Physiological Foundations of Behavior

Moreover, A being the region of primary excitation is to some degree physiologically dominant over other regions (Bb, C, etc.), to which the excitation is transmitted, because through this transmission it has more effect upon them than they upon it. There is no escape from the conclusion that the excitation of A and the transmission of this excitation to a greater or less distance gives rise, at least momentarily, to a new org yanismic pattern. The region of primary excitation, A, becomes the dominant region and

other regions b—H within the range of the transmissive correlation become subordinated to it. Before the excitation occurred at A such pattern was not present, nor represented in any way in the protoplasmic system. The potentiality of excitation and transmission was of course present, but this in itself could not determine the pattern which results from excitation at A. Here then the action of an external factor is necessary for the realization in the form of a definite physiological pattern of the potentialities of the protoplasmic system. Moreover, such a pattern cannot possibly arise in the first instance except through the local or differential action of an external factor.

Such an excitation-transmission pattern possesses all the fundamental characteristics of a new organismic pattern in the protoplasmic mass. It determines localized differences at different points, A, B, D, in the dynamic changes constituting life, these differences determine physiological correlation between the different regions with A as the dominant region and these differences and relations constitute a physiological axis with A as one pole. This pattern constitutes for the time being a new physiological integration, a new order and unity in the protoplasmic mass, and this new integration is determined, not by heredity, but arises as a reaction of the living protoplasm to environmental factors. In other words, it is a behavior pattern and the most primitive behavior pattern which can arise in a living protoplasmic system. Only the potentiality of excitation and transmission is determined by heredity in the protoplasm. The actual excitation-transmission pattern arising in any particular protoplasmic mass is a matter of the behavior of that mass in a particular environment.

There can be no question then that pattern of organismic character and magnitude can arise at least temporarily through excitatory reaction of a protoplasm to an environment. Such a pattern is obviously a behavior pattern, even though in the absence of specialized mechanisms it does not lead to movement or other directly visible reaction. If such an excitation-transmission gradient is able to bring about more or less persistent changes in the protoplasm it may become the starting point of a permanent physiological axis and so of the pattern of an axiate organism. In following chapters it will appear that the physiological axes in their simplest terms are very similar to, if not identical with such excitation-transmission gradients and that they may arise through the non-specific differential action of external factors.

We have seen that physiological correlation and the integration which constitutes the organism as a whole are impossible without the existence of orderly and definite differences, either quantitative or qualitative, in different regions and parts of the organism. Such differences are characteristic features of organisms and individual development appears to consist in the localization and progressive specification of such differences and the progressive complication of mechanisms of correlation between the different parts. In Chapter ITI it was pointed out that current theories of heredity do not provide any basis for the process of differentiation in individual development. If we accept these theories, differentiation in the individual must apparently originate in the action of external factors upon the protoplasm. External factors may conceivably act directly and specifically, determining specific differentiations in the parts acted upon, or they may produce non-specific or quantitative effects. In the latter case specific or qualitative differentiations can result only indirectly from their action.

Examination of the specific material relations between protoplasm and the external world indicates that such relations do not play any considerable réle, if any réle at all, in directly localizing and initiating differentiation. For example, we do not usually find that a region of a cell or a cell of a group, into which a specific substance enters from the exterior, is thereby made specifically different from other regions or cells. If the specific substance is nutritive in character, it is either broken down and parts of it are synthesized into the protoplasm of the species, or it becomes a source of energy. In either case it loses its specific character without determining a persistent specific differentiation in the part entered by it. A specific substance may of course produce excitation, but this is not a specific effect for that substance: again, it may be toxic, but the action of toxic agents is certainly not of great importance in initiating differentiation of parts in the individual. There may be cases of the origin of specific differences in organismic pattern through specific differences in the material relations of different regions or cells with environment, but it is evident that organismic pattern in general does not originate in such manner. Even if specific differences do arise in this way in a protoplasmic region, a cell, or a cell group, we find in general that the specific substances are gradually distributed to other regions, cells, or cell groups. Certainly the localized entry of specific sub-

stances is not of fundamental importance as a direct factor in originating the specific regional differentiations of organismic pattern. Gravity may conceivably be a factor in distributing and localizing specifically different substances on a basis of weight and so in initiating differentiation. The question of the relation of gravity to differentiation in organisms has been the subject of much investigation and discussion. It has long been known that in many plants the localization of regions of outgrowth of roots and stems may be determined in part by gravity. Loeb (’91) has maintained that localization of regions of outgrowth of stem-axes and of stolon-axes is determined by gravity in the hydroid Antennularia, but the later work of Morgan (01) and Stevens (’02, ’10) has shown at least that other factors than gravity may determine this localization. Moreover, a similar localizing action of gravity has not been observed in other animals.

