The Animal Mind: A Textbook of Comparative Psychology

Thus the mere fact that an animal reacts to stimulation, even selectively and for its own best interests, offers no evidence for the existence of mind that does not apply equally well to particles of inanimate matter. Moreover, there is some ground for holding that the reactions of the lowest animals are unconscious. This ground consists in the apparent lack of variability which characterizes such reactions. In our own case, we know that certain bodily movements, those of digestion and circulation, for example, are normally carried on without accompanying consciousness, and that in other cases where there is consciousness of the stimulus, as in the reflex knee-jerk, it occurs after the movement is initiated, so that the nervous process underlying the sensation" would seem to be immaterial to the performance of the movement. These unconscious reactions in human beings are characterized by their relative uniformity, by the absence of variation in their performance. Moreover, when an action originally accompanied by consciousness is often repeated, it tends, by what is apparently one and the same process, to become unconscious and to become uniform. There is consequently reason for believing that when the behavior of lower animals displays perfect uniformity, consciousness is not present. On the other hand, an’ important reservation must be made in the use of this negative test. It is by no means easy to be sure that an animal’s reactions are uniform. The more carefully the complexer ones are studied, the more are variability and difference brought to light where superficial observation had revealed a mechanical and automatic regularity. It is quite possible that even in the simple, apparently fixed response of microscopic animals to stimulation, better facilities for observation might show variations that do not now appear.

This matter of uniformity versus variability suggests a further step in our search for a satisfactory test of the presence of mind. Is mere variability in behavior, mere irregularity in response, to be taken as such a test? Not if we argue from our own experience. While that portion of our own behavior which involves consciousness shows more irregularity than the portion which does not, yet the causes of the irregularity are often clearly to be found in physiological conditions with which consciousness has nothing to do. There are days when we can think clearly and recall easily, and days when obscurities refuse to vanish and the right word refuses to come; days when we are irritable and days when we are sluggish. Yet since we can find nothing in our mental processes to account for this variability, it would be absurd to take analogous fluctuations in animal behavior as evidence of mind. So complicated a machine as an animal organism, even if it be nothing more than a machine, must show irregularities in its working.

to give evidence of mind. The criterion most frequently ‘ applied to determine the presence or absence of the psychic is a variation in behavior that shows definitely the result of previous individual experience. “Does the organism,” says Romanes, “learn to make new adjustments, or to modify old ones, in accordance with the results of its own individual experience?” (641, p. 4). Loeb declared that “the fundamental process which occurs in all psychic phenomena as the elemental component” is “the activity of the associative memory, or of association,” and defines associative memory as “that mechanism by which a stimulus brings about not only the effects which its nature and the specific structure of the irritable organ call for, but by which it brings about also the effects of other stimuli which formerly acted upon the organism almost or quite simultaneously with the stimulus in question.” “If an animal can be trained,” he continued, “if it can learn, it possesses

associative memory,” and therefore mind (429, p. 12). The psychologist finds the term “associative memory” hardly satisfactory, and objects to the confusion between mental and physical concepts which renders it possible to speak of a ‘‘mechanism” as forming an “elemental component” in “psychic phenomena,” but these points may be passed over. The power to learn by individual experience \ is the evidence which Romanes, Morgan, and Loeb will accept as demonstrating the presence of mind in an animal. Does the absence of proof that an animal learns by experience show that the animal is unconscious? Romanes is careful to answer this question in the negative. ‘Because a g vn lowly organized animal,” he says, ‘‘does mot learn by its own is individual experience, we may not therefore conclude that in performing its natural or ancestral adaptations to appropriate stimuli, consciousness, or the mind element, is wholly absent; we can only say that this element, if present, reveals no evidence of the fact” (641, p. 3). Loeb, on the other hand, wrote as if absence of proof for consciousness amounted to disproof, evidently relying on the principle of parsimony, that no unnecessary assumptions should be admitted. ‘Our criterion,” he remarked, “puts an end to the metaphysical ideas that all matter, and hence the whole animal world, possesses consciousness” (429, p. 13). If learning by experience be really a satisfactory proof of mind, then its absence in certain animals would indeed prevent the positive assertion that all animals are conscious; but it could not abolish the possibility that they might be. Such a possibility might, however, be of no more scientific interest than any one of a million wild possibilities that science cannot spare time to disprove.

