STKUCTUEE OF EAIITHWOEM OF GENUS DIACH^TA. iGl 



The setge of this Diachseta are remarkable for three 

 diflPerent reasons. 



In the first place^ they are irregularly disposed, and the 

 irregularity commences, as in D, Thomasii, from the very 

 first, and continues to the end of the body ;^ to the end of the 

 xith segment the setse are grouped in two lots on either side of 

 the median ventral line, as shown in fig. 1, but their 

 arrangement does not exactly agree in any two consecutive 

 segments ; further back there are four setae separated from 

 each other by considerable intervals, and two closely approxi- 

 mated on each side to form a pair; towards the tail end 

 the paired arrangement is again lost, and the irregular dis- 

 position of the setse is returned to. Fig. 8 illustrates this 

 arrangement. 



Another remarkable fact about the setse of this species of 

 Diachseta is that in the first three (setigerous) segments, at 

 any rate, they are not situated along one line running 

 parallel with the intersegmental furrow; they have a 

 curiously alternate arrangement as seen in the figure (fig. 1), 

 some being situated further forwards, others further back in the 

 segment to which they belong ; they form, in fact, almost 

 a double row. It might, perhaps, be supposed that this 

 appearance is due to the simple fact that I have confounded 

 two segments and regarded them as one ; and this supposition 

 is strengthened by the fact that in two out of the three seg- 

 ments a faint groove divided the segment into two. Never- 

 theless, I regard this groove as the division between two 

 annuli; it is frequently the case among earthworms that the 

 anterior segments, when large, are marked by one or more 

 annulations ; moreover, in Segments vi and vii the setae, 

 although showing the curious arrangement referred to, are only 

 eight in number. The ixth segment, on the other hand, 

 in one of the three specimens, was certainly fur- 

 nished with nine setae; indeed, I actually counted eleven; 

 but it is possible that two of these, being placed each very close 



^ The irregularity in the arrangement of tlie setse is much like what 

 Schmarda (11) has described in his genus Pontoscolex. 



