SUMMARY1The behaviour of a femaleArgonautakept alive for a week at Naples is described.2The animal usually swam near the surface but was capable of going down to the bottom and of attaching itself to the floor or sides of the tank.3The web is suddenly retracted from the shell when the animal is disturbed The resulting white flash produces a startling (dymantic) effect, causing flight of an attacker.4When a dead sardine was placed near the argonauta there were colour changes, quickened mantle contractions and movements of the arms, but no definite forward swimming or attack.5When a food particle touches the web the fourth arm of that side is brought out with a sweeping movement that captures the food.6No reactions were seen to live fishes or crustaceans.7On several occasions the argonauta spread out its web upon the glass side of the tank. The animal twice left the shell and then lay helpless. When re‐placed in the shell it recovered completely on the first occasion but died upon the second.8Eggs were laid in the shell on both occasions before the animal left it.9The web and shell thus serve many purposes. The shell provides protection and flotation and allows attachment of the eggs. The web, besides secreting the shell, acts as a receptor for the feeding reaction, and provides a startling colour when the animal is disturbe