V •. ■.- -•• .fe?l ^^^^i oi PRINCETON, N. J. *'»S. Division .... A LL i rTTI^ i 5/5^//^ Section ^ -R l_ Number • P»o™c„ 0, B„,.,„«,. 0.„.0,„ = .. EMOT.O. W,.U lNTE..ECr. ,»r...JZr'."°:oeMC.r s. =, = -.. 50 50 (e>\ // 49 4S 48 /i/ 48 48 47 47 /.f/ 47 47 4" 46 * /v 4(. 46 45 0 rl 45 44 ^ 44 44 43 \t\ j^ c /^' 43 43 42 42 \>\ 41 X'iiX \i\ /j/ 41 40 40 V \ \a /■'V 40 40 39 3P \e;\ "^ \»\ /*/ 39 ,39 3« 38 i' \ \ 1^1 38 38 37 .37 \^ 1 c\ V\ /// /) 37 37 -35- 36 ) 1 * \.\ \-Vv^7 A/ 36 36 35 )i; /VV * v\ \^\v // 35 35 34 34 yyy \*\ \> / A/ 34 34 33 * \>\ \-\ /V 33 33 32 ,2 !•?/' 0 \A \"\ /y 32 32 }'■ {"■ C ^ V-\ \A/y 3" y 30 \ \ 1^ .30, 30 2g \\ \ \ \ v \ / /Y 2^ Recognition of Pictttres, Understanding of words. Dreaming Birds. 5 monih. 25 \<\ \» \ // 24 i m,-~.ch.. 24 23 ,, \ \ ^ \''\ /v 2-, Recognitiiin of persons. Reptiles and Cephalopodi , ^,o•.l^. 23 Affection, 77 \\ \' \ /■/ 22 R..».„. Higher Cr.,ac,a. ■ ».xeU. 22 21 Jealoo^y. Anger. Play. 2, ill \ \/»/ 21 Association by similarity. i.-.ee;j. 20 20 Parental affection. Social feelings, Sexual selection, Pugnacity, Industry, Curiosity. 70 — ^£iZI2i^o/v Of ik \ \ >/ ^ 20 Recognition of offspring. Secondary instincts. lOweeVi 19 ■Se.sual emotions without sexual selection. iq ~ — -i^fj^s er sf, "* ) y'^i^ IQ Ass,c,a,ionl.y contiguity. 3 weeks. 19 18 Surprise, Fear. IS J l^^J-^ iS Primar,' .ns.mcts. -s LarM of Insects. .\nnel,d.. 3 weels- 17 ■* ^\ ^> ,7 . Echinoderma,., , »ee<. ■7 .6 Tft' ^^ j^^ Ifi Ple„,r,s..„.lpa,„., J m ■s ,, = CKlenterai.-!. 15 * ^-" 14 '4 13 |, M ■3 12 17 12 Unkno»-n inmiaK " 11 ,, ,, proboblv Cielcn.erj,., n 10 "uT '* ~i in perhaps extmc. Embr)-o, 10 9 ^ ■- q 9 S 8 Lh \ 8 _L 7 At*A -i.=\ 7 Non-oep.mis adjustments. Unicellular organtsni,. ± /v / \ " -\ 6 5 y.-v/ \— \ 5 ,| ^'^,\'/ \'.'-v 3 ■ X J , p,„iopla 46 MENTAL EVOLUTION IN ANIMALS. deal. But here we have to remember that besides size or mass, there must certainly be a no less important factor to be L taken into account — that, namely, of structure or complexity. Now we really know so little about the relations of intelli- gence to neural structure, that I do not think we are justified in forming any very strong conclusions a priori concerning the relation of intelligence to mere size or mass of brain. Know- ing in a general way that mass 7:'/?is structure of brain is necessary for intelligence, we do not know how far the second of these two factors may be increased at the expense of the first. And, as a mere matter of complexity, or of riiultum in paTvo, I am not sure that even the brain of an ant deserves to be considered more wonderful than the ovum of a human being. Lastly, in this connection it may be as ' well to observe that there is as good evidence to show the importance of cerebral structure as a factor in determining the level of mental development, as there is to show the importance of cerebral mass. Throughout the vertebrated series of animals the convolutions of the brain — which are the coarser expressions of more refined complexities of cerebral structure — furnish a wonderfully good general indi- cation of the level of intelligence attained; while in the case of ants Dujardin says that the degree of intelligence exhibited stands in an inverse proportion to the amount of cortical substance, or in direct proportion to the amount of the peduncular bodies and tubercles. In view of these con- siderations, therefore, I do not feel that the supposed diffi- culty, which I have thought it desirable to mention, is one of any real solidity. THE ROOT-PRIXCIPLES OF MIND. CHAPTER IV. The Eoot-principles of Mind. Although tlie phenomena of Mind, and so of Choice, are both complex, and as to their causation obscure, I think we liave now seen that we are justified in behevino- that they all present a physical basis. That is to say, whatever opinion we may happen to entertain regarding the ultimate nature of these phenomena, in view of the known facts of physiology, we ought all to be agreed concerning the doctrine that the mental processes wdiicli w^e cognize as subjective, are the psychical equivalents of neural processes which we recog- nize as objective. As already stated, I have elsewhere con- sidered the various hypotheses concerning the nature and the various attempts at an explanation of this equivalency between mental processes and neural processes ; but here I desire to consider the fact of this equivalency merely as a fact. It will therefore signify nothing to my discussion whether, with the materialists, we rest in this fact as final, or endeavour, with men of other schools, to seek an explanation of the fact of some more ultimate character. It is enough if w^e are agreed that every psychical change of which we have any experience is invariably associated with a definite physical change, wdiatever w^e may suppose to be the nature and significance of this association. Looking, then, at the phenomena of Mind as invariably presenting a physical, or, as we may indiiferently call it, a physiological side, I shall endeavour to point out wdiat I con- ceive to be the most ultimate principle of physiology which analysis show^s to be common to them all. On the mental side, as w^e have already seen, we have no difficulty in dis- tinguishing this ultimate principle, or common characteristic, as that which we designate by the terra Choice. Now if the power of choice is the distinctive peculiarity of a mental 48 MENTAL EVOLUTION IN ANIMALS. being, and if, as we have taken for granted, every change of Mind is associated with some change of Body, it follows that this distinctive peculiarity ought to admit of being trans- lated into some physiological equivalent. Further, if there is any such physiological equivalent to be found, we should expect to find it much lower down in the scale of physio- loo-ical development than in tlie functions of the human brain. For not only do the lower animals manifest, in a lono- descending scale, powers of choice which gradually fade away into greater and greater simplicity ; but we should be led a 2^riori to expect, if there is a physiological principle which constitutes the objective basis of the psychological principle, that the former should manifest itself more early in the course of evolution than the latter. For, whatever views we may entertain concerning the relation of Body and Mind, there can be no question, on the basis of the evolution theory which I assume, that, as a matter of his- torical sequence, the principles of physiology were prior to those of psychology ; and therefore, if in accordance with our original agreement we allow that the latter have a phy- sical basis in the former, it follows that the principles of physiology, which now constitute the objective basis of choice, whatever they may be, probably came into operation long before they were sufficiently evolved thus to constitute the foundation of psychology. Now I think that the d ]3riori expectation thus briefly sketched is fully realized in the occurrence of a physiological principle, which first appears very low down in the world of life, and which, in its relation to psychology, has not yet received the attention which it deserves. I may best state the principle by giving an example. I have observed that if a sea-anemone is placed in an aquarium tank, and allowed to fasten upon one side of the tank near the surface of the water, and if a jet of sea water is r^ade to play continuously and forcibly upon tlie anemone from above, the result of course is that the animal becomes surrounded with a turmoil of water and air-bubbles. Yet, after a short time, it becomes so accustomed to this turmoil that it will expand its tentacles in search of food, just as it does when placed in calm water. If now one of the expanded tentacles is gently touched with a solid body, all the others close around that body, in just the same way as they would were they expanded in calm THE ROOT-PPJNCIPLES OF MIND. 49 water. That is to say, the tentacles are able to discrimi- nate between the stimulus which is supplied by the turmoil of the water and that which is supplied by their contact with the solid body, and they respond to the latter stimulus notwithstanding that it is of incomparably less intensity than the former. And it is this power of discriminating between stimuli, irrespective of their relative mechanical inten- \ sities, that I regard as the objective principle of which we are in search ; it constitutes the physiological aspect of Choice. A similar power of discriminative response has long been known to occur in plants, though tlie most carefully observed facts with regard to this interesting subject are those which we owe to the later researches of llr. Darwin and his son. The extraordinary delicacy of discrimination which these researches show the leaves of plants to exercise between darkness and light of the feeblest intensity, is not less wonderful than the delicacy of discrimination which they show the roots of plants to exercise in feeling about for moisture and lines of least resistance in the soil. But in the present connection the most suggestive facts are those which have been brought to light by Mr. Darwin's previous re- searches on the climbing and insectivorous plants. For, from these researches it appears that the power of discrimi- nating between stimuli, irrespective of relative mechanical intensity or amount of mechanical disturbance, has here proceeded to an extent that rivals the function of nerve- tissue, although the tissues which manifest it have not in structure passed beyond the cellular stage. Thus, the tenta- cles of Drosera, which close around their prey like the tentacles of a sea- anemone, will not respond to the violent stimulation supplied by rain-drops falling upon their sensi- tive surfaces or glands, while they will respond to an incon- ceivably slight stimulus of the kind caused by an exceedingly minute particle of solid matter exerting by gravity a con- tinuous pressure upon the same surfaces. For Mr. Darwin says, " The pressure exerted by a particle of hair, weighing only -j^] 40 of a grain, and supported by a dense fluid, must have been inconceivably slight. We may conjecture that it could hardly have equalled the millionth of a grain ; and we shall hereafter see that far less than the millionth of a grain of phosphate of ammonia in solution, when absorbed by a gland, acts on it and induces movement. ... It is D 50 MENTAL EVOLUTION IN ANIMALS. extremely doubtful whether any nerve in the human body, even if in an inflamed condition, would be in any way affected by such a particle supported in a dense fluid, and slowly brought into contact with the nerve. Yet the cells of the glands of Drosera are thus excited to transmit a motor impulse to a distant point, inducing movement. It appears to me that hardly any more remarkable fact than this has been observed in the vegetable kingdom." But the case does not end here. For in another insec- tivorous plant, Dionoea, or Venus' Fly-trap, the principle of discriminating between different kinds of stimuli has been developed in a direction exactly the opposite to that which obtains in Drosera. For while Drosera depends for capturing its prey on entangling the latter in a viscid secretion from its glands, Dionoea closes upon its prey with the suddenness of a spring-trap ; and in relation to this difference in the mode of capturing prey, the principle of discrimination between stimuli has been correspondingly modified. In Drosera, as we have seen, it is the stimulus supplied by continuous pressure that is so delicately perceived, while the stimulus supplied by wijMct is disregarded ; but in Dionoea the smallest impact upon the irritable surfaces, or filaments, is immediately re- sponded to, while the stimulus supplied even by compara- tively great pressure upon the same surfaces is wdioUy disregarded. Or, in Mr. Darwin's own words, '' Although the filaments are so sensitive to a momentary and delicate touch, they are far less sensitive than tlie glands of Drosera to pro- longed pressure. Several times I succeeded in placing on the tip of a filament, by the aid of a needle moved with extreme slowness, bits of rather thick human hair, and these did not excite movement, although they were more than ten times as long as those which caused the tentacles of Drosera to bend ; and although in this latter case they were largely supported by the dense secretion. On the other hand, the glands of Drosera may be struck with a needle, or any hard object, once, twice, or even thrice, with considerable force, and no movement ensues. This singular difference in the nature of the sensitiveness of the filaments of Dionoea and of the glands of Drosera evidently stands in relation to the habits of the two plants. If a minute insect alights with its delicate feet on the glands of Drosera, it is caught by the viscid secretion, and the slight, though prolonged pressure THE ROOT-PRIXCIPLES OF MIND. '51 gives notice of the presence of prey, which is secured by the slow bending of the tentacles. On the other hand, the sensi- tive filaments of Dionoea are not viscid, and the capture of insects can only be assured by their sensitiveness to a momentary touch, followed by the rapid closure of the lobes." So that in these two plants the power of discriminating between these two kinds of stimuli has been developed to an equally astonishing extent, but in opposite directions. But we find definite evidence of this power of discrimina- tive selection even lower down in the scale of life than the cellular plants ; we find it even among the protoplasmic organisms. Thus, to quote an instructive case from Dr. Car- penter : — " The Deep-Sea researches on which I have recently been engaged have not ' exercised ' my mind on any topic so much as on the following : — Certain minute particles of living jelly, having no visible differentiation of organs .... build up ' tests ' or casings of the most regular geometrical sym- metry of form, and of the most artificial construction . . . From the same sandy bottom, one species picks up the coarser quartz-grains, cements them together with phosphate of iron (?), which must be secreted from their own substance; and thus constructs a flask-shaped ' test ' having a short neck and a single large orifice. Another picks up the finer grains, and puts them together with the same cement into perfectly spherical ' tests ' of the most extraordinary finish, perforated with numerous small tubes, disposed at pretty regular inter- vals. Another selects the minutest sand-sprain and the terminal points of sponge-spicules, and works these up together — apparently with no cement at all, but by the ' laying ' of the spicules — into perfect spheres, like homoeo- pathic globules, each having a single fissured orifice." * Thus, co-extensive with the phenomena of excitability, that is to say, with the phenomena of life, we find this func- tion of selective discrimination ; and, as I have said, it is this function that I regard as tlie root-principle of Mind. I so regard it because, if we consider all the faculties of mind, we shall observe that the one feature which on their objective side they present as common, is this power of discriminating among stimuli, and responding only to those which, irrespec- tive of relative mechanical intensity, are the stimuli to which * Contemporari/ Review, April, 1873. D 2 52 MENTAL EVOLUTION IN ANIMALS. responses are appropriate. In order to see this, let us take the principal faculties of mind in their ascending order, and consider what they are, in their last analysis, upon their physiological side. First we have the organs of special Sensation, the physiological functions of which clearly con- stitute the basis of the whole structure psychological. Yet no less clearly, these functions in their last analysis are merely so many specially developed aptitudes of response to special modes of stimulation. Thus, for instance, the struc- ture of the eye is specially adapted to respond only to the particular mode of stimulation that is supplied by light, the ear to that which is supplied by sound, and so on. In other words, the organs of special sense are so many structures which have been variously and extremely differentiated in several directions, for the express purpose of attaining a severally extreme sensitiveness to special modes of stimula- tion without reference to any other mode. And this is merely to say that the function of an organ of special sense is that of sorting out, selecting, or discriminating the par- ticular kind of stimulation to which its responsive action is appropriate. J Again, many of the nervous mechanisms which minister to various Keflex Actions are only thrown into activity by special modes of stimulation. This is notably the case with those highly complicated neuro-muscular mechanisms which are thrown into activity only by the mode of stimulation which we caU tickling. Such instances are of special interest in the present connexion from the fact that the distinguishing peculiarity of this mode of stimulation consists in its being a stimulation of low intensity. The comparatively violent stimulation that is caused by the passage of food down the gullet, or by contact of the soles of the feet with the ground, is unproductive of any response on the part of the mechanisms which are thrown into violent activity by the gentlest possible stimula- tion of the same surfaces. Similarly with regard to Instincts. These, physiologically considered, are the activities of highly differentiated nervous mechanisms which have been slowly elaborated, through successive generations, for the express purpose of responding to some particular stimulus of a highly wrought character, and which, on its psychological side, is a recognition of the circumstances to which the instinctive adjustment is appropriate. And so with the Emotions. For, THE KOOT-PRINCIPLES OF MIND. 53 physiologically considered, the emotions are the activities of highly wrought nervous mechanisms, and these activities are only excited by tlie very special stimuli which, on their sub- jective side, we recognize as the particular kind of ideas which are appropriate to call up particular emotions. We do not laugh at a painful sight, nor does a ludicrous sight cause us to weep ; and this, physiologically considered, merely means that the nervous machinery whose action is accompanied by one emotion, will only respond to one kind of very specialized and complex stimulation ; it will not respond to another and probably in many respects very similar kind of stimulation, which, nevertheless, is competent to evoke re- sponses from another and probably very similar piece of nervous machinery. And thus, also, it is with Eeasoning and Judg- ment. Eeasoning, on its physiological side, is merely a series of highly complicated nervous changes, regarding which the , only thing we certainly know is, that not one of them can ; take place without an adequate physical accompaniment, and ■ therefore that on its physiological side a train of reasoning is a series of nervous changes, every one of wdiich must be produced by physical antecedents. And hence on its objec- tive side every step in a train of reasoning consists in a selective discrimination among all those exceedingly delicate stimuli w^hich, on their subjective side, we know as argu- ments. Similarly regarded. Judgment is likewise nothing more than the final result of the incidence of a vast number of very delicate stimuli ; and this final result, like all the intermediate steps of the reasoning which led to it, is nothing more than the exercise of a power to discriminate between the stimulus which on its subjective side we recognize as the right, and that which w^e similarly recognize as the wrong. Lastly, Volition, subjectively considered, is the faculty of consciously selecting motives ; and motives, objectively con- sidered, are nothing more than immensely complex and inconceivably refined stimuli to nervous action. If we turn from the ascending scale of mental faculties in man, to the ascending^ scale of mind in the animal king^- dom, we shall meet with further and still more definite evi- dence that the distinguishing property of mind, on its physiological side, consists in this power of discriminating between different kinds of stimuli, irrespective of their degrees of mechanical intensity. But, before giving a brief 54" MENTAL EVOLUTION IN ANL^L1LS. review of the evidence on this point, I may here meet a difficulty which has already arisen. The difficulty is that I began by showing it necessary to define Mind as the power of exercising Choice, and then proceeded to define the latter as a power belonging only to agents that are able to feel. Yet, on looking at the objective side of the problem, I pointed out that the physiological or objective equivalent of Choice is found to occur in its simplest manifestations at least as low down as the insectivorous plants, which are certainly not agents capable, in any proper sense of the term, of feeling. Therefore it seems that my conception of what constitutes Choice is in antagonism with my view that the essential element of Choice is found to occur among organ- isms which cannot properly be supposed to feel. And this antagonism, or inherent contradiction, is a real one, though I hold it to be unavoidable. For it arises from the fact that neither Feeling nor Choice appears upon the scene of life suddenly. We cannot say, within extensive limits, where either can properly be said to begin. They both dawn gradually, and therefore in our everyday use of these terms we do not w^ait to consider where they are first applicable ; we only apply them where we see their applicability to be apparent. But when we endeavour to use these same terms in strict psychological analysis, we are at once met Avith the difficulty of drawing the line where the terms are applicable and where they are not. There are two ways of meeting the difficulty. One is to draw an arbitrary line, and the other is [ not to draw any line at all ; but to carry the terms down through the whole gradation of the things until we arrive at the terminal or root-principles. By the time that we do arrive at these root-principles, it is no doubt true that our terms have lost all their original meaning ; so that we might as well call an acorn an oak, or an egg a chicken, as speak of a Dionoea feeling a fly, or of a Drosera ehoosing to close upon its prey. Yet this use, or rather let us call it abuse, of terms serves one important purpose if, while duly regarding the change of meaning which during their gradual descent the terms are made gradually to undergo^ we thus serve to emphasize the fact that they refer to things which are the product of a gradual evolution — things which came from other things as unlike to them as oaks, to acorns or chickens to eggs. And this is my justification for tracing back the root-principles of THE ROOT-PEINCIPLES OF MIND. 55 Feeling and of Choice into the vegetable kingdom. If it is true that plants manifest so little evidence of Feeling that the term can only be applied to them in a metaphorical sense, it is also true that the power of Choice wliich they display is of a similarly undeveloped character ; it is limited to a single act of discrimination, and therefore no one would think of applying the term to such an act, until analysis reveals that in such a single act of discrimination we have the germ of all volition. Let it therefore be understood that the difficulty which we are considering arises merely from the gradual manner in wliich the faculties in question arose. The rudimentary power of discriminative excitability which a plant displays is commensurate with the rudimentary power of selective adjustment which it manifests in its movements ; and, just as | the one is destined by developmental elaboration to become a self-conscious subjectivity, so the other is destined, by a similar elaboration, to become a deliberative volition. I shall now briefly glance at the ascending scale of organisms, with the view of showing that this proportional relation between the grade of receptive and that of executive ability is manifested throughout the series. I desire to make it plain that the power of discrimination which in its higher manifestations we recognize as Feeling, and the power of selective adjustment which in its higher manifestations we , recognize as Choice, are developed together, and throughout their development are commensurate. Amoeba is able to distinguish between nutritious and non- nutritious particles, and in correspondence with this one act of discrimination it is able to perform one act of adjustment ; it is able to enclose and to digest the nutritious particles, while it rejects the non-nutritious. Some protoplasmic and unicellular organisms are able also to distinguish between light and darkness, and to adapt their movements to seek tlie one and shun the other ; while in " Animal Intelligence " some observations are given which seem to show that the discriminative and adjustive powers of these organisms may go farther even than this. The insectivorous plants, as we have already seen, are able to distinguish, not only between nutritious and non-nutritious particles, but also between different kinds of contact ; and, in correspondence with this advance in receptive power, we observe a commensurate 56' MENTAL EVOLUTION IN ANIMALS. advance in the mechanism of adaptive movement. Number- less other cases of such simple powers among plants might here be noticed ; but none of them rise above the level of distinguishing between one or two alternatives of stimula- tion, and supplying the correspondingly simple movements of response. Where nerve-structure first appears, we find that the animals which present it — the Medusse — have organs of special sense wherewith to distinguish with comparative delicacy and rapidity between light and darkness, and probably also between sound and silence. They are also provided with an elaborate tentacular apparatus, wherewith they are able to distinguish quicldy and accurately between moving and not moving objects coming upon them from various sides, as well as between nutritious and non-nutri- tious particles. And in correspondence with this advance of receptive capacity we observe a considerable advance of executive capacity — the animals being highly locomotive, swinmiing away rapidly from sources of contact which they distinguish as dangerous, and manifesting several other reflex actions of a similarly adaptive kind. Thus, also, the higher organizations of Star-fish, Worms, &c., while serving to supply the neuro-muscular mechanisms with still more detailed information regarding the outer world, serve likewise to supply them with the means of executing a greater variety of adaptive movements. In the Mollusca, again, we observe another advance in both these respects; the animals feel their way with sensitive feelers, select varied kinds of food, choose mates of their own species to pair with, and may even remember a particular locus as their home, &c. Among the Articulata the lower forms present co-ordinated movements wdiich are few and simple as compared with the many and varied movements of the higher members of the class ; and their powers of distinguishing between stimuli are propor- tionally small. But in the complicated anatomy of the Crabs and Lobsters there is a large provision for the co-ordina- tion of movements, and the selective actions are correspond- ingly numerous and varied; while among the Insects and Spiders the power of muscular co-ordination surpasses that of the lower Vertebrata, and the power of intelligent adapta- tion, assisted by delicate antennae and highly perfected organs of special sense, is also greater. And the same principles hold throughout the Yertebrated series. It has already been THE EOOT-PEIXCIPLES OF MIND. 57 remarked by Mr. Spencer that there is here a general corre- spondence to be observed between the possession of organs capable of varied actions, and the degree of intelligence to which the animal attains. Thus of Birds the Parrots are the most intelligent, and they, more than any other members of their class, are able to use their feet, beaks, and tongues in the examination of objects. Similarly, the wonderful intelligence of the Elepliant may be safely considered as correlated with the no less wonderful instrument of co-ordinated movement which he possesses in his trunk ; while the superior intelli- gence of the Monkey, and the supreme intelligence of Man may no less safely be considered as correhited with the still more wonderful instrument of co-ordinated movement which has attained to almost ideal perfection in the human hand. Again, and more generally, we may say that throughout the animal kingdom the powers of sight and of hearing stand in direct ratio to the powers of locomotion ; and the latter are conducive to the growth of intelligence.* We may now observe that this correlation between muscular and mental evolution — or, more generally, between power of discrimination and variety of adaptive movements — is only what we should expect to find a priori For it is , clear that the development of the one function could be of no use without that of the other. On the one hand, it would be of no use to an organism that it should be able to discern a stimulus as hurtful or beneficial, if at the same time it lacked the power of co-ordinated movement necessary to adapting itself to the result of its discernment ; and, on the other hand, it would be equally useless that an organism should possess the needful power of co-ordinated movement, if at the same time it lacked the power of discernment which alone could render the power of co-ordinated movement use- ful. Now we know that all the mechanisms of muscular co-ordination are correlated with mechanisms of nervous co- ordination, and, indeed, that the former without the latter would be utterly useless. Yet we know next to nothing of * The Dog and Cat seem at first sight to constitute an exception to the principle above set forth ; but it must be remembered that both these animals, and all their tribe, possess very efficient instruments of touch and movements in their tongues, lips, and jaws, as well as to some extent in the paws. I think the superior intelligence of the Octopus, among mollusks, is to be attributed to the excepfional advantages which are rendered bj its large and flexible, sensitive and powerful arms. 58 MENTAL EVOLUTION IN ANIMALS. tlie ultimate nervous mechanisms which play down upon the muscular mechanisms ; we only see a mazy mexus of cells and fibres, the very function of which, much less their inti- mate mechanism, could not be guessed, were it not that we have the grosser mechanisms of the muscular system whereby I to study the effects of these finer mechanisms. I I Muscular co-ordinations, then, are so many indices, "writ large," of corresponding co-ordinations taking place in the nervous system. Now we have seen that mental processes may be regarded as indices in precisely the same way, and indeed that, like muscular movements, they are the only indices we have of the operations of the nervous mechanisms with which they are connected. Moreover, we have seen that when this new set of indices has reached a certain level of development, marking of course a corresponding level of development in the nervous system, it begins unmistake- ably to show that the functions of receptive discrimination and of adaptive movement are taking yet another point of departure in the upward course of their development — that the nervous system is beginning to discriminate between novel and enormously complex stimuli, having reference not only to immediate results, but also to remote contingencies ; we see in short that the nervous mechanism is beginning to develope those higher functions of discriminative and adaptive ability which on their subjective side we know as rational. Therefore it is clear that these two faculties not only do but must proceed together. Every advance in the power of discrimination will be followed, in the life of the individual and in that of the species, by efforts towards the movements of needful adaptation, and in all cases where such movements require an advance on the previous power of co-ordination, such advance will be favoured by natural selection. Thus every advance in the power of discrimination favours an advance of the power of co-ordination. And, conversely, we ' may now remark that every advance in the power of co- ordination favours an advance of the power of discrimina- tion. For, as a greater power of co-ordinated movement implies the bringing of nerve-centres into new and more varied relations with the outer world, there is thus afforded to the nerve-centres a proportionately increased opportunity of discrimination — an opportunity which will sooner or later be sure to be utilized by natural selection. THE EOOT-PPJXCIPLES OF MIND. 59 Thus the two faculties are, as it were, necessarily bound together. But here another consideration arises. They are i thus bound together only up to the point at which the adap- j tive movements are dependent upon the machinery supplied / by nature to the organism itself. As soon as the power of ' discrimination has advanced far enough to be, not only con- sciously precipient, but deliberatively rational, a wholly new state of things is inaugurated. For now the organism is no. longer dependent for its adjustments upon the immediate results of its own co-ordinated movements. From the time that a stone was first used by a monkey to crack a nut, by a bird to break a shell, or even by a spider to balance its web, the necessary connexion betwxen the advance of mental dis- crimination and muscular co-ordination was severed. With^^ the use of tools there was given to Mind the means of pro- / gressing independently of further progress in muscular co^ ordination. And so marvellously has the highest animal availed itself of such means, that now, among the civilized races of mankind, more than a million per cent, of his adjus- tive movements are performed by mechanisms of his own construction. Wonderful as are the muscular co-ordinations of a tight-rope dancer, they are nothing in point of utility as A compared with the co-ordinated movements of a spinning- I jenny. Therefore, although man owes a countless debt of ' gratitude to the long line of his brutal ancestry for bequeath- , ^^ ing to him so surpassingly exquisite a mechanism as that of / the human body — a mechanism without which it would be 1 impossible for him, with any powers of mind, to construct / the artificial mechanisms which he does — still man may justly feel that his charter of superiority over the lower animals is before all else secured by this, that his powders of adjustive movement have been emancipated from their necessary alliance with his powers of muscular co-ordination. I say, from his powers of 7iiuscular co-ordination, because it is evident that our powers of adjustive movement, and so of adaptation in general, have never been, and can never be, emancipated from a necessary alliance with our powers of nervous co-ordination. I shall now sum up the results of our enquiry so far as it has hitherto gone. First, we found the Criterion ofcX Mind, ejectively considered, to consist in the exhibition of 60 MENTAL EVOLUTION IN ANIMALS. Choice, and the evidence of Choice we found to consist in the yp' performance of adaptive action suited to meet circumstances which have not been of such frequent or invariable occur- rence in the life-history of the race, as to have been specially and antecedently provided for in the individual by the in- . herited structure of its nervous system. The power of learn- ] ing by individual experience is therefore the criterion of ' Mind. But it is not an absolute or infallible criterion ; all / that can be said for it is that it is the best criterion available, and that it serves to fix the upper limit of non-mental action ' more precisely than it does the lower limit of mental ; for it is prol3able that the power of feeling is prior to that of con- sciously learning. Having thus arrived at the best available criterion of Mind considered as an eject, we next proceeded to consider the objective conditions under which known Mind is invari- ably found to occur. This led us briefly to inspect the >f structure and functions of the nervous system, and, while treating of the physiology of reflex action, we found that everywhere the nervous machinery is so arranged that there is no alternative of action presented to the nerve-centres other than that of co-ordinating the group of muscles over the combined contractions of which they severally preside. The question therefore arose — How are we to explain the fact that the anatomical plan of a nerve-centre with its attached nerves comes to be that which is needed thus to direct the nervous stimuli into the channels required ? The answer to this question we found to consist in the property which is \ shown by nervous tissue to grow by use into the directions ' which are required for further use. This subject is as yet an obscure one — especially where the earliest stages of such adaptive growth are concerned — but in a general way we can understand that hereditary usage, combined with natural selec- tion, may have been alone sufficient to construct the number- less reflex mechanisms which occur in the animal kingdom. Passing from reflex action to cerebral action, we first ^^ noticed that as the cerebral hemispheres pretty closely re- semble in their intimate structure ganglia in general, there can be no reasonable doubt that the mode of their operation is substantially the same. Moreover we noted that, as such ^ operation is here unquestionably attended with mental action, a strong presumption arises that the one ought to constitute THE EOOT-PRIXCIPLES OF MIXD. 61 a kind of obverse reflection of the other. Turning, therefore, to contemplate this presumably obverse reflection, we found that in many respects it is most strikingly true that the fundamental principles of mental operation correspond with the fundamental principles of ganglionic operation. Thus, we found that such is the case witli memory and the association of ideas, both of which we found to have their objective counterparts in the powers of non-mental acquisition which are presented by the lower ganglia. For we found that these ganglia unconsciously learn such exercises as they are made frequently to perform, that they forget their exercises if too long an interval is allowed to elapse between the times of practising them, but that even when apparently quite for- gotten such exercises are more easily re-acquired than originally they were acquired. Alore particularly we found that the association of ideas by contiguity presents a remark- ably detailed resemblance to the association of muscular movements by contiguity. For, agreeing to take ideas as the objective analogues of muscular movements, we observed when we thus changed the index of nervous operation from muscles to ideas, that the strongest evidence was yielded of the method of nervous evolution being everywhere uniform. Thus we remarked that sensations, perceptions, ideas, and emotions all more or less resemble muscular co-ordinations in that they are usually blended states of consciousness, wherein each con- stituent part must correspond with the activity of some particular nervous element — a variety of such elements being therefore concerned in the composite state of consciousness, just as a variety of such elements are concerned in a com- bined movement of muscles. Further, just as the associa- tion of ideas is not restricted to a blending of simultaneous ideas into one composite idea, but extends to a linking of one idea with another in serial succession ; so we saw that mus- cular movements exhibit a precisely analogous tendency to recur in the same serial order as that in which they have previously occurred. Lastly, we noted that all the patholo- gical derangements which arise in the nerve-centres that preside over muscular activities, have their parallels in simi- lar derangements which arise in the nerve-centres that are concerned in mental activities. Having thus dealt with the Physical Basis of Mind, we passed on in the next chapter to consider the Eoot-principles 62 MENTAL EVOLUTIOX IN ANIMALS. of Mind. Here the object was to trace the ultimate principles of physiology that might be taken as constituting the objec- tive side of those phenomena which on their subjective and ejective sides we regard as mental. These principles we found to be the power of discriminating between different kinds of stimuli irrespective of their relative degrees of mechanical intensity, coupled with the power of performing adaptive movements suited to the results of such discrimina- tion. These two powers, or faculties, we saw to occur in germ even among the protoplasmic and unicellular organisms, and we saw that from them upwards all organization may be said to consist in supplying the structures necessary to an ever-increasing development of both these faculties, which always advance, and must necessarily advance, together. When their elaboration has proceeded to a certain extent, they begin gradually to become associated with Feeling, and when they are fully so associated, the terms Choice and Pur- pose become to them respectively appropriate. Continuing in their upward course of evolution, they next become con- sciously deliberative, and eventually rational. But although when viewed from the subjective or ejective side they thus appear, during the upward course of their development, to become transformed from one entity to another, such is not the case when they are viewed from their objective side. For, when viewed from their objective side, the most elaborate process of reasoning, or the most comprehensive of judg- ments, is seen to be nothing more than a case of exceedingly refined discrimination, by highly-wrought nervous structures, between stimuli of an enormously complex character ; while the most far-sighted of actions, adapted to meet the most remote contingencies of stimulation, is nothing more than a neuro-muscular adjustment to the circumstances presented by the environment. Thus, if we again take mental operations as indices whereby to study the more refined working of nervous centres, as we take muscular movements to be so many indices, " writ large," of the less refined working of such centres, we again find forced upon us the truth that the method of nervous evolution has everywhere been uniform; it has everywhere consisted in a progressive development of the power of discriminating between stimuli, combined with the complementary power of adaptive response. EXPLANATION OF THE DIAGRAM. 63 CHAPTEE V. Explanation of the Diageam. We have now sufficiently considered the sundry first prin- ciples and preliminary questions which lie at the threshold of our subject proper. It seemed to me desirable to dispose of these principles and questions before we enter upon our attempt at tracing the probable history of Mental Evolution. But now that these first principles and preliminary questions have been disposed of, so far as their nature renders possible, the way is as clear as it can be for us to pursue our enquiry concerning the Genesis of ]\Iind. In order to give definition to the somewhat laborious investigation on which we are thus about to embark, I have thought it a good plan to draw a diagram or map of the probable development of Mind from its first beginnings in protoplasmic life up to its culmination in the brain of civilized man. The diaOTam embodies the o results of my analysis throughout, and will therefore be repeatedly alluded to in the course of that analysis — i.e., throughout the present and also my future work. I may therefore begin by explaining the plan of this diagram. The diagram, as I have just said, is intended to represent in one view the whole course of mental evolution, supposing, in accordance with our original hypothesis, such evolution to ^ave taken place. Being a condensed epitome of the results of my analysis, it is in all its parts carefully drawn to a scale, the ascending grades or levels of which are e\^erywhere determined by the evidence which I shall have to adduce. The diagram is therefore not so much the product of my indi- vidual imagination, as it is a summary of all the facts which science has been able so far to furnisli upon the subject ; and although it is no doubt true that the progress of science may affect the diagi-am to the extent of altering some of its details, I feel confident that the general structure of our knowledge concerning the evolution of mind is now suthciently coherent 64 MENTAL EVOLUTION IN ANIMALS. to render it higlily improbable that this diagrammatic repre- sentation of it will, in the future, be altered in any of its main features by any advances that science may be destined to make. From the groundwork of Excitability, or the distinguish- ing peculiarity of living matter, I represent the structure of mind as arising by a double root — Conductility and Discrimi- nation. To what has already been said on these topics it is needless to add more. We have seen that the distinguishing property of nerve-fibre is that of transmitting stimuli by a propagation of molecular disturbance irrespective of the pas- sage of a contraction wave ; and this property, laying as it does the basis for all subsequent co-ordination of protoplasmic (muscular) movements, as well as of the physical aspect of all mental operations, deserves to be marked off in our map as a distinct and important principle of development ; it is the principle which renders possible the executive faculty of appropriately responding to stimuli. Not less deserving of similar treatment is the cognate principle of Discrimination, which, as we have seen, is destined to become the most important of the functions subsequently distinctive of nerve- cells and ganglia. But we have also seen that both Conduc- tility and Discrimination first appear as manifested by the cellular tissues of plants, if not even in some forms of apparently undifferentiated protoplasm. It is, however, on]y when these two principles are united within the limits of the same structural elements that we first obtain optical evidence of that differentiation of tissue which the histologist recognizes as nervous ; therefore I have represented the function of nerve-tissue in its widest sense, Neurility, as formed by a confluence of these two root-principles. Neurility then passes into Keflex Action and Volition, which I have repre- sented as occupying the axis or stem of the psychological tree. On each side of this tree I have represented the out- growth of branches, and for the sake of distinctness I have confined the branches which stand for the faculties of Intellect on one side, while placing those which represent the Emotions upon the other. The level to which any branch attains re- presents the degree of elaboration which the faculty named thereon presents ; so that, for instance, when the branch Sensation, taking origin from Neurility, proceeds to a certain level of development, it gives off the commencement of Per- EXPLANATION OF THE DIAGRAM. 65 _ce£tion, and then continues in its own line of development to a somewhat higher level. Similarly, Imagination arises out of Perception, and so with all the other branches. Thus, the fifty levels which are drawn across the diagram are intended to represent degrees of elaboration ; they are not intended to represent intervals of time. Such being the case, the various products of mental evolution are placed in parallel columns upon these various levels, so as to exJnbit the comparative degrees of elaboration, or evolution, which they severally present. One of these columns is devoted to the psycho- logical scale of intellectual faculties, and another to the psychological scale of the emotional. But for the danger of rendering the diagram confused, these faculties might have been represented as secondary branches of the psychological tree ; in a model this might well be done, but in a diagram it would not be practicable, and therefore I have restricted the branching structure to represent only the most generic or fundamental of the psychological faculties, and relegated those of more specific or secondary value to the parallel columns on either side of the branching structure. In these two columns I have throughout written the name of the faculty at what I conceive to be the earliest stage, or lowest level of its elaboration ; i.e., where it first gives evidence of its existence. In another parallel column I have given the grades of mental evolution which I take to be characteristic of sundr}^ groups in the animal kingdom, and in yet another column I have represented the grades of mental evolution which I take to be characteristic of different ages in the life of an infant. In my subsequent work I shall fill up all the levels in these vertical columns which are now left blank, on account of the text of the present work being restricted to the mental evolution of animals. At first I intended in this work to truncate the whole diagram at the level where mental evolu- tion in animals ends — i.e., at the level marked 28 — and to reserve the continuation of the stem and branches, as well as that of the parallel colunnis, for my ensuing work. But afterwards I thought it was better to supply the continuation of the stem and branches, in order to show the proportion which I conceive to obtain between the elaboration of the liigher faculties as they occur in animals and the same faculties as they occur in man. Confining, then, our attention to the first twenty-eight F 66 MENTAL EVOLUTIOX IX ANIMALS. levels with which alone the present essay is to be concerned, if we pitch upon any one of them at random, we shall obtain a certain rough estimate of the grade of mental evolution which is presented by the animals named upon that level. To avoid misapprehension I may add that in thus render- ing a diagrammatic representation of the probable course of mental evolution with the comparisons of psychological development exhibited in the parallel columns, I do not suppose that the representation is more than a rough or general outline of the facts; and, indeed, I have only resorted to the expedient of thus representing the latter for the sake of convenience in my subsequent discussion. Eough as this outline of historical psychology may be, it will serve its purpose if it tends to facilitate the exposition of evidence, and afterwards serves as a dictionary of reference to the more important of the facts which I hope this evidence will be able to substantiate. Such being the general use to which I intend to put the diagram, I may here most fitly make this general remark in regard to it. In the case alike of the stem, l^ranches, and the two parallel columns on either side — i.e., all the parts of the diagram which serve to denote psychological faculties — we must remember that they are diagrammatic rather than truly representative. For in nature it is as a matter of fact impos- sible to determine any hard and fast lines between the com- pleted development of one faculty and the first origin of the next succeeding faculty. The passage from one faculty to another is throughout of that gradual kind which is charac- teristic of evolution in general, and which, while never pre- venting an eventual distinction of species, always renders it impossible to draw a line and say — Here species A ends and species B begins. Moreover, I cannot too emphatically im- press my conviction that any psychological classification of faculties, however serviceable it may be for purposes of analysis and discussion, must necessarily be artificial. It would, in my opinion, be a most erroneous view to take of Mind to regard it as really made up of a certain number of distinct faculties — as erroneous, for example, as it would be to regard the body as made up of tlie faculties of nutrition, excitability, generation, and so on. All such distinctions are useful only for the purposes of analysis ; they are abstractions of our own making for our own convenience, and not EXPLANATION OF THE DIAGRAM. 67 naturally distinct parts of tlie structure which we are examining. But although it is desirable to keep these caveats in our memory, I do not think that either the artificial nature of psychological classification or the fact that we have to do with a gradual process of evolution, constitutes any serious vitiation of the mode of representation which I have adopted. For, on the one hand, some classification of faculties we must have for the purposes of our inquiry ; and, on the other hand, I have as much as possible allowed for the unavoidable defect in the representation which arises from evolution being gradual, by making the branches of the arborescent structure wide at their bases, and by allowing each of them, after giving off the next succeeding branch, to continue on its own course of development ; so that both the parent and daughter faculty are represented as occupying for a more or less considerable distance the same levels of develoj^ment — in each case my estimate of the comparative elaboration which the completed faculty betokens being represented by the vertical height of its apex. Besides, as already stated, faculties named in the two parallel columns are written upon those levels where !'■ have either a j^'^^iori reasons or actual evidence to conclude > that they first definitely appear in the growing structure of' Mind ; in this way the difficult question of assigning the lower limit of evolution at which any particular faculty begins to dawn is as much as possible avoided. It is almost needless to add that in preparing this diagram I have resorted to speculation in as small a measure as the nature of the subject permits. Nevertheless it is obvious' that the nature of the subject is such that, in order to com- plete the diagram in some of its parts, I have been obliged to resort to speculation pretty largely. I think, however, that as the exposition proceeds, it will be seen that, if the funda- mental hypothesis of mental evolution having taken place is granted, my reasoning as to the probable history of the pro- cess does not anywhere involve speculation of an extravagant or dangerous kind. In matters of detail — such, for instance, as the comparative elevation of the different branches in the psychological tree — my estimates may, probably enough, be more or less erroneous ; but the main facts as to the sequence of the faculties in the order of their comparative degrees of elaboration are mere corollaries from our fundamental h}^o- E 2 68 MENTAL EVOLUTION IN ANIMALS. thesis ; aad, as we shall see, these facts, as I have presented them, are sustained or corroborated by many others drawn from observations on the psychology of animals and children. Again, in the columns devoted to the emotions and faculties of intellect, the results of actual observation predominate over those yielded by speculation ; while in the remaining columns the results tabulated are for the most part due to observa- tion. Therefore I submit that if the hypothesis of mental evolution be granted, and if all the matters of observable fact which the diagram serves to express are eliminated, com- paratively little in the way of deductive reasoning is left ; and of this little most follows as necessary consequence from the original hypothesis of mental evolution having taken place. Of course any one who does not already ciccept the theory of evolution in its entirety, may object that I am thus escaping from the charge of speculation only by assum- ing the truth of that which grants me all that I require. To this I answer that as far as the evidence of Mental Evolution, considered as a fact, is open to the charge of being specula- tive, I must leave the objector to lodge his objection against Mr. Darwin's '' Origin of Species " and " Descent of Man." I shall be abundantly satisfied with my own work if, taking the process of Mental Evolution as conceded, I can make it clear that the main outlines of its history may be determined without any considerable amount of speculation, as dis- tinguished from deduction following by way of necessary consequence from the original hypothesis. Having thus explained the plan and principles of the diagram, I shall now consider the levels from the lowest as far as the rise of the first branch, i.e., from 1 to 14. After what has already been said in the foregoing chapters on the Physical Basis and Eoot-principles of Mind, our consideration of this part of the diagram need not detain us long. Levels 1 to 4 are occupied by Excitability, Protoplasmic Movements, Protoplasmic Organisms, and \h.Q generative elements which have not yet united to start the Embryo of Man. From 4 to 9 we have the levels filled by the rise and progress of the functions Conductility and Discrimination, which by their subsequent union at 9 lay the basis of Xeurility, or the stem of Mind ; in these levels occur the EXPLANATION OF THE DIAGRAM. 69 Non-nervous Adjustments, Unicellular Organisms, and part of the Life-history of the Embryo. Between 9 and 14 is repre- sented the development of Neurility and its passage into Eeflex Action ; the parallel columns within this space are therefore respectively filled with Partly-nervous Adjustments and the beginning of True Nervous Adjustments, Unknown Animals, probably Coelenterata, perhaps extinct, and another portion of the Life-history of the Embryo. I here speak of ^ "unknown animals" because, so far as investigation has hitherto gone, the animals in which nerve-tissue first began to be differentiated have not yet been found. In the lowest animals where this tissue has been found — the Medusae — it appears as already well differentiated. The ganglion cells, however, show in a most unmistakeable manner their parent- age from epithelium — their structure, in fact, often resembling that of modified epithelium more than that of true nerve- cells.* In these structures, therefore (as in the analogous histological elements met with in the embryonic nerve-tissue of higher animals), we have a link which connects true nerve- tissue with its cellular ancestry, and thus it is comparatively immaterial wdiether or not the animals which presented the earlier stages of this histological transition are still in exist- ence. Thus we need not wait to discuss Kleinenberg's view on the " neuro-muscular " cells of Hydra. * See Prof. E. A. Schafer on Nervous System of Atirelia Aurita, Phil. Trans., 1878, and Profs. O. and R. Hertwig on Das Nervensystem und die Sinnesorgane der Medusen. cyr^ 70 MENTAL EVOLUTION IN xVNIMALS. CHAPTEK VI. Consciousness. Hitherto in this work I have been considering, as exclu- sively as the nature of the subject permits, the physical or objective aspect of mental processes, and of the antecedents of these processes in the non-mental activities of living organisms. It now devolves upon us to turn to the sub- jective side of the matter, and still more closely, I may observe, to the ejective side of it. That is to say, from this point onward my endeavour will be to trace the probable course of Mental Evolution by having regard to truly mental phenomena, so far as these admit of analysis by subjective or ejective methods. I desire, therefore, to draw promicent attention to the fact that fram this point in my treatise I take, as it were, a new departure ; for if this is not kept in mind, my exposition may appear to resemble two separate essays bound together rather than one continuous whole. In my endeavour to draw a sharp line of demarcation between the physiology and the psychology of my subject, I have found it impossible to discuss the one without numerous allusions to the other — the consequence being that hitherto, while treating as exclusively as I could of the physiology of vital processes, I have been obliged frequently to refer to the psychology of mental processes, a knowledge concerning the main facts of which I have taken for granted on the part of any one who is likely to read this book. Thus it happens that in now turning to investigate the psychology of these processes, it is impossible to avoid a certain amount of over- lapping with what has gone before. For example, in my chapter on the Physical Basis of Mind, it was clearly impos- sible not to allude to such leading principles of psychology as sensation, perception, ideation, and others. Therefore, in now undertaking an investigation of these various principles CONSCIOUSNESS. 71 in the order of their probable evohition, it may often appear chat I am, as it were, going back upon, or in part repeating, what I have already said. But this apparent defect in the method of my exposition will, I think, be seen on closer attention to be more than compensated for by the advantage of avoiding confusion between physiology and psychology. It would, for instance, liave been easy to have split up the chapter on the Physical Basis of ]Mind already alluded to, and to have apportioned its various parts to those among the succeeding chapters which treat of the psychological aspects of the physiological principles set forth in those various parts ; but the result would have been largely to have obscured the doctrine which I desired to make plain througli- out — viz., that all mental processes must be regarded as pre-\U senting physical counterparts.* 1\» So much in explanation of my method being understood, I shall begin the psychology of mental evolution by con- sidering that in which the mind-element must be regarded as consisting — namely. Consciousness. Turning to the diagram, it will be observed that I have written the word " Con- sciousness " in a perpendicular direction, beginning at level 14 and extending to level 19. My reason for doing tliis is because the rise of Consciousness is probably so gradual, and' certainly so undefined to observation, that any attempt to draw the line at which it does arise would be impossible, even on the rough and general scale wherewith I have endea- voured to draw the lines at which the sundry mental faculties may be regarded as taking origin. Therefore I have repre- sented the rise of Consciousness as occupying a considerable area in our representative map, instead of a definite line. This area I make to begin with the first development of " Xervous Adjustments," and to terminate with the earliest appearance of the power of associating ideas. In now proceeding to justify this assignment of limits between the earliest dawn of Consciousness and the place where Consciousness may first be regarded as truly such, I may best begin by saying that I shall not attempt to define * It seems almost needless to add that the impossibility of entirely sepa- rating psycliology from pliysiology for the purposes of exposition will, mutafist ynufandis, continue to meet us more or less throughout the following, as it has throughout the preceding chapters ; but I shall endeavour always to make it clear when I am speaking of mental processes and when of physical. 72 MENTAL EVOLUTION IN ANIMALS. what is meant by Consciousness. For, like the word " Mind," " Consciousness " is a term which serves to convey a meaning well and generally understood, but a meaning which, from the peculiar nature of the case, cannot be comprehended in any definition. If we say that a man or an animal is con- scious, we mean that the man or animal displays the power of Feeling, and if we ask what we mean by Feeling, we can only, I think, answer — that which distinguishes Non-extended Existence from Extended. Deeper than this we cannot go, because Consciousness, being itself the basis of all thought, and so of all definition, cannot be itself defined except as the I antithesis of its logical correlative — No-consciousness. Let us first regard the phenomena of Consciousness as disclosed in our own or subjective experience. We shall subsequently see that the elementary or undecomposable I units of consciousness are what we call sensations. If we interrogate experience we find that an elementary state of consciousness, or sensation, may exist in any degree, from that of an almost unrecognizable affection, up to that of unendurable pain, which monopolizes the entire field of con- sciousness. More than this, from the lowest limit of per- ceptible sensation there arises a long and indefinite descent through sensation that is not perceptible, or through sensation that is sub-conscious, before we arrive at nervous action which we feel entitled to regard as unconscious. This is proved by those grades of almost unconscious action, passing at last into wholly unconscious action, which we all know as frequently occurring in the descent, through repetition or habit, of consciously intelligent adjustments to automatic adjustments, or adjustments performed unconsciously. Thus it is evident, not only that consciousness admits of numberless degrees of intensity, but that in its lower degrees its ascent ' from no-consciousness is so gradual, that even within the range of our own subjective experience we find it impossible to determine within wide limits where consciousness first emerges.* , With this gradual dawn of consciousness as revealed to j subjective analysis, we should expect some facts of physiology, '* or of objective analysis, to correspond; and this we do find. * Any one who has gradually fainted, or has slowly been put under the influence of an anaesthetic, will remember the peculiar experience of feeling consciousness becoming obliterated by stages. CONSCIOUSNESS. 