186 



COMPARATIVE ANATOMY 



The Cephalopoda have a posterior and an anterior pair of salivary 

 glands. Were the fore-gut, which here rises vertically in the visceral 

 dome, to occupy the horizontal position it has in the Gastropoda, the 

 anterior pair would lie dorsally and the posterior ventrally with regard 

 to it. The two posterior glands (Fig. 127, 29, p. 147) are always 

 present (except in CirrJwtc^dhis and LoHgopsis, in which they are said to 

 be wanting), and lie on the oesophagus. Each gland has a duct, which 

 soon unites with that from the other gland, forming a terminal portion 

 which accompanies the oesophagus through the cephalic cartilage, and 

 opens above the radula into the pharyngeal cavity. The jwsterior 



Fjg. 157.— Alimentary canal of Helix, dissected out and seen from the riglit side (after 

 Howes). 1, 3, Tentacles ; 2, constrictor pharyngis ; 4, levator pharj-ngis ; 5, depressor ; 6, pro- 

 tractor pharyngis ; 7, pharyngeal bulb ; 8, radular sheath ; 9, columellar muscle, divided into a 

 retractor pedis and retractor pharyngis ; 10, salivary glands; 11, digestive gland (liver); 12, ducts 

 of the same (gall ducts) partly cut open ; 13, hermaphrodite gland ; 14, stomach cut open, in its 

 base are seen the apertures of the gall ducts 15 ; 10, mid-gut; 17, hind-gut ; 18, anus. 



glands occasionally (e.g. in Oegopsklw) fuse behind the gullet, in which 

 case the duct is single throughout its whole length. 



The anterior salivary glands are specially well developed in the 

 Odopoda (Fig. 127, 33, p. 147), and lie on the pharynx, into which 

 they empty their secretions by a duct, which seems always to be 

 unpaired. In the Decapoda the anterior glands are much smaller or 

 rudimentary ; they are generally represented by a single gland hidden 

 within the muscular wall of the pharynx. 



Nautilus has no posterior salivary glands, but there are glandular 

 outgroAvths of the pharyngeal cavity on each side of the tongue, 

 which perliaps correspond with the anterior salivary glands of other 

 Cephalopods. 



The Cephalopoda ( ? without exception) have an additional acinose 



