PHYLUM ANNELIDA. SEGMENTED WORMS 



171 



OUGOCHAETA 

 (Earthworm) 



POLYCHAETA 

 (Lugworm) 



HIRUDINEA 

 (Leech) 



Figure 90. Representatives of 4 classes of segmented worms. They are varied in form and 

 widely distributed. The figures are not drawn to scale. 



LUMBRICUS TERRESTRIS- 

 AN EARTHWORM 



The common earthworm, Lumbricus ter- 

 restris, serves well to illustrate the principal 

 characteristics of the annelids. Figure 91 

 shows many of the structural features of a 

 segmented worm. 



Earthworms are soft and naked, and hence 

 must live in moist earth; for this reason also 

 they venture out of their burrows chiefly on 

 damp nights. They are never "rained down" 

 but are "rained up" out of their burrows 

 when these are flooded. The burrows usually 

 extend about two feet underground. Earth- 



worms can force their way through soft 

 earth, but must eat their way through 

 harder soil. The earth which has been eaten 

 passes through the digestive tract and is 

 deposited on the surface as castings. 



External anatomy 



The body of Lumbricus is cylindrical and 

 varies in length from about 6 inches to 1 

 foot. The ventral surface is slightly flat- 

 tened, and the dorsal surface is darker col- 

 ored than the ventral surface. The segments 

 (somites), of which there are over 100, are 

 easily determined externally because of the 



