134 J- Stephenson: Description of an Oligochcete Worm. [Vol. I, 



SetcB. — There are two bundles of setae in each segment in which 

 they occur, and there are about six setse in each bundle ; five and 

 seven are also met with. They are ventro-lateral in position ; the 

 portion which projects externall}^ is approximately equal in length 

 to the portion within the body ; and the whole length of a seta 

 is equal to about two-thirds the diameter of the body when the latter 

 is in the condition of moderate extension. Each seta has the form 



of an elongated / , the end is unequally forked, and there is a 



small nodulus {v. plate v, fig. 2). 



When the animal is at rest, most of the setse project at about 

 a right angle ; those of the most anterior bundles, however, lie flat 

 against the surface of the body, their free ends forwards. The 

 somewhat hooked free ends of the setae may point either forwards 

 or backwards (I do not refer to the direction of the seta as a 

 whole) ; in the setae of a single bundle, the hooks of some may 

 point forwards, of others backwards ; and a bundle of setae, the 

 hooks of which are pointing forwards, may be seen shortly after- 

 ward with hooks pointing backwards ; some of the muscular fibres 

 attached to the setae have, therefore, the power of rotating the setae 

 about their longitudinal axes. A common arrangement is for the 

 hooks to point backwards in the anterior, forwards in the posterior 

 segments. Backward-pointing hooks are presumably of use in for- 

 ward progression, forward-pointing hooks in backward progression. 

 The first bundles, however, appear always to have their hooks 

 pointing backwards. 



The distribution of setal bundles in the anterior part of the 

 body is apparently subject to slight variation ; on one occasion a 

 few small setae were noted in the third body-segment ; in another 

 case those of the sixth segment were fewer and smaller than normal. 

 Asexual reproduction. — The smallest number of segments ob- 

 served was eight [v. plate v, fig. 3 a) ; the body, that is, came to an 

 end at the end of what I have called the " stomach," and comprised 

 only four pairs of setal bundles ; there was, in addition a commenc- 

 ing constriction visible, which if completed would separate off the 

 posterior two segments. This specimen may have been pathologi- 

 cal ; the body-cavity contained numerous clear, oval or irregular 

 corpuscles, apparently non-nucleated, which were seen in no other 

 specimens ; it was in this animal also that the setae of the sixth 

 segment were fewer and smaller than usual. 



All the other animals examined were divided by a well-marked 

 constriction into two parts, an anterior, of at least eight body-seg- 

 ments, and a posterior, of varying length ; these two principal 

 divisions of the worm were usually again divided by slighter con- 

 strictions. Thus the anterior portion might consist of eight body- 

 segments, the posterior of four setigerous segments (plate v, fig. 

 36); or the anterior of eight body-segments, the posterior of six 

 setigerous segments (c) ; or the anterior of eleven body-segments, 

 the posterior of seven setigerous {d) ; or the posterior portion might 

 comprise eight setigerous segments, and be again divided into two 



