AN EARTHWORM 61 



ANNELIDA 



AN OLIGOCHAETOUS ANNELID. AN EARTHWORM 



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

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

 ing many 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. 



Study the animal first alive, but have one also at hand which 

 has been killed in weak alcohol. Notice its color, or rather 

 lack of color. How is this correlated with its underground 

 life ? Note its cylindrical, elongated body, the very small head, 

 and the absence of appendages. Note also the absence of a 

 hard shell, the external integumentary covering being the glis- 

 tening cuticula which has not been stiffened by the presence of 

 calcareous salts. As the animal lacks appendages, locomotion is 

 accomplished by means of body-movements. Study its method 

 of locomotion. The animal will be observed successively to 

 elongate and to shorten its bod}^, 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 

 control 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 

 importance of the setse in locomotion. 



