Behavior of the Lower Organisms

the hungry Hydra reacts positively to chemicals. In certain physiological conditions the flatworm reacts positively to almost any stimulus. At other times the opposite conditions prevail; the animal reacts negatively to the stimulus to which it before reacted positively. In closely related organisms differing in their metabolic processes, the reaction to a given agent depends on the nature of the metabolic processes, tending to retain the conditions favoring these processes. This is especially well illustrated in the bacteria (pp. 36, 39) and in the ccelenterates (pp. 224, 231), but is equally true for other organisms. Thus what the organism does depends on the course of its life processes, and upon the completeness or incompleteness of their performance. In other words, the behavior of the animal under stimulation corresponds to its needs, and is determined by them. This correspondence is of course not always perfect ; with this point we can deal after we have considered the nature of the reactions given. But a study of the determining factors of behavior demonstrates that the relation of external conditions to internal processes is the chief factor, and that hence behavior is regulatory in essential nature.

(6) We may sum up the external factors that produce or determine reactions as follows: (1) The organism may react to a change, even though neither beneficial nor injurious. (2) Anything that tends to interfere with the normal current of life activities produces reactions of a certain sort ("negative"). (3) Any change that tends to restore or favor the normal life processes may produce reactions of a different sort ("positive"). (4) Changes that in themselves neither interfere with nor assist the normal stream of life processes may produce negative or positive reactions, according as they are usually followed by changes that are injurious or beneficial. (5) Whether a given change shall produce reaction or not, often depends on the completeness or incompleteness of the performance of the metabolic processes of the organism under the existing conditions. This makes the behavior fundamentally regulatory.

In the preceding section we have dealt primarily with the causes and conditions of movements and reactions ; here we are to deal with the movements and reactions themselves. Every organism has certain characteristic ways of acting, which are conditioned largely by its bodily structure, and which limit its action under all sorts of conditions. This perhaps seems a mere truism. Amoeba of course cannot swim through the water like Paramecium, and the latter cannot fly through the air nor walk about on dry land. But the behavior of any given lower organism is actually confined in this way within narrower limits than is frequently recognized. Formulae have at times been proposed to explain the movements of various organisms, when the latter are incapable of performing the movements called for by the formulae. It is usually possible to determine with some approach to completeness the various movements which a given organism has at command. These form as a rule a coordinated system, which we have called in previous pages the action system. The action system of an organism determines to a considerable extent the way it shall behave under given external conditions. Under the same conditions, organisms of different action systems must behave differently, for to any stimulus the response must be by some component of the action system. Thus, Amoeba, the bacteria, Paramecium, Hydra, and the flatworm have action systems of different character, and their behavior under given conditions must differ accordingly. This matter has been dealt with in detail in the descriptive portion of the present work, so that we need not dwell upon it here. In studying the behavior of any organism, the first requisite to an understanding is the working out of the action system.1

1 The action system corresponds largely to what Putter (1904) calls the " Symptomatology" of organisms. In our discussion of the causes of reaction we found that we could classify most stimuli into two groups — those that interfere with the normal life processes, and those that do not. It will be best to consider separately the reactions to these two classes of stimulation, and to take up the reactions to unfavorable stimuli first, since these seem to present the most primitive conditions.

The simplest reaction to unfavorable stimuli is merely a change in the direction or character of the movement. The organism is moving in a certain direction; when subjected to an unfavorable change, it changes its direction of movement. This is the case in Amoeba, in bacteria, in infusoria, in rotifera, in the flatworm; indeed, in most free organisms. The mere fact of a change is in itself regulatory or adaptive. The original behavior has brought on the unfavorable change, hence the best thing to do is to change this behavior. If the unfavorable condition still persists, the behavior is changed again ; this being continued, the organism is bound to escape from the unfavorable conditions if it is possible to do so. The repeated change in behavior under unfavorable stimulation is very striking in Paramecium, in Stentor, in Hydra, in the flatworm, and elsewhere.

