SOME POINTS IN THE ANATOMY OF POLYOH^TA. 251 



no internal opening or nephrostome can be found in them. In 

 front of the most anterior nephridium, that belonging to 

 somite vn, are seen traces of a rudimentary nephridium (see 

 fig. 10). In order to trace out the relations of these nephridia 

 more accurately, the anterior part of a specimen was cut into a 

 series of horizontal longitudinal sections commencing with the 

 ventral surface, and the reason why the successive nephridia 

 could not be isolated from one another was seen on examina- 

 tion of these sections ; the lower parts of the efferent limbs of 

 the four anterior normal nephridia, in somites vi to ix, and the 

 whole of the nephridial sacs in somites x to xm are in open 

 communication, forming a wide continuous longitudinal tube 

 extending from somite vi to somite xm (see figs. 11 and 12). 

 Openings to the exterior from this tube were found in somites vi 

 to ix inclusive, corresponding to the four large looped nephridia ; 

 each of these openings was close behind the upper end of an 

 uncinigerous torus. The internal openings of the same four 

 nephridia could be traced with ease and certainty ; they are 

 attached to the body wall close behind the notopodial fascicles 

 of somites v to viii. These openings are wide, and are overhung 

 dorsally by a longitudinal lip furnished with a series of small 

 ciliated digitate processes; lower down, the anterior and posterior 

 lips of the opening are simple, thick-walled, and ciliated. The 

 aperture leads into a thin tube, which passes inwards and back- 

 wards, curving round the inner end of the fascicle of bristles 

 behind the aperture, and then, crossing the continuous tube, 

 passes up on the inner or mediad side of the loop, at the apex of 

 which it is continued into the efferent wider limb of the loop, 

 which passes down on the outer side to open into the longi- 

 tudinal tube. Neither internal nor external openings could 

 be found in that part of the longitudinal tube which is 

 behind the loops ; it seems evident that this part of the 

 tube represents four somewhat reduced nephridia which have 

 coalesced, but whose openings have disappeared. Anteriorly 

 to the four looped nephridia are traces of three others ; the 

 longitudinal tube extends forwards into somite v as if it in- 

 cluded a nephridium belonging to that somite, but I could find 