73 For in our own orc^anisms we know that reflex actions are not accompanied by consciousness, although the complexity of the neuro-muscular systems concerned in these actions may be very considerable. Clearly, therefore, it is not mere complexity of ganglionic action that determines conscious- ness. What, then, is the difference between the mode of operation of the cerebral hemispheres and that of the lower ganglia, which may be taken to correspond witli the great subjective distinction between the consciousness which may attend the former and the no-consciousness which is inva- riably characteristic of the latter ? I think the only difference that can be pointed to is a difference of rate or time. We know by actual measurement, as we shall sul)sequently see in more detail, that the cerebral hemispheres work more slowly while undergoing those changes which are accom- panied by consciousness than is the case with the activities of the lower centres. In other words, the period between the fall of a stimulus and the occurrence of responsive movement is notably longer if the stimulus has first to be perceived, than it is if no perception is required. And this is proved, not only by comparing the latent period (or the time which elapses between the stimulation and the response) in the case of an action involving one of the lower centres and that of an action involving the cerebral hemispheres in perception ; but also by comparing the latent period in the case of one and the same cerebral action which from having originally involved perception has through repetition become automatic. An old sportsman will have his gun to the shoulder, by an almost unconscious act, the moment that a bird unexpectedly rises ; a novice similarly surprised will spend a valuable second in "takincf in" the situation. And anv number of similar facts might be given to show that if few things are " as quick as thought," reflex or automatic action is one that is quicker. Further, in a general way it can be shown that the more elaborate a state of consciousness is, the more time is required for its elaboration, as we shall see more in detail when we come to treat of Perception. Now what does this greater consumption of time imply ? It clearly implies that the nervous mechanism concerned has ' not been fully habituated to the performance of the response required, and therefore that instead of the stimulus merely needing to touch the trigger of a ready- formed apparatus of 74 MEXTAL EVOLUTION IX ANIMALS. response (liowever complex this may be), it has to give rise in the nerve-centre to a play of stimuli before the appropriate response is yielded. In the higher planes of conscious Jife this play of stimuli in the presence of ''difficult circum- stances " is known as indecision ; but even in a simple act of consciousness — such as that of signalling a perception — more time is required by the cerebral hemispheres in supplying an appropriate response to a non-habitual experience, than is required by the lower nerve-centres for performing the most complicated of reflex actions by way of response to their habitual experience. In the latter case the routes of nervous discharge have been well worn by use ; in the former case these routes have to be determined by a complex play of forces amid the cells and fibres of the cerebral hemispheres. And this complex play of forces, which finds its physiological expression in a lengthening of the time of latency, finds also a psychological expression in the rise of consciousness. The function, then, of the cerebral hemispheres is that of dealing with stimuli which, although possibly and in a com- parative sense simple, are yet so varied in character that , special reflex mechanisms have not been set aside to deal I with them in one particular way ; and it is the consequent perturbation of these highest nerve-centres in dealing with such stimuli that is accompanied by the phenomena of con- sciousness. Or, in the words of Mr. Spencer, " there cannot ' be co-ordination of inanv stimuli without some s^andion through which they are all brought into relation. In the pro- cess of bringing them into relation, this ganglion must be subject to the influence of each — must undergo many changes. And the quick succession of changes in a ganglion, implying as it does perj)etual experiences of differences and likenesses, constitutes the raw material of consciousness."* Thus we see, so far as we can ever perhaps hope to see, how conscious action gradually arises out of reflex. As the stimuli to be dealt with become more complex and varied (owing to the advancing evolution of organisms bringing * Principles of Psychology, voL i, p. 435. I think, however, that Mr. Spencer is not sufficiently explicit, either in the above quoted passage or else- where, in showing that " the raw material of consciousness " is not necessarily constituted by the mere complexity of ganglionic action. Indeed, as I have said, such complexity in itself does not appear to liave anything to do with the rise of consciousness, except in so far as it may be conducive to what we may term the ganglionic friction, which is expressed by delay of response. CONSCIOUSNESS. 7o them into more and more complex and varied relations with their environment), the primitive assignment of a special nervous mechanism to meet the exigencies of this or that special group of stimuli becomes no longer practicable, and the higher nerve-centres have therefore to take on the func- tion of focussing many and more or less varied stimuli, in order to attain to that higher aptitude of discrimination in which we have already seen to consist the distinctive attri- bute of Mind. And, as Mr. Spencer has observed, " the co- ordination of many stimuli into one stimulus is, so far as it goes, a reduction of diffused simultaneous chanires into con- centrated serial changes. AVhether the combined nervous acts which take place when the fly-catcher seizes an insect are regarded as a series passing through its centre of co- ordination in rapid succession, or as consolidated into two successive states of its centre of co-ordination, it is equally clear that the changes going on in its centre of co-ordination have a much more decided linear arrangement than have the changes going on in the scattered ganglia of a centipede." And this linear character of the change is, of course, one of the most distinctive features of consciousness as known to ourselves subjectively. It will have been observed that this interpretation of the rise of consciousness is purely empirical. We know by immediate or subjective analysis that consciousness only occurs when a nerve-centre is engaged in such a focussing of varied or comparatively unusual stimuli as have been described, and when as a preliminary to this focussing or act of discriminative adjustment there arises in the nerve-centre a comparative turmoil of stimuli coursing in more or less unaccustomed directions, and therefore giving rise to a com- parative delay in the occurrence of the eventual response. But we are totally in the dark as to the causal connection, if any, between such a state of turmoil in a ganglion and the occurrence of consciousness. Whether it is the Angel that descends to trouble the waters, or the troubling of the waters that calls down the Angel, is really the question which divides the Spiritualists from the Materialists ; but with this question we have nothing to do. It is enough for all the objects of the present work that we never get the Angel without the troubling, nor the troubling without the Angel ; we have an empirical association between the two which is as valid for 76 MENTAL EVOLUTION IX ANIMALS. the purposes of merely historical psychology as would be a full understanding of the causal connection, if there is any such connection to be understood. So much, then, for the physical conditions under which consciousness is always and only found to occur. It remains brieiiy to conclude this chapter by showing that these con- ditions may most reasonably be regarded as first arising within the limits between which I have represented the origin of consciousness. Eemembering what has already been said concerning the gradual or undefined manner in which consciousness probably dawned upon the scene of life, and that I therefore represent its rise as occupying a wide area on the diagram instead of a definite line, I think it least objectionable to place the begin- ning of this dawn in nervous adjustments or reflex action, and the end of it in the association of ideas. For, on the one hand, it is clear from what has been said that it is impossible />: to draw any definite line between reflex and conscious action, inasmuch as, considered objectively or as action, the latter differs from the former, not in kind, but only in a gradual advance in the degree of central co-ordination of stimuli. Therefore, where such central co-ordination is first well established, as it is in the mechanism of the simplest reflex act, there I think we may with least impropriety mark the advent of consciousness. On the other hand, where vague [ memory of past experiences first passes into a power of asso- ciating simple ideas, or of remembering the connections between memories, there I think consciousness may most properly be held to have advanced sufficiently far to admit of our regarding it as fairly begun. In this scheme, therefore — which of course it is needless to say I present as a somewhat arbitrary estimate where no more precise estimate is possible — the Coelenterata are repre- sented as having what Mr. Spencer calls " the raw material of consciousness," the Echinodermata as having such an amount of consciousness as I think we may reasonably sup- pose that they possess, if we consider how multifarious and complicated their refiex actions have become, and if we remember that in their spontaneous movements the neuro- muscular adjustments which they exhibit almost present the appearance of being due to intelligence.* The Annelida I * See F/iil. Trans., Croonian Lecture, 1881. CONSCIOUSNESS. 7V place -upon a still higjher level of consciousness, because, both from the facts mentioned in " Animal Intelligence " and from those published by Mr. Darwin,* it seems certain that their actions so closely border on the intelligent that it is difficult to determine whether or not they should be classed as intel- ligent. Upon this level, also, I represent the period of the embryonic life of Man as coming to a close ; for although the new-lDorn child, from the immaturity of its experience, dis- plays no adjustments that can be taken as indicative of intelligence, still, as its nerve-centres are so elaborate (embo- dying the results of a great mass of hereditary experience, which although more latent in the new-born child than in the new^-born of many other mammals and all birds, must still, we should infer from analogy, count of something), that we can scarcely doubt the presence of at least as much conscious- ness as occurs among the annelids. Moreover, pain appears to be felt by a new-born child, inasmuch as it cries if injured ; and although this action may be largely or chiefly reflex, we may from analogy infer that it is also in part due to feeling. The remaining levels occupied by the dawn of consciousness may be considered as assigned to the lower Mollusca — an assignment which I think will be seen to be justified by con- sulting the evidence given in my former work of actions performed by these animals of a nature which is unrpies- tionably intelligent. * See his work on Earthicorms, 1S81. 78 MENTAL EVOLUTION IN ANIMALS. CHAPTER VIL Sensation. By Sensation I mean simply Feeling aroused by a stimulus. In my usage, therefore, the term is of course exclusive of all the metaphorical meanings which it presents in such applications as " sensitive plates," &c. It is also exclusive, on the one hand, of Eeflex Action, as well as of non-nervous adjustments, and on the other, of Perception. Thus, too, it is exclusive of the carefully defined meaning which it bears in the writings of Lewes. He defined Sensation as the reaction of a sense-organ, whether or not accompanied by Feeling, and thus he habitually speaks of unfelt sensations. In his nomen- clature, therefore, Sensation is a process of a purely physical kind, with which consciousness may or may not be involved. In my opinion, however, it is most desirable, notwithstanding his elaborate justification of this use of the term, to abide by its original signification, which I have explained. AVhen I have occasion to speak of the physical reaction of a sense- organ, I shall speak of it as a physical reaction, and not as a sensation. The distinction which, in common with other psychologists, I draw between a Sensation and a Perception, I shall explain more fully in the chapter where I shall have to treat of Perception. Meanwhile it is enough to say that the great distinction consists in Perception involving an element of Cognition as well as the element of Feeling. It is more difficult to draw the distinction between Sensation and non-nervous adjustments, and still more so between Sensation and nervous adjustments which are un- felt (Pieflex Action). Here, however, we are but again encountering the difficulty which we have already con- sidered, viz.^ that of drawing the line where consciousness begins ; and, as we have previously seen, this difficulty has nothing to do with the validity of a classification of psychical SENSATION. 79 iaculties ; it only 1ms to do with tlie question whether such and such a faculty occurs in such and such an organism. Therefore, so long as the question is one of classifying psychical faculties, we can only say that wherever there is -Feeling there is Sensation, and wherever there is no Feeling there is no Sensation.* But where the question is one of classifying organisms witli reference to their psychical facul- ties, it is clear that the difficulty of determining whether or not this and that particular low form of life has the begin- nings of Sensation, is one and the same as the question whether it has the beginnings of Consciousness. Now we have already considered this question, and we have found it impossible to answer; w^e cannot say within broad limits where in the animal kingdom consciousness may first be re- garded as present. But for the sake of drawing the line somew^here with reference to Sensation, I draw it at the place in the zoological scale where we first meet with organs of special sense, that is to say, at the Ccelenterata. In doing this, it is needless to observe, I am drawing the line quite arbitrarily. On the one hand, for anything tliat is known to the contrary, not only the sensitive plant which responds to a mechanical stimulus, but even tlie protoplasmic organisms which respond to a luminous stimulus by congregating in or avoiding the light, may, while executing their responses, be dimly conscious of feeling ; and, on the other hand, the mere presence of an organ of special sense" is certainly no evidence that its activities are accompanied by Sensation. What we call an organ of special sense, is an organ adapted to respond to a special form of stimulation ; but wdiether or not the pro- cess of response is accompanied by a sensation is quite another matter. We infer by a strong analogy that it is so accompanied in the case of organisms like our own (whether of men or of the higher animals) ; but the vaHdity of such inference clearly diminishes wdth the diminishing strength of the analogy — i.e., as we recede in the zoological and psycho- logical scales from organisms like our own towards organisms less and less like. Having thus made it as clear as I can that it is only for the matter of convenience that I have supposed the rise of Sensation to coincide with the rise of organs of special * Although this sounds like a truism, it is in direct opposition to the classification of LewcF, alluded to above. 80 MENTAL EVOLUTION IN ANIMALS. sense, I shall next proceed to take a brief survey of the animal kingdom with reference to the powers of special sense. In doing this, however, it is needless, and indeed undesirable, that I should enter with much closeness into the anatomy of the innumerable organs of special sensation which the animal kingdom presents. My object is merely to give a general outline of the powers of special sensation pro- bably enjoyed by different classes of animals ; for, as these powers constitute the foundation of all the other powers of mind, it is of importance for us to have a general idea of the grade of their development in the sundry grades of the zoological scale. In some of his recently published experiments, Engel- mann found that many of the protoplasmic and unicellular organisms are affected by light ; that is to say, their move- ments are influenced by light, in some cases causing accele- ration, in others slowing, of their movements ; in some cases the organisms seeking the light, while in other cases they shun it, &c., &c. He found that all these effects were re- ducible to one or other of three causes : (1) alteration pro- duced by the light in the interchange of gases, (2) consequent alteration in the conditions of respiration, and (3) specific processes of luminous stimulation. It is with the latter only that we are concerned, and the organism which Engelmann names as exhibiting it typically is Eitgleiia viridis. After precautions had been taken to eliminate causes 1 and 2, it w^as still found that this organism sought the light. More- over, it was found that it would only do so if the light were allowed to fall upon the anterior part of its body. Here there is a pigment-spot, but careful experiment showed that this was not the point most sensitive to light, a colourless and transparent area of protoplasm lying in front of it being found to be so. Hence it is doubtful w^hether this pigment- spot is or is not to be regarded as an exceedingly primitive organ of special sense. Of the rays of the spectrum, Englena 'viriclis prefers the blue.* The remarkable observation recorded by Mr. H. J. Carter, F.R.S., and quoted from him in my previous work,t seems to display almost incredible powers of special sense among the * For fall account of these experiments, see PJliiger^s Arckiv.f. d. ges. Fhijsiologie, Bd. XXIX, 1882. t Animal Intelligence, pp. 19-21. SENSATION. . 81 Ehizopoda; and Professor Haeckel observes, in his essay on the " Origin and Development of the Sense-Organs," that " already among the microscopic Protista there are some that love light, and some tliat love darkness rather than light. Many seem also to have smell and taste, for they select their food with great care. . . ' . Here also we are met by the weighty fact that sense-function is possible without sense-organs, without nerves. In place of these, sensitiveness is resident in that wondrous, structureless, albuminous substance which, under the name of protoplasm, or organic formative material, is known as the general and essential basis of all the phenomena of life." Again, Engelmann describes a chase of one infusorium by another. The former in its free course happened to cross the route of a free-swarming vorticella. There was no con- tact, but it immediately gave chase, and for five seconds the two darted about with the utmost activity, the chasing infu- sorium maintaining a distance of about yV mm. behind the chased one. Then, owing to a sudden sideward dart of the vorticella, its pursuer lost the object of pursuit. The powers of discrimination shown by certain deep-sea protoplasmic organisms in selecting sand-grains of a particular size where- with to construct their tests has already been alluded to. But passing now to animals in which we first meet with; nerves, viz., the Medusse, it is among them also that we first meet with organs of special sense. I have myself observed that several species of Medusae seek tlie light, following a lantern if this is moved round a bell-jar containing them in a dark room. The pigmented bodies round the margin of the swimming-disk were proved to be the organs of special sense here concerned, and the rays in the spectrum by which they are affected were shown to be confined to the luminous part. It was further observed that some genera of Medusae had more highly developed visual sensation than others. The least efficient occurs in Tiaropsis polydiadcmata, as shown by the prolonged interval of delay between the fall of a luminous stimulus and the occurrence of the response. As the case is an interesting one, I shall state the particulars more fully. This Medusa, then, always responds to strong luminous stimulation by going into a spasm or cramp ; but it will not respond at all unless the light is allowed to fall upon its sense-organs for a period of more than one second ; if a slip- shutter is opened and closed again for a shorter period, no F 82 MENTAL EVOLUTION IN ANIMALS. response is made. It therefore seems certain that here we have not to deal with what physiologists call the period of latent stimulation, but with the time during^ which the lio^ht requires to fall in order to constitute an adequate stimulus ; just as a pliotographic plate requires a certain period of expo- sure in order to admit of the luminous vibrations throwing down the salt, so with the ganglionic material of this sense- ori^jan. How different is the efficiency or development of such a visual apparatus from that of a fully perfected retina, which is able to effect the needful nervous changes in response to a stimulus as instantaneous as that supplied by a flash of lightning.* It is remarkable, looking to the Medusae as a whole, in what a wonderful degree these primitive sense- organs vary as to their minute structure in different species. Nerve-cells and fibres, wrought up into more or less complex forms, are clearly discernible in all those which have hitherto been carefully examined; but when the particular specific forms are compared with one another, it seems almost as if organs of special sense, where they first undoubtedly occur in the animal kingdom, revel, as it were, in the variety of forms which they are able to present. It is probable, from the structure of the lithocysts, that the Medusae are also affected by sonorous vibrations, and it is certain that they are richly supplied with a variety of organs ministering to the sense of touch. For not only are they furnished with numerous long, highly sensitive, and contractile tentacles, but in some species the marginal ganglia are provided with minute hair-like appendages, which must enable the nerve-cells to which they are attached to be exceedingly sensitive to anything touching the hairs. And, in connection with the sense of touch in the Medusae, I may allude to my own observations on the precision with which the point of contact of a foreign body is localized. A Medusa being an umbrella-shaped animal, in which the whole of the surface of the handle and the whole of the con- cave surface of the umbrella is sensitive to all kinds of stimu- lation, if any point in the last-named surface is gently touched with a camel-hair brush or other soft (or hard) * For a full account of these experiments, see Phil. Trans., vol. 166, Pt. I, Croonian Lecture, where it is shown that in otlier species of Medusae, the sense-organs of which are more highly developed, there is no such pro- longed delay in the response to luminous stimulation. SENSATION. 83 object, the handle or manubrium is (in the case of many- species) immediately moved over to that point, in order to examine or to brush away the foreign body. This is especially the case in a species which for this reason I have called Tiaropsis indicans ; and here it is of interest to observe that if the nerve-plexus, which is spread all over the concave sur- face of the umbrella, is divided by means of an incision carried in the form of a short straight line parallel to the margin of the umbrella, and if a point below the line of incision is touched, the manubrium is no lon.fjer able to localize the seat of contact. Nevertheless it feels that con- tact is taking place somewhere, for it begins actively to dodge about from side to side of the umbrella, applying its ex- tremity now to one point and now to another of the umbrella surface, as if seeking in vain for the offending body. This of course shows that the stimulus, on reaching the ends of the severed nerve-fibres, spreads through the general nerve- plexus, and so arriving at the manubrium by a number of different routes, conveys a corresponding number of conflict- ing messages to the manubrium as to the point in the umbrella at which the stimulus is being applied. This irra- diation of a stimulus into other nerve-fibres when the stimulus reaches the cut ends of the fibres which constitute the habitual route of a stimulus between two points, is ren- dered the more interesting from the fact that in the case of tlie external nervous plexus of the Echinodermata there is no vestige of such a phenomenon. So much for the senses of sight (at least to the extent of distinguishing light from darkness), hearing, and touch, as localized in organs of special sense among the Medusae. In the allied Actinite Mr. Walter Pollock and myself have ob- 5' tained conclusive evidence of the sense of ^mell. For we found that when a morsel of food is dropped into a pool or tank containing sea-anemones in a closed state, the animals quickly expand their tentacles.* It has been said that this may be taken to argue a sense of taste no less than a sense of smell ; but I conceive that here no distinction can be drawn between these two senses, any more than we can draw such a distinction in the analogous case of fish. Looking, then, to , the Ccelenterata as a whole, we find that where we first meet with unmistakeable organs of special sense, we also first meet * See Journal Linnean Society, 1882. F 2 84 MENTAL EVOLUTION IN ANIMALS. with unmistakeable evidence of the occurrence of all the five senses — or, more correctly, with nnmistakeable evidence of a power of adaptive response to all the five classes of stimuli which respectively affect the five senses of man. , Coming next to the Echinodermata, Professor Ewart and h myself have observed that Star-fish and Echini crawl towards and remain in the light, even though this be of such feeble intensity as scarcely to be perceptible to human eyes. Moreover, we proved that this exceedingly delicate power of discrimination between light and darkness is localized in the pigmented ocelli situated at the tips of the rays in Star-fish, and occupying the homologous positions in Echini. The sense of touch we found likewise to be highly delicate, and provided for by a variety of specially modified organs. Lastly, I found that the sense of smell occurs in Star-fish, though it is not localized in any special olfactory organs, being in fact distributed equally over the whole of the ventral surface of the animal, to the exclusion, however, of the dorsal.* Among the Articulata we meet with numberless grades of / visual apparatus, from that of a simple ocellus, capable only of distinguishing light from darkness, up to the greatly elaborated compound eyes of insects and the higher Crus- tacea. These compound eyes are remarkable from the fact that each one of their possibly many thousand facets forms an image of the coiTesponding portion of the visual field — the multitude of separate sensory impressions being then combined into a mosaic-like whole by a sensorial operation taking place in the cephalic ganglion. In these compound eyes, moreover, the images are thrown upon the receptive nerve-surface without inversion. In the uncompounded or simple type of eye, on the other hand, the image is inverted, and as in the case of ants both kinds of eyes occur in the same individual, it has been thought a psychological puzzle how to explain the fact that mental confusion in the inter- pretation of images does not result. A little thought, how- ever, will show that the apparent puzzle is not a real one. Thus it is commonly said that we ourselves really see objects reversed, and that long practice enables us to correct the erroneous impressions. But this statement of the case is * See Phil. Trans., 1881, Pt. Ill, Croonian Lecture ; and, for smell in Star-fish, Journ. Linn. Soc, 1883. SENSATION. 85 not correct. " We do not really see things reversed, for the mind is not a perpendicular object in space, standing behind the retina in the manner that a photographer stands behind his camera. To the mind there is no up or down in the retina, except in so far as the retina is in relation to the external world ; and this relation can only be determined, not by sight, but by touch. And if only this relation is constant, it can make no difference to the mind whether the images are direct, reversed, or thrown upon the retina at any angle with reference to the horizon ; in any case the corre- lation between sight and touch would be equally easy to establish, and we should always sec things, not in the position in wdiich they ai'e thrown upon the retina, but in that which they occupy with reference to the retina. Thus it really re- quires no more ' practice' correctly to interpret inverted images than it does similarly to interpret upright images ; and therefore the fact that some eyes of an ant are sup- posed to throw direct images, wdiile others are supposed to throw inverted, is not any real objection to the theory" that they do.* There is no one group in the animal kingdom where we have so complete a series of gradations in the evolution of an organ of special sense as is presented by the organ of sight in Worms. " In the lowest Vermes," — I quote from Professor HcTeckelf — "the eye is only made up of individual pigment-cells. In others, refractive bodies are associated with these, and form a very simple lens. Behind these refractive bodies sensory cells are developed, forming a retina of the simplest order presenting a single layer, the cells of which are in connection with extremely delicate terminal fibres of the optic nerve. Lastly, in the Alcipidse, which are highly organized Annelidas that swim on the surface of the sea, adaptation to this mode of life has brought about such perfection of the eye that this organ in these animals is in no way inferior to that of the lower vertebrata. In these creatures we find a large globular eye-ball, enclosing externally a laminated globular lens, internally a vitreous body of large circumference. Imme- diately investing these are rods of the usual cells sensitive to light, which are separated by a layer of pigment-cells from the outer expansion of the optic nerve or retina. The ex- * Quoted from an article of my own in Nature, June 8, 1882. t Essay on Origin and Development of Sense-organs. 86 MENTAL EVOLUTION IN ANIMALS. ternal epidermis invests the whole of the prominent eye-ball, and forms in front of it a transparent horny layer, the cornea." Fnrther, from the more recent observations of Mr. Darwin, it is certain that Earthworms, although destitute of eyes, are able to distinguish with much rapidity and pre- cision between light and darkness ; and as he found that it is only the anterior extremity of the animal which displays this power, he concludes that the light affects the anterior ganglia immediately, or without the intervention of a sense-organ.* Lastly, Schneider says that Serpulse w411 suddenly Avithdraw their expanded tufts when a shadow falls upon them ; but the shadow must be that of an object moving with some rapidity. -|- Turning now to the sense of hearing in the Articulata, we find the simplest type of ear among the Vermes, where it occurs as a closed globular vesicle containing fluid in which there is suspended an otolith.J In some of the Crustacea, such as the cray-fish and lobster, the organ of hearing is much more complex, and here, " if we give rise, by playing the violin, to notes of varying pitch, and at the same time observe the auditory organ under the microscope, we see that at each note only a particular auditory hair is set in vibra- tion."§ Among Insects organs of hearing certainly occur, at least in some species, although the experiments of Sir John Lubbock appear to show that ants are deaf. The evidence that some insects are able to hear is not only morphological, but also physiological, because it is only on the supposition that they do that the fact of stridulation and other sexual sounds being made by certain insects can be explained ; and Brunelli found that when he separated a female grasshopper from the male by a distance of several metres, the male began to stridulate in order to inform her of his position, upon which the female approached him.|| I have myself published observations proving the occurrence of a sense of hearing among the Lepidoptera.^ Turning to the morphological side of the subject, it is remarkable that in the Articulata the * See EartJiioorms^ pp. 19-45. f Ber thierisohe Wille, s. 194. X Earthworms have no ears and are totally deaf, although very sensitive to vibrations communicated through contact with solid bodies. (See Darwin, loc. cit., pp. 26-7.) § Hseekel, loc. cit., English translation. International Library of Science and Freethought, vol. vi, p. 325. II See Houzeau, Fac. Mem. des Animaux, t. i, p. 60. i See Nature, vol. xv, p. 177. SENSATION. 87 auditory orojans occur among different members of the group in widely different parts of the body. Thus in tlie lobster and cray-fish they are situated in the head at the base of the antennules, while in some of the crabs {e.g., Mysis) they occur in the tail. Among the Orthoptera, again, they are found in the tibit^ of the front legs, or, in other species, upon the sides of the thorax. In other insects, probability points to the organs of hearing being placed in the antennae. These facts prove that in the Articulata the sundry kinds of auditory organs must have arisen independently, and have not been \P inherited from a common ancestor of the group ; and it is remarkable that this should have been the case even within the limits of so comparatively small a subdivision as that which separates a crab from a crayfish or a lobster."^ There can be no question that the sense of smell is well • developed in at least many of the Articulata, although, save in a few cases, we are not yet in a position to determine the olfactory organs. Thus the account which I quoted in '' Animal Intelligence" (p. 24), from Sir E. Tennent, concern- ing the habits of the land leeches of Ceylon, proves that these animals must be accredited with a positively astonishing delicacy of olfactory perception, seeing that they smell the approach of a horse or a man at a long distance. In earth- worms the sense of smell is feeble, and seems to be confined to certain odours.-f- Sir John Lubbock has proved by direct experiment that ants are able to perceive odours, and that they appear to do so by means of their antennse. The same ' remark applies to bees, and the general fact that many insects can smell is shown by the general fact that so many species of flowering plants, which depend for their fertilization upon the visits of insects, give out odours to attract them. That the Crustacea are able to smell is rendered evident by the rapidity with which they find food. I have recently been able to localize the olfactory organs of crabs and lobsters by a series of experiments which I have not yet published, and which would occupy too much space here to detail. I shall therefore merely say that they are situated in the pair of small antennules, the ends of which are curiously modified in order to perform the olfactory function. That is to say, the * Analogous facts are to be observed in the case of the Eye among Yermes, and also, as we shall presently see, among Moliusca. f Darwin, loc. cit.^ p- 30. 88 MENTAL EVOLUTION IN ANIMALS. terminal joint works in a vertical plane, and supports the sensory apparatus, which is kept in a perpetual jerking motion up and down, so as to bring that apparatus into sudden con- tact with any minute odoriferous particles which may be sus- pended in tiie water — just on the same principle as we our- selves smell by taking a number of small and sudden sniffs of air. Any one visiting an aquarium can have no difficulty in observing these movements upon any crab or lobster in a healthy condition. The sense of taste certainly occurs at least among some species of the Articulata (as, e.g., among the honey-feeding insects), and the sense of touch is more or less elaborately provided for in all. Turning now to the Mollusca, we pass in a tolerably uniform series from the simple eye-spots of certain of the Lamellibranchiata, through the Pteropoda, to the more com- pletely organized eyes of the Gasteropoda and the Heteropoda. But when we arrive at the Cephalopoda, we encounter, as it were, a vast leap of development ; for the eye of an octopus, in point of organization, is equal to that of a fish, which it so closely resembles. And, while remembering that the resemblance, striking though it be, is only superficial, we must not fail to note that this enormous development in the organi- zation of the molluscous eye, which brings it so strangely to resemble the eye of a fish, is clearly correlated with the no less enormous development of the neuro-muscular system of the animal, in which respect it more resembles a fish than it does the other Mollusca. This case is therefore analogous to the similarly high development which has been attained by the eye of the swimming worm previously described. If we look to the Mollusca as a class, we meet with the same kind of variation in the position of the eye which we have already noticed with respect to the ear in the Articulata. Thus, while in the Cephalopoda and Gasteropoda the eyes are situated in the head, in some of the latter group there are supplementary eyes upon the back, which greatly differ in structure from the eyes in the head. In the Lamelli- branchiata, again, the eyes occur in large numbers on the margin of the mantle. The sense of hearing is general to all the Mollusca, and the auditory organs exhibit a progressive elaboration as we ascend from the lower to the higher groups, which is analo- SENS ATI ox. 89 gous to that already noticed with reference to the organs of sight. Thus, among the lower Mollusca the organs of hearing consist of a pair of small vesicles attached to auditory nerves, and filled with fluid in which an otolith is suspended. In the Cephalopoda, however, while the same general plan of structure is adhered to, we find an approximation to the auditory apparatus of a fish ; for the vesicle or sac is now embedded in the cartilage of the head, is of larger size, and in general analogous to the organ of hearing of the Verte- brata. That at all events the majority of the Mollusca are able to smell, is proved by the readiness with which they find food, and the octopus is said to show a strong aversion to certain odours (Marshall). In the Cephalopoda the olfactory organs are probably two small cavities near the back of the eye, and in the other Mollusca they are surmised to be situated in the small tentacles near the mouth. Touch is provided for both by these and by the larger tentacles (as well as by the general soft exterior) ; but in the Cephalopoda by the long, snake-like arms, which I think must be regarded as giving these animals a greater power of receiving tactile impressions than is enjoyed by any other marine animal. Among Fish sight is well developed. A trout will dis- ) "? tinguish a worm suspended in muddy water ; a salmon can avoid obstacles when swimming with immense velocity ; and a Chelmon rostratus can take unerring aim with its little water projectile at a fly. The blind fish, which live habitually in the dark, have lost their eyes merely from disuse ; but in this connection it must be noted that we meet with a curious biological puzzle in the case of many of the deep sea fishes dredged by the Challenger. For although living at depths to which no light can be supposed to penetrate, some of these fish have large eyes. It may be suggested that the use of these eyes is that of seeing the many self-luminous forms of life which, as the Challenger dredgings also show^, inhabit the deep sea. But if this is suggested, the question immediately arises as to why these forms have become luminous; for if thus rendered conspicuous to the fish, their luminosity must so far be a disadvantage to them. In the case of the lumi- nous animals which themselves have eyes, we may suppose that this disadvantage is more than compensated for by the advantage of enabling the sexes to find each other; but this explanation does not apply to the blind forms. 90 MENTAL EVOLUTION IN ANIMALS. Fish, as we have already observed, are well provided with the organs both of hearing and of smell, Amphioxus being the only member of the class which is destitute of ears, and the olfactory lobes in the case of some species {e.g., the Skate) being of enormous size in relation to the other parts of the brain. Tlie sense of touch is provided for in many species by tentacular in the neighbourhood of the mouth. The soft lips, and in some species the pectoral fins, are also tactile in function, and in certain gurnards there are digitate appendages connected with the latter which doubtless serve to increase their efficiency as organs of touch. It is doubtful whether taste, as distinct from smell, occurs in fish ; but we must remember, as before observed, that in the case of an aquatic animal tliere is no true distinction to be drawn between these two senses. For as there is here no gaseous medium (like the air) in question, the only distinction that can be drawn is as to whether the nerve terminations, which are affected by the suspended particles in the water, happen to be dis- tributed over any part of the mouth where the food passes, or over any other j)art of the animal. I say over any other part of the animal (and not only in the nasal fosscc), because in some species of fish there are embedded in the skin along the sides of the body a number of curiously-formed papillae, which on morphological grounds may reasonably be regarded as ministering to the sense of smell, or, as we may indifferently call it, of taste. H?eckel, however, speculates upon these organs, and is inclined to think that they minister to some unknown sense. The sense of sight in Amphibia and Eeptiles offers nothing specially worthy of remark, except that the crystal- line lens has not so high a refracting power as in Fish. The transition from an eye adapted to see under water and an eye adapted to see in air, appears to be curiously shown by one and the same eye in the case of the Surinam Sprat. This animal has its eyes placed on the top of its head, so that when it comes to the surface of the water part of the eyes come into the air, and " the pupil is partly divided, and the lens is also composed of two portions, so that it is supposed that one part of this curious eye is adapted for aerial, and the other for aquatic, vision."* The senses of hearing, smell, taste, and touch, although all present in the * Marshall, Outlines of Physiology ^ vol. i, p. 603. SENSATIOX. 91 Amphibia and Eeptiles, are not much, if at all, in advance of these senses as they occur in Fish. Among Birds the sense of sight is proverbially keen, and in point of fact the animal kingdom has no parallel to the excellence of the organ of vision as it occurs in some species of this class. Whether we consider the eye of a Hawk, which is able to distinguish from a great height a protectively coloured animal from the surface of the ground which it so closely imitates ; or the eye of a Solen Goose, which is able from a height of a hundred feet in the air to see a fish at the deprli of many fathoms in tlie water ; or the eye of a Swift, which is able so suddenly to form its adj ustments ; we must alike conclude that the visual apparatus has attained to its highest perfection among birds. And in this connection it is of interest to note that protective colouring has attained its highest degree of perfection among animals which constitute the prey of birds. So surprising, indeed, is the perfection to which protective colouring has attained in some of these cases, that it has been adduced as a difficulty against the theory of evolution ; for it seems incredible that such perfec- tion should have been attained by slow stages through natural selection before the species exhibiting it had been extermi- nated by the birds. The answer to this difficulty is that the ^'isual organs of the birds cannot be supposed to have been always so perfect as they are now, and therefore that a degree of protective colouring which might have afforded efficient protection at an earlier stage in the evolution of those organs would not supply such jDrotection at the present day. In other w^ords, the evolution of the eyes of birds and of the protective coloration of their 23rey must be supposed to have progressed ;pari j^ctssic, each stage in the one acting as a cause in the succeeding stage of the other. The crystal- line lens is flat in birds which are remarkable for long^ sig'lit, such as the vulture ; rounder in owls, which are very near- sighted ; and becomes progressively more spherical in aquatic birds, according to their aquatic habits. All birds are able to hear, and it is in this class that we first meet with definite evidence of an ear capable of appre- ciating with delicacy differences of pitch. Among many species of birds the delicacy of such appreciation (as well as that of timbre) is so remarkable that it may be questioned whether even human ears are more efficient in this respect. 92 MENTAL EYOLUTIOX IN ANIMALS. The anatomical difficulty of accounting for this fact I need not wait to consider. I am myself inclined to think that the sense of hearing in birds (at all events of some species) is likewise highly delicate with reference to the intensity of sound. My reason for so thinking is that I have observed Curlews dig their long bills up to the base into smooth unbroken surfaces of sea-sand left bare by the tide, in order to draw up the concealed worms. Under such circumstances no indication can be given by the worm of its position to any other sense of the curlew than that of hearing. Similarly, I suspect that the common Thrush is guided to the worm buried beneath the turf by the sense of hearing, and my suspicion is founded on the peculiar habits of feeding shown by the bird, which I have described elsewhere.* The sense of smell in Birds is in advance of that of Eeptiles, but not to be compared with its excellency in Mammals ; for the old hypothesis that vultures find their prey by the aid of this sense has been abundantly disproved.! The sense of taste in Birds is likewise very obtuse as com- pared with this sense in Mammals ; and as compared with the same class they are also defective in their organs of touch. Indeed, the parrot tribe is the only one in which this sense is well or specially provided for, except the ducks, snipes, and other mud-feeding species, in which the bill is specially modified for this purpose. If we regard Mammals as a class we must say that, with the exception of the sense of vision which reaches its greatest supremacy in Birds, aU the special senses are more highly developed than in any other class. This is more particularly the case with the senses of smell, taste, and touch. The sense of smell reaches its highest perfection among the Carnivora and the Euminants, and, on the other hand, is totally absent in some of the Cetacea. Any one accustomed to deer-stalking must often have been astonished at the pre- cautions which it is needful to take in order to prevent the game from getting the " wind " of the sportsman ; indeed to a novice such precautions are apt to be regarded as implying a superstitious exaggeration of the possibilities of the olfac- * Nature, vol. xv, pp. 177 and 292, wliere also see in more detail my observations on the feeding habits of the curlew, t See Animal Intelligence, pp. 286-7. SENSATION. 93 tory sense ; and it is not until lie ]ias himself seen tlie deer scent him at some almost incredible distance that he lends himself without disguised contempt to the discretion of the keeper. But among the Carnivora the sense of smell is even more extraordinary in its development on account, no doubt, of its being here of so much service in tracking prey. I once tried an experiment with a terrier of my own which shows, better than anything that I have ever read, the almost supernatural capabilities of smell in Dogs. On a Bank holiday, when the broad walk in Regent's Park was swarm- ing with people of all kinds, walking in all directions, I took my terrier (which I knew had a splendid nose, and could track me for miles) along the walk, and, when his attention was diverted by a strange dog, I suddenly made a number of zig-zags across the broad walk, tlien stood on a seat, and watched the terrier. Finding I had not continued in the direction I was going when he left me, he went to the place where he had last seen me, and there, picking up my scent, tracked my footsteps over all the zig-zags I had made until he found me. Now in order to do this he had to distinguish my trail from at least a hundred others quite as fresh, and many thousands of others not so fresh, crossing it at all angles. Such being the astonishing perfection of smell in dogs, it has been well observed that the external world must be to these animals quite different from what it is to us ; the whole fabric of their ideas concerning it being so largely founded on what is virtually a new sense. But in this con- nection I may point out tliat speculation on such a subject is shown to be useless by the fact that the sense of smell in dogs does not appear to be merely our own sense of smell greatly magnified. For if this were the case it seems incredible that highly bred sporting-dogs, which have the finest noses, should be those which take the keenest pleasure in rolling in filth which literally stinks in our nostrils to the degree of being physically painful. The sense of hearing is acute in Mammals as a class, and it is worthy of remark that this is the only class provided with movable ears. As Paley observes, in beasts of prey the external ear is habitually directed forwards, while in species which they prey upon the ear admits of being directed back- wards. AVith the exception of the singing monkey {Hylohates agilis), there is no evidence of any mammal other tlian man 94 MENTAL EVOLUTION IN ANIMALS. having any delicate perception of pitch. I have, however, heard a terrier, which used to accompany a song by howling, follow the prolonged notes of the human voice with some approximation to unison ; and Dr. Huggins, who has a good ear, tells me that his large mastiff " Kepler " used to do the same to prolonged notes sounded from an organ. The sense of taste is much more highly developed in the Mammalia than in any other class, and the same general statement applies to the sense of touch. Looking to the class as a whole, the principal organs of the latter are the snout, lips, and tongue ; the modified hairs, or " whiskers," are also very generally present. Among the Rodents, some of the Mustelid?e and all the Primates, the principal organs of touch are the hands. And it would appear that the extreme modification which these members have undergone in the Cheiroptera has been attended with an extraordinary exalta- tion of their power of tactile sensation. For in the celebrated experiment of Spallanzani (since repeated and confirmed by several other observers), it was found that when a Bat is deprived of its eyes, and has its ears stopped up with cotton- wool, it is still able to fly about without apparent inconveni- ence, seeing that it avoids all obstacles in its flight, even though these be but slender strings stretched through the room in which the animal is allowed to fly. The only expla- nation of this surprising fact is that the membranous expanse of the wing, which is richly supplied with nerves, has developed a sensibility to touch, to temperature, or to both, so extreme as to inform the bat of the proximity of a solid body even before contact — either through the increase in the air-pressure as the wing rapidly approaches the solid body, or through the difference in the exchange of heat between the wing and the solid as compared with such ex- change between the wing and the air. When groping our way through a dark room we are ourselves able to feel a large solid body (such as a wall) before we actually touch it, especially, I have observed, with the skin of the face. Pro- bably, therefore, it is a great exaltation of this power which enables these night-flying animals to avoid so slender a solid body as a stretched string. But when we remember the rapidity and accuracy with which the sensation must here be aroused, we may well consider it to equal, if not to surpass, in the domain of touch, the evolutionary development of SEXSATIOX. 95 sense-organs as it occurs in the sight of the vulture or the smell of the dog. Indeed, Haeckel and others have specu- lated whether the facts in this case do not call for the suppo- sition of some additional and unknown sense, different in kind from any that we ourselves possess. But I think it is safer not to run into any such obscure hypothesis unless actually driven to do so, and therefore I shall not here enter- tain it. For this reason, also, I shall not follow Haeckel in his view that the " homing " faculty of certain animals is due to some additional and inexplical3le sense, and therefore I shall reserve my treatment of this topic for my chapters on Instinct. After this rapid survey of the powders of Special Sense as they severally occur in different classes of the animal king- dom, I shall conclude the present chapter by briefly consider- ing certain general principles connected with Sensation. The muscular sense, the sense of hunger, thirst, satiety, and others of the like general kind need not detain us; for although their causation is somewhat obscure, we know at least that they are dependent upon nervous adjustments, and, being of so much importance to animals, we infer that they have been developed under the general principles of neuro-muscular evolution already considered in previous chapters. My object here is rather to consider the mecha- nisms of certain more special senses from the point of view of those general principles. First as to the sense of Temperature, there is good evi- dence that in ourselves and at least in all the higher animals, thermal sensations can only be received by the nerve-endings in the skin and adjacent parts of the mucous membranes ; if the nerve-tibres immediately above their terminations in these localities (as in the raw surface of a wound) be stimu- lated by heat or cold, the sensation produced is merely one of pain. There is strong evidence that not only the nerve- endings, but even the whole of the nerve-tracts of which they are the endings, are specialized for the purpose of re- ceiving thermal impressions. These impressions, when received, are not absolute, but relative to tlie temperature of the part receiving them — the greater the difference of tem- perature between the part and the object touching it, the greater being the impression. Moreover, the greater the CT- 96 MENTAL EVOLUTION IN ANIMALS. extent of the receiving surface, the greater is the impression ; so that if tlie whole hand be immersed in water at 102°, the temperature of the water will be erroneously judged to be higher than that of another body of water at 104°, the tem- perature of which is simultaneously estimated by a single finger of the other hand ; and, similarly, smaller differences of temperature can be appreciated by the whole hand than by a single finger. According to Weber, the left hand is considerably more sensitive to temperature than the right ; and it is certain that different parts of the body differ greatly in this respect. The more sudden the change of temperature, the greater is the sensory effect. We have no means of testing the truth of any of these statements with reference to any of the Invertebrata, or even with reference to the cold-blooded Vertebrata ; but we can scarcely doubt that they apply in a general way to all the warm-blooded. The facts certainly show an elaborate provision for appreciating local changes of temperature occurring upon this and that part of the external surface (the general comfort or discom- fort arising from the body being kept at a normal tempera- ture or not is another matter, and one wdth w^hich the special mechanism we are considering is not concerned) ; and there- Ifore we have to contemplate the probable cause of its origin land development. At first sight we appear to encounter a difficulty which I wonder never to have seen adduced by opponents of evolu- tion. For in nature the only differences of temperature which normally occur in objects with which animals have any opportunity of coming into contact, are those between ice and objects heated by a tropical sun ; and no one animal ever has the opportunity of experiencing changes of tem- perature extending through anything like so great a range ; for in the arctic regions there is no tropical sun, in the tropics there is no ice, and in the temperate zones the solar heat is moderate. Of course since the introduction of fire by man, the sense of temperature has become of much use to sundry species of animals for the examination of food, &c., and in this connection is of almost indispensable service to man himself ; but, looking to the antecedents of these animals and also to the antecedents of man, it may at first sight seem remarkable that such an elaborate provision should have been developed, and, as I have said, I wonder that no SEXSATIOX. 97 opponent of evolution has pointed to the fact. For it might be argued that here we have a complicated piece of special organic machinery constructed in obvious anticipation of the advent of cookery and warm batlis. But I think the matter may be explained on evolutionary principles, if we remember that the only use of a sense of temperature is not that of examining food. We know that differences of temperature on the surface of the body (whether local or general) greatly modify the conditions of the circulation in the part or parts affected, and therefore it must always have been of use for animals to be provided with a sensory apparatus upon the surface of their bodies to give them immediate information of such differences. Its development along special lines (so that some parts of the body should be more sensitive to changes of temperature than other parts) is easily to be explained by the effects of habit or use. Thus, for example, the fact that the lips of man, although provided with a skin so delicate and so sensitive to tactile impressions, are never- theless able to endure a sudden rise of temperature which would be painful to the skin of the face, must be taken to mean that habit has adapted the nerves in the lips to with- stand a sudden rise of temperature — and this certainly within the period since the invention of cookery. Mr. Grant Allen takes a more general view of this sub- ject, and says : " To an animal, cold is death, and warmth is life. Hence it is not astonishing that animals should very early have developed a sense which informed them of changes of temperature taking place in their vicinity ; and that this sense should have been equally diffused over the whole organism As soon as moving creatures began to feel at all, they probably began to feel heat and cold."* The truth of such a general statement of this must be obvious, and the step between a sense of temperature equally diffused over the whole organism, and the specializa- tion of superficial nerve-endings to minister to this sense alone, is not a large step. IMoreover, the step between this and the development of a rudimentary visual organ is like- wise not a large one. For the deposition of dark-coloured pigment in particularly exposed parts of the skin must have been of benefit to animals by enabling (in virtue of the increased absorption of heat thus secured) the nerve-endings * Colour Sense, p. 13. G 98 MENTAL EVOLUTION IN ANIMALS. in those parts to be more sensitive to changes of temperature. iBut the deposition of pigment in such localities constitutes a ;favouring condition to the origination of an eye, or of an ,'organ whose sense of temperature becomes sufficiently 'developed to enable it to begin to distinguish between light and darkness. Thus, as Professor H?eckel eloquently re- marks : " The ordinary nerves of the skin which pass to these dark pigment-cells of the integument, have already trodden the first steps of that magnificent march, at the end of wliich they have attained to the highest development of the nerves of sensation — the optic nerves." Turning next to the sense of Colour, it appears from the • experiments of Engelmann already alluded to, that colour- j sense of a kind occurs as low down in the zoological scale as • the protoplasmic and unicellular organisms, inasmuch as particular species showed particular preferences for certain rays of the spectrum. But as in these organisms there are no organs of special sense, a ad probably no beginnings of consciousness, I do not think that any true analogy can be drawn between these cases and those in which there is a true sensation of colour. Nor have we any evidence of such a true sensation till we arrive at the Crustacea. Here we have proof, furnished by the direct experiments of Sir John Lubbock, that Daphnia pulex prefers certain rays of the spectrum to others,* and the Chameleon Shrimp (Mysis cha- meleo) is known to cliange its colour in imitation of the surface on which it reposes, provided that it is not blinded or otherwise prevented from seeing that surface. Precisely J^ analogous facts occur among the Cephalopoda {e.g., odojy^is), Batrachia (e.g., Common Frog), Pteptilia (e.g., Cameleon), and Pisces (e.g.. Flounder) ; in all these cases, if the animals are blinded, the effects no longer occur. Moreover, Pouchet found that in the Pleuronectidse the mechanism whereby these imitative changes of colour are produced is bilaterally disposed, so that if only one eye of the animal is stimulated by coloured light, only one side of the animal changes colour. M. Fredericq afterwards found the same thing to be true of the Octopus, and in conjunction with Professors Burdon- * Joiirn. Linn. Soc, 1881. These observations have been adversely criti- cized by Merejkowsky {Comj)tes Hendus, xciii, pp. 160-1), but his criticisms have been fully met by further experiments recently pubhshed by Sir John {Journ. Linn. Soc, 1883). SENSATION. 99 Sanderson, Cossar Ewart, and Mr. W. D. Scott, I have corroborated M. Fredericq's observations by a number of experiments ; stimulation of one eye alone by means of light produces immediate unilateral flushing of the whole of the same side of body, but no change of colour beyond the median line. As further proof that a well-developed sense of colour occurs in some of the Arfciculata, I may allude to the experi- ments of Sir John Lubbock on the Hymenoptera; but as these have been already twice published in the International Scientific Series,* I need not here wait to recapitulate them, and shall therefore only remark that it is without any rea- sonable question to the presence of this sense in insects that we owe the beauty both of floral and of insect coloration. Again, as further proof that a well-developed sense of colour occurs in Fish, I may remark that the elaborate care with which anglers dress their flies, and select this and that com- bination of tints for this and that locality, time of day, &c., shows that those who are practically acquainted with the habits of trout, salmon, and other fresh-water fish, regard the presence of a colour-sense in them as axiomatic. And, with reference to the sea-water fish in general, we have the highly competent opinion of Professor H. I^. Moseley to the effect that the great majority of the colours of marine animals have been acquired either for the protection or the allure- ment of prey, and that they refer particularly to the eyes of Fish, and also to those of Crustacea.! The fact that a sense of colour occurs in Birds is unques- tionable, and meets with its most general proof in the more or less conspicuous coloration of the fruits on which they feed ; for as in the analogous case of conspicuously coloured flowers depending on insects for their fertilization, so con- spicuously coloured fruits depend for the dissemination of their seeds upon being eaten by birds or mammals. Again, I have already mentioned the fact that nowhere in the animal kingdom does the protective and imitative colouring of animals attain to such nicety as it does where the eyes of birds are concerned. Lastly, the elaborate coloration of birds themselves, and the pleasure which some species take in the decoration of their nests, constitute supplementary * Viz., in Ants, Bees, and Wasps, and in Animal Intelliqenee. t Quarterly Journ. Micro. Science^ New Series, vol. xyii, pp. 19-22. G 2 100 MENTAL EYOLUTIOX IN ANIMALS. proof of the high development to which the colour-sense has attained in this class. All the remarks just made with reference to Birds, apply 5^ likewise, though not perhaps in quite so high a degree, to Mammals, considered as a class. And here it becomes need- ful to consider the speculation of Dr. Magnus and Mr. Glad- stone, that the colour-sense of man has undergone a great improvement within the last two thousand years, inasmuch as before that time mankind are supposed by this specula- tion to have perceived only the lower colours of the spec- trum, or red, orange, and yellow, and to have been colour- blind to the higher, or green, blue, and violet. Professor H^eckel lends his support to this speculation ; but to me it seems a highly improbable one, and this for the following reasons. In the first place the speculation is based merely on etymological grounds, which in a matter of this kind are exceedingly unsafe. For the absence in a language of words denoting particular colours is, at best, but negative evidence that the men who spoke the language were blind to those colours; the absence of such words may quite as well be due to the imperfection of language as to the imperfection of the visual sense. Thus, for instance, Professor Blackie tells us that the Highlanders call both sky and grass "gorm," and are nevertheless quite able to discriminate between the colours blue and greeiu In the next place, it is antecedently im- probable, upon the general principles of evolution, that a considerable change in the visual apparatus of man should have taken place within so short a period as the speculation in question assigns — especially in view of the fact that other Mammals, Birds, and even some of the Invertebrata un- questionably distinguish the higher as well as the lower colours of the spectrum. Lastly, Mr. Grant Allen has taken the trouble to enquire, by means of a table of questions addressed to educated Europeans in all parts of the world, whetlier any of the savage races of mankind now living display any inability to distinguish between the colours of the spectrum, and the answers which he has received have been uniformly in the negative.