WORMS 



43 



e b <i~ 



Fig. 70. — Mouth and Setve. 



it avoids or seeks a bright light, as of a window; also whether any 

 parts of the body are especially sensitive to touch, or all equally 

 sensitive. What effect when a bright light is brought suddenly near 

 it at night ? 



Is red blood visible through the skin ? Can you notice 

 any pulsations in a vessel along the back? Do all earth- 

 worms have the same number of divisions or rings ? Com- 

 pare the size of the rings or segments. Can it crawl faster 

 on glass or on paper ? 



A magnifying glass will show on most species tiny bristle- 

 like projections called setoz. How are the setae arranged ? 

 (d, Fig. 70.) How many on 

 one ring of the worm ? How 

 do they point ? Does the worm 

 feel smoother when it is pulled 

 forward or backward between 

 b the fingers ? Why ? Are setae on the lower sur- 



face ? Upper surface ? The sides ? What is the 

 use of the setae ? Are they useful below ground ? 

 Does the worm move at a uniform rate ? What 

 change in form occurs as the front part of the 

 body is pushed forward ? As the hinder part is 

 pulled onward ? How far does it go at each 

 movement ? At certain seasons a broad band, 

 or ring, appears, covering several segments and 

 making them seem enlarged (Fig. 71). This is 

 the clitellum, or reproductive girdle. Is this girdle 

 nearer the mouth or the tail ? 



Draw the exterior of an earthworm. 

 Dorsal and Ventral Surfaces. — The earthworm 

 always crawls with the same surface to the ground ; this 

 is called the ventral surface, the opposite surface is the 

 dorsal surface. This is the first animal studied to which 



Fig. 71.— 

 Earth- 

 worm, 



mouth end 

 above. 



