220 PROCEEDINGS OF THE ACADEMY OF [1883. 



the upper (anterior) side of the cavity of the mouth." ^ These 

 long pieces are the denticles. 



The buccal mass, which is of a spheroidal form, lies in the head, 

 between the two tentacles. Immediately over the mouth is found 

 the opening of the oesophagus, and in the middle between these 

 two openings projects the tongue, which is covered by the radula. 

 The odontophore is in Ancylus exceptionally long, and reaches 

 from the buccal mass to the middle of the body. The opening of 

 the odontophore lies in the superior part of the buccal mass : the 

 first part of the odontophore itself lies sunken in a groove of the 

 buccal mass, so that seen from the side it appears to spring from 

 the posterior wall. 



The diagramatic figure (PI. X, fig. 2) represents a longitudinal 

 section of the odontophore (od), which opens into the spheroidal 

 buccal mass. In the figure the odontophore is relatively much 

 shorter than it is in reality. 



After the odontophore leaves the buccal mass it passes back- 

 wards, lying directly under the oesophagus and parallel with it ; 

 then it passes in A. Jtiiviatilis to the right, and in A. lacustris to 

 the left side. The oesophagus and odontophore are at the position 

 of insertion in the buccal mass, separated from one another by 

 the commissure of the buccal ganglia. Soon after leaving this 

 commissure the odontophore passes to the side and then upwards 

 and over the oesophagus, so that in the latter part of its course it 

 lies above it. 



The alimentary canal has in both species nearly the same form, 

 except that the windings are different. The esophagus arises in 

 the middle of the superior and anterior angle of the buccal mass, 

 directl}' over the position where the mouth enters from below (PI. 

 X, fig. 2oe). 



The salivary glands cpen by a very short duct into the oesoph- 

 agus, immediately behind the position of its exit from the buccal 

 mass. These glands are two in number, and lie on the side of the 

 oesophagus. 



The stomach is of a good size and spheroidal in form, the walls 

 are thick and muscular. It is embedded in the liver, which lies 



^ Bel Ancylus sehen wir an die Stelle der einfachen Kiefeis ein grosse 

 Menge kleiner langlicher Stiicke treten, welche ziemlich symmetrisch 

 angeoidnet, die Oberseite der Muudhohle umgiirten. Bronn's Klass. u. 

 Ord. d. Thieneichs, Bd. ill, 2 Abth., 1862-1866, p. 1190. 



