454 



ZOOLOGY 



SECT. 



prostomium of the adult. The part immediately behind forms 

 the peristomium, which bears setse, and is to be looked upon as 

 the specially modified first segment. The body increases in length, 

 and additional segments with their setigerous sacs become dis- 

 tinguishable [E) until, on the development of the tentacles, the 

 outgrowth of the parapodia {para) with their cirri and the 

 permanent setae (which replace those first formed), the formation 

 of the full number of segments, and the completion of the internal 

 organs, the adult condition of the worm is attained. 



b. The Earthworm (Lumbricus). 



General External Features. — The Earthworm (Fig. 357) 

 has a long narrow body, which may be described as approximately 



Fig. Lumbricus berculeus. A, entire specimen, lateral view ; B, ventral view of 



anterior portion of the body, magnified. 1, 15, 33, first, fifteenth, and thirty-third segments. 

 Each of the black dots represents a pair of seta;. (After Vogt and Jung.) 



cylindrical, but slightly depressed towards the posterior end. 

 Dorsal and ventral surfaces are readily recognisable, the latter 

 being much paler in colour than the former, and exhibiting a 