The fundamental principle for this method of reaction is that a change 0} behavior under unfavorable conditions is in itself regulatory. As we have before pointed out, the reactions of organisms are based on the principle, usually correct, that it is the previous behavior of the organism that has brought on the present conditions. Hence if these conditions are unfavorable, a change of behavior is required. The developments of this method of behavior found indifferent organisms consist in defining, varying, and systematizing the changes that occur. In Amoeba we find perhaps the simplest condition. When this animal in its forward course meets unfavorable conditions it merely goes in some other direction. In what direction it will go cannot be predicted from either the structure of the organism or from the localization of the stimulus, for Amoeba can move with any part in advance. It is evidently determined by transient internal conditions. In organisms with definite body axes and other structural relations, the change of motion becomes more definite. In bacteria the organism moves after stimulation in the opposite direction. In the free-swimming infusoria, as illustrated by Paramecium, and in the free Rotifera, there is an elaborate system of movements which make the reaction effective. The animal stops or reverses the movement which has -brought on the unfavorable condition, then swings its anterior end about in a circle as it moves for-

ward, so as to try successively many different directions. The behavior shows the "method of trial" reduced to a system. It would be almost impossible to suggest any modification of this reaction, as exemplified in Paramecium, that would make it better fitted, under the given relations, for meeting all sorts of conditions. In fixed infusoria, such as Stentor, this behavior is modified to adapt it to the fixed life. In the free-swimming animal the organism is subjected to new conditions every time the reaction is repeated, hence there is little occasion to try other methods of behavior. But if the organism is fixed in one place, this is not true ; when a given reaction is repeated it merely brings on the same conditions its first performance induced. So different methods are developed. Under unfavorable conditions the organism first turns to one side, then reverses its ciliary current, then contracts, etc. (see p. 174), trying many different changes of behavior. In Hydra, in the starfish, in the flatworm, we have seen this same "method of trial" appearing under various forms. In all these organisms persistent unfavorable stimulation induces first one physiological state, then another, then another, and to each state there corresponds a certain method of behavior.

C. Selection from the Conditions produced by Varied Movements In all this behavior we find the manifestations of a most important principle, one of far-reaching significance for the understanding of behavior. The stimulus does not produce directly a single simple movement (a reflex act), of a character that relieves the organism at once from the stimulating condition. On the contrary, stimulation is followed by many and varied movements, from which the successful motion is selected by the fact that it is successful in causing cessation of stimulation. This is the principle of the "selection of overproduced movements," of which much use has justly been made by Spencer, Bain, and especially by Baldwin (1897, 1902), in attempting to explain behavior. It is more accurate to speak of the selection of the proper conditions of the environment through varied movements. It is primarily the proper environmental conditions that are selected; the movements are only a means to that end. From this point of view what we have often called in the foregoing pages the method of trial may be formulated as follows : When stimulated the organism performs movements which subject it to varied conditions. When in this way it reaches a condition that relieves it of stimulation the reacton movement ceases, since there is no further cause for it. The organism may then resume its usual movements. In the case where the reaction consists of changes in direction, as in infuso-

ria, the resumption of the usual forward motion of course carries the organism in a new direction brought about by the reaction. What movements are produced by the stimulating agent depends on the action system of the organism; it performs the movements that it is accustomed to perform. In some cases these movements are of a rather uniform character, yet are of such a nature as to subject the animal to many changes of the environmental conditions. This is the case, for example in the reactions of such infusoria as Paramecium. In other cases the movements themselves are varied; the organism first reacts in one way, then in another, running thus through a whole series of activities, till one succeeds in ridding the organism of the stimulating condition. This is the method of behavior seen in Stentor and in most higher organisms. In both methods the essential point is the same — the subjection of the organism to varied environmental conditions, until one of these relieves it from the stimulation. This condition is then said to be "selected." In some cases the maintenance of this favorable environmental condition involves continuance of the movement finally resulting from the varied trial movements ; in other cases it does not.

