786 tROF. G. C. BOURNE ON THE 



wall of the mantle-cavity, but there is no apertm^e into the mantle. 

 I have not been able to find this tube in other species, but this 

 may be due to the imperfection of my sections and to the fact that 

 it is too small to be recognizable in dissections. It is a well-defined 

 structure in E lUrochatella and is lined throughout by a non-glan- 

 dular cubical epithelium. I am inclined to the opinion that the 

 anterior third of the terminal sac of the male is the equivalent 

 of the body of the ootype of the female ; the diverticulum of the 

 male represents the ctecum of the ootype, and the narrow tube 

 (PI. XXX \^II. fig. 42, k.r) represents the vagina of the female, 

 but has lost its opening into the mantle-cavity. If this iden- 

 tification is correct, a relic of the right kidney-sac is I'etained in 

 the male, at least in Eutrochatella jjulchella and Lucidella aureola. 

 It may be noted that Isenkrahe's drawing of the male organs 

 of Helicina titanica is very nearly correct. 



The Nervous System. 



Nobody has given a detailed account of the nervous system of 

 any Helicinid since Bouvier dealt with this subject in his 

 classical memoir on the nervous system of Prosobranch Gastropods 

 (3). In that work he gives an elaborate figure of the nerve- 

 centres and principal nerve-trunks of Helicina sagraiana d'Orb., 

 and also several figures of the buccal ganglia of the same species 

 and of the cei'ebral and pleuro-pedal centres of H. hrasiliensis 

 Gray. As is always the case, Bouvier's figures possess a high 

 degree of accuracy, and if I have some criticisms to ofi"er, they 

 must not be taken as depreuiatory of his excellent work, but 

 as an elaboration of it, rendered possible by careful study of 

 sections and by the opportunities for exceedingly fine dissection 

 afforded by the Braus-Driuier microscope. 



In the first place, it was necessary to determine whether the 

 supra-intestinal nerve exists in the Helicinidse. Bouvier had 

 failed to find it in the Neritidae, and when in a subsequent memoir 

 he announced its discovery in the latter group, he hazarded the 

 opinion that it would probably be found in the Helicinidse. 

 But it does not exist in these pvdmonate rhipidoglossate.s ; it has 

 disappeared in them as completely as the organs with which, 

 when present, it is associated, the ctenidium and the osphradium. 

 I can speak with certainty on this point, for I have made so 

 many dissections and have studied such a sufficient number of 

 serial sections that I could not have overlooked it if it were 

 present. 



In the second place, I am unable to verify some of the details of 

 Bouvier's figure of the nervous system of H. sagraiana. In none of 

 the species that I have studied are the pedal, pleural, and subintes- 

 tinal centres as distinct as shown b}^ him. As may be seen in 

 fig. 44 (PI. XXXIX.), the pleural ganglia are ill-defined swellings, 

 scarcely distinguishable from the swollen anterior ends of the 

 pedal cords, and the subintestinal ganglion is so intimately fused 



