SOME POINTS IN THE ANATOMY OF POLYCH^TA. 247 



north-west Europe. It is, however, common enough between 

 tide marks in the sand at Granton. Claparede 1 does not give 

 any description of the segmental organs, he merely mentions 

 that the ovaries are attached to them, and render their study 

 difficult. There is, of course, no great difficulty in making 

 out the relations of the nephridia in longitudinal and transverse 

 sections. These relations are in some small points exceptional, 

 and longitudinal sections are the most instructive. The nephro- 

 stome is a wide ciliated funnel, the lips of which are simple 

 and entire, not produced into lobes. The aperture of the 

 nephrostome is large and gaping as in Cirratulus. The lower 

 lip of the nephrostome projects into the cavity of the somite, 

 while the upper is continuous with the transverse septum, on 

 whose front face the nephrostome lies. The nephrostome is 

 situated at the lower and outer corner of the septum, and leads 

 into a narrow tube, which pierces the septum and then dilates 

 into a small spherical vesicle, which on the median side is 

 produced into a point, and to this point the gonad is attached 

 (fig. 7). A little more to the exterior side the vesicle gives off 

 a long duct, which passes upwards to the body wall and opens 

 to the exterior (fig. 8). As a general rule the efferent duct of 

 the nephridium in Polychseta passes downwards ventrally, and 

 opens below the level of the neuropodium. Iu Terebellidse the 

 external aperture is near the upper end of the uncinigerous 

 torus, but in this case the ventral band of muscle extends 

 some distance upwards, and thus, although the nephridial 

 aperture has an exceptional position with regard to the neuro- 

 podium, it has its normal relation to the ventral muscles. In 

 Nerine there is no such reason for the extremely dorsad position 

 of the nephridial aperture ; the ventral band of longitudinal 

 muscles on each side is folded in at its borders, and the two 

 bands occupy only the ventral surface of the transverse section ; 

 the dorsal bands in like manner occupy only the dorsal wall; 

 the whole of the lateral region of the transverse section, which 

 approaches a parallelogram in shape, is destitute of thick 

 muscular bands, and the fascicles of bristles are widely sepa- 

 1 'Ann. Chet. du Golfe de Naples,' Geneva, 1868. 



