The Molluscs in general.--The Cephalopods.--Dibranchiates and Tetrabranchiates.--Arms and Tentacles.--Suckers.--Hooked Acetabula of the Onychoteuthis.--Mandibles.--Ink Bag.--Numbers of the Cephalopods.--Their Habits.--Their Enemies.--Their Use to Man.--Their Eggs.--Enormous size of several species.--The fabulous Kraken.--The Argonaut.--The Nautili.--The Cephalopods of the Primitive Ocean.--The Gasteropods.--Their Subdivisions.--Gills of the Nudibranchiates.--The Pleurobranchus plumula.--The Sea-Hare.--The Chitons.--The Patellæ.--The Haliotis or Sea-Ear.--The Carinariæ.--The Pectinibranchiates.--Variety and Beauty of their Shells.--Their Mode of Locomotion.--Foot of the Tornatella and Cyclostoma.--The Ianthinæ.--Sedentary Gasteropods.--The Magilus.--Proboscis of the Whelk.--Tongue of the Limpet.--Stomach of the Bulla, the Scyllæa, and the Sea-Hare.--Organs of Sense in the Gasteropods.--Their Caution.--Their Enemies.--Their Defences.--Their Use to Man.--Shell-Cameos.--The Pteropods.--Their Organisation and Mode of Life.--The Butterflies of the Ocean.--The Lamellibranchiate Acephala.--Their Organisation.--Siphons.--The Pholades.--Foot of the Lamellibranchiates.--The Razor-Shells.--The Byssus of the Pinnæ.--Defences of the Bivalves.--Their Enemies.--The common Mussel.--Mussel Gardens.--The Oyster.--Oyster Parks.--Oyster Rearing in the Lago di Fusaro.--Formation of new Oyster Banks.--Pearl-fishing in Ceylon.--How are Pearls formed?--The Tridacna gigas.--The Teredo navalis.--The Brachiopods.--The Terebratulæ.--The Polyzoa.--The Sea-Mats.--The Escharæ.--The Lepraliæ.--Bird's Head Processes.--The Tunicata.--The Sea-Squirts.--The Chelyosoma.--The Botrylli.--The Pyrosomes.--The Salpæ.--Interesting Points in the Organisation of the Tunicata.