44 



THE AMPHINEURA 



recurved thick and dark lateral tooth. Externally are six polygonal 

 marginal teeth : of these the third differs from the rest, being more 

 or less narrow, elongated, and curved, and sometimes its concave 



edge is ciliated (Trachydermon). 

 The fore part of the radula rests 

 upon a cartilaginous mass, 

 moved by a great many mus- 

 cular bundles. 



Two pairs of glands open 

 into the buccal cavity. The 

 true salivary glands lie at the 

 sides, well forward, but behind 

 the cerebral commissure ; they 

 are slightly branched, but rather 

 short, and have a very short 

 duct. On the ventral wall, 

 under the subradular organ, lie 

 two very small mucous glands 

 close to one another and to the 

 middle line. On either side, at 

 the point where the pharynx 

 passes into the short oesophagus, 

 is the opening of the sugar 

 gland a large glandular pouch 

 with a papillose internal surface. 



The large and thin-walled stomach is surrounded by the liver mass. 

 The two liver lobes are symmetrical in young Chitons, but become 

 asymmetrical in the adult, the right lobe being the smaller and 



Boreochiton cinereus, dorsal view of a female, 

 without the shell-plates. I, first " intersegmen- 

 tura " ; II, ovary; III, oviduct; IV, ventricle 

 of heart ; V, dorsal right muscle ; VI, dorsal 

 oblique shell-muscle; VII, retractor muscle of 

 the radula. 



Fir,. 20. 



Cfjiptoplax larvacjwmis, left-side view, the posterior end partially opened. I, gonad ; II, 

 genital duct ; III, genital pore ; IV, ventricle of heart ; V, anus ; VI, renal pore ; VII, gills ; 

 VIII, foot; IX, mantle ; 0, 7, 8, position of the sixth, seventh, and eighth shell-plates. 



anterior. They open into the stomach either by two distinct orifices 

 (Chiton aculeatus), or by two orifices in a single duct (Lepidopleurus), 

 or by a single aperture (Hanleya). The intestine is very long, as 

 is usual in phytophagous animals, and is thrown into numerous 