* I think, therefore, we may safely dismiss the speculation of Dr. Magnus and Mr. Glad- stone as opposed to all the evidence wliich is at once trust- worthy and available. But in saying this I do not intend to * Colour-sense^ Chapter X. SENSATION. 101 dispute the probability, which indeed amounts almost to a certainty, that as civilization advances and the fine arts become developed, the colour-sense undergoes a progressive improvement in its power of distinguishing between fine shades, and also in its power of ministering to a more and more evolved condition of a?stlietic feeling. And this, I believe, is the true explanation of the class of facts alluded to by Professor Hseckel as proof of the speculation which I have now discarded — the fact, namely, that '' nowadays we see in the surviving savage races a crudity as to their sense of colour .... Our little ones, also, like the savages, love assemblages of glaring hues which grate upon us, and susceptibility to the liarmony of delicate shades of colour is the latest product of aesthetic education." Professor Preyer has published within the last year or two a very interesting theory touching the origin and development of the colour sense, and as it has not, to my knowledge, been noticed in any English publication, I shall here state the main points. The theory is that the colour-sense is a special and highly-exalted development of the sense of temperature. To sustain this theory, Professor Preyer first compares the sensi- bility of the skin to temperature with that of the retina to light, and points out that the analogy has already been recognized by artists, who speak of colours as " warm " and " cold." " The warm colours arouse sensations of a character antagonistic to those which are aroused by the cold colours, in just the same way as the hot and cold sensations of skin- temperature are antagonistic ; and the more this analogy is pursued, the closer is the agreement found to be.'' Therefore ^/ the suggestion arises, " that the sense of colour has been , developed out of the sense of temperature," bespeaking a high refinement of functional activity which has its struc- tural correlative in the extremely differentiated and delicately organized expansion of nerve-endings which we find in the retina. A further analogy is that of contrasts. A finger that has been warmed or cooled retains its change of temperature for some time after it has ceased to be warmed or cooled ; and this is taken to correspond with the phenomena of positive after-images in sensations of colour. Moreover, while the after-efi'ect of warming or cooling a portion of the skin remains, the temperature-sense of that portion is altered in 102 MEXTAL EVOLUTION IN ANIMALS. such wise that, if it has been cooled, it over-estimates the temperature of any object it may touch, and vice versd. This is taken to be analogous to the appearance of warm colours in the eyes when closed immediately after having been exposed to intense cold colours, and vice versd. So, too, it is with simultaneous contrasts. It is well known that if a small colovnless surface is enclosed between two surfaces of cold or warm colours, the small surface will appear inversely coloured warm or cold, as the case may be ; and Professor Preyer has found by experiment, that if a small portion of the skin be enclosed by cold or warm surfaces on either side, the small enclosed area will feel cool if the neighbouring parts are heated, and vice versd. After showing that in his view illumination is to the sense of colour what contact is to the sense of fceinperature, and pointing out several subordinate analogies which I have no space to mention, Professor Preyer goes on to remark an important fact in relation to his theory, viz., that diiferent parts of the skin manifest in their estimations of tempera- ture great differences in their estimates of what he calls the " neutral point," i.e., the point at which it cannot be said that a body is felt to be either hot or cold. The retina, then, being supposed to be merely a nerve-expansion having a much higher " neutral point " in the appreciation of temperature (ethereal vibrations) than has any nerve-expansion of the skin, colour-blindness is explained by supposing that the retina of the individual so affected has a neutral point either above or below the normal. " An over- warm eye must be l)lind to yellow and blue ; an over -cool one must be blind to red and green." Total colour-blindness, which is a physio- logical characteristic among certain nocturnal animals, has its parallel in the pathological condition sometimes met with in man, of a total absence of the sense of temperature without impairment in the sense of touch. Lastly, it is observed that the first condition to the validity of any physiological hypothesis is that it should accord with morphological fact. But this is not the case with the theory of Young and Helmholtz, which ascribes the colour-sense to the functions of three retinal elements ; for it has been proved that the number of fibres in the optic nerve immediately before it enters the retina is much smaller than the number of rods and cones in the retina. SENSATION. 103 In my opinion tliis theory, in its main outlines, seems a probable, as it certainly is a plausible one. I do not, indeed, quite understand why, in accordance with the theory, the " neutral point " of the colour-blind should not merely be found to be shifted to another part of the spectrum, nor am I quite clear about the explanation of the fact that the warm colours are those havincj the lowest and not the hi^diest order of vibrations, as analogy would lead us to expect. But the theory has the merit of being antecedently probable, when we remember that in all likelihood the visual sense arose by the ' progressive elaboration of nerve-endings in particular parts of the skin, which before their special elaboration presumably ministered to the senses of touch and temperature. And this remark leads me to the last topic that I have to dwell upon in the present chapter. I refer to the body of morphological evidence which we now possess, showing that all the organs of special sense have had their origin in special ' elaborations of these nerves of the integument. For the uniform result of histological and embryological investigation is to show that all organs of special sense, wherever they occur and whatever degree of elaboration they present in the adult animal, are fundamentally alike in that their receptive surfaces are composed of more or less modified epithelium cells which originally constituted part of the external layer of the animal. Thus, the origin of the olfactory membrane in the embryo of the Vertebrata is found to consist in a pitting of the skin of the fore part of the head — the pits, therefore, being lined by the general layer of epidermic cells. The subsequent grow^th of the surrounding parts of the face eventually brings this lining to occupy the position which it does in the hollow parts of the nose. Similarly, the organs of hearing first begin as a pair of pits on the side parts of the head, situated somewhat far back, and likewise lined by the cells of the general integument. These pits rapidly deepen, so that their lining is pinched off or separated from the general integument of which it originally formed a part. The deep pit then becomes a closed sac, and the adjacent tissues becoming first cartilaginous and then osseous, this sac is enclosed well within the skull by bony w^alls. While its structure is undergoing further anatomical and histological changes, the drum, the chain of ear-bones, and the external ear are being formed, and thus eventually the auditory organ \ 104 MENTAL EVOLUTION IN ANIMALS. is completed. In the case of the eye, a gam, the earliest sign of commencement consists in a similar pitting of the general integnment, bnt the lining of this pit is not destined, as in the previous cases, to become the receptive surface of the sensory impressions. For, after it has deepened considerably it undergoes sundry changes which result in its forming the cornea, aqueous humour, and crystalline lens; while the retina arises as an offshoot from the brain in the form of a sac growing, as it were, upon a slender stalk towards the crystalline lens. At first the anterior surface of this sac is convex, but the posterior part afterwards becomes pushed into the cavity of the sac ; so that the anterior surface eventually becomes strongly concave. Therefore the sac is now, as Professor Huxley graphically describes it, "like a double night-cap, ready for the head, but the place which the head would occupy is taken by the vitreous humour, while the layer of night-cap next it becomes the retina." Thus the rods and cones of the retina are not developed immediately out of the epidermic cells of the integument ; but inasmuch as the brain is itself begun as an infolding of the epidermic layer, the rods and cones of the retina are ultimately derived from those epidermic cells. Or, again to quote Professor Huxley, "the rods and cones of the vertebrate eye are modified epidermal cells, as much as the crystalline cones of the insect or crustacean eye are."* Therefore, in the words of Professor I Hseckel, " the general conclusion has been reached that in ' man, and in all other animals, the sense-organs as a whole ari^e in essentially the same way, viz., as parts of the external integument or epidermis. The external integument is the origiual general sense-organ. Gradually the higher sense- organs detach themselves from this their primal condition, whilst they withdraw more or less completely into the pro- tecting parts of the body. Nevertheless in many [inverte- brate] animals, even at the present hour, they lie in the integument, as e.g., in the Vermes." I have entered thus fully into this general fact, because it is of importance, not only to the theory of evolution, but also to the philosophy of sensation, to know from such direct historical sources that all the special senses are chfferentiations of the general sense of toucli. * Science and Culture^ &c., p. 271. PLEASURES AND PAINS. 105 CHAPTEE YIIL Pleasures and Patns, Memory, and Association of Ideas. In the diagram I have represented Pleasures and Pains as occupying in their hrst origin a level not far removed from that at which Sensation takes its rise. I have also repre- sented a short interval between Sensation and the origin ot Perception, which is filled up in the lateral column by Memory and Primary Instincts. Therefore, before we pass on to consider the rise of Perception out of Sensation, I shall devote a chapter to a consideration of Pleasures and Pains Memory, and Association of Ideas. Pleasures and Pains. On this topic I have little to add to the treatment which it has received at the hands of Mr. Herbert Spencer, and of his disciple, Mr. Grant Allen.* Pains, as Mr. Spencer points u out, may be due to the want, of action (" craving"), or to an[' excess of action. These two classes correspond largely, ^ though not entirely, with the division of pains into massive and acute, which is formulated by Professor Bain. It also indicates the doctrine of Sir W. Hamilton and others, that Pain is due to excessive stimulatioQ. But it is important to observe that the statement of Mr. Spencer, while " recognizing at one extreme the positive pain of excessive actions," recog- nizes also " at the other extreme the negative pains of in- actions ; the implication is that Pleasures accompany actions / lying between these extremes." Mr. Grant Allen in the course of his able exposition of this subject, shows by many examples that " the Acute Pains, as a class, arise from the action of surrounding * See Principles of Psycholoqy and Physiological ^Esthetics, in both cases the chapter on " Pleasures and Pains." 106 MEXTAL EVOLUTION IN ANIMALS. destructive agencies; the Massive Pains, as a class, from excessive function or insufficient nutriment :" also that " Massive Pains, when pushed to an extreme, merge into the Acute Class," so that " the two classes are rather indefinite in their limits, being simply a convenient working distinction, not a natural division." Hence it follows that Pains of both classes " are the subjective concomitants of an actual disrup- tion or disruptive tendency in some one (or more) of the bodily tissues, provided the tissue be supplied with afferent cerebro-spinal nerves in unbroken connexion with the brain." Eeferring the reader to Mr. Allen's own essay for all matters of detail and criticism, I shall merely say that in my opinion he has successfully established this formula as applicable to all cases of Pain. His view concerning the physiology of Pleasure is substantially the same as that of Mr. Spencer already quoted ; but it is somewhat more extended and pre- cise. This view is that Pleasure is " the concomitant of a normal amount of activity in any portion or the whole of the oi'ganism," supplemented with the important addendum that " the strongest Pleasures result from the stimulation of the largest nervous organs, where activities are most intermittent ;" so that the amount of Pleasure is "in the direct ratio of the number of nerve-fibres involved, and in the inverse ratio of the natural frequency of excitation." Hence " we see wdierein the feeling of Pleasure fails to be exactly antithetical to the feeling of Pain, just as their objective antecedents similarly fail. Massive Pleasure can seldom or never attain the inten- sity of Massive Pain, because the organism can be brought down to almost any point of innutrition or exhaustion ; but its efficient working cannot be raised very high above the average. Similarly any special organ or plexus of nerves can undergo any amount of violent disruption or wasting away, giving rise to extremely Acute Pains ; but organs are very seldom so highly nurtured and so long deprived of their appropriate stimulant as to give rise to very Acute Pleasure." Now towards what conclusion do these generalizations point ? They clearly point to the conclusion, which I do not think is open to any one valid exception, that Pains are the subjective concomitants of such organic changes as are harm- ful to the organism, while Pleasures are the subjective con- comitants of such organic changes as are beneficial to the organism — or, we must add, to the species. The more this PLEASUEES AND PAINS. 107 doctrine is pursued in detail, the more unquestionable does its truth become. Thus there is to be perceived, not merely a general qualitative, but also a roughly quantitative relation between the amount of pain and the degree of hurtfulness, as well as between the amount of pleasure and tlie degree of tvJwlcsomeness* As Mr. Allen observes, " nothing can more thoroughly militate against the etticiency of the mechanism than the loss of one of its component parts : and we find accordingly that to deprive the body of any one of its mem- bers is painful in a degree roughly proportionate to the general value of such member to the organism as a whole. Take, for example, the relative j)ainfulness of severing from the body a leg, an arm, an eye, a finger-nail, a hair, or a piece of skin." Similarly with Pleasures, the least pleasurable are th'ose attending activities of the organism which are least important for its welfare (or for that of its species), while the most pleasurable are those which attend the satisfaction of hunger, thirst, and sexual desire — especially if, in terms of Mr. Allen's formula, the needs to which these cravings minister have been long unsatisfied, so that the organism is either in danger of enfeeblement and death, or in the most fit condition for propagating its kind. Pleasures of the intel- lectual kind, although subservient to the same general laws of nutrition and exhaustion, have reference to such complex nervous states, involving mental prevision of future contin- gencies, &c., that for the purposes of clear analysis they had best be here disregarded. The superficial or apparent objection to the doctrine we are considering which arises from the fact that feelings of Pleasure and Pain are not infallible indices of what is respec- tively beneficial or injurious to the organism, is easily met by the consideration that in all such exceptional cases it is not the doctrine but its application which is at fault. Thus, again to quote Mr. Allen, who in my opinion has given in brief compass the best analysis of the philosophy of Pleasure and Pain that has hitherto appeared, " every act, so long as it is pleasurable, is in so far a healthy and useful one ; and conversely, so long as it is painful, a morbid and destructive one. The fallacy lies in the proleptic employment of the words ' deleterious ' and ' useful.' To j^ut it in a simple form, * I use these antithetical words because their etymology alone suggests forcibly the doctrine in question. 108 MENTAL EVOLUTION IN ANIMALS. "^ tlie nervous system is not prophetic. It informs us of what is its actual state at the moment, not what the after-effects of that state will be. If we take sugar of lead, we receive at first a pleasant sensation of sweetness, because the immediate effect upon the nerves of taste is that of a healthy stimu- lation. Later on, when the poison begins to work, we are conscious of a painful sensation of griping, because the nerves of the intestines are tlien being actually disintegrated by the direct or indirect action of the irritant." Now if the doctrine before us is found to apply generally f; to all cases of Pleasure and of Pain, the implication is suffi- \ ciently apparent; Pleasures and Pains must have been evolved as the subjective accompaniment of processes which are respectively beneficial or injurious to the organism, and so evolved for the purpose or to the end that the organism should seek the one and shun the other. Or, to quote Mr. Spencer, " if we substitute for the word Pleasure the equivalent phrase — a feeling which we seek to bring into consciousness and retain there, and if we substitute for the word Pain the equivalent phrase — a feeling which we seek to get out of consciousness and to keep out; we see at once that, if the states of consciousness which a creature endeavours to maintain are the correlatives of injurious actions, and if the states of consciousness which it endeavours to expel are the correlatives of beneficial actions, it must quickly disappear through persistence in the injurious and avoidance of the beneficial. In other words, those races of beings only can have survived in which, on the average, agreeable or desired feelings went along with activities conducive to the mainten- ance of life, while disagreeable and habitually-avoided feelings went along with activities directly or indirectly destructive of life, and there must ever have been, otlier things equal, the most numerous and long-continued survivals among races in which these adjustments of feelings to actions were the best, tending ever to bring about perfect adjustments. " If we except the human race and some of the highest allied races, in which foresight of distant consequences intro- duces a complicating element, it is undeniable that every animal habitually persists in each act which gives j)leasure, so long as it does so, and desists from each act which gives pain. It is manifest that, for creatures of low intelligence, there can be no other guidance." PLEASURES AND TAIXS. 109 Thus, then, we see that the affixing of painful or disagree- able states of consciousness to deleterious changes of the organism, and the reverse states to reverse changes, has been a necessary function of the survival of the fittest. We may further see that in bringing about tliis adjustment or corre- spondence, the zoological principle of the survival of the littest must have been largely assisted by the physiological principle that Pleasure tends to accompany the normal activity of an organ and Pain to accompany its abnormal. For as organs are invariably of use to the organism, their normal activity must always be beneficial to it ; while, con- versely, their abnormal activity, tending to cause or being caused by their own disintegration, must always be liarmful to the organism. Survival of the fittest is thus provided with a ready-formed condition or tendency of psycho-physio- logy on which to work — a tendency which survival of the fittest may itself in earlier times have been instrumental in producing ; but which, in any case, wlien once established must greatly assist survival of the fittest in apportioning the appropriate state of consciousness to any particular organic process. Another principle of pyscho-physiology must likewise have greatly assisted natural selection in its execution of this work. This principle is that which obtains in so-called acquired tastes and distastes. Thus, as Mr. Spencer observes, " Pleasures and Pains may be acquired — may be, as it were, superimposed on certain feelings which did not originally yield them. Smokers, snuff-takers, and those who chew tobacco, furnish familiar instances of the way in which lono- persistence in a sensation not originally pleasurable, makes it pleasurable — the sensation itself remaining unchanged. The like happens with various foods and drinks, which, at first distasteful, are afterwards relished if frequently taken. Common sayings about the effects of habit imply recognition of this truth as holding with feelings of other orders. That acute pain can be superinduced on feelings originally agree- able or indifferent, we have no proof. But we have proof that the state of consciousness called disgust may be made inseparable from a feeling that once was pleasurable :" so that even in the life-time of the individual the states of consciousness as pleasurable or painful may reverse their character with reference to the same organic changes or sen- 110 MENTAL EVOLUTION IN ANIMALS. sations, and if this is the case it becomes evident with what plastic material natural selection has had to deal in moulding through numberless generations the form of consciousness which best fits, with reference to the welfare of the organism, the circumstances of stimulation. Thus we may well believe that survival of the fittest, acting always in co-operation with these principles of psycho- physiology, must have been successful in accomplishing the adjustments here assigned to its agency — the adjustments, that is, between states of consciousness as agreeable or dis- agreeable and circumstances of stimulation as beneficial or deleterious. And thus it is that in the process of evolution organisms "have gone on establishing a consensus between the various organs of the body, so that at last, for the most part, whatever will prove deleterious to any organ proves deleterious also to the first nerves of the organism which it affects," and therefore disagjreeable to consciousness, althouc^h of course, as we should from these principles expect, this is only the case "when the deleterious object is found suffi- ciently often in the environment to give an additional point of advantage to any species which is so adapted as to discriminate and reject it."* Thus then, it seems to me, we have as full a rationale of Pleasures and Pains as we can expect or need desire. The only difficulty is to understand the connection between the objective fact of injuriousness or the reverse, and the corre- sponding subjective state of consciousness ; how is it that injuriousness or the reverse comes to be, as it were, translated into the language of Pleasure and Pain. But this is only the old difficulty of understanding the connection of Mind with Body, and has no reference to historical psychology, which takes the fact of this connection as granted. Possibly, how- ever— and as a mere matter of speculation, the possibility is worth stating — in whatever way the inconceivable connection between Body and Mind came to be established, the primary cause of its establishment, or of the dawn of subjectivity, * Grant Allen, loc. cit., p. 27. The latter consideration disarms any criti- cism Avliich might be advanced against our doctrine on account of the agree- able taste of certain poisons, both to ourselves and to the lower animals. But it is astonishing even here how rapidly the appropriate distaste arises after experience of the injurious effects : witness the dislike of wine which may fre- quently be caused, even in those who are addicted to excess, by surreptitiously mixing it with nux-vomica. MEMORY AND ASSOCIATION OF IDEAS. Ill may have been this very need of inducing organisms to avoid the deleterious, and to seek the beneficial ; the raison cTetre of Consciousness may have been that of supplying the con- dition to the feeling of Pleasure and Pain. Be this as it may, however, it seems certain, as a matter of observable fact, that the association of Pleasure and Pain with organic states and processes which are respectively beneficial and deleterious to the organism, is the most important function of Conscious- ness in the scheme of Evolution. And for this reason I have placed the origin of Pleasures and Pains very low down in the scale of conscious life. Indeed, if we contemplate the subject, we shall find it difficult or impossible to imagine a form of consciousness, however dim, which does not present, in a correspondingly undeveloped condition, the capacity of preferring some of its states to others — that is, of feeling a distinction between quiescence and vague discomfort, which, with a larger accession of the mind-element, grows into the vivid contrast between a Pleasure and a Pain. I think, therefore, it is needless to say more in justification of the level on the diagram at which I have written these words. Memory and Association of Ideas. It is obvious that Memory must be, and is, a faculty which appears very early in the development of Mind. A priori, this must be so, because consciousness without memory would be useless to the animal possessing it, and a posteriori we find that this is so whether we contemplate the scale of mental evolution in the animal kingdom or in the growing child. I have therefore assigned the rise of Memory to the level immediately succeeding that which is occupied by the rise of Pleasures and Pains. In a previous chapter* I have endeavoured to show that, even before the dawn of Consciousness, nervous actions of adjustment when frequently repeated present conclusive evidence that the nervous machinery concerned in them becomes more or less organically adapted to perform them, and so exhibits the objective aspect of memory. This objec- tive aspect I spoke of as the memory of a ganglion. Since that chapter was A^Titten, M. Ptibot has published his excel- * On " tlie Physical Basis of Mind." y 112 MENTAL EVOLUTION IN ANIMALS. lent work on the " Diseases of Memory," wliicli has now been translated, and forms a member of the International Scientific Series. In this work M. Eibot deals fully Avith the complete analogy that obtains on the objective side between ganglionic memory — or, as he calls it, organic memory — and the physical changes in the cerebral hemispheres which are (concerned in true or conscious memory. I should like to express my satisfaction at finding so singularly close a corre- spondence between the views of M. Eibot and myself upon these matters, which extends into so many details that I have left my chapter already referred to verbatim as it was origi- nally written ; for it speaks in favour of the truth of one's results when they have been independently arrived at by another worker in the same field.* And here I may observe that I also agree with M. Eibot in his view that the phenomena of memory, whether " organic '"' or " psychological," present no point of true analogy with any such purely physical phenomena as the permanent effects upon a photographic plate of a short exposure to light, or any other phenomena where living organisms are not concerned. I further agree with him in his view that the earliest analogy we can find to memory is to be sought in living tissues other than nervous, and that it occurs in protoplasm. Thus he quotes Hering to the effect that muscular fibre " becomes stronger in proportion to its use." To this it may, I think, be objected that there is no evidence of individual muscular fibres thus gaining in strength by use. I think a better, because a more unexceptionable, parallel is afforded by the fact that when a constant galvanic current is allowed to pass for a short time through a bundle of mus- cular fibres, in the direction of their length, and is then opened, a change is found to have been produced in the excitability of the fibres such that they are less excitable than before to a stimulus supplied by again passing the current in the same direction, and more excitable to the stimulus sup- plied by passing the current in the opposite direction. This memory of a muscle touching the direction in which a gal- vanic stimulus has passed endures for a minute or two after the current has ceased to pass (Frog). I have found this * Any one who cares to trace the correspondence may do so by comparing my chapter above alluded to with the first chapter of M. Eibot's work. MEMORY AND ASSOCIATION OF IDEAS. 113 curious fact to hold in the case of muscular tissues of various animals, from the Medusa? upwards.* Again, I concur with M. Eibot in his opinion that the iy physical basis of memory consists partly in a more or less "^ permanent molecular change or " impress " produced upon the nervous element affected by the stimulus which is re- membered, and partly upon " the establishment of stable ■^■ connections between different groups of nervous elements." I do not think that the view can be too strongly reprobated which crudely supposes that the first of these physical con- ditions is alone sufficient to explain all the facts of memory, and therefore that a given remembrance is, as it were, stored up in a particular cell, as a particular *' impression " upon the substance of that cell. On the contrary, as M. Eibot shows, " Each of these supposed unities (memories) is com- posed of numberless and heterogeneous elements ; it is an association, a group, a fusion, a complexus, a multiplicity; . . . . Memory supposes not only a modification of , nervous elements, hut the formation among them of determi- nate associatio7is for each particular act. We must not, how- ever, forget that this is pure hypothesis — the best available one, no doubt, but still not to be taken as implying that we really know anything definitely concerning the physical sub- stratum of memory." Erofound, however, as our ignorance unquestionably is concerning the physical substratum of memory, I think w^e are at least justified in regarding this substratum as the same both in ganglionic or organic, and in conscious or psycholo- gical memory — seeing that the analogies between the two are so numerous and precise. Consciousness is but an adjunct which arises when the physical processes — owing to infre- quency of repetition, complexity of operation, or other causes — involve what I have before called gans^lionic friction. And this view is confirmed by the large and general fact noted in * See " Coneludiug Obserrations on tlie Locomotor System of Medusa?," Fhil. Trans., Pt. I, 1880; and on "Modification of "^Excitability," &e., Froc. Foy. Soc, Nos. 171 and 211. Also, Journal of Anatomy and Physio- logy, Tol. X. Another equally good instance of what may be termed proto- plasmic memory is to be found in the facts of the so-called " summation of stimuli," which occur more or less in all excitable tissues, i.e., -nherever living protoplasm is concerned. These facts are that if a succession of stimuli are applied to the excitable tissue, the latter becomes progressively more and more quick, as well as more and more energetic, in its response ; each stimulus leaves behind it an organic memorj of its occurrence. H 114 MENTAL EVOLUTION IN ANIMALS. our chapter on the Physical Basis of Mind, that conscious memory may become degraded into unconscious memory by repetition; associations originally mental lapsing into asso- ciations that are automatic. Thus much being premised touching the physical basis of memory, we may next pass on to consider the evolution of memory on its psychological side. The earliest stage of true or conscious memory may, I think, be regarded as consisting in the after-effect produced upon a sensory nerve by a stimulus, which after-effect, so long as it endures, is continuously carried up to the sensorium. Such, for instance, is the case with after-images on the retina, the after-pain of a blow, &c.* The next stage of memory that it appears to me possible to distinguish by any definite interval from the first-named, is that of feeling a present sensation to be like a past sensa- tion. In order to do this there may be no memory of the sensation between the two successive occasions of its occur- rence, and neither need there be any association of ideas. Only this takes place ; when the sensation recurs the second, third, or fourth time, &c., it is recognized as like the sensa- tion when it occurred the first time — as like a sensation which is not unfamiliar. Thus, for example, according to Sigismund, who has devoted much careful attention to the psychogenesis of infants, it appears that the sweet taste of milk being remembered by newly-born infants, causes them to prefer sweet tastes in general to tastes of any other kind. This preference of course endures long after the time of weaning is past, and generally continues through childhood ; but the interesting point in the present connection is that it occurs too early in the life of the child to admit of our sup- posing that any association of ideas can take part in the process. For Sigismund says that the memory of the taste of milk becomes attached to the perception '' immediately," and Preyer states, from independent observations of his own, that the preference shown for sweet tastes over tastes of all other kinds may be clearly seen as early as the first day. The next distinguishable stage of memory is reached when, still without any association of ideas, a present sensa- tion is perceived as unlike a past one. Thus, again turning to the observations of Sigismund and Preyer, it appears from * Compare Wundt, Qrundziige der philosophischen Psychologie, p. 791. MEMORY AND ASSOCIATION OF IDEAS. 115 them that after the accustomed taste of milk has become well fastened in the memory by several successive acts of sucking-, the child when a few days old is able to distinguish a change of milk. Similarly, I find among Mr. Darwin's MSS the following note : — " It is asserted (by Sir B. Brodie) that if a calf or infant has never been suckled by its mother, it is very much easier to bring it up by hand than if it has sucked only once. So again, Kirby and Spence state (from Eeaumur, ' Entomology,' vol. i, p. 391) that larv?e after having ' fed for a time on one plant will die rather than eat another, which would have been perfectly acceptable to them if accustomed to it from tlie first.' " It will be observed that in dealing with these stages of memory in very young infants, where as yet no association of ideas can either be supposed to be present or is needed to explain the facts, we at once encounter the question whether the memory is to be considered as really due to individual experience, or as an hereditary endowment, i.e., an instinct. And here it becomes apposite to refer to the old and highly interesting experiment of Galen, which definitely answers this question with reference to animals. For soon after its birth, and before it had ever sucked, Galen took a kid and placed before it a row of similar basins, filled respectively with milk, wine, oil, honey, and flour. The kid, after examin- ing the basins by smell, selected the one which was filled with milk. This unquestionably proves the fact of hereditary memory, or instinct, in the case of the kid ; and therefore it is probable that the same, at all events in part, applies to the case of the child. In proof of which I may allude to the experiments of Professor Kuszmaul, who found that even prior to individual experience derived from sucking milk, newly-born children show a preference for sweet tastes over all others. For, on their tongues being wetted with sugar or salt solutions, vinegar, quinine, &c., the new-born infants made all manner of grimaces, being pleased with the sugar solution, but with the others showing displeasure by a " sour face," a " bitter face," and so on. But although we freely admit that the memory of milk is. at all events in large part, hereditary, it is none the less memory of a kind, and occurs without the association of ideas. In other words, hereditary memory, or instinct, belongs to H 2 116 MEXTAL EVOLUTION IN ANIMALS. what I have marked off as the second and third stages of conscious memory in the largest acceptation of the term — the stages, that is, where, without any association of ideas, a pre- sent sensation is perceived as like or unlike a past one. It makes no essential difference whether the past sensation was actually experienced by the individual itself, or bequeathed to it, so to speak, by its ancestors. For it makes no essential difference whether the nervous changes which constitute the obverse aspect of the perceptive aptitude were occasioned during the life-time of the individual, or during that of the species and afterwards impressed by heredity on the indi- vidual. In either case the psychological as well as the physiological result is the same ; a present sensation is alike perceived by the individual as like or unlike a past sensation. It is not easy at first to grasp the truth of this statement ; but the source of the difticulty is in not clearly distinguish- ing between memory and the association of ideas. Memory in its lower stages which we are now considering has, in my opinion, nothing to do with the association of ideas. It only has to do with perceiving a present sensation as like or unlike a past sensation, which never can have formed the object of an idea between times, and which does not even arise as an ideal remembrance when the sensation again occurs. In other words, there is no act of conscious comparison between the two sensations ; there is not even any act of ideation ; but the past sensation has left its record in the nervous tissues of the animal in such wise that when it again occurs it emerges into consciousness as a feeling that is familiar — or if another unlike sensation takes its place, this emerges into consciousness as a feeling that is not familiar. And whether such feelings of familiarity or unfamiliarity arise in the experience of the individual or in that of the species, makes, as I have said, no essential difference either in the physiolo- gical or in the psychological aspect of the case. As showing how close is the connection between here- ditary memory, or instinct, and memory individually acquired, I shall briefly state some very interesting experiments which were made by Professor Preyer on newly-hatched chickens. He laid before a newly-hatched chicken some cooked white of egg, some cooked yolk of egg, and some millet seed. The chick pecked at all three, but no more frequently at the two latter than it did at pieces of egg-shell, grains of sand, or tlie MEMORY AND ASSOCIATION OF IDEAS. 117 spots and cracks of a wooden floor on which it was placed. But at the yellow yolk it pecked often and earnestly. He then removed all tln^ee substances, and after the lapse of an hour replaced them. The cliick instantly recognized them all, as proved by its immediately beginning to devour them while showing a complete disregard of all other and inedible objects. Yet in the first experiment the chick only once tasted the white of egg, and only took a single millet seed. The experi- ment therefore shows how apt a young chicken is to learn by its own individual experience, while in the opinion of Pro- fessor Preyer the original preference shown to the yolk of egg proves an inherited faculty of taste-discrimination. These experiments serve to introduce us to the stage of Memory at which the Association of Ideas is first concerned — a principle which throughout all subsequent stages consti- tutes what may be termed the vital principle of ]\Iemory — for the chickens which first pecked at inedible objects in tlie presence of edible ones, and an hour later were able to dis- tinguish between the two classes of objects, must have established a definite association of ideas between each of the particular objects of its former experience with reference to their edible or inedible character. But it is noteworthy that, as these definite associations were established so quickly and as the result of only a single individual experience in each case, we can scarcely avoid concluding that heredity must have had a large, if not the largest, part in the process — ^.just as in the case of distinguishing from the first the boiled yolk of egg, we must suppose that heredity had the exclusive part.* And this shows how closely the phenomena of here- ditary memory are related to those of individual memory ; at this stage in the evolution of mnemonics, where the simple association of ideas first occurs in very young animals, it is practically impossible to disentangle the effects of hereditary memory from those of individual. Association of Ideas. I shall reserve for my chapter on Imagination a full * It seems to me doubtful, however, wliether heredity here had reference to taste-discrimination, as Preyer supposes, seeing that in nature a young chicken can never have had an opportunity of tasting boiled yolk of egg. Probably the bright yellow colour had something to do with the selection, as many seeds are more or less yellow in tint. 118 MEXTAL EVOLUTION IN ANIMALS. analysis of Ideation. But in connection with Memory it is necessary to touch upon the Association of Ideas, and there- fore I shaU do so now, notwithstanding^ the disadvantao-e which arises from considering the property that ideas pre- sent of becoming associated before we consider the ideas themselves. The truth is that here as elsewhere one labours under a difficulty in dealing with the faculties of Mind in the probable order of their evohition, from the fact that these faculties require to be treated separately, although they have not arisen separately, or in historical sequence. Therefore one has to meet the difficulty by occasionally forestalling in earlier chapters general and well-known principles, the de- tailed consideration of which forms the subject-matter of later chapters. Such a difficulty arises now, and necessitates a somewhat premature treatment of what I may call the elements of ideation. Throughout the present work I shall use the word Idea in its widest sense. As few terms have been used with a greater variety of meanings, I think it is better to state here at the outset what I take to be its most general meaning, and therefore the one which, as I have said, I shall always attach to it. If after looking at a tree I close my eyes and then arouse a mental picture of what I have just seen, I may say indif- ferently that I remember or imagine the tree, or that I have an idea of it. The idea in this case would be simple or con- crete— the mere memory of a previous sensuous perception. Now between this and the highest product of ideation there is all the interval between the lowest and the highest develop- ment of Mind. The range of meaning over which the term Idea thus extends has seemed to many writers inconveniently large, and they have therefore imposed upon it various limi- tations. But as all such limitations are of a purely artificial kind, I shall nowhere limit the term in itself, but whenever I have occasion to specify one or other class of ideas, I shall do so by employing the convenient adjectives, Concrete, Abstract, and General, in the senses which I shall have to explain further on. Meanwhile it is enough to say that whenever I employ the term Idea alone, I mean it to be a generic term. We have already seen, while treating of the obverse or physiological side of ideation (in the chapter on the Physical ASSOCIATION OF IDEAS. 119 Basis of ]\Iiricl) that ideas have a strong tendency to cohere together in groups, so as to constitute one compound idea out of many simpler or more elementary ideas ; and also that they show no less strong a tendency to coliere together in concatenated series, such that the arousing of the first member determines the successive arousing of the other members. On its physiological side, as we saw, this is pre- cisely analogous on the one hand to the co-ordination of muscular movements in space (i.e., the grouping of such movements to form a simultaneous act, such as striking), and on tlie other hand to the co-ordination of muscular movements in time (i.e., the grouping of such movements to perform a serial act, such as vomiting). Now it is found by observa- tion that this cohesion of ideas is determined either by con- tiguity or by similarity. This fact is too well and generally known to call for more than a bare statement. Association by contiguity is more primitive than associa- tion by the similarity, for in order that there should be asso- ciation by similarity, the similarity must be iMrceived ; and this implies a higher level of mental evolution than is required to establish an association by contiguity — which, as we have seen, may be established even in non-mental nervous processes, while there is nothing truly analogous to associa- tion by similarity observable in such processes.* But it will be observed that even association of ideas by contiguity of the simplest possible kind, implies a higher development of the powers of memory than any of the three stages of memory which I have already indicated. For now there is not merely the memory of a past sensation (which is dormant till aroused by another like or unlike sensation) ; but there is the memory of at least two things, and also the memory of a previous relation of sequence between them. * The nearest approach to such an analogy is perhaps to be found in the curious fact, which I find to hold true in most persons, that if a pencil is taken in each hand, and while the habitual signature is being written with the right hand, moving from left to right, the movements are imitated by the left hand moving in the opposite direction, the signature will be found to bave been written backwards by the left hand, and even tbe hand-writing can be recognized on holding the paper before a mirror. As the left hand may never have performed this feat before, and cannot perform it unless the right hand is working simultaneously, the case looks like one of association by similarity. But I think it is really due to association by contiguity ; and the same applies to the extreme difficulty of moving the two hands simul- taneously as if carding wool in opposite directions. 120 MENTAL EVOLUTION IN ANIMALS. This, therefore, we may mark off as another distinct stage in the evolution of mnemonics. After this stage has advanced to a considerable extent, so that numerous concrete and compound ideas are associated in a great many chains of more or less length or number of links, a sufficient body of psychological data has been fur- nished to admit of the next stage of memory being reached, or that of association by similarity. Professor Bain remarks : '•' The force of contiguity strings together in the rnind words that have been uttered together ; the force of similarity brings forward recollections from different times and circumstances and connexions, and makes a new train out of many old ones."* And as in these higher planes of human memory, so in the lower ones of animal memory ; association by similarity implies a better development of ideation than does associa- tion by contiguity. The next and final stage of Memory is attained when reflection enables the mind to localize in the past the time when an event remembered took place. This is the stage of memory which is called EecoUection, and occurs in all cases where the mind knows that some particular association of ideas has previously been formed, and is therefore able deli- berately to search the memory until the particular association required is brought into the light of consciousness. I have now given a sketch of the successive stages in the evolution of Memory, drawing a line to mark o& a stage wherever I have been able to distinguish a place where a line could be drawn. It is needless to say that here, as in all similar cases, I deem these lines to be of a purely arbitrary character, and introduce them only to give a general idea of the upward growth of a continuously developing faculty. I shall now conclude this chapter by briefly glancing at the animal kingdom and the growing child with reference to the evolution of Memory. , Taking first the case of the child, I have assigned the ' seventh week as the appropriate age at which to mark the first evidence of memory in the association of ideas. I do so because I have observed that this is the age at which hand- fed children first recognize the feeding-bottle, i.e., an artificial object without smell or other quality that can arouse any ancestral instincts, and one which young infants always * Senses and Intellect, p. 469. ASSOCIATION OF IDEAS. 121 appear to recognize earlier than any other object. Locke, indeed, mentions recognition of the feeding-bottle as con- temporaneous with that of the rod; but as our ideas on matters of education have undergone some improvement since his time, this statement would now be difficult to verify. In my own child I observed that the power of asso- ciating ideas extended in the ninth week frord the feeding- bottle to the bib, which was always and only put on before feeding; for as soon as this was put on the child used to cease to cry for the bottle. At this age, also, I observed that when I put her woollen shoe upon her hand she gazed at it intently, as if perceiving that some curious change had come over the habitual appearance of the hand. At ten weeks she knew her bottle so well that she would place the nipple of it in her own mouth, and, when allowed to do so, w^ould hold the bottle herself while sucking. Generally, however, she would fail in her attempts at introducing the nipple into her mouth, clearly from a lack of co-ordinating power in her muscles — the nipple striking various parts of her face. She would then cry for the nurse to help. Preyer says* that at eight months old his child was able to classily all glass bottles as resembling, or belonging to the same order of objects, as a feeding-bottle. I may add that at seven weeks old my child used to cry wdien left alone in a silent room for a few minutes — a fact which also seems to show a rudimentary power of associating ideas, with the consequent perception of a change in the habitual environment. Turning now to the animal kingdom, the first evidence of memory that I have found in the psychological scale is in the Gasteropoda, and consists in the Limpet returning to its groove in the rock after having been crawling about upon a browsing excursion.! This fact, I think, clearly proves the power of remembering locality, and as such a grade of memory can scarcely be regarded as the earliest, we may reasonably suppose that the faculty really occurs still lower in the psycho- logical scale of animals, although we have not as yet any observations to prove the fact. Moreover, as Oysters learn by individual experience, acquired in the "Oyster-schools," to keep their shells closed for a much longer time than is natural to uneducated individuals, J we must conclude that a dim power * Loc. cit., p. 42. t Animal Intelligence, pp. 28-9. t -Z'5?(/., p. 25. 122 l^IEXTAL EVOLUTION IN ANIMALS. of memory is also present in the division of the Mollusca. The Razor-fish, likewise, shows memory, and this in a high degree, inasmuch as if only once alarmed upon coming to the surface of its burrow, it cannot be again induced to approach the surface for a long time, even by the application of irri- tants.* Still more remarkable is the level of development to which memory has attained in the Snail, if the observation of Mr. Lonsdale is to be accepted of the Helix pomatia, which, after leaving its sickly mate and crawling over a garden wall, returned next day to the place where it had left its mate.f But the highest level to which the development of memory attains in the Mollusca is unquestionably in the Cephalopoda, for according to Hollmann an Octopus remembered its en- counter with a lobster in a remarkable manner,t while according to Schneider these animals learn to know their keepers. J Seeing that memory in various stages of development thus unquestionably occurs among the Mollusca, I thought it worth while to try some experiments in this connection with the Echinodermata, but they all yielded negative results. It has, however, been alleged that if a star-fish be removed from its eggs, it will crawl back again to the place where they were ; and if this statement were confirmed, it would of course prove memory in the Echinodermata. Hitherto I have myself had no opportunity of testing it, and therefore my expe- riments were confined to endeavouring to teach star-fish a few simple lessons, which, as I have already implied, they would not learn. I am more surprised with my failure in this respect with the higher Crustacea ; for although I have tried similar experiments with them, I have never been able to teach them the simplest things. Thus, for instance, I have taken a hermit crab, put it into a tank filled with water, and when he had protruded his head from the shell of the whelk in which he was residing, I gently moved towards him a pair of open scissors, and gave him plenty of time to see the glistening object. Then, slowly including the tip of one of his tentacles between the open blades, I suddenly cut off the tip. Of course the animal immediately drew back into th« shell, and remained there for a considerable time. When he again came out I repeated the operation as before, and so on * Animal Intelligence, p. 26. f Ibid., p. 27. % Ibid., p. 30. ASSOCIATION OF IDEAS. 123 for a great number of times, till all the tentacles had been progressively cut away little by little. Yet the animal never learnt to associate the appearance of the scissors with the effect which always followed it, and so never drew in until the snip had been given. Nevertheless, that memory does occur among the higher Crustacea is proved by an observation quoted in "Animal Intelligence" (p. 233), concerning a lobster mounting guard upon a heap of shingle beneath which it had previously hidden some food. In another class of the Articulata, however, the faculty of memory has been developed to an extraordinary degree, and far surpasses that which has been attained by any other class of Invertebrata. The class of the Articulata to which I allude are the Insects, and, more particularly, the Hymenoptera. Without quoting in extenso the evidence on this head which has already been given in my previous work, it is enough to say in general terms that ants and bees are unquestionably able to remember the places wdiere many months before they have obtained honey or sugar, &c. ; and will also, when occasion requires, return to nests and hives which they have deserted the year before. Many interesting observations have also been made on the rate of acquisition and the length or duration of particular memories in these animals, which, however, it is needless for me again to quote.* Perhaps the most interesting of these are the observations of Sir John Lubbock on bees gradually learning to know the difference between an open and a closed window, and the observations of Messrs. Bates and Belt on the sand- w^ asps carefully teach- ing themselves (by taking mental notes of landmarks) the localities to w^hich they intend to return in order to secure the prey which they have temporarily concealed. Incidental evidence of memory in other orders of Insects will also be found on referring to my previous w^ork — viz., for Beetles, pp. 227 — 9, for Earwigs, p. 229, and for the common House- ^y, p. 230. Turning now to the Vertebrata, we find that in Fish memory is certainly present, although it never reaches more than such a degree of development as is implied by remem- bering in successive years the locality for spawning, learning to avoid baits, removing young from a nest which has been * For a full account of all these observations, see Animal Intelligence^ under the heading " Memory," of Chap. Ill and IV. 124 MENTAL EVOLUTION IN ANIMALS. disturbed, and associating the sound of a bell with the arrival of food.* Batrachians and Eeptiles are able to remember localities, and also to identify persons.f The annual migration of Turtles further proves the duration of memory for at least a year. In Birds the power of memory has advanced considerably beyond that of remembering, as in the case of the swallow, the precise locality of their nests from season to season, and even beyond that of identifying persons from year to year.J For the facts which I have previously detailed at length touching the acquisition by talking birds of tones, words, and phrases, show not only an exceedingly high development of the powers of special association, but even the power of genuine recollection to the extent of knowing that there is a missing link in the train of a previously formed association, and of purposely endeavouring to recover it. Quotations from Dr. Wilks, Mr. Venn, and Mr. Walter Pollock were also given, in order to show from direct and careful observation that the process of forming special associations is in such cases identical with that which occurs in man.§ Among Mammals the highest development of memory is presented by the Horse, Dog, and Elephant. Thus there is unexceptionable evidence of a horse remembering a road and a stable after an interval of eight years ;|| of a dog remem- bering the sound of his master's voice after an interval of five years,ir and the sound of a clinking collar after an interval of three years ;1 and of an elephant remembering his keeper after having run wild for an interval of fifteen years.** It is probable, also, that if observations were made, the memory of Monkeys would be found to be very retentive, as it certainly is most minute, and largely assisted by the intentional efforts of the animals themselves. ft * See Animal Intelligence, pp. 248-51. f Ibid., pp. 254-62. X Ibid., p. 266. § For all these facts, see ihid., pp. 266-70. II Ibid., p. 330. IT Ibid., p. 438. ** Ihid., p. 387. ft Ibid., pp. 485-98. PERCEPTION. 125 CHAPTER IX. Perception. At the level marked 18 I represent the rise from Sensa- tion to Perception. By this term I mean, in accordancef with general usage, the faculty of cognition. " The contrast' between Sensation and Perception is the contrast l)etween the sensitive and the cognitive, intellectual, or knowledge- giving functions." (Bain.) " Perception is an establishment of specific relations among states of consciousness ; and this is distinguished from the establishment of these states of consciousness themselves," which constitutes Sensation. (Spencer.) " In Perception the material of Sensation is\ acted on by the mind, wliich embodies in its present attitude | all the results of its past growth." (Sully.) Sensation, then, does not involve any of the powers of' the intellect as distinguished from consciousness, but Percep- tion implies the necessary occurrence of an intellectual or cognitive process, even though it be a process of the simplest possible kind. The term Percej)tion, therefore, may be applied to all cases where a process of cognition occurs, whether such process arises directly or indirectly out of sen- sation ; thus it is equally correct to say that we perceive the colour or the scent of a rose, and that we perceive the truth or the probability of a proposition. Otherwise phrased we may state the distinction between Sensation and Perception thus. A sensation is an elementary; or uu decomposable state of consciousness, but a perception involves a process of mentally interpreting the sensation in terms of past experience. For instance, there is a closed book lying on the table before me ; my eyes have been resting on its cover for a considerable time while I have been thinking how I should arrange the material of the present chapter. All that time I have been receiving a visual sensation of a 126 MENTAL EVOLUTION IN ANIMALS. particular kind ; but, as I did not attend to it, the sensation did not involve any element of cognition, and therefore did not minister to any act of perception. All at once, however, I became conscious that I was looking at a book, and in cognizing that the particular object of sensation was a book, I performed an act of perception. In other words, I men- tally interpreted the sensation in terms of past experience ; I made a mental synthesis of the qualities of the object, and assigned it to the class of objects which had previously produced a like sensation. Perception, then, is a mental classifying of sensations in terms of past experience, whether ancestral or individual ; it is sensation |7/?6S the mental ingredient of interpretation. Now, as a condition to the possibility of this ingredient, it is clearly essential that there should be present the power of memory ; for only by a memory of past experience can the process be conducted of identifying present sensations or experiences as resembling past ones. Therefore in the diagram I have placed the dawn of Memory on the level, just below tliat at which the faculty of Perception takes its rise. Both Sensation and Perception are represented as attaining a considerable vertical elevation from base to apex, i.e., from their first origin to their completed evolution. That this ought to be so represented is evident if we reflect on the difference in the sensuous faculties of a medusa and an eagle, or between the perceptive faculties of a limpet and a man. It may, indeed, be thought that in my representative diagram I have not allowed enough for such differences, and therefore have made the vertical elevation of these branches too low. But here we must remember that in the case of Sen- sation, as already shown, the advance of the faculty from its earliest to its latest stages consists essentially, on its morpho- logical aspect, of a greater and greater degree of specializa- tion of end-organs of nerves ; and I think that the degree of such advance is sufiiciently expressed by the vertical elevation which I have given to the branch in question, seeing how much more intricate must be the morphological development of the nerve-tissues which are concerned in ministering to the next and to all succeeding faculties. And, as regards Perception, we must remember that in its more highly elaborated phases this faculty shades off into the higher representative branches marked " Imagination," &c. ; so that PERCEPTION. 127 the branch marked " Perception " is not intended to include all that might possibly be included by the term if we did not separately name the higher faculties to which I aUude. Now concerning the development of Perception, I may here make a general remark, which is first applicable at this stage of mental evolution, and which continues to be appli- cable to the development of all the faculties which we have subsequently to consider. This remark is that we have ceased to possess any data of a morphological kind — such as we had in the case of Sensation and the pre-mental faculties of adjustment — to guide us in our estimate of the degree of elaboration to which the faculty has attained. That morpho- logical evolution has here, as in the coarser instance of Sen- sation, always gone hand in hand with psychical evolution, is amply proved in a general way by the advancing complexity of the central nerve-organs ; but just because this complexity is so great, and the steps in morphological evolution which it represents so refined, we are totally at a loss to follow the process on its morphological side ; we are unable even dimly to understand the mechanisms which we see. Therefore, in j| order to estimate the ascending grades of excellence which!