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 (Zrachydermon). 
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 le 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, he 
two very small mucous glands 
close to one another and to the 
middle line. On either side, at 
Boreochiton cinereus, dorsal view of a female, the point where the pharynx 
without the shell-plates. I, first “intersegmen- passes into the short oesophagus, 
tum”; II, ovary; III, oviduct; IV, ventricle - : 
of heart; V, dorsal right muscle; VI, dorsal 18 the. opening of the sugar 
eho eel ese: VII, retractor muscle of 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 
Fic. 26. 
Cryptoplax larvaeformis, left-side view, the posterior end partially opened. I, gonad; IT, 
genital duct; III, genital pore; IV, ventricle of heart; V, anus; VI, renal pore; VII, gills; 
VIII, foot ; IX, mantle ; 6, 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 
