Metazoa L umbricus. 



235 



FIG. 120. Linnb 

 terrestris. 



greatly in length, some giant earthworms being known to 

 naturalists who have investigated speci- 

 mens from tropical countries. A com- 

 mon length for the species so abundant 

 in our own country is from three to 

 nine inches. The body is of tolerably 

 uniform diameter throughout, and is 

 pointed at either end. Its length is 

 subdivided into compartments by a 

 series of rings from one to three hundred 

 in number. The compartment between 

 every two rings is known as a segment 

 or somite. Although at first sight the 

 distinction is not very apparent, yet if 

 a careful examination be made it will 

 be found that the earthworm possesses, 

 if not a head, at least an anterior or 

 head end, which may be recognised by 

 its more pointed character and darker 

 colour. The posterior end, though also 

 tapering, ends more abruptly. The 

 dorsal aspect is more darkly coloured 

 than the ventral aspect, which latter is 

 further distinguished by the presence of 

 bristles, or setae. The setae may be 

 readily felt if the forefinger and thumb 

 be gently drawn from the tail to the 

 head of the living worm. On the ventral 

 surface of the anterior end will be found 

 the mouth or anterior opening of the 

 alimentary system. The projection of 

 the body above and in front of the 

 mouth is known as the prostomium. 

 Similarily at the posterior end, but in p, pnstomium; c , ciitei- 



.1 . -ii i lum. (The number of 



this case at its very extremity, will be Semites Lehind the 

 found the posterior opening of the ali- g3 should be 



-XXVIII 



-mvi 



