• 1Octopuses readily learn not to attack a crab shown with a square of one size, while continuing to attack a crab shown with a larger or a smaller square.
  • 2They can also learn to attack when a square of one size is shown, food being given as reward, but not to attack squares of other sizes if the attack results in a shock.
  • 3An octopus can learn to attack a square of 4 cm. but to avoid squares of 2 and 8 cm.
  • 4A square of 4 cm. presented at half the usual distance is not confused with a square of 8 cm.
  • 5By the same method it was shown that octopuses can make distinet reactions to certain figures that differ only in shape but not in area and length of outline, for instance rectangles and squares, or rectangles turned up at the ends, which differ in extent in vertical and horizontal directions.
  • 6They can also make distinct reactions to a rectangle according to whether it is shown vertically or horizontally, or to a square shown in various orientations in relation to gravity.
  • 7The accuracy of forecasting becomes less as an octopus is presented with situations that are more nearly similar.
  • 8Distinct reactions were also set up to crosses and squares and, less accurately, to figures with internal differences.
  • 9No clearly distinct responses could be set up to a square and a circle.
  • 10Octopuses trained to give distinct reactions to two different figures give the appropriate reaction to smaller figures, except when the differences are slight.
  • 11Change of other attributes of the situation, for example by moving to another tank, may disturb the animal's performance but does not destroy the memories.
  • 12After anaesthesia with urethane there is a period in which attacks are not made on either figure (though crabs are normally taken). Later, response to the positive figure returns but the negative is not attacked. The memories have therefore survived the treatment. Anaesthesia produces greater disturbance of performance if the two situations are nearly alike or involve attacking the larger rather than the smaller of two figures.
  • 13After removal of the vertical lobes octopuses continued to attack the figure that had been associated with food. They showed some attacks on a “negative” figure but when shocks were given they again ceased to attack this figure.
  • 14The animals without vertical lobes were unable to retain memories preventing attack on crabs from which shocks had been received (Boycott & Young, 1955 b). The vertical lobes are therefore necessary for the reversal of well-established memories, such as that leading to attacks upon crabs. They play a part in setting up memories that prevent attack upon previously unknown figures but are not essential for the retention of such memories.