184 COMPARATIVE ANATOMY chap. 



Docoglossa {Patella) the sheath, which lies above the foot on the floor of the body 

 cavity, is even longer than the body (Fig. 158). 



3. Salivary glands (buccal glands, pharyngeal glands) are universally 

 found in Glossophora, i.e. in Molluscs which have a pharynx and lingual 

 appatatus. They are universally absent in Lamellibranchs. They may 

 occur in one or two pairs. The posterior or in other cases the only 

 pair often lies on the wall of the oesophagus, and sends forward two 

 ducts which enter the pharynx laterally, usually somewhat behind the 

 point where the radular sheath opens into the pharyngeal cavity. 

 Very little is known of the function of these glands ; an exact 

 morphological comparison of the various pharyngeal glands of the 

 Gastropoda is at present hardly possible. 



Amphlneura. (a) Chiton. — Two small delicate buccal glands lie 

 on the roof of the buccal cavity and open into the mouth. They can 

 therefore hardly be regarded as pharyngeal or salivary glands. 



(b) Solenogastres. — Salivary glands are here found in all genera 

 except Neomenia, and in Ghcetoderma. They are present in some species 

 but appear to be absent in others. A pair of long glandular tubes 

 with high glandular cells ^ and strong muscular walls lie anteriorly under 

 the intestine and are produced in the form of two narrow ducts, which 

 enter the pharyngeal cavity on the tongue either separately or through 

 a common terminal portion. Besides these there is another pair in 

 some species [Paramenia impexa, Param. palifera, Proneomenia vagavs, 

 Dondersia flavens) ; the ducts of these open together through an un- 

 paired terminal portion on the dorsal wall of the pharyngeal cavity, 

 at the point of a papilla which rises from the base of a pit-like 

 depression. 



Gastropoda, {a) Prosobranehia. — In most cases there is only 

 one pair of salivary glands. These are usually lobed or branched 

 glandular masses, which lie, in the Diotocardia, at the sides of the 

 pharynx, in the Monoiocardia, at the sides of the cesophagus. In the 

 former case, the ducts are short and do not pass through the cesophageal 

 ring formed by the nerve centres and their connectives and commis- 

 sures, which in these forms surrounds the anterior end of the pharynx. 

 In the Monotocardia, the ducts are long, and generally accompany the 

 oesophagus through the oesophageal ring (which lies behind the pharynx), 

 and open on the posterior lateral wall of the latter. 



Two pairs of salivary glands are found in certain Diotocardia [e.g. 

 HaUoti.-<, Fissurelki), and further in Patella, the Scalariidce, lantJiinidce, 

 certain Purpuridce, Muricidce, and in the Cancellariidce. 



One of the two pairs of glands in Haliotis is developed in the form 

 of large lateral glandular sacs covering the pharynx on the right and 

 left (Fig. 105, p. 121). 



In the Ampidlariida', the ducts of the salivary glands do not pass 



^ This differs somswhat from the description found in Simroth (Bronn's Klassen 

 uiid Ordnungen, vol. iii, pp. 183-185). 



