58 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



serabling in appearance a gizzard, and contains within it the mastica- 

 tory apparatus. Just within the upper hp, attaclied to the entrance 

 of the buccal body, is the dental plate or jaw, — a crescentic, corneous 

 lamina, used for cutting the food. Its anterior face is convex, and 

 presents several vertical ridges. Into its upper convex edge a band 

 of muscular fibres is inserted, by the contraction of which the inferior, 

 concave, cutting edge is advanced beyond the line of the upper. The 

 middle of the cutting edge is extended into a short, conical beak. This 

 jaw is brought into view when the animal is eating, by the advance- 

 ment of the buccal body. The floor of the cavity is occupied with 

 a gouge-shaped, muscular tongue,^ the tip and upper surftice of which 

 are free, and are covered by a corneous lamina studded with a great num- 

 ber of conical dentures, with the points projecting backwards, arranged 

 in transverse rows. These teeth preserve the same form in the lines 

 from before backwards ; the central line always differs from the others, 

 and the teeth also vary gradually in form and size as they pass off 

 from the central line laterally. They also vary slightly in form in 

 different species. This lamina protrudes from the buccal body pos- 

 teriorly, into a short, rounded, protuberant, blind sac, within which 

 it appears to undergo a constant growth, as it is worn aw^ay by at- 

 trition anteriorly ; for its use appears not only to facilitate the pas- 

 sage of the food onwards to the oesophagus, but also to act as a sort of 

 rasp for triturating it, by means of the powerful muscles composing the 

 buccal body. Into the posterior, inferior part of the buccal body, below 

 the blind sac of the lingual lamina, is inserted, in a transverse, curved 

 line, its retractor muscle. This muscle has its origin, in common with 

 the retractors of the eye-peduncles, from the muscular investment of 

 the visceral cavity, posterior to the pulmonary cavity, and to the right 

 of the rectum. 



The oesophagus proceeds from the upper, posterior part of the buccal 

 body backward to the stomach. It is short, and dilates gradually into 

 the latter. 



The stomach is a capacious, membranous receptacle, when extended 

 being two thirds the length of the animal. In L. flavus and L. agrestisy 

 anteriorly it is dilated, and elongated-oval in form, posteriorly it is in- 

 testiniform. In L. campestris, it is nearly uniformly cylindrical through- 

 out. Where the stomach terminates in the small intestine, it makes a 

 turn forward with the latter, producing, in L. flavus and L. campestris, 



1 See above, p. 45. 



