'852 PROF, G. C. BOURNE ON THE [NoV. 17, 



longis2nna, with the coils of the gut unravelled, is given in fig. 35, 

 and the relative positions of buccal bulb, intestine, and stomach, 

 and the division of the last-named into oesophageal and pyloric 

 moieties, are indicated in fig. 41. The characters of the 

 epithelial lining of difi'erent portions of the gut, and the ridges 

 and folds into which the lining of the stomach is thrown, are 

 remarkably similar in all the species I have examined, and Lenssen's 

 ■description of the digestive system of JSferitinafluviatilis may be 

 taken as typical for all the Neritida?. Such small differences as 

 occur chiefly aflfect the relative size and length of the radular sac, 

 .and the lengi}h and consequently the complexity of the coils of 

 the intestine. Marine species pass a considerable quantity of 

 sand through their bodies, and their intestine is longer and 

 thicker-walled than is the case in freshwater species. The 

 radular sac is also longer, and the radular teeth coarser and more 

 powerful, in marine than in freshwater forms. The relative size 

 of the pharyngeal bulb also differs. It is, for example, very large 

 in Nerita peloronta and plexa, relatively small in Paranerita 

 vanegata and gagates, but in every case the essential structure 

 and relations of the cartilages of the odontophore, the salivary 

 glands, and diverticula of the pharyngeal cavity are the same. 

 There are seven buccal cartilages in all ISTeritidse, as described by 

 Lenssen, and the differences in size observed in the i^haryngeal 

 bulb are due to the greater or less size of these cartilages and 

 the more or less powerful development of the intrinsic muscles 

 attached to them. In all cases I have found the pair of lateral 

 glandular sacs opening into the lateral extension.- of the sub- 

 ra-dular diverticulum as described by Thiele. In some species 

 the walls of these sacs are pigmented and their lumina contain 

 •dark-coloured concretions. I must add that I have in no case 

 been able to find salivaiy glands with long ducts such as are 

 described by Bela Haller in Nerita ornata. (" In diesen miinden 

 dorsalwarts an der gewohnlichen Stelle mit sehr langen, wohl 

 difFerenzirten Ausfuhrungsgangen, zwei compacte acinose Buccal- 

 driisen," loc. cit. p. 131, Taf. xi. fig. 123.) These salivary or 

 buccal glands always have the structure and relations described 

 by Lenssen. They are closely a|3plied to the hinder end of the 

 pharyngeal bulb and pass round to its lower surface, embracing 

 the origin of the radular sac. They have no ducts, properly 

 speaking, but are large saccular diverticula of the anterior end of 

 the oesophagus, and are comparable with the oesophageal pouches 

 of other Rhipidoglossa. 



The Nervo\is System. 



I have already given on pp. 819-821 an analysis of the different 

 accounts of the nervous system given by different authors, from 

 which it may be gathered that while there is agreement on the 

 main points, there are still questions about which there is 

 considerable difTerence of opinion. Having nothing to add on 



