BY J. J. FLETCHER, 1009 



the posterior fourth or fifth of the body, except on about the last 

 half dozen segments on which setse are not visible) but with 

 any tendency to irregularity more marked in the case of the 

 second row of each of these couples ; the rows of the two outer 

 couples at first regular, in some specimens continuing so for a 

 considerable distance (for the anterior half of the body, or even 

 more) but sooner or later, or in others even on some of the pre- 

 clitellar segments, the setse of one or the other (most commonly 

 the outer) and further back of both rows on each side of the body 

 only here and there or continuously become displaced, at fiist 

 slightly and then more and more markedly so that in about the 

 hinder fourth or fifth of the body where always the two outer, 

 and sometimes all four, rows of each side are out of place, the 

 irregularity is sometimes very remarkable ; the set?e of the same 

 rows on different segments may be quite close or widely separated, 

 the seta) of different rows sometimes alternating roughly for a few 

 segments. In one specimen five set^e were present on one and 

 four on the other side of the same segment. Even in worms 

 without girdles and undeveloped male papilla) I have not noticed 

 the inner couples of setae on segment xviii. 



The ventral surface of segment xviii in all but very young 

 specimens is more or less modified, most marked in mature worms 

 with well developed clitella in which (in spirit specimens) there is 

 usually a rather broad but shallow transverse depression bounded 

 by a tumid rim, most thickened just round and a little beyond 

 the ends of the depression which reaches on each side to a little 

 beyond the second row of setre, the depression a little narrower 

 (from before backwards) for a little way on each side of the median 

 line of the body, then widening out towards the extremities thus 

 bearing some resemblance in shape to a dumb-bell, the papillae with 

 the male pores in but not quite at the extremities of the enlarged 

 ends corresponding in position with the interval between the setae 

 of the inner couples, and confluent with the posterior slope of the 

 depression so that the depressed area passes in front and beyond 

 them ; sometimes a small papilla or only a little pit dorsad of each 

 of the male papillae. In less mature individuals the same arrange- 



