132 WORMS. 



(c) The numerous similar transverse segments compos- 

 ing the body. 



(d) The absence of appendages. 

 2. In its motions 



(a) Rhythmic contractions and corresponding changes 

 in form of its body. 



(6) Irregular progression forward. 



Place the worm on a smooth, clean pane of glass, and 

 observe, that, while its contractions continue, its progres- 

 sion ceases. 



Draw the worm backward across a finger, to feel the 

 minute setae (or bristles) by means of which it holds its 

 ground on any except the smoothest surfaces. 



Observe how it crawls backward when touched near 

 the anterior end, performing reflexly the acts which under 

 its ordinary conditions of life would carry it to a safe re- 

 treat within its burrow. 



Turn it over on its back and observe what follows. 



Tap the paper, or jar the table, on which it lies, and note 

 the result. 



External Features. For a study of the general struc- 

 ture of the earthworm, use specimens that have been 

 anaesthetized with chloroform. Select the largest speci- 

 men obtainable, and dissect it under weak alcohol ; but, 

 before dissecting, observe with a lens the following 

 among its external features : 



1. The darker color of the dorsal surface. 



2. The greater length of the body -segments at the 

 tapering anterior end. 



3. The dorsal flattening of the posterior end of the 

 body. 



4. The mouth at the anterior end, and the prostomium 

 projecting forward above it, from the dorsal side of the 

 foremost segment. 