-' these mechanisms present, we require to look to what we may most conveniently regard as the products of their operation ;f we have to use the mental equivalents as indices of the mor-' phological facts. We have seen that Perception is essentially a process of mentally interpreting Sensation in terms of past experience, ancestral or individual. The successive steps in the elabora-' tion which this process undergoes in the course of its evolution must now be considered. The first stage of Perception consists merely in perceiving \ an external object as an external object, whetlier by the sense of touch, taste, smell, hearing, or sight. But confining our- selves, for the sake of brevity, to the sense of sight, in this stage Perception simply amounts to a cognition of an object in space, having certain space relations with other objects of perception, and especially with the percipient organism. The next stage of Perception is reached when the simplest 1 qualities of an object are re-cognized as like or unlike the qualities presented by such an object in past experience. The most universal of such qualities in objects pertain to size form, colour, light, shade, rest, and motion ; less universally 128 MENTAL EVOLUTION IN ANIMALS, sucli qualities pertain to temperature, hardness, softness, roughness, smoothness, and other qualities appealing to the sense of touch, as well as qualities appealing to the senses of smell, taste, and hearing. In the case of these more universal qualities, the part which the mind takes in the process of cognizing them as belonging to the objects is immediate and automatic, and, as Mr. Sully observes, " may be supposed to answer to the most constant and therefore the most deeply organized connections of experience." The third step in the advance of Perception consists in the mental grouping of objects with reference to their quali- ties, as when we associate the coolness, taste, &c., of a particular fruit with its size, form, and colour. Here the more frequently a certain class of qualities has been con- joined with another class in past experience, the more readily or automatically is the percej)tive association established ; but in cases where the conjunction of qualities has not been so frequently or so constantly met with in past experience, we are able by reflection to recognize the perceptive association "as a kind of intellectual working up of the materials supplied us by the past." A further develojDment of the perceptive faculty is re- quired to meet cases in which the qualities of objects have become too numerous or complex to be all perceived simulta- neously. In meeting such cases the faculty in question, while perceiving some of the qualities through sensation, supplements the immediate information so derived with information derived from previously formed knowledge ; the qualities which are not recognized immediately through sen- sation are inferred. Thus, in my perception of a closed book I have no doubt that the covers are filled with a number of printed pages, although none of these pages are actually objects of present sensation. Or, if I hear a savage growl, I immediately infer the presence of an object presenting so complex a group of unseen qualities as are collectively com- prised in a dangerous dog. In a later chapter I shall have to dwell more minutely on this, which I may term the inferential stage of perception, and I shall therefore not deal more with it at present. It will be evident that the various stages which I have named in the development of Perception shade into one another, so as not really to be distinguishable as separate PERCEPTION. 129 stages ; they constitute rather one uniform growth on which, as in the case of Memory, I have arbitrarily marked these several grades of evolution. Moreover, it will be evident that the term " Perception " is really a very wide one, and may be said to cover the whole area of psychology, from the confines of an almost unfelt sensation up to the recognition of an obscure truth in science or philosophy. On this account the term has been condemned by some psychologists as too extensive in its application to be distinctive of any particular faculty ; but nevertheless it is clearly impossible to do without it, and if we are careful to remember the sense in which we employ it — whether with reference to the lower or to the higher faculties of mind — no harm can arise from its use. I have just said that in the highest stage of its develop- ment Perception involves Inference ; and I have previously said that in its lowest stages it involves Memory. I must now point out more particularly that in its ascending stages Perception involves Memory of ascending stages. Thus the perception shown by a new-born infant of sweet tastes as distinguished from sour tastes and the rest, implies the presence of that lowest stage of memory which we have seen to consist in cognizing a present sensation as like a j)ast sen- sation. Again, the power of discerning a change of milk implies the power of cognizing a present sensation as unlike a past sensation. Next, when memory advances to the stage of associating ideas by contiguity, perception also advances to the stage of re- cognizing objects with their qualities and relations of coexistence and sequence. This in turn leads to the power of recognizing objects, qualities, and relations by similarity — the power on which w^e have seen the next phase of memory to depend. And, lastly, from this point onwards perception throughout depends exclusively upon the associa- tion of ideas, no matter how elaborate or refined such association may become. The fact that perception is thus everywhere and indis- solubly bound up with memory, is an important fact to be clear about ; for when memory becomes so habitual as to be virtually automatic or unconscious, we are apt to lose sight of the connection between it and perception. Thus, as Mr. Spencer observes, we do not speak of remembering that the sun shines ; yet we speak of perceiving that the sun shines. As a matter of fact, however, we do remember that the sun I 130 MENTAL EVOLUTION IN ANIMALS. shines, and in all the habitual phenomena of experience such memories as this become so blended with our perceptions of tlie phenomena that the memories may be said to form integral parts of the perceptions. Suppose, for instance, we see a man whose face we know, but cannot remember who the man is. Here the perception that the object which we see is a man, and not any other of the innumerable objects in Nature, is so intimately bound up with a well organized association of ideas, that we do not think of the perception thus far as really depending on memory. It is only when we turn to the incompletely organized association of ideas between the particular face and the particular individual, that we recognize the incompleteness of this part of the perception to depend upon the incompleteness of memory. Now these considerations, obvious though they appear, constitute the first stage in a disagreement on an important matter of principle, which will become more pronounced when I have to deal with the liigher faculties of mind, and which, I regret to say, has reference to the writings of Mr. Spencer. In his chapter on Memory Mr. Spencer takes the view that, so long as " psychical changes are completely automatic, memory, as we understand it, cannot exist — there cannot exist these irregular psychical changes seen in the association of ideas." Now, I have already given my reasons for not restricting the term Memory to the association of ideas ; but, passing over this point, I cannot agree that if psychical changes (as dis- ' tinguished from physiological changesj are completely auto- matic, they are on this account precluded from being regai'ded as mnemonic. Because I have so often seen the sun shine, that my memory of it, as shining, has become automatic, I see no reason why my memory of this fact, simply on account of its perfection, should be called no-memory. And similarly with all those well-organized memories which constitute integral parts of perceptions. In so far as they involve true " psychological changes," and therefore imply the presence of conscious recognition as distinguished from reflex action, so far, I think, no line of demarcation should be drawn between them and any less perfect memories. I shall recur to this point when I come to consider Mr. Spencer's views on Instinct and Eeason. Another point which we have here to consider is the part which heredity has played in forming the perceptive faculty PERCEPTION. 131 of the individual prior to its own experience. We have abeady seen that heredity plays an important part in forming memory of ancestral experiences, and thus it is that many animals come into the world with their powers of perception already largely developed. Tliis is shown not only by such cases as those of Galen's kid, and Preyer's chickens before mentioned, but by all the host of instincts displayed by newly-born or newly-hatched animals, both Vertebrate and Invertebrate. This subject will be fully considered when I come to treat of Instinct, and then it will be found that the wealth of ready-formed information, and therefore of ready- made powers of perception, with wliich many newly-born or newly-hatched animals are provided, is so great and so precise, that it scarcely requires to be supplemented by the subsequent experience of the individual. In different classes of animals these hereditary endowments vary much both in kind and in degree. Thus, with mammals as a class, heredi- ^ tary perception has reference in its earliest stages to the senses of smell and of taste ; for while many mammals are born blind, some probably deaf, and all certainly very deficient in powers of locomotion, they invariably show more or less perceptive powers of taste, and very frequently well-advanced perceptive powers of smell. This we have already seen in the case of Galen's kid, and in the case of the dog (whose ancestors have depended so largely upon the perfection of smell) the same thing occurs in so high a degree, that so special an olfactory impression as is produced by the odour of a cat will cause a litter of newly-born puppies to " putf and spit."* Birds come into the world with better endowments of perception than animals of any other class. For they are in full possession of every sense almost immediately after they are hatched, and, as we shall see later on, they are then able to use their senses nearly as well as they are ever able to use them. Reptiles are likewise hatched with their powers of percep- tion almost as highly developed as they are ever destined to become,! and the same as a rule is true of invertebrated animals. I must now say a few words on the physiology of Percep- * See p. 164. t See Animal Intelligence, pp. 256-7. I 2 132 MENTAL EVOLUTION IN ANIMALS. tion — or, more correctly, on what is known touching the physiological processes which accompany Perception. In earlier chapters I have already stated that the only distinction which is known on the physiological side between a nervous activity which is accompanied by consciousness, and a nervous activity which is not so accompanied, consists in a difference of time. I shall now give the experimental data on which the statement rests. Professor Exner has determined the time which is occu- pied by a nerve-centre of man in executing its part in the performance of a reflex action. That is to say, the rate of transmission of a stimulus along a nerve being known, and the length both of the afferent and efferent nerves concerned in a particular reflex act being known, as also is the " period of latency " of a muscle ; the time occupied by the nerve-centre in conducting its operations was determined by subtracting the time occupied by the passage of the stimulus along the afferent and efferent nerves, plus the period of latency of a muscle, from the total time between the fall of the stimulus and the occurrence of the muscular contraction. This time was found in the case of the reflex closure of the eye-lid to vary between 0-0471 and 0-0555 of a second according to the strength of the stimulus.* By a similar process Exner has estimated the time required for the central nervous operations which are together comprised in having a simple sensation, perceiving the sensation, and the volitional act of signalling the perception. That is to say, an electrical shock being administered to one hand, and as quickly as possible signalled by the other, the time occupied by the nerve-centre in performing its part of the process was esti- mated as in the previous case. This time in the case of this experiment was found to be 0-0828'^, which is nearly twice as long as that which, as we have just seen, is required for a nerve-centre to perform its x^^rt in a reflex action.-f- Acts of perception in which different senses are concerned occupy difterent times. This interesting topic has been investigated by a number of physiologists.| According to Bonders the total "reaction-time" {i.e., between stimulus and response) is, roughly speaking, for touch -f , for hearing ^, * Arcli.f. d. ges. Physiol., xliii, 526 (1874). t Ibid., vii, p. 610. X See Herman, Sandh. d. Fhysiol, Bel. II, Tli. 2, s. 264. PERCEPTION. 133 and for sight y of a second.* The observations of Von Wit- tichf, Vintscligau, and Honig-Schnied:|: show that the reaction- time for taste varies between 0'1598^' to 0*2 3 51'' according to the kind of taste ; being least for salt, more for sugar, and most for quinine. A constant electrical current applied to the tongue gives a reaction-time for the resulting gustatory impression of 0'16 V. I am not aware that any experiments have been made with regard to smell. Exner has more minutely determined on himself the reaction- time for touch, sound, and sii>-ht, with the results which are embodied in the following table. The signal was in all cases given by the right hand depressing an electrical key : — Direct electrical stimulation of retina . . , . 0*1139'' Electrical shock on left hand . . . . . . 0"1276 Sudden sound 0-1360 Electric shock on forehead. . .. .. .. 0"1370 Electric shock on right hand . . . . . . 0'1390 Visual impression from electric spark . . . . 01 506 Electric shock on toe of left foot . . . . . . 0'1749§ It is thus noticeable that although the sensation of light pro- duced by vision of an electric spark is much greater than that produced by electrical stimulation of the optic nerve, the interval between the stimulation and the perception is much longer in the former case. Seeing that the optic nerve is so short, this difference cannot be attributed tc the time lost in transmission along the nerve, and must therefore be supposed due to the time required for the nerve-endings in the retina to complete all the changes (whatever they may be) in which their response to luminous stimulation consists. Thus in the case of hearing, as the above table sliows, some- what less time is consumed in the whole act of perception than is consumed in the case of sight by the peripheral changes taking place in the retina. According to HeLmholtz and Baxt, the more complex an object of visual perception is, the greater must be the dura- tion of its image upon the retina, in order that the perception may be made ; while, within certain limits, the intensity of the image does not affect the time required to make the per- * Arch.f. Anat. und PhijsioL, 1^68, p. 657. t qt. Ret. Med. (3), xxxi, p. 113. X Arch.f. Anat. und PhifftioL, x, p. 1. § Pfiiiger'sArchiv., Bd.'VII, p. 620. 134 MENTAL EVOLUTION IN ANIMALS. ception.* The last-named author found j that an exposure of §L- second is required for the perception of a row of six or seven letters. Other experiments prove that the more complex an act of perception, the more time is required for its performance. Thus Donders has shown that when an experiment in re- action-time is made to consist, not merely in signalling a perception, but in signalling one of two or more perceptions, the reaction-time is lengthened, owing to the greater time required for performing the more complex psychical process of distinguishing which of the expected stimuli is perceived, and in determining to make or to withhold the response accordingly. The state of matters thus presented to the mind is called by Donders a " Dilemma,'" and the following is his table of results : — Dilemma between two spots of tlie skin, rigM or left foot stimulated by an electric shock ; signal to be made in one case only 0'066" Dilemma of visual perceptions between two coloui's, sud- denly exhibited ; signal to be made on seeing the one but not on seeing the other . . . . . . . . . . 0'184 Dilemma between two letters ; signal to be made on seeing one only . . . . . . . . . . . . . . 0*166 Dilemma between five letters ; signal as before .. .. 0*170 Dilemma of hearing ; two vowels suddenly called ; signal to be made on hearing one only . . . . . . . . 0*056 Dilemma between five vowels ; signal' as before . . . . 0*088 The above table gives, in each case, not tlie whole period between the occurrence of the stimulus and the occurrence of the response, but the difference between the time required for this whole period when a single stimulus has to be answered, and when only one of two or more possible stimuli has to be answered. It will tlius be seen that the time required for the act of meeting a dilemma is from -J- to ^ of a second longer than that which is required to signal a simpler perception.! This " Dilemma- time"" has also been estimated where the other senses are concerned by Kries and Auerbach, with the following results : — % * Archiv. f. d. ges. Fhysiol., Bd. TV, p. 329 ; Monatsher. d. JSer. Acad., June, 1871. t For Donders' investigations, see Archiv. f. Anat. und Phyaiol., 1868, pp. 657-81. X Archiv. f, d. ges. Physiol., 187^, pp. 298-380. PEECEPTION. 135 Localization by sight . . . . . . « . 0*011'' Distinguishing colour . . . . . . . . 0"012 Localization by licaring (least interval) .. 0*015 Distinguishing pitch (high notes) . . . . 0'019 Localization by touch . . . . . . . . 0021 Distinguishing pitch (low notes) . . . . 0'034 Localization by hearing (greatest interval) . . 0062 If a greater number of alternatives are allowed by the ' preconcerted arrangement, a still longer interval is required for the response. The time required for perception in the case of all the senses varies with different persons, and, under the name of "personal equation," has to be carefully determined by astronomers. It is increased by old age, sundry kinds of sickness, and sundry kinds of drugs. But it is not neces- sarily less in young people full of vitality than it is in young- people of less vigorous or lively temperaments. According to Exner, persons who are accustomed to allow their ideas to run slipshod are relatively slow in forming their perceptions, or, at least, have a long reaction-time between receiving and re- sponding to a stimulus. He gives the following table to show the difference in the reaction-time of seven indi- viduals : — * Age. Eeaction-time. Kemarks. 26 0 1337 Rough, lively labouring-man. 23 0-3311 Lively in movements, but rather slow in apprehen- sion. 76 0-9952 Infirm and not intelligent. 24 0-1751 Slow and deliberate in movements. 20 0 -2562 Slow and somewhat uncertain in movements. 22 0-1295 Slow and very precise in movements. 35 0-1381 Accustomed to manual work. Concerning the effects of drugs it is enough to say that Exner found two bottles of Ehine-wine increased his reaction- time from 0-1904^' to 0-2269'' ;t and I have myself observed while shooting that an amount of alcohol not sufficient to produce any consciously psychical effects, is apt to make one shoot behind one's birds. And here, with reference to the personal equation, I may briefly allude to some * Loc. cit., p. 612. t Loc. cif., p. 628. 136 MENTAL EVOLUTION IN ANIMALS. hitherto unpublished observations of my own, which has served to display a positively astonishing difference between different individuals with respect to the rate at which they are able to read. Of course reading implies enormously intricate processes of perception both of the sensuous and of the intellectual order ; but if we choose for these observa- tions persons who have been accustomed to read much, we may consider that they are all very much on a par with respect to the amount of practice which they have had, so that the differences in their rates of reading may fairly be attributed to real differences in their rates of forming com- plex perceptions in rapid succession, and not to any merely accidental differences arising from greater or less facility acquired by special practice. My experiments consisted in marking a brief printed paragraph in a book which had never been read by any of the persons to whom it was to be presented. The paragraph, which contained simple statements of simple facts, was marked on the margin with pencil. The book was then placed before the reader open, the page however being covered with a sheet of paper. Having pointed out to the reader upon this sheet of paper what part of the underlying page the marked paragraph occupied, I suddenly removed the sheet of paper with one hand, while I started a chronograph with the other. Twenty seconds being allowed for reading the paragraph (ten lines octavo), as soon as the time was up I again suddenly placed the sheet of paper over the printed page, passed the book on to the next reader, and repeated the experiment as befoi^e. Meanwhile the first reader, the moment after the book had been removed, wrote down all that he or she could remember having read. And so on with all the other readers. Now the results of a number of experiments conducted on this method were to show, as 1 have said, astonishing differ- ences in the maximum rate of reading which is possible to different individuals, all of whom have been accustomed to extensive reading. That is to say, the difference may amount to 4 to 1 ; or, otherwise stated, in a given time one indi- vidual may be able to read four times as much as another. Moreover, it appeared that there was no relationship b,etween slowness of reading and power of assimilation ; on the con- trary, when aU the efforts are directed to assimilatiu'^ PEECEPTION. 137 much as possible in a given time, the rapid readers (as shown by their written notes) usually give a better account of the portions of the paragraph which has been compassed by the slow readers than the latter are able to give ; and the most rapid reader whom I have found is also the best at assimi- lating. I should further say that there is no relationship between rapidity of perception as thus tested and intellectual activity as tested by the general results of intellectual work ; for I have tried the experiment with several highly dis- tinguished men in science and literature, most of whom I found to be slow readers. Lastly, it is worth observing that every one who tries this experiment finds that it is impossi- ble, with any amount of effort at recollection, to remember, immediately after reading the paragraph, all the ideas which have been communicated to the mind by the paragraph. But as soon as the paragraph is read a second time, the forgotten ideas are instantly recognized as having been present to the mind while reading. This sliows that tlie memory of a full perception may, as it were, be immediately crowded out by rapidly succeeding perceptions, to the extent of being rendered latent, although it may be instantly recalled by the recurrence of the same perception. So much, then, to show that the personal equation in different individuals varies the more the greater the number and the higher the intricacy of the perceptions which are to be made in a given time. I must now say a few words to show that the personal equation in the same individual admits of being greatly reduced by practice in making par- ticular perceptions. This is well known to astronomers so far as simple acts of perception are concerned, and in all the researches above mentioned touching the time-measurements of simple perceptions, the experimenters found that practice had the effect of reducino- the reaction-time. The deo'ree of reduction which might thus be produced was itself made the subject of experiment by Exner, who chose tlie old man already mentioned in one of tlie above quoted tables as having the unusually long reaction-time of 0-99o2''. After a little more than six months' practice at the rapid signalling of an electric shock, the old man's reaction-time was reduced to 0-1866'^ This universal fact of repetition serving greatly to reduce the physiological time required for the performance of phy- 138 MENTAL EVOLUTION IN ANIMALS. sical processes even of the simplest kind, is a fact of great significance. And, that the same applies to perceptions of the most mnltitudinous and complex kind, is proved in every-day life by the acquired rapidity with which bankers' clerks are able to add np figures, musicians to read a compli- cated score at sight, &c. But perhaps one of the best cases to quote in this connection is the celebrated one of the result of a systematic course of training to which the conjuror Houdin submitted his son. The training consisted in making the boy walk rapidly before a shop window, and perceive as many objects in the window as possible. After several months the boy was able to devour so many objects at a glance, that his father advertised him as " gifted with a mar- vellous second sight ; after his eyes have been covered with a thick bandage he will designate every object presented to him by the audience."* That is to say, the boy, before his eyes were bandaged, was able to perceive all the objects in the room which were likely to be presented to him. It is of interest to note that Houdin, who thus paid special attention to the development of rapidity of perception, observes that women as a rule have a greater rapidity than men, and says that he has known ladies who were able while seeing another lady " pass at full speed in a carriage, have time to analyze her toilette from her bonnet to her shoes, and be able to describe not only the fasliion and quality of the stuffs, but also say if the lace were real or only machine made."t I mention this opinion of Houdin because in my own obser- vations on rapid reading I have been struck with the fact that ladies nearly always carry off the palm. Dr. G. Buccola has shown in a recently published essay that the reaction-time is, as a general rule, less among edu- cated than it is among uneducated persons, and greatest among idiots.J I may also direct attention to an interesting paper published a few months ago by Mr. G. Stanley Hall,§ " On the lengthening of the Eeaction-time under the Influence of Hypnotism :" the lengthening is not so considerable as might have been anticipated. I have dwelt thus at length on all the main facts which * Memories of Hohert Soudin, voL ii, p. 9. Professor Preyer lias also published some observations on this subject. f Ihid., p. 7. X La durata del discernimento e della determinazione volition, Rivisti di Fllos. Scientif., I, p. 2. § Mind, No. XXX. PERCEPTION. 139 are at present known concerning the time-relations observ- able in Perception, because with reference to the theory of the rise of consciousness, and also of the physiological side of mental evolution in general, these facts are of the highest importance. They prove by actual measurement that the simplest psychical actions are slow as compared with reflex actions, that they can be rendered more rapid by practice, , but that they can never be brought to be so rapid as reflex actions. We have a further exemplification of the effects of practice in thus quickening the act of perception in the higher stages of the process. For universally the effect of previous acts of perception is that of placing the mind in readiness, as it were, for performing acts of the same kind. The mental attitude as regards these particular acts of per- ception is then the attitude of what Lewes appropriately called pre-perception.* When the pre-perceptive stage is well established, the memory, or the memory and inference as the case may be, arise in or together with the act of per- ception, so forming an integral part of the act. It is owing to the want of special experiences that young children are so slow in forming perceptions of more than the lowest degree of complexity ; as Mr. Spencer observes, they take a long time to " integrate " a strange face or other unfamiliar object ; and this, otherwise stated, means that their mental attitude of pre-perception has not yet been fully attained for such and such classes of objects ; the processes of memory, classifica- tion, and inference do not occur immediately in the act of perception, and therefore the full mental interpretation of the object perceived is only arrived at by degrees. Similarly, in adult life the powers of perception may be trained to a mar- vellous extent in special lines by practice, as we have already seen in the example of Houdin's son, and as we may also see in the fact that an " artist sees details where to other eyes there is a vague or confused mass." The influence of per- sistent attention is the most important of all influences in developing the rapidity and accuracy of the perceptive powers in which their highest excellence consists. We have now to consider the important question whether jj * Problems of Life and Mind, 3rd ser., p. 107. See also Dr. J. Hugh- lings Jackson in Brain, Nos. Ill and IV ; and Mr. Sully, in Illusions, pp. 27-30. 140 MENTAL EVOLUTION IN ANIMALS. Perception arises out of Eeflex Action, Eeflex Action out of Perception, or whether tliere is any genetic continuity be- tween the two at all. This is a most difficult question, and one which I do not think we are as yet entitled to answer with any kind of scientific confidence. According to Mr. Spencer the perceptive faculties arise out of the reflex when these attain a certain level of intricacy in their structure, or a certain degree of rarity in their occur- rence. Thus he says, " When, as a consequence of advancing complexity and decreasing frequency in the groups of external relations responded to, there arise groups of internal relations which are imperfectly organized and fall short of automatic regularity ; then, what we call Memory, becomes nascent."* But as a matter of fact it seems, I think, very questionable whether the only factors which lead to the differentiating of psychical nervous processes from reflex nervous processes are thus complexity of opei^ation combined with infrequency of occurrence. For it is obvious that in ourselves certain truly reflex actions are of immense intricacy and of exceed- ingly rare occurrence — such, for example, as vomiting and parturition. The truth is that, so far as definite knowledge entitles us to say anything, the only constant physiological difference between a nervous process accompanied by con- sciousness and a nervous process not so accompanied, is that of time. In very many cases, no doubt, this difference may be caused by the intricacy or by the novelty of the nervous process which is accompanied by consciousness ; but, for the reason which I have given, I do not think we are justified in concluding that these are the only factors, although I have no doubt that they are highly important factors. For all that we know to the contrary, natural selection or other causes may have determined the physiological conditions necessary to the rise of consciousness (and so to the perception of pleasure and pain), without any question as to intricacy or infrequency being concerned ; in which case the time- relations needed to meet these conditions would have become evolved together with them. And I think it speaks in favour of some such view as this that the structure of the cerebral hemispheres is in some respects strikingly unlike the structure of the reflex centres. Be the factors what they may, however, it is a great * Frinciples of Psychology ^ voL i, p. 446. PERCEPTION. 141 matter to have the sure ground of experiment on which to rest the fact that universally psychical processes represent comparative delay of ganglionic action. For from this fact the obvious deduction is, as stated in a previous chapter, that psychical processes constitute the subjective expression of objective turmoil among molecular forces ; reflex action may be regarded as the rapid movement of a well-oiled machine, consciousness is the heat evolved by the internal friction of some other machine, and psychical processes as the lio^ht which is mven out when such heat rises to redness. Presumably, tlierefore, psychical processes arise with a vivid- ness and intricacy proportional to the amount of ganglionic friction — as, indeed, appears to be experimentally proved by' the observations of Bonders before described. Now it is certain that by frequency of repetition, — i.e., by practice in the performance of any particular psychical act — the amount of this ganglionic friction admits of being lessened (as shown by the time required for the ganglionic action being reduced), and that concurrently with this change on the objective side of matters, a change takes place on the subjective, in that the action which was previously conscious tends to become automatic. Now from these considerations I think the inference would appear to be, that reflex action and perception probably advance together — each stage in the development of the one serving as the groundwork for the next stage in the develop- ment of the other. And in corroboration of this view is the sjeneral fact, that throuo-hout the animal kinodom there is a pretty constant correspondence between the complexity of the reflex actions presented by an organism and the level of its psychical development. 142 MENTAL EVOLUTION IN ANIMALS. CHAPTEE X. Imagination. We have already considered the psychology of Ideation to the extent of dehning the sense in which I employ the word " Idea" or " Image," and also to the extent of tracing, both on the side of physiology and on that of psychology, the prin- ciple of the association of ideas.* We have now to analyze the psychology of Ideation somewhat more in detail. The simplest case of an idea is the memory of a sensa- l tion. That a sensation may be remembered even when there has been no perception is proved, not only by the fact before mentioned that an infant only a day or two old can distin- guish a change of milk, but also by the fact, which must be familiar to all, that several minutes after an unperceived sensation is past, we are able by reflection to remember that we have had the sensation. For example, a man reading a book may hear a clock strike from one to five strokes (or perhaps more) without perceiving the sound, yet a minute or two afterwards he can recall the past sensation and tell the number of strokes which have occurred. And in simpler instances the memory of a sensation may extend over a much longer time. The simplest case of an idea, then, being the memory of a past sensation (as distinguished from the memory of a past perception), it follows that the earliest stages of ideation must be held to correspond with those earlier stages of memory which we have already described, wherein as yet there is no association of ideas, but merely a perception of a present sensation as like or unlike a past one. Hence in its most elementary form an idea may be said to consist in the faint revival of a sensation. This view has already been advanced with much clearness by Mr. Spencer, Professor * See Chapters II and III. IMAGINATION. 143 Bain, and others, who also maintain, with considerable pro- bability, that the cerebral change accompanying the idea of a past sensation is the same in kind and place, though not in degree of intensity, as was the cerebral change which accom- panied the original sensation.* In its next stage of development Ideation may be re- garded as the memory of a simple perception, and imme- diately after this the principle of association by contiguity 11 ' comes in. Later on there arises association by similarity, V** and from this point onwards Ideation advances by abstrac- /" tion, generalization, and symbolic construction, in ways and degrees which will constitute one of the topics to be con- sidered in my next work. From this brief sketch, then, it will be seen that we have \ already considered the lowest stages of Ideation while treating ll of Memory and the Association of Ideas. Eesuming, there- fore, the analysis at the point where we there left it, I shall devote this chapter to a consideration of those higlier phases of the idea-forming powers which we may conveniently in- clude under the general term Imagination. Now, under this general term we include a variety of mental states, which although all bearing kinship to one another, are so diverse in the degree of mental development which they betoken that we must begin by analyzing them. As used in popular phraseology, the word Imagination is * Tlius, Mr. Spencer says, " The idea is an imperfect and feeble repetition of the original impression . . . There is first a presented manifestation of the riyid order, and then, afterwards, there may come a represented manifestation that is like it except in being much less distinct." {First Principles, p. 145.) And Professor Bain says, " What is the manner of occupation of the brain with a resuscitated feeling of resistance, a smell, or a sound ? There is only one answer that seems admissible. The renewed feeling occtipies the very same parts, and in the same manner, as the original feeling, and no other parts, nor in any other assignable manner." {Senses and Intellect, p. 338.) While quite assenting to this view of ideation, so far as the psychology of the sub- ject is concerned, I think we are much too ignorant of the physiology of cerebration to indulge in any such confident assertions respecting the precise seat and manner of the formation of ideas. Again, with reference to Mr. Spencer's views, it is needless to repeat the point in n-hich I disagree with him touching the earliest stages of memory — or those before the advt nt of the association of ideas. Only I may point out tliat as the simplest possible idea is held to consist in a faint revival of a sensation (as distinguished from a perception), it follows that the occurrence of the simplest possible idea precedes the occurrence of its association with any other idea ; and if so, the memory of the sensation, or the faint revival of the sensation in which the idea is held to consist, must also precede any association with other faint revivals of the same kind. 144 MENTAL EVOLUTION IN ANIMALS. taken to mean the highest development of the faculty in the intentional imaging of past impressions. In this sense we speak of the imaginations of the poet, imaginations of the heart, scientific use of the imagination, and so on ; in all of which cases we presuppose the powers of high abstraction as well as those of intentional ideal combinations of former actual impressions. It is needless to say that even in man, long before the faculty in question attains to this degree of development, it occurs in lower degrees. Indeed, this highest degree may be said to bear the same relation to the lower degrees that recollection bears to memory ; it implies the introspective searching of the mind with the conscious purpose of forming an ideal structure. But just as recollec- tion is preceded by memory, or the power of intentional association by that of sensuous association, so is imagination of the intentional kind preceded by imagination of the sensuous. After considering the subject I think we may, for the purposes of analysis, conveniently divide the grades of Imagination into four classes : — 1. On seeing any object, such as an orange, we are at once re-minded of the taste of an orange — have an imagina- tion of that taste ; and this is ^called up by the force of mere sensuous association. This is the lowest stage of mental imagery. 2. Next we hai^e the stage in which we form a mental picture of an absent object suggested to us by some other object, as when water may suggest to us the idea of wine. 3. At a still higher stage[we may form an idea indepen- dently of any obvious suggestion from without, as when a lover thinks of his mistress even in spite of external dis- tractions ; the course of ideation is here self-sustained, and no longer dependent for its mind-pictures (ideas) upon the suggestions of immediate sense-perceptions. At this stage we have dreaming in sleep, where the course of ideation runs on in a continuous stream when all tlie channels of sense are closed. 4. Lastly we have the stage of intentionally forming mind-pictures with the set purpose of obtaining new ideal combinations. Such being the great differences in the degrees to which the faculty of Imagination may attain, I have made the IMAGINATION. 145 branch in tlie diagram wliich represents the faculty a very long one, reaching from level 19 to level 38. The top of the branch therefore reaches as high as the top of Abstraction,' about as high as two-thirds of Generalization, and beyond the origin of Keflectio]!. Of course these comparative esti- mates are intended here, as elsewhere, to indicate merely with some rough approximation to the probable truth the relative amount of elaboration presented by each of the mental species which we denominate faculties. I consider, indeed, as I have said before, that these species are them- selves of an artificial or conventional character — that what we call faculties are abstractions of our own making rather than objective or independent actualities, -and therefore that the classification of these faculties by psychologists only deserves in some remote sense to be regarded as a natural one. Still it is the best classification available for the purpose of comparing one grade of mental evolution w4th another, and there can be no harm in adopting it if we remember, what I desire ahvays to be remembered, that my representative tree is designed only to show the general relation between the faculties of mind as these have been formulated by psychologists. But even on this rough and general plan it may seem to , require explanation why I represent the apex of Imagina- tion as attaining to the same level as the apex of Abstraction, for psychologists might naturally infer from my doing so that I am inadvertently endorsing the doctrine of f¥infln[rtimi1imTi J^L^ Such, however, is not the case. For, althoucrh it is true that, if we were able to imagine every abstraction, Conceptualism would become the only rational theory, I do not intend the diagram to favour any so absurd a notion. In my next work, when I shall have occasion to explain the higher branches of the representative tree, it will become apparent that, as I do not intend Abstraction to include Generalization or \\A^ Eeflection, I am careful to keep well within the lines of Xominalism. Turning now to the lateral columns, it will be seen that 1 place upon a level with the rise of imagination the classes MoUusca, Insecta, Arachnida, Crustacea, Cephalopoda, and the cold-blooded Vertebrata. My justification for assigning to these animals the first manifestation of this faculty will be found, as in other cases, in " Animal Intelligence." Thus K 146 MENTAL EVOLUTION IN ANIMALS. the octopus which followed a lobster with which it had been fighting into an adjacent tank, by laboriously climbing up the perpendicular partition between tlie two tanks, must have been actuated by an abiding mental image, or memory, of its antagonist ; the spiders which attach stones to their webs to hold them steady during gales must similarly be actuated by a faculty of Imagination ; and the same is no less true of the crab which, when a stone was rolled into its burrow, removed other stones near its margin lest they should roll in likewise. The limpet which returns to its home after a browsing excursion, must have some dim memory or mental image of the place. So much, then, for proof of Imagination of the first degree. Imagination of the second degree — or that wherein one object or set of circumstances suggests another and similar object or set of circumstances, occurs first, so far as my evidence goes, among the Hymenoptera. But here the cases of an association of ideas leading to the establishment of a mental imagery more or less remote from the immediate circumstances of perception are much too numerous to quote. I shall therefore merely refer to the headings " General Intelligence " in the chapters on Ants, Bees, and Wasps.* Among the higher animals imagination of this grade is of frequent occurrence and strong force. Thus, to supply only one example, Thompson, in his " Passions of Animals " (p. 59), gives the case of a dog " which refused dry bread, and was in the habit of receiving from his master little morsels dipped in gravy of the meat remaining in the plate, snapped eagerly after dry bread if he saw it rubbed round the p)late, and as, by way of experiment, this was re- peatedly done till its hunger was satisfied, it is evident that the imagination of the animal conquered for the tune its faculties of smell and taste." To this order of imagination also belongs the wariness of wild animals. Thus Leroy, who in his capacity of Eanger had a large experience, says, " In the first hours of the night, when the countenance of darkness is in itself a fertile source of hope to the fox, the distant yelping of a dog will check him in the midst of his career. All the dangers which he has on various occasions passed through rise before him ; but at dawn this extreme timidity is overborne by the calls of * Animal Intelligence, pp. 122-40, and 181-19. IMACxIXATIOX. 147 appetite ; the animal tlien becomes bold by necessity. He j even runs to meet danger, knowing [i.e., forecasting by j imagination] that it will be redoubled by return of light."''' And again, speaking of the wolf where rendered timid by the hostility of man, he says that it " becomes subject to illusions and to false judgments, which are the fruit of the imagination ; and if these false judgments become extended to a sufficient number of objects, he becomes the sport of an illusory system, which may lead him into infinite mistakes, although perfectly consistent with the princijdes which have taken root in his mind. He ^^'ill see snares where there are none; his imagination, distorted by fear, will invert the order of his various sensations, and thus produce deceptive shapes, to which he will attach an abstract notion of danger," &c.* I shall only give one other fact to prove the existence of Imagination of the second order in animals, but I think it is a good one, because showing that this faculty exists in this degree in an animal not having a very high grade of intelligence — I mean the wild rabbit. Every one who has ferreted wild rabbits must have noticed that if the warren has been ferreted before, the rabbits are very unwilling to " bolt," allowing themselves to be seriously injured by the ferrets rather than face the dangers awaitino- them outside. This shows that the rabbits associate (owing to past experience) the presence of a ferret in their burrows with the presence of a sportsman outside them (for it does not signify how" careful the sportsman may be to keep silent), and so vivid is * Intelligence of Animals, pp. 24, 120-1 (Englisli translation). The well-known cunning of tlie fox and wolf in eluding the hounds is also evi- dence of a rivid imagination. In addition to the cases of this given in Aniynal Intelligence (pp. 426-30), I may now publish the following, which has recently been communicated to me by Dr. C. M. Fenn, of San Diego : — " jS'ear the south coast of San Francisco a farmer had been much annoyed by the loss of his chickens. His hounds had succeeded in capturing several of the marauding coyotes (a kind of small wolf), but one of the number constantly eluded the pursuers by making for the coast or beach, where all traces of him would be lost. On one occasion, therefore, the farmer divided his pack of hounds, and with two or three of the dogs took a position near the shore. The wolf soon approached the ocean with the other detachment of hounds in close pursuit. It was observed that as the waves receded from the shore he would follow them as closely as possible, and in no instance made foot-prints in the sand that were not quickly obliterated by the swell. When, finally, lie had gone far enough, as he supposed, to destroy the scent, he turned inland." K 2 148 MENTAL EVOLUTION IN ANIMALS. the mental picture of this outside enemy, that the animal will for a long time suffer the immediate pain and terror at the teeth and claws of the ferret before venturing to expose itself to the more remote hut still more deadly pain which it fears at the hands of the man. Coming now to Imagination of the third degree, or that which implies the power of forming ideas independently of any obvious suggestions from without, we have first to con- sider how this kind of imagination, even if present in animals, could be expressed. Now, apart from articulate expression or intelligent gesture, it is evident that the objective indices of imagination in this degree are so limited in number as to be well-nigh absent. Even, therefore, if we assume such imagination as present in any given animal, we might find it difficult to suggest the kind of action to which it might give rise, and which might be taken as unequivocal proof of such faculty. What we require, it will be observed, is some class or classes of actions which must be due to imagination of this degree and can be due to nothing else. I only know of three such classes, which, however, are conclusive as establish- ing the fact of such imagination being present in the animals which display them. It is almost needless to add that imagination, even of this level of development, may well be present among animals lower in the scale, which yet is not apparent on account of being developed in lines which do not express themselves in either of the three classes of actions on which I rely in the case of the liigher animals. h The first of these actions is Dreaming. This, wherever it is found to occur, constitutes certain proof of imagination belonging to what I have called the third degree. The fact that Dogs dream is proverbial, and was long ago remarked by Seneca and Lucretius. According to Dr. Lauder Lindsay the Horse also dreams, as shown by its " shuddering, shivering, quivering, quaking, or trembling. These phe- nomena are concomitants or results in the waking state of excitement, fear, ardour, impetuosity, or impatience. Hence it is quite legitimately inferred by Montaigne and others that the same feelings or mental conditions are developed during sleep and dreaming, and are likely to be associated in the racehorse with imaginary races, as in the sporting dog with imaginary coursing."* * Mind in the Loioer Animals, vol. ii, pp. 95-6. IMAGINATION. 149 The authorities which I have been able to find who assert that dreaming occurs in Birds are Cu^der, Jerdon, Houzeau, Bechstein, Bennet, Thompson, Lindsay, and Dar- win.* Thompson also says that Crocodiles dream, but as he gives no references to substantiate the statement, I have ignored it, and in the diagram placed dreaming on a level with Birds, as the lowest animals which I feel there is adequate evidence to accredit with this faculty. According to the writer last named, who is generally accurate, " Among Birds the stork, the canary, the eagle, and the parrot ; and among the MammaHa the elephant, the horse, and the dog, are incited in their dreams." Bennet noticed that water- birds moved their legs in their sleep, as if in the act of s\vdmming ; and Hennabe heard the hyrax utter a faint cry. Bechstein has described dreaming in a bullfinch, and the dreams appeared to be of the character of nightmares, for " the terror begotten during sleep was such that it required its mistress's interference to prevent bad effects. It fre- quently fell from its perch, but became immediately tranquil- lised and reassured by the voice of its mistress." Lastly, Houzeau asserts that parrots sometimes talk in their sleep."*!" The second class of facts on which I rely as proof of Imagination of the third degree in animals is that of Delu- sions. Dr. Lauder Lindsay writes with truth: — "Delusions of sight in animals take the form, as in man, of phantoms or phantasms. ... of imaginary persons, animals, or things. And, moreover, it would appear to be the same kind of spectral images tliat occur in other animals as in man, in canine rabies, for instance, as in human hydrophobia." J On tliis subject Fleming writes : — "It {i.e., a rabid dog) aj)peared - as if it was haunted by some horrid pliantoms. ... At times it would seem to be watching the movements of some- thing on the floor, and would dart suddenly forward and bite * See, for original passages or references, Birds of India, vol. i, p. xxi ; Facidtes-Mentales des Animav^, Sfc., tome ii, p. 183 ; Mind in the Loicer Animals, vol. ii, p. 96 ; Passions of Animals, p. 60 ; and Descent of Man, p. 74. f According to Pierguin, Guer, Elam, and Lindsar, dreaming in animals may be so vivid as to lead to somnambulism (see Lindsay, loc. cit., p. 97, ef seq.). Thus Guer asserts that "the somnambulistic watch-dog prowls in search of imaginary strangers or foes, and exhibits towards them a whole series of pantomimic actions," including barking. X Loc. cit., p. 103, 150 MENTAL EVOLUTIOX IN ANIMALS. at the vacant air, as if pursuing something against which it had an enmity." And, indeed, this peculiarity of heing liable to optical delusions is so usual and well marked a feature in rabid dogs, that it generally constitutes the earliest and most certain symptom of disease.* My friend Mr. Walter Pollock sends me the following account of a Scotch terrier bitch which he possessed : — " She had a curious hatred or horror of anything abnormal— for instance, it was long before she could tolerate the striking of a spring bell, which when I first knew her was a new experience to her. She expressed her dislike and seeming fear by a series of growls and barks, accompanied by setting her hair up on end. She used from time to time to go through exactly the same performance after gazing fixedly into what seemed to be vacancy. This attracted my attention, and I used to be on the look out for it, but carefully avoided in any way tempting her to make any display of this peculiarity. I simply watched her when- ever I was alone with her. The constant repetition in these circumstances of her seeming to see some enemy or portent unseen by me, and giving vent to her feelings in the way already described, led me to the conclusion that at these times she was the victim of optical illusion of some kind. I could, as I have already hinted, produce the same eflect upon her by doing some unexpected and irrational thing, until she had become accustomed to this kind of experiment. But after this the seeing, as it seemed to be, of some sort of phantom remained unabated. I had no opportunity of dis- cerning whether the phenomena occurred at any regular intervals, or whether they were more frequent after sleep than at other times." Pierc|uin describes a female ape which had a sun-stroke, and afterwards use to become terror-struck by delusions of some kind. She also used to snap at imaginary objects, and " acted as if she had been watching and catching at insects on the wing."t It seems needless for our present purpose to give more evidence on the fact of animals being subject to delusions, and so I shall pass on to the third class of facts on which I rely as evidence that animals present Imagination of what I have called the third order. This class of facts consists of * See Youat, On the Dag, tinder Eabies. t Traite de la Folie des Animavix^ Sfc, tome i, p. 93. IMAGINATION. 151 animals showing by their actions tliat they have in tlieir " mind's eye " a picture or representation of absent objects. Every one must have observed, for instance, the greater spirit with which jaded horses return on their homeward journey, as compared with the sluggislniess and lack of energy on tlieir out-going journey. This can only be ex- plained by supposing that the animals have a mental picture of their stables, with its ideal accompaniments of food and repose. Again, tlie desire which many animals show to return to their habitual haunts when removed from them can only be explained by supposing them to retain a mental picture, or imagination, of their previously happy experience. The promptings of this imagination are frequently so strong as to induce the animals to brave the dano-ers and fatigues of hundreds of miles of travel for the sole purpose of returning to the scenes which occupy tlieir imaginations. " Pigeons, dogs, cats, and horses, when removed from their former homes, give repeated and daily instances of the fact. It crushes and overwhelms the faculties of ihe mind, and pros- trates the energies of the body. Thus many birds, when encaged, become so utterly spirit-broken, that they refuse all nourishment, pine for a few days, and die. This is particu- larly the case with song-birds. ... If the Howling Monkey is caught when full-grown, it become melancholy, refuses all food, and dies in a few weeks ; it is also the same with the Puma; and Burdach states that death sometimes ensues so immediately, that it can only arise from a sudden and violent pressure on the mind."* Although it may be objected to this interpretation of pining under confinement that the fact may be due to the mere absence of liberty or changed condition of life, without any mental and contrasted picture of previous experience, I think that this objection is precluded in other and analogous cases to which I shall next refer, and which serve in larger if not in full measure to disarm this criticism as applied to such cases as the above. I allude to all those cases so frequently observed among domestic animals where similar pining occurs without there being any change in the conditions of life, except the sudden withdrawal of a master or companion to which the animal is strongly attached. I have myself known a case in which a terrier of my own household, on the * Thompson, Fassions of Animals, pp. 64-5. 152 MENTAL EVOLUTION IN ANIMALS. sudden removal of his mistress, refused all food for a number of days, so that it was thought he must certainly die, and his life was only saved by forcing him to eat raw eggs. Yet all his surroundings remained unchanged, and every one was as kind to him as they always had been. And that the ca^^se of his pining was wholly due to the absence of his beloved mistress, was proved by the fact that he remained perma- nently outside her bedroom door (although he knew she was not inside), and could only be induced to go to sleep by giving him a dress of hers to lie upon. No one could have seen this dog without being persuaded that he had a constant mental picture of his mistress in his imagination, and suffered the keenest mental anguish from her continued absence. Similarly there are numberless anecdotes on record, most of which are probably true, of dogs actually dying under such circumstances. All these facts, then, taken together — viz., dreaming, de- lusions, '' home sickness," and pining for friends — clearly prove the presence among higher animals of Imagination in what I have called the third order. A question may here arise as to whether I have not in the diagram placed the rise of Imagination too low. I place the first origin of this faculty on level 19, which corresponds with that of the Mollusca and an infant seven weeks old. This question, like all others of line-drawing among the psychological faculties, is confessedly a difficult one.; but the reasons why I have placed the dawn of Imagination so low in the psychological scale are as follows : — It will be remembered that the kind of Imagination which we have recently been considering belongs to what I consider a high level of development. That is to say, I con- sider the power of dreaming to occupy a place about one third of the distance between the first dawn of the imagina- tive faculty and its maximum development in a Shakespeare or a Faraday. I so consider it because I believe that to pass t'lrouoh what I have called the first three stages, so as to arrive at the power of forming mental pictures independently of sensuous suggestions from without, the imaginative faculty has made so enormous a progress from its earliest begin- nings, that the rest of its development along the same lines is really nothing more than a function of the faculty of Abstraction. Superimpose upon the psychology of a IMAGINATION. 153 terrier which pines for its absent mistress an elaborate | structure of abstract ideation, and the terrier's imaginative ' faculty would begin to rival that of man. Of course it will be said that abstraction presupposes imagination, and so undoubtedly it does; still the two are not identical, as is jDroved by the fact that for the building up of abstraction to any exalted height, language, or mental symbolism of some kind, is indispensable ; and mental symbols are so many artifices for the saving of imagination. Now if at first sight it seems aljsurd to accredit a moUusk with imaginatiun, we must remember exactly what we mean by imagination in the lowest possible phase of its develop- ment. We mean merely the power of forming a definite mental picture, or of retaining a memory, no matter of how rudimentary a kind ; provided that the memory implies some dim idea of an absent object or experience, and not, as in the case of an infant disliking the taste of strange milk, merely an immediate perception of contrast between an habitual and a present sensation. And that we find such a level of mental development as low down in the zoological scale as the Gasteropoda, would seem to be proved by the fact already alluded to of limpets returning to their homes in the rocks after feeding. Of course the mental image wdiich a limpet forms of its home in a rock cannot be supposed to be com- parable in point of vividness or complexity with the mental image that a horse retains of its stall, or a dog of its kennel ; still, such as it is, it is a mental imao-e, and therefore betokens imagination. More vivid, and therefore more definite, is the mental image that a spider forms of her lair, who when dis- lodged and carried away to a short distance again returns to her old home. (Level 20.) AVith a stiU further advance in the power of mental imagery (level 21) we find supplied the psychological conditions for the ideation of cold-blooded Ver- tebrata, such as the determination displayed by migratory Fishes (notably the salmon) to visit particular localities in the spawning season. On the next level (22) we reach the ^ higher Crustacea, which, as we have already seen, are able to \\ imagine in a high degree. Next we come to Keptiles, con- ■ • cerning which I may quote the following anecdote from Lord Monboddo : " I am well informed of a tame serpent in the East Indies, which belonged to the late Dr. Vigot, once kept by him in the suburbs of Madras. This serpent was 154 MENTAL EVOLUTION IN ANIMALS. taken by the French, when they invested Madras, in the late war, and was carried to Pondicherry in a close carriage. But from thence he found his way back again to his old quarters, though Madras is over one hundred miles distant from Pondicherry." If we substitute yards for miles, similar cases are on record with regard to frogs and toads — which from being so numerous can scarcely all be false. And that some reptiles have an imagination passing into what I have called the third stage is proved by the case of the python mentioned in "Animal Intelligence/' which, when sent to the Zoological Gardens, pined for its previous master and mistress. The Cephalopoda and Hymenoptera have already been alluded to. Lastly, on the next level (25) we attain in Birds to imagination proved to be unquestionably of the third degree by the phenomenon of dreaming. Above this level it is not of so much interest to trace the improvement of the faculty. Such improvement throughout the subsequent levels till man, probably consists only in a progressive advance through imagination of the third degree — it being I think highly improbable, and cer- tainly not betokened by any evidence, that imagination in any animal attains to what I have called the fourth degree, which I therefore consider distinctive of man. " For know tliat in the soul Are many lesser faculties tliat serve Reason as chief. Among these, Fancy next Her office holds. Of all external things, Which the five watchful senses represent. He forms imaginations, airy shapes ; Which Reason joining or disjoining, forms All that we affirm, or what deny, And call our knowledge." — Milton. I Before taking leave of Imagination there are two branches I of the subject which I should like briefly to consider. One I is the opinion held by Comte that the higher animals present \- ( ideas of Fetishism. On this topic I cannot more briefly convey the material which I have to render than by quoting a previous publication of my own from " Nature."* " Mr. Herbert Spencer in his recently published work on the ' Prin- ciples of Sociology ' treats of the above subject. He says, ' I believe M. Comte expressed the opinion that fetichistic conceptions are formed by the higher animals. Holding, as I * Vol. xvii, p. 168, et seq. IMAGIXATIOX. 