54 PHYLUM ANNELIDA 



Class : Chcetopoda, Order : Oligochceta 

 AN EARTHWORM 



The earthworm is, to most people, the most familiar annelid. 

 It is distributed over the entire earth, the United States pos- 

 sessing several species. The animal is nocturnal in its habits. It 

 lives in long burrows in the ground, in which it lies during the day 

 and the inclement seasons of the year. Its food consists of leaves 

 and other vegetable substances and also of the organic matter 

 contained in the soil which passes through its alimentary canal. 



First study the animal alive, if possible, but also have one at 

 hand which has been killed in very weak alcohol. Notice its color, 

 its cylindrical, elongated body, its very small, pointed head, and 

 the absence of appendages, — all of which characteristics are 

 correlated with its burrowing life. Note also the absence of a 

 hard shell, the external integumentary covering being the glis- 

 tening cuticula. As the animal lacks appendages, locomotion is 

 accomplished by means of body movements. Place the animal 

 on moist filter paper or a piece of moist newspaper and study 

 its method of locomotion. It will be observed successively to 

 elongate and to shorten its body, which of course would be 

 impossible if it were covered by a hard shell. Notice that along 

 the ventral and the lateral surfaces are several rows of minute 

 bristles, the setae ; they aid in locomotion and are under the con- 

 trol of muscles. Determine, by passing the animal through the 

 fingers and with the aid of a hand lens, how many rows there 

 are and their relation to the segments. Determine also whether 

 the setae at the forward end of the body project in the same 

 direction as those at the hinder end. Observe carefully the im- 

 portance of the setae in locomotion. 



The animal is segmented externally ; that is, it is made up of 

 a number of somites, or metameres, like the crustacean body. 

 Count the somites, beginning with the segment just back of the 

 mouth, which is the first somite. Notice the close similarity of 

 the somites. This lack of specialization is always a primitive 