Reaction by selection of excess movements depends largely on the fact, previously brought out (p. 283), that the movement itself is not directly produced by the stimulus. The movement is due, as we have seen, to the internal energy of the organism. In the case of free-moving animals like Paramecium, stimulation usually neither increases nor decreases the amount of motion, but merely causes it to change in various ways. Reaction, of course, sometimes does take the form of an increase of motion ; this is seen in the increased movements of infusoria under strong chemicals or heat ; of Planaria under light, etc. But even in these cases the energy for the motion comes from within and is merely released by the action of the stimulus. It is important to remember, if the behavior is to be understood, that energy, and often impulse to movement, come from within, and that when they are released by the stimulus, this is merely what James has called "trigger action." There is thus no reason to expect that upon stimulation an organism will perform merely a single simple movement (a "reflex action"), and then become quiet. Movement of one sort or another is its natural condition, and after stimulation has ceased it may show movements (the character or direction of which may have been determined by the stimulus) for an. indefinite period.

Behavior by selection from the results of varied movements is based on general principles. The reactions are not specific ones, definitely adapted to particular kinds of stimulation, but are responses to any stimulation of a certain general character, — namely, to any condition that interferes with the normal course of the life processes. On receiving an unfavorable stimulus that it has never before experienced, the organism behaving on this plan is not at a loss for some method of reacting; it merely responds in the usual way, performing one movement after another, till one of these relieves it of the stimulation, if this is possible.

Of course special circumstances may arise in which this general method of reacting may be ineffective. If dropped into a strong chemical, Paramecium reacts in the usual manner, though this does not help it. If the water containing a flatworm is heated, the animal goes through, one after the other, almost every reaction it has at command, though all are unavailing (p. 245). The difficulty, of course, lies in the fact that under these circumstances nothing the organism can do is of any avail, and a man in similar conditions would be equally helpless. The infusorian and the flatworm, like the man, merely try everything possible before succumbing.

D. "Discrimination" The effectiveness of reaction bv continued varied movements in preserving the organism depends upon several factors. One of these is what is called in higher animals the power of discrimination, — that is, the accuracy with which the tendency to react is adjusted to the injuriousness of the stimulating agent. If an injurious agent resembles in its first action a non-injurious one, so that the animal reacts in the same way toward both, its behavior will not preserve it from injury. Using the more subjective form of expression, if the organism does not discriminate between the first action of injurious and non-injurious agents, it cannot react differently to them, until perhaps the injury has become irremediable. The facts show that in both higher and lower organisms the power of discrimination under weak stimulation is far from perfect. Thus, in the sense in which we have used the term, Paramecium discriminates acids from alkalies and salts, and these again from sugar. But it does not effectively discriminate the first effects of different acid substances, so that it swims into weak carbonic acid, which is harmless, and likewise into weak sulphuric acid and copper sulphate, which kill it. It does not discriminate the first action of a 10 per cent sugar solution from that of water, hence it swims readily into the sugar solution and is killed by the osmotic action. In all these cases it does discriminate and react to the injurious agent when its effect has become marked, but injury has then already occurred and the reaction does not preserve the

animal. In regard to these injurious substances Paramecium thus makes what we would call in ourselves a "mistake." The whole scheme of reaction by the selection of the results of varied movements is not a set, perfected, final one, but is a tentative plan, based on the confusing world taken as it comes ; it is liable to mistakes, and is capable of development. Progress in this method of behavior takes place largely through increase in the accuracy of discrimination of different stimuli. This may occur through the law of the increased readiness of resolution of physiological states after repetition, in the way that we shall attempt to set forth later (Chapter XIX).

The second chief factor on which depends the effectiveness of behavior by selection of overproduced movements lies in the relative fitness of the movements to relieve the organism from the unfavorable conditions. This, of course, depends on many things. If a powerful chemical is diffusing from a certain direction, the rapid movements of Paramecium are more likely to save than is the slow motion of Amoeba. There are two factors on which the effectiveness of the movements depends, that are worthy of special consideration.