But we shall find that learning by experience, taken by itself, is too indefinite a concept to be of much service, and that when defined, it is inadequate to bear the whole weight of proving consciousness in animals. Such being the case, the possibility that animals which have not been shown to learn may yet be conscious acquires the right to be reckoned with. J ‘test is that the learning by experience must not be too slow, or we can find parallels for it in the inanimate world. An animal may be said to have learned by experience if it behaves differently to a stimulus because of preceding stimuli. But it is one thing to have behavior altered by a single preceding stimulus, and another to have it altered by two hundred repetitions of a stimulus. The wood of a violin reacts differently to the vibrations of the strings after it has ‘‘experienced” them for ten years ; the molecules of the wood have gradually taken on an altered arrangement. A steel rail reacts differently to the pounding of wheels after that process has been long continued; it may snap under the strain.

individual experience? If the obvious retort be made that it is only in living creatures that learning by experience should be taken as evidence of mind, let us take an example from living creatures. When a blacksmith has been practising his trade for a year, the reactions of his muscles are different from what they were at the.outset. But this difference is not merely a matter of more accurate sensediscrimination, a better ‘‘placing”’ of attention and the like; there have been going on within the structure of his muscles changes which have increased their efficiency, and with which consciousness has had nothing to do. These changes have been extremely slow compared to the learning which does involve consciousness. In one or two lessons the apprentice learned what he was to do; but only

very gradually have his muscles acquired the strength to do it as it should be done. Now among the lower animal forms we sometimes meet with learning by experience that is very slow; that requires a hundred or more repetitions of the stimulus before the new reaction is acquired. In such a case we can find analogical reasons for suspecting that a gradual change in the tissues of the body has taken place, of the sort which, like the attuning of the violin wood or the slow development of a muscle, have no conscious accompaniment.

We must then ask the question: What kind of learning by experience never, so far as we know, occurs unconsciously ? “Suppose a human being shut up in a room from which he can escape only by working a combination lock. As we shall see later, this is one of the methods by which the learning power of animals has been tested. The man, after prolonged investigation, hits upon the right combination and gets out. Suppose that he later finds himself again in the same predicament, and that without hesitation or fumbling he opens’ the lock at once, and performs the feat again and again, to show that it was not a lucky accident. But one interpretation of such behavior is possible. We know from our own experience that the man could not have worked the lock the second time he saw it, unless he consciously remembered the . movements he made the first time; that is, unless he had in mind some kind of idea asa guide. Here, at least, there can have been no change in the structure of the muscles, for such changes are gradual; the change must have taken place in the most easily alterable portion of the organism, the nervous system; and further, it must have taken place in the most unstable and variable part of the nervous system, the higher cortical centres whose activity is accompanied by consciousness. In other words, we may be practically

assured that consciousness accompanies learning only when the learning is so rapid as to show that the effects of previous experience are recalled in the guise of an idea or mental image of some sort. But does even the most rapid learning possible assure us of the presence of an idea in the mind of a lower animal? Where the motive, the beneficial or harmful consequence of action, is very strong, may not a single experience suffice to modify action without being revived in idea? Moreover, animals as high in the scale as dogs and cats learn to solve problems analogous to that of the combination lock so slowly that we cannot infer the presence of ideas. Are we then to conclude that these animals are unconscious, or that there is absolutely no reason for supposing them possessed of consciousness? Yerkes has criticised the “‘learning by experience’’ criterion by pointing out that ‘“‘no organism ... has thus far been proved incapable of profiting by experience.” It isa question rather of the rapidity and of the kind of learning involved. ‘The fact that the crayfish need a hundred or more experiences for the learning of a type of reaction that the frog would learn with twenty experiences, the dog with five, say, and the human subject with perhaps a single experience, is indicative of the fundamental difficulty in the use of this sign” (814). Nagel has pointed out that Loeb, in asserting “‘associative memory” as the criterion of consciousness, offers no evidence for his statement (524). The fact is that while proof of the existence of mind can be derived from animal learning by experience only if the learning is very rapid, other evidence, equally valid on the principle of analogy, makes it highly improbable that all animals which learn too slowly to evince the presence of ideas are therefore unconscious. ‘This evidence is of a morphological character.

animal’s nervous system and sense organs to those of human beings ought to be taken into consideration in deciding whether the animal is conscious or not. Lukas suggests that the criteria of consciousness should be grouped under three heads: morphological, including the structure of the brain and sense-organs, physiological, and teleological. Under the second rubric he maintains that ‘individual purposiveness” is characteristic of the movements from which consciousness may be inferred; that individual purposiveness pertains only to veluntary acts, and that voluntary acts and acts “which are preceded by the intention to ‘perform a definite movement, hence by the idea of this movement.” We have reached the same conclusion in the preceding paragraph. The third test of the presence of consciousness, the teleological test, rests on the consideration: ‘‘What significance for the organism may be possessed by the production of a conscious effect by certain stimuli?” (445). This test, however, being of a purely @ priori character, would seem to be distinctly less valuable than the others. ' Yerkes proposes “the following six criteria in what seems to me in general the order of increasing importance. The functional signs are of greater value as a _ rule than the structural; and within each of the categories the particular sign is usually of more value than the general. In certain cases, however, it might be maintained that neural specialization is of greater importance than modifiability.

