ANIMAL BEHAVIOUR CHAPTER I ORGANIC BEHAVIOUR I.—BEHAVIOUR IN GENERAL WE commonly use the word "behaviour" with a wide range of meaning. We speak of the behaviour of troops in the field, of the prisoner at the bar, of a dandy in the ball-room. But the chemist and the physicist often speak of the behaviour of atoms and molecules, or that of a gas under changing conditions of temperature and pressure. The geologist tells us that a glacier behaves in many respects like a river, and discusses how the crust of the earth behaves under the stresses to which it is subjected. Weather-wise people comment on the behaviour of the mercury in a barometer as a storm approaches. Instances of a similar usage need not be multiplied. Frequently employed with a moral significance, the word is at least occasionally used in a wider and more comprehensive sense. When Mary, the nurse, returns with the little Miss Smiths from Master Brown's birthday party, she is narrowly questioned as to their behaviour; but meanwhile their father, the professor, has been discoursing to his students on the behaviour of iron filings in the magnetic field; and his son Jack, of H.M.S. Blunderer, entertains his elder sisters with a graphic description of the behaviour of a first-class battle-ship in a heavy sea. The word will be employed in the following pages in a wide and comprehensive sense. We shall have to consider, not only the kind of animal behaviour which implies intelligence, sometimes of a high order; not only such behaviour as animal play and courtship, which suggests emotional attributes; but also forms of behaviour which, if not unconscious, seem to lack conscious guidance and control. We shall deal mainly with the behaviour of the animal as a whole, but also incidentally with that of its constituent particles, or cells; and we shall not hesitate to cite (in a parenthetic section) some episodes of plant life as examples of organic behaviour. Thus broadly used, the term in all cases indicates and draws attention to the reaction of that which we speak of as behaving, in response to certain surrounding conditions or circumstances which evoke the behaviour. The middy would not talk of the behaviour of his ship as she lay at anchor in Portland harbour; the word is only applicable when there is action and reaction as the vessel ploughs through a heavy sea, or when she answers to the helm. Apart from gravitation the glacier and the river would not "behave in a similar manner." Only under the conditions comprised under the term "magnetic field" do iron filings exhibit certain peculiarities of behaviour. And so, also, in other cases. The behaviour of cells is evoked under given organic or external conditions; instinctive, intelligent, and emotional behaviour are called forth in response to those circumstances which exercise a constraining influence at the moment of action. It is therefore necessary, in a discussion of animal behaviour, that we should endeavour to realize, as far as possible, in every case, first, the nature of the animal under consideration; secondly, the conditions under which it is placed; thirdly, the manner in which the response is called forth by the circumstances, and fourthly, how far the behaviour adequately meets the essential conditions of the situation. From what has already been said it may be inferred that our use of the term "behaviour" neither implies nor excludes the presence of consciousness. Few are prepared to contend that the iron filings in a magnetic field consciously group themselves in definite and symmetrical patterns, or that sand grains on a vibrating plate assemble along certain nodal lines because they are conscious of the effects of the bow by which the plate is set in sounding vibration. But where organic response falls under our observation, no matter how simple and direct that response may be, there is a natural tendency to suppose that the behaviour is conscious; and where the response is less simple and more indirect, this tendency is so strengthened as to give rise to a state of mind bordering on, or actually reaching, conviction. Nor is this surprising : for, in the first place, organic responses, even the simplest, are less, obviously and directly related to the interplay of surrounding circumstances; and, in the second place, they are more obviously in relation to some purpose in the sense that they directly or indirectly contribute to the maintenance of life or the furtherance of well-being. Now where behaviour is complex and subserves an end which we can note and name, there arises the supposition that it may well be of the same nature as our own complex and conscious behaviour. Take for example the behaviour of the Slipper-animalcule, Paramecium, one of the minute creatures known to zoologists as Protozoa. The whole animal is constituted by a single cell, somewhat less than one-hundredth of an inch in length, the form and behaviour of which may be readily studied under the microscope. Thousands may be obtained from water in which some hay has been allowed to rot. The surface of the Paramecium is covered with waving hair-like cilia, by which it is propelled through the water, while stiffer hairs may be shot out from the surface at any point where there is a local source of irritation, as indicated at the top of the accompanying figure. Two little sacs expand and contract, and serve to drain off water and waste products from the substance of the cell. Food is taken in at the end of the funnel, shown in the lower part of the figure. The cilia here work in such manner as to drive FIG. 1.-Paramecium. the particles into and down the tube, and on reaching its inner end these particles burst through into the semi-fluid substance, and circulate therein. Just above the funnel there are two bean-like bodies, the larger of which is known as the macronucleus, the smaller as the micronucleus. The process of multiplication is by "fission," or the Idivision of each Paramecium into two similar animalcules. Not infrequently, however, two Paramecia may be seen to approach each other and come together, funnel to funnel; and in each the nuclei undergo curious changes. The macronucleus breaks up, and is scattered. The micronucleus in each divides into four portions, of which three break up and disappear; while the fourth again divides into two parts, one to be retained and the other to be exchanged for the similar micronuclear product of the other Paramecium. The retained portion and that received in exchange then unite to form a new micronucleus. M. Maupas concludes from his careful observations that, in the absence of such "conjugation" in the mid-period of life, Paramecia pass into a state of senility which ends in decrepitude and death. If this be so, conjugation is in them necessary for the continuance of a healthy race. Here we have what a zoologist would describe as a specialized mode of behaviour of the nuclei; and we have also the behaviour of the minute creatures (which contain the nuclei) as they approach each other and come together in conjugation. Can one wonder that the latter, at any rate, has been regarded as an example of conscious procedure? In truth we do not know in what manner and by what subtle influences the Paramecia are drawn together in conjugation. But it is scarcely logical to base on such ignorance any positive assertion as to conscious attraction. It is better to confess that here is a piece of organic behaviour, the exact conditions of which are at present unexplained. We may take from the writings of Dr. H. S. Jennings, of Harvard, some account of other modes of behaviour among Paramecia. They largely feed upon clotted masses of bacteria. If a number are placed upon a glass slip, together with a small bacterial clot, they will be seen to congregate around the clot and to feed upon it. All apparently press in so as to reach it, or get as near it as possible. And if a number be placed on another slide without any clot, they soon collect in groups in one or more regions, as in Fig. 2, III. It appears as if they were actuated by some social impulse leading them to crowd together and shun isolated positions. Nay, more; it seems as if, after thus collecting and crowding in to some centre of interest, the attractive influence gradually waned; the group spreads, and the Paramecia are less densely packed; the assembly scatters more and more, but still seems to be retained by an invisible boundary beyond which the little creatures do not pass. Furthermore, if kept in a jar, the Paramecia crowd up towards the surface where the bacteria clots are floating; and if, beneath the cover glass of a slip on which they are under microscopic examination, a drop of liquid be introduced through a very fine tube, they will seem either to be attracted to it, as in Fig. 2, I., or repelled from it, as in Fig. 2, II., according to its nature. From alkaline liquids they are * See "The Psychology of a Protozoon," in the Amer. Jour. of Psychology, vol. x., No. 4, July, 1899, and the fuller papers there quoted. |