155 have given reasons for doing, that fetichism is not original but derived, I cannot, of course, coincide in this view. Nevertheless I think the behaviour of intelligent animals elucidates tlie genesis of it. I have myself witnessed in dogs two illustrative cases.' One of these consisted in a large dog, which, while playing with a stick accidentally thrust one end of it against his palate, when ' giving a yelp, he dropped the stick, rushed to a distance from it, and betrayed a consternation which was particularly laughable in so ferocious-looking a creature. Only after cautious ap- proaches and much hesitation was he induced again to lay hold of the stick. This behaviour showed very clearly the fact that the stick, while displaying none but the properties he was familiar with, was not regarded by him as an active agent ; but that when it suddenly inflicted a pain in a way never before experienced from an inanimate object, he was led for a moment to class it with animate objects, and to regard it as capable of again doing him injury. Similarly, in the mind of the primitive man, knowing scarcely more of natural causation than a dog, the anomalous behaviour of an object previously classed as inanimate suggests animation. The \ idea of voluntary action is made nascent ; and there arises a tendency to regard the object with alarm, lest it should act in some other unexpected and perhaps mischievous way. The vague notion of animation thus aroused will ob\dously become a more definite notion, as fast as the development of the ghost-theory furnishes a special agency to which the anomalous behaviour can be ascribed.' " The other case observed by Mr. Spencer was that of an intelligent retriever. Being by her duties as a retriever led to associate the fetching of game with the pleasure of the person to whom she brought it, this had become in her mind an act of propitiation ; and so, ' after wagging her tail and giinning, she would perform this act of propitiation as nearly as practicable in the absence of a dead bird. Seeking about, she would pick up a dead leaf or other small oliject, and w^ould bring it with renewed manifestations of friendliness. Some kindred state of mind it is wdiich, I believe, prompts the savage to certain fetichistic observances of an anomalous kind.' " These observations remind me of several experiments I made some years ago on this subject, and which are perhaps 156 MENTAL EVOLUTION IN ANIMALS. worth publishing. I was led to make the experiments by reading the instance given by Mr. Darwin in the ' Descent of Man' of the large dog which he observed to bark at a parasol as it was moved along a lawn by the wind, so presenting the appearance of animation. Tlie dog on which I experimented was a Skye terrier — a remarkably intelligent animal, whose psychological faculties have already formed the subject of several communications to this and other periodicals. As all my experiments yielded the same results, I will only mention one. The terrier in question, like many other dogs, used to play with dry bones, by tossing them in the air, throwing them to a distance, and generally giving them the appearance of animation in order to give himself the ideal pleasure of w^orrying them. On one occasion, therefore, I tied a long and fine thread to a dry bone, and gave him the latter to play with. After he had tossed it about for a short time, I took the opportunity, when it had fallen at a distance from him and while he was following it up, of gently drawing it away from him by means of the long invisible thread. Instantly his whole demeanour changed. The bone which he had pre- viously pretended to be alive now began to look as if it were really alive, and his astonishment knew no bounds. He first approached it with nervous caution, as Mr. Spencer describes ; but as the slow receding motion continued, and he became quite certain that the movement could not be accounted for by any residuum of the force which he had himself communicated, his astonishment developed into dread, and he ran to conceal himself under some articles of fur- niture, there to behold at a distance the 'uncanny' spectacle of a dry bone coming to life. " N"ow in this and all my other experiments I have no doubt that the behaviour of the terrier arose from his sense of the mysterious, for he was of a highly pugnacious disposition, and never hesitated to fight any animal of any size or fero- city ; but apparent symptoms of spontaneity in an inanimate object which he knew so well, gave rise to feelings of awe and horror, which quite enervated him. And that there was nothing fetichistic in these feelings may safely be concluded if we reflect, with Mr. Spencer, that the dog's knowledge of causation for all immediate purposes being quite as correct and no less stereotyped than is that of 'primitive man,' when an object of a class which he knew from uniform past experience to be inanimate suddenly began to move, he must IMAGINATION. 157 have felt tlie same oppressive and alarming sense of the mysterious which unciilturecl persons feel under similar cir- cumstances. But further, in the case of this terrier, we are not left with a priori inferences alone to settle this point, for another experiment proved tliat the sense of the mysterious in this animal was sufiiciently strong in itself to account for his behaviour. Taking him into a carpeted room, I blew a soap-bubble, and by means of a fitful draught made it inter- mittently glide along the floor. He became at once intensely interested, but seemed unable to decide whether or not the fitful object was alive. At first he was very cautious, and followed it only at a distance ; but as I encouraged him to examine the bubble more closely, he approached it with ears erect and tail down, evidently with much misgiving, and the moment it happened to move he again retreated. After a time, however, during wdiich I always kept at least one bubble on the carpet, he began to gain more courage, and the scientific spirit overcoming his sense of the mysterious, he eventually became bold enough slowly to approach one of the bubbles, and nervously to touch it wdth his paw. The bubble, of course, immediately burst, and I certainly never saw astonish- ment more strongly depicted. On then blowing another bubble, I could not persuade him to approach it for a good while ; but at last he came, and carefully extended his paw as before, with the same result. But alter this second trial nothing would induce him again to approach a bubble, and on pressing him he ran out of the room, which no coaxing would persuade him to re-enter. " One other example will suffice to show how strongly developed was the sense of the mysterious in this animal. When alone w^ith him in a room I once purposely tried the effect on him of making a series of hideous grimaces. At first he thought I was only making fun ; but as I persistently disregarded his caresses and wdiining while I continued unna- turally to disturb my features, he became alarmed ; slunk away under some furniture, shivering like a frightened child. He remained in this condition till some other member of the family happened to enter the room, wdien he emerged from his hiding place in great joy at seeing me again in my right mind. In this experiment, of course, I refrained from making any sounds or gesticulations, that might lead him to think I was angry. His actions therefore can only be explained by his horrified surprise at any apparently irrational behaviouj-, 158 MENTAL EVOLUTION IN ANIMALS. i.e., by the violation of liis ideas of uniformity in matters psychological. It must be added, however, that I have tried the same experiment on less intelligent and less sensitive terriers with no other effect than causing them to bark at me. I will only add that I believe the sense of the mysterious to be the cause of the dread which many animals show of thunder. I am led to think this, because I once had a setter which never heard thunder till he was eighteen months old, and on then hearing it I thought he was about to die of fright, as I have seen other animals do under various circum- stances. And so strong was the impression which his extreme terror left behind, that whenever afterwards he heard the boom of distant artillery practice, mistaking it for thunder, he became a pitiable object to look at, and, if out shooting, would endeavour to bury himself or bolt home. After having heard real thunder on two or three subsequent occasions, his dread of the distant cannon became greater than ever; so that eventually, though he keenly enjoyed sport, nothing would induce him to leave his kennel, lest the practice might begin when he w^as at a distance from home. But the keeper, who had a large experience in the training of dogs, assured me if I allowed this one to be taken to the battery in order that he might learn the true cause of the thunder-like noise, he would again become serviceable in the field. The animal, however, died before the experiment was made."* Thus I think we may safely set down the sense of the mysterious as thus undoubtedly displayed by intelligent dogs — and also, I may add, by many horses when going along a dark road, hearing strange sounds, or seeing unaccustomed sights — to the effects of imagination in suggesting vague pos- sibilities in circumstances perceived to be unusual; just as with children under similar circumstances the undefined imagination of possible harm springing out of such circum- stances in some unthought-of manner, engenders that feeling of unreasonable dread which we may in both cases call a sense of the mysterious. * That sucli -would hare been the case, however, I have little doubt, for on one occasion when a number of apples were being shot out of bags upon the wooden floor of an apple-room, the sound in the house as each bag was shot closely resembled that of distant thunder. The setter, therefore, became terribly alarmed ; but when I took him to the apple-room and showed him the real cause of the noise, his dread entirely left him, and on again returning to the house he listened to the rumbling with all cheerfulness. IXSTIXCT. 159 CHAPTER XI. Instinct. Definition. I SHALL begin this important and extensive part of my subject by repeating the definition of Instinct which I laid down in my former work. It will be remembered that for the sake of precision 1 there limited the term Instinct as follows : — " Instinct is reflex action into which there is imported the element of consciousness. The term is therefore a generic one, comprising all those faculties of mind which are concerned in conscious and adaptive action, antecedent to in- dividual experience, without necessary knowledge of the relation between means employed and ends attained, but similarly performed under similar and frequently recurring circumstances by all the individuals of the same species." Eef erring the reader to the context for my justification of this definition,* I shall here only further make this general statement. It follows from the above definition of Instinct, that a stimulus which evokes a reflex action is, at most, a sensation ;t but a stimulus which evokes an instinctive action is a perception. After what I have already said in Chapter IX concerning the distinction between a sensation and a perception, my meaning now will be clearly under- stood. For if a perception differs from a sensation in that it presents a mental element, and if an instinctive action differs from a reflex action in that it presents a mental element, it is easy to see that a stimulus supplied by a sensation is to a reflex action what a stimulus supplied by a perception is to an instinctive action ; because if a sensation could act as a * Animal Intelligence, pp. 10-] 7. f I say "at most," because sueli a stimulus may be less than a sensation, in that it may never cross the field of consciousness. 160 MENTAL EVOLUTION IX ANIMALS. stimulus to an action apparently instinctive, ex liypotlusi the action could not be (according to my definition) really instinctive ; and conversely, if a perception could act as a stimulus to an action apparently reflex, the action could not be (according to my definition) a true reflex. Therefore, if we agree to limit the term Instinct to nervous processes involving a mental element, it follows that this element is perception, aud that it is always involved in every stimulus leading to instinctive action. With reference to general principles of classification it is only needful for me further to quote the following extract from my previous work : — " The most important point to observe in the first instance is that instinct involves mental operations; for this is the only point that serves to distinguish instinctive from reflex action. Eeflex action, as already explained, is non-mental neuro-muscular adaptation to appropriate stimuli ; but in- stinctive action is this and something more ; there is in it the element of mind. No doubt it is often difficult, or even impossible, to decide whether or not a given action implies the presence of the mind-element — i.e., conscious as distin- guished from unconscious adaptation ; but this is altogether a separate matter, and has nothing to do with the question of defining instinct in a manner which shall be formally exclusive, on the one hand of reflex action, and on the other of reason. As Virchow truly observes, ' it is difficult or impossible to draw the line between instinctive and reflex action ;' but at least the difficulty may be narrowed down to deciding in particular cases whether or not an action falls into this or that category of definition ; there is no reason why the difficulty should arise on account of any ambiguity of the definitions themselves. Therefore I endeavour to draw as sharply as possible the line which in theory should be taken to separate instinctive from reflex action ; and this line, as I have already said, is constituted by the boundary of non-mental or unconscious adjustment, with adjustment in which there is concerned consciousness or mind." I shall now proceed to show, by a few selected examples, what has been called the Perfection of Instinct; next I shall similarly illustrate the Imperfection of Instinct ; and lastly, I shall discuss the important question of the Origin and Development of Instinct. PERFECTION OF INSTINCT. 161 Perfection of Instinct. An instinct may be said to be perfect when it is perfectly adapted to meet those circumstances in the life of an animal for the meeting of which the instinct exists ; and if it is an instinct this perfection must be exhibited as independent of the animal's individual experience. We may therefore best illustrate the perfection of instinct l)y considering the won- derful accuracy of many among the highly refined and com- plex adjustments which are manifested by the newly-born young of the higher animals. The late Mr. Douglas Spalding in his brilliant researches on this subject has not only placed beyond question the falsity of the view " that all the supposed examples of instinct may be nothing more than cases of rapid learning, imitation, or instruction,"* but also proved that a young bird or mammal comes into the world with an amount and a nicety of ancestral knowledge that is highly astonishing. Thus, speak- ing of chickens which he liberated from the egg and hooded before their eyes had been able to perform any act of vision, he says that on removing the hood after a period varying from one to three days, " almost invariably they seemed a little stunned by the light, remained motionless for several minutes, and continued for some time less active than before they were unhooded. Their behaviour, however, was in every case conclusive against the theory that the perceptions of distance and direction by the eye are the result of experience, or of associations formed in the history of each individual life. Often at the end of two minutes they followed with their eyes the movements of crawling insects, turning their heads with all the precision of an old fowl. In from two to fifteen minutes they pecked at some speck or insect, showing not merely an instinctive perception of distance, but an original ability to judge, to measure distance, with something like in- fallible accuracy. They did not attempt to seize things beyond their reach, as babies are said to grasp at the moon ; and they may be said to have invariably hit the objects at * Quoted from his article in Macmillan''s Magazine, February, 1873, from which likewise all the subsequent quotations are made. We are now- adays so ready to assimilate scientific truth, that in reading this article — not yet ten years old — it seems difficult to realize that so recently there was such a considerable clinging of competent opinion to the non-evolutionary view of instinct as the quotations in the article show, Ii 162 MENTAL EVOLUTION IN ANIMALS. which they struck — they never missed by more than a hair's breadth, and that, too, when the specks at which they aimed were no bigger, and less visible, than the smallest dot of an i. To seize betw^een the points of the mandibles at the very instant of striking seemed a more difficult operation. I have seen a chicken seize and swallow an insect at the first attempt ; most frequently, however, they struck five or six times, lifting once or twice before they succeeded in swallow- ing their first food. The unacquired power of following by sight was very plainly exemplified in the case of a chicken that, after being unhooded, sat complaining and motionless for six minutes, when I placed my hand on it for a few seconds. On removing my hand the chicken immediately followed it by sight backward and forward, and all round the table. To take, by way of example, the observations in a sinsjle case a little in detail : — A chicken that had been made the subject of experiments on hearing, was unhooded when nearly three days old. For six minutes it sat chirping and looking about it ; at the end of that time it followed with its head and eyes the movements of a fly twelve inches distant ; at ten minutes it made a peck at its own toes, and the next instant it made a vigorous dart at the fly, which had come wdthin reach of its neck, and seized and swallowed it at the first stroke ; for seven minutes more it sat calling and looking about it, when a hive-bee coming sufficiently near was seized at a dart and thrown some distance, much disabled. For twenty minutes it sat on the spot where its eyes had been unveiled without attempting to walk a step. It was then placed on rough ground within sight and call of a hen with a brood of its own age. After standing chirping for about a minute, it started off towards the hen, displaying as keen a perception of the qualities of the outer world as it was ever likely to possess in after life. It never required to knock its head against a stone to discover that there was ' no road that way.' It leaped over the smaller obstacles that lay in its path and ran round the larger, reaching the mother in as nearly a straight line as the nature of the ground would per- mit. This, let it be remembered, was the first time it had ever walked by sight." Further, " When tw^elve days old one of my little proteges, while running about beside me, gave the peculiar chirr wheieby they announce tlie approach of danger. I looked PERFECTION OF INSTINCT. 163 up, and Leliokl a sparrow-hawk was hovering at a great height over head. Equally striking was the effect of the hawk's voice when heard for the first time. A young turkey, which I had adopted when chirping within the uncracked shell, was on the morning of the tenth day of its life eating a comfortable breakfast from my hand, when the young hawk, in a cupboard just beside us, gave a shrill chip, chip, chip. Like an arrow the poor turkey shot to the other side of the room, and stood there motionless and dumb with fear, until the hawk gave a second cry, when it darted out at the open door right to the extreme end of the passage, and there, silent and crouched in a corner, remained for ten minutes. Several times during the course of that day it again heard these alarming sounds, and in every instance with similar mani- festations of fear." Again referring to young chickens, Mr. Spalding con- tinues,— " Scores of times I have seen them attempt to dress their wings when only a few hours old — indeed as soon as they could hold up their heads, and even when denied the use of their eyes. The art of scraping in search of food, wdiich, if anything, might be acquired by imitation — for a hen wdth chickens spends the half of her time in scratching for them — is nevertheless another indisputable case of instinct. Without any opportunities of imitation, when kept quite isolated from their kind, chickens began to scrape wdien from two to six days old. Generally, the condition of the ground was suggestive; but I have several times seen the first attempt, which consists of a sort of nervous dance, made on a smooth table." In this connection I may here insert an interesting obser- vation which has been communicated to me by Dr. Allen Thomson, F.E.S. He hatched out some chickens on a carpet, where he kept them for several days. They showed no inclination to scrape, because the stimulus supplied by the carpet to the soles of their feet was of too novel a character to call into action the hereditary instinct; but when Dr. Thomson sprinkled a little gravel on the carpet, and so supplied the appropriate or customary stimulus, the chickens immediately began their scraping movements. But to return to Mr. Spalding's experiments, he says : — " As an example of unacquired dexterity, I may mention that on placing four ducklings a day old in the open air for L 2 164 MENTAL ETOLmOX IX AXIMALS. the first time, one of them almost immediately snapped at and e^^nght a fly on the Tring, More interesting, however, is the deliberate art of catching flies practised by the tiirkey. When not a day and a half old I observed the young turkey already spoken of slowly pointing its beak at flies and other small insects without actually pecking at them. In doing this, its head could be seen to shake like a hand that is attempted to be held steady by a visible eflbrL This I ob- served and recorded when I did not understand its meaning. For it was not until after, that I found it to be the invariable habit of the turkey, when it sees a fly settled on any object, to steal on the unwary insect with slow and measured step until sufliciently near, when it advances its head very slowly and steadily till within an inch or so of its prey, which is then seized by a sudden dart.'' Mr. Spalding subsequently tried similar experiments, with similar results, on newly born manrmals. He found, for instance, that new-K">m pigs seek to suck almost immediately alter birth. If removed twenty feet from the mother, they wri^le straight back to her guided apparently by her grunt- ing. He put a pig into a bag immediately it was born, and kept it in the dark till seven hours old, and then placed it outside the sty ten feet from its mother. It went straight to her, although it had to struggle for five minutes to squeeze under a bar. A pig blindfolded at birth went about freely, though tumbling against things. It had the blinder taken off next day, and then " went round and round as if it had had sight, and had suddenly lost it In ten minutes it was scarcely distinguishable from one that had had sight all along. When placed on a chair, it knew the height to require considering, went down on its knees, and leaped down. . . One day last month, after fondling my dog. I put my hand into a basket containing four blind kinens three days old. The smell my hand had carried with it sent them puffing and spitting in a most comical fashion'** Here I may quote an observation of my own from the succeeding issue of " Xature." *•■ ApropiiS to what Mr. Spalding says about the early age at which the instinctive antipathy of the cat to the dog tecomes ajiparent, I may state that some months ago I tried an experiment with rabbits and ferrets somewhat similar to that which he describes with cats and dogs. Into an out- * Sature, toL si. p. 507. FEKFECnOS or ISSTISCT. l&^t house which contained a doe rabbit with arefj jonng Uasdij, I turned loose a ferret. The doe rabbit left her jomig ones, and the latter, as soon as thej amdled die femt, h^m to crawl about in so enexgedc a wiaiww»r as to leacre no doubt that the cause of the coimnotioii was fear, and not merefy the discomfort azisii^ from the temporsDj abBeuce ai Iht mother."* With reference to the instinctiTe endowmentB of tins kind in kittens, I may also qiiote die kXkmJag, wUdi I find amon^ ^Ir. Darwin's iiSS : — "the many cases of inborn liear or ferocitj in joung animals direeted towards porticidar objeets, as wdl as tlie loss of these indiTidiialized paaaoos, seems to me extreme^' corions. Let anj one who doubts their erjatenfle gire a mouse to a kitten taken eazlj from its mother, and wfaieh has never befose seen one, acd obserre how soon the kittea growls with hair erect, in a mannfa- whc^^ diiieteiit from. when at play or when fed with ^- * Smimrm, -wtA, xL p. df-L 166 MENTAL EVOLUTION IN ANIMALS. markable cases. Thus, to give only a few. Eeaumur and Swanderdam assert that a young Bee, as soon as its wings are dry, w^ill collect honey and construct a cell as efficiently as the oldest inhabitant of the hive.* Numberless insects, also, can never have seen their parents, and yet they perform instinctive actions perfectly, though it may be only once in their life-times — such, for instance, as the Ichneumon, wdiich deposits its eggs in the body of a larva hidden between the scales of a fir-cone, which it can never have seen, and yet knows where to seek.f A kind of insect called the Bembex conveys food to its young which are shut up in a cell, and it has recently been made the subject of some interesting experiments by M. Fabre. Of these the following is an epitome : — " The insect brings from time to time fresh food to her young, and it is remarkable how the Bembex remembers the entrance to her cell, covered as it is with sand, exactly to our eyes like that all round. Yet she never makes a mistake or loses her way. On the other hand M. Fabre found that if he removed the surface of the earth and the passage, thus ex- posing the cell and the larva, the Bembex was quite at a loss, and did not even recognize her own oft spring. It seems as if she knew the doors, nursery, and the passage, but not her child. Another ingenious experiment of M. Fabre's was made with Chalicodoma. This genus is enclosed in an earthen cell, through which at maturity the young insect eats its way. M. Fabre found that if he pasted a piece of paper round the cell the insect had no difficulty in eating through it, but if he enclosed the cell in a paper case, so that there was a spacp even of only a few lines between the cell and the paper, in that case the paper formed an effectual prison. The instinct of the insect taught it to bite through one enclosure, but it had not wit enough to do so a second tinie."| But I think that perhaps the most remarkable instance of all that can be quoted from the insect world to show the extraordinary perfection of early-formed instincts, is one which is apt to be overlooked — and indeed, so far as I know, has been overlooked — on account of its frequency. I refer to the enormous body of instincts, all having reference to a totally different environment and habits of life, which those insects that undergo a complete metamorphosis present fuUy- * Kirbj and Spence, loc. cif., vol. ii, p. 470. t Ibid., i, p. 357. X Sir J. Lubbock, Address to Entemol. Soc, 1882. nirERFECTIOX OF INSTINCT. 167 formed and ready for complete action as soon as the imago escapes from its pupa stage. The difference between its pre- vious Hfe as a larva and its new life as an imago, is as great as the difference between tlie lives of two animals belong- ing to two different sub-kingdoms ; and the complete adapta- tion which all the new class of instincts exhibit to the requirements of this new life, is (|uite as remarkaljle as is the adaptation of the new structures to the same requirements. Imperfection of Instinct. I shall first give a few cases to show that instinct is not an infallible guide to action, and for this purpose shall choose aberrations of those instincts which we should expect to be most fixed, because of most importance to the well-being of the animals or their progeny — I mean the instincts of pro- pagation and the procuring of food. The flesh-fly {Musca carnarict) deposits its- eggs in the flowers of the '' carrion plant " (Stapelicc hirsutci), the smell of which resembles that of putrid meat, and so deceives the fly.* Similarly, the house-fly has been observed to deposit eggs in snuff* t Again, the Eev. Mr. Bevan and Miss C. Shuttleworth, write me independently that they have seen wasps and bees visiting representations of flowei^ upon the wall-paper of rooms ; and Trevellian saw the same mistake made by the sphinx-moth.j Swainson in his " Zoological Illustrations," gives an analogous case in a vertebrated animal ; an Austra- lian parrot, whose food is taken from the flowers of the Eucalyptus, was observed endeavouring to feed on the repre- sentation of flowers on a cotton-print dress. Likewise, Professor Moseley, F.E.S., informs me that he has noticed honey-seeking insects mistake for flowers the bright coloured salmon flies stuck in his hat wdiile fishing ; and Mr. F. M. Burton, ^^Titing to " ^^ature " (xvii, p. 162), says that he has observed the humming bird hawk-moth {Macroglossa stella- tarum) mistake artificial flowers in a lady's bonnet for real ones. Still more curiously, the naturahst Couch observed a * E. Darwin, Zoonomia, i, § 16, art. 11. Also Kirbv and Spence, loc. rit., ii, 469, who state the fact on the authority of Dr. Zinken. t Zinken, in Qermar. Mag. der Ento., Bd. I, abth. 4, § ISO. X See Houzeau, loc. cit., I, 210. 168 MENTAL EVOLUTION IN ANIMALS. bee mistake a sea-anemone {Tealia crassicornis), whicli was " covered merely by a rim of water," for a flower— darting into the centre of the disk, " and thouoh it struo-oled a o-ood deal to get free, was retained till it was drowned, and was then swallowed.* The fact, alluded to by Mr. Darwin in the Appendix, that the workers of the humble-bee attempt to devour the eggs laid by their own queen, appears to constitute a remarkable case of imperfect instinct. Again, Huber saw a bee begin a cell in a wrong direction, and other bees tear it to pieces. Bees have also been observed to collect rye-flower when damp instead of pollen.t " Pollen-getting, according to Gebien, is the weak point in the character of bees ; " for this author observes (p. 74) that they " lay up useless hoards of it, which they go on augmenting every year, and this is the only point on which they can be accused of want of prudence." Mr. Darwin's MS notes contain a brief record of a number of observations on ants {F. riifa) carrying pupa skins, with a great and apparently useless exj)enditure of labour, far away from the nest, and even up trees. He tried taking away the skins from some of the carriers, and replacing them near the nest ; the flrst ants that happened to fall in with them again carried them off. This, as the notes observe, appears to be a case of " blundering instinct ; " and the same epithet may be applied to mistakes made by the harvesting ants observed by Mr. Moggridge, which carefully stored in their granaries the gall- apples of a small species of Cynips, clearly imagining that they were nuts; and also, under a similar delusion, stored small beads which Mog- gridge, in order to test their instinct, scattered in their harvesting fields.:j: Among Birds we find mistaken instinct exhibited by the cuckoo when it lays two eggs in the same nest, with the inevitable result that one of the young birds will afterwards eject the other. In the same category we may place the promiscuous dropping of her eggs on the part of the rhea ; small birds frequently mistaking a larger and unfamiliar bird for a hawk, as shown by their mobbing it ; and numberless special cases could be given of mistaken instinct in the matter of nest-building — in the selection of unsuitable sites, unsuitable materials, and so on. * Critic, March 24, 1860. t Cottage Gardener, April, 1860, p. 48. X Hai'vesting Ants and Trap-door Spiders, p. 37, et seq. IMPERFECTION OF IXSTIXCT. 169 Among Mammals it must be deemed a mistaken instinct which leads the Norwegian lemming to swim out to sea in its migrations, and perish by millions in consequence. Under existing circumstances it is an imperfect instinct which leads the quadrupeds in South Africa, mentioned by Mr. Darwin in the Appendix, to migrate, seeing that by so doing they expose themselves to persecution. The shrewmouse, also mentioned by Mr. Darwin in the Appendix, which " continually betrays itself by screaming out when approached," is another, and perhaps a better instance. The instincts of rabbits with regard to the attacks of weasels appear to me to be imperfect, or not completely formed. For, as I observe in " Animal Intelligence " (p. 359), I have witnessed the mode of capture practised by weasels in the open field, and it consists merely in the rabbit " toddling along, with the weasel toddling behind, until tamely allowing itself to be overtaken . . . There seems to have been here a remarkable failure of natural selection in doing duty to the instincts of these swift-footed animals " — a failure, however, which time would doubtless remedy, if weasels were sufficiently numerous in relation to the breeding power of the rabbit to give natural selection the opportunity of perfecting the instinct of escape from this particular enemy. Many other instances of the imperfection of instinct might be quoted, but enough have now been given to render unquestionable the only point with which we are concerned, viz., that although well established instincts are, as a rule, adjusted with astonishing nicety to certain definite and frequently recurring circumstances, the adjustment is made only with reference to these, so that a very small variation in them is sufficient to lead the instinct astray. It is also of interest here to note what seems to be a complementary truth, viz., that small variations taking place in the organism itself when not in normal converse with its environment, are suffi- cient to throw the delicate mechanism of instinct out of gear when this is afterwards brought into such converse. This fact, for instance, is familiar enouo-h in the case of tamed animals (which when again " turned down " in their native haunts are not at first at home in them), but is brought out in a much more striking manner by the experiments of Mr. Spalding. Thus he says : — "Before passing to the theory of instinct, it may be 170 MENTAL EVOLUTION IN ANIMALS. worthy of remark that, unlooked for, I met with in the course of experiments some very suggestive, but not yet sufficiently observed, phenomena ; which, however, have led me to the opinion that not only do the animals learn, but they can also forget- -and very soon — that whicli they never practised. Further, it would seem that any early interference with the established course of their lives may completely derange their mental constitution, and give rise to an order of manifestations, perhaps totally and unaccountably different from what would have appeared under normal conditions. Hence I am inclined to think that students of animal psychology should endeavour to observe the unfolding of the powers of their subjects in as nearly as possible the ordinary circumstances of their lives. And perhaps it may be because they have not all been sufficiently on their guard in this matter, that some experiments have seemed to tell against the reality of instinct. Without attempting to prove the above propositions, one or two facts may be mentioned. Untaught, the new-born babe can suck — a reflex action ; and Mr. Her- bert Spencer describes all instinct as 'compound reflex action ; ' but it seems to be well known that if spoon-fed, and not put to the breast, it soon loses the power of drawing milk. Similarly, a chicken that has not heard the call of the mother until eight or ten days old then hears it as if it heard it not. I regret to find that on this point my notes are not so full as I could wish, or as they might have been. There is, however, an account of one chicken that could not be returned to the mother when (? until) ten days old. The hen followed it, and tried to entice it in every way ; still it continually left her and ran to the house or to any person of whom it caught sight. This it persisted in doing, though beaten back with a small branch dozens of times, and indeed cruelly maltreated. It was also placed under the mother at night, but it again left her in the morning. Something more curious, and of a different kind, came to light in the case of three chickens that I kept hooded until nearly four days old — a longer time than any I have yet spoken of Each of these on being unhoocled evinced the greatest terror of me, dashing off in the opposite direction whenever I sought to approach it. The table on which they were unhooded stood before a window, and each in its turn beat against the glass like a wild bird. One of them darted behind some books, and, squeezing itself into a IMPERFECTION OF INSTI^XT. 171 corner, remained cowering for a length of time. We might guess at the meaning of this strange and exceptional wild- ness; but the odd fact is enough for my present purpose. Whatever might have been the meaning of this marked change in their mental constitution — had they been unhooded on the previous day they would have run to me instead of from me — it could not have been the effect of experience ; it must have resulted wholly from changes in their own organiza- tion." Subsequently Mr. Spalding tried the experiment of keeping young ducklings away from the water for several days after they were hatched ; on then bringing them to a pond they showed as much dislike to the. water as young chickens would have done. (See Lewes, article Instinct, " Problems of Life and Mind.") The change produced in the instincts of male animals by castration may also be mentioned in the present connectioti^ and particularly the tendency which is thus induced among cock birds to adopt the incubating and other habits of the hen. I quote the following from a recently published article by Dr. J. W. Stroud of Port Elizabeth, who has devoted a good deal of attention to the subject of caponizing : — " Aristotle, more than two thousand years ago, tells us of a cock that performed all the duties of a hen. (' Hist. An. Lib.' ix, 42.) Pliny, too, speaks of the motherly care bestowed by a cock on chickens. ' He did everything for them,' says he, ' like to the very hen that hatched them, and ceased to crow.' (' Pliny Trans.' i, 299.) Albertus Magnus witnessed the same thing ; and iElian (' Hist.' iv, 29) mentions a cock which on the death of the hen while hcitching, took to the eggs, sat on them, and brought out chicks.' Says Willoughby (in 'Piay's Willoughby 's Natural History'), ' We have beheld more than once, not without pleasure and admiration, a Capon bringing up a brood of chickens, like a hen clucking over them, feeding them, and brooding them under his wings with as much care and tenderness as their dams are wont to do.' ' Once accustomed to this office,' says Baptista Eosa (' Magia Naturalis' iv, 26), 'a Capon will never abandon it, but when one brood is grown up another batch of newly hatched chickens may be put to him and he will be as kind to them and take as much care of them as of the first, and so in succession.' Eeaumur (' Art de Faire Eclore,' tom. ii, p. 8) 172 MEXTAL EA^OLUTIOX IN ANIMALS. bears testimony to similar facts and also to the propensity of Capons to sit. (See also ' Cottage Gardener,' 1860, p. 379."*) In this connection I may also quote the following in- stance, which I find recorded among Mr. Darwin's MS notes : — "April, 1862. We had a kitten which sucked its mother, and, when a month old, taken to and sucked another cat ; then to and sucked two other cats, and then its instinct w^as confounded, and became mixed wdth reason or experience : for it tried repeatedly to suck three or four other kittens of its own age, which no one, as far as I am aware, ever saw any other kitten do. Thus born instinct may be modified by experience." In his " Naturgeschichte der Saugethiere von Paraguay," p. 201, Dr. Eeugger gives the following curious instance of interference with natural instincts brought about by changed conditions of individual life. Speaking of a kind of Cat, native in Paraguay, he says that there is no instance on record of the animal breeding when in captivity, and that on one occasion a female having been pregnant when captured and kept in confinement by Herr Nozeda, brought forth her young, but immediately afterwards devoured them. This, which took place in her own country, shows that even so well rooted an instinct as the maternal may be greatly altered in the individual by even a few months of change in the conditions of life. Similar facts in the case of the domestic Sow, pet Mice, and other animals exposed to the influence of domestication are, of course, very common. It is needless, I think, to give further instances to prove the general principle that derangement of instinctive organi- zation is apt to arise when an animal ceases to be in normal converse with its environment. But I may here adduce a curious instance of the derangement of the instinctive organization in an animal which was apparently in all respects in normal converse with its environment, and this to such an extent that it may properly be regarded as a case of insanity. But although perhaps pathological in nature, it is none the less available as showing the imperfection of in- stinct— the only difference between it and the cases previously * Ostronization, or the Caponizing of the Ostrich (S. Breutnall, Port Elizabetli, 1883). IMPERFECTION OF INSTINCT. 173 cited consisting in the changing causes being internal instead of external. The case was communicated to me by a lady, who, from its peculiar nature, desires me to withhold her name ; but I quote the account in her own words : — " A white fantail pigeon lived with his family in a pigeon- house in our stable-yard. He and his wife liad been brought originally from Sussex, and had lived, respected and admired, to see their children of the third generation, when he sud- denly became the victim of the infatuation I am about to describe. . . . " No eccentricity whatever was remarked in his conduct until one day I chanced to pick up somewhere in the garden a ginger-beer bottle of the ordinary brown stone description. I flung it into the yard, where it fell immediately below the pigeon-house. That instant down flew paterfamilias, and to my no small astonishment commenced a series of genuflexions, evidently doing homage to the bottle. He strutted round and round it, bowing and scraping and cooing and performing the most ludicrous antics I ever beheld on the part of an ena- moured pigeon. . . . Nor did he cease these perform- ances until we removed the bottle ; and, which proved that this sino-ular aberration of instinct had become a fixed delusion, whenever the bottle was thrown or placed in the yard — no matter wdiether it lay horizontally or was placed upright — the same ridiculous scene was enacted ; at that moment the pigeon came flying down with quite as great alacrity as when his peas were thrown out for his dinner, to continue his antics as long as the bottle remained there. Sometimes this would go on for hours, the other members of his family treat- ing his movements with the most contemptuous indifference, and taking no notice whatever of the bottle. At last it became the regular amusement with which we entertained our visitors to see this erratic pigeon making love to the interesting object of his affections, and it was an entertain- ment which never failed, throughout that summer at least. Before next summer came round he was no more." It is thus evident that the pigeon was affected with some strong and persistent monomania with regard to this particular object. Although it is well known that insanity is not an uncommon thing among animals, this is the only case I have met with of a conspicuous derangement of the instinctive as distinguished from the rational faculties — unless, indeed, 174 MENTAL EVOLUTION IN ANIMALS. i^ we so regard tlie exhibitions of erotomania, infanticidal mania, &c., which occnr in animals perhaps more frequently than they do in man. But with reference to the imperfection of instinct, we have now some more important matters to consider than the mere enumeration of cases in wliich instinct may have been observed at fault. Let it first be observed that under the general heading *' Imperfection of Instinct," we may include two very different classes of phenomena ; for instincts may be imperfect because tliey have not yet been completely developed, or they may appear to be imperfect because not completely answering to some change in those circumstances of life with reference to which they have been fully developed. Now, if instincts have been developed at all, it is obvious that they must have passed through various stages of imper- fection before they attained to perfection, and therefore we might expect to meet with some cases of instinct not yet per- fected— cases, be it observed, which differ from those already mentioned, in that their faultiness arises, not from a novelty of experience with reference to v/hich the instinct has not been developed, but from the fact of the instinct not being yet fully formed ; and this ought more especially to be the case with instincts the perfection of which is not of vital importance to the species ; for such instincts would not have been so rigorously trained or perfected by natural selection. A good illustration on this head seems to be afforded by the instinct of destroying the drones as exhibited by the hive-bee. Thus, to quote from " Animal Intelligence " : — " Evidently the object of this massacre is that of getting rid of useless mouths ; but there is the more difficult question as to why these useless mouths ever came into existence. It has been suggested that the enormous disproportion between the pre- sent number of males and the single fertile female, refers to a time before the social instincts became so complex or con- solidated, and when, therefore, bees lived in lesser communi- ties. Prol^ably this is the explanation, altliough 1 think we might still have expected that before this period in their evolution had arrived bees might have developed a compen- sating instinct, either not to allow the queen to lay so many drone eggs, or else to massacre the drones while still in the larval state. We must remember, also, that among the wasps IMPERFECTION OF INSTINCT. 175 the males do work (cliiefly domestic work, for which they are led by their foraging sisters) ; so it is possible tliat in the hive-bee the drones were originally useful members of the community, and that they have lost their primitively useful instincts. But Avliatever the explanation, it is very curious that here, among the animals which are justly regarded as exhibiting the highest perfection of instinct, we meet with ' perhaps the most Hagrant instance in the animal kingdom of instinct unperfected. It is the more remarkable that the drone-killing instinct should not have been better developed in the direction of killing the drones at the most profitable time — namely, in their larval or oval state — from the fact that in many respects it seems to have been developed to a high degree of discriminative refinement." And, to take only one other illustration, Mr. Spalding writes : — " Another suggestive class of phenomena that fell under my notice may be described as imperfect instincts. When a week old my turkey came on a bee right in its path — the first, I believe, it had ever seen. It gave the danger chirr, stood for a few seconds with outstretched neck and marked expression of fear, then turned off' in another direction. On this hint I made a vast number of experiments with chickens and bees. In the great majority of instances the chickens gave evidence of instinctive fear of these sting-bearing insects ; but the results were not uniform, and perhaps the most accurate general statement I can give is, that they were un- certain, shy, and suspicious. Of course to be stung once was enough to confirm their misgivings for ever. Pretty much in the same way did they avoid ants, especially when swarming in great numbers." Similarly, and daring the life-time of the individual, Mr. Spalding found an instinct in the course of development in the case already quoted of the turkeys catching flies. And precisely analogous facts may be noticed in the developing instincts of the child. Thus, for instance, the balancing of the head in an upright position may be said in man to be instinctive, for the power of doing so is first acquired about the tenth week, by constantly recurring efforts, and eventually becomes independent of intentional thought. Preyer describes the stages by which the latter, or completed, stage is reached through numberless gradations, the passage of which occupies 176 MENTAL EVOLUTION IN ANIMALS. about six weeks.* He says that the child first accidentally finds the comfort of the attitude, and so adopts it more and more constantly until through habit it becomes instinctive. He also gives exactly parallel facts in the case of learning to , creep, sit, stand, walk, &c.t Among animals in a state of nature we may, I think, regard all instincts which, so far as we can see, are trivial or useless, as instincts which are imperfect, in that they do not answer to any apparent needs in the animals' present condi- tions of life. Such instincts are not very numerous, and, as Mr. Darwin observes in the Appendix, they may be quoted as objections to his theory of the development of instinct by natural selection. I shall subsequently consider this diffi- culty, but here I have only to note the fact that instincts of this apparently purposeless kind occut, and that, qud pur- poseless, they are imperfect. Such, for instance, is the instinct of a hen cackling when she has laid an egg, the cock- pheasant crowing when going to roost, cattle and elephants goring their sick or wounded companions, sundry instincts connected with excrements — such as burying them in earth, always depositing them in the same place, &c. — and other cases mentioned by Mr. Darwin in the Appendix. But the most important class of considerations for us is one to which the foregoing may be said to lead up. We have seen that if instincts have been developed by evolution, we should expect to find cases in which they are in process of evolution, or not yet perfect ; and we have also seen that this expectation is realized. Xow in so far as instinct requires to be mixed with intelligence in order to be effective, it is as an instinct imperfect ; it is as an instinct in course of formation, or at any rate not perfectly adapted to the possible circum- stances of life. Therefore all cases of the education of instinct by intelligence — whether in the individual or the I'ace — fall to be considered in the present connection. The consideration of this subject, however, lands us directly in a larger and deeper topic as to the origin and development of instinct in general. To this topic, therefore, we shall next address ourselves. * Die Seele des Kindes, Leii>zig, 1882, pp. 166-7. t Ibid., pp. 167-75. ORIGIN AND DEVELOPMENT OF INSTINCTS. 17 CHAPTER XII. Instinct (continued). Origin and Development of Instincts. Instincts probably owe their origin and development to one or other of two principles. I. The first mode of origin " consists in natural selection, ^ or survival of the fittest, continuously preserving actions which, although never intelHgent, yet happen to have been of benefit to the animals which first chanced to perform them. Thus, for instance, take the instinct of incubation. It is quite impossible that any animal can ever have kept its eggs warm with the intelligent purpose of hatching out their con- tents, so we can only suppose that the incubating instinct began by warm-blooded animals showing that kind of atten- tion to their eggs which we find to be frequently shown by cold-blooded animals. Thus crabs and spiders carry about their eggs for the purpose of protecting them; and if, as animals gradually became warm-blooded, some species, for this or for any other purpose, adopted a similar habit, tlie imparting of heat would have become incidental to the car- rying about of the eggs. Consequently, as the imparting of heat promoted the process of hatching, those individuals which most constantly cuddled or brooded over their eggs would, other things equal, have been most successful in rearing progeny; and so the incubating instinct would be developed without there ever having been any intelligence in the matter."* II. The second mode of origin is as follows : — By the > efiects of habit in successive generations,, actions which Avere originally intelligent become, as it were, stereotyped into per- * Quoted from my own article on "Instinct," in the EncijclopcBdia Bri- tannica. M 178 MENTAL EVOLUTION IX ANIMALS. manent instincts. Just as in the life-time of the individual adjustive actions which were originally intelligent may by frequent repetition become automatic, so in the life-time of the species actions originally intelligent may, by frequent repetition and heredity, so write their effects on the nervous system that the latter is prepared, even before individual experience, to perform adjustive actions mechanically which in previous generations were performed intelligently. This mode of origin of instincts has been appropriately called the " lapsing of intelligence."* For the sake of subsequent reference, I shall allude to instincts which arise by w^ay of natural selection, without the intervention of intelligence, as Primary Instincts, and to those which are formed by the lapsing of intelligence as _Secondary Instincts. Let us now consider the reasons which a 'priori lead us to assign the probable origin of instincts to these principles. Taking first the case of primary instincts, these reasons may be briefly rendered thus : — (1.) Many instinctive actions are performed by animals too low in the scale to admit of our supposing that the adjust- ments which are now instinctive can ever have been intel- ligent. (2.) Among the higher animals instinctive actions are performed at an age before intelligence, or power of learning by individual experience, has begun to assert itself. (3.) Considering the great importance of instincts to species, we are prepared to expect that they must be in large part subject to the influence of natural selection. As Mr. Darwin observes, " it will be universally admitted that instincts are as important as corporeal structures for the welfare of each species under its present conditions of life. Under changed conditions of life it is at least possible that slight modifica- tions of instinct might be profitable to a species ; and if it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and con- tinually accumulating variations of instinct to any extent that was profitable." That instincts may arise by way of lapsed intelligence is ' rendered probable ^d priori by all the facts which show the resemblance between instincts and intelligent habits. To take only a few of these facts for the present purpose, I * By Lewes, see Problems of Life and Mind. ORIGIN AND DEVELOPMENT OF INSTINCTS. 179 cannot do better than confine myself to making a quotation from Mr. Darwin's MSS ; for this will show how deep-seated and detailed is the resemblance between habit and instinct. " In repeating anything by heart, or in playing a tune, every one feels that, if interrupted, it is easy to back a little, but very difficult suddenly to resume the thread of thought or action a few steps in advance. Now P. Huber has described a caterpillar which makes by a succession of processes a very complicated hammock for its metamorphosis; and he found that if he took a caterpillar which had completed its ham- mock up to, say the sixth stage of construction, and put it into a hammock completed up only to the third stage, the caterpillar did not seem puzzled, but repeated the fourth, fifth, and sixth stages of construction. If, however, a cater- pillar was taken out of a hammock made up, for instance, to the third stage, and put into one finished to the ninth stage, so that much of its work was done for it, far from feeling the benefit of this, it was much embarrassed, and even forced to go over the already finished work, starting from the third stage which it had left off before it could complete its hammock. So, again, the hive-bee in the construction of its comb seems compelled to follow an invariable order of work. M. Fabre gives another curious instance how one instinctive action invariably follows another. A Sphex makes a burrow, flies away and seeks for prey, which it brings, paralyzed by having been stung, to the mouth of its burrow ; but always enters to see that all is rioiit within before drac^s^imy in its prey; whilst the Sphex was within its burrow, M. Fabre removed the prey to a short distance ; when the Sphex came out it soon found the prey and brought it agaiu to the mouth of the burrow ; but then came the instinctive necessity of reconnoitering the just reconnoitered burrow ; and as often as M. Fabre removed the prey, so often was all this gone over again, so that the unfortunate Sphex reconnoitered its burrow forty times successively ! When M. Fabre altogether removed the prey, the Sphex, instead of searching for fresh prey and then making use of its completed burrow, felt itself under the necessity of following the rhythm of its instinct, and before making a new burrow, completely closed up the old one as if it were all right, although in fact utterly useless as containing no prey for its larva.* * Anns, des Sci. Kaf., 4 ser., tome vi, p. 148. "With respect to Bees, see M 2 180 MENTAL EVOLUTION IN ANIMALS. " In another way we perhaps see the relation of habit and instinct, namely in the latter acquiring great force if practised only once or twice for a short time ; thus it is asserted that if a calf or infant has never sucked its mother, it is very much easier to bring it up by hand than if it has sucked only once.* So again Kirbyf states that larva, after having ' fed for a time on one plant, will die rather than eat another, which would have been perfectly acceptable to them if ac- customed to it from the first.' " Such, then, are some of the a priori reasons for believing tliat instincts must have arisen from one or other of these two sources — natural selection or lapsing intelligence ; it now remains to prove, a posteriori, that they have so arisen. I may first give a brief sketch of how this proof ought to proceed. The proof, then, that instincts have had a primary mode of origin requires to show : — I. That non-intelligent habits of a non-adaptive character occur in individuals. II. That such habits may be inherited. III. That such habits may vary. IV. That when they vary the variations may be inherited. V. That if such variations are inherited, we are justified in assuming, in view of all that we know concerning the analogous case of structures, that they may be fixed and intensified in beneficial lines by natural selection. The proof that instincts have had a secondary mode of origin requires to show : — VI. That intelligent adjustments when frequently per- formed by the individual become automatic, either to the extent of not requiring conscious thought at all, or, as consciously adjustive habits, not requiring the same degree of conscious effort as at first. VII. That automatic actions and conscious habits may be inherited. Primary Instincts. Proceeding, then, to consider these sundry heads of proof, it is easy to establish Proposition I, inasmuch as the fact Kirby and Spence, Entomology, voL i, p. 497. For the hammock caterpillar, see Mem. Soc. Phys. de Geneve, tome vii, p. 154. * Zoonomia, p. 140. f Intro, to Entomol., vol. i, p. 391. ORIGIN AND DEVELOPMENT OF INSTINCTS. 181 which it states is a matter of daily observation. " Tricks of manner," indeed, are of such frequent occurrence in the nursery and schooboom, that it usually entails no small labour on the part of elders to eradicate them, and when not eradicated in childhood they are apt to continue through life, unless afterwards conquered by the efforts of the indi- vidual himself. But in cases where the trick of manner is not obnoxious, or sufficiently unusual to call for checking, it is allowed to persist, and thus it is that almost every one presents certain slight peculiarities of movement which we recognize as characteristic* Such peculiarities of movement as we meet with them in ordinary life are slightly marked ; but their significance in relation to instinct has been obtruded on my notice by observing them in the much more striking form in which they are presented by idiots. This is a class of persons which, as we shall find in my next work, is of peculiar interest in relation to mental evolution, because in them we have a human mind arrested in its development as weU as deflected in its growth — therefore in many cases supplying to the comparative psychologist very suggestive material for study. Now one of the things which must most strike any one on first visiting an idiot asylum, is the extraordinary character and variety of the meaningless tricks of manner which are everywhere being displayed around him. These tricks, often ludicrous, sometimes painful, but usually meaningless, are always individual and wonderfully per- sistent. Generally speaking, the lower the idiot in the scale of idiotcy, the more pronounced is this peculiarity ; so that if one sees a patient moving to and fro continually, or otherwise exhibiting " rhythmical movements," one may be pretty sure that the case is a bad one. But even among the higher idiots and " feeble-minded," strange and habitual movements of the hands, limbs, or features are exceedingly common. Among animals similar facts are to be noticed. Scarcely any two sporting dogs " point " in exactly the same manner, * Dr. Carpenter says {Mental Physiology, p. 373), "What particular ' trick ' each individual may learn, depends very much upon accident. Thus, in the old times of dependent watch-chains and massive bunches of seals, these were the readiest playthings," &c. In view of the relation which such '"tricks" bear to the formation of primary instincts, this remark has some importance ; it shows that even aimless movements may be determined and rendered habitual by the conditions of the environment. 182 MENTAL EVOLUTION IN ANIMALS. althougli every dog adheres to his particular attitude through life. Nearly all domestic animals exhibit slight but indi- vidually constant differences of movement when caressed, when they are threatened, when at play, &c. But perhaps a more striking view of this subject may be obtained by con- sidering the sum of the neuro-muscular conditions, leading to individual peculiarities of movement, which we comprise under the term " disposition," or, if more prominent, " idiosyn- cracy." Thus many dogs develop the meaningless habit — which has all the strength of an incipient instinct, and in the case of the collie breed, as we shall subsequently see, inherited or innate — of barking round a carriage. Some cats take to " mousing " with 9.vidity, while others can never be taught to care about the sport. All who keep pet birds — and indeed domestic animals of any kind — must have noticed the diversity of their dispositions in respect of play, boldness, amiability, &c. ; and Mr. W. Kidd, who had a very large experience, is sure that the diversity of disposition in larks and canaries is displayed by nestlings reared from the nest.* Almost innumerable instances might be given of indi- vidual variations in the instincts of nest-building.f Even as * See Gardener's Chronicle, 1851, p. 181, wliicli is referred to in this connection in Mr. Darwin's MSS. t For example, the Nut-hatch usually builds in the hollow branch of a tree, plastering up the opening with clay ; but Mr. Hewetson found a pair which for many years occupied a hole in a wall {YarreVs Birds), and Mr. Bond describes another nest placed in the side of a hay-stack, built up with a mass of clay weighing no less than eleven pounds, and the nest measuring thirteen inches in height {Zoologist, 2nd ser., p. 2850). The golden-crested Wren, also, frequently exhibits variations in the structure and situation of its nest {Hist. Brit. Birds, 4th ed., vol. i, p. 450). The Grolden Eagle builds in precipitous crags of rock ; but Mr. D. E. Knox {Autumns on the S^ey, 1872, pp. 141-3), describes a nest which he himself examined on a fir-tree, not above twenty feet from the ground. Couch says that "more than one pair of birds will sometimes unite in occupying one nest, and either rear their broods in com- mon, or one of them will surrender the future care of them to the other {Illus- trations of Instinct, p. 233). Mr. S. Stone, writing of the Missel -thrush says, " From what has been written, it appears plain that some individuals use clay or plaster in the construction of the nest, while others contrive to do without it, which agrees with my own observation, for although I have found nests which did not contain plaster, the greater part of those which have fallen in my way — and they have been not a few — certainly have had a plastering of some kind between tlie twigs and lichens outside and the fine grasses which invariably constitute the lining ; this has been more especially the case when the bird has selected as a site the horizontal branches of a tree {Field, Jan. 8, 1861. This is a clipping which I find among Mr. Darwin's MS notes). As ORIGIN AND DEVELOPMENT OF INSTINCTS. 