=Some Lower Vertebrates Profit by Experience.--=Among vertebrates it is known that those as low in organization as fish will profit by experience. They will learn to come for food at a regular time and apparently learn more or less to appreciate the presence of certain obstacles with which they have had unsatisfactory experiences. Professor Sanford sums up what he believes are the limitations of the piscine mental organization as follows: "No fish is ever conscious of himself; he never thinks of himself as doing this or that, or feeling in this way or that way. The whole direction of the mind is outward. He has no language and so can not think in verbal terms; he never names anything; he never talks to himself; as Huxley says of the crayfish, he 'has nothing to say to himself or any one else.' He does not reflect; he makes no generalizations. All his thinking is in the present and in concrete terms. He has no voluntary attention, no volition in the true sense, no self-control." =Rational Behavior.--=Finally, however, out of these first dull glimmerings of intelligence as exemplified in the higher invertebrates and the lower vertebrates, which can modify behavior as the result of experience, come the still higher factors so dominant in man, of _rational_ behavior. This higher mental process can realize the end to be reached and can deliberate on the means to be employed. By means of his _reason_ man can overcome difficulties in advance by "thinking" out suitable schemes of action. Some naturalists believe that man stands alone in possessing the power to reason, although others believe that some of the other mammals, notably the other primates, possess the same attribute although in a much less degree. =Conceptual Thought Probably an Outgrowth of Simpler Psychic States.--=Is the capacity for such conceptual thought, however, which appears as the final efflorescence of complex neural activity something entirely new? Most students of comparative psychology maintain that it is not. Just as one kind of an instinct frequently grows out of another, so has this grown out of the complex of _psychic_ states which preceded it. It apparently is the product of the increasing awareness on the part of animals of their neural processes and the outcome of these processes, which becomes more and more prominent as we ascend the scale of animal life. With the advent of associative memory the mind comes more and more to deal with attributes of objects instead of merely with each single concrete object as it presents itself, and these attributes being common to many objects, come to represent definite ideas which can be manipulated by the mind. Language, of course, has been an indispensable aid to man in this regard, for words become descriptions of facts and symbols of concepts, and thereby allow of abstract thought.