Behavior of the Lower Organisms

The simplest reaction of an organism is the performance of a definite simple act in response to a definite stimulus. Such is the contraction of Vorticella, such the reversal of movement in a bacterium or in Paramecium or the flatworm. A simple responsive action of this sort is commonly known as a reflex. The question has been raised as to whether the behavior of the lower organisms differs from that of higher animals in being purely reflex or not ; in other words, whether all their reactions to stimuli are reflexes. For various organisms this question is answered by many authors in the affirmative. In some cases the behavior of animals much higher in the scale than most of those we have considered is characterized as purely reflex. This is v. Uexkull's view for the sea urchin. We must examine briefly the question whether behavior in these lowest organisms is properly characterized as reflex.

What is "a reflex? The concept of reflex action has had a complex origin, and as a result it is defined in various ways. One of the phenomena on which the concept is based is the contraction of a muscle when a certain nerve is stimulated. The stimulation is supposed to pass from the nerve to the spinal cord, whence it is reflected back to the muscle; hence the name reflex. Some authors hold that the term can be properly used only of acts thus performed by the aid of the nervous system. This would of course exclude reflexes from the behavior of unicellular organisms, and introduce uncertainty in dealing with the lower Metazoa, for in many of these we do not know whether the reactions are throughout mediated by the nervous system or not. But it is more usual to consider the reflex as a certain type of action, without regard to the particular anatomical structures involved. Even where the term is limited to actions produced through the nervous system, some other term is employed to indicate the corresponding type of action in animals without a nervous system, so that the existence of a particular kind of action, indicated usually by the word " reflex," is recognized. Thus, Beer, Bethe, and v. Uexkull (1899) use for reflexes performed without a nervous system the word "antitype." We may then ex-

amine the reflex (or antitype) simply as a type of action, without regard to the existence of a nervous system. A second phenomenon on which the concept of reflex action is based is the following : In ourselves, certain acts are performed unconsciously. These acts have been considered identical with those due to the passage of an impulse from the nerve-ending to the spinal cord, and thence back to the muscle ; that is with reflexes. Hence the reflex is often defined as an unconscious or involuntary action : " Such involuntary responses we know as 'reflex' acts" (James, "Psychology," Vol. I, p. 13). "Reflexes are voluntary acts that have become mechanical" (Wundt). This definition of a reflex act as involuntary or unconscious is widely employed. If we accept this definition, there is of course no way by which we can tell whether the reactions of lower animals are reflex or not. By observation we cannot tell whether the reacting organism is conscious, for this would require, as Titchener (1902) says, an objective criterion of the subjective, — an objective criterion of that which is not objective, and this is impossible. It is certainly as dogmatic and unscientific to assert that the actions of organisms are reflex in the sense of unconscious, as to assert the opposite, for we have no knowledge on this point. We can recognize reflex acts, from this point of view, only in ourselves.

A third phenomenon on which the conception of a reflex is based is the supposed uniformity of certain reactions. The muscle responds to all sorts of stimuli by contracting. This uniformity is considered by many authors the essential feature in reflexes. Hobhouse (1901, pp. 28, 29) defines reflexes as "uniform responses to simple stimuli." According to Beer, Bethe, and v. Uexkiill (1899, p. 3), reflexes are reactions "always recurring in the same manner." Driesch (1903) says a reflex is "a motor reaction which as a response to a stimulus occurs the first time completely and securely."

This objective definition of a reflex as an invariable reaction to a simple stimulus is the only one which we can really use in determining by means of objective study whether the behavior of animals is reflex in character. Is the behavior of lower organisms composed of reflexes in this sense? Possibly the best case for an affirmative answer to this question could be made out for the bacteria. Here there is so far as known only one form of motor reaction, — the reversal of movement when stimulated. But even in the bacterium the uniformity is disturbed by the fact that on coming in contact with a solid the organism sometimes comes to rest against it, while at other times it reacts by the reversal of motion. Owing to their minuteness, the behavior of these organisms is less known than