2. Nervous system (Neural organization). 3. Specialization in the nervous system (Neural specialization). 1. General form of reaction (Discrimination). 2. Modifiability of reaction (Docility). 3. Variability of reaction (Initiative) ” (814). The terms “discrimination,” “docility,”’ and “initiative” in this connection are borrowed from Royce’s ‘Outlines of Psychology” (649). If resemblance of nervous and sense-organ structure to the human type is to be taken along with rapid learning as coordinate evidence of consciousness, it is clear that here also we have to deal with a matter of degree. The structure of the lower animals differs increasingly from our own as we go down the scale. At what degree of difference shall we draw the line and say that the animals above it may be conscious, but that those below it cannot be? No one could possibly establish such a line. The truth of the whole matter seems to be this: We can say neither what amount of resemblance in structure to human beings, nor what speed of learning, constitutes a definite mark distinguishing animals with minds from those without minds, unless we are prepared to assert that only animals which learn so fast that they must have memory ideas possess mind at all. And this would conflict with the argument from structure. |For example, there is no good experimental evidence that cats possess ideas, yet there is enough analogy between their nervous systems and our own to make it improbable that consciousness, so complex and highly developed in us, is in them wholly lacking. We know not where consciousness begins in the animal world. We know where it surely resides — in ourselves; we know where it exists beyond a reason-

able doubt—in those animals of structure resembling ours which rapidly adapt themselves to the lessons of experience. Beyond this point, for all we know, it may exist in simpler and simpler forms until we reach the very lowest of living beings. WE have seen in the last chapter that no one can prove the absence of consciousness in even the simplest forms of living beings. It is therefore perfectly allowable to speculate as to what may be the nature of such consciousness, provided that the primitive organisms concerned possess it. Perfectly allowable, yet also perfectly useless, many authorities would argue; the remoteness of the creatures from ourselves in structure and behavior renders theorizing about their conscious experience, which is probably non-existent and certainly unimaginable in any definite terms by us, the idlest form of mental exercise.

Undeniably the formation of a positive notion regarding the character and content of psychic states in the mind, say of an Ameeba, is next door to an impossibility. Yet it may not be wholly a waste of time if we spend a few pages in the ttempt to discover wherein the simplest type of mind, supsing it to be that belonging to the simplest type of animal, necessarily differs from our own. Some light, perhaps, may be cast upon the growth of mental life in complexity if we try to make clear to ourselves what primitive consciousness is not, though we may not be able to find in our own experience any elements that shall properly represent what it is.

the Ameeba presents itself as a good subject. Structurally, it consists of a single cell, as do all the Protozoa, the lowest group of animals; it is so small that it can be studied only through the microscope; its form, at least that of Ameba proteus, the most typical species, is irregular and constantly changing in locomotion or in response to stimulation. While the internal substance of its body shows a certain amount of differentiation, there is no trace whatever of special modifications that might be supposed to serve for the conduction of stimuli to different parts of the body, and thus represent the prototype of a nervous system. Nor have any structures been found that could conceivably be used for the special reception of stimuli; that is, there are no sense organs. So far as the anatomy of the animal is concerned, then, it differs so widely from our own that we could only conclude from it the absence of all those features which our conscious experience involves.

