Some experiments on the chemotactile sense of octopuses.

Abstract

ABSTRACT A method of training octopuses to make chemotactile discriminations is described. The animals can readily be taught to distinguish between porous objects soaked in sea water and similar objects soaked in sea water with M/10 KC1 added. Using pairs of objects soaked in solutions with different amounts of KC1 added, minimum distinguishable concentrations were determined over the range M/10−M/100. Effective discrimination broke down when the ratio of the two test concentrations was of the order of 1·3. This approximates to the values found in chemical discrimination experiments with mammals and insects. Attempts were made to determine the minimum detectable concentration of added KC1 by progressive dilution of the M/10 KC1 solution used in the initial training. Additions to sea water down to M/105 were distinguished and there was some indication that octopuses can, in fact, detect added KC1 at much smaller concentrations; the addition of M/1010 KC1 produced a significant decline in the ability of animals under training to discriminate between M/106 KC1 and sea water. Experiments on acid discrimination indicated that acids were distinguished on a basis of their pH, with acetic tasting noticeably more acid than HC1 or H2SO4 at the same pH. Again, the results closely parallel those that have been obtained with mammals and insects.