2l6 



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 

 fyph 



neph 



estntplv 



nephrost 



coel 

 veitt.v 



sub.nyess 



Fig. 153. — Transverse section through the middle region of the bod3' of 

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

 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; lyph, typhlo- 

 sole; vent.v, ventral vessel. (From Parker and Has well, after Marshall and 

 Hurst.) 



At the anterior end a fleshy lobe, the prostomium (Fig. 156, 1), 

 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 



