:862 PROF. G. C. BOURNE ON THE [Nov. 17, 



fig. 58, the reader will be able to understand the following- 

 account of it. For descriptive purposes and without prejudice to 

 any theoretical conclusions, the ccelom may be regarded as con- 

 sisting of a left or pericardial division (figs. 29, 42, 58, 2^<^-co-) 

 and i-ight, or gonadial division (figs. 41, 43, & 58, g.co.). The 

 pericardial division lies on the left side of the body and is of 

 considerable vertical depth. Anteriorly it extends to the base of 

 the ctenidium, posteriorly to the union of the pyloric and 

 esophageal divisions of the stomach (fig. 42). Its outer wall is 

 very thin ; its inner wall tough and muscular. Its postei-ior end 

 is traversed by the rectum, and in it lie the ventricle and the two 

 auricles of the heart. On the inner or right side the pericai-dial 

 ccelom is continued into a wide passage (cap.) which runs under 

 the kidney, above and in front of the anterior lobes of the liver. 

 From this passage a diverticulum is given off on the left side, 

 which passes under the non-glandular part of the kidney and 

 stretches forward towards the uropore (fig. 43), below which it 

 ends in a dilatation and receives the coelomic o]3ening of the reno- 

 pericardial canal. To the right the passage widens out to foi-m 

 the gonadial ccelom, a flattened sac of ii-regular form lying between 

 the base of the genital complex and the liver. Its right-hand 

 corner is produced into a diverticulum extending as far as the 

 posterior end of the right columellar muscle, and here it comes 

 into close relation with the gonad, but it does not surround any 

 portion of the latter organ, as is the case in S'eptaria. The 

 oviduco-ccelomic funnel opens into the right-hand corner of the 

 gonadial coelom (fig. 41, od.c.f.) at the base of the diverticulum 

 just mentioned and not far from the columellar muscle. In the 

 male the sperm-duct runs very close to the wall of the same part 

 of the coelom, but after an assiduous search through many series 

 of sections I have been unable to find any trace of a spermiduco- 

 ccelomic funnel. The cavity of the gonadial division of the 

 ccelom is largely obliterated by the spermatophore-sac of the 

 female or the epididymis of the male, which projects into it like a 

 hernia from the posterior end of the genital complex, and, carrying 

 the posterior wall of the ccelomic cavity in front of it. lies 

 enclosed in a coelomic pocket in the position shown in figs. 44, 49, 

 and 58. It is clear that these I'elations are similar to those 

 described for Septaria, the difi"erence being that in the latter 

 genus the straightening' out of the visceral spire has allowed the 

 gonadial ccelom to extend much further alotig the right side of 

 the body, so that its relation to the gonad is obvious. There can 

 be no cloubt, however, that in the more spirally coiled Ner\ta, 

 Paranerita, and Neritina the gonad has been derived from the 

 wall of the right corner of the gonadial coelom. The oviduco- 

 ccelomic funnel of the female is evidence of this primitive 

 connection ; and as the cavity of the gonad is morphologically a 

 part of the coelom, the latter must be regarded as co-extensive 

 with the gonad, and therefore as occupying the whole of the 

 rupex of the visceral spire. If, as a result of the large development 



