the 

 shell should be punctured in several places, so that the al- 

 cohol may reach the internal parts. It is well to mix with 

 the alcohol a small amount of glycerine, about one fourth 

 of the amount of alcohol, in order to keep the body of the 

 animal soft and flexible after drying. 



The Live Specimen. — (i) Observe the general shape. 

 The front division is the cephalothorax, and all the poster- 

 ior part, the abdomen. 



(2) 'Note tht walking appendages. How many? Shape, 

 size, structure? How many does the animal use in walk- 

 ing ? What other use is made of them ? 



(3) Notice the hinge in the front claw. Put a pencil 

 in the claw and if the animal grasps it, test the strength of 

 the muscles of the claw. 



(4) Touch one of the eyes with a pencil and note what 

 follows. Notice the range of vision of the eye, and also the 

 range of muscular movement. 



(5) Study the animal in watei;, thrust a pencil at it 

 quickly, and note how it darts backward. Study the under 

 part of the abdomen and see how this movement may be 

 accomplished. 



(6) Describe briefly the different motions possible to a 

 crayfish and tell how each is accomplished. 



The External Parts. — (i) Kill the specimen with 

 chloroform, or by plunging it in boiling water. (The for- 

 mer method is better for study of internal structure, while 

 the latter is better for study of external parts.) 



