SPECIAL ANATOMY. 207 



teeth preserve the same form in the lines from before 

 backwards ; the central line ahvajs 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 posteriorly, into 

 a short, rounded, protuberant, blind sac, within which it 

 appears to undergo a constant growth, as it is worn away 

 by attrition anteriorly ; for its use appears not only to 

 facilitate the passage of the food onwards to the oesoph- 

 agus, 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 trans- 

 verse, curved line, its retractor muscle. This muscle has 

 its origin, in common with the retractors of the tentacles, 

 from the muscular investment of the visceral cavity, pos- 

 terior 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. variegata and L. agrestis, anteriorly it is dilated, 

 and elongated-oval in form, posteriorly it is intestiniform. 

 In L. campestris, it is nearly uniformly cylindrical 

 throughout. Where the stomach terminates in the small 

 intestine, it makes a turn forward with the latter, pro=- 



