164 FRANK E. BEDDAED. 



they are disposed along a line encircling the segment ; in 

 two individuals (the only ones examined from this point of 

 view) this regularity in the first three setigerous segments 

 was lost. The setae of each segment were placed in 

 two quite distinct lines, separated by a slight 

 furrow. This abnormal state of affairs may perhaps seem 

 capable of being explained by the simple theory that the 

 supposed " segment" was in reality two segments. But in 

 this case there should be sixteen setae, whereas I counted them 

 very carefully and only found a total of eight, except in one of 

 the three segments of one individual; here there were eleven 

 setae, distributed fairly equally between the two annuli of the 

 segment. On first noting these facts (which, as they occurred in 

 three individuals selected at random, must surely be fairly con- 

 stant) it appeared possible that there was in this earthworm 

 just a trace left of a primitive condition, in which the setse, 

 like the nephridial pores, were scattered irregularly. There 

 is, however, no evidence that the setae have, like the nephridia, 

 been derived from some unsegmented aucestor. If this be the 

 case, there is no reason to suppose that the setfB were not dis- 

 posed in a perfectly metameric fashion from the first. 



It seems, therefore, that these facts, if they have any mean- 

 ing, point to the conclusion that the scattering of the setae is 

 a preliminary to the formation of two segments out of one ; it 

 does not seem likely that the reverse interpretation — viz. the 

 nearly complete fusion of two segments — is the right one. If 

 this be allowed, we then have a means of under- 

 standing the varying position of certain important 

 organs in allied genera. 



The third point in which the setae of Diachaeta are 

 remarkable is their very unusual degree of specialisation. 

 Examples of the various setae are illustrated in figs. 3 — 7, all 

 carefully drawn to scale by the help of the camera lucida. 



On the first few segments of the body the setae are all of the 

 form indicated in fig. 6 : there is a long shaft ornamented 

 with raised arches, like the setae of Rhinodrilus, and the 

 clitellar setae of Urochaeta ; the distal end of the setae is 