that of other unicellular forms, so that it is difficult to make a positive generalization on such a point as the present one. If we attempt to apply our definition of a reflex to the behavior of the infusoria, — of Paramecium, for example, — we at once get into difficulties. The "avoiding reaction" of Paramecium is sharply limited in many ways, and always takes place in accordance with a definite type. But it is far from being invariable. The reaction is composed of three factors, which may vary more or less independently of each other, in such a way that an absolutely unlimited number of combinations may result, all fitting the generalized type. The possible variations may be summed up as follows : If the animal be taken as a centre about which a sphere is described, with a radius several times the length of the body, then as a result of the avoiding reaction the animal may traverse the peripheral surface of this sphere at any point, moving at the time either backward or forward. In other words, the reaction may carry it in any one of the unlimited number of directions leading from its position as a centre. While the direction of turning is absolutely defined by the structure of the animal, yet the combination of this turning with the revolution on the long axis permits the animal to reach any conceivable position with relation to the environment. In other words, Paramecium, in spite of its curious limitations as to method of movement, is as free to vary its relations to the environment in response to a stimulus as an organism of its form and structure could conceivably be. Such behavior does not fall within the concept of a reflex, if the latter is defined as a uniform reaction.

Still less does the behavior of Stentor yield itself to formulation as purely reflex. To the same stimulus, under the same external conditions, this animal may react, as we have seen, in several different ways; its reaction depends upon its physiological condition. The same is true for Hydra and other Ccelenterata, for the echinoderm, the flatworm, and many other invertebrates, as we have set forth in detail in the description of the behavior of these organisms. In the sea anemone we have examples of indecision, parts of the positive reaction being combined with parts of the negative. In all these cases the behavior is far from that sureness and fixity that characterizes the supposed reflex.

Even in Amoeba it is difficult to apply the reflex concept to the behavior. So far are the reactions here from being uniform, that we can almost say, on the contrary, that Amoeba never does the same thing twice. The behavior is here formless, undefined, not held within narrow bounds by structural conditions, as in the infusoria and in most higher animals; the essential criteria of reflex action seem lacking. It would be very difficult to apply the reflex concept, for example, to the

behavior of a floating Amoeba in attaining a solid support, as described on page 8, or to the food reaction illustrated in Fig. 21. Further, as we have seen on page 20, Amceba may at different times react in opposite ways to the same stimulus. Indeed, consideration shows that it is impossible to apply rigidly the conception of a reflex, as an invariable reaction to a definite stimulus, to the behavior of any organism having more than one motor reaction at its command. James ("Psychology," Vol. I, p. 21) and Pearl (1903, p. 704) have given us sketches of what would be the behavior of an organism whose acts were purely reflex. Taking the reaction to food as an example, James says : "The animal will be condemned fatally and irresistibly to snap at it whenever presented, no matter what the circumstances may be; he can no more disobey this prompting than water can refuse to boil when a fire is kindled under the pot. His life will again and again pay the forfeit of his gluttony. Exposure to retaliation, to other enemies, to traps, to poisons, to the dangers of repletion, must be regular parts of his existence. His lack of all thought by which to weigh the danger against the attractiveness of the bait, and of all volition to remain hungry a little while longer, is the direct measure of his lowness in the mental scale" (I.e., p. 21). Such a picture has only to be presented to make us see the impossibility of constructing the entire behavior of an organism out of such irresistible reflexes. For the reactions to dangers and enemies must then be reflexes, as well as the reactions to food, and the two are incompatible. Suppose the food and the danger are present together, as often happens. The organism cannot react fatally and irresistibly to both, for the movements required are in opposite directions. It must decide to react either with relation to one or to neither, and in either case the fatality and irresistibility of at least one of the reflexes disappears.

If, then, we consider the reflex an invariable reaction to a given stimulus, we cannot hold that behavior in lower organisms is made up of reflexes. Indeed, the fact that stands out most clearly in the behavior is the following: Each stimulus causes as a rule not merely a single definite action that may be called a reflex, but a series of "trial" movements, of the most diverse character, and including at times practically all the movements of which the animal is capable. The reaction to a given stimulus depends on the physiological state of the organism, not alone on its anatomical structure ; and physiological states are variable. This is true both for the infusoria and for man.

The attempt to characterize the behavior of the lower organisms as purely reflex has risen from the desire to show that the structural conditions of the organism and the physical and chemical action of the stimulus are sufficient to account for their behavior, without the necessary intervention of consciousness. This is well expressed by v. Uexkiill (1897, p. 306) when he says that we are to regard the reflex as "the necessary course of a process that is conditioned by nothing else than the mechanical structure of the organism." Shall we include the physiological state of the organism as part of its mechanical structure? If we answer this question in the negative, then it is clear that the behavior of the lower organisms is not reflex in character. If on the other hand we answer this question in the affirmative, holding that the physiological state is some chemical or physical configuration of the substance of the organism, and therefore to be included in its mechanical structure, then the entire question concerning the reflex character of behavior in a given organism loses its objective character and evaporates into thin air. For in the highest as well as the lowest organism the reactions must be supposed to depend upon the physical and chemical constitution of the organism, unless we are to accept vitalism. And if when we say that the behavior of an organism is reflex in character, we mean only that its behavior depends upon its physical and chemical make-up, we can make no distinction upon this ground between the behavior of lower and higher organisms. This point is indeed well recognized by thoughtful psychologists. "The conception of all action as conforming to this [the reflex] type is the fundamental conception of modern nerve physiology," says James ("Principles of Psychology," Vol. I, p. 23).

