Sectional diagram of a schematic mollusc. *m. mouth; *g.c. cerebral ganglia; *g.pl. pleural ganglia; *g.pe. pedal ganglia; *g.v. visceral ganglia; *p. foot; *z.l. left lobe of digestive gland; *k. genital opening; *n. posterior end of the foot; *c. edge of the mantle; *u. kidney; *f. edge of primary shell-sac; *v. ventricle of the heart; *s. pericardial cavity. ::Based on the work of Lankester.