The localizing action of gravity in plants appears to be a general predisposing rather than a definitely localizing action. It may favor or determine outgrowth of roots or rhizoids in a certain general region of the plant and of shoots in another region, but so far as is known it does not determine the localization or the polarity of individual root axes or bud axes. For example, in a piece of willow stem as well as various other plants in horizontal position gravity favors development of roots on the under side and of shoots on the upper side, but although the action of gravity on all the cells along the mid line of the lower side must be the same, not all these cells give arise to roots, nor do all the cells of the mid line of the upper side give rise to shoots. In Bryophyllum also gravity does not determine buds nor root-forming regions, but merely favors the growth of preformed buds on the upper side of a stem and the development of roots from predetermined root-forming regions on the lower side. In certain plants which normally lie flat on the earth, e. g. certain liverworts, and in certain branches growing horizontally, gravity may determine the normal dorsoventrality.

It is by no means clear how gravity brings about such localizing effects in plants. Loeb (19, ’20) postulates an action on the distribution of sap in the case of Bryophyllum and a distribution or segregation of substances of some gort is commonly regarded as underlying such action. It is, however, a question of some interest whether the effect of gravity is the direct determination of specific material differences representing, for example, shoot and root as Loeb apparently assumes, or a determination of non-specific dynamic condition. Segregation of inert substances in one region, for example, may de-

termine a decrease in rate of dynamic change in the region in which the substances accumulate, and an increase in the region from which they are removed. If the distribution of the sap in the plant is directly influenced by gravity as Loeb assumes, the significance of the distribution may be dyanmic rather than material and specific. In fact there is no conclusive evidence that the effect of gravity on organismic pattern is exerted by localization of specific “formative” materials. So far as the facts go such distributing or segregating action of gravity may equally well be regarded as merely a physical basis for non-specific dynamic differences. The fact that light is far more effective than gravity in determining polarity and symmetry in plants is also significant in relation to the dynamic conception of organismic pattern.

In the light of these considerations it appears at least doubtful whether specific material differences in constitution of different protoplasmic regions are in any case primary factors in organic pattern. Moreover, if they were, we should expect to find axial relations even more diverse than in crystal forms, instead of only the three fundamental types of relation, radiate, polar, and bilateral as the basis of all spatial and regional organismic pattern.

Even more convincing than these general considerations are the data of reconstitution of new individuals from parts of others. Such processes as the development of whole embryos from one of the first two or four cells of the dividing egg, of whole animals from small fragments of the bodies of hydroids, flatworms, etc., are not readily accounted for in terms of specific material pattern. Either Driesch is right in turning to vitalism for an interpretation, or else these processes must be interpreted in terms of a dynamic pattern, primarily quantitative, rather than in terms of specific materials. That is tosay, the pattern originates in the first instance as a dynamic differential of degree, rather than of kind, e. g., an excitation-transmission gradient resulting from the local or differential action of an external factor and the specific material differentiations result secondarily from the regional differences in relation of the specific constitution of the protoplasm to the dynamic pattern. To sum up, the evidence points clearly to a non-specific, dynamic factor as the most important factor in the origin of organismic pattern. Excitation is such a factor and I have already pointed out (pp. 50-52) that local or differential excitation gives rise, at least temporarily, to an organismic pattern. The question whether such an excitation-transmission pattern may become more or less permanent and constitute a physiological axis and a basis for differentiation is considered in later chapters.