Those who have been most strenuous in attempting to demonstrate that the behavior of certain lower organisms is "purely reflex" in character would probably be the last to hold that in the higher organisms behavior must be explained on essentially different principles. The attempt often made to contrast the behavior of lower organisms as reflex with that of higher organisms as something else, seems therefore a shortsighted and pointless proceeding. What a given organism does under stimulation is limited by its action system, and within these limits is determined largely by its physiological condition at the time stimulation occurs. In the lowest organism the action system confines the variations in behavior within rather narrow limits, and the different physiological conditions distinguishable are few in number ; hence the behavior, is less varied than in higher animals. But the difference is one of degree, not of kind. The behavior of Paramecium and the sea urchin is reflex if the behavior of the dog and of man is reflex ; objective evidence does not indicate that there is from this point of view any fundamental difference in the cases.

The importance attributed to the concept of reflex action is of course due to the desire to find a simple invariable unit for behavior, comparable to the atom in physics. To obtain such a unit it is necessary to take into consideration as an additional possible variable, the physiological state of the organism. Dr. E. G. Spaulding has suggested the following: We cannot properly say for a given organism "same stimulus, same reaction," as appears to be the usual idea of a reflex. On the other hand we can say "same physiological state, same stimulus, same reaction," and this supplies whatever need there may be for a simple invariable element of behavior. To this element the term "reflex" or an equivalent one might be applied, and we might then maintain that the behavior of all organisms is made up of reflexes. But on this definition the question whether the behavior of a given organism is made up of reflexes is not a problem for objective investigation; but the conception that it is thus made up is a postulate, in accordance with which we interpret the results of our observations ; and this applies to the highest as well as to the lowest organisms. The assumption that varied physiological states exist is of course one of these interpretations, made to save what is essentially this very postulate, — the principle that like causes always produce like effects.

In the following sections we shall analyze the behavior of the lower organisms described in previous chapters, attempting to determine the essential characteristics of behavior and to bring out the chief factors of which it is made up. We shall take up first the factors causing or determining the movements and reactions, treating first the inner, then the outer, factors. Then we shall consider the movements and reactions themselves, attempting to bring out the features of essential importance. From a synthesis of our results on both sets of factors — the causes and the effects — we shall try to arrive at a general statement of the fundamental character of behavior in the lower organisms.

The external factors in behavior are usually known as stimuli, and their effects on movement as reactions. The term " reaction " has been used in various ways. In our analysis we shall employ the word "reaction" as signifying an actual change in movement. The word is sometimes used in a looser sense. For example, the movement toward a source of light is often spoken of as the reaction to light, even though the only observable change of movement was that by which orientation was brought about. This looser sense is sometimes unavoidable, either from our ignorance of the facts, or for other reasons ; when used in this loose sense in the following, the context will clearly indicate it. Where question might arise, reacton is to be understood as meaning an observable change of movement. To avoid ambiguity, the latter phrase will sometimes be used in place of the word " reaction." The following discussion will be intelligible only if this meaning of the word "reaction" is kept in mind.

(i) Activity does not require Present External Stimulation. — A first and essential point for the understanding of behavior is that activity occurs in organisms without present specific external stimulation. The normal condition of Paramecium is an active one, with its cilia in rapid motion ; it is only under special conditions that it can be brought partly to rest. Vorticella, as Hodge and Aikins (1895) showed, is at all times active, never resting. The same is true of most other infusoria and, in perhaps a less marked degree, of many other organisms. Even if external movements are suspended at times, internal activities continue. The organism is activity, and its activities may be spontaneous, so far as present external stimuli are concerned.

The spontaneous activity, of course, depends finally on external conditions, in the same sense that the existence of the organism depends on external conditions. The movements are undoubtedly the expression of energy derived from metabolism. The organism continually takes in energy with its food and in other ways, and continually gives off this energy in activities of various sorts. The point of importance is that this activity often depends more largely on the past external conditions through which the energy was stored up than upon present ones. Thus the organism may move without the present action of anything that may be pointed out as a specific external stimulus to this movement.

