254 POLYCHAETA CHAP. 



the cells forming the wall of the tube ; they remove waste mate- 

 rials from the blood distributed over the surface of the organ. 

 But, in addition, there is a removal from the coelom, by means of 

 the funnel, of any dead or dying coelomic corpuscles which in 

 their turn have eaten up or otherwise destroyed foreign bodies 

 (such as Bacteria, etc.) that may have entered the animal. 



In Nereis there is in each segment, in addition to the pair of 

 nephridia, a pair of " dorsal ciliated organs" (Goodrich) (cil.org in 

 Fig. 124). Each appears as a wide-mouthed funnel, greatly folded, 

 and without any permanent outlet. But it is possible that these 

 organs function as genital ducts, and that the external aperture 

 will make its appearance temporarily at the period of maturity. 



FIG. 129. Nephridium of Arenicola. (Prom Benham.) x 4. d, Dorsal lip of funnel ; 

 v, ventral lip of funnel ; b, blood-vessel (all the black lines are blood-vessels) ; m, 

 dilated bladder ; x, part cut away from body-wall where the uephridium is pass- 

 ing to the exterior. 



This " dorsal ciliated organ " has not been met with in allied 

 genera such as Eunice, Nephthys, Polynoe, Glycera where the 

 nephridium is a wide tube, and serves as a genital duct. 



The nervous system, as in all Chaetopods, consists of a dorsal 

 cerebral ganglion or " brain " (Fig. 127, &?')> connected by circum- 

 buccal commissures with the anterior end of a ventral chain of 

 ganglia. The brain occupies the prostomium, 1 and from it nerves 

 pass away to the prostomial tentacles and palps. The circum-buccal 

 commissures spring from the outer corner of the brain, and from 

 each arises a nerve to the first pair of peristomial cirri. The 

 first ventral ganglion lies in the third segment, and represents 

 at least two ganglion-pairs fused together, for from it arise (1) 

 a pair of nerves to the second pair of peristomial cirri and (2) a 



1 It is worthy of note that in Aedosoma alone amongst the Oligochaeta does the 

 brain lie in the prostomium in the adult. 



