4908.] ASPIDOBRANCH GASTROPOD MOLLUSCS. 827 



The Alimentary Tract. 



Fig. 2 is an illustration exhibiting the macroscopic characters 

 •of the buccal bulb, oesophagus, stomach, and intestine. It would 

 be possible to write at considerable length on the structure and 

 histology of these various regions, but I purposely refrain from 

 -doing so, although my preparations have enabled me to study 

 them with considerable accui-acy. Allowance being made for 

 small and unimportant differences in proportion and detail, the 

 ■structure of the alimentary tract of Septaria is so closely similar 

 to that of Xerithta Jiuviatilis as described by Lenssen (35), that it 

 is superfluous to give a description which would be little more 

 than a repetition of his accurate observations. I need only call 

 attention to one or two minor poiirts. I find that in Septaria^ as 

 in N.Jiuviatilis, there are seven buccal cartilages, three pairs and 

 one median and azygos. The smallest pair, discovered for the 

 first time by Lenssen, does not strictly belong to the odontophore, 

 but lies in the antero-inferior walls of the buccal bulb and serves 

 as supports for a pair of pads, covered by a horny cuticle, against 

 which the right and left halves of the anterior end of the radula 

 work. In Septaria there is a small pair of glandular sacs, one 

 ■on each side, opening into the lateral extensions of the subradular 

 diverticulum of the buccal cavity. These have been noted by 

 Thiele in Nerita pica, but are not recorded by Lenssen in 

 Xeritina jluviatilis. The oesophagus in Septaria passes to the 

 left on leaving the buccal bulb and shows clear traces of the 

 larval torsion so carefully described by Amaudrut (1). Just 

 I)efore its junction with the stomach it expands considerably and 

 receives three large diicts from the liver. The oesophagus may 

 be said to join the stomach tangentially ; hence its aperture is 

 prolonged backwards as a wide groove, bounded by thickened 

 epithelial lips, which, while they diflfer slightly in detail, have 

 the same relations as are described by Lenssen in Neritina 

 Jluviatilis. The stomach of Septaria consists, as is the case in all 

 the jSTeritidse I have examined, of a dilated oesophageal and a 

 narrower pyloric moiety. In the former there is a large and 

 prominent epithelial ridge, described by Lenssen as the "crete 

 stomacale," conspicuous for its triangular appearance in section. 

 Its extremely long columnar epithelial cells are always covered 

 'by a thick apparently cuticular product, which in appearance and 

 composition seems to be similar to the cuticular lining continuous 

 with the crystalline style found in so many Molluscs. In Septtaria 

 there is fi small digitiform diverticulum of the oesophageal moiety 

 of the stomach, situated between the lower end of the " crete 

 stomacale " and the upper border of the oesophageal groove. 

 This diverticulum, which is probably homologous with the spiral 

 diverticulum of the stomach of Haliotis, appears to be absent in 

 Neritina fiuviatilis. The intestine and rectum do not call for 

 any special mention. The histology of the different regions 

 varies, and the variations have been sufficiently described by 



