1908.] ASPIDOBRANCH GASTROPOD MOLLUSCS. 863 



of the liver and intestines, the visceral spire were elongated, the 

 ^onad would remain at its apex, and the gonaduct would be 

 coi-respondingly elongated. This, in fact, is the typical position 

 of the gonad in multispiral gastropods, and the primitive connec- 

 tion of gonad with ccelom is well illustrated by the Neritidse. 



The Excretory System. 



The kidney in Nerita and 'Paranerita has essentially the same 

 sti'ucture and relations as in Septaria and Neritma fluviatilis. 

 It consists of a glandular and a non-glandular part or bladder 

 communicating posteriorly behind the rectum. The bladder is a 

 very wide sac (fig. 43, K^) lying between the glandular part and 

 the pericardium. Anteriorly it twists under the glandular part 

 and leads into a small thick-walled chamber (fig. 47) which opens 

 to the exterior by the lu^opore (fig. 45, Uiy.). As in Septaria 

 the posterior moiety of the glandular part seems always to differ 

 somewhat in histological character from the anterior moiety ; this 

 difi:erence is indicated in figs. 43, 44, k 46. The only direct 

 connection between the glandular and the non-glandular parts 

 of the kidney is at the posterior end, but there is an indirect 

 anterior connection, similar to that described in Septaria depressa. 

 The reno-pericardial funnel opens, as explained above, into a 

 diverticulum of the coeloni which passes below the non-glandular 

 part of the kidney (fig. 46). Its further course is that of an g , 

 and for some distance it jorojects into the bladder, and eventually 

 becomes attached to the wall of the chamber which opens to the 

 exterior by the uropore (fig. 45). Passing up the wall of this 

 chamber it opens into it by a small but distinct ciliated passage 

 (fig. 47, cil.p.), and continuing its course, up the wall of the 

 uropore-sac dilates to form a canal of considerably wider diameter 

 which divides into two branches. The main branch passes to the 

 left over the uropore-sac, and opens into the glandular part of the 

 kidney ; the smaller branch passes to the right and is connected 

 with some small detached renal lobes lying in the blood-sinus 

 leading to the afferent branchial vessel. The characteristic 

 epithelial lining of the reno-pericardial canal, described in detail 

 by Lenssen and Thiele, is confined to the section lying between 

 the ccelomic opening and the ciliated connection with the uropore- 

 sac. This section is very long ; I have calculated that it is at 

 least "9 mm. long in a specimen of Paranerita gagates measuring 

 13 mm. in length. The transition from the characteristic epithe- 

 lium of the duct to an ordinary columnar ciliated epithelium, and 

 from the latter to the glandular epithelium of the kidney, is 

 shown in fig. 47, 



The wide thin-walled sac which I have described as the bladder 

 or non-glandular part of the kidney is generally named the 

 ureter, I have not used this term because in those Gastropods in 

 which a long ureter is present running alongside of the rectum 

 (e. g. Paludina) there is evidence that it is formed from the 



Piioc. ZooL. Soc— 1908, No. LV. 55 



