1. The pedal gland is an internal aggregation of mucous cells, whose products form a locomotory slime track, and are expelled from the gland by ciliary action in the excretory canal of the gland, and by contractions of muscular fibres among the cells and by the movements of the foot. The pedal gland of Arion is intermediate in position and structure between that of Limax and that of Milax. 2. The caudal gland is an aggregation of mucous and calcic cells at the posterior end of the body. Its secretion is used, in the young stages, to form a slime thread for descent; during the period of sexual activity the slime gland becomes much more active, probably owing to the influence of the developing sexual organs. Its secretion is devoured mutually by slugs about to copulate. 3. There is an aggregation of unicellular mucous glands on the outer side of the peripodial groove, which I propose to call the gland. This pours out its secretion on to the foot-fringe and into the peripodial groove, an open ciliated channel which carries the mucous secretion of the body down to the caudal gland. 4. The skin of Arion contains mucous, calcic and pigmentary glands which are most numerous on the mantle margin and foot-fringe. (a) The mucous cells provide a secretion all over the body, especially on any ciliated region, which keeps the integument moist. (b) The calcic concretions are probably an excess of lime formed by the calcic cells, which in a shelled species would be employed in building up the shell. They may exercise a protective function, as do the spicules of sponges. (c) The black pigment cells, or chromatophores, are minute irregular cells found just under the epithelial layer, and are often clustered round the blood lacunae. It is probable that the black pigment is produced as a degeneration product of the blood. (d) The red pigment is not contained in special cells but lies in the dermal mucous glands and intercellular spaces. It is probably a compound produced by a lipochrome and the lime of the calcic cells, and it is stored in the tissues in default of a shell on which it might be deposited. It is excreted, possibly as a waste product from the body, along with the body mucus.