Turning from structure to behavior, we find the external activities of Amoeba, that is, those not confined to the inner processes of its cell body, to be superficially, at least, divisible into two classes: movements of locomotion and responses to stimulation. Amoeba, though a water-dwelling animal, is not a free-swimming one, but moves by crawling on a solid body. This method of locomotion involves in Ameba proteus changes of form on the animal’s part, projections, called pseudopodia, being sent out in advance of the movement of the whole body. The protoplasm of the body shows in this process certain flowing movements which | are differently described by different observers, and doubtless vary in different species: thus Rhumbler finds that the protoplasmic currents move backward along the sides of the animal and forward through the middle in a way quite comparable to the behavior of currents in a drop of any

fluid where the tension of the surface is diminished in front, i.e., at the point toward which the drop, in consequence of the diminished tension there, rolls. Such movements, Rhumbler shows, can be reproduced by placing, say, a drop of clove oil under the proper conditions of surface tension (632, 633). Jennings, on the other hand, has observed, at least in certain species of Amceba, that the protoplasmic currents are all forward in direction, the movement being really one of rolling, complicated by the attachment of the lower part of the body to the solid object on which the animal crawls. Mechanical conditions of surface tension would not account for such currents (371, 373, 378). Dellinger rejects both the surface tension and the “rolling” theories, and from a study of side views of the moving Amoeba concludes that progression occurs through the advancement of the front end freely through the water and its subsequent attachment, the rest of the body follow- — ing through active contraction brought about by a contractile substance (181). The problem is of great interest to the student of vital phenomena, but its bearing on the question of mind in the Amceba is so obscure that we need not consider it further, but may pass at once to the study of the animal’s reactions to special stimulation. These are, according to Jennings (373, 378), the foremost authority on the behavior of the lowest organisms, three in number; namely, the negative, the positive, and the foodtaking_reactions. First, if an Amceba comes into strong contact with a solid obstacle in its movements, or if a solution of different composition from the water in which it lives strikes against it, or if one side of it is heated, the animal responds by contracting the part stimulated, releasing it from the substratum, and moving in another direction, usually one forming only a small angle with the

preceding one. If the whole of one side or end receives a strong stimulus, if light falls on one side, or an electric current is passed through the water, the side stimulated — in the case of the electric current, the side toward the positive pole — contracts as a whole, and the movement takes place in the opposite direction. These phenomena constitute the negative reaction (Fig. 1). Secondly, the reaction to solid bodies sometimes takes a positive form. In this case a pseudopodium is pushed forward in the direction of the stimulus, and the animal moves toward the solid. As the negative reaction serves the pur- Fic. 1.— Negative reaction of

*4° Ameeba to stimulation by a glass pose of avoiding obstacles, so rod: ep Apulication ok the atimts the positive reaction is useful ulus. 5. Change of direction in securing contact with a supoe eet aan port on which to creep, and with food. It seems to be given in response to weak mechanical stimuli, stronger ones producing the negative reaction. No chemicals have been found to occasion it, but weak chemical stimulation very likely codperates with mechanical stimulation when the positive reaction is given to food.

Schaeffer (659) has recently obtained evidence that Ameeba can give the positive reaction to insoluble and inedible objects before they come into contact with it. The way in which such objects can act as stimuli is ~still unexplained. It is possible that the movement of the Amceba produces water currents which are reflected back in a peculiar way by such particles. He reports also (660) that the positive reaction is given to beams of light which pass no nearer than 100-150 thousandths of an inch to the animal. The Amoeba moves towards the beam, but when it comes into contact with it, the movement ceases, and in some cases a negative response occurs.

Thirdly, there is the food-taking reaction. This consists for Ameba proteus, according to Jennings, in the pushing forward of a pseudopodium on either side of the particle of Be ence? Fic. 2. — Food-taking reaction of Ameeba. 1, 2, 3, 4, successive stages. After Jennings (378). food that has come into contact with the animal; the bending over of the ends of the pseudopodia so as to grasp the food, while ‘‘a thin sheet of protoplasm” spreads from the upper surface of the animal over it; and the final fusion of the ends of the pseudopodia and the ends of this sheet, so as to take the food directly into the animal’s body. The reaction may occur anywhere on the body surface, there being no specialized mouth. It appears to be made only in response to edible substances, hence there is doubtless some chemical peculiarity about the stimulus which