It is of course evident that for any sort of behavior of the organism as a whole some kind of integrative pattern must be present. The behavior of the organism as a whole must result first from the pattern already present and second from the possibilities of further development and integration in response to particular external factors which the pattern presents. The excito-motor behavior pattern at any given moment may be only one of an indefinite number of such patterns possible on the basis of the general pattern of the organism, and its particular character may depend on many different factors besides the general pattern, e. g., the localization, intensity, duration, form of energy, etc., of the external agent and the physiological condition or state of the organism as determined by the effects of preceding or simultaneous reactions. Before attempting to analyze organismic pattern in general it seems desirable to call attention to its relation to the behavior of the organism as a whole, particularly excito-motor behavior. In Chapter IV it was pointed out that the fundamental integrative relation of physiological character is a relation of dominance and subordination and that this relation may appear in three spatial patterns, the completely radiate or spherically symmetrical, the polar, and the bilateral, and in various combinations and modifications of these. The present chapter is a very brief and fragmentary consideration of the significance of these fundamental factors of organismic pattern as a basis of behavior patterns in the organism.

It scarcely need be repeated that the physiological relation of dominance and subordination between different parts of the organism lies at the very foundation of orderly and definite reaction of the organism as a whole to its environment. In its absence such reaction would be quite impossible, there would be no reflex arcs, no coérdination, and any reaction of the organism as a whole could be referred only to some sort of preéstablished harmony or to some metaphysical

integrating principle, such as Driesch’s entelechy. This possibility of one molar region of a cell or a cell mass determining what shall occur in another region at a greater or less distance from it, underlies all except perhaps the simplest processes of reaction to environment, those in which reaction is apparently limited to the region directly affected by the external factor. Even in such cases, however, there is probably some transmission or transport from the region primarily concerned to others. In fact, as soon as regional differences in excitation or in chemical constitution arise in protoplasm the relation of dominance and subordination appears in some form. It is an essential physiological factor in making the organism an orderly and in- _ tegrated whole capable of behaving as a unit with reference to its

The spatial plan of the organism is obviously a factor in its behayior as an organism. The spherically symmetrical organism behaves in general differently from the axiate-radiate form and this again differently from the axiate-bilateral form and the spiral and asymmetric modifications also affect behavior in one way or another. In the case of a spherically symmetrical organism, if an external factor acts locally on a part of the surface or differentially on different parts of the surface, the reaction of the organism must either be purely local on that part of the surface directly affected or else it must give rise to an axiate pattern, which may be either temporary or permanent. The purely local reaction, if it ever occurs, is not organismic in character and needs no consideration here. With the appearance of an axiate pattern, even if only temporarily, the organism, if motile, may move toward, or away from the external factor, or if not motile it may show a differential in growth rate or other processes with respect to the external factor.

The case of Ameba will serve for illustration. So far as we know, Ameba possesses no fixed, permanent axiate pattern, but as a whole is essentially a spherically symmetrical organism. Consequently all regions of the surface are primarily alike and any region may react like any other by giving rise to a pseudopod or by retracting pseudopods already present. Any region of the surface may become temporarily an “anterior” end, and when the animal reacts to an external factor by change in direction of movement the body does not turn about so that the same region is in advance in the new direction, but another region becomes the chief region of pseudopod extension, and

so functionally anterior (Fig. 12). Hyman (’17) has found that each pseudopod of Amba possesses for the time being the graded quantitative differences characteristic of a simple physiological axis. The pseudopod represents then a temporary axiate pattern. In the physiological condition or species often called Ameba limaz in which the whole body is advancing in one direction and the anterior region is a single blunt pseudopod (Fig. 13), the whole body has acquired, for the time being, an axiate pattern. Such a pattern is also present to some degree, though less distinct and perhaps not involving the whole body, in many individuals advancing in a definite direction with pseudopod extension chiefly or only in the general direction of movement (Fig. 14). But even in such cases the protoplasm may change its position with respect to the pattern, so that the anterior end or any other level of the axis represents a physiological condition, not a definite region or portion of the protoplasm. In those forms which advance by means of a rolling movement, a particular region of the ectoplasm, as indicated by particles adhering to it, oceupies successively every level from anterior to posterior and then from posterior to anterior (Fig. 15). In all these cases the axiate pattern persists for the time being, but the material changes position from moment to moment. In Ameba, however, even the axiate patterns are not permanent, but are merely reactions to differentials in certain environmental factors. They are in fact very evidently behavior patterns in the strict sense, excito-motor patterns, in protoplasm as material and as the action of the external factors changes they undergo change. An axis in a new direction may replace the earlier axis, or the axiate pattern may give place to radiate pattern.

