EARTHWORM 



(Lumbricus terrestris) 



Classification : — Phylum Annelida, Class Cliaetopoda, Sub- 

 class Oligochaeta. 



There are numerous species and genera of earthworms. The 

 one chosen for this study is not a native of this country but was 

 introduced from Europe and has become established in some lo- 

 calities. The small worms which are found in the soil and on 

 walks after heavy rains are usually not the young of this same 

 species but represent a number of separate genera and species 

 differing considerably in internal structure. Information given 

 in this outline does not apply to all earthworms. 



I. External Characters 



1. Note that the body is composed of a series of similar 

 rings placed end to end. Each of these divisions or rings is 

 called a somite or segment. Notice that the body is almost cylin- 

 drical in form but is slightly flattened on one surface. This 

 flattened surface, which is also usually light in color, is the ven- 

 tral surface of the worm. The anterior region is the more robust 

 of the two body extremities, 



2. The most anterior part, the prostomium, is not a true 

 segment. How far does it extend through the next division, the 

 peristomium, or first true somite? Make a drawing, X5, of the 

 dorsal view to show the relation of these two parts. 



3. The clitellum consists of several thickened segments 

 forming a partial ring in the anterior region of the body. On 

 which surface of the body is this ring incomplete in this species ? 

 Count the number of segments anterior to the clitellum, in the 

 clitellum, and posterior to the clitellum. Record the results of 

 counting after your desk number on the table outlined upon the 

 blackboard. What part of body has a constant number of seg- 

 ments ? 



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