SOME POINTS IN THE ANATOMY OP POLYCHZETA. 245 



Cosmovici (loc. cit.) was unable to see the large anterior 

 nephridia described by Keferstein and Claparede, but states 

 that in C. filiform is, Kef., segmental organs are present in 

 pairs in nearly all the segments, especially of the middle and 

 posterior region : that they are attached to the anterior face of 

 each diaphragm : the figures of this species which he gives do 

 not show the organs mentioned. The Errantia, among which 

 he places Cirratulus, according to Cosmovici's peculiar views, 

 have only segmental organs and no organs of Bojanus, and he 

 denies altogether that the internal opening of the segmental 

 organ communicates with the cavity of the somite in front of 

 the one which contains the organ itself. 



In Cirratulus cirratus both the large anterior pair of 

 nephridia described by Keferstein and Claparede, and the 

 series of pairs in the middle and posterior region mentioned by 

 Cosmovici, are present. The nephrostome of the first nephri- 

 dium opens into the cavity of the buccal somite, being situated 

 on the anterior face of the first septum, somewhat ventrally, 

 in the angle between the septum and the lateral body wall. 

 The proximal part of the bent tube passes backwards from the 

 nephrostome till it reaches the second septum (PI. XVII, fig. 3), 

 then passes upwards to the dorsal body wall, where it opens 

 into the wider distal part of the tube which opens to the 

 exterior beneath the neuropodium of the second somite. The 

 posterior nephridia are smaller and simpler; they appear first 

 in the twelfth somite, and are repeated hence to the eud of the 

 body. Each of them has a nephrostome of the typical form, 

 an elongated funnel with its aperture directed forwards. The 

 nephrostome has a similar position to that of the large anterior 

 nephridium, that is to say, it is placed in the lower external 

 corner of the anterior face of its septum. The lips of the 

 funnel are composed of a columnar ciliated epithelium resting 

 on a thin fibrous membrane ; this membrane is continued on 

 the one hand into the transverse septum, on the other into the 

 body wall; the lips of the funnel project inwards and forwards 

 into the cavity of the somite. The nephridial tube when 

 traced from the nephrostome (in a series of horizontal sections) 



