THE EARTHWORM 



229 



Annulata (Lat. annulus, a ring). The segmented worms are 

 long, jointed creatures composed of body rings or segments. The 

 digestive tract is a tube within a tubelike body. They have no 

 jointed appendages. There are about 4000 known species. 



Hirirdinecc 



sccnduwovytx 



Class I. Chaetop'oda. Many bristles along the sides of the body, 



worm or sandworm. 

 Class II. Hirudin'ea. Without bristles and having suckers at both ends of the body 



amples are the leeches or bloodsuckers. 



leech 



Examples are the earth- 

 Ex- 



Laboratory Exercise. Study of a living earthworm. Put several 

 earthworms in shallow tin trays with moist blotting paper in bot- 

 tom. Have paper wet at one end of tray and dry at the other. At 

 which end of the tray do the worms gather? Wet the paper uni- 

 formly and then cover one half of the tray with an opaque object. 

 What happens to the worms? How do earthworms react to light 

 and presence of moisture? 



Count the number of rings (segments) in your worm and compare 

 with the estimates of others in the class. What conclusions do you 

 draw? 



Watch a worm move. Describe exactly what happens. 



Notice the little swelling located about the thirty-first segment 

 from the anterior tip. This is the clitellum and forms a bag in 

 which the eggs are placed when laid. Rub the upper and lower sur- 

 face of the worms with your fingers. Any differences ? Account for 

 this. 



Find the mouth and posterior opening of the food tube. Can you 

 find any other structures or openings ? 



Make a diagram of the first forty and the last five segments of the 

 earthworm. 



The earthworm. The common earthworm is familiar to most 

 of us. It has an elongated body made up of segments or rings. It 

 is sensitive to food, to odors, to heat, to light, and to other 

 stimuli. Four rows of tiny, movable bristles called setae are 

 found on all the segments except the first three and the last. 

 Locomotion is accomplished by the thrusting forward of the 



H. BIO — 16 



