greater the number of ommatidia and the more convex the surface of the eye, it is very probable that only ants with well developed eyes, like Formica, Pseudomyrma, etc., can distinguish objects by means of these organs. Wasmann's experiments (1899g) indicate that workers of various species of Formica can see resting objects as large as a finger at a distance of 5-10 cm., but that they are unable to see small objects, like beetles, at a greater distance than 4-5 mm. My own observations tend to confirm these statements. Moving objects are, of course, much more readily perceived. Indirect evidence of visual discrimination in ants is furnished by the mimetic coloration and form of certain myrmecophiles (see Chapters XXI and XXII). Undoubtedly male ants, which always have very large, convex eyes, are able to see the flying females at a considerable distance. The function of the ocelli, so highly developed in the males and females, has not been determined. It has been suggested that they may be of use in seeing objects at very close range and in dark places, like the galleries of the nest.

On the whole, we are led to conclude that vision in worker and female ants is very poorly developed, compared with the chemical and mechanical senses (contact-odor and the perception of vibrations). Indeed, ant behavior is so profoundly influenced by these senses, that it may be said to differ fundamentally, not only from the behavior of man and the higher mammals, but even from that of such closely allied Hymenoptera as the bees and wasps.

CHAPTER XXIX

THE INSTINCTIVE BEHAVIOR OF ANTS

"Est sind keine anderen als die Erscheinungen des thierischen Instinctes, die für jeden nachdenkenden Menschen zu den allergrössten gehören-wahrer Probirstein ächter Philosophie."-Schelling, "System der gesammten Philosophie," I Bd.

"Der Instinkt ist nicht Resultat bewusster Ueberlegung, nicht Folge der körperlichen Organisation, nicht blosses Resultat eines in der Organisation des Gehirns gelegenen Mechanismus, nicht Wirkung eines dem Geiste von aussen angeklebten todten, seinem innersten Wesen fremden Mechanismus, sondern selbsteigene Leistung des Individuums, aus seinem innersten Wesen und Charakter entspringend."-E. von Hartmann, "Philosophie des Unbewussten," 9th ed., 1882.

If ants exhibited merely the reflexes, or such brief and simple responses to sensory stimuli as we have been considering in the preceding chapter, their lives would flow on with the same monotonous regularity as those of many other insects and the lower invertebrates in general. In addition to these reflexes, however, ants manifest more complicated trains of behavior, the so-called instincts; and both these and the reflexes may be affected with a certain modifiability or plasticity which, in its highest manifestations, has been called intelligence. Leaving for my last chapter a consideration of this latter aspect of behavior, I shall here confine myself to the instincts.

Many attempts have been made to define instinct, but it is evident that none of these could be completely successful, because instinct transcends intelligence and has its mainspring in the depths of the lifeprocess itself. Perhaps as good a formal definition as I am able to give is the following: An instinct is a more or less complicated activity manifested by an organism which is acting, first, as a whole rather than as a part; second, as the representative of a species rather than as an individual; third, without previous experience; and fourth, with an end or purpose of which it has no knowledge. This definition will satisfy the person of scholastic mind, but to the biologist it is a mass of obscurities; for it is certain that the man lives not who can tell where the whole begins and the part leaves off in a living organism, or can frame a satisfactory definition of a living individual or a species; and the intellect abdicates when it is called upon to grasp an activity that is unconsciously purposeful.

In all probability these very obscurities have attracted many stu

dents to the study of instinct. At any rate, there is no end of the literature on the subject.1 Instinct could not, of course, be studied by so many authors without much controversy, and the employment of the word in many different senses. This is pardonable, at least to some extent, since the subject itself presents no less than four aspects, according as it is studied from the ethological, physiological, psychological or metaphysical points of view. From the first two of these instinct is open to objective biological study in the form of the "instinct. actions." These may be studied by the physiologist merely as a regularly coördinated series of movements depending on changes in the tissues and organs, and by the ethologist to the extent that they tend to bring the organism into effective relationship with its living and inorganic environment. But that these movements have a deeper origin in psychological changes may be inferred on the basis of analogy from our own subjective experience which shows us our instincts arising as impulses and cravings, the so-called "instinct-feelings "; and these in turn yield abundant material for metaphysical and ethical speculation.

Modern biological writers naturally wish to restrict the term instinct to the instinct-actions, whereas scholastic, psychological, metaphysical and theological writers throw the emphasis on the instinct-feelings. That this was the original meaning of the word is shown by its derivation from the Latin instinguere, to incite, and its probable relation to the Greek evoTiety. The contrast between the subjective and objective aspects of instinct is brought out sharply in Descartes' notion of the animal as an automaton, a conception which has profoundly affected biological and even theological thought. The following passage, quoted from the Seventh Bridgewater Treatise by the Rev. William Kirby, will make this clear: "An eminent French zoologist [Virey] has illustrated the change of instincts resulting from the modi