18:^) low down in the psychological scale as the insects, we are not without evidence of individual variations of instinct. Thus, for instance, Forel observed great diversities of building among the F. truncicola — the nests being sometimes domed, sometimes made under stones, and sometimes excavated in the wood of old trees. Likewise, Buchner observes, " one ant will let herself be killed ratlier than let go the pupa whicli she holds, while another will let them fall and run away like a coward," and similar statements are made by Moggridge. But as showing strongly marked individual differences of disposition in animals, and also that such differences may lead to useless or capricious actions having all the strength of incipient instincts, I think a good class of cases to select are those in which one animal conceives a strong though senseless attachment to another animal of a different species. Thus, for instance, I once found a wounded widgeon on the shore, and took it home to my poultry yard. After a time its wounds healed, and I then cut its wings to keep it as a pet. The bird soon became perfectly tame, and then con- ceived a strong, persistent, and unremitting attachment to a peacock which also belonged to the establishment. Wherever the peacock went the widgeon followed like a shadow, so that during the day time the one bird was never seen without the other being in close attendance. If a separation were forcibly effected, the distress of the widgeon was very great, and she would whistle incessantly till restored to her old place waddling behind the tail of the peacock. This devoted attachment was the more remarkable from the fact that it was not in the smallest degree reciprocated by the peacock. He never paid the slightest heed to his constant companion, nor, indeed, did he seem to notice that she was always just behind him. At night he used to roost upon the gable of a cottage. The poor widgeon could not fly to accompany him, and even if she could would probably not have been able to sit upon the gable ; but she always kept as near him as cir- cumstances would permit, for as soon as he flew up to his gable she would squat herseK down upon the ground just observed in the text, such instances might be multipUcd indefinitelj ; but as a considerable number of additional and well selected cases are given in Mr. Darwin's essay at the end of this book, it is needless for me to adduce any further illustrations. 184 MENTAL EVOLUTION IN ANIMALS. below it — a devotion which eventually cost her her life, as she thus fell a prey to a prowling cat. Now here we have a curious case of a bird that had been wild, taking a violent fancy for the wholly useless companionship of another and very dissimilar bird ; for it should be added that she chose the peacock as the object of her persistent regard out of a large number of other kinds of domestic birds which lived about the place. Similarly, cats often like to associate with horses, and in some cases with dogs, birds, rats, and other unlikely creatures. Dogs not unfrequently make friendships with a variety of animals, and in a case recorded by F. Cuvier a terrier found so much delight in the companionship of a caged lion, that when the lion died the dog pined away and died also. Thompson gives cases in which horses have become " ex- tremely attached to dogs and to cats, and seemed pleased to have them placed on their backs in their stalls."* Eengger mentions a monkey which was so fond of a dog that it cried with grief during the absence of its friend, caressed it on its return, and assisted it in all its quarrels with other dogs. " A peccari in the menagerie at Paris formed a strong attach- ment with one of the keeper's dogs, and a seal in the same place allowed a little water-dog to play with it and to take fish from its mouth, which it always resented if this were attempted by the other seals in the same tank. Dogs have lived on terms of friendship with gulls and ravens .... and a rat has been known to accompany his master in his walks," &c., &c.t Colonel Montagu, in the Supplement to his "Ornitho- logical Dictionary," p. 165, relates the following singular instance of an attachment which took place between a Chinese goose and a pointer. " The dog had killed the male bird, and had been most severely punished for the mis- demeanour, and finally the dead body of his victim was tied to his neck. The solitary goose became extremely distressed for the loss of her partner and only companion ; and probably having been attracted to the dog's kennel by the sight of her dead mate, she seemed determined to persecute the dog by her constant attendance and continual vociferations ; but after a little time a strict friendship took place between these incongruous animals. They fed out of the same trough, lived * Thompson, Passions of Animals, pp. 360-1. f Ibid. ORIGIN AND DEVELOPMENT OF INSTINCTS. 185 Tinder the same roof, and in tlie same straw bed kept each other warm ; and when the dog was taken to the field, the lamentations of the choose were incessant." The same author gives cases of attachment between a pigeon and a fowl, a terrier and a hedgehog, a horse and a pig, a horse and a hen, a cat and a mouse, a fox and harriers, an alligator and a cat, &c., all as having fallen under his own observation. (Ibid., p. 162.) It is not impossible that the so-called " domestic pets " which are kept by many species of ants* may really be use- less adjuncts to the hive, capricious love of association having perhaps in these ants become by inherited habit truly instinctive. This, at any rate, must be the explanation of the fact that birds of different species will, even in a state of nature, occasionally associate, as is the case with Guinea- fowls and partridges, and, according to Yarrell, with par- trido-es and landrails. Such unusual cases amon^:^ birds in a state of nature are of special interest, because they may then properly be regarded as the beginnings of such a firmly set and truly instinctive association as that which obtains between rooks and starlings, &c.t Enough lias now been said in support of Proposition I, viz., that non-intelligent habits of a non-adaptive character occur in individuals. We shall next proceed to Proposition II, viz., that such habits may be inherited. That this is the case with tricks of manner in man is a matter to be observed in almost every family, and was long ago pointed out by John Hunter. Mr. Darwin in his MSS gives a case which he himself observed, " and can vouch for its perfect accuracy." " A child who as early as between her fourth and fifth year, when her imagination was pleasantly excited, and at no other time, had a most peculiar trick of rapidly moving her fingers laterally with her hands placed on the side of her face; and her father had precisely the * See Animal Intelligence, pp. 83-4. t Prof. Newton, F.R.S., informs me that " bands of the G-olden-crested Wren may frequently be observed in winter consortin;^ with bands of the Coal-Titmouse, and in a less degree with those of the Long-tailed Titmouse ; while parties of Eedpoles and Siskins will for a time join their company, or vice versa. The flocking together of Rooks and Daws is, of course, an everyday occurrence, as is also for some months the association of Starlings with them, and in many cases the combination of all with Lapwings. 186 MENTAL EVOLUTION IN ANLMALS. same trick under the same frame of mind, and wliicli was not quite conquered even in old age : in this instance there could not possibly have been any imitation."* That the more frequent and more pronounced tricks of manner which are manifested by idiots are likewise inherited is highly probable ; but I have no evidence on this point, as idiots in civilized countries are not allowed to propagate. In the case of animals, however, the evidence is abun- dant. Thus, again to quote from Mr. Darwin's MSS, " the Eev. W. Darwin Fox tells me that he had a Skye terrier bitch which when begging rapidly moved her paws in a way very different from that of any other dog which he had ever seen ; her puppy, which never could have seen her mother beg, now when full grown performs the same peculiar move- ment exactly in the same way."t As regards the inheritance of disposition, we have only to look to the sundry breeds of dogs to see how marked differences of this kind may become signally distinctive of different breeds. It will be remembered that at present we are only concerned with the inheritance of useless, unintelli- gent, or non-adaptive habits, and therefore have here nothing to do with the useful and intelligent habits which are bred into our various races of dogs by means of artificial selection combined with training. But even in the case of j)u,rely meaningless traits of character, which are of no use either to the animals themselves or to man, we find the influences of heredity at work. Thus, for instance, the useless and even annoying habit of barking round a carriage, which occurs among sundry breeds of dogs, is particularly pronounced in the collie, and is truly innate or not dependent on imitation. This is shown by the fact that collies which from puppyhood have never seen other dogs bark at horses, will nevertheless spontaneously begin to do so.J Several other useless traits of character or disposition peculiar to different breeds might be mentioned ; but I shall pass on to the most remarkable instance * This case is stated in differcDt words in Variation of Animals and Plants, &c., ToL i, pp. 450-1. t Here, however, I may remark that I have noticed several Syke terriers perform these movements while begging, so that the action seems to be due to some race-distinction of a psychological kind, and not merely to an indi- vidual peculiarity. It therefore leads on to the class of cases next considered in the text. X See Nature, vol. xix, p. 234. ORIGIN AND DEVELOPMENT OF INSTINCTS. 187 I have met with in dogs of the inheritance of a tlioroughly sense- less psychological peculiarity. I refer to the instance which was communicated some years ago to Mr. Darwin by Dr. Huggins, F.R.S., and which I shall quote in his own words. " I wish to communicate to you a curious case of an inherited mental peculiarity. I possess an English mastiff, by name Kepler, a son of the celebrated Turk out of Venus. I broucrht the doii:, when six weeks old, from the stable in which he was born. The first time I took him out he started back in alarm at the first butcher's shop he had ever seen. I soon found he had a violent antipathy to butchers and butchers' shops. When six months old a servant took him with her on an errand. At a short distance before coming to the house she had to pass a butcher's shop ; the dog threw himself down (being led with a string), neither coaxing or threats would make him pass the shop. The dog was too heavy to be carried, and as a crowd collected, the servant had to return with the dog more than a mile, and then go without liim. This occurred about two years ago. The antipathy still continues, but the dog will pass nearer to a shop than he formerly would. About two months ago, in a little book on dogs, published by Dean, I discovered that the same strange antipathy is shown by the father, Turk. I then wrote to Mr. JSTicholls, the former owner of Turk, to ask him for any information he might have on the point. He replied, ' I can say that the same antipathy exists in King, the sire of Turk, in Turk, in Punch (son of Turk out of Meg), and in Paris (son of Turk out of Juno). Paris has the greatest antipathy, as he w^onld hardly go into a street where a butcher's shop is, and would run away after passing it. When a cart with a butcher's man came into the place where the dogs were kept, although they could not see him, they all were ready to break their chains. A master-butcher, dressed privately, called one evening on Paris' master to see the dog. He had hardly entered the house before the dog (thougli shut in) was so much excited that he had to be put into a shed, and the butcher was forced to leave without seeing the dog. The same dog at Hastings made a spring at a gentleman who came into the hotel. The owner caught the dog and apologised, and said he never knew him to do so before, except when a butcher came to his house. The gentleman at once said that was his business.' " 188 MENTAL EVOLUTION IN ANIMALS. We see, then, that non-intelligent habits of non-adaptive or useless character may be strongly inherited by domestic animals. As showing that the same is true of breeds or strains in wholly wild animals, I may quote Humboldt, who says,* that the Indians who catch monkeys to sell them " knew very well that they can easily succeed in taming those which inhabit certain islands ; while monkeys of the same species, caught in the neighbouring continent, die of terror or rage when they find themselves in the power of man :" and in his MSS I find that Mr. Darwin has a note saying, " divers dispositions seem to run in families of crocodiles." But one of the most curious instances that I have met with of the commencement of a racial and useless deviation from a strong ancestral instinct, is one which is communicated to Mr. Darwin in a letter from Mr. Thwaits, who writes from Ceylon under the date 1860, and whose letter I find among Mr. Darwin's MSS. Mr. Thwaits here says that his domestic ducks quite lost their natural instincts with regard to water, which they never enter unless driven. The young birds, when forcibly placed in a tub of water are " quite alarmed," and have to be quickly taken out again " or they would drown in their struggling." Mr. Thwaits adds that this peculiarity does not extend to aU the ducks in the island, but only occurs in one particular breed or strain. In Mr. Darwin's MSS I also find the following remarks : " So many independent authors have stated that horses in different parts of the world inherit artificial paces, that I think the fact cannot be doubted. Dureau de la MaUe asserts that these different paces have been acquired since the time of the Eoman classics, and that from his own observation they are inherited.! .... Tumbler pigeons offer an excellent instance of an instinctive action, acquired under domestication, which could not have been taught, but must have appeared naturally, though probably afterwards vastly improved by the continued selection of those birds which showed the strongest propensity — more especially in * Personal Narrative, vol. iii, p. 383. f After giving numerous references on this point in a footnote, Mr. Darwin concludes tlie latter thus : — " I may add that I was formerly struck by no horse on the grassy plains of La Plata having the natural high action of some English horses." For a number of other instances of here- ditary transmission of qualities in the case of the Horse, see Variation of Animals and Plants, &c., vol. i, pp. 454-6. ORIGIN AND DEVELOPMENT OF INSTINCTS. 189 ancient times in the East, when flying pigeons was much esteemed. Tumblers have the habit of flying in a close flock to a great height, and as they rise tumbling head over tail. I have bred and flown young birds, which could not possibly have ever seen a tumbler; after a few attempts even they tumbled in the air. Imitation, however, aids the instinct, for all fanciers are agreed that it is highly desirable to fly young birds with first-rate old ones. Still more remarkable are the habits of the Indian sub-breed of tumblers, on which I have given details in a former cliapter, showing that during at least the last 250 years these birds have been known to tumble on the ground, after being slightly shaken, and to continue tumbling until taken up and blown upon. As this breed has gone on so long, the habit can hardly be called a disease. I need scarcely remark that it would be as impossible to teach one kind of pigeon to tumble as to teach another kind to inflate its crop to the enormous size which the pouter pigeon habitually does."* This case of the tumblers and pouters is singularly interesting and very apposite to the proposition before us, for not only are the actions utterly useless to the animals them- selves, but they have now become so ingrained into their psychology as to have become severally distinctive of different breeds, and so not distinguish a.ble from true instincts. Tliis extension of an hereditary and useless habit into a distinction of race or type is most important in the present connection. If these cases stood alone they woidd be enough to show that useless habits may become hereditary, and this to an extent which renders them indistinguishable from true instincts.f In the Appendix several instructive cases of the same kind will be found, such as that of the Abyssinian pigeon, which, when fired at, " plunges down so as almost to touch the sportsman, and then mounts to an immoderate height ;";[: the biscacha, which " almost invariably collects all sorts of * For further particulars on the instinct of tumbling, see Variation of Animal.t and Plants, vol. i, p. 219, and 230. I Some years ago the Ratels which were confined in one cage at the Zoological Gardens acquired the apparently useless habit of perpetually tumbling head over heels. If their progeny were to be exposed for a number of generations to similar conditions of life, they would probably develope a true instinct of turning somersaults analogous to that of the tumbler- pigeon. J I have frequently noticed a similar propensity in the Lapwing. 190 MENTAL EVOLUTION IN ANIMALS. rubbish, bones, stones, dry dung, &c., near its burrow ; " the guanacoes which " have the habit of returning (like flies) to the same spot to drop their excrement ; " horses, dogs, and the hyrax, showing a somewhat similar and equally useless propensity ; hens cackling over their eggs, &c., &c. So that I think the evidence is abundant in support of the proposi- tion that senseless or useless habits may be inherited, and thus become racial characteristics, or purposeless instincts. Passing on, then, to Propositions III and TV, — viz., that such habits may vary, and that vjhen they vary the variations may he inherited — the truth of these facts has already been made apparent. The paces of the horse in different parts of the world are so many race-characteristics of the animals ; the ground-tumblers display an inherited variation as compared with the air-tumblers, and if tumblers are not allowed to exercise their art, it undersjoes the variation of becominsr obliterated — ^just as we shall presently see is the case with many true instincts. The different dispositions of the same species of monkeys on different islands, prove that the ancestral disposition must have varied in the progeny, and have then continued to be inherited in its varied states along the several lines of descendants. Prom the exclusive nature of the requirement, it is not easy to find many examples of inherited varieties of useless habits, nor is it important that I should give a number of illustrations on this head. There is abundant evidence that non-intelligent and purposeless habits are inherited, and this is the main point ; for that such habits, when inherited, should vary, is a matter of certainty, seeing, as w^e presently shall, that such is the case even with intelligent and useful habits. If the latter are liable to vary in their course of inheritance, a fortiori the former must be similarly liable, inasmuch as they arise in a manner analogous to fortuitous " sports " of structure (which are always eminently variable), and after- wards have no check imposed on their variability either by intelligence or by selection. Similarly Proposition V requires very little to be said in the w^ay of proof. If among a number of meaningless habits, all more or less hereditary and more or less variable, any one should happen from the first to be, or afterwards to vary so ORIGIN AND DEVELOPMENT OF INSTINCTS. 191 as to become accidentally beneficial to the animal, then we ^ are bound to believe that natural selection would fix this habit, or its beneficial variations. And the proof that such a process has taken place is given by the fact of their being- many instincts — such as the incubating instinct before alluded to — which cannot conceivably have been developed ' in any other way. Whether or not tliis instinct began in , J|r habits adapted to the protection of the eggs, it is certain that ^ '^ it cannot have begun with any intelligent reference to hatch- jJ'*jJ\ ing them ; and it is no less certain that before the instinct Y^*^ attained its present degree of perfection, it must have passed f,J^ through many stages of variation, few if any of which can ' have been due to intelligent purpose on the part of the birds. And further proof is rendered, as I have also previously observed, by the fact that many instincts are displayed by animals too low in the zoological scale to admit of our sup- posing that they can ever have been due to intelligence. To give only one illustration, the larva of the caddice tly lives in water and constructs for itself a tubular case made of various particles glued together. If during its construction this case is found to be getting too heavy — i.e., its specific gravity greater than that of the water — a piece of leaf or straw is selected from the bottom of the stream to be added to the structure ; and conversely, if the latter is found to be getting too light, so as to show a tendency to float, a small stone is morticed in to serve as ballast.* In such a case as this it seems impossible that an animal so low in the zoological scale can ever have consciously reasoned — even in the most concrete way — that some particles have a higher specific gravity than others, and that by adding a particle of this or that substance, the specific gravity of the whole structure may be adjusted to that of the water. Yet the actions involved are no less clearly something more than reflex ; they are instinctive, and can only have been evolved by natural selection. Similarly, Professor Duncan suggests, in a lecture before the British Association, 1872, that "the instinct of the Odynerus — which forms a tubular ante-chamber and provision- chamber filled with stung grubs for the future use of offspring which it never saw — probably arose in this way. M. Fabre has observed that Bemhex inclica lays an Qg^^ in a chamber, * A Monographic Revision and Sj/n->p.s-is of the Trichoptera of the JiJuropean Fauna, 1881, by Robert M'Lachlan, F.R.S. 192 MENTAL EVOLUTION IN ANIMALS. and that the egg hatches very shortly. The insect then visits its living offspring every day, bringing it small larvae stung to keep them quiet. Now this instinct may have been altered in Odynerus by a delay arising in the time of hatch- ing, and a series of victims having been therefore placed in the provision-chamber in obedience to the primitive instinct, which has thus become modified into a new one. ISTumerous other instincts will be found mentioned in the Appendix, the origin of which can only be attributed to the uncompounded influence of natural selection. I feel, there- fore, that it is needless for me to adduce further illustrations, and so shall here conclude my observations on instincts of the primary class. Secondary Instincts. Coming now to the second series of propositions, we shall find that their proof casts a good deal of reflected light upon those which we have just considered — light which tends still further to demonstrate the latter. First, then, we have to show that " intelligent adjustments, yjlien frequently 'perfm^med hy the individual, hcconie autoynatic, either to the extent of not requiring conscious thought at all, or, as consciously adjustive habits^ not requiring the same degree of conscious effort as at fir d. The latter part of this proposition has already been proved in an earlier chapter of this book. That '' practice makes perfect" is a matter, as I have previously said, of daily observation. Whether we regard a juggler, a pianist, or a billiard player, a child learning his lesson, or an actor his part by frequently repeating it, or any one of a thousand other illustrations of the same process, we see at once that there is truth in the cynical definition of a man as '' a bundle of habits/' And the same, of course, is true of animals. " Training " an animal is essentially the same process as educating a child, and, as we shall presently have occasion to show, animals in a state of nature develop special habits in relation to local needs. The extent to which habit or repetition may thus serve to supersede conscious effort is a favourite theme among psychologists ; and one or two instances have already been given in the chapter on the Physical Basis of Mind. To this point, therefore, I need not recur. ORIGIN AND DEVELOPMENT OF INSTINCTS. 193 It remains to mention another class of acquired mental habits, and one which is still more suggestive in relation to instinct, inasmuch as the habits are purely mental, and not associated with mechanically distinctive movements. Thus, as Professor Alison remarks,* the sense of modesty in man is not a true instinct, because it is neither innate nor is it ex- hibited by all the members of the species — being, in fact, only displayed by the civilized races. Yet, altliough merely a taught habit of mind, among morally cultured persons it is in strength and precision indistinguishable from a true instinct. Similarly, though in a lesser degree, the influences ; of refinement and good taste, operating upon the individual from childhood, produce such a powerful and unremitting influence, that the extreme nicety, spontaneity, and readiness of adjustment to highly complex conditions which result are recognized even in ordinary conversation as akin to the promptings of instinct; for we commonly say that a man has "the instincts of a gentleman," or that so and so is "underbred." This latter term, however, introduces us to the division of our subject which we have to consider under the next heading — namely, the extent to which habits of mind, intentionally or intelligently acquired by the individual, may be transmitted to progeny. To this branch of oiu^ dis- cussion, therefore, we shall now pass.f Accepting, then. Proposition VI as beyond dispute, we have here to substantiate Proposition VII, viz.. That cmtomatic 7 actions and conscious habits may he inherited. Now we have already seen that this is certainly the case ' * Article " Instinct," Todd's Cijclo. of Anat., rol. iii, 1839. t Mr. Darwin's MS points ont that persons of weak intellect are very apt to fall into habitual or automatic actions, and these, from not being performed under the mandates of the will, are more nearly allied to reflex actions than are properly voluntary or deliberate movements. This correlation is also to be observed in animals, and the MS gives a case which Mr. Darwin observed of an idiotic dog, whose instinct of turning round before lying down (a remnant, probably, of the instinct of forming a bed in long grass) was so strongly developed, or so little checked by intelligence, "that he has been counted to turn round twenty times before lying down," This action of turning round may certainly be regarded as the survival of a secondary instinct. Now secondary instincts are formed by a descent from intelligent action, through habitual action, towards reflex action; there- fore it is interesting that when, as in such a case as this, they are fully formed as instincts, tliey are found to resemble automatic habits in showing most unrestricted play when intelligence is enfeebled or idiotic. N c_ 194 MENTAL EVOLUTION IN ANIMALS. with automatic actions which have arisen accidentally, or without intelligent purpose ; and it would be anomalous were the fact otherwise with automatic actions which have been acquired consciously. The evidence that the fact is not otherwise is considerable. First we may take the case of man. " On what a curious combination of corporeal structure, mental character, and training," says Mr. Darwin, "must hand-writing depend! Yet every one must have noted the occasional close similarity of the hand-writing in father and son, although the father had not taught the son .... Hof acker, in Germany, remarks on the inheritance of hand -writing; and it has been even asserted that English boys, when taught to write in France, naturally cling to their English manner of writing." Dr. Carpenter says he is " assured by Miss Cobbe that in her family a very characteristic type of hand-writing is traceable through five generations;" and in his own family there occurred a curious case of a gentleman who inherited a " constitutional " character of hand-writing, and lost his right arm by an accident; "in the course of a few months he learnt to write with his left hand, and before long the hand- writing of the letters thus written came to be indistinguish- able from that of his former letters." This case reminds me of a fact which I have frequently observed — and which has doubtless been observed by others — viz., that if I write in any unusual direction (as, for instance, on the perpendicular face of a recording cylinder), the hand-writing is unaltered in character, although both the hand and the eye are working in a most unusual manner ; so strong is the mental element in hand-writing. Similarly, as observed in a previous chapter, if one takes a pencil in each hand and writes the same word with both hands simultaneously — the left hand writing from right to left — on holding the backward written word before a mirror, the hand- writing may at once be recognized. Many other instances might be given of the force of inheritance in the mental acquisitions of man.* But turning * See Carpenter, Mental Physiology, pp. 393-4, where he discusses and gives cases of hereditary aptitude for music and painting. Also Gralton's Hereditary Genius, for high mental qualities running in families, either in the same or in analogous lines of activity ; and Spencer {Psychology, i, p. 422) for race-characteristics of psychology in man. The effects of " good breeding " or " blood " in bequeathing hereditary disposition and refinement have already ORIGIN AND DEVELOPMENT OF INSTINCTS. 195 now to the more important case of animals, I shall give only a few examples among almost any number tliat I could quote. Thus, in Norway, the ponies are used without bridles, and are trained to obey the voice ; as a consequence a race-peculiarity has been established, for Andrew Knight says " the horse breakers complain, and certainly with very good reason, that it is impossible to give them what is called a mouth; they are nevertheless exceedingly docile, and more than ordinarily obedient, when they understand the commands of their masters."* Again, Mr. Lawson Tait tells me that he had a cat which was taught to beg for food like a terrier, so that she developed the habit of assuming this posture — so very unusual in a cat — whenever she desired to be fed. All her kittens adopted the same habit under circumstances which precluded the possibility of imitation; for they were given away to friends very early in life, and greatly surprised their new owners when, several weeks afterwards, they began spontaneously to beg.f In order to show that the same principles apply to animals in a state of nature, it will be enough to adduce the one instance of hereditary wildness and tameness, for this i Qstance affords evidence of the most conclusive kind. Wild- ness or tameness simply means a certain group of ideas or disposition, having the character of an instinct, so that we may properly speak of a wild animal as " instinctively afraid " of man or other enemy, and of a tame one as instinctively the reverse. Indeed, one of the most typical and remarkable illustrations of instinct that could be given is that of the in- born dread of enemies, as exhibited, for instance, by chickens at the sight of a hawk, by horses at the smell of a wolf, by monkeys at the appearance of a snake, &c. Now, fortunately, there is material for amply proving both that these instincts may be lost by disuse, and, conversely, that they may be acquired as instincts by the hereditary transmission of ancestral experience. been alluded to, and I think observation will sliow that the same applies to the sense of modesty. * Phil. Trans., 1839, p. 369. t Inasmuch as the action of "begging" is so unusual in the Cat, the above case of its hereditarv transmission is more remarkable than the similar cases which occur in the Dog ; see Lewes, Problems of Life and Mind. vol. i, p. 229, and Fiske, Cosmic Philosophy, vol. ii, p. 150, and more especially a case recorded by Mr. L. Hm-t, in Nature (Aug. 1, 1872) of a Skve terrier N 2 196 MENTAL EVOLUTION IN ANIMALS. The proof that instinctive wildness natural to a species may be lost by disuse is strikingly rendered by the case of rabbits. As Mr. Darwin remarks, ''hardly any animal is more difficult to tame than the young of the wild rabbit ; scarcely any animal is tamer than the young of the tame rabbit ; but I can hardly suppose that domestic rabbits have often been selected for tameness alone ; so we must attribute at least the greater part of the inherited change from extreme wildness to extreme tameness, to habit and long-continued close confinement ;* and in his MSS he adds, " Captain Sulivan, E.N., took some young rabbits from the Falkland Islands, where this animal has been wild {i.e., feral) for several generations, and he is convinced that they are more easily tamed than really wild rabbits in England. The facility of breaking in the feral horses in La Plata can, I think, be accounted for on the same principle of some little of the effects of domestication being long inherent in the breed." Similarly Mr. Darwin points out in his MSS that there is a great contrast between the natural tameness of the tame duck and the natural wildness of the wild.t The still more remarkable contrasts which are presented between our domestic dogs, cats, and cattle I shall consider later on ; for in them it is probable that the principle of selection has belonging to him which had great difficulty in acquiring by tuition the accomplishment of begging, but afterwards habitually practised it as a general expression of desire. Mr. Hurt then adds, " One of his daughters, who has never seen her father, is in the constant habit of sitting up, although she has never been taught to do so, and has not seen others sit up." * Origin of Species, p. 211. t With reference to these points I may here appropriately quote the fol- lowing note, which occurs among Mr. Darwin's MSS. " ' The wild rabbit,' says Sir J. Sebright {On Instincts, 1836, p. 10) ' is by far the most untameable animal that I know, and I have had most of the British Mammalia in my possession. I have taken the young ones from the nest, and endeavoured to tame them, but could never succeed. The domestic rabbit, on the contrary, is perhaps more easily tamed than any other animal, excepting the dog.' We have an exactly parallel case in the young of the wild and tame Duck." I may also quote the following interesting corroboration of the above statement with reference to ducks, from a letter recently published in Nature, by Dr. Rae, F.E.S. (July 19, 1883) :— "If the eggs of a wild duck are placed with those of a tame one under a hen to be hatched, the ducklings from the former, on the very day they leave the egg, will immediately endeavour to hide themselves, or take to the water, if there is any water, should any person approach, whilst the young from the tame duck's eggs will show little or no alarm, indicating in both cases a clear instance of instinct or ' inherited memory.' " ORIGIN AND DEVELOPMENT OF INSTINCTS. 197 played an important part, and at present we are confininfr our attention to the evidence concerning the formation of secondary instincts, or the mere lapsing of intelligence into instinct without the aid of selection. We see, then, that the instinct of wildness may be eradi- ' Gated by mere disuse, without any assistance from the principle of selection, and further, that this effect persists, or becomes but gradually obliterated, through successive genera- tions of the animals when feral, or restored to their abori- ginal conditions of life. Conversely, it has now to be shown that instincts of wildness may be acquired by the hereditary transmission of novel experiences, also without the aid of selection. This is shown conclusively by the original tame- ness of animals in islands unfrequented by man, gradually passing into an hereditary instinct of wildness as the special experiences of man's proclivities accumulate ; for although selection may here play a subordinate part, it must be a very subordinate one. Paoes mi^ht be filled with facts on this head from the writings of travellers, but to economize space I cannot do better than refer to Mr. Darwin's remarks, with their appended references in his chapter at the end of this volume. To these remarks, however, I may add that the developmentof fire-arms, together with the growth of sporting- interests, has given game of all kinds an instinctive know- ledge of what constitutes " safe distance," as every sportsman can testify; and that such instinctive adaptation to newly developing conditions may take place without much aid from selection is shown by the short time, or the small number of generations, which is sufficient to allow for the change — witness, for instance, the following, which I quote from the paper on "Hereditary Instinct" by the careful observer, Andrew Knight : — " I have witnessed, within the period above mentioned, of nearly sixty years, a very great change in the habits of the Woodcock. In the first part of that time, when it had recently arrived in the autumn, it was very tame ; it usually chuckled when disturbed, and took only a very short flight. It is now, and has been during many years, comparatively a very wild bird, which generally rises in silence, and takes a comparatively long flight, excited, I conceive, by increased hereditary fear of man."* * Phil. Tram., 1837, p. 369. 198 MENTAL EVOLUTION IN ANIMALS. But the force or influence of heredity in the domain of instinct (whether of the primary or secondary class) is per- haps most strongly manifested in the effects of crossing. It is not, indeed, easy to obtain this class of evidence in the case of wild species, because hybrid forms in a state of nature are rare. But when a wild species is crossed with a tame one, it usually happens that the hybrid or mongrel progeny present a blended psychology. And still more cogent is the evidence of such blending when two different breeds of domesticated animals are crossed, having diverse hereditary habits, or as Mr. Darwin calls them, " domestic instincts." Thus a cross-breed between a setter and a pointer will blend the movements and habits of working peculiar to these two breeds; Lord Alford's celebrated strain of greyhounds ac- quired much courage from a single cross wdth a bull-dog ; * and a cross with a beagle " generations back will give to a spaniel a tendency to hunt hares."t Again, Knight says : — " In one instance I saw a very young dog, a mixture of the Springing Spaniel and Setter, which dropped upon crossing the track of a Partridge, as its male parent w^ould have done, and sprang the bird in silence ; but the same dog, having a couple of hours afterwards found a Woodcock, gave tongue very freely, and just as its female parent would have done. Such cross-bred animals are, how- ever, usually worthless, and the experiments and observations I have made upon '1 ein have not been very numerous or interesting." On this point Mr. Darwin writes: — "These domestic instincts, when thus tested by crossing, resemble natural instincts, which in like manner become curiously blended together, and for a long time exhibit traces of the instincts of either parent ; for example, Le Eoy describes a dog, whose great-grandfather w^as a wolf, and this dog showed a trace of its wild parentage only in one way, by not coming in a straight line to his master when called.":]: Some further remarks on this subject will be found in Mr. Darwin's appended essay on instinct ; and here I may fitly conclude the present chapter by quoting the following paragraph which occurs in another part of his MSS. * Youatt on Dog, p. 311. t Blaine, Rural Sports, p. 863, quoted by Darwin. X Origin of Specie-t, p. 210. ORIGIN AND DEVELOPMENT OF INSTINCTS. 199 " In Chapter VII I have given some facts showing that when races or species are crossed there is a tendency in the crossed offspring, from quite unknown causes, to revert to ancestral characters. A suspicion has crossed me that a slight tendency to primeval wildness sometimes thus appears in crossed animals. Mr. Garnett in a letter to me states that his hybrids from the musk and common duck 'evinced a singular tendency to wildness.' Waterton (' Essays on Natural History,' p. 197) says that in his duck, a cross between the wild and the tame, ' their wariness w^as quite remarkable.' Mr. Hewitt, who has bred more hybrids between pheasants and fowls than any other man, in letters to me speaks in the strongest terms of their wild, bad, and troublesome dispositions ; and this was the case with some which I have seen. Captain Hutton made nearly the same remark to me in regard to the crossed offspring from a tame goat and a wild species from the western Himalaya. Lord Powis' agent, without my having asked him the question, remarked to me that the crossed animals from the domestic' Indian Bull and common cow ' were more wild than the thorough-bred breed.' I do not suppose that this increased wildness is invariable; it does not seem to be the case, according to Mr. Eyton, with the crossed offspring from the common and Chinese geese; nor, according to Mr. Brent, with crossed breeds from the Canary." 200 MENTAL EVOLUTION IN ANIMALS. CHAPTEE XIII. Instinct (contimced). Blended Origin, or Plasticity of Instinct. From the foregoing discussion it may, I think, be taken as established : — 1st. That propensities or habitual actions may originate and be inherited without education from parents or other- wise, as in the case of " tricks of manner," peculiar disposi- tions, tumbling of tumbler pigeons, &c. ; in such cases there need be no intelligence concerned in the propensity or action, but if such propensities or actions occur in nature (and, as we have seen, there can be no doubt that they do), those which happen to be of benefit to the animals performing them, will be fixed and improved by natural selection ; when thus fixed and improved they constitute what I have called instincts of the primary class. 2nd. That adjustments originally intelligent may by frequent repetition become automatic, both in the individual and in the race ; as instances of such " lapsed intelligence " in the individual I have given the highly co-ordinated and laboriously acquired actions of walking, speaking, and others ; as instances of the same thing m the race I have dwelt on the hereditary character of handwriting, artistic talent, &c., and in the case of animals, on peculiar habits — such as grinning in dogs, begging in cats — being transmitted to progeny, as well as the more instructive facts with regard to the loss of wildness by certain domesticated animals, and the gradual acquisition of this instinct by animals inhabiting islands previously unfrequented by man. All these and other such cases have been chosen as illustrations, because in none of them can the principle of selection have operated in any considerable degree. BLEXDED OEIGIN, OR PLASTICITY OF INSTINCT. 201 Although for the sake of clearness I have so far kept separate these two factors in the formation of instinct, it has now to be shown that instincts are not necessarily confined to one or other of these two modes of origin exclusively ; but, on the contrary, that instincts may have, as it were, a double root — the principle of selection combining with that of lapsing intelligence to the formation of a joint result. Thus, hereditary proclivities or habitual actions, which were never intelligent but, being useful, were originally fixed by natural selection, may come to furnish material for furtlier improve- ment, or be put to improved uses, by intelligence ; and, con- versely, adjustments originally due to lapsed intelligence may come to be greatly improved, or put to improved uses, by natural selection. As an example of the first of these complementary cases — or that of a primary instinct modified and improved by intelligence — let us regard the case of the caterpillar which, before changing into a crysalis, crosses a small space with a web of silk (to which the crysalis can be firmly suspended), but which when placed in a box covered with a muslin lid perceives that this preparatory web is unnecessary, and therefore attaches its crysalis to the already woven surface supplied by the muslin ;* or let us regard the case of the bird described by Knight, which observed that, having placed her nest ujDon a forcing house, she did not require to visit it during the day when the heat of the house was sufficient to incubate the eggs, but always returned to sit upon the eggs at night when the temperature of the house fell.t In. both these cases of primary instincts modified by intelligent adaptation to particular circumstances — and hundreds of others might be added — it is evident that if the particular circumstances were to become general, the adaptation to them, becoming likewise general, would in time become instinctive by lapsed intelligence : if muslin and forcing houses were to become normal additions to the environment of the caterpillar or the bird, the former would now cease to build its web, and the latter cease to incubate her eggs by * See Kirby and Spence, Entomoloqif, rol. ii, p, 476. It is evident that the -wearing of a web by a caterpillar adapted to the needs of its future con- dition as a crysalis, must be due to instinct of the primary kind, inasmuch as no individual caterpillar prior to the formation of such a structure can have known by experience what it is to be a crysalis. t Loc. cit. 202 MENTAL EVOLUTION IN ANIMALS. day ; in each case a secondary instinct would become blended with a previously existing primary one, so producing a new instinct with a double root or origin. Conversely, as an example of a primary instinct becoming similarly blended with a previously existing secondary, let us take the following : — The grouse of North America display the curious instinct of burrowing a tunnel just below the surface of the snow. In the end of this tunnel they sleep securely ; for, when any four-footed enemy approaches the mouth of the tunnel, the bird, in order to escape, has only to fly up through the thin covering of snow. Now in this case the grouse probably began to burrow for the sake of protection, or concealment, or both ; and, if so, thus far the burrowing was probably an act of intelligence. But the longer the tunnel the better would it have served the purposes of escape, and therefore natural selection would almost certainly have tended to , preserve the birds which made the longest tunnels, until the utmost benefit that length of tunnel could give had been attained.* Thus then we see that in the formation of instincts there are two great principles in action, which may operate either singly or in combination ; these two principles being the lapsing of intelligence and the agency of natural selection. In the previous chapter we were engaged in considering instincts which are due to either one or other of these prin- ciples alone ; in the present chapter we shall consider instincts w^hich are due to the joint operation of both prin- ciples. Now it is clear at a glance that if even in fully formed instincts we often find, as in the above examples, a " little dose of judgment," it becomes difficult to estimate the im- portance, either of this little dose of judgment becoming habitual by repetition, and so improving the previous instinct, or of its becoming mixed with the influence of natural selec- tion. For, taking the latter case alone, if, as we have seen, intelligent actions may by repetition become automatic (secondary instincts), and if they may then vary and have their variations fixed in beneficial lines by natural selection, how much more scope may be given to natural selection in * Tlie facts of tliis case have been told me by Dr. Eae, F.R.S. BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 203 this further development of an instinct, if the variations of the instinct are not wholly fortuitous, hut arise as intelligent adaptations of ancestral experience to the perceived require- ments of individual experience. Trusting then it is sufficiently clear that the two princi- ples which "may operate either singly or together in forming instincts, may operate together whichever of the two may happen to have, in any parti cidar case, the historical priority, I may in future neglect ta entertain the question of such priority ; without considering whether in tliis and that case selection was prior to lapsing of intelligence, or lapsing of intelligence was prior to selection, it will be enough to prove that the two principles are conjoined. To prove this we have to show, much more copiously than has been done in the above two or three illustrations, not only, as was proved in the previous chapter, that fully formed instincts may vary, but further that their variation may be determined by intelligence. Plasticity of Instinct. In former publications I have used this term to express the modifiability of instinct under the influence of intelligence. I shall now give some chosen instances of such modifiability, and then proceed to indicate the causes which most fre- quently lead to intelligence thus acting upon instinct. It is of importance that I should begin by rendering the fact of the plasticity of instinct beyond question, not only because it is still too much the prevalent notion that instincts are un- alterably fixed, or rigidly opposed to intelligent alteration under changed conditions of life ; but also because it is this principle of plasticity that largely supplies to natural selec- tion those variations of instinct in beneficial lines, which are necessary to the formation of new instincts of a primo- secondary kind. Huber observes : " How ductile is the instinct of bees, and how readily it adapts itself to the place, the circum- stances, and the needs of the community." If this may be said of the animals in which instinct has attained its highest perfection and complexity, even without evidence we might be prepared to expect that instinct is everywhere ductile. Moreover the bees constitute a good 204 MENTAL EVOLUTION IN ANIMALS. class to clioose for our present purpose, because, as I have shown in " Animal Intelligence," their wonderful instinct of making hexagonal cells can only be regarded as an instinct of the primary kind ; yet, as we shall see, though so well fixed an instinct of the primary kind, it may be greatly modified by an intelligent appreciation of novel circum- stances. Kirby and Spence, detailing the observations of Huber, ^vrite as follows : — " A comb, not having been originally well fastened to the top of his glass hive, fell down during the winter amongst the other combs, preserving, however, its parallelism with them. The bees could not fill up the space between its upper edge and the top of the hive, because they never construct combs of old wax, and they had not then an opportunity of procuring new ; at a more favourable season they would not have hesitated to build a new comb upon the old one ; but it being inexpedient at that period to expend their provision of honey in the elaboration of wax, they provided for the stability of the fallen comb by another process. They furnished themselves with wax from the other combs by gnawing away the rims of the cells more elongated than the rest, and then betook themselves in crowds, some upon the edges of the fallen comb, others between its sides and those of the adjoining combs, and there securely fixed it by con- structing several ties of different shapes between it and the glass of the hive ; some were pillars, some buttresses, and others beams artfully disposed and adapted to the localities of the surfaces joined, Nor did they content themselves with repairing the accidents which their masonry had ex- perienced ; they provided against those which might happen, and appeared to profit by the warning given by the fall of one of the combs to consolidate the others and prevent a second accident of the same nature. " These last had not been displaced, and appeared solidly attached by their bavSe : whence Huber w^as not a little sur- prised to see the bees strengthen their principal points of connexion by making them much thicker than before with old wax, and forming numerous ties and braces to unite them more closely to each other and to the walls of their habita- tion. What was still more extraordinary, all this happened in the middle of January, at a period when the bees ordinarily BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 205 cluster at the top of the hive, and do not engage in labours of this kind " Having placed in front of a comb which the bees were constructing a slip of glass, they seemed immediately aware that it would be very difficult to attach it to so slippery a surface, and, instead of continuing the comb in a straight line, they bent it at a right angle, so as to extend beyond the slip of glass, and ultimately fixed it to an adjoining part of the woodwork of the hive which the glass did not cover. This deviation, if the comb had been a mere simple and uniform mass of wax, would have evinced no small ingenuity ; but you will bear in mind that a comb consists on each side or face of cells having between them bottoms in common ; and if you take a comb, and, having softened the wax by heat, endeavour to bend it in any part at a right angle, you will then comprehend the difficulties wliich our little archi- tects had to encounter. The resources of their instinct, however, were adequate to the emergency. They made the cells on the convex side of the bent part of the comb much la.rger, and those on the concave much smcdler than usual ; the former having three or four times the diameter of the latter. But this was not all. As the bottom of the small and large cells were as usual common to both, the cells were not regular prisms, but the smaller ones considerably wider at the bottom than at the top, and conversely in the larger ones ! What conception can we form of so wonderful a flexibility of instinct ? How, as Huber asks, can we com- prehend the mode in which such a crowd of labourers, occupied at the same time on the edge of a comb, could agree to give it the same curvature from one extremity to the other ; or how they could arrange together to construct on one face cells so small, while on the other they imparted to them such enlarged dimensions ? And how can we feel adequate astonishment that they should have the art of making cells of such different sizes correspond ? " * Other observations of Huber show that even under ordi- nary circumstances bees are frequently in the habit of altering the construction of their cells. Thus, for instance, the cells which are destined to receive drones requiring to be considerably larger than those which are destined to receive neuters, and the rows of all the cells being continuous, where * Kii'bj and Spence, loc. cit., pp. 485-495. 206 MENTAL EVOLUTION IN ANIMALS. a transition takes place from one class of cell to the other, a complex geometrical problem arises how to imite hexagonal cells of a small with others of a large diameter, without leaving any void spaces or interfering with the regularity of the comb. Without occupying space with what would necessarily be a rather lengthy exposition of the manner in which the bees solve the problem, it is enough to say that in passing from one form of cell to the other, they require to construct a great many rows of intermediate cells which differ in form, not only from the ordinary cells, but from each other. When the bees arrive at any stage in this process of transition, they might stop at that stage and continue to build the whole of their comb upon this pattern. But they inva- riably proceed from one stage to another until the transition from small hexao'ons to larc^e hexao'ons, or vice versd, is effected. On this subject Kirby and Spence remark : ''' Eeaumer, Bonnet, and other naturalists cite these irregu- larities as so many examples of imperfections. What would have been their astonishment if they had been aware that part of these anomalies had been calculated (? adaptive) ; that there exists as it were a moveable harmony in the mechanism by which the cells are composed ! ... It is far more astonishing that they know how to quit their ordinary routine when circumstances require that they should build male cells : that they should be instructed to vary the dimensions and the shape of each piece so as to return to a regular order ; and that, after having constructed thirty or forty ranges of male cells, they again leave the regular order in which they were formed, and arrive by successive diminu- tions at the point from which they set out .... Here again, as observed in a former instance, the wonder would be less if everj/ comb contained a certain number of transition and of male cells, constantly situated in one and the same part of it ; but this is far from being the case. The event which alone, at whatever period it may happen, seems to determine the bees to construct male cells, is the oviposition of the queen. So long as she continues to lay the eggs of workers, not a male cell is provided ; but as soon as she is about to lay male eggs, the workers seem aware of it, and you then see them form their cells irregularly." Here, then, w^e have concerted variation in the mode of constructing the cells of a normal and definite kind, and we BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 207 find that in this case the variation is determined by an event (the o\dposition of male eggs) which we may suppose all the bees simultaneously to perceive. But in the present connec- tion the important thing to note is that during even the ordinary work of bees occasion frequently arises to modify the construction of their cells, so that the instincts of the animal are not, as it were, rigidly set to the undeviatincr formation of the ordinary cell ; there is a "moving harmony" in the operation of the instinct which secures plasticity in the formation of the comb, so that when occasion arises the " moving harmony " as it were, changes its key ; and it does so in obedience to an intelligent perception of the exigencies of the occasion. The same thing is shown iu a higher degree by some other i experiments of Huber, which consisted in making the bees ' deviate from their normal mode of building their combs from above downwards, to building them from below upwards, and also horizontally. Without describing these experiments in detail, it is enough to say that his contrivances were such that the bees had either to build in these abnormal directions or not to build at all ; and the fact that under such circum- stances they built in directions which none of their ancestors or none of themselves had ever built before, is good evidence of a primary instinct being greatly modified by intelligence — better evidence, be it observed, of modification than that which is furnished by the previously cited cases, inasmuch as bees often require in a state of nature to change the shape of their cells, but cannot ever have required to reverse the direction of building them. The same remarks apply to the following observations, which are also due to Huber. A very irregular piece of comb, when placed on a smooth table, tottered so much that the humble bees could not work on so unsteady a basis. To prevent the tottering, two or three bees held the comb by fixing their front feet on the table, and their hind feet on the comb. This they continued to do, relieving guard, for tiiree days, until they had built supporting pillars of wax. " Kow," as Mr. Darwin observes in his MSS, " such an accident as this could hardly have occurred in nature." Some other humble bees when shut up, and so prevented from getting moss wherewith to cover their nests, tore threads from a piece of cloth, and " carded them with their feet into 208 MEXTAL EVOLUTION IN ANIMALS. a fretted mass," wliich they used as moss. Again, Andrew Knight observed that his bees availed themselves of a kind of cement made of wax and turpentine, with which he had covered decorticated trees — using this material instead of their own propolis, the manufacture of which they discon- tinued ;* and more recently it has been observed that bees, " instead of searching for pollen, will gladly avail themselves of a very different substance, namely, oatmeal." t Again, Osmia aurulenta and 0. hicolor are species of bees which construct tunnels in hard banks of earth or clay, in which they afterwards deposit their eggs — one in each parti- tioned cell. But when they find tunnels ready-made (as in the straws of a thatched roof) they save themselves the trouble of employing their instincts in the way of tunnel- making — merely building transverse partitions in the tube to form a series of separate cells. It is specially remarkable that when they thus utilize the whorl of an empty snail-shell, the number of cells which they partition off is regulated by the size of the shell, or the length of the whorl. Moreover, if the whorl proves too wide near the orifice of the shell for its walls to constitute the boundaries of a single cell, the bee will build a partition at right angles to the plane of the others, so forming a double cell, or two cells side by side.J Now, in all these cases it is evident that if, from any change of environment, such accidental conditions were to occur ordinarily in a state of nature, the bees would be ready * PMl. Trans., loc. cit. f Origin of Species, p. 228. It is interesting in connection witli these facts to note liow singularly well tliey happen to meet a criticism of Kirby and Spence, wliicli was advanced before tbey bad been observed, with the object of discrediting the view of instinct being modified by intelligence. These authors ask {loc. cit., vol. ii, p. 497), why, if such were the case, should not bees sometimes be found to use mud or mortar instead of precious wax or propolis : '' Show us," they say, " but one instance of their having substituted mud for propolis .... and there could be no doixbt of their having been guided by reason." It is curious that this demand should so soon have been met by so apposite an obsei-vation. Doubtless mud is not so good a material for the purposes required as propolis, but as soon as the bees are fm*nished with a substance that is as good, they are ready enough to prove their '" reason," even to the satisfaction of what was supposed, a priori, a crucial test. This case should serve as a warning against the use of the ques- tion-begging argument, which where any degree of evidence is presented of intelligence compounded with instinct, forthwith raises the standard and says — ShoA\- us an animal doing this or that, wliich would be still more remark- able, and then we shall be satisfied. X See F. Smith, Catol. Brit. Kymenoptera, pp. 159-60. BLENDED ORIGIN, OR RLASTICITY OF INSTINCT. 209 to meet them by intelligent adjustment, wliich, if continued sufficiently long and aided by oelection. would pass into true instincts of building combs in new directions, of support- ing combs during their construction, of carding tlireads of cloth, of substituting cement for propolis, or oatmeal for pollen. Were it necessary, other instances of the plasticity of instinct could be drawn from bees and likewise from ants,* but quitting now the Hymenoptera, I shall pass to other animals. Dr. Leech gives,t on the authority of Sir J. Banks, a case of a web-spinning spider wliich had lost five of its legs, and, as a consequence, could only spin very imperfectly. It was observed to adopt the habits of the hunting spider, which does not build a web, but catches its prey by stalking. This change of habit, however, was only temporary, as the spider recovered its legs after moulting. But it seems evident from this case that, so far as the plasticity of instinct is concerned, the web-spinning spider would be ready at any time to adopt the habit of hunting, if for any reason it should not be able to build a web — and this even by way of sudden transition in the life-time of an individual. Coming now to vertebrated animals, we may easily find that the same principles obtain in them. And here, for the sake of brevity, I shall confine myself to instances drawn from the oldest, most constant, and, therefore, presumably the most fixed of the instincts which vertebrated animals display, viz., the maternal. With regard to Birds, I showed in the preceding chapter that individual variations of nest-building are not uncommon. AVe have now to remark that such variations, or deviations from the ancestral modes, are not always the result of mere caprice, but sometimes of intelligent purpose. In order to * See Animal Intelligence, from wliich I may specially quote the follow- ing, in order to show briefly that ants quite as much as, or more than bees, present a " moving harmony " in the construction of their arcliitecture : — " The characteristic trait of the • uilding of ants," says Forel, " is the almost complete absence of an unchanireable moiiel peculiar to each species, such as is found in wasps, bees, and others. The ants know how to suit their indeed little perfect work to circumstances, and to take advantage of each situation. Besides, each works for itself on a given plan, and is only occasionally aided by others when they understand its plan" (p. 129). t Transactiuns Linn. Soc., vol. xi, p. 393. This case is briefly alluded to by Mr. Darwin in the Appendix. 