III.] THE EARTHWORM. 249 



stricted as a rule to 6 or 7 segments in Lumbricus, 

 5 to 9 in Allolobophora. It usually commences on 

 segment 26, or on from i to 6 segments behirid that. 



This is best studied in a chloroformed specimen. 



The capacity of the whole body is greatest at this 

 point. Posteriorly to the clitellum it is uniform in 

 calibre, except for the postero-terminal region (cf. 

 i. a), where its transverse diameter is greatest. An- 

 teriorly, it is enlarged in the genital region (segments 

 8 to 12) tapering off to a point in front. 



c. The locomotor organs or seta, four double rows 

 (two lateral and two ventral) of bristle-like ap- 

 pendages, which project freely from all but the 

 extreme anterior and posterior segments. 



The body is flattened ventrally between the two 

 sets of ventral setas, and laterally between the 

 lateral and ventral ones. The setae project out 

 at the angles formed by these flattened areas, the 

 lateral ones arising within the limits of the pig- 

 mented portion of the body-wall. 



d. The apertures. 



a. The mouth, antero-terminal. It perforates the 

 first segment, which is subdivided into a dorsal 

 prostomium which overhangs the mouth, and a 

 circumoral peristomiun? . Examine the latter with 

 a lens ; its free edge is delicately serrated. 



Compare the living animal. The movements of 

 the body clearly show that the first segment is 

 highly sensitive. 



ft. The anus, postero-terminal, and laterally com- 

 pressed. It perforates the last segment. 

 Note the valve-like nature of its lips. 



1 Cf. Lumbricus and Allolobophora (p. 240 foot-note). 



