326 W. ELAXLAND BENHAM. 



Both the above-named authors figure and describe the net- 

 work of blood-vessels on the funnel and the body of the 

 nephridium, but neither mentions the blind dilated termina- 

 tions and irregularities in the capillary vessels (PI. XXV, fig. 

 34), recalling those in Lumbricus; Cosmovici, however, does 

 mention these as occurring elsewhere in Arenicola. 



Notwithstanding the general accuracy of the descriptions 

 given by these authors, I have thought it worth while to 

 introduce another figure of the whole organ, which to my 

 mind represents the form and relations of the parts more 

 clearly than either of those already published. 



The nephridium of A. piscatorum (PL XXV, fig. 33) 

 consists of (a) a large, wide, tapering tube or " body," lined by 

 a single layer of ciliated vesicular cells (fig. 40) ; (b) of a very 

 wide funnel attached to the broad end of the " body " by a 

 narrow " neck ;" (c) of a dilated, more muscular region, open- 

 ing to the exterior and separated from the narrow part of the 

 body by a well-marked constriction. 



A very noticeable contrast to the nephridium of Oligo- 

 cheeta is presented by that of Arenicola and other Poly- 

 chseta, e. g. Polynoe (A. G. Bourne, 15, pi. xxvi, figs. 22, 

 23, 24), in that the lumen is intercellular throughout ; and 

 this point deserves mention because Baldwin Spencer (30, 

 p. 44) has argued against the theory that the genital ducts of 

 Oligochseta are modified nephridia, because, whilst the lumen 

 of the latter is mainly intra-cellular, that of the former is 

 wholly intercellular ; yet, I imagine, he would not deny that 

 the nephridia in the two groups are homogeneous ; and they 

 appear to serve as genital ducts in some Polycheeta. 



The wide " body " contains no convoluted tube, as is the 

 case in Nereis and other genera, but consists of one very 

 wide, simple tube, as is readily to be seen in sections through 

 the organ (PI. XXV, figs. 35, 36, 37). The epithelium is one 

 cell deep, is ciliated throughout (figs. 40, 41), and for the 

 most part contains brown concretions (fig. 41), giving the 

 whole organ a yellowish colour. In the lumen of the gland, 

 in section, is a granular mass, frequently having the appear- 