0 210 MENTAL EVOLUTION IN ANIMALS. show this, it will be sufficient to state the following in- stances. Thread and worsted are now habitually used by sundry species of birds in building their nests, instead of wool and horsehair, which in turn were no doubt originally substitutes for vegetable fibres and grasses ; this is specially noticeable in the case of the tailor-bird and Baltimore oriole, and Wilson believes that the latter improves in nest-building by practice — the older birds making the better nests. The com- mon house-sparrow furnishes another instance of intelligent adaptation of nest-building to circumstances ; for in trees it builds a domed nest (presumably, therefore, the ancestral type), but in towns avails itself by preference of sheltered holes in buildings, where it can afford to save time and trouble by constructing a loosely formed nest. A similar case is furnished by the gold-crested warbler, which builds an open cup-shaped nest where foliage is thick, but makes a more elaborate domed nest with a side entrance, where the site chosen is more exposed. Moreover, the chimney and house-swallows have taken to building in chimneys and under the roofs of houses by way of an intelligent or plastic chanoe of instinct, and in America this chancre has taken place within the last three centuries or less. Indeed, accord- ing to Captain Elliott Coues, all the species of swallow on the American continent (with one possible exception) have modified the structure of their nests in accordance with the novel facilities afforded by the settlement of the country ; for he writes : — " Various species, indeed, now regularly accept the arti- ficial nesting-places man provides, whether by design or otlierwise. Such is notably the case with several kinds of Wrens, with at least one kind of Owl, with one Bluebird, the Pewit Flycatcher, and especially the House-sparrow. Various other birds occasionally avail themselves of like privileges, still retaining in the main their original habits. But in no other case than that of the Swallows is the modification of habit so profound, or so nearly without exception throughout the entire family. , . . All of our Swallows have been modified by human agency, excepting tlic Bank Swallow. . . . Some of them, like the Purple Martin and the Violet-green Swallow, are still surviving their apprenticeship under the new regime, which the settlement of the country BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 211 lias brought about. . . . Those whose acquired habits have become thoroughly ingrained are now pretty constant in tlieir adherence to a single plan of architecture; but the Violet-green Swallow, for instance, at present nests in a very loose fashion, according to circumstances." * The statement made in 1870 by the distinguished naturalist Pouchet to the effect that within the same interval of half a century the house-swallow had materially altered its mode of nest-building at Eouen,t was subsequently shown by M. Noulet to be erroneous;; but this passage which I have quoted from Captain Elliott Coues is sufficient to show that facts analogous to those stated' by M. Pouchet have occurred among many species of the swallow tribe. In " Animal Intelligence " I gave some cases of the remarkable intelligence which is displayed by certain birds when they remove their eggs or their young from places where they have been disturbed (pp. 288-9), and I added the remark that it is easy to see that if any particular bird is in- telligent enough, as in the cases quoted, to perform this adjustive action of conveying young — whether to feeding- grounds, as in the case of the hen, or from sources of danger, as in the case of partridges, blackbirds, and goat-suckers — inheritance and natural selection might develop the originally intelligent adjustment into an instinct common to the species. And it so happens that this has actually occurred in at least two species of birds — viz., the woodcock and wild duck, both of which have been repeatedly observed to fly with their young to and from their feeding-ground. Since writing the above, I have found among Mr. Darwin's MSS a letter from Mr. Haust, dated New Zealand, December 9th, 1862, and stating that the « Paradise Duck," which naturally or usually builds its nest along the rivers on the ground, has been observed by him on the east of the island, w^hen disturbed in their nests upon the ground, to build '' new ones on the tops of high trees, afterwards bringing their young ones down on their backs to the water," and exactly the same thing has been observed of the wild ducks of Guiana. § Now, if intelligent adjustment to peculiar circumstances is * Birds of Colorado Valletf, pp. 292-4. + Comptes Rendiis, Ixx, p. 492. X Ihid., Ixxi, p. 7*^. In the first edition of Animal Intelligence I quoted this statement of Pouchet without knowing that it had been questioned. § 6ee Geol. Journ., vol. iv, p. 325. 0 2 212 MENTAL EVOLUTION IN ANIMALS. thus adequate, not only to make a bird transport her young upon her back, or, as in the case of the woodcock, between her legs, but even to make a web-footed water-fowl build her nest on a high tree, I think we can have no doubt that, if the need of such adjustment were of sufficiently long continuance, the intelligence which leads to it would eventu- ally produce a remarkable modification in the ancestral instinct of nest-building. Lastly, " a curious example of a recent change of habits has occurred in Jamaica. Previous to 1854, the palm swift (Tachornis phcenicohea) inhabited exclusively the palm trees in a few districts of the island. A colony then established themselves in tw^o cocoa-nut palms in Spanish Town, and remained there till 1857, when one tree was blown dow^n, and the other stripped of its foliage. Instead of now seeking out other palm trees, the swifts drove out tlie swallows who built in the piazza of the House of Assembly, and took possession of it, building their nests on the tops of the end walls and at the angles formed by the beams and joists, a place which they continue to occupy in considerable numbers. It is re- marked that here they form their nests with much less elaboration than when built in the palms, probably from being less exposed."* Turning now from the instinct of nidification to that of incubation, I shall give the results of some observations and experiments which I made several years ago and published in " Nature," from which I quote the account. In tliese cases the plasticity of the maternal instinct was shown by the fact that the instinct was directed in all its force to the young of other animals, although there is ample evidence to prove that the foster-mothers perceived the unnatural character of their brood. Indeed, it is just because of this evidence that I quote these cases in tlie present connection, for otherwise they might rather be taken to exemplify non-intelligent variations of instinct with wliich w^e were concerned in the last chapter. But inasmuch as the intelligence of the animals was displayed by the manner in which they adapted their ancestral instincts to the requirements of their adopted progeny, the cases become available rather as proof of the intelligent variation of instinct.f * Wallace, Natural Selection, Chapter VI, where see for some of the pre- eeclins: and also for other instances. + The yearning for progeny which arises from the parental instinct being BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 213 " Spanisli hens, as is notorious, scarcely ever sit at all ; but I have one purely bred one just now that sat on dummies for three days, after which time her patience became exhausted. However, she seemed to think that the self-sacrifice she had undergone during those three days merited some reward, for on leaving tlie nest, she turned foster-mother to all the Spanish chickens in the yard. They were sixteen in number, of all ages, from that at which their own mothers had just left them up to full-grown chickens. It is remarkable, too, that although there were Brahma and Hamburg chickens in the yard, the Spanish hen only adopted those of her own breed. It is now four weeks since this adoption took place, but the mother as yet shows no signs of wishing to cast oft' her heterogeneous brood, notwithstanding that some of her adopted chickens have grown nearly as large as herself. " The following, however, is a better example of what may be called plasticity of instinct. Three years ago I gave a pea- fowl's eostcriori proof of the two ways which, either singly or in combination, must be regarded as those by which all properly so-called instincts have been developed. A diagram was given to show graphically how the sundry principles concerned are related and inter-related with one another. Here it was shown that when an instinct, whether of single or blended origin, was perfected, it might vary or ramify into modified forms, and even blend, or, as it were, inarch with other instincts to produce a new growth. It is difficult, or rather impossible, to trace the history of actual instincts in this respect, from the fact that instincts are not fossilized, and therefore leave no record of their transi- tional states. But from all the evidence together — and especially from what we may almost denominate the historical evidence supplied by the facts of domestication — there can be no reasonable doubt that instincts may not only have a double root — one in the principle of selection, and the other in that of lapsing 'intelligence — but also a more or less branching stem, which (or the branches of which) may in some cases become grafted with the stem or branches of other instincts. In estimating the comparative importance of the two great factors in the formation of instinct, we had occasion to differ on the one hand from Mr. Spencer, wlio attributes the origin of all instincts to reflex action with little or no aid from natural selection, and on the other hand with ^Ir. Lewes, who goes to the opposite extreme of regarding all instincts as cases of lapsed intelligence. It was shown, however, that Mr. Spencer's view might be held to explain the rise of doubtfully instinctive actions displayed by very low animals, and that it is of much importance as an explanation of the origin of Consciousness. The view, however, which I adopt to explain the origin of instincts is substantially the same as that which has been propounded by ]\Ir. Darwin, and which, while recognizing both the factors which I have now so repeatedly named — i.e., natural selection and lapsing intelli- gence— whether singly or in combination, attributes most importance to the former, especially if it be remembered that 272 MENTAL EVOLUTION IN ANIxMALS. in its work of organizing instincts, intelligent adjustment is always under the direction and control of natural selection, so that its chief function in the formative process is probably that of supplying to natural selection variations of ancestral instincts which are not merely fortuitous, but intentionally adapted to tlie conditions of the environment. SIMILAR INSTINCTS IN UNALLIED ANIMALS. CHAPTER XVIII. Instinct (continued). Cases of Special Difficulty with Regard to the Fore- going Theory of the Origin and Development of Instincts. We must not take leave of Instinct without looking into all the known cases of it& exhibition which admit of being reasonably cited against the views here expressed on the rise and development of instincts generally. I shall therefore consider sen^iatim all such cases which I have met with in the writings of others, or which occur to me as admitting of being possibly cited in this connection. Similar Instincts in JJnallied Animals. Mr. Darwin observes in the Appendix, " We occasionally meet with the same peculiar instinct in animals widely remote in the scale of nature, and which consequently cannot have derived the peculiarity from community of descent." The difficulty, of course, is to account for the parallelism, andj the instances given by Mr. Darwin are those of the Molothrus having the same instinct of parasitism as the Cuckoo, the Termites having much the same instincts as the Ants, and a neuropterous and a dipterous larva having the same instinct of digging a pitfall for prey. He shows satisfactorily that the last-mentioned is the only case that offers any real diffi- culty ; but even here, it seems to me, the difficulty is not one of any magnitude. For the instinct in question is not one of such complexity, or of such remote probability as to its formation where a larva habitually lives in sand, tliat we may not readily believe a similarity of environment should |i have determined its development mdependently in two lines 1 ' 274 MENTAL EVOLUTION IN ANIMALS. of descent — ;just as for the same reason wings, for example, have been developed independently in at least four lines of descent. Dissimilar Instincts in Allied Animals. Mr. Darwin in the Appendix also alludes to this subject, and the few remarks which he makes upon it seem to me fully to dispose of the difficulty — which, indeed, wdth his characteristic candour, I cannot but think that he unduly magnifies. As I have observed in my chapter on Local and Specific Variations of Instinct, the theory of the formation of instincts by natural selection really leads us to anticipate the not infrequent occurrence of what we may term isolated instincts ; for only if we were to suppose that all considerable variations of instinct (local or otherwise) are permanent, could we anticipate — in the absence of any palaeontology of instinct — a graduated series of instincts in all cases, with the consequent absence of isolated instincts in every case. But to suppose this would be to run counter to the first principles of our theory. Of course if specific instincts were of very general occurren.ce, it might reasonably be objected that this theory would require to suppose too great a slaughter of intermediate species to be accepted as credible; but as matters actually stand I have felt that the occasional appear- ance of isolated instincts in about the proportion of cases that the theory would lead us to anticipate, really constitutes a corroboration of, rather than an objection to, the theory. Trivial and Useless Instincts. Mr. Darwin in tlie Appendix also refers to trivial and useless instincts, and says : — " I have not rarely felt that small and trifling instincts were a greater difficulty on our theory, than those which have so justly excited the wonder of mankind ; for an instinct, if really of no considerable I importance in the struggle for life, could not be modified \ or formed through natural selection." This is no doubt an important point, and must be care- fully considered. First of all it ought to be observed that if any such difiiculty can be shown to stand against the theory of the formation of instinct by natural causes, much more , must the difficulty stand against the older theory of the TRIVIAL AND USELESS INSTINCTS. 275 implanting of instincts by a supernatural cause. Next, we ^ must be perfectly sure, in any given case, that the instinct! which appears to be trivial or useless is really such. This point is mentioned by Mr. Darwin, and he cites some very good cases to show how the important utility, or even abso- lute necessity, of an instinct may readily escape observation. But even after due allowance is made on this score, some few instincts certainly do remain which it seems impossible to suppose of the smallest utility. How, then, are these to be explained ? I believe they admit of being satisfactorily explained by two considerations. The first of these is that our theory does not suppose natural selection to be the only influence at work in the formation of instincts. We have repeatedly insisted that the lapsing of intelligence is another influence of scarcely less importance ; and we have also seen abundant evidence to show that non-adaptive habits occur in indi- viduals and may be inherited in the race. Therefore, if from play, affection, curiosity, or even mere caprice, the intelligence of the animal should lead the animal to perform any useless kind of action habitually (as, for instance, in the case of the ratels tumbling head-over-heels),* and if this habit were to become hereditary in the similarly constituted progeny, we should have a trivial or useless instinct. The only condition, so far as I can see, that would require to be satisfied would be that the trivial or useless habit should not be actually detrimental to the species exhibiting it, so that its growth into an instinct should not be prevented by natural selec- tion. The other consideration to which I have alluded as mitigating or dispelling the difficulty in question is this. In the analoo'ous case of structures, as is well known, we meet with innumerable cases of useless organs ; but here, so far from the fact being deemed a difficulty in the way of the theory of evolution by natural selection, it is justly deemed one of its strongest supports ; and the reason is that in all such cases we have evidence of the useless and perhaps rudimentary organs being of use in other and allied animals. iS'ow I see no reason to doubt that the same may be true of instincts, and therefore that what we now find to be ap- ; j)arently trivial and certainly useless exhibitions of hereditary * See p. 189. S 2 276 MENTAL EVOLUTION IN ANIMALS. habit may, at an earlier period in the history of the species or of its allies, have been of real utility. We may, for example, readily imagine that the instinct displayed by many herbivorous animals of goring sick or wounded companions, is really of use in countries where the presence of weak members in a herd is a source of danger to the herd from the prevalence of wild beasts ; and Mr. Darwin in the Appendix gives evidence that such is actually the case. Or, to take a more fanciful illustration, we may suppose the Megapodidae mentioned in the Appendix, which incubate their eggs by placing them in a large heap of fermenting vegetable matter which they collect for this purpose, were to find, from a change of their habitat or of the Australian climate, that it was difficult to collect a sufficient quantity of vegetable matter, or that it would not ferment sufficiently for the pur- pose of incubation. The birds might then gradually revert to the usual mode of incubation, but might still retain a marked propensity to make tumuli of vegetable matter as nests. If so, the labour expended in making such tumuli would be obviously useless, and there being no analogy among the incubating habits of other birds to give us a clue as to the origin of such an instinct, we should be quite at a loss to account for it. Instincts apparently Detrimental to the Species which exhibit them. It constitutes no difficulty or objection to our general theory of instinct-formation to point to cases in which in- stincts are obviously detrimental to the individuals which manifest them ; for it is of the essence of the theory of natural selection to suppose that the interests of the indi- vidual are, in the process of selection, subordinated to those of the species. It is, for example, manifestly to the detri- ment of an individual fly to procreate its kind, inasmuch as its own death is speedily induced by the act; but seeing that the act is essential to the continuance of the species, we perceive how natural selection must here have developed an instinct which virtually amounts to that of suicide. And the same remark appHes to all similar cases, such as that alluded to in "Animal Intelligence" of soldier ants and termites sacrificing themselves for the benefit of the community — i.e., the species. IXSTIXCTS APPARENTLY DETRIMENTAL TO THE SPECIES. 277 But of course the case is entirely altered where we appear to meet with an instinct the operation of which is detrimental to the individual, without being attended with any com- pensating benefit to the species ; for in such a case the detriment to the individual would also become a detriment to the species. Such apparent cases, in fact, are precisely analogous to those in which certain structures appear to be detrimental to their possessors, without seeming to confer any compensating benefit upon their species;* and, as Mr. Darwin observes, such an apparent case, if it could be shown to be a real one, would be incompatible with the theory of natural selection, inasmuch as '' natural selection acts solely by and for the good of each." further, as Mr. Darwin adds, " if it could be proved that any part of the structure of any one species had been formed for the exclusive good of another, it would annihilate my theory ; " and it is obvious that the same remark would equally apply to the case of instincts. It is therefore of the utmost importance to take a survey of all known instincts, in order to see whether there is any one case, either of an instinct which is detrimental to the species exhibiting it, or of one which has exclusive reference to the benefit of other species. For, on the one hand, if there is any one such case of an indisputable kind, we should clearly have to modify our wdiole theory in order to meet it ; while, on the other hand, if there is no such case, the fact of all the innumerable multitude of animal instincts being of obvious use to the species which manifest them, and never of exclusive use to other species, must be taken as the strongest possible evidence of the theory that ascribes all instincts to the causes which we have assigned. I may as well say at once that there is only one apparent case of an instinct in one species having exclusive reference to the benefit of another, although there are cases of instincts beneficial to the species presenting them being also beneficial to other species. With the latter cases we are not, of course, concerned. The former is the case of aphides yielding up their secretion to ants, and has already been considered by Mr. Darwin. His explanation is that, " as the excretion is extremely viscid, it is no doubt a convenience to the aphides * See Origin of Species, 162-4, wliere the case of tlie rattle of the rattle- snake, &c., is considered. 278 MENTAL EVOLUTIOX IN ANIMALS. to have it removed ; therefore probably they do not excrete solely for the good of the ants."* Coming now to the other branch of the subject, after due reflection I can only think of two or three instincts which could possibly be cited as presenting the appearance of being detrimental to the species which manifest them. I shall therefore consider these cases separately. 1. Suicide of Scorpion. — The state of the evidence on this subject will be found in my other work.f It will there be seen that two or three independent witnesses — including a friend of Dr. Allen Thomson on whose accuracy he says he can rely — bear testimony to the truth of the popular saying that when a scorpion is surrounded by fire, or otherwise exposed to undue heat, it will commit suicide by stinging itself to death. It will be seen, however, by referring to the correspondence in question, that the alleged facts are disputed by other observers, and also, as I have already indicated, that they were not observed by Dr. Thomson himself. The effect of republishing this correspondence and of pointing out the desirability of obtaining further evidence upon the matter, has been to induce two very competent naturalists to make some observations upon the subject. One of these naturalists is Professor Lankester, who published his observations in the "Journal of the Linnean Society " (1882), and the other is Professor Lloyd Morgan, who published his results in " Nature " (vol. xxvii, p. 313). Both these observers agree that the scorpions never commit suicide, and as Mr. Morgan exposed the animals to a variety of dreadful tortures with a uniformly negative result, I think the question may now be considered as closed. Moreover Mr. G. Bidie, who started the previous correspondence in "Nature," has recently addressed another letter to that Journal^ in which he makes the not improbable suggestion that, as in his experiments he applied heat by condensing the rays of the sun with a lens upon a small point of the scorpion's back, the animal in stinging itself " may have merely been trying to get rid of an imaginary enemy." 2. hisects flying through Flame. — The determination shown by many kinds of insects to fly towards and through a flame is unquestionably due to instinct, and as such might be ad- * Origin of SpecieSy p. 208. + Animal Intelligence, pp. 222-5. :j: July 12, 1883. INSTINCTS APPARENTLY DETRIMENTAL TO THE SPECIES. 2 t 9 duced as evidence of an instinct detrimental alike to the individual and to the species. But before this conclusion could be reached, several possibilities require to be attended to. In the first place, flame in Nature is an exceedingly rare phenomenon, so that we could scarcely expect that any instinct should have been developed for the express purpose of its avoidance. Therefore, if the general economy of night- flying insects is such that it is of advantage to approach and examine shining objects, there would be nothing anomalous in their failing to distinguish between flame and other shining objects — such as white flowers or, in the case of moths, pale coloured members of the opposite sex. But as the instinct of flying into flame is of such general occurrence among many species of insects, I think we certainly cannot attribute all the cases of it to a mistaking of flame for some other shining object ; to meet all the cases some still more general explanation is required, and this, I think, is afforded by considering other and analogous cases. Thus many species of birds display an exactly similar propensity, as is proved by the experience of lighthouse keepers ; and, accord- ing to Professor A. Newton, some species of birds are more readily attracted by light than others.* Here there can be no question about a possible mistaking of flame for white flowers, &c., and therefore the habit must be set down to mere curiosit)^ or desire to examine a new and striking object ; and that the same explanation may be given in the case of insects seems not improbable, seeing that it must certainly be resorted to in the case of flsh, which, as I pointed out in '•' Animal Intelligence," are likewise attracted by the light of lanterns, &c. ; and the psychology of a fish is not much, if at all, in advance of that of many insects. Thus, in any case, it seems certain that we have no reason to regard the propensity in question as an expression of any instinct specially formed with reference to flame, and this is really the only point with wliich we are directly concerned. But, as the subject is in itself an interesting one, I shall here add a few remarks with reference to other aspects of it. Among Mr. Darwin's MSS I find the following note, which, however, is not in his hand-writing. " Query. Why do moths and certain gnats fly into candles, and why are they not all on their way to the moon — at least * YarrelVs Brit. Birds, 4th ed., II, 235 280 MENTAL EVOLUTION IN ANIMALS. when the moon is in the horizon ? I formerly observed that they liy very much less at candles on a moon-light niglit. Let a cloud pass over, and they are again attracted to the candle." I do not know to whom this observation is due ; but I quote it for the sake of the query. The answer, I think, must be, that as the moon is a familiar object, the insects regard it as a matter of course, and so have no desire to examine it. I have little doubt that if moonlight were con- centrated to a point in a dark room, the moths and gnats would approach it. In " Nature " (vol. xxv, p. 436), Mr. J. S. Gardener writes : — " Whilst watching the great horse-shoe falls of the Skjal- fandafljot near Sjosavan in Iceland, I saw moth after moth fly deliberately into the falling water and disappear. Some which I noticed arriving from a distance, fluttered at first deviously, but as they neared the water flew straight in. The gleaming falls seemed at least as attractive as artificial light." And doubtless the same explanation applies, inas- much as a gleaming waterfall is not a sufficiently common oliject in Nature, either to fail in arresting the curiosity of the moths, or to ensure that a special instinct should be developed to warn the insects from approaching it. 3. Mr. Da^rwin in the Appendix points out two or three cases of instinct which are apparently at first sight detri- mental to the species exhibiting them. Thus, the crowing of the cock-pheasant on going to roost reveals his presence to the poacher, the cackling of a hen after having laid an egg informs the natives of India where the nest is concealed, certain birds place their nests in very conspicuous situations, and a kind of Shrew-mouse betrays itself by screaming when approached. Now it seems to me that in all these cases — and many similar or analogous ones might be given — the difficulty is, if I may use the term, fictitious ; for it only arises when we shut our eyes to some of the most important prin- ciples which in the previous chapters I have been endeavour- ing to explain. These principles do not imply that an instinct should ever be formed or modified with reference to a j^rospec- tive change of environment, while they do imply that when such a change has taken place, time must be allowed for the compensating modification of the instinct — even suppos- INSTINCTS APPARENTLY DETRIMENTAL TO THE SPECIE?. 281 ing that any such modification is urgently required. Xow it can scarcely be held probable on these principles that the instinct of crowing on the part of the pheasant should have been modified by natural selection during the short time that his ancestors have been naturalized in this country, and in consequence of one in a hundred having thus fallen a victim to poachers. The case of a wild hen cackling over its eggs may seem a stronger one ; but here again the whole question really consists in the actual percentage of eggs thus discovered by the natives, and I should think this must be exceedingly small. Birds building in exposed situations only become an argument against the modificability of instinct by natural selec- tion, when it is shown that the exposure has led to the destruc- tion of nests by man or other animals for a great number of generations ; and this has never been shown. Even in the most remarkable case — that of the Furnarius of La Plata — Mr. Darwin merely says that this bird " in a thickly peopled country, with mischievous boys, ivoulcl soon he exterminated." And similarly it would require to be shown that the habit of the Shrew-mouse at the Mauritius has long led to the destruction of many individuals of each generation by man. In all such cases we must remember how very insignifi- cant the infiuence of man — and especially of savage man — usually is, as compared with the sum of other infiuences, organic and inorganic ; we must remember tlie time which in any case is required for the modification of an instinct ; and we must have proof that the instinct which is now in- jurious in some percentage of cases, has long been highly injurious in a large percentage of cases. I am not aware of any instance where all these conditions have been fulfilled, and where the species has not either been exterminated by man, or the required modification of instinct has not actually taken place. 4. Mr. Darwin in the Appendix also alludes to the in- jurious effects which frequently attend the exercise of the instinct of migration in certain animals. Thus, he says, the congregating of quadrupeds in Africa, and of the Passenger Pigeons in America is detrimental to the animals, in conse- quence of their being thus readily followed by beasts of prey as well as by man. But when we remember the enormous numbers of both kinds of animals wliich thus congTegate, I cannot see that any difficulty remains ; for not only is the 282 MENTAL EVOLUTION IN ANIMALS. percentage of individuals destroyed in itself small, but I doubt whether it is much larger than would be the case if these multitudes of animals were segregated over a very much wider area. A stronger case, I think, is afforded by that of the Norwegian Lemming, and therefore I shall consider it at greater length. Since Mr. Darwin wrote his remarks on this subject which are presented in the Appendix, further statements with reference to it have been published. These, therefore, I shall quote. Mr. Crotch, who has had the opportunity of observing the phenomena for a number of years, thus briefly gives his account of the facts, so far as they concern us. " The Lemmings (which are little rodents) certainly do not visit my part of Norway at any recurring period of years ; but every third or fourth year they may be expected with tolerable regularity, though in variable numbers. Thus it is quite probable that some migrations may have so far escaped notice as to give rise to the old idea that they took place every tenth year. " They are, however, always directed westwards ; and thus the theory that they are caused by deficiency of food fails so far, that these migrations do not take place in a southerly direction by which a larger supply might be ob- tained. M. Guyne {loc. cit.) suggested that the course fol- lowed was merely that of the watershed. However, this runs east as well as w^est, and follows valleys which often run north and south for hundreds of miles, whereas the route pursued by the Lemming is due west. At all events this is the case in Norway, where they traverse the broadest lakes filled with water at an extremely low temperature, and cross alike the most rapid torrents and the deepest valleys. " With no guiding pillar of fire, they pass on through a wilderness by night ; they rear their families on their journey, and the three or four generations of a brief subarctic summer serve to swell the pilgrim caravan. They winter beneath more than six feet of snow during seven or eight weary months ; and with the first days of summer (for in those regions there is no spring) the migration is renewed. At length the harassed crowd, thinned by the increasing attacks of the wolf, the fox, and even the reindeer, pursued by eagle, hawk and owl, and never spared by man himself, yet INSTINCTS APPARENTLY DETRIMENTAL TO THE SPECIES. 283 still a vast multitude, plunges into the Atlantic Ocean on the first calm day and perishes with its front still pointing westward. No faint heart lingers on the way, and no sur- vivor returns to the mountains. Mr. R. Collett, a Norwegian naturalist, writes that in November, 1868 (quoted by Fille- burg, infra) y a ship sailed for fifteen hours through a swarm of Lemmings, which extended as far over the Trondhjemsfiord as the eye could reach."* Such, according to i\Ir. Crotch, are the facts, and the follow- ing are the hypotheses which have been propounded to ex- plain them. Mr. Wallace suggests! that natural selection has played an important part in causing migration, by giving an advantage to those animals which enlarge their breeding area by travel. To this view, as applied to the lemming, Mr. Crotch objects that the animal, " it is true, always breeds during migration ; but if none return or survive, it is difficult to say what becomes of the fittest." His own theory is a remarkable one. " There is," he says, " a solution of this difficulty, involving a subject of the deepest interest, and which led me to spend two years in the Canaries and adjacent islands. I allude to the island or continent of Atlantis. , . It is evident that land did exist in the North Atlantic Ocean at no very distant date. . . . Is it not then conceivable, and even probable, that when a great part of Europe was submerged and dry land connected Norway with Greenland, the lemmings acquired the habit of migrating westward for the same reasons which govern more familiar migrations ? . . . It appears to me quite as likely that the impetus of migration towards this continent should be retained as that a dog should turn round before lying down on a rug, merely because his ancestors found it necessary thus to hoUow out a couch in the long grass." In a later paperj he combats by the aid of charts the popular theory " that these migrations follow the natural declivities of the country," and then proceeds to add, " It is very remarkable that the average depth from Norway to Ice- land does not exceed 250 fathoms, with the exception of a deep and narrow channel of 682 fathoms at 14° W. This probably represented the old Gulf Stream ; and if this were so, the lemmings did wisely to migrate westwards in search * Linn. Soc. Jour., toL xiii, p. 30, et seq. f I^ature, voL x, p. 459. X Lmn. Soc. Jour., voL xiii, p. 157, et ,seq. 284 MENTAL EVOLUTION IN ANIMALS. of its genial influence. As little by little the ocean encroached on the land, the same advantages would remain, as in fact they do to this day." To this ingenious theory dissent is expressed by another gentleman who ]ias had a very large experience in observing these migrations, namely Mr. Eobert CoUett, of the University Museum, Christiania.* His view is that in years when re- production is excessive, multitudes of individuals are led by hunger, as well as by " the natural desire to wander possessed by this species," to overflow the limits of their plateaux home, and spread out " over an area that is considerably larger than obtains in any other of the species under similar circumstances." As breeding continues throughout the wandering, in cases where in two or three succeeding years the production of young has been excessive, " the masses are incessantly pushed towards the sides of the fells ; and the migration becomes an overrunning of the lower and far remote portions of the country, as the individuals gradually penetrate further in search of localities suitable to their habits (and which are capable of giving them a permanent subsistence), until they are stopped by the sea or destroyed in some other manner." Looking to Mr. Collett's large experience on the subject, as well as to tlie intrinsically probable nature of his views, 1 think we may most safely lend countenance to the latter. The most important point of difference between Mr. Crotch and Mr. CoUett has reference to a question of fact. For while Mr. Crotch states that the migrations are made west- wards without reference to the declivities of the country, Mr. CoUett is emphatic in saying that " the wanderings take place in the direction of the valleys, and therefore can branch out from the plateaux in any direction." If this is so, there is an end of Mr. Crotch's theory, and the only difficulty left to explain would be why, when the lemmings reach the sea, they still continue on their onward course to perish in their multitudes by drowning. The answer to this, however, is not far to seek. For their ordinary habits are such that when in their wanderings they come upon a stream or lake, they swim across it ; and therefore when they come upon the coast line it is not surprising that they should behave in a similar manner, and, mistaking the sea for a large lake, swim per- * Linn. Soc. Jour., voL xiii, p. 327, et seq. MIGRATIOX. 285 sistently away from land with the view to reacliing tlie opposite shore, till they succumb to fatigue and the waves. Therefore, pending further observations on the question of fact above alluded to, I cannot feel that the migration of the lemming furnishes any difficulty to the theory of evolution over and above that which is furnished by the larger and more important case of migration in general, to the considera- tion of wliich I shall now proceed. Migration. Taking the animal kingdom from below upwards, the first animals that can properly be said to present the instincts of migration are to be found in the group Articulata. I think it is sufficient to refer to " Animal Intelligence " for the facts concerning the migrations of Crabs (pp. 231-2)* and Cater- pillars (238-40), though as regards the latter I may add tlie following remarkable account, which I quote from the " Colonies and India." " To say that a train had been stopped by caterpillars would sound like a Yankee yarn, yet such a thing (according to the " Eangitikei Advocate ") actually took place on the, local railway a few days ago. In the neighbourhood of Tura- kina, New Zealand, an army of caterpillars, hundreds of thousands strong, was marching across the line, bound for a new field of oats, when the train came along. Thousands of the creeping vermin were crushed by the wheels of the engine, and suddenly the train came to a dead stop. On examination it was found that the wheels of the engine had become so greasy that they kept on revolving without ad- vancing— they could not grip the rails. The guard and the engine-driver procured sand and strewed it on the rails, and the train made a fresh start, but it was found that during the stoppage caterpillars in thousands had crawled all over the engine, and over all the carriages inside and out." With regard to Butterflies many instances of large migra- tions are on record. Thus, Madame de Meuron Wolft' describes an immense swarm of the Painted Lady butterfly passing over Grandson, Canton de Vaud, flying closely together from south to north. The column, which was from ten to fifteen feet broad, flew low and equally, and took two hours to pass. * See also Professor Moselej, A Naturalist on the Challenger, p. 5G1. 286 MENTAL EVOLUTION IN ANIMALS. The caterpillar of this species is not gregarious. Professor Bonelli also describes a migration similar in all respects, including locality, except that it lasted longer — the insects covering the flowers at night and proceeding on the journey by day. Immense. swarms of migratory Dragon-flies have been at times observed, the most remarkable case being one that occurred in May, 1839, and which seems to have extended over a great part of Europe. The insects flew at a height of 100 to 150 feet, and seemed to follow the direction of the rivers.* ]\Iany species of Fish are known to migrate regularly for purposes of spawning, such as the herring, salmon, &c., and also to And water ; t while among Eeptiles the most remark- able instance seems to be that which is furnished by the Turtles which visit Ascension Island to deposit their eggs. How the animals can find this comparatively small speck of land in the midst of a vast ocean is very unaccountable. I have recently written to Professor Moseley upon the subject, and in reply he says, " No man without proper modern means of finding latitude and longitude could reach either Tristan or Ascension; and it is especially difficult for animals whose eyes cannot be raised above the sea-level, and to whom, therefore, the islands are visible for a comparatively small radius only. Merchant skippers have several times been unable to find Bermuda, and on return baffled have reported the island gone down." But, as Professor Moseley adds, '' It is just possible that the animals do not retire far from the land after all, but hang about unobserved," I think it is undesirable to enter into any discussion where the facts are still of an uncertain character. Among Mammals, from whales to mice, we meet with many migratory species, but it is among Birds that the propensity is most prevalent. Indeed, a very competent authority on all matters pertaining to ornithology has said in the new " Encyclopaedia Britannica : " " Every bird of the northern hemisphere is to a greater or less degree migratory in some part of its range. Such a conclusion brings us to a still more general inference — viz., that Migration, instead of * For a full account see Weissenborne, Loundoun's Mag. Nat. Hist., N.S., vol. iii. t See Animal Intelligence, 248-50. MIGRATION. 287 being the exceptional characteristic it used formerly to be thought, may really be almost universal."* I have neither the occasion nor the space to discuss the large question of migration in general ; and having now indicated the animals in which the instinct is most pro- nounced, I shall pass on to consider the theory of its forma- tion. First I may allude to Mr. Darwin's remarks on Migration at the beginning of the Appendix. It will be seen from them that among others he establishes the follow- ing points : — 1. There is " in different breeds of birds a perfect series from those which occasionally or regularly shift their quarters ^vithin the same country, to those which periodically pass to far distant countries." 2. " The same species often migrates in one country and is stationary in another ; or different individuals of the same species in the same country are migratory or stationary." 3. " The migratory instinct is laade up of two very distinct factors — viz., an impulse to travel periodically, and a faculty of knowing the direction in which to travel." 4. " Savage man shows a sense of direction which may be analogous to that shown by migratory animals." 5. " Certain cases are on record of breeds of domesticated animals having truly migratory instincts." Such being the data, the problem is to account for the ' origin of the instinct. Mr. Darwin's theory is that the ancestors of migratory animals were annually driven, by cold or want of food, slowly to travel southwards ; " and in time ■ ^ we may well believe that this compulsory travelling would become an instinctive passion," as is the case with domesti- cated sheep in Spain. In the case of birds, the wings would be used, and if in the course of many successive generations the land over which they flew in their annual journeys were to become slowly submerged, the line of flight would remain unaltered, and thus we should have the state of things which we now perceive — viz., migratory birds flying over wide stretches of ocean. Before I proceed to consider this theory, I should like to ( call prominent attention to the fact that it has been inde- * Professor NeAvton, F.R.S., Art. Birds, where see for a good rh ume oi tlie main facts of migration as regards bii'ds. 288 MENTAL ETOLUTIOX IX ANIMALS. pendently arrived at by Mr. Wallace. It is only now tbat Mr. Darwin's Adews upon this subject are published, although they were committed to writing as they appear in the Appendix between twenty and thirty years ago. Mr. Wallace however enunciated substantially the same views in a letter to "Nature" in 1874 (Oct. 8),* from which I shall quote in - c^enso, not only for the purpose of showing the coincidence to which I have alluded, but also because I think that the additional element which Mr. Wallace mentions — i.e., the separation of breeding and subsistence areas — is a most im- portant one. " Let us suppose that in any species of migratory bird, breeding can as a rule be only safely accomplished in a given area ; and further, that during a great part of the rest of the year sufficient food cannot be obtained in that area. It will follow that these birds which do not leave the breeding area at the proper season wiU suffer, and ultimately become extinct ; which will also be the fate of those which do not leave the feeding area at the proper time. Now if we sup- pose that the two areas were (for some remote ancestor of the existing species) coincident, but by geological and climatic changes gradually diverged from each other, we can easily understand how the habit of incipient and partial migration at the proper season would at last become hereditary, and so fixed as to be what we term an instinct. It will probably be found that every gradation still exists in various parts of the world, from a complete coincidence to a complete separa- tion of the breeding and subsistence areas ; and when the natural history of a sufficient number of species in all parts of the world is thoroughly worked out, we may find every link between species which never leave a restricted area in which they breed and live the whole year round, to those other cases in which the two areas are absolutely separated. The actual causes that determine the exact time, year by year, at which certain species migrate, will of course be diffi- cult to ascertain. I would suggest, however, that they will be found to depend on those climatic changes which most affect the particular species. The change of colour, or the fall of certain leaves; the change to the pupa state of certain insects ; p^^evalent winds or rains ; or even the * Captain Hutton also foreshadowed these Tiews in 1872 ; see Trans. New Zealand Inst., p. 235. MIGRATION. 289 decreased temperature of the earth and water, may all have their influence." It will be observed that this theory, besides being intrin- sically probable, derives a good deal of support from the enquiries made by Mr. Darwin, which have shown that there is a general relationship between oceanic islands which there is independent reason to conclude have never been joined to the mainland, and an absence of migratory birds.* It will also be observed this theory makes two important assumptions — first, that the birds have a very accurate sense of direction, and second, that a no less accurate knowledge of the particular direction to be pursued is inherited ; for it is certain that the young Cuckoo (which leaves England after its parents) cannot be guided on its first journey by any other means, and it is asserted that the same is true of theyoimg of many other species.t Taking then these assumptions separately, the first is no more than a statement of fact, un- accountable though the fact may be. That is to say, a verv accurate sense of direction migratory birds unquestionably possess, and it is probably the same in kind as the so-called " homing " faculty which is shown by many domesticated animals, and also, as Mr. Darwin points out, by savage man. I could fill pages with letters which I have received from all parts of the world describing more or less remarkable cases of the display of this faculty by dogs, cats, horses^J * To be quite fair, however. I must here allude to the only fact I have met with which seems to me opposed to this theorr. Mr. Uurdis in his work entitled The XaturaU-st in Bermuda, obserres that the miffratorv golden plover (CA<7ra. J I have one instance of a cat returning in four days firom London to 290 MENTAL EVOLUTION IN ANIMALS. asses, cows, sheep, goats, and pigs ; but as so many similar cases are already on record, I feel it is needless to add to the number. The remarkable fact is that the animals are able to find their way back over immense distances, even though the outgoing journey has been made at night, or in a closed box ; so that it is truly upon some sense of direction, and not merely upon a memory of landmarks, that they must rely. Moreover, it is certain that in many cases, if not as a o-eneral rule, the animals on their return journey do not traverse the exact route which they had taken in the out- o-oing journey, but take the " bee-line";* so that, for instance, if the out-going journey has been made over two sides of a triangle, the return journey will most probably be made over the third side. One instan^^e, the account of which I have received from a correspondent in Australia, is of suffi- cient interest in this connection to quote. " A pair of horses were sent many hundred miles round the Australian coast by ship ; as they did not like their new quarters, they started back by land ; but after returning 230 miles they were pulled up by a peninsula on the coast, where they were eventually recovered. They did not attempt to retrace their steps to clear this difficulty ."f Huddersfield, a distance of two hundred miles. A still more remarkable case, however, was published by Mr. J. B. Andrews in Nature several years ago (vol. viii, p. 6). The Archduchess Marie Regnier passed the winter of 1871-2 at the Hotel Victoria, in Mentone, and while there took a fancy to a spaniel belonging to the landlord, M. Milandri. In the spring of 1872 she brought the dog with her by rail to Vienna. Not long afterwards it reappeared at the hotel in Mentone, having thus run a distance of nearly a thousand miles. On arriving it died of fatigue and was buried m the hotel gardens, where a monument now commemorates the performance. Mr. A. W. Howitt writing to Nature from Victoria at about the same time (vol. viii, p. 322) gives a number of cases of horses and cattle finding their way home over greater or less distances, and I specially allude to his communication because he says that in some of the cases the return journey was made after a considerable lapse of time — months and even years. * This is an American term which I employ because in itself showing the observed regularity of the fact as regards bees — it being the custom to find wild hives of honey by catching several bees, and letting them go again from different places. The insects under these circumstances make straight for their hive, so that by observing the point where several " bee-lines " intersect, the honey seekers are able to find tbe hive. t I may here also quote an observation by Mr. Dar■^^dn to the same effect : — ** I sent a riding-horse by railway from Kent via Yarmouth, to Freshwater Bay, in the Isle of Wight. On the first day that I rode eastward, my horse, when I turned to go home, was very unwilling to return towards his stable, and he several times turned round. This led me to make repeated trials, and every MIGRATION. 291 Now it is evident that this fact alone — i.e., of animals not requiring to return by the same route — is sufficient to dis- pose of the hypothesis advanced by Mr. Wallace* to the effect that the return journey is due to a memory of the odours perceived during the out-going journey, these odours thus serving as land- marks. Therefore it seems to me there are only two hypotheses open to us whereby to meet the facts. First, it has been thought possible that animals may be ^ endowed with a special sense enabling them to perceive the magnetic currents of the earth, and so to guide themselves as by a compass. There is no inherent impossibility attaching to this hypothesis, but as it is wholly destitute of evidence, we may disregard it. The only other hypothesis is that Jfj- animals are able to keep an unconscious register of the turns and curves taken in the outgoing journey, and so to retain a general impression of their bearings. This hypothesis is substantiated by the fact that, as Mr. Darwin observes, savage man is certainly endowed with some such faculty ; and a friend of my own (Mr. Henry Forde quoted below), who has spent many years in the forests and prairies of America, informs me that even civilized man when long accustomed to such primitive habits of life, acquires this faculty in a degree of perfection quite comparable with that of savages. He also informs me that, occasionally, without any assignable reason, the sense of direction becomes confused, leading to a distressed sensation of bewilderment. He has seen a hunter thus reduced to a lamentable condition of nervousness, and when at last he abandoned himself to the leadership of his companions (who relied entirely on their own sense of direction), he felt persuaded tliat they were going the wrong way. But on approaching his dwelling- place he recognized one of the trees, and declared that a particular notch upon it had passed round to the other side of the trunk. Eventually he said that the whole world time that I slackened tlie reins, he turned sharply round and began to trot to the eastward by a little north, which was nearly in the direction of his home in Kent. I had ridden this horse daily for several years, and he had never before behaved in this manner. My impression was that he somehow knew the direction whence he had been brought. I should state that the last stage from Yarmouth to Freshwater is almost due south, and along this road he had been ridden by my groom ; but he never once showed any wish to return in this direction " {Nature, vol. vii, p. 360). See also Nature, viii, p. 322. * Nature, loc. cit. T 2 292 MENTAL EVOLUTION IN ANIMALS. seemed to have turned round him as a centre. In this con- nection I may quote the following passage from a letter published some years ago by Mr. Darwin in " Nature " (vol. vii) : — " The manner in which the sense of direction is sometimes suddenly disarranged in very old and feeble persons, and the feeling of strong distress which, as I know, has been experi- enced by persons when they have suddenly found out that they have been proceeding in a wholly unexpected and wrong direction, leads to the suspicion that some part of the brain is specialized for the function of direction. Whether animals may not possess the faculty of keeping a dead-reckoning of their course in a much more perfect degree than man ; or whether this faculty may not come into play on the com- mencement of a journey, when an animal is shut up in a basket, I will not attempt to discuss, as I have not sufficient data." He also alludes to the case of Audubon's pinioned wild goose, which showed a very determined impulse to migrate at the proper season, but mistook the direction and went due north instead of south. Lastly, I may quote the following from Dr. Bastian's work on the Brain.* " On this subject, G. C. Merrill, writing from Kansas, says : — * I have learned from the hunters and guides who spend their lives on the plains and mountains w^est of us, that no matter how far, or with what turns, they may have been led, in chasing the bison or other game, they, on their return to camp, always take a straight line. In explanation, they say that, unconsciously to themselves, they have kept all the turns in their mind.' " Referring to his travels in the State of Western Virginia, Mr. Henry Forde ('Nature,' April 17, 1873, p. 463) writes as follows : — ' It is said that even the most experienced hun- ters of the forest-covered mountains in that unsettled region are liable to a kind of seizure — that they 'lose their heads* all at once, and become convinced that they are going in quite the contrary direction to what they had intended, and that no reasoning nor pointing out of land-marks by their companions, nor observations of the position of the sun, can * Brain a-f an Organ of Mind, p. 215, wliere see also for cases of way- finding in animals. MIGRATION. 293 overcome their feeling ; it is accompanied by great nervous- ness and a general sense of dismay and ' upset.' The nervous- ness comes after the seizure, and is not the cause of it. Tliis is spoken of by the natives as ' getting turned round.' The feeling sometimes ceases suddenly, or it may wear away gradually. Colonel Lodge, in his ' Hunting Grounds of the Far West,' 1876, speaks of the same kind of feelings seizing upon, and occasionally demoralizing, old and experienced prairie travellers. Indian chiefs all concurred in assuring Gr. Catlin (' Life amongst the Indians,' p. 90) that 'whenever a man is lost on the prairies, he travels in a circle, and also that he invariably turns to the left ; of which singular fact,' the author adds, ' I have become doubly convinced by subse- quent proofs.' " But it is evident that definite experiments on this homing I faculty, both in men and in animals, are required before we \ can be in a position to say anything more with regard to it | than admitting it as a matter of fact. The only experiments which have been made, so far as I am aw^are, are those of Sir John Lubbock, on the sense of direction in the Hymenoptera Cto which I shall allude presently), and those which have more recently been published by M. Faljre,* who also ex- perimented upon the Hymenoptera. As the last-named author believes that he has established a very definite conclu- sion by means of his experiments, it is necessary that I should make a few remarks upon them. At the suggestion of Mr. Darwin, he placed some marked mason-bees in a closed paper box, carried them thus im- prisoned for some distance in one direction, then rotated the box and carried them a much greater distance in the opposite i direction, after wdiich he released the insects. He found , / that when the distance to which the bees were taken was as / much as three kilometres, and even when the rotation was ) very considerable (the box being placed in a sling and rotated in various planes at several points in the route) a certain percentage of the bees returned home. It made no difference whether the bees w^ere released in an open space or in a thick wood ; neither did it make any difference whether the outgoing journey were performed in a straight line or in a circuitous curve. From these experiments ]\I. Fabre con- * Noiiveatix Sotivenirs Entomologiqucs, 18S2, pp. 99-123. 294 MENTAL EVOLUTION IN ANIMALS. j eludes that the sense of direction cannot depend upon any I process of dead-reckoning. At the suggestion of Mr. Darwin he also tried the effect of attaching a magnetized needle to the thorax of a bee ; but the bee having succeeded in getting rid of the encumbrance, he did not repeat the experiment. , Now, although the observations with the rotating box are no doubt very interesting, they do not appear to me to sustain the definite conclusion that the sense of direction is not due to a process of dead-reckoning. It is of course impossible to suppose that the bees could retain a register of all the turns to which they were submitted in the sling, and, there- fore, if it were certain that they found their way home by means of their sense of direction, I should agree with M. Fabre in concluding, once for all, against the theory of dead-reckoning. But there is no evidence to show that the bees which found their way home did so by means of their sense of direction. It is quite possible that they found their way home simply from their knowledge of land-marks ; for the distance to wdiich they were taken w^as only three kilo- metres, and it is known that the hive-bee will go three times that distance in its ordinary foraging excursions.* Moreover, the fact that only a comparatively small number of the bees succeeded in returning (about 22 per cent.), is suggestive of the explanation that these w^ere the only ones which, during the random flight of the whole number in sundry directions, happened to encounter land-marks with which they were familiar. I am therefore inclined to feel that any sense of direction which existed in these insects may very well have been rendered useless by these experiments, and yet that the results of the experiments might have been exactly those which M. Fabre describes. Eeturning, however, to the case of migration, I think it is not very improbable that the sense of direction may be greatly assisted by observing the direction of the sun with reference to the appropriate line of flight. It is true that many migra- tory birds fly at night ; but in this case, even if the moon is not available to steer by instead of the sun, during much of the night the directions of sun-set and sun-rise are clearly indicated by the light of the sky ; and it appears that on very dark and cloudy nights migratory birds are apt to become * See Animal Intelligence, p. 150. MIGRATION. 295 confused.* The possibility thus suggested receives, I think, some countenance from the following fact. In "Animal lutelligence " I recorded a number of observations which had been made by Sir John Lubbock on the sense of direction as exhibited by ants. These experiments yielded results of a most definite nature, and thus led Sir John to conclude that ants are endowed with the sense of direction in a singular degree. Subsequently, however, he has found (accidentally in the first instance) that in all these experiments the ants found their way by observing the direction in which the light was falling; so that, as long as the source of light was stationary, no matter how many times he turns them round upon a rotating table, when the rotation ceased they knew their road to and from the hive as well as they did before the rotation; whereas, if the source of light were shifted, the insects at once became confused as to their bearings, even though not rotated at all.t Now if ants thus habitually guide themselves by observing the direction in which the light is falling (i.e., the position of the sun), I do not see why migratory birds should not be assisted by similar means. This, however, I only put forward as a conjecture. The fact that migratory birds, like many other animals, are in some way able to hold a true course in order to reach a par- ticular locality, is a fact which confessedly we are not able to explain. But — and this is the most important point for us — our inability to explain this fact in the present state of our information, is no objection to the theory of instinct on which we are engaged. We cannot doubt that the fact admits of some explanation, and when we certainly know, what this explanation is, we shall first be able to ascertain -whether the faculty of way-finding is or is not compatible with the foregoing theory of the evolution of instinct. Let ns turn now to the second of the two assumptions above alluded to as necessary in order to embrace the facts of migration under the theory — viz., the assumption that some at least among migratory birds must possess, by inheritance alone, a very precise knowledge of the particular dii'ection to * See Professor Newton in Nature, vol. xi, p. 6, who says, " Dark cloiidy nights seem to disconcert the travellers. On such nights the attention of others besides myself has often been directed to the cries of a mixed multitude of birds hovering over this (Cambridge) and other towns, apparently at a loss whither to proceed, and attracted by the light of the street lamps." t See Jonrn. Linn. Soc, 1883. 