makes it effective (378). Kepner and Taliaferro (399) find the food-taking reaction more complex and variable than Jennings’s account describes it to be. They observed cases where only one pseudopodium was formed, and cases where it was put forth not at the exact point acted upon by the stimulus. The nature of the reaction varied in such a way as to prevent the ‘‘swallowing” of too much water along with the food: “the parts that could most advantageously respond did so.” McClendon (451 a) has attempted to apply the surface tension theory to the positive, negative, and feeding reactions of Amceba, suggesting that the stimuli may exert an electric influence whereby the surface tension at the point stimulated becomes less in the case of the positive reactions and feeding, greater in the negative reaction. But such variations as those just described are difficult to reconcile with a surface tension theory. Moreover Mast and Root (477) have observed Amceba crushing its prey with a force far greater than surface tension could account for. Schaeffer (658) suggests that a chemical discrimination may occur inside the Amceba after substances have been taken in, for, he says, when carmine grains have been swallowed, the Amceba at once begins to move off in such a way as to bring the grains to the hinder part of the body where they will be ejected. ‘“‘The carmine grains aretejected . . . because they are actually disagreeable and not merely because they are (presumably) indigestible.” A hungry Amceba, when it comes within 100 thousandths of an inch from an organism, which is as a whole at rest but moving certain portions of its body, will begin to move towards it and to form a food cup before actual contact occurs. Probably the slight water currents produced by the movements of the prey act as the stimulus in this case. Any stimulus which proceeds from a moving object tends, as we shall see, to be peculiarly effective.

These three reactions make up, together with the ordinary crawling locomotion, the variety of the Amceba’s experience as displayed in behavior, with the addition of a peculiar set of movements occurring in the absence of all mechanical stimulation. When an Ameceba is floating in the water, through some chance, unattached to any solid, “such a condition,” says Jennings, ‘‘is most unfavorable for its normal activities; it cannot move from place to place, and has no opportunity to obtain food.” Its mode of getting out of the difficulty is to send out ‘long, slender pseudopodia in all directions,” until ‘‘the body may become reduced to little more than a meeting point for these pseudopodia’”’ (378, p. 8). As soon as one of these ‘‘feelers” comes in contact with a solid, it attaches itself, and the whole animal © following soon takes up its normal crawling locomotion.

Now what light does the behavior of Amceba throw upon the nature of the animal’s possible consciousness? The first thought which strikes us in this connection is that the number of different sensations occurring in an Ameba’s mind, if it has one, 7s very much smaller than the number forming the constituent elements of our own experience. We thousand different qualities of color, brightness, tone, noise, temperature, pressure, pain, smell, taste, and other sensation classes. Thus the content of our consciousness is capable of a great deal of variety. It is hard to see how more than three or four qualitatively different processes can enter into the conscious experience of an Ameeba. The negative reaction is given to all forms of strong stimulation alike, with the single exception of food. We shall

in the following chapter discuss more fully the nature of the evidence that helps us to conjecture the existence of different sensation qualities in an animal’s mind; but it is clear that where an animal so simple in its structure as the Amceba makes no difference in its reactions to various stimuli, there can be no reason for supposing that if it is conscious, it is aware of them as different. The réaction to edible substances is, however, unlike that to other stimulations. The peculiarity of edible substances which occasions this difference must be a chemical one. In our own case, the classes of sensation which result from the chemical pecularities of food substances are smell and taste; evidently to a waterdwelling animal smell and taste would be practically indistinguishable. We may say, then, that supposing consciousness to exist in so primitive an animal as the Amceba, we have evidence for the appearance in it of a specific sensation quality representing the chemical or food sense, and standing for the whole class of sensations resulting from our own organs of smell and taste. The significance of the positive reaction is harder to determine. It seems to be given in response not to a special kind of stimulus, but to a mechanical or food stimulus of slight intensity. In our own experience, we do not have stimuli of different intensity producing sensations of different quality, except in the cases of temperature and visual sensations. We do, however, find that varying the strength of the stimulus will produce different. affective qualities; it is a familiar fact that moderate intensities of stimulation in the human organism are accompanied by pleasantness, and stronger intensities by unpleasantness. The motor effects of pleasantness and unpleasantness in ourselves are opposite to each other in character.

Pleasantness produces a tonic and expansive effect on the body, unpleasantness a depressive and contractive effect. In the Amceba, the positive and negative reactions seem to be opposed. The essential feature of the negative reaction is the checking of movement at the point stimulated; that of the positive reaction is the reaching out of the point stimulated in the direction of the stimulus. This much evidence there is for saying that besides a possible food sensation, the Amceba may have some dim awareness of affective qualities corresponding to pleasantness and unpleasantness in ourselves. It should, however, be borne in mind that wide differences must go along with the correspondence. In us, pleasantness brings a thrill, a ‘bodily resonance,” due to its tonic effect upon the circulation, breathing, and muscles; unpleasantness has also its accompaniment of vague organic sensation, without which we can hardly conceive what it would be like. In an Ameeba, it is clear that this aspect, as found in human consciousness, must be wholly lacking. Again, in the human mind pleasantness and unpleasantness are connected with various sensation qualities or complexes ; we are pleased or displeased usually ‘‘at” something definite. The vagueness of the affective qualities in an Amceba’s consciousness can only be remotely suggested by our own vague, diffused sense of bodily well-being or illbeing; and this is undoubtedly given its coloring in our case by the structure and functioning of our internal organs.