Apparently the only sort of organismic pattern that persists in Ameba is the surface-interior pattern, and all the other patterns are temporary functional modifications of this primary pattern. They represent, in short, the various possibilities of behavior on the basis of a surfaceinterior pattern in certain kinds of protoplasm.! The egg or spore of the alga Fucus evidently consists of a very different kind of protoplasm from that of Ameba, for it gives rise to a multicellular plant, and its behavior when subjected to the differential action of an external factor, viz., light, is strikingly different from that of Amwba. Whether or not this °& possesses physiological polarity at the time of extrusion from the parent plant is uncertain. There is no structural or functional indication of such polarity and under the usual conditions in nature the axis of the thallus to which

1 See Herrick’s discussion of the behavior of Ameba, Herrick,’ 24, Chap. VI. Fic. 12A-D.—Negative reaction of Ameba to a mechanical stimulus: (A) and (B) reaction in which the change in direction is about ninety degrees; (C) and (D), reaction in which the change in direction is greater than ninety degrees (from Jennings, 04). Fra. 14.—Ameba angulata advancing in general direction of the arrows. The body as a whole is temporarily axiate, but axiation is less highly developed than in A. l- maz shown in Fig. 13 (from Jennings, ’04).

Fia. 15.—A rolling Ameba, A. verrucosa. The positions of the black dot indicate the movements of a particle attached to the surface (from Jennings, ’04). the egg gives rise has, at least in some species, no relation to any such polarity, but is determined by incident light (Farmer and Williams, 98; Winkler, ’00b; Kiister, ’06; Kniep, ’07; Hurd, 719, ’20). The first division of the egg, which gives rise to a larger thallus cell and a smaller rhizoid cell, occurs with cell wall perpendicular to the direction of incident light and the region toward the light becomes

Figs. 16-18.—Early development of the alga, Fucus: Fig. 16, outgrowth of rhizoid and first division of egg. Direction of light indicated by arrow; Fig. 17, stage of several cells; Fig. 18, many celled young thallus with rhizoid. the apical pole, the region away from the light the basal, or rhizoid pole of the thallus (Figs. 16-18). In the absence of light development is delayed, but a polarity may appear ‘sooner or later. Whether such polarity represents a polarity predetermined from the parent plant or a polarity determined by some other external factor than light is uncertain. Hurd (’19) has found that external factors other than light may determine the polarity of these eggs. When groups of eggs lie within 0.2 mm: of each other the apical poles of the members are determined on the side away from the center of the group, the rhizoid poles on the side

toward the center. It is not known what factor is concerned in these cases. This cell either possesses only a surface-interior pattern when it leaves the parent plant, or any polarity it may have is usually replaced by a new one. If the cell is exposed to light of a certain minimum intensity for a certain minimum time the action of light determines, _ not a transitory differential excitation with directed locomotion, as in Ameba, but a new axiate organismic pattern which persists and determines growth and form of the plant throughout its life. The appearance of this new axiate pattern and its consequences are just as truly behavior as is the directed locomotion of the Ameba in reaction to light. The Fucus egg possesses a certain organismic pattern when it leaves the parent plant, but it is subjected to the differential action, that is, it undergoes a new experience. To this experience it reacts by the development of an axiate pattern which persists and becomes an important physiological factor in the further behavior of the individual. Here then the later reactions of the plant are modified by the effect of its reaction when first exposed to light after extrusion from the parent plant. The change of pattern determined in the cell by its primary reaction to light becomes an essential physiological factor in determining its later behavior.

Something of the same sort must occur in every case of modification of behavior by a previous reaction. The earlier reaction must have determined changes of some sort in the pattern, which persist and so become a factor in determining the character of later reactions. Such determination of polarity by incident light in Fucus, or in any other plant (see for example Stahl, ’85; Noll, ’00; Winkler, ’00 a), even though it does not result in locomotion and its effects are to a considerable extent morphological, represents the behavior of a certain kind of pattern in a certain kind of protoplasm, no less than the movement of Ameba away from the light. Both are reactions to an external factor and in both the kind of reaction depends primarily upon the constitution of the protoplasm and the pattern which it already possesses.