'During the past ten years I have read a small library of books on instinct. Among these the following have been most suggestive from the physiological point of view: Chapter XIII of Loeb's “Physiology of the Brain," Driesch's "Die Seele' als Elementarer Naturfaktor," and the second volume of his "Science and Philosophy of the Organism"; from the psychological point of view: G. H. Schneider's "Der Thierische Wille," Wundt's "Vorlesungen uber die Menschen- und Thierseele," Chapter XXIV of the second volume of Wm. James's "Principles of Psychology," and Groos's "Die Spiele der Thiere"; from the metaphysical point of view: Chapter XXVII of the second volume of Schopenhauer's "Welt als Wille and Vorstellung," Chapter III of von Hartmann's "Philosophie des Unbewussten" and Chapter II of Bergson's "L'Évolution Créatrice"; from the scholastic and doctrinaire points of view: Reimarus's "Allgemeine Betrachtungen uber die Triebe der Thiere" (1798), Joly's “L'Instinct, ses Rapports avec la Vie et avec l'Intelligence," Wasmann's "Instinct und Intelligenz im Thierreich," and Supplement A of Maher's "Psychology: Empirical and Rational."

fication of the nervous system, which takes place in a butterfly in the transit to its perfect or imago state from the caterpillar, by a novel and striking simile. He compares the animal to a portable or hand organ, in which, on a cylinder that can be made to revolve, several tunes are noted; turn the cylinder and the tune for which it is set is played; draw it out a notch and it gives a second; and so you may go on till the whole number of tunes noted on it have had their turn. This, happily enough, represents the change which appears to take place in the vertebral cord and its ganglions on the metamorphoses of the caterpillar into the butterfly, and the sequence of new instincts which result from the change. But if we extend the comparison, we may illustrate it by the two spheres of organized beings that we find on our globe, and their several instinctive changes and operations. We may suppose each kingdom of nature to be represented by a separate cylinder, having noted upon it as many tunes as there are species differing in their respective instincts-for plants may be regarded, in some sense, as having their instincts as well as animals-and that the constant impulse of an invisible agent causes each cylinder to play in a certain order all the tunes noted upon it; this will represent, not inaptly, what takes place with regard to the development of instincts in the vegetable and animal kingdoms, and our simile will terminate in the inquiry, whose may be that invisible hand that thus shakes the sistrum of Isis, and produces that universal harmony of action, resulting from that due intermixture of concords and discords, according to the will of its Almighty Author, in that infinitely diversified and ever-moving sphere of beings we call nature." Kirby concludes that the powers. which turn the hand organ of instinct are "the physical Cherubim of the Holy Scriptures, or the heavens in action, which under God govern the universe."

This specimen, extracted from the theological dust-bin, derives its interest from the fact that it is a caricature of views that are still held on the subject of instinct. It is, in fact, more like the scholastic conception of instinct than would appear at first sight. Considering for the present only the objective, or hand organ, portion of the above simile, and neglecting the "physical Cherubim," who keep turning the handle, we see that the peculiarity of instinct-the combination of complexity with automatic or mechanical fixity-that impressed earlier thinkers is the one that still arrests our attention. Indeed, this peculiarity is responsible both for the "lapsed intelligence" and the "reflex" hypotheses of instinct. The former of these seems to be moribund, the latter, according to which instincts are merely chain reflexes ("Kettenreflexe"), still flourishes, at least, in our biological

laboratories. Spencer, Loeb, Bethe, Driesch and others have supported this hypothesis with much clean-cut argument; but the way to its conception was prepared long ago by Claude Bernard in his description of certain complex physiological activities, like those of the alimentary tract, as "mouvements reflexes régulièrement enchaînés." The difficulty with the hypothesis is its schematism, for while we may admit that an instinct may be described as a compound reflex, we must also admit that it is more than this, since the reflexes are not merely strung along in sequence, but constitute an organized system of coördinated activities which coimplicate and interpenetrate one another, so to speak, and grow and change by modification in toto, or by intersusception and not by simple apposition of new activities.

Biologists find it increasingly difficult to draw a hard and fast line between instinct and reflexes, or between either of these and the simple vital activities of protoplasm. The definition of instinct cited above is perfectly applicable to a unicellular organism, or to a single Metazoan cell, considered as a whole. It is difficult or impossible, moreover, as Loeb and Driesch have insisted, to dissociate the instinctive activities from those of growth and development. This is due to the fact that instinct is so intimately and inextricably involved in the structure of the organism. As Bergson says: "It has often been remarked that most instincts are the prolongation, or better, the achievement, of the work of organization itself. Where does the activity of instinct begin? Where does that of nature end? It is impossible to say. In the metamorphoses of the larva into the nymph and into the perfect insect, metamorphoses which often require appropriate adaptations and a kind of initiative on the part of the larva, there is no sharp line of demarcation between the instinct of the animal and the organizing work of the living matter. It is immaterial whether we say that instinct organizes the instruments which it is going to use, or that the organization prolongs itself into the instinct by which it is to be used." The spinning of the cocoon by the larval ant is a good example of the kind of instinct to which Bergson refers. From one point of view this is merely an act of development, and the cocoon, or result of the secretive activity of the sericteries and of the spinning movements of the larva, is a protective envelope. But an envelope with the same protective function may be produced by other insect larvæ simply as a thick, chitinous secretion from the whole outer surface of the hypodermis. Here, too, we have an activity which, though manifested in a very different way, is even more clearly one of growth and development. And when. the workers of Ecophylla or Polyrhachis use their larvæ for weaving the silken envelope of the nest, as described in Chapter XIII, we have