and cover up dead bodies, just as they do anything else that is in their way. They can then pass to and fro over them without hindrance. In the observed case they were evidently interrupted in this occupation by another ant, and resisted its interference. The cemetery, the sextons, the feelings of the disconsolate mourner, which impelled her to exhume the body of the departed — all this is a fiction of the sympathetic imagination of the observer."
Sometimes, however, the observer's attitude to the animal mind is precisely the reverse: there is extreme underestimation, in place of extreme overestimation. Descartes (1596-1650), the founder of modern philosophy, after sharply distinguishing between matter and mind, body and soul, asserts that man is a composite being, a combination of soul and body, but that the animals are mere automata, all their actions and movements taking place automatically. It is plain that there can be no "animal psychology" for the Cartesians. There were, however, some among the earlier thinkers who did not deny consciousness to the lower creation. Aristotle, the "father of psychology," declared that animals exercise the functions of assimilation and reproduction, and possess a "faculty of feeling," to which is added in higher forms the capacity to retain sense-impressions, or memory, Man is distinguished from the animals by his endowment with the "faculty of knowledge" or "reason." But, at the best, animal psychology was never recognized as a worthy — or even as a possible — line of special inquiry.
The work of Darwin is admittedly the root of our present interest in animal intelligence. From the point of view of the theory of evolution, which regards not only the entire physical struc- ture of the human body, including the nervous system, but also our entire mental structure, which stands in such intimate relation to the nervous system, as the result of a long period of development in the animal world, the close observation of the pre-human mind becomes a matter of the utmost importance. We always understand things better when we know how they have grown. Hence the psychologist has turned his attention to the problem of genesis. or the growth of mind. The problem may be attacked in two ways. We may trace the growth of mind in the individual: this is the application of the genetic method to child-study, and gives us child psychology (q.v,). Or, since man is but a highly developed animal, we may trace the growth of mind in the animal world: this is the application of the method to mind at large, and gives us comparative (or animal) psychology.
The literature of animal psychology immediately after Darwin is characterized by a mass of observations industriously collected but unfortunately not tempered by careful and conservative interpretation. There was a marked tendency to write in anecdotal vein of the doings of pet animals, and an equally marked tendency to that overestimation of animal capacity which we have mentioned above. Romanes and Lindsay may be taken as typical of this period. Recent literature attempts a more rigid application of experimental methods, The majority of present-day investigators bring their animals into the laboratory, endeavoring in this way, even at the risk of artificiality, to standardize conditions and to secure the possibility of varying at will the environmental factors which control organic life. This method of procedure finds its most obvious application in the case of those lower forms whose life history can be followed only with difficulty, if at all, in the natural state.
The reactions of micro-organisms, e.g., to me- chanical, chemical, and thermal stimuli, have been studied beneath the microscope by numerous observers. And the results of investigation upon these minute unicellular forms, carried out by Gruber, Verworn, Möbius, Balbiani, and others, have had an important bearing upon that inter- esting and fundamental question of animal psy- chology, the origin of mind at large, Binet, reviewing the work of these authors, writes as follows: "If the existence of psychological phe- nomena in lower organisms is denied, it will be necessary to assume that these phenomena can be superadded in the course of evolution, in pro- portion as an organism grows more perfect and complex. Nothing could be more inconsistent with the teachings of general physiology, which shows us that ail vital phenomena are already present in undifferentiated cells. Furthermore, it is interesting to note to what conclusion the admission would lead ... that psychological properties are wanting in beings of a low order, and appear at different stages of zoölogical evolu- tion, Romanes has minutely particularized, on a large chart, the development of the intellectual powers, but it is done in quite an arbitrary manner. According to his scheme, only proto- plasmic movements and the property of excitabil- ity are present in organisms of the lower class. Memory begins with the echinoderms; the pri- mary instincts with the larvæ of insects and the annelids; the secondary instincts with insects and spiders; and, finally, reason appears with the higher crustaceans, I do not hesitate to say that all this laborious classification is artificial in the extreme, and perfectly anomalous." For instance. "Romanes assigns the first manifesta- tions of surprise and fear to the larvæ of insects and to the annelids. We may reply upon this point, that there is not a single infusoria, that cannot be frightened, and that does not show its fear by a rapid flight through the liquid of the preparation. If a drop of acetic acid be intro- duced beneath the glass slide in a preparation containing a quantity of infusoria, the animals will be seen to fly at once and from all directions, like a flock of frightened sheep."
Binet's fundamental thought is probably sound: his estimation of the infusorian consciousness is probably exaggerated. Jennings, e,g., argues from a very careful study of the paramecium, one of the protozoa, that the organism, if we may judge by its reactions, stands at the very bottom of the psychological scale, "We have in this animal perhaps as near an approach to the theoretical reaction postulated by Spencer and Bain for a primitive organism — namely, random movement in response to any stimulus — as is likely to he found in any living organism." All the activities of the paramecium can be accounted for by "simple irritability, or the property of responding to a stimulus by a fixed set of movements." Even more interesting, and fully as convincing, are the inferences drawn by Bethe from his study of ants and bees. We are accustomed to rank these creatures very high in the mental scale; but all Bethe's evidence goes to show that they are practically automata. Their remarkably complicated activities must, then, be