In organisms in which an axiate pattern is already present at the beginning of embryonic development, however it may have arisen, it, becomes a factor in the later behavior. In general in sessile forms the apical end of the polar axis is the free end and the dominant region of the body. This is true both of the growing tip in plants and of the apical region in sessile animals, so far as data are at hand. In hydroids the relations of dominance and subordination between the different parts of the colony are apparently much the same as in plants (Child, 19 b). In both the plants and many sessile animals new axes may arise by budding and each axis becomes the basis of an axiate behavior pattern which is subject to more or less modification by the relation of any particular axis to the other axes of the system. In the conifer, for example, the growing tip of the lateral branch reacts differently from the tip of the main stem. It grows in a more or less horizontal direction and is in most forms more or less bilaterally sym-

Figs. 19-21.—Reaction of conifer to removal of growing tip: Fig. 19, apical region of fir with young lateral branches forming a whorl about main axis; Fig. 20, main tip has been removed and two of young lateral branches have turned upward. One or both will replace main stem; Fig. 21, reaction in an older branch. Lower part of branch developed before removal of tip retains the bilateral form and the direction of a lateral branch, but later growth occurs in vertical direction and this part of branch is radially symmetrical and continues growth as the main axis while other branches which do not change direction of growth retain bilaterality.

metrical or dorsoventral, 7. é., Secondary branches arise only laterally on it. If, however, the growing tip of the main stem is removed the action of the uppermost lateral branch or branches undergoes change. The direction of growth becomes vertical instead of horizontal and the branch becomes radially instead of bilaterally symmetrical (Figs. 19-21). Experimental data along this line for the hydroids are not yet at hand, but many facts indicate that the relations in the hydroid colony are essentially similar, As regards the corals, however, some facts are known. Wood-Jones (12, pp. 82-83, 111-116) has shown that in the staghorn coral the relations are very similar to those in the plant axis. The apical zooid is dominant, radially symmetrical and gives rise by budding to the bilaterally symmetrical lateral zooids which do not bud at all under ordinary conditions. But if the apical zooid is removed or if the branch attains a certain length, one or more of the lateral zooids may transform into a dominant apical zooid

and become the tip of a new branch, changing its symmetry in the process from bilateral to radial and beginning to bud. In some forms the polar pattern of the earlier stages may disappear and give place to another. In many hydroids, for example, the apical end of the free swimming planula (Fig. 22) becomes the attached end of the hydroid and the new apical end _ develops as a bud from the original basal end (Figs. 23, 24). Discussion of the physiological factors concerned is postponed, but it may be noted that in both the planula and the later hydroid the _ polar pattern constitutes the basis of the behavior pattern, though the reaction complex is different in the two stages.

Fias. 22-24.—Development of hydroid from planula of Phialidiwm: Fig. 22, free swimming planula, locomotion in direction of arrow; Fig. 23, attachment of planula by original apical end; Fig. 24, development of hydranth as a bud from original basal end of planula. The planula swims with apical end in advance and finally becomes attached by this end, while the hydranth which arises from the basal end of the planula reacts to external factors by movement, extension and contraction of tentacles and body.

Among animals the axiate radiate pattern appears in two chief modifications - the coelenterate (Figs. 4, p. 38, 24) and the echinoderm types (Figs. 5, p. 38, 25-32, pp. 65-67). The apico-basal axis determines certain relations to external factors in position and locomotion and the radiate symmetry becomes the basis of other relations. In the sea anemone, the hydroid (Fig. 24), or the jellyfish (Fig. 4) any region of the circumference, e. g., any tentacle, which is directly excited by an external factor, such as contact with food in the case of the tentacle, may become for the time being dominant over all other regions of the circumference and determine their behavior. Such a relation arises when food is caught by one or a few tentacles. The excitation of these tentacles brings about a codrdinate reaction of adjoining or even of all tentacles, which assist in holding the food and in carrying it to the mouth which also reacts as a subordinate component of the system. At another time another tentacle or tentacle group may be the dominant component. In certain unattached sea anemones which are able to creep about (e. g., the Cerianthide) there are indications of a bilateral differential in the radiate pattern. The creeping surface is in a particular radius and the structure shows indications of bilaterality with respect to this radius. Certain other traces of bilaterality appear in other forms. In the free-swimming jellyfish the apico-basal, polar pattern determines locomotion in the