In what we may call the pure method of trial, a most important requirement for effectiveness is that the movements shall be so varied as to give much opportunity for finding other conditions. There are great differences in the behavior of different organisms from this standpoint. This may be illustrated by a comparison of the reactions of Paramecium and Bursaria to heat, as previously described. When a portion of the area containing the organisms is heated, these two infusoria react in accordance with essentially the same plan, yet practically none of the Paramecia are injured, while a large proportion of the Bursariae are killed. The difference is due chiefly to the fact that Paramecium rapidly repeats its reactions and revolves on its long axis as it turns, so that in a short time it has tried in a really systematic way many different directions, and is practically certain to find one leading away from the heated region, if such exists. Bursaria, on the other hand, changes its direction of movement only at longer intervals, and usually soon ceases to revolve on its long axis as it turns toward the aboral side. This failure to turn on the long axis deprives it of the great advantage of being directed successively in many different directions in the different planes of space. The result is that it is likely to be destroyed by the heat before it has found a direction leading to a cooler region.

A second factor that is of great importance in making the movements effective lies in the proper localization of the reactions. An organism that moves directly away from an unfavorable agent (or directly toward a favorable one) has a great advantage over an organism whose movements are not thus accurately directed. There are great differences in different organisms in this respect ; some react very precisely with reference to the position of the stimulating agent, while others do not.

How is the relation of the reaction to the localization of the stimulus brought about, and what is the cause of the differences between different organisms in this respect? In answering this question, we can distinguish three different classes of phenomena. These are the following : — (i) First we have the simple phenomenon that when a portion of an organism is stimulated this portion may respond by contraction, extension, or other change of movement. If the remainder of the body does not respond, or responds in a different way, this gives at once a reaction localized in a certain way with reference to the place of stimulation. Such local responses we find in Amoeba, where the part strongly stimulated contracts, or if stimulated by a food body it extends. The same phenomenon is found in Hydra, in the bending of the body when one side is powerfully stimulated, in the bending of the tentacles of Sagartia toward the point stimulated, and in the local contractions of the medusa and of stimulated points on the body of the flatworm and many other soft-bodied animals. The same thing is seen even in man when the electrode of a battery is applied directly over a muscle ; this muscle now contracts. This seems a simple and primitive phenomenon, and as such has been seized upon by the "tropism theory" and made the chief factor in the behavior of lower organisms, and particularly in all directed reactions. As we have shown in our chapter on that theory, this factor plays by no means the extensive part assumed by the theory, and is quite inadequate to account for most of the behavior of lower organisms. Even in the behavior of the organisms mentioned above, where it clearly does play a part, this part is a subordinate one (see Chapter XIV). In many organisms, such as the free infusoria and some rotifers, it is hard to detect any part of the effective behavior that is due to local reaction at the point stimulated. The fact that such local reactions may and do occur in organisms is of course a fact of much importance, but taken by itself it is utterly inadequate as a general explanation of directed reactions.

(2) In many cases we find that the relation of the movement to the source of stimulation is brought about indirectly through selection from among varied movements. The organism tries moving in many directions, till it finds one in which there is no stimulus to further change. In this way it may become oriented very precisely if the conditions require. This is the prevailing method in the infusoria and in various other organisms, as we have seen. It is becoming evident that this method is more common even among higher organisms than has been hitherto set forth. Movements of the head from side to side, such as we find in the flatworm and many other animals, movements of the eyes or other sense organs, such as are common in higher animals, or movements of the body from side to side, as in the swimming of many creatures, give opportunity for determining which movement tends to retain the stimulus, which to get rid of it. In this way they form a basis for the determination of the direction of locomotion through the method of trial. How much part such movements play needs careful study.

