An inventory of the sense organs

Abstract

Anyone watching an octopus for the first time is bound to notice that he is being observed. The animal has eyes that stare back. It responds to movement, cowering if anything large approaches it, or leaning forward in an alert and interested manner to examine small happenings in its visual field. Anyone who keeps the creatures in a laboratory, or any diver who approaches them in the sea soon discovers that they can see just about as well as we can. The eyes are very prominent and so clearly important that they have tended to distract attention from the rest of the animal’s sensory equipment. We know more about the structure and physiology and the use that an octopus makes of its eyes than about all the rest of the sense organs put together. Because we are ourselves so dependent on vision we find it relatively easy to manipulate the stimuli and devise experiments to investigate visual systems. We can think of ways to test hypotheses about the visual analysing system so that there is a considerable literature on Octopus’ responses to figures of differing shapes, sizes and shades. There is no equivalent body of information about, for example, the animal’s chemotactile sense, which is probably quite as important to it.