62 A GUIDE FOR THE STUDY OF ANIMALS 



and right and left sides. Animals which do not have such 

 differentiated surfaces are usually radially symmetrical, 

 but sometimes asymmetrical (without symmetry). 



Girdle, the somewhat transparent band frequently found 

 near the anterior end of an earthworm. 



Atial opening, the posterior opening of the food canal. 



5i?/i^ (singular form, seta^, small bristles or stiff hairs. 

 In the earthworm these are set in the body wall at definite 

 intervals, and aid in locomotion. 



Cuticle, in the earthworm a delicate, shining cover over 

 the body. 



Egg capsules, small, light-colored, spindle-shaped sacks, 

 about the size and somewhat the shape of a grain of wheat, 

 containing the eggs or young of earthworms. 



Directions. 



Take a living earthworm to your table and keep it damp 

 by placing it in a wet tray or upon moist paper. Identify 

 the anterior and posterior ends, the dorsal and ventral sur- 

 faces, and the right and left sides. Identify also the somites 

 and the girdle, the mouth with its projecting lip, and the 

 anal opening. 



Observations. 



1. Watch a living worm for some time. Does it seem to 

 have a definite object in its moving .' If so, what is it } 

 Upon what sense or senses does it seem to depend for 

 guidance .' Which end usually leads .■' Why } 



2. Over what sort of surface does it move most easily 1 

 Why .^ Watch it closely for some time and discover how it 

 is able to move from place to place. {Suggestion. What 

 is the function of the setae in this process .? How can you 

 explain the alternate contraction and expansion of parts t ) 



3. From time to time, for perhaps a week, examine the 



