COLLEGE ZOOLOGY 



External Features. - The body of Lumbricus is cylindroid, 

 and varies in length from about six inches to a foot. The seg- 

 ments, of which there are over one hundred, are easily determined 

 externally because of the grooves extending around the body. 



dors.V 

 typh 



neph 



hep 



FIG. 153. - - Transverse section through the middle region of the body of 

 the earthworm, Lumbricus. circ.mus, circular muscle fibers; coel, axiom; 

 dors.v, dorsal vessel; epid, epidermis; ext.neph, nephridiopore; hep, chloro- 

 gogen cells; long.mus, longitudinal muscles; neph, nephridium; nephrost, nephro- 

 stome; n.co, nerve-cord; set, setae; sub.n.vess, subneural vessel; typh, typhlo- 

 sole; venl.v, ventral vessel. (From Parker and Haswell, after Marshall and 

 Hurst.) 



At the anterior end a fleshy lobe, the prostomium (Fig. 156, i), 

 projects over the mouth (5); this is not considered a true seg- 

 ment. It is customary to number the segments with roman 

 numerals, beginning at the anterior end, since both external and 

 internal structures bear a constant relation to them. Segments 



