214 



THE WORMS 



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around the body, and an inner set which runs the length of the 

 body. The body is lengthened by the contraction of the cir- 

 cular muscles. How might the body be shortened ? 



The under surface of the worm is provided 

 with four double rows of tiny bristles called 

 setae, every segment except the first three and 

 the last being provided with setae. Each seta 

 has attached to it small muscles, which turn 

 the seta so it may point in the opposite direc- 

 tion from which the worm is moving. If you 

 watch a specimen carefully, you ■will see that 

 locomotion is accomplished by the thrusting 

 forward of the anterior end; then a wave of 

 muscular contraction passes down the body, thus shortening the 

 body by drawing up the posterior end. The setae at the anterior 

 end serve as anchors which prevent the body from slipping back- 

 ward as the posterior end is drawn up. 



How the Worm digs Holes. — A feeding worm will show the proboscis, 

 an extension of the upper lip which is used to push food into the mouth. 



Diagram to show how 

 movement of a seta 

 is accomplished ; 

 M, muscles; S, 

 seta ; W, body wall. 

 (After Sedgwick 

 and Wilson.) 



Forepart of an earthworm with the left body wall removed to show the body cavity 

 and food tube within it: m, mouth ; p, pharynx, v, g, i, food tube. 



The earthworm is not provided with hard jaws or teeth. Yet it literally 

 eats its way through the hardest soil. Inside the mouth opening is a part of 

 the food tube called the pharynx. This is very muscular so that it can be 

 extended and withdrawn by the worm. When applied to the surface of 

 the soil, which is first moistened by the worm, it acts as a suction pump 

 and draws it into the food tube. As the worm.s take organic matter out 

 of the ground as food, they pass the earth through the body in order to 