As for the peculiar behavior of an Amceba suspended in the water and deprived of solid support, the stimulus for this must lie within the cell body itself. If any consciousness accompanies it, then the nearest human analogy to such consciousness is to be found in organic sensations, and these, as has just been said, must necessarily be in the human mind wholly different in quality from anything to be found in an animal whose structure is as simple as the Amceba’s.

A consequence of this lack of qualitative variety in the sense experiences of an Amceba is a lack of what we may call complexity of structure in that experience. The number of stimulus differences which are in the human mind represented by differences in the quality of sensations is so great that at any given moment our consciousness of the external world is analyzable into a large number of qualitatively different sensations. At the present instant the reader’s consciousness ‘‘contains,”’ apart from the revived effects of previous stimulation, many distinguishable sensation elements, visual, auditory, tactile, organic, and so on. The Amceba’s consciousness, if it possesses one, must have a structure inconceivably simpler than that of any moment of our own experience.

A second point in which the mind of an Amceba must, if it exists, differ from that of a human being, consists in its entire lack of menial imagery of any sort. Not only has the () Amceba but three or four qualitatively different elements in its experience, but none of these qualities can be remembered or revived in the absence of external stimulation. How may we be sure of this? If our primitive animal could revive its experiences in the form of memory images, it would give some evidence of the influence of memory in its behavior. Indeed, as we shall learn, it is possible, in all probability, for an animal’s conduct to be influenced by its past experience even though the animal be incapable of reviving that experience in the form of a memory image. Therefore, if we find no evidence that the Ameba learns, or modifies its behavior as the result of past stimulation, we may conclude a fortiori that it does not have memory images. Now it would be stating the case too strongly to say that past stimulation does not affect the behavior of Amceba at all. In the first place, this animal shows, in common with

all other animals, the power of “‘getting used”’ to certain forms of stimulation, so that on long continuance they cease to provoke reaction. “Thus,” Jennings says, “Amobe react negatively to tap water or to water from a foreign culture, but after transference to such water they behave normally” (378, p. 20). Such cessation of reaction occurs when the continued stimulus is not harmful. In a sense, it may be called an effect of experience; but there is clearly no reason for supposing that it involves the revival of experience in the form of an idea or image. We have parallel phenomena in our own mental life. A continued stimulus ceases to be ‘‘noticed,” but the process involves rather the disappearance of consciousness than the appearance of a memory image. Jennings, however, is inclined to think that preceding stimulation may modify the Amceba’s behavior in a way more nearly suggesting memory in a higher type of mind. He describes an interesting observation to illustrate this. A large Amceba, c, had swallowed a smaller one, 6, but had left a small canal open, through which the swallowed one made efforts to escape, which were several times foiled by movements on the part of the large Amceba toward surrounding it again. Finally it succeeded in getting completely out, whereupon the large Amceba ‘‘reversed its course, overtook 5, engulfed it completely again, and started away.”” Thesmall Amceba contracted into a ball and remained quiet until through the movements of the large one there chanced to be but a thin layer of protoplasm covering it. This it rapidly pushed through, escaped completely, and was not pursued by the large Amoeba (378, pp. 17-18), (Fig. 3).

Of this performance Jennings says: “It is difficult to conceive each phase of action of the pursuer to be completely determined by a simple present stimulus. For example “(g4£) sSuruuef Jay ‘p ‘reqjoue Jo yuowFeY & Ayfeursiio sem ‘eqeoury poinjzdeo aqy ‘q ‘edeosa yeuy founjdeoer sy pue eqawy painjdes eq} jo adeosa ‘doqjoue Aq eqaury suo jo UoTsesur pue ‘amnydeo “ymsaing —°f “ony. . after Amoeba b has escaped completely and is quite separate from Amceba c, the latter reverses its course and recaptures b. What determines the behavior of c at this point? If we can imagine all the external physical and chemical conditions to remain the same, with the two Amcebz in the same relative positions, but suppose at the same time that Amceba c has never had the experience of possessing b, — would its action be the same? Would it reverse its movement, take in J, then return on its former course? One who sees the behavior as it occurs can hardly resist the conviction that the action at this point is partly determined by the change in ¢ due to the former possession of b, so that the behavior is not purely reflex” (378, p. 24).