30 



mass extending from behind the mouth backwards to the 

 posterior end of the body. This is the characteristic 

 molluscan "foot." (Fig. 15, A). 



Fig. 15, Archi-Mollusc. Three diagrammatic views taken from Lankester's 

 figures. A, Vertical antero-posterior section. B, Dorsal view, in which the body- 

 wall is supposed to be transparent, allowing the circulatory, renal, reproductive, 

 and other organs to be seen through. C. Ventral view shewing the nervous system, 

 a, cephahc tentacle; &, head; c, free edge of mantle skirt; cZ, anus; e, edge of the 

 foot; /, edge of the shell follicle ; £/, gonad, or reproductive organ; g\ opening of 

 duct from gonad ; h, osphradium ; i, ctenidium ; Tc, liver ; I, nephridium ; l^, opening 

 of nephridium ; m, mouth ; n, posterior end of foot ; o, cephalic eye ; r, auricle of 

 heart; s, pericardium; v, ventricle of heart, giving off an anterior and a posterior 

 vessel; y, otocyst; g.a, abdominal ganglion; g.c, cerebral ganglion ; g^.o, olfactory 

 ganglion; g.p, pedal ganglion; g.pl, pleural ganglion; g.v, visceral ganglion; 

 n.p, pedal nerve ; n.v, visceral nerve. 



Covering the rounded dorsal surface (the " visceral 

 dome ") is a cap-shaped shell, which is exposed in the 

 centre but has its edge all round embedded in a flattened sac 

 in the body-wall — the primary shell follicle (fig. 15, A andB). 

 On the edge of the visceral dome the wall of the body 