This fact is of great importance for understanding behavior, and many errors have arisen from its neglect. If we see an organism moving, it is not necessary to assume that some external stimulus now acting is producing this movement. In studying the reactions to present particular stimuli, as light or gravity or a chemical, it is in many cases not necessary to account for the fact of movement, for the movement comes from the discharge of internal energy, and often the organism was moving (though perhaps in another direction) before the stimulus began to act. It is only the change in the movement when the stimulus acts that the present stimulus must account for. In the movement of Paramecium toward the cathode, it is not necessary to assume, as some have done, that a special force (as cataphoric action) is required, to carry the animals. They were moving equally before the electric current began to act; the difference that the stimulus has made is in the direction of motion, and it is only this that the stimulus must account for. In the movements of infusoria toward chemicals, some have supposed that an attractive force from the chemical was necessary, actually bearing the organisms along; this is quite superfluous. In general, when an organism moves toward or away from any agent, it is unnecessary to assume that an actually attractive or repellent transporting force is acting upon it. Often — perhaps usually in the lower organisms — movement in a certain direction is due only to the release of inhibition. The organism moves in the given direction because it is moving from internal

impulse, and because movement in this direction is not prevented. This possibility must be considered in all cases. Further, when the action of a stimulus actually changes the direction of movement in an organism, persistence in this new direction by no means demands persistence in stimulation. The new direction once attained may be followed, from the internal impulse to movement, merely because there is nothing to change this direction, or because stimulation does occur when this direction is changed, bringing the organism back to it. This is apparently the case, as we have seen, in the reactions of infusoria to gravity, to water currents, and to light coming from a certain direction.

Often, of course, stimulation does rouse an organism to increased activity. But even in this case the activity is due to the release of internal energy. It may, therefore, continue long after the stimulation which inaugurated the release has ceased to act. Such continuance thus does not necessarily imply continued action of the stimulus. In many cases the specific stimulus to action is only the change of conditions. Thus, if light or a chemical acts upon an organism, the only stimulus may be the sudden change, even though the organism continues to move after the conditions have become constant. Whether the effective stimulation actually continues, must be determined by experiment; it cannot be simply assumed.

In general, when an organism is moving in a certain way — even when toward or from a certain agent — careful analytical experimentation is necessary to determine whether this movement is due to present stimulation, or to the simple outflow of the stored-up energy of the organism through the channels provided by its structure. In most cases, apparently, the latter is true. The spontaneous activities of the organism — those not due directly to present specific external stimulation — are, perhaps, the most important factors in its behavior.

(2) Activity may change without External Cause. — If we watch a specimen of Vorticella under uniform conditions, we find that its behavior does not remain uniform. At first the animal is outstretched, its cilia bringing a current of water to the mouth. After a certain period its stalk contracts, its peristome folds inward, and its cilia cease moving. Soon it extends and resumes its normal activity. These alternations of different ways of behaving occur at rather regular intervals, though the external conditions remain unchanged. Hydra shows parallel changes of behavior at intervals, under uniform external conditions (p. 189) ; the medusa contracts at intervals, though there is no change in the outer conditions, and similar examples could be given for many other organisms.

(3) Changes in Activity depend on Changes in Physiological States. — What causes the changes in behavior described in the foregoing paragraph ? Since the external conditions have not changed, the animal itself must have changed. The Vorticella which contracts and folds its cilia is in certain respects a different animal from the one that remains extended and keeps its cilia in active motion, otherwise it would not act thus differently. Its internal or physiological condition has been changed. Soon its original condition is restored ; it unfolds and behaves as it did at first. In the same way, the physiological condition of the Hydra that stands quiet with outspread arms is different from that of the Hydra which, without external cause, contracts and changes its position. The behavior produced by these differences in physiological condition is the same as that producible by an external stimulus.

Other examples of changes in behavior due to changed physiological states are shown in the different reactions of hungry and of well-fed individuals, which we have seen in so many cases, and in the different reactions of organisms as determined by their respiratory processes. The precise nature of these internal changes of condition we of course do not know. The expression "physiological states" evidently includes a great many things of heterogeneous character, having merely the common characteristic that they are internal modifications of the living substance resulting in changed behavior. In the lower organisms it is difficult to define the different classes of physiological states in an objective way, though the progress of investigation will doubtless make this possible. Certain fundamental differences in diverse states will be pointed out in the following pages.

