204 



GENERAL ZOOLOGY 



in the body wall. They usually take the form of stiff horny 

 bristles which serve for locomotion. The earthworms are 

 the most familiar representatives of the class, and one of the 

 commoner species will therefore be considered as an example. 



THE EARTHWORM, Lumbricus hercukus Savigny 



This is the large earthworm found burrowing in humus 

 soil throughout the northeastern United States (Fig. 83). 

 It sometimes reaches a length of ten or twelve inches, and 

 is most often seen above ground after rains. 



Self -maintenance. Lumbricus eats its way through the 

 ground and thus obtains considerable food from the organic 

 matter present. Most of the material excavated passes 



A .* 



FIG. 83. Earthworms. A, castings; B, mating; C, egg cocoon in ground; D, 

 crawling in burrow; E, pulling a leaf into burrow. 



through the alimentary canal and is voided into the burrow 

 behind the worm or taken to the surface at night and left 

 as a pile of castings (Fig. 83, A). The method by which an 

 earthworm moves through its burrow is of interest. The 

 setae and two muscle layers are the chief agents in locomo- 

 tion. If an earthworm is at rest and begins to move for- 

 ward the sequence of events will be somewhat as follows: 

 the setae at the posterior end of the body are protruded and 

 take firm hold on the sides of the burrow, then the circular 

 muscles (running around the body) contract to make the 

 body longer, and as the posterior portion is anchored, the 



