SALIVARV GLANDS 



237 



each of which has a small accessory plate at the base. The two 

 laterals and the central tooth are small, very similar to one 

 another, nnicnspiel on a square l)ase. 



Salivary (/lands are found in most Glossophora. They occur in 

 one or two pairs on each side of the pharynx and oesophagus, the 

 duet usually leading I'orwards and opening into the anterior part 

 of the pharynx (see Figs. 143, 144). They are exceptionally 

 large in the carnivorous (Tasteropoda. In certain genera, e.ff. 

 Murex, Dulium, Cassis, Flc/urohranclms, the secretions of these 

 glands are found to contain a considerable proportion (sometimes 

 as much as 4'25 per cent) of free sulphuric acid. This fact was 



Fig, 



14.3. — Alimentiiry canal of Helix aspersa L. : «, anus; b.d,h.(l', riglit and left 

 biliary ducts ; b.i/i, buccal mass ; c, crop ; h.ff, lierniaplirodite gland ; i, intestine ; 

 {.0, opening of same from stomach (pyloric orifice); /, I', right and left lobes of 

 liver ; m, mouth ; oc, oesophagus ; r, rectum ; s.d, salivary duct ; s.g, salivary 

 gland ; st, stomacli ; t, left tentacle. (After Howes and Marshall, slightly 

 modified. ) 



lirst noticed l)y Troschel, who, while handling a Dulinm galea at 

 Messina, saw the creature spit a jet of saliva upon a marble slab, 

 which immediately produced a brisk effervescence. A number 

 of the genera thus provided Ijore through the shells of other 

 ]\Iollusca and of Echinoderms, to prey upon their soft tissues, and 

 it is possible that the acid assists in the piercing of tlie shell by 

 converting tlie hard carbonate of lime into sulphate of lime, 

 wdiich can easily be removed by the action of the radula.^ In 

 the majority of the Ceplialopoda there are two pairs of salivary 

 glands, one lying on each side of the mouth, the other on the 

 middle of the oesophagus. 



o. The Oeso2:)ha(jus. — That part of the alimentary canal which 



' Seinon, Biol. Cenlralhl. ix. ji. 80. 