(4) Reactions to External Agents depend on Physiological States. — Change of activity is, of course, often produced by external agents. With this point we are to deal later ; here what interests us is the fact that in any given organism the reaction to a given external agent depends on the physiological condition of the organism. This principle is of such importance that we must dwell upon it. First we have the important fact that the reaction to a given stimulus depends upon the progress of the metabolic processes. To a given external condition the nature of the reaction often depends upon whether it favors these metabolic processes. If material for these processes is lacking, the reaction to stimuli is of such a character as to secure such material. In such organisms as the ccelenterates almost the whole character of the behavior, down to the details of the reactions to specific stimuli, depends thus on the condition of the processes of metabolism (sec Chapter XI). The behavior of organisms is similarly determined

by the course of other internal processes ; these are, perhaps, the most important factors determining physiological states. Of a somewhat different character are the changes in physiological state exemplified in the behavior of Stentor and the flatworm. In Stentor, as we have seen in Chapter X, we can distinguish at least five different physiological states in which the same individual reacts differently to the same conditions. Under stimulation by numerous grains of carmine in the water, the Stentor in condition No. 1 does not react at all. In condition No. 2 it reacts by turning into a new position. In condition No. 3 its reaction is a reversal of the ciliary current. In No. 4 it responds by contracting at brief intervals. In No. 5 the contractions are stronger and the organism remains longer in the contracted condition, finally breaking its attachment to its tube and swimming away. Throughout this entire series of reactions the external conditions remain the same, so that we can attribute the different reactions only to different conditions of the organism.

In the flatworm we have seen in Chapter XII that six different physiological conditions may be distinguished, in each of which the flatworm is a different animal, so far as its reactions to stimuli are concerned. We need not repeat the details regarding these conditions here. Illustrations of the fact that the reaction of the organism depends on its physiological state might be drawn from the behavior of many other animals. (5) .The Physiological State may be changed by Progressive Internal Processes, particularly those of metabolism. The well-fed sea anemone or Hydra is a very different animal, so far as its behavior is concerned, from the specimen that has fasted. Under uniform conditions, the sea anemone that is well fed remains quiet; while the individual that has exhausted the material for metabolism toils painfully away on a tour of exploration. The well-fed individual reacts negatively or not at all to that to which the hungry individual reacts positively. The Paramecium bursar id that has exhausted its supply of oxygen behaves in one way with regard to light, the individual in which respiration is progressing normally in another way. Innumerable examples illustrating this principle can be found in the behavior of lower and higher organisms. It is hardly too much to say that the progress of the metabolic and other physiological processes is the chief factor in determining the behavior of lower organisms.

(6) The Physiological State may be changed by the Action 0} External Agents. — This follows directly from the behavior of Stentor and the flatworm, to which we have referred in the preceding paragraph. The Stentor in condition No. 1, as we have seen, does not respond to the stimulus of the carmine grains in the water. The stimulus continues, and after a time the physiological condition changes so that the animal does respond. The change in physiological state can then be due only to the action of the stimulus. In the same way the other changes in the physiological condition of Stentor and the flatworm are evidently due largely, at least, to the continued action of the stimulus.

(7) The Physiological Slate may be changed by the Activity of the Organism. — This is demonstrated by the spontaneous changes in the behavior of Vorticella or Hydra, of which we have already spoken. At first the animal is in a certain condition which corresponds to extension and activity. It then passes into a condition which results in contraction. But it does not remain contracted ; the contraction itself restores the original condition, so that the animal now again extends and becomes active. Certain of the changes in physiological state seen in Stentor and the flatworm are probably clue to the reactions of the organism. Thus, we find that the flatworm, after turning for a long time away from a lateral stimulus, suddenly changes and turns in the opposite direction (p. 253). The change of physiological state conditioning this change of reaction was probably due, not alone to the continuance of the stimulus, but to the previous prolonged turning of the flatworm in a certain direction.

(8) External Agents cause Reaction by changing the Physiological State 0} the Organism. — We have found that external stimuli cause changes in physiological state, and that changes in physiological state induce changes in behavior, — activities of a definite character. It is evident, then, that external agents must change the behavior of organisms by changing their physiological condition. In other words, in a reaction to an external stimulus the course of events is probably as follows : The stimulus causes first a change in the physiological condition of the organ or organism. This, then, causes a change in behavior, which we call a reaction to the stimulus. What the organism reacts to is the change produced within it by the external agent. Hence, if two different external agents induce the same internal change (as by blocking certain processes) they will receive the same reaction.