(3) In still other cases the reaction shows a definite relation to the localization of the stimulus, yet it is not due to local reaction of the part stimulated, nor is it brought about by trial. If an infusorian is stimulated at the anterior end it swims backward ; stimulated at the posterior end it swims forward. Both these movements are reactions of the entire organisms, all the motor organs of the body concurring to produce them; they are not produced by local reactions of the organs at one end or the other. The flatworm turns toward or away from the side stimulated, by reactions involving the muscles of both sides, as well as transverse and dorso-ventral muscles, all at a distance from the point stimulated. If stimulated on the upper surface of the head, a complicated twisting reaction occurs, involving many sets of muscles in various regions (p. 273), by which the ventral surface is made to face the stimulating agent (p. 236). Innumerable instances of this class of reactions could be given; they include perhaps the greater number of the directed movements of organisms.

In these reactions a stimulus at one side or end evidently produces a different reaction from a stimulus at the opposite side or end, though the reaction is not primarily at the point stimulated. Doubtless the stimulus starts a physiological process of some sort at the point upon which it impinges, and this determines in some way the direction in which the organism shall move. This effect in the region directly acted upon corresponds to the "local sign" in human physiological psychology. Behavior thus brought about is of course more effective than that of the two preceding classes, permitting more direct and rapid reaction than the method of trial, and meeting the conditions in an incomparably

more adequate way than the simple local reaction of the part stimulated. Such behavior apparently represents not a primitive condition, but a product of development. How has it been brought about? It is evident that the operation of the law of the readier resolution of physiological states after repetition, taken in connection with behavior by selection from varied movements, would in course of time produce such reactions. Let us suppose that the original reaction to a stimulus at the anterior end was simply the production of a change resulting in varied movements, according to the principles governing the actual reactions of Paramecium. These varied movements would include forward as well as backward motion. The forward movement would induce still further stimulation, hence it would be changed. The backward movement would give relief from stimulation, hence would not be changed (till internal conditions require). Hence after stimulation at the anterior end the physiological states induced will always be resolved finally into that state corresponding to backward movement. This resolution will in time become spontaneous ; the physiological state due to stimulation at the anterior end will pass at once into that producing movement backward. Trial movements will no longer occur, but the organism will respond at once by backward motion. A similar exposition will account, mutatis mutandis, for other localized reactions.

Whether this condition has been brought in the way above sketched or not, its existence is evidently a factof great importance. It is a step forward from the pure "trial movement" condition. Wherever the organism can react in this manner, and this will meet the conditions equally well, we may expect such behavior in place of repeated trials. In higher organisms especially we find this behavior playing a large part. Such organisms could not be expected, for example, to orient to gravity or to light rays by trial movements, as the infusoria do, but rather to turn directly toward or from the source of action of the stimulating agent. This is, of course, known in many cases to be true.

But under many circumstances the reaction by trial is surer, though less rapid, than that depending directly on the localization of the stimulus, so that we find the trial method much used even by higher organisms (see Chapter XII). Further, the more direct reactions due to precise localization are again combined as elementary factors to produce behavior based on the method of trial, as when the flatworm turns toward and "tries" any source of weak stimulation, accepting or rejecting it finally, according as it proves fit for food or not. Thus we have behavior rising to a higher degree of complexity, — the method of trial in the second or third degree, as it were. Examples of this character are abundant.

We have thus far dealt primarily with reactions to environmental conditions that interfere with the normal life processes. We find that these induce changes in behavior, subjecting the organism to new conditions, the more favorable one of which is selected. This gives us a basis for the understanding of reactions toward conditions which favor the normal life processes, — that is, positive reactions. In conditions that are completely favorable — so that all the life processes are taking place without lack or hindrance — there is of course no need for a change in behavior, for definite reactions of any sort. The most natural behavior on reaching such conditions, and that which is actually found as a general rule among lower organisms, is a continuation of the activities already in progress. These activities have resulted in favorable conditions, hence it is natural to keep them up ; there is no cause for a change. This we find strikingly exemplified in bacteria, infusoria, rotifers, and many other organisms under most classes of stimuli. A change in behavior takes place only when the activities tend to remove the organism from the favorable conditions. Unfavorable conditions cause a change in behavior; favorable conditions cause none. It is perhaps a general rule in organisms, high or low, that continued completely favorable conditions do not lead to definite reactions. Of course while the external conditions remain the same, the internal processes may change in such a way that these conditions are no longer favorable, and now the behavior may change.

