LEARNING BY IKARINE INVERTEBRATES
47
show that starfish can be trained to use or not to use particular arms.
Discrimination experiments with Astropecten, Ophiothrix and
Psarnrnechinus have been made by Diebschlag (1938). The experiments
were carried out in a dish with a difference in surface or illumination
defining a 6-cm wide strip across the centre. The animals, about 3 cm
in diameter, were punished for transgressing the edges of the strip, by
touching the tube feet of the leading arm with a group of pedicellariae
held on the end of a dissecting needle. This rather curious " biological "
stimulus was sufficiently unpleasant to cause retreat, the animal
generally reversing until it overstepped the opposite edge of the central
strip, whereupon it was again touched with the pedicellariae. After a
few punishments, contact with the edge of the strip was followed
increasingly often by spontaneous reversal. A variable number of
these trials was made, continuing generally until the animals stopped
moving about. Similar results were obtained in some of the experiments
where the dish was divided into halves with a central boundary. Some
of the results are plotted in Fig. 25. Diebschlag made no attempt to
check the possibility that he was sensitizing his animals by punishment
and it is possible that his results are accountable on the grounds that
the repeated punishments merely made the animals more responsive to
any change in stimulation.
Coordination of the five arms depends on the circumoral nerve ring.
When this is cut in two places integrated stepping by the tube feet
ceases. Those on each of the two groups of arms disconnected by the
cuts remain coordinated ; those on the separate groups do not. The two
halves of the animal may eventually pull apart (Moore, 1939). In this
situation it is not surprising to find, for example, that the animals fail
to right themselves as usual and that the effect of central nervous
lesions on learning has not been investigated ; with the training techniques so far adopted everything depends on movements by the
animal as a whole.
Works on the nervous organization of starfish and the coordination
of the tube feet have most recently been reviewed by Smith (1950) and
Kerkut (1964).
VIII. COELENTERATES
Whether a coelenterate learns or not depends very much on your
definition of learning. The animals have a considerable repertoire of
patterns of activity, and in anemones at least some of these (the cycle
of events that follows feeding, to take an example) continue for many
hours. As a result of these very slow reactions, it is sometimes difficult
to separate what is and what is not an immediate response. Netridium,
47
show that starfish can be trained to use or not to use particular arms.
Discrimination experiments with Astropecten, Ophiothrix and
Psarnrnechinus have been made by Diebschlag (1938). The experiments
were carried out in a dish with a difference in surface or illumination
defining a 6-cm wide strip across the centre. The animals, about 3 cm
in diameter, were punished for transgressing the edges of the strip, by
touching the tube feet of the leading arm with a group of pedicellariae
held on the end of a dissecting needle. This rather curious " biological "
stimulus was sufficiently unpleasant to cause retreat, the animal
generally reversing until it overstepped the opposite edge of the central
strip, whereupon it was again touched with the pedicellariae. After a
few punishments, contact with the edge of the strip was followed
increasingly often by spontaneous reversal. A variable number of
these trials was made, continuing generally until the animals stopped
moving about. Similar results were obtained in some of the experiments
where the dish was divided into halves with a central boundary. Some
of the results are plotted in Fig. 25. Diebschlag made no attempt to
check the possibility that he was sensitizing his animals by punishment
and it is possible that his results are accountable on the grounds that
the repeated punishments merely made the animals more responsive to
any change in stimulation.
Coordination of the five arms depends on the circumoral nerve ring.
When this is cut in two places integrated stepping by the tube feet
ceases. Those on each of the two groups of arms disconnected by the
cuts remain coordinated ; those on the separate groups do not. The two
halves of the animal may eventually pull apart (Moore, 1939). In this
situation it is not surprising to find, for example, that the animals fail
to right themselves as usual and that the effect of central nervous
lesions on learning has not been investigated ; with the training techniques so far adopted everything depends on movements by the
animal as a whole.
Works on the nervous organization of starfish and the coordination
of the tube feet have most recently been reviewed by Smith (1950) and
Kerkut (1964).
VIII. COELENTERATES
Whether a coelenterate learns or not depends very much on your
definition of learning. The animals have a considerable repertoire of
patterns of activity, and in anemones at least some of these (the cycle
of events that follows feeding, to take an example) continue for many
hours. As a result of these very slow reactions, it is sometimes difficult
to separate what is and what is not an immediate response. Netridium,