296 MENTAL EVOLUTION IN ANIMALS. be pursued. It is, without question, an astonishing fact that a young cuckoo should be prompted to leave its foster-parents at a particular season of the year, and without any guide to show the course previously taken by its own parents ; but , this is a fact which must be met by any theory of instinct [l which aims at being complete. Now upon our own theory it can only be met by taking it to be due to inherited memory. I confess to me it seems incredible that many hundred miles of landscape scenery should constitute an object of inherited memory,* to say nothing of long stretches of ocean ; but the case is not quite so hopeless as to require so extreme a hypothesis. When we say that upon our theory the young cuckoo must be supposed to find its way on its first journey by inherited memory, we need not necessarily affirm that this is the memory of a landscape. As I have said in the pre- vious paragraphs, we do not yet know what it is that guides the course of migratory birds in general ; but whatever this may be, it can scarcely be the appearance of the country over which they pass, seeing not only that the distances are so great and that two hundred or three hundred miles of ocean may separate one piece of country over which they travel from another, but also that the journeys may be taken by night. Of what, then, is the inherited memory on which the young cuckoo (if not also other migratory birds) depends ? j We can only answer. Of the same (whatever this may be) as ' that upon which the old birds depend. When we certainly know what this is, we shall first be able to ascertain whether it is incompatible with the theory of evolution to suppose that it can be an object of hereditary memory. Thus, for the sake of example, let us suppose that the old birds in their outgoing journey guide their way by flying towards the south wind (as has been suggested to me by Mr. William Black, who believes that swallows always start against the south wind); heredity would in this case have an easy task in associating the warm moist breath of this wind with a desire to fly against it. Of course I only adduce this suggestion in order to show how simple the mere question of heredity might become, if once we knew the means whereby migratory birds in general find their way. The only difference between the faculty of homing and the instinct of migration, so far as * This theory was first advanced bj Canon Kingsley {Nature, Jan. 18, 18G7), and has since been independently suggested by several writers. INSTINCTS OF NEUTER INSECTS. 297 the matter of way-finding is concerned, seems to me to be this — that in the case of the young cuckoo, and perliaps also in that of certain other migrator}' birds, tlie animals know their way histinctively, or without even one lesson. P>ut if we could ascertain upon what it is that the faculty of homing depends (which, be it observed, is not an instinct, seeing that its occurrence is the exception and not the rule, even in the species which exhibit it), we might very probably get a clue to explain the manner in which heredity has been able to work up this faculty into the instinct of migi-ation. No doubt this discussion is most unsatisfactory, and the reason is that we are so much in the dark about the facts. All, therefore, that I have attempted to do is to show that, in the present state of our information, the migratory instinct cannot fairly be quoted as a difficulty in the way of our theory of the formation of instincts in general. And, in order to give emphasis to this statement, I may allude to the general facts already mentioned — viz., that the migratory instinct is both variable and graduated, that it is occasionally exhibited by domesticated animals, and that the sense of direction on which it depends is a very general one among animals, if not also in savage man ; for all these facts tend to show that whatever the causation of the migratory instinct may be, it has probably been proceeding upon the lines of evolution in general. Instincts of Neuter Insects. Mr. Darwin has pointed out a serious difficulty lying ! against his theory of the origin of instincts by natural selection, j and one which, as he justly remarks, it is surprising that no ^ one should have previously advanced against the well-known doctrine of inherited habit, as taught by Lamarck. The difficulty is that among various species of social insects, such as bees and ants, there occur " neuter," or asexual individuals, which manifest entirely different instincts from the other or sexual individuals, and, as the neuters cannot breed, it is difficult to understand how their peculiar and distinctive instincts can be formed by natural selection, which, as we have seen, requires for its operation the transmission of mental faculties by heredity. The difficulty is increased by the fact that among the termites and many species of ants 298 MENTAL EVOLUTION IN ANIMALS. several varieties or " castes " of neuters occur in the same nest, which differ widely from one another both in structure and in instincts. The only possible way in which this difficulty can be met is the way in which it has been met by Mr. Darwin, viz., by supposing "that selection may be applied to the family as to the individual." " Such faith may be placed in the power of selection that a breed of cattle always yielding oxen with extraordinarily long horns could, it is probable, be formed by carefully watching which individual bulls and cows, when matched, produced oxen with the longest horns ; and yet no one ox would ever have propagated its kind ;" and similarly, of course, with regard to the instincts of neuters. Otherwise stated, we may regard the nest or hive as itself an organism of which the sexual insects and the several castes of neuters constitute the organs ; and we may then suppose natural relation to operate upon this organism as a whole, somewhat in the same way as we habitually suppose it to operate upon the " social organisms " or com- munities of mankind. Xo doubt, when carefully considered, the analogy between a hive and an organism, or even between a hive and a social community, is not a close analogy so far as the modus operandi of natural selection is concerned ; for in the one case the analogue of organs is a variety of separate individuals, while in the other case there is no such great contrast between different classes of a human community as that which obtains amonoj the different castes of an insect community. The root of the question really consists in whether or not it is possible to suppose that natural selection may operate upon specific types as distinguished from indivi- dual members of species. During his life-time I had the advantage of discussing this question with Mr. Darwin, and I ascertained from him that it had greatly occupied his thoughts while writing the " Origin of Species ;" but that, finding it to be a question of so much intricacy, he deemed it unadvisable to enter upon its exposition. It would occupy too much space were I to attempt such an exposition here, and I have alluded to the subject only because I desire to show that it is really this general question which is involved iu the case of the special difficulty with which we are now concerned. On some future occasion I intend to argue this general question, and then I shall hope to mitigate the force of this special difficulty. I may, however, point to one fact INSTINCTS OF THE SPllEX. 299 which Mr. Darwin has observed, and which is of much importance as indicating that the ditlerent castes of neuters have arisen by degrees, and therefore presumably under the influence of natural selection. This fact is that, when care- fully searched for, neuters presenting more or less well- marked gradations of structure between one caste and another may be occasionally found in the same nest.* On the whole, therefore, I conclude, with regard to this particular case of difficulty, that it is not so formidable as to exclude the explanation furnished by the hypothesis of natural selection, supposing that we have already accepted this hypothesis as explanatory of other and less difficult cases. Instincts of the Sphex. Several species of this division of the Hymenoptera dis- play what I think may be justly deemed the most remarkable instincts in the w^orld. These consist in stinging spiders, insects, and caterpillars in their chief nerve-centres, in con- sequence of which the victims are not killed outright, but rendered motionless ; they are then conveyed to a burrow previously formed by the Sphex, aud, continuing to live in their paralyzed condition for several ^veeks, are at last avail- able as food for the larvae w^hen these are hatched. Of course the extraordinary fact which stands to be explained is that of the precise anatomical, not to say also physiological know- ledge wdiich appears to be displayed by the insect in stinging only the nerve-centres of its prey. The following, so far as is at present known, are the main features of this very sur- prising case. The same species of Sphex always preys upon the same species of victim. When the victim is a spider, the instinct of its assailant dictates that a single sting shall be given in the large ganglion wdiere, in the case of the spider, most of the central nervous matter is aggregated. When the victim is a beetle, the Sphex wdiich preys upon it — there are eight species which prey upon two genera — tirst throws the insect upon its back, then embraces it and plunges the sting through the membranes between the first and the second pairs of legs ; the sting thus strikes the main nerve-centre, which is unusually agglomerated in beetles of this genus. When the prey is a * See Oricfin of Species, 231-2. 300 MENTAL EVOLUTION OF ANIMALS. cricket, the insect is thrown, as in the previous case, "upon its back, and while holding it down with her mandibles firmly fastened upon the last segment of its abdomen, her feet on the sides liolding down the body of the cricket — the anterior feet holding down the long posterior legs of the prey, and the hind feet holding back the mandibles, so as to prevent these from biting, and at the same time making tense the mem- branous junction of the head with the body — the Sphex darts her sting successively into three nerve-centres ; first into the one below the neck which she has stretched back for the pur- pose, next into the one behind the prothorax, and lastly into the one lower down. A cricket thus paralyzed will live for six weeks or more. When the prey is a caterpillar, a series of six to nine stings are given, one between each of the seg- ments of the body beginning from the anterior end ; the brain is then partially crushed by a bite with the man- dibles.* Now so far as the spider and the beetle are concerned, I do not see much difficulty presented by the facts to our theory of the formation of instincts. For as both the large nerve-centres of the Spider and the sting of the Sphex occur upon the median line of their respective possessors, if the stinging of the ganglion were in the first instance accidentally favoured by this coincidence — which appears to me not im- probable, seeing that the nerve-centre is thus the most likely place for the sting to strike, — it is evident that natural selec- tion would have had excellent material on which to work for the purpose of developing such an instinct as we now observe. Again, in the case of the beetle, M. Fabre expressly notices that the only vulnerable point in the hard casing of the animal is in the articulation where the Sphex thrusts her sting ; so tliat there is nothing very remarkable in natural selection having developed an instinct to sting at the only place in the body of the prey where stinging is mechanically possible. But the case is certainly very different with the cricket and the caterpillar ; for here — or at least in the latter case — we encounter the extraordinary and unavoidable fact of an insect, without any accidental guiding or mechanicall}' * All the above facts are taken from the works of M. J. H. Fabre {Somienirs Entomologiques, 1879 and 1883), who was the first to observe and describe them. INSTINCTS OF TilE SPIIEX. 301 imposed necessity, instinctively choosing a number of minute points in the uniformly soft body of its prey, with an appa- rently very precise knowledge tliat it is only at these par- ticular points that the peculiar paralyzing influence of its sting can be exercised. After duly considering this case, I must candidly say that I feel it to be the most perplexing which has yet been brought to light, and the one whicli is most difficult of explanation upon the principles of tlie fore- going theory. It is, however, most desirable that tlie facts should be more thoroughly investigated, for it might then appear that some clue would be given as to tlie origin and development of this instinct. So far as our information at present extends, I can only suggest that this origin must have been of a purely secondary kind, although its subsequent development may probably hav^e been assisted by natural selection. In other words, so far as we have any means of judging, I can see no alternative but to conclude that these w^asp-like animals owe their present instincts to the high intelligence of their ancestors, who found from experience the effects of stinging caterpillars between the segments of their bodies, and consequently practised the art of so stingmcr them till it became an instinct. During the last year of his life I had some conversation with Mr. Darwin upon this matter, and, after deliberating upon it for some time, he eventually came to the conclusion which I have just stated — as will be at once apparent from the following letter wdiich he wrote to me, and which will serve in a few words to indicate what appears, I think, to be the most probable steps by which these singular instincts were acquired. " I have been thinking about Pompilius and its allies. — Please take the trouble to read on perforation of the corolla by Bees, p. 425 of my "Cross-fertilization," to end of chapter. Bees show so much intelligence in their acts, that it seems not improbable to me that the progenitors of Pompilius originally stung caterpillars and spiders, &c., in any part of their bodies, and then observed by their intelligence that if they stung them in one particular place, as between certain segments on the lower side, their prey was at once paralyzed. It does not seem to me at all incredible that this action should then become instinctive, i.e., memory transmitted from one genera- tion to another. It does not seem uesessary to suppose that 302 MENTAL EVOLUTION IN ANIMALS. when Pompilius stung its prey in the ganglion it intended or knew that their prey would keep long alive. The development of the larv£e may have heen subsequently modified in relation to their half-dead, instead of wholly dead prey ; supposing that the prey was at first quite killed, which would have required much stinging. Turn this over in your mind," &c. Now in Chapter XIV I have already given a short epitome of the facts concerning the boring by humble-bees of holes in corollas, and the subsequent utilization of the holes by hive- bees, it will be remembered that the connection in which I there alluded to the facts was that of the power of imitation by one species of the habits of another— the hive-bees observ- incr that the humble-bees were saving time by sucking through the holes instead of entering the tiowers. But the point which is of importance in the present connection is the intelli- o-ence displayed by the humble-bees in originating the idea, so to speak, of boring the holes. For close observation shows that they bore the holes with as precise an appreciation of the morphology of the flowers, as is shown by the Sphex of the morphology of spiders, insects, or caterpillars. Thus in the case of leguminous flowers they bite only through the standard petal, and always on the left side just over the passage to the nectar, which is larger than the corresponding passage on the right side. Therefore, as Mr. Francis Darwin observes, "it is difficult to say how the bees could have acquired this habit. Whether they discovered the inequality in the size of the nectar-holes in sucking the flowers in the proper way, and then utilized this knowledge in determining where to gnaw the hole ; or whether they found out the best situation by biting through the standard at various points, and afterwards remembered its situation in visiting other flowers. But in either case they show a remarkable power of making use of what they have learnt by experience."* Seein sporting dogs, 236. Blue-bird, local variation of instinct of, 210, 216. Blyth, on a fox feigning death, 304. Bod, on carnivorous habits of wasp, 245. Bond, on variation in nest of nut-hatch, 182. Bonelli, Professor, on a migration of butterflies, 286. Brain, relation of intelligence to mass of, 44-6. Brehm, on old birds educating young, 226. Brent, on instincts of crossed canaries, 199. Brewster, Sir D., on unconscious inference in perception, 321. Brodie, Sir B., on infants remembering taste of particular milk, 115 ; on inheritance of instinct as due to cerebral organization, 264. Brunelli, on stridulation of grasshopper, 86. Bryden, Dr. W., on a monkey feigning death, 312-13. Buccola, Dr. G-., on length of the reaction-time in perception among the uneducated and idiotic, 138. Buchanan, Professor, on imperfect instincts of young ferrets, 228. Biichner, on individual dispositions shown by ants, 183. Bidl, wildness of cross between Indian and common cow, 199 ; Brahmin feigning death, 313-14. Burdach, on imagination in animals, 151. Burrowing, instinct of, 248-9. Burton, F. M., on mistaken instinct of a moth, 167. Butterflies, littoral, continuing to frequent an area whence the sea has retired^ 246 ; migration of, 285-6. c. Caddice-fly, instincts of the, 191. Calderwood, Professor, on the relation of intelligence to the mass of the brain. 44. Callin, Gr., on sense of direction in man, 293. Cameleon, sense of colour in the, 98. Canary, diversity of individual disposition of the, 182 ; instincts of crossed breeds of the, 199 ; instinctive nidification of the, 226. Capon, instincts of the, 171. Carpenter, Dr. W. B., on discrimination shown by protoplasmic organisms ;. on acquired habits, 181 ; on cats not howling in S. America, 250 ; on a case of couching for cataract, 322 ; on inheritance of handwriting, 194. Carter, H. J., on sensation in Rhizopoda, 80. Castration, changes produced by, on instinct, 171-2. Cat, idiosyncracies of the, as regards mousing, 182 ; associating with hares,. &c., 184 ; hereditary disposition to beg in a family of the, 195 ; rearing progeny of other animals, 217-18 ; loss of instinctive wildness of the,, under domestication, 231 ; not howling iu S. America, 249-50 ; sense of direction in the, 289 ; cruelty and benevolence in the, 345-6 ; mider- standing of mechanism by the, 351. Caterpillar, instincts of the processional, 342-3. Caterpillars, migrations of, 285. Cattle, learning to avoid poisonous herbs, 224, 227 ; instincts of wild under domestication, 231 ; dwindling of natural instincts of in Grer- many, 232 ; sucking Ijones, 247 ; sense of direction in, 290. Causation, appreciated by animals, 155-8. 2 B 2 :388 MENTAL EVOLUTION IN ANIMALS. CepTialopoda, intelligence of related to organs of toucli, 57 ; eyes of, 88 ; ears of, 89 ; tactile organs of, 89 ; colour-sense in, 98 ; memoiy in, 122 ; imagination in, 145 ; grade of mental evolution of, 349-50. Cerebrum, functions of the, 34-46. Chalicodoma, instincts of, 166. Character, individual. See Disposition. Chelmon rosfrcttus, 89. Cheselden, on a case of couching for cataract, 322-3. Chickens. See Birds. Choice, as criterion of mind, 17-20 ; physiological aspect of, 47-55. Clifford, Professor, on ejects, 16. Cobb, Miss, on inheritance of handwi'iting, 194. Caelenterata, consciousness in, 76, 348 ; special sense of, 83-4 ; emotions of, 342 ; grade of mental evolution of, 348. Collett, E-., on migration of the lemming, 283-5. Colour- sense, 98-104. Comparative Psychology in relation to comparative anatomy, 5 ; obiects of, as a science, 6-7. Comte, on Fetishism in animals, 154. Conceptualism, 145. Conductility, 68. Conscience, evolution of, 352. Consciousness as the distinctive character of mind, 17 ; evolution of, 70-77 ; definition of impossible, 72 ; degrees of, 72 ; time relations of, 73 ; possibly developed to supply conditions of feeling pleasure and pain, 111. Conte, Le, on cattle sucking bones, 247. Couch, on mistaken instinct of a bee, 167-8 ; on variations in the instinct of incubation, 182 ; on a dog learning how to attack a badger, 221 ; on a goldfinch singing instinctively, 222 ; on birds learning and forgetting the songs of other birds, 223 ; on the instinct of feigning death, 303-8, 315. ■Coues, Captain Elliot, on local variations of instinct in birds, 210, 246-7. Crab, olfactory organs of, 87-8 ; experiments in psychology of the Hermit, 122-3 ; migration of the Land, 146, 285 ; feigning death, 305 ; reason in the, 336, 350. Crayfish, kataplexy of the, 308. Crex, aquatic habits of the, 253. Cripps, on an elephant feigning death, 305. Crocodile, alleged dreaming in the, 149 ; divers dispositions in families of the, 188. Crossing, effects of, in blending instincts, 198-9. Crotch, on migration of the lemming, 282-5. Cruelty in animals, 541, 345. Crustacea, special senses of, 84, 87 ; colour-sense of, 98-9 ; memory of, 122 imagination of, 145-6; grade of mental evolution of, 349-50. Cuckoo, mistaken instincts of the, 168 ; parasitic and non-parasitic habits oi the, 251-2 ; parallelism of instincts of the, with those of Molothrus, 273-4 ; migration of the young, 289. CucuUdce. See Cuckoo. Curlew, sense of hearing in the, 92. Curiosity in animals, 279-80, 341, 344. Cuttle-fish. See Cephalopoda. Cuvier, on birds dreaming, 149. Cuvier, F., on attachment of a dog to a lion, 184. INDEX. 389- D. Darwin, Charles, on the relation of intelligence of ant3 to the size of their brains, 45 ; on movements of plants, 49-51 ; on intelligence of earthworms, 77 ; on special senses of earthworms, 86-7 ; on birds dreaming, 149 ; on mis-' taken instincts of humble-bees, 168; on mistaken instincts of an African shrew-mouse, 169 ; on variability and natural selection of instincts, 178 ; on inherited tricks of manner, 185-6 ; on inherited paces of the horse, 188 ; on tumbler and Abyssinian pigeons, 188-90 ; on instincts of biscacha, 189-90 ; on inheritance of handwriting, 194 ; on wildness and tameness in rabbits, horses, and ducks, 196, and in wild animals, 197 ; on effects of crossing upon instincts, 198-9 ; on intelligent imitation by animals, 220-2 ; on protrusion of lips by orang-outang, 225 ; on sheep and cattle learning to avoid poisonous herbs, 227 ; on obliteration of wild instincts under domestication, 231-2 ; on acquisition of domestic instincts, 236-9 ; on bees eating moths, 245 ; on local variations of instinct in birds, 245-6 ; on the hyaena not burrov\'ing in South Africa, 249 ; on specific variations of instinct as difficulties against the theory of natural selection, 251 ; on parasitic habits of Molotlu-us, 251 ; on adaptive structures developed by natural selection, 253-4 ; on evolution of instinct, 263-5 ; on similar instincts of unallied animals, 273 ; on dis- similar instincts of allied animals, 274 ; on trivial and useless instincts, 274^6 ; on instincts apparently detrimental, 276-82 ; on migration of lemming, 282 ; on theoiy of migration, 287-97 ; on sense of direction, 290-3 ; on instincts of neuter insects, 297-9 ; on instincts of sphex, 299 and 303 ; on bees boring corollas of flowers, 220-1, 301-2 ; on instinct of feigning death, 308 ; on instinct of feigning injury, 316-17 ; on reason in a crab, 336 ; on emotions of earthworms, 344 ; on sexual selection, 344-5. [For all references to matter now published in the Posthumous Essay on Instinct, see Index to the Essay. The following are references to all the quotations from, and allusions to, the unpublished MSS of Mr. Darwin which occur in the pages of the present work.] On changes produced in instinct by abnormal individual expe- rience, 115 ; on instinctive fear and ferocity in young animals as directed against particular enemies or kinds of prey, 165 ; on mistaken instincts of ants, 168 ; on instinct of a kitten modified by individual experience, 172 ; on analogies between instincts in species and acquired habits in individuals, 179-80 ; on diversity of disposition in birds, 182 ; on hereditary tricks of manner displayed by a child, 185-6, and by a terrier, 186 ; on peculiar dispositions and habits transmitted in croco- diles, ducks, horses, and pigeons, 188-9 ; on automatic actions displayed by idiots and by an idiotic dog, 193 ; on instinctive wildness and tame- ness respectively displayed by the progeny of wild and tame horses, rabbits, and ducks, 196 ; on efiects upon instinct of crossing, 199 ; on intelligent modification of instinct in bees, 207 ; on wild ducks building in trees, 211 ; on hive-bees sucking through holes made in corollas by humble-bees, 220-1 ; on dogs learning modes of attack by experience and imitation, 221 ; on birds of one species learning danger cries of birds of another, 221-2 ; on a dog learning by imitation the habits of a cat, and lambs and cattle learning to avoid poisonous herbs, 224 ; on canaries reared in a felt nest afterwards constructing a normal nest, 226 ; on the non-instinctive character of the drinking movements of chickens, 228-9 ; on the incorrigibly wild instincts of sundi'y wild animals when 390 MENTAL EVOLUTION IN ANIMALS. domesticated, 232 ; on the stupidity of Chinese dogs, 233 ; on the arti- ficially bred instincts of sheep-dogs, pointers, and retrievers, 235-7 ; on the effects upon artiflcially bred instincts of crossing, 241 ; on structures adapted to obsolete uses, 253-4 ; on the causes of the evolution of instinct, 2-64 ; on insects flying into flame, 278-80 ; on the instinct of feigning injury as exhibited by the duck, partridge, &c., 316-17. Darwin, Dr. E., on mistaken instinct of Musca carnaria, 167; on a cat imitating a dog, 224 ; on effects of domestication on instincts, 229 ; on bees ceasing to collect honey in California, 245 ; on rabbits not bur- rowing in Sor, 248. Darwin, Francis, on bees boring holes in corollas of flowers, 302. Daphnea pulex, colour-sense of, 98. Davis, on instincts of the processional caterpillar, 342-3. Davy, Sir H., on an eagle teaching young to fly, 227. Death, feigning of, by animals, 303-16. Death-watch, feigning death, 309. Deceit, in animals, 341, 347. Delusions, in animals, 149-50. Diagram, explanation of the, 63-9. Dilemma-time in perception, 134-5. DioTKsa, discrimination shown by, 50-1. Direction, sense of, 289-94. Discrimination, in relation to choice, 47-62 ; shown by vegetable tissues, 49- 51 ; by protoplasmic organisms, 51. Disposition, individual, of men and animals, 182. Dog, sense of smell in the, 93 ; sense of musical pitch in the, 94 ; imagina- tion in the, 146 and 148-9 ; homesickness and pining of the, as proof of imagination, 151-2 ; appreciation of cause by the, 155-8 ; instinct of collie barking round a carriage, 182 ; attachment of the to other animals, 184 ; inherited antipathy of a, to butchers, 187 ; useless instincts of the, 176, 190 ; instinct of, in turning round to make a bed, 193 ; hereditary transmission of begging in breeds of the, 195-6 ; effects of crossing upon instincts of the, 198; learning by imitation, 221, 223-4; teaching young, 227 ; influence of domestication ujDon psychology of the, 231-42 ; barking of the, 249-55; sense of direction in the, 289-90; inability of the, to appreciate mechanism, 351 ; grade of mental evolution of the, 352. Domestication, effects of, upon instinct, 230-42. Donders, Professor, on reaction-times in perception, 132, 135. Donovan, on cattle sucking bones, 247. Dragon-flies, migrations of, 286. Dreaming, in animals, 148-9. Drosera, discrimination shown by tentacles of, 49-50. Duck, sense of touch in the, 92 ; instincts of the young, 171, 196 ; a breed of _sho\ving fear of water, 188 ; natural wildness and tameness of the, 196 ; instincts of the, modified by crossing, 199 ; conveying young, 211 ; build- ing on trees, 211 ; instinct of the, in feigning injury, 316. Dudgeon, P., on a cat rearing rats, 218. Dujardin, on relation of intelligence of ants to size of peduncular bodies, 46. Duncan, on spiders feigning death, 309. Duncan, Professor P. M., on instinct of Odynerus, 191-2. E. Eagle, variation in nest-building of the, 182 ; teaching young to fly, 227 ; teach- ing a goose to eat flesh, 227. INDEX. 391 Ear. See Hearing. Earthworms. See Worms. Earwig, memory in, 123 ; parental affection of, 344. Echinodermata, nci'vous system of, 28-30 ; consciousness in, 76, 348 ; special senses of, 56, 84 ; memory in, 122, 348-9 ; emotions of, 342 ; grade of mental evolution of, 348-9. Education of young animals by their parents, 226-9. EdAvard, on local variation of instinct in the swallow, 247. Eject, 16. Elam, on somnambulism in animals, 149. Elephant, intelligence of the, related to the trunk, 57 ; memory in the, 124 ; dreaming in the, 149 ; instinct of the, in goring woimded companions, 176 ; feigning death, 305 ; emotions of the, 346 ; using tools, 352. Emotions, physiological aspect of, 53 ; which occur in animals, 341 ; origin of, 342 ; distinctive, of different animals, 342-7. Emulation, 341, 345. Engelmann, on protoplasmic and unicellular organisms being affected by light, 80; on one infusorium chasing another, 81; on colour sense of JEnglena viridis, 98. JEnglena viridis, as affected by light, 80 ; colour sense of, 98. Equation, personal, 135-7. Evolution, Organic, taken for granted, 7 ; Mental, a necessary corollary, 8 ; human, excluded from present work, 8-10 ; of nerves by use, 30-33 ; of discriminative and executive powers, 47-62; of mental faculties as shown in the diagram, 63-9 ; of consciousness, 70-7 ; of sense of tem- perature, 97-8 ; of visual sense, 97-8 ; of colour-sense, 98-103 ; of organs of special sense, 103-4 ; of pleasures and pains, 105-11 ; of memory, 111-17 ; of association of ideas, 117-24 ; of perception, 127- 9; of imagination, 144-54; of fetishism, 154-8; of instinct, 177-255; of reason, 318-35 ; of conscience, 352. Ewart, Professor, on Echinodermata, 84 ; on colour-sense of Octopus, 99. Excitability, 68. Excrement, instinct of burying, 176. Exner, Professor, on physiology of perception, 132-7. Eye. See Sight. Eyton, on instincts of crossed Geese, 199. F. Eabre, J., on instincts of Bembex, 166, and of Sphex, 179, 299-303 ; on sense of direction in bees, 293-4. Fear in animals, 341 ; in young children and low animals, 342-3. Feeling. See Sensation. Feelings, logic of, 325. Feigning death, 303-16 ; injui-y, 316-17. Fenn, Dr. C. M., on imagination in a wolf, 147. Ferrets, reared by a hen, 216-17 ; imperfect instincts of young, 228 ; analogy between instincts of, and those of Sphex, 303. Ferrier, on fimctions of the cerebrum, 35. Fish, sense of sight in, 89 ; blind, 89 ; luminous, 89 ; sense of hearing in, 90 ; of smell, taste, and touch, 90 ; of colour, 98-9 ; memory in, 123-4 ; imagination in, 153, 286 ; feigning death, 303 ; emotions of, 345 ; grade of mental evolution of, 349-50. Fish, E. E., on birds imitating each other's songs, 222. 392 MENTAL EVOLUTION IN ANIMALS. Fiske, on hereditary transmission of begging in dogs, 165 ; on tlie subordinate part played by natural selection in tbe development of instinct, 256. Fitch, Oswald, on benevolence shown by a cat, 345-6. ritzEoy, Capt., on instincts of wild dogs under domestication, 232. Fleming, on delusions shown by rabid dogs, 149-50. Flesh-fly, mistaken instinct of the, 167. Flounder, sense of colour in the, 98. Ford, W., on sense of direction in man, 291, 292. Forel, on variations of instinct and individual disposition in ants, 183, 209, 244-5. Fowl. See Hen. Fox, the, feigning death, 304, 314-15 ; understanding of mechanism by the, 351. Fox, the Eev. W. D., on inherited tendency to beg in a terrier, 186 ; on in- stincts of a retriever, 236. Fredericq, on colour-sense of Cephalopoda, 98-9. Fritsch, on functions of the cerebrum, 35. Frog, colour-sense in the, 98 ; changed instincts of the tree, 254. Furnarius, imperfect instincts of the, 281. G. G-alen, on instinct of a kid, 115. Gallus lanJciva, wildness of chickens reared from wild stock of, 232. Gralton, Francis, on hereditary genius, 194. Granglia, structui'e and functions of, 26-33 ; Mr. Spencer's theory of genesis of, 32. Grardener, J. S., on moths flying into a waterfall, 280. G-ardner, on intelligence of a crab, 336. Garnett, on instincts of crossed ducks, 199., Gasteropoda, eyes of, 88 ; memory in, 121 .. See Mollusca. G-eneralization, 145. Grentry, W. K. Gr., on carnivorous habits of herbivorous rodent, 248. Grladstone, W. E., on colour-sense, 100. Groatsucker, conveying young, 211. Gold-crested warbler, nidification of the, 210. Goltz, on functions of the cerebrum, 35. Goose, eye of the Solen, 91 ; instincts of crossed, 199 ; learning to eat flesh,, 227 ; instinct of upland, 253; Siberian, feigning death, 303-4; attach- ment of a, to a dog, 184-5. Goring, instinct of, 176, 379. Gosse, on gregarious habits in nidification, 253 Gould, on instincts of terrestrial geese, 253. Grebe, aquatic instincts of the, 253. Grief, in animals, 341, 345. Grouse, instincts of North American, 201. Guanacoe, instincts of the, 190. Guer, on somnambulism in animals, 149. / Guyne, on migration of the lemming, 282-5. H. Hseckel, Professor, on sense - organs, 81, 85-6 ; on supposed unknown sense possessed by Fish, 90 ; on supposed unknown senses possessed INDEX. 393 by Mammals, 95 j on evolution of sense-organs, 98 104 ; on colour- sense, 100. Hall, G-. Stanley, on hypnotism lengthening reaction-time in perception, 138. Hamilton, Sir W., on pleasures and pains, 105 ; on inverse relation between instinct and reason, 338. Hancock, on dogs not barking in Guinea, 250. Handcock, on obliteration of natural instincts under domestication, 231. Hand\^Titing, inheritance of, 194. Hate, in animals, 341, 345. Haust, on ducks building in trees, 211. Hawfinch, learning the song of a blackbu'd, 222. Hawk, eye of, 91 ; old, teaching young to capture prey, 226 ; changed in- stincts of Swallow-tailed, 254. Hearing, sense of, in Medusae, 82 ; in Articulata, 86-7 ; in Mollusca, 88-9 ; in Fish, 90 ; in Amphibia and Keptiles, 90 ; in Birds, 91-2 ; in Mam- mals, 93-4 ; reaction-time of, 132. Selix pomatia, memory in, 122. Helmholtz, Professor, on reaction-time as increased by complexity of percep- tion, 133. Hen, instinct of cackling in the, 176, 289 ; wildness of the, when crossed with a pheasant, 199; conveying young, 211; experiments and observations on the incubating and natural instincts of the, 213-17 ; drinking move- ments of tbe, not instinctive, 229 ; loss of incubating instinct of the Spanish, 212. Hennabe, on the hyrax dreaming, 149. Heredity, in relation to reflex action, 17-18 ; influence of, on formation of nervous structures, 33 ; in association of ideas, 43 ; in reference to sensa- tion, 95-104 ; to pleasures and pains, 105-11 ; t.o memory and associa- tion of ideas, 111-24 ; to perception, 130-41 ; to instinct, 180, 185-92, 200-3, 231-42 ; of handwriting and psychological character, 194-5 ; of begging in dogs and cats, 195-6 ; of wildness and tameness, 195-7 ; of artificial paces in horses, 188 ; with reference to migration, 289, 296-7. Hering, on muscle strengthening by use, 112. Herman, on reaction-times of different senses, 132 ; on inherited knowledge shown by sporting dogs, 239. Meteropoda, eyes of, 88. Hertwig, Professors O. and E., on nervous system of Medusce, 69. Hewetson, on variation in the nest of the nuthatch, 182. Hewett, on wildness of hybrids between fowls and pheasants, 199. Hill, Richard, on gi-egarious habits in nidification, 253. Hitzig, on functions of the cerebrum, 35. Hofacker, on inheritance of handwriting, 194. Hoffmann, Professor, on a puppy learning to imitate a cat, 224. Hogg, on instincts of a sheep-dog, 240-1. Hollman, on memory in Cephalopoda, 122. Homing-faculty of animals, 95, 153-4. Home-sickness in animals, proof of imagination, 151-2. Honig-Schnied, on reaction-time for taste, 133. Hornbill, nidification of the, 255. Horse, memory in the, 124; inheritance by the, of artificial paces, 188; useless instincts of the, 190 ; natural tameness of the feral, 196 ; sense of direction in the, 289-91. Houdin, Robert, remembering his art of juggling with balls, 36; on rapidity of perception acqiured by training, 138. House-fly, mistaken instinct of the, 167. 394 MENTAL EVOLUTION IN ANIMALS. House-sparrow, nidification of the, 210. Houzeau, on stridulation, 86 ; on birds dreaming, 149 ; on mistaken in- stincts, 167 ; on inability of infants to localize pain, 326. Howitt, A. W., on homing faculty of horses and cattle, 290. Huber, on instincts of bees, 168, 203-9. Huber, P., on instincts of a caterpillar, 179. Huggins, Dr., on sense of musical pitch in a dog, 94 ; on inherited antipathy of a dog to butchers, 187. Humboldt, on individual disposition in monkeys, 188. Humming-bird hawk-moth, mistaken instinct of the, 167. Hunger, sense of, 95, Hunter, John, on tricks of manner being inherited, 185. Hurdis, on migration of the golden plover, 286. Hutchinson, Colonel, on inherited tendency to bark in sporting dogs, 236. Hutton, Captain, on wildness of the hybrid between the tame and wild goat, 199 ; on wildness of chickens reared from wild Gallus hankiva, 232 ; on migration, 288. Huxley, Professor T. H., on evolution of sense-organs, 104. Syclrozoa, nerve-tissues in, 24. Hyaena, not burrowing in South Africa, 244. Hylohates agilis, its sense of musical pitch, 93. Symenoptera. See Ants and Bees. Hypnotism, reaction-time under influence of, 138 ; of animals, 308-11. Hyrax, dreaming in the, 149. Ichneumon, instincts of the, 166. Ideas, association of, 37-8, 111-24; definition of, 118; composite, ana- logous to muscular coordinations, 42-4. Idiots, size of brain of, in relation to intelligence, 45; personal equation of, 138 ; tricks of manner shown by, 181 ; automatic actions of, 193 ; imita- tive actions of, 225. Industry, 341. Imagination, 142-58 ; analysis of, 142-4 ; stages and evolution of, 144-5 ; stages of, as occurring in difierent animals, 145-54. Imitation, effects of, on formation of instinct, 220-9; by hive-bees of humble bees, 220-1 ; by dogs of other dogs, 221 ; by dogs of cats, 223- 4 ; by birds of one another's songs, and of articulate speech, 222-3 ; by monkeys, children, savages, and idiots, 225 ; by young birds in nidifica- tion suggested by Mr. Wallace, 225-6 ; of parents by young of sundry animals, 226-9. Incubation, instinct of, 177. Infant, consciousness in the, 77 ; preferring sweet tastes, and remembering taste 'of milk, 114-16; earliest power of associating ideas, 120-1, and mental images, 152 ; when spoon-fed forgetting to suck, 170, 180 ; learn- ing to balance the head, &c., 175-6 ; imitative movements of the, 225 ; inability of the, to localize pain, 326 ; emotions of fear and surprise in the, 342. Inference. See Reason. Infusoria. See Protozoa. Injury, feigning of, by animals, 316-17. Insects, eyes of, 84-5 ; colour-sense of, 99 ; imagination of, 145-6 ; instmcts of, 165-8, 179, 201-2, 203-9, 220-1, 246, 277-81, 285-6, 290, 293-5, 297-309 J emotions of, 344. INDEX. 395 Instinct, physiological aspect of, 52 ; as hereditary memory, 115-17, 131 ; definition of, 159; involves a mental element, 160; perfection of, 160-7 ; in young birds and mammals, 161-5 ; in insects, 1G5-8, 179, 201-2, 203-9, 220-1, 277-81, 285-6, 290-5, 297, 303-8; of flying, 165; imperfection of, 167-76; as affected by interruption of normal con- verse with environment, 169-72, by castration, 171-2, by insanity, 173-4 ; trivial and useless, 176 ; origin and development of, 177-99 ; primary, 180-92 ; secondary, 192-9 ; effects of crossing upon, 198-9 ; blended origin or plasticity of, 200-218 ; of nidification, 210-12 ; of incubation, 177, 212-13 ; maternal, 212-18 ; as moulded by imita- tion, 219-25, by education, 226-9, and by domestication, 230-42 ; of singing in birds, 222-3 ; of attacking rabbits in ferrets, 228 ; of drinking in fowls, 229 ; local and specific varieties of, 243-55 ; not fossiHzed, 250, 254-5 ; evidence of transformation yielded by specific varieties of, 250-5 ; views of other writers on evolution of, 256-72 ; general sum- mary on and diagram of development of, 265-72 ; cases of special diffi- culty in display of, 273-317 ; similar in unallied animals, 273-4 ; dis- similar in allied animals, 274 ; trivial and useless, 274-6 ; apparently detrimental, 276-85 ; alleged, of scorpion in committing suicide, 278 ; of flying through flame, 278-80 ; of hen cackling, pheasant crowing, shrew- mouse screaming, &c., 280-1 ; of migration injurious, 281-5 ; of lemming, 282-5 ; of migration, 285-97 ; of neuter insects, 265, 297-9 ; of sphex, 299-303; of feigning death, 303-16; of feigning injury, 316-17; in relation to reason, 338-9. J. •Jackson, C. J., on instinct of the Californian woodpecker, 255. Jackson, Dr. J, Hughlings, on pre-perception, 139. Jealousy, 341, 345. Jeens, C. H., on a puppy learning to imitate a cat, 224. Jelly-fishes. See MeduscB. Jerdon, on birds dreaming, 149. Jesse, on changed instincts of a hen, 215 ; on snakes feigning death, 305. Kataplexy. See Hypnotism. Kidd, W., on diversity of disposition in larks and canaries, 182. Kingsley, Canon, on migration of birds, 296. Kirby, on modified instincts of larvae, 180. Kirby and Spence, on larvae remembering the taste of particular leaves, 115 ; on instmcts of insects, 166, 167, 179-80, 201, 204-8, 244, 245. Kittens, instincts of, 164-5, 172. Knight, Andrew, on hereditary transmission of acquired mental endowments in animals, 195, 197, 198, 237, 238 ; on intelligence of a bird, 201, and of bees, 208. Knox, D. E., on a variation in nest-building of the golden eagle, 182. Kries, on dilemma-time in perception, 134-5. Kuszmaul, Professor, on infants preferring sweet tastes, 115. 396 MENTAL EVOLUTION IN ANI]\L\LS. Lamarck, his theory of evolution of nerves by use, 33. LamelUbranchiata, eyes of, 88. Landrail, feigning death, 304-5. Language, as mental symbolism, 153. Lankester, Professor, on alleged instinct of scorpion to commit suicide, 278. Lapsing of intelligence, 178-80. Lapwing, habit of, in flying down to sportsman when fired at, 189 ;. associating with rooks and starlings, 185 ; instinct of, in feigning death, 317. Lasius acerhorum, local variation of instinct of, 244-5. Leech, Dr., on modified instincts of a spider, 209. Lemming, migratory instincts of the, 169, 282-5. Lepidoptera, sense of hearing in, 86. See Butterfly. Le Roy, on imagination of animals, 146-7. Leuret, on intelligence of an orang outang, 328. Leveret, reared by a cat, 217. Lewes, G-. H., case of sleeping waiter described by, 36; on sensations as groups of components, 41 ; his definition of Sensation, 78 ; on pre- perception, 139 ; on instincts of ducklings, 171 ; on hereditary trans- mission of begging in dogs, 195 ; ignores natural selection in development of instinct, 256. Lewis, on carnivorous habits of wasp, 245. Limpet, memory in the, 121. Lindsay, Dr. Lauder, on dreaming and delusions in animals, 148-9. Linnaeus, on dogs not barking in S. America, 250. Lodge, Colonel, on sense of direction in man, 293. Logic of feelings and signs, 325. Lonbiere, on local variations of instinct in ants, 244. Lonsdale, on memory in a snail, 122. Lord, J. K., on instinct of the Cahfornian woodpecker, 255. Lubbock, Sir John, on deafness of ants, 86 ; on sense of smell in ants, 87 ; on colour-sense of Daphnea pulex and Hymenoptera, 98-9; on memory of bees, 123 ; on sense of direction in Kymenoptera, 293-5. Lucretius, on dreaming in dogs, 148. Ludicrous, emotion of, in animals, 341, 347. Lunacy, analogous to ataxy, 44. Lyon, Captain, on a wolf feigning death, 304. M. MaeFarlane, Mrs. L., on changed instincts of fowls, 215. Mackillar, Miss, on changed instincts of a hen, 215. Macpherson, H. A., on benevolence shown by a cat, 346. Macroglossa stellatarum, mistaken instinct of, 167. Magnus, Albertus, on instincts of the capon, 171. Magnus, Dr., on colour-sense, 100. Malle, Dureau de la, on inheritance by horses of artificial paces, 188 : on birds imitatiag the songs of other birds, 222 ; on a terrier imitating a cat, 233-4 ; on old birds educating young, 226 ; on instinct of burying superfluous food, 233, INDEX. 397 Mammals, special senses of, 57; sight, 92; hearing, 93-4; taste and touch, 94; colour, 99 ; memory of, 124 ; perception of young, 131 ; imagina- tion of, 146-54 ; instincts of young, 164-5 ; mistaken instincts of, 169 ; trivial and useless instincts of, 176 ; attachment between dif- ferent species of, and with other animals, 184-5 ; imitation in, 223-5 ; teaching their young, 227 ; local variations of instinct in, 247-50 ; migrations of, 286 ; homing faculty of, 289-91 ; feigning death, 304-5 ; emotions of, 345-7. Man, mental evolution of, questioned by some evolutionists, 8-10 ; subjective and ejective evidence of mind in, 15, et seq. ; relation of size of brain of, to intelhgence, 45 ; substitution of machinery by, for muscular action, 59 ; imagination in, 14i, 152-4 ; sense of direction in, 291-3 ; imperfec- tion of hereditary endowments of, 326; reason alleged special pre- rogative of, 335-40. Mania, analogous to convulsiou, 44, Marshall, Professor John, on sense of smell in Octopus, 89 ; on sense of sight in Surinam Sprat, 90. Martins, nidiiication of, 210-11 ; warning chickens against hawks, 221-2. McCready, on larvae of a Medusa sucking their parent, 259-60. MeduscB, larvse of, sucking parent, 259-60 ; following light not instinctive, 258 ; nervous system of, 24, 28 ; special sensation in, 56, 81-83. Melanerpes formicivarus, peculiar instinct of, 255. Memory, of ganglia without consciousness, 35-6 ; analysis of, 111-17; of infant, 114-16, 120-1 ; in Mollusca, 121-2 ; in Echinodermata and Crustacea, 122 ; in Insects, 123 ; in Fish, 123 ; in other Yertebrata, 124 ; as involved in perception, 129-30. Merejkowsky, on colour-sense of Daplinea pulex, 98. Merganser, instinct of the, in feigning injury, 316. Merrill, G-. C, on sense of direction in man, 292. Mierzejewskis, Dr., on relation of intelligence to mass of brain, 44. Migration, 281-97. Mill, James, on composite ideas, 44. Mill, J. S., ignores heredity, 256 ; on reason, 336-7. Milton, on reason of animals, 340 ; on imagination, 154. Mind, Criterion of, 15-23 ; considered as subject, object, and eject, 15-16 ; activities indicative of, 16 ; physical basis of, 34-46 ; root-principles of, 47-62. Missel-thrush, variation in nest -building of the, 182. Mitchell, Sir J., on dogs learning how to attack the Emu, 221. Mivart, St. a., on reason, 325, 335-40. M'Laclilan, E,., on instincts of the Caddice-fly, 191. Mocking-bird, 222. Modesty, sense of, 193. Moggridge, on instincts of ants, 168, and on individual variations of the same, 183. Mollusca, consciousness in, 77 ; special senses of, 56, 88-9 ; memory in, 121-2 ; imagination in, 145-6 ; emotions of, 344 ; grade of mental evolu- tion of, 349. Molothrus, parasitic instincts of, 251-2, 273-4. Monboddo, Lord, on homing faculty of a snake, 153-4. Monkeys, sense of musical pitch shown by, 93 ; imagination in, 151 ; dif- ferences in disposition of, 188 ; instinctive dread of snakes shown by, 195 ; love of imitation shown by, 225 ; feigning death, 311-12 ; using tools, 252. Montagu, Col., on attachments between animals of different species, 184-5. 398 MENTAL EVOLUTION IN ANIMALS. Montaigne on dreaming in animals, 148. Morality, indefinite, and evolution of, 352. Morgan, Lewis H., on intelligence of the bearer, 329. Morgan, Professor Lloyd, on alleged instinct of tlie scorpion to commit suicide, 278. Moseley, Professor H. N., on colour-sense of marine animals, 99; on imper- fection of instinct in lioney-sucking insects, 167 ; on beavers of Oregon not constructing dams, 249 ; on migration of turtles, 286. Mouse feigning death, 306-7. Musca carnaria, mistaken instinct of, 167. Muscles, coordination of, an index of nerve evolution, 38-44. My sis, ear of, 87 ; colour-sense of, 98. Mysteriousness, sense of, in animals, 155-8. Natural selection. See Heredity. Nerve-tissue, structui'e and function of, 24-33. Neurility, 68. Newall, on carnivorous habits of wasps, 245. Newbury, Dr., on beavers not constructing dams, 249. Newton, Professor A., on attachments between birds of different species, 185 ; on starlings imitating ducks, 222 ; on instincts of ring-plover, 246 ; on birds flying towards light, 279 ; on migration of birds, 286-7, 295. Nidification, variations in instinct of, 182 ; supposed to be due to imitation, 225-6 ; associated, 253 ; of Thrush and Hornbills, 255. Nightingale, midnight singing of, inherited, 246. Noulet, on nidification of swallows, 211. Nuthatch, variation in nest-building of the, 182. 0. Octopus, eye of, 88 ; olfactory sense in, 89 ; imagination in, 146 ; sense of colour in, 98-9. Odynerus, instinct of, 171-2. Offspring, recognition of, 349. Orang-outang, protrusion of lips by the, 225 ; intelligence of a, 328. Oriole, Baltimore, improvement of nest-building of the, 210. OrtJioptera, ears of, 87. Osmia aurulenta, 208. Osmia hicolor, 208. Ostrich, caponizing of the, 172. Owl, local variation of instinct of the, 210, 246 ; nidification of the, 210. Oyster, memory in the, 121. Packard, on local variation of instinct in bees, 245. Paget, Su' James, on a parrot learning to open a lock, 351. Pains, 105-11. Paley on direction of the external ear, 93, INDEX. 399 Paralysis analogous to unconsciousness, 44. Parental affection in animals, 344. Parrot, intelligence of the, related to organs of touch, 57 ; sense of touch in the, 92 ; association of ideas in the, 124 ; dreaming and talking in sleep, 149 ; mistaken instinct of the Australian, 167 ; imitating other birds, talking, and singing, 223 ; carnivorous tastes developed by the Mountain, 248 ; changed instincts of the G-roimd, 254 ; learning to open a lock, 351. Partridge, conveying young, 211; not using voice when flushed in Ireland, 245 ; instinct of the, in feigning injury, 317. Passu, aquatic habits of, 253. Pea-fowl, 213-14. Peccari, attachment of a, to a dog, 184. Perception, 125-41 ; definition of, 125-6 ; evolution of, 127-9 ; as cogni- tion, 127 ; as recognition, 127-8 ; as grouping of previous perceptions, 128 ; as involving inference, 128, and memory, 129 ; as afPected by heredity, 130-1 ; in Mammals, Birds, Keptiles, and Invertebrata, 131 ; physiology of, 132-41 ; time -relations of, 132-9 ; relation of, to reflex action, 139-41 ; as stimulus to instinctive action, 159-60 ; illusions of, 321-2 ; relation of, to reason, 319-26. Petrel, changed instincts of the, 254. Pewit. See Lapwing. Flycatcher, variation of instinct of the, 210, 246. Pheasant, crowing of the cock, 176, 280 ; wildness of hybrid between the, and fowl, 199. Pig, instincts of young, 164 ; becoming omnivorous, 247 ; homing faculty of the, 290. Pigeon, insane, 173-4 ; tumbler, 188-9 ; Abyssinian, 189 ; pouter, 189 ; in- stinctive fear of the, of cats, lost under domestication, 232 ; migration of the passenger, 281. Pike, W., on an eagle teaching a goose to eat flesh, 227. Pining in animals, proof of imagination, 151-2. Pitch, musical, appreciated by birds, 91 ; by Kylohates agilis, 93 ; and by dogs, 94. Play, 341, 345. Pleasures, 105-11. PleiironectidcB, sense of colour in, 98. Pliny on instincts of the capon, 171. Plover. See Ring-plover and Lapwing. Pointer. See Dog. Polecat, instinct of the, in paralyzing frogs, 303. Pollock, Walter, on sense of smell in actiniae, 83 ; on association of ideas in a parrot, 124 ; on delusions in a dog, 150. Pope on instinct and reason, 266. Potts, I. H., on carnivorous tastes developed by parrots, 248. Pouchet, on relation between instinct and reason, 339 ; on colour-sense of fish, 98 ; on nidification of swallows, 211. Pre-perception, state of, 139. Preyer, Professor, on evolution of colour-sense, 101-4 ; on infants prefen'ing sweet tastes, 114, and remembering taste of milk, 115 ; on instinct of chickens, 116-17 ; on rapidity of perception acquired by training, 138 ; on infant learning to balance the head, &c., 175-6 ; on imitative move- ments and dreaming shown bv the infant, 225 ; on kataplexy of animals, 308-11 ; on emotions of the'iufant, 342, 344. Prichard, on a puppy reared bv a cat, 217, 224. Pride, 341, 345. Progeny, yearning for, 212-13. 400 MENTAL EVOLUTION IN AMIMALS. Protista as affected by liglit, 80-1. Protozoa as affected by ligbt, 80-1 ; chasing one another, 81. Pteropoda, eyes of, 88. Pugnacity, 341 , 344. Pierguin on somnambulism in animals, 149 ; on delusions of an ape, 150. Psychology, relation of Comparative to Comparative Anatomy, 5 ; distinction between, and Philosophy, 11. R. Rabbit, imagination in the, 147-8 ; instinctive antipathy of the young to ferrets, 164-5 ; imperfect instinct of the, with regard to weasels, 169 ; natural wildness and tameness of the, 196 ; not biu'rowing in Sor, 248. Rae, Dr. J., on instinct of ducks, 196 ; on instinct of grouse, 201. Eage, in animals, 346. Katel, habit of the, in turning somersaults, 189, 275. Eats, understanding of mechanisms by, 351. Eattle-snake, tail of the, 277. Eazor-fish, memory in the, 122. Eeaction-time, in perception, 132-5. Eeason, physiological aspect of, 63 ; supplementing muscular co-ordination by machinery, 59 ; definition of, 318 ; evolution of, 319-35 ; relation of, to perception, 319-26 ; grades of, 318-25 ; in animal kingdom, 325-9 ; Mr. Spencer's views on development of, 330-5; Mr. Mivart's views upon, 335-40 ; Mr. Mills' views upon, 336-7 ; in relation to instinct, 330-40. Eeaumur, on larvae remembering the taste of particular leaves, 115 ; on instincts of bees, 166 ; on instincts of the capon, 171-2. Eecognition of olFspring, 349. Eecollection, 120. Eeflection, 145. Eeflex action, explanation of, and theory of its evolution, 26-33; arising from habit, 38; rise of consciousness from, 74-5; distinction between, and sensation, 78-9 ; in reference to memory and association of ideas, 111-24 ; to perception, 139-41 ; to instinct, 159-60. Eegret, in animals, 347. Ehea, mistaken instinct of the, 168. Eemorse, in animals, 341. Eengger, on changed instincts of a wild cat in confinement, 172 ; on attach- ment of a monkey to a dog, 184. Eeptiles, sense of sight in, 90 ; hearing, smell, taste, and touch of, 90 ; colom* sense of, 98 ; memory in, 124 ; perception in, 131 ; imagination in, 149, 153-4 ; migrations of, 286 ; feigning death, 305 ; emotions of, 345 ; grade of mental evolution of, 350. Eesentment, 341, 345. Eetriever. See Dog. Eevenge, in animals, 341, 346. Mhizojjoda, powers of special sense in, 80. Eibot, on memory, 111-13. Eing-plovers, continuing to build where sea has retired, 246. Eomanes, Gr. J., observations on Medusce, 31-2; on sea-anemones, 48, 83; on EcMnodermata, 84, 342, 348-9 ; on sense of hearing in Lepi- doptera and Birds, 86, 92 ; on sense of smell in crabs, 87-8 ; on sense of musical pitch in a dog, 94 ; on colour-sense of Octopus, 98-9 ; on INDEX. 401 earliest age at which an infant is abk^ to associate ideas, 120-1 ; on inability of hermit-crab to associate simple ideas, 122 3; on time-rela- tions in perception, 136-7 ; on sense of mysterious in, and appreciation of cause by dogs, 155-8 ; on instinctive antipathy of young rabbits to ferrets, 164-5; on handwriting, 19-4; on incubatory instincts, 213-14; on animals dying of terror, 307-8 ; on instincts and emotions of the pro- cessional caterpillar, 342-3 Rooks, associating with starlings, 185. Rosa, Baptista, on instincts of the capon, l7l. Ross, Sir J., on dogs learning how to attack wild cattle, 221. Roulin, on cats not howling in South America, 250. Routh, Dr., on a puppy learning to imitate a cat, 224. Roy, Le, on imagination of wild animals, 146-7 ; on mental characters of a dog of wild parentage, 198 ; on the migration of birds, 289. s. Sainfc-Hilaire, Greoffroy, on intelligence of an orang-outang, 328. Salmon. See Fish. Satiety, sense of, 95. Savages, sense of direction in, 289, 291 ; tendency to imitation shown by, 225. Schafer, Professor E. A., on nervous system of Aurelia aurita, 69. Schneider, on sense of vision in Serpulce, 86. Scorpion, alleged instinct of the, to commit suicide, 278. Sebright, Sir J., on natural wildness and tameness of rabbits and ducks, 196 ; on instincts of an Austi-alian puppy, 232 ; on love of man as in- stinctive in domestic dogs, 239. Seebohm, on migi'ation of biixis, 289. Scinus hudsonms, change of instincts in, 248. Seneca, on dreaming in dogs, 148. Sensation, as compound, 40-1 ; physiological aspect of, 51-2 ; defined, 78 ; survey of, in animal kingdom, 80-95 ; of temperature, 95-8 ; of colour, 98-103 ; as distinguished from perception, 125-6 ; as stimulus to reflex action, 159-60. Sense, muscular, 95 ; of hunger, thirst, and satiety, 95; of temperature, 96-8 ; of colour, 98-104. Serpent. See Reptiles. Serpulce, sense of vision in, 86. Setter. See Dog. Sexual affection- and selection, 341, 344. Shame, in animals, 341, 347. Shaw, J., on stupidity of dogs in China and Polynesian Islands, 233. Sheep, learning to avoid poisonous herbs, 224, 227 ; changed instincts of under domestication, 232 ; killed by parrots, 248 ; sense of direction in, 290. Sheep-dog. See Dog. Shrew-mouse of South Africa, injurious instinct of the, 169 and 280. Shuttleworth, Miss C, on mistaken instinct of bees and was])s, 167. Sight, sense of, in Protista, 81 ; in Medusae, 81-2 ; in Echiuodcrmata, 84 ; of simple and compound eyes, 84-5; of Worms, 85-6; of Fish, 89; of Amphibia and Reptiles, 90-1 ; of Birds, 91 ; of Mammals, 92 ; reaction- time of, 133 ; in young animals, 161-4. Sigismund, on infants remembering the taste of milk, 114. 2 c 402 MENTAL EVOLUTION IN ANIMALS. Signs, logic of, 325. Skate, oliactory organs of the, 90. Skylark, feigning death, 304. Smith, Adam, on a case of couching for ca,taract, 323-4. Smith, Dr. Andrew, on hysenas not burrowing in South Africa, 249. Smith, F., on instinct of bees, 208. Smith, Col. H., on instincts of wild dogs imder domestication, 232. Smith, W. Gr., on carnivorous habits of wasps, 245. Snail, memory in the, 122. Snake, homing faculty of the, 153^4; feigning death, 305. Smell, sense of in Protista, 81 ; in sea-anemones, 83 ; in leeches, ants, and crabs, 87-8 ; in Mollusca, 89 ; in Fish, Amphibia, and Eeptiles, 90 ; in Birds, 92 ; in Mammals, 92-3. Snipe, sense of touch in the, 92. Social feelings, in animals, 341, 344. Solen Goose, eye of the, 91. Spalding, Douglas, on instincts of young birds and mammals, 161-5, 170-1, 175^213, 216. Spallanzani, on sensibility of blinded bats, 94. Spaniel. See Dog. Speech, acquirement of, by volition, 41-2. Spence and Kirby. See Kirby and Spence. Spencer, Herbert, on evolution of nerves, 30-2 ; on consolidation of states of consciousness, 42-3 ; on evolution of consciousness, 74-6 ; on plea- sures and pains, 105-7 ; on perception, 125 ; on memory, 129-30 ; on pre-perception, 139 ; on perceptive faculties arising from reflex, 140 ; on ideas as faint revivals of perceptions, 142-3 ; on Fetishism in animals, 154-5 ; on race characteristics in psychology of man, 194 ; on evolution of instinct, 256-62 ; on instincts of bees, 265. Sphex, instincts of the, 179, 299-303. Sphinx-moth, mistaken instinct of the, 167. Spider, using stones to balance web, 59 ; imagination in the, 146 ; modified instincts of a, 209; distribution of the trap-door, 255 ; feigning death, 303. See Arachnida. Sprat, Surinam, eje of the, 90. Squirrel, a, dying of terror, 307. Star-fish. See Echinodermata. Starlings, associating with rooks, 185. Snarling, imitating songs of other birds, 222-3. St. John, on inherited tendency to bark in sporting dogs, 236. Stone, S., on variation in nest-building of the missel-thrush, 182. Stroud, Dr. J. W., on change of instincts produced by castration, 171-2. Stuorn, on dwindling of maternal instincts of cattle, 232. Sturm, on instincts of the dung-beetle, 244. Sulivan, Capt., on natxiral tameness of feral rabbits, 196. Sully, J., on distinction between sensation and perception, 125 ; on percep- tion as automatic, 126; on pre-perception, 139; on illusions of percep- tion, 321-2. Surinam Sprat, eye of the, 90. Siu'prise, 341, 344. Swallow, plasticity and local variation of instincts of the, 210, 246-7 ; migra- tion of the, 296. Swallows, nidification of, 210-11. Swainson, on mistaken instinct of the Australian j^arrot, 167. Swanderdam, on instincts of bees, 166. INDEX. 403 Swift, eye of the, 01. See Swallow. Sjiiipathy, 311, 345. Sparrow, ludification of the, 210 ; changed instincts of a, 213 ; learning song of a linnet, 222 ; local variations of instinct of the, 21-7. Tachornls phoenlcohea, 212. Tailor-bird, modified instincts of the, 210, Tait, Lawson, on hereditary transmission of begging in a cat, 195. Tameness. See Wildness. Taste, sense of, in Protista, 81 ; in Articulata, 88 ; in Fish, 90; in Anipliibia and Reptiles, 90 ,- in Birds, 92 ; in Mammals, 94. Temmick, on migration of birds, 28^^. Tennent, Sir E., on elephants feigning death, 305, Temperature, sense of, 95-8. Terrier. See Dog. Terror, in animals, 345. Thirst, sense of, 95. Thompson, on imagination in dogs, 146, and other animals, 151 ; on crocodiles dreaming, 149 ; on horses becoming attaclied to dogs and cats, 184 ; on effects of domestication in modifying instinct, 242 ; on a monkey feign- ing death, 311-12. Thompson, Rev. L., on bees eating moths, 245. Thomson, Allen, on instinct of young chickens, 163 ; on instinct of scorpion to commit suicide, 278 ; on benevolence shown by a cat, 346. Thrush, sense of hearing in the, 92. Thwaites, on a breed of ducks showing fear of "water, 188. Tiarojjsis indicans, sense of touch in, 83. Tiaropsis polydiademata, sense of sight in, 81-2. Tickling, caused only by gentle stimulation, 52. Touch, sense of, in plants, 49-51, and 55 ; in Medusae, Echinodermata, Mollusca, and Articulata, 56 ; in Yertebrata, 58 ; in Fish, Ampliibia, and Reptiles, 90 ; in Birds, 92 ; in Mammals, 94 ; as origin of all special senses, 103-4 ; reaction-time of, 132. Trevellian, on mistaken instinct of a sphinx moth, ]67. Trichoptera, instincts of, 191. Tricks of manner inherited, 181, 185-6 ; displayed by individuals, 181-2. Turkeys, instincts of young, 164, 175. Turtle, migration of the, 286. u. UUoa, on dogs not barking in Juan Fernandez, 250. Venus' Fly-trap. See Dionfpa. Venn, on association of ideas by talking birds, 124. Villiers, De, on instincts of the processional caterpillar, 342. 404 MENTAL EVOLUTION IN ANIMALS. Vintschgau, on reaction-time for taste, 133. Virchow, Professor, on distinction between instinct and reason, 160. Volition, physiological aspect of, 53, 352. Vorticella, chased by another infusorium, 81. Vulture, sense of sight of the, 91 ; of smell, 92. w. Wallace, A. E., on erolution of Man, 9 ; on changed instincts of nidification, 212 ; on nidification as due to imitation, 225-6 ; on migration of the lemming, 283 ; on migration, 288 ; on homing faculty, 291. Water-hen, aquatic instincts of the, 253. Water-owzel, changed instincts of the, 254. Waterton, on instincts of young pheasants, 232 ; on instincts of crossetl ducks, 199. Wasps. See Insects. Weasel, feigning death, 307. Weber, on sense of temperature, 96. Wedderburn, Sn* D., on carnivorous habits of wasps, 245. Weir, on Wallace's theory of nidification as influenced by imitation, 226. Weissenborne, on a migration of dragon-flies, 286. Whately, Archbishop, on cattle sucking bones, 247 ; on the functions of the syllogism, 337. White, C. Coral, on a fox feigning death, 314-15. White, the Eev. Gr., on loss of taste for flesh shown by dogs of China, 233 ; on a leveret reared by a cat, 217. Widgeon, attachment of a, to a peacock, 183-4. Wildness, acquired instinct of, 195-7, Wilks, Dr., on association of ideas by talking birds, 12 i. Will. See Volition. Willoughby, on instincts of the capon, 171. Wilson, on improved nest-building by the Baltimore Oriel, 210. Wilson, Sir J., on instincts of a tamed dingo dog, 232. Wittich, von, on reaction-time for taste, 133. Wolf, feigning death, 304 ; imagination in the, 147. Wolff, Madame de Meuron, on a migration of butterflies, 285. Wolvei'ine, understanding of mechanism by the, 351. Woodcock, wildness and tameness of the, 197; carrying young, 211. Wood-louse, feigning death, 309. Wood-pecker, changed instincts of the G-round, 254 ; peculiar instincts of the Californian in storing acorns, 255. Worms. See Annelida. Wrangle, on geese feigning death, 303-4. Wren, local variation of instinct of the, 210, 246 ; variation in nest-building of the golden-crested, 182. Wuiidt, on analogy between conscious and unconscious memory, 114. Y. Yarrel, on Birds, 222, 247. Youatt, on the Dog, 150, 198, 241 ; on the Sheep, 224, 227. z. Zinken, Dr., on mistaken instinct of flies, 167. INDEX. 405 INDEX TO Mr. DARWIN'S POSTHUMOUS ESSAY. Alison, on instinct, 357, 367, 370, 375. Ambli/)-hi/nc7iu.s. The Principles of Colliery Ventilation. Second Edition, greatly enlarged, crown Svo. cloth, price '^s. 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