2
M. J. WELLS
rence of " learning " depends on the defhitions one cares to employ.
This phyletic approach is more appropriate than a summary based
on a classification of learning itself because of the diversity of the
organisms concerned. Terms such as " habituation " or " trial and
error learning " will be used, but it is intended throughout that these
shall be understood to be descriptions of observations rather than
implications that the phenomena depend in any sense on common
mechanisms. For learning is just one of many ways in which animals
adapt to their environment. In one species the ability to learn permits
survival in more complex and diverse situations, in others it can be read
as evidence of insufKcient genetic variability. Learning implies mistakes
and selection for appropriate innate responses is inevitable in any
relatively unchanging habitat. Marine animals inhabit such a variety of
environments that it would be absurd to regard them as faced with
common problems in any but the broadest sense. Learning is not always
the best solution in survival problems and it would be surprising to find
these phenomena occurring other than erratically. Some animals
learn only certain things under rather special circumstances ; at other
times their capabilities in this respect seem remarkably limited.
Learning in invertebrate animals, in short, cannot sensibly be considered
except in relation to their particular ways of life; the physiological
background must be known and the capacities of each species investigated in relation to the things that the system is built to do. It is surprising
how often this is forgotten, with the result that our knowledge of
invertebrate learning is all too frequently based on their performance
under conditions appropriate only for vertebrates. A t best this can
give only indirect evidence of the capabilities of the systems studied.
The present review is, therefore, in part a plea for a broad approach :
learning cannot be studied in isolation. It is not intended as an exhaustive list of references. Some fields, cephalopod and crustacean learning
for examples, have been the subject of comprehensive reviews within
the last five years. Others have been practically neglected for deoades.
In general an attempt has been made to summarize the literature produced since the last substantial review, and where such is lacking, to
cite key references with bibliographies that cover as many a,s possible
of the experiments and observations that are not specifically mentioned.
11. CEPHALOPOD MOLLUSCS
More information is available about learning in cephalopods than
for any other invertebrate group. For once, the primary concern is not
whether the animals can learn or not, since they clearly do so whatever
definition of learning one chooses, but rather what they can l e h and
M. J. WELLS
rence of " learning " depends on the defhitions one cares to employ.
This phyletic approach is more appropriate than a summary based
on a classification of learning itself because of the diversity of the
organisms concerned. Terms such as " habituation " or " trial and
error learning " will be used, but it is intended throughout that these
shall be understood to be descriptions of observations rather than
implications that the phenomena depend in any sense on common
mechanisms. For learning is just one of many ways in which animals
adapt to their environment. In one species the ability to learn permits
survival in more complex and diverse situations, in others it can be read
as evidence of insufKcient genetic variability. Learning implies mistakes
and selection for appropriate innate responses is inevitable in any
relatively unchanging habitat. Marine animals inhabit such a variety of
environments that it would be absurd to regard them as faced with
common problems in any but the broadest sense. Learning is not always
the best solution in survival problems and it would be surprising to find
these phenomena occurring other than erratically. Some animals
learn only certain things under rather special circumstances ; at other
times their capabilities in this respect seem remarkably limited.
Learning in invertebrate animals, in short, cannot sensibly be considered
except in relation to their particular ways of life; the physiological
background must be known and the capacities of each species investigated in relation to the things that the system is built to do. It is surprising
how often this is forgotten, with the result that our knowledge of
invertebrate learning is all too frequently based on their performance
under conditions appropriate only for vertebrates. A t best this can
give only indirect evidence of the capabilities of the systems studied.
The present review is, therefore, in part a plea for a broad approach :
learning cannot be studied in isolation. It is not intended as an exhaustive list of references. Some fields, cephalopod and crustacean learning
for examples, have been the subject of comprehensive reviews within
the last five years. Others have been practically neglected for deoades.
In general an attempt has been made to summarize the literature produced since the last substantial review, and where such is lacking, to
cite key references with bibliographies that cover as many a,s possible
of the experiments and observations that are not specifically mentioned.
11. CEPHALOPOD MOLLUSCS
More information is available about learning in cephalopods than
for any other invertebrate group. For once, the primary concern is not
whether the animals can learn or not, since they clearly do so whatever
definition of learning one chooses, but rather what they can l e h and