But when the organism is not completely enveloped by favorable conditions, but is on the boundary, if we may so express it, between favorable and unfavorable ones, then there is often a definite change in the behavior leading toward the favorable conditions, — a positive reaction. To understand such reactions, we may start from the fact that unfavorable internal conditions (as well as external ones) cause a change of behavior. The Hydra or sea anemone whose metabolic processes are interfered with by lack of material, exchanges its usual behavior for activities of a totally different character, setting forth on a tour of exploration. It is a general fact that the hungry animal sets in operation trains of activity differing from the usual ones. Interference with respiration or with other internal processes has similar effects. An increase of temperature above that favorable for the physiological processes likewise starts violent activities. Indeed, it is a general rule that changes of internal condition unfavorable to the physiological processes set in operation marked changes in behavior.

But the activities thus induced are in themselves undirected, save by structural conditions. There is nothing in the cause that produces them, taken by itself, to specifically direct them with reference to external things. Let us suppose, however, that certain of these movements lead to a condition which relieves the interference with the internal processes. The cause for a change of behavior is now removed, hence the organism continues its present movement — continues in the direction, we will say, that has led to the favorable conditions. But perhaps later — sometimes at the very next instant — this same movement may tend to remove the organism from the favorable conditions — as when a heated Paramecium passes across a small area of cool water, or a hungry organism comes against food. Thereupon the cause for a change — interference with the life processes — is again set in operation, and this movement changes to another. Thus the animal changes all behavior that leads away from the favorable condition, and continues that which tends to retain it, so that we get what we call a positive reaction. The change of behavior is due primarily in each case to the unfavorable condition, internal or external — perhaps in last analysis always internal.

Behavior of this character is seen with diagrammatic clearness in the free-swimming infusoria. These animals continue their movements so long as they lead to favorable conditions, changing at once such movements as lead away. They thus retain favorable conditions by avoiding unfavorable ones; the positive reaction is seen to be a secondary result of negative ones. In the infusoria we have then the most elementary condition of the positive reaction. Let us now examine a more pronounced type of positive reaction, — movement directly toward the favorable condition. Amoeba flows toward and follows a food body with which it comes in contact, as illustrated in Fig. 19, p. 14. Take, for example, its action at 3 in this figure. It moves forward with broad front, part of the movement taking it toward the food, part away. On coming in contact with the food, all movement is changed which takes it away, only that being retained which keeps the animal in contact with the food. We have here then, as in infusoria, a case of selection from varied movements, the central point being the changing of all motion that leads to less favorable conditions.

This is, perhaps, the fundamental condition of affairs, from which all positive reactions are derived. The animal moves (partly or entirely from internal impulse, as we have seen), but changes all movements that lead to less favorable conditions. It therefore moves toward the favorable conditions. In many higher animals, even, this behavior is seen in the random movements by which food is sought, by the aid of the chemical stimulation which it sends forth. The movements leading to loss of the favorable stimulation are changed, the others continued, till the food is found (see p. 247).

But many animals have developed, in some way, as we have seen in the account of the negative reactions, the power of localizing their reactions precisely, so as to move in a certain definite way with relation to the position of the source of stimulation. Let us suppose that such an organism is reached by a favorable stimulus on one side — food, or the optimum temperature. It has the power of turning directly toward this favorable condition — and this, of course, is what happens in many higher organisms. There is the same reason to think that this condition is not primitive that we saw in the case of negative reactions. It may, perhaps, be conceived as derived from behavior through selection of overproduced movements in the way set forth on page 308. The precise reactions shown in the actual taking of food are perhaps derivable in the same way.