Boston Medical Library 8 The Fenway Digitized by tine Internet Arciiive in 2010 with funding from Open Knowledge Commons and Harvard Medical School http://www.archive.org/details/mentalevolutioni1884roma MEIN'TAL EYOLUTIO^ IK AI^IMALS. MENTAL EVOLUTION IN ANIMALS. BY ^ GEOEGE JOHN EOMANES, M.A., LL.D., F.E.S., ATJTHOE OF " ANIMAL INTELLIGENCE." POSTHUMOUS ESSAY ON mSTINCT. BY OHAELES DARWm, M.A., LL.D., F.E.S. NEW YORK: D. APPLETON AND COMPANY, 1, 3, AND 5 BOND STEEET. 1884. /^^^r^ PEE FACE. It will be observed that the title of this volume is " Mental Evolution in Animals." The reasons which have led me to depart from my intention (as expressed in the Preface of " Animal Intelligence") to devote the present essay to mental evolution in man as well as in animals, are given in the introductory chapter. It may appear that in the following pages a somewhat disproportionate amount of space has been allotted to the treatment of Instinct; but, looking to the confusion which prevails with reference to this important branch of psychology in the writings of our leading authorities, I have deemed it desirable to consider the subject exhaustively. It is, I think, desirable briefly to explain the circum- stances under which I have been enabled to produce so much hitherto unpublished material from the MSS of the late Mr. Darwin, and also to state the extent to which I have availed myself of such of this unpublished material as came into my hands. As I have already explained, in the Preface of " Animal Intelligence," Mr. Darwin himself gave me all his MSS relating to psychological subjects, with the request that I should publish any parts of them that I chose in my works on Mental Evolution. But after his death I felt that the cir- cumstances with reference to this kind offer were changed, and that I should scarcely be justified in appropriating so much material, the value of which had become enhanced. I therefore pubUshed at the Linnean Society, and with the consent of Mr. Darwin's family, as much of this material as 2 PREFACE. could be piiblislied in a consecutive form ; this is the chapter which was intended for the " Origin of Species," and which, for the sake of reference, I have added as an Appendix to my present work. For the rest, the numerous disjointed para- graphs and notes which I found among the MSS I have woven into the text of this book, feeling on the one hand that they were not so well suited to appear as a string of disconnected passages, and on the other hand that it was desirable to publish them somewhere. I have gone through all the MSS carefully, and have arranged so as to introduce every passage in them of any importance which I find to have been hitherto unpublished. In no case have I found any reason to suppress a passage, so that the quotations which I have given may be collectively regarded as a full supple- mentary publication of all that Mr. Darwin has written in the domain of psychology. In order to facilitate reference, I have given in the Index, under Mr. Darwin's name, the numbers of all the pages in this work where the quotations in question occur. 18, CoHNWAii Teebace, Eegent's Park, London, N.W., November, 1883. CONTENTS. Peefacb Inteoductiok Chaptee I. IL » in. „ IV. „ VI. „ VII. ., VIII. „ IX. X. „ XI. „ XII. „ XIII. „ XIV. „ XV. „ XVI. „ XVII. The Ckiterion of Mind The Stkuctube and Functions of Neete-Tissue The Physical Basis of Mind The Root-peinciples of Mind Explanation op the Diageam Consciousness . . Sensation Pleasuees and Pains, Memoey, aed Association OP Ideas PAGE 1 5 15 24 31 47 63 70 78 105 125 142 Peeception Imagination . . . . .... Instinct .. .. .. .. .. .. •• 159 .. 177 Instinct (continued). Origin and Development of Instincts Instinct (continued). Blended Origin, or Plasticity of Instinct. . . . 200 Instinct (continued) . Modes in which Intelligence determines the Varia- tion of Instinct in Definite Lines . . • . 19 Instinct (continued) . Domestication - .. .. .. «. •• 230 Instinct (continued). Local and Specific Varieties of Instinct . . . . 243 Instinct (continued). Examination of the Theories of other Writers on the Evolution of Instinct, with a General Sum- mary of the Theory here Set Forth . . . . 256 CONTENTS. Chapter XVIII. Instinct (continued). Cases of Special Difficulty with Eegard to the Foregoing Theory of the Origin and Develop- ment of Instincts . . . . . . . . 273 „ XIX. Keason 318 „ XX. Animal Emotions, and Summaky of Intel- lectual Facplties . . 341 Appendix •• •• 353 P.O.„CT..,E-0T,0..LO...L0.-.„. Emotion, Will, Intellect. I.T,LL.e''T°"°"ci" "of-SHT T„. P-.OHOLOO.C.L P.--".. 50 ;o w 50 49 4S 49 Co\ q 49 49 4S \A /if 48 48 47 47 v\ /f/ 47 47 46 40 \vA •^ 40 46 45 4,1 0 Ay 45 45 44 44 ^ 44 44 43 43 y-A n 'i' 43 43 42 42 \>\ \\ /v 42 42 4" 41 \ A /i 1 41 4' 40 40 Y \ \\ 1^1 40 40 J9 39 \=.\ " \J\ /»/ 39 39 3« 38 ^ \ \ A"*/ 3S 3S 3> 37 \\ (\ \\ ifi 1 / ) 37 37 36 Si" y. / _^^ \\ x-^y^^"' ^/ 36 36 J5 35 ysJ "'^ \ \ \^^ / /o y 3.5 34 34 yyy t\ \' i /''/ 34 34 33 33 V\ \"'\ / / 33 32 32 f^y a V\ \~ \ / y 32 ;, 3" 3" ^ \-\ \" \/, / 31 31 30 \ \ k \'\ \* -^ / 30 30 29 \ \ \ \ ) '0/ 29 Shame, Rtmorsc, Li.c.ufnlnu.. L.ul.cr^,,.. 2S v\. V \ / » / ^^ 2S Indefinite morality. Arthropud Apes and Dog ,5 month. 28 27 \°\ V\/v 0 27 Use of tools. <• l.lOn[^s — 26 VA \y / /, V 26 Understanding ol mechanisms. lomooil,,. 26 Emuhlioi., Pndc, R«m,n,c,.i, ^Eahi.ic lov= of o.n,.m™i, 1 error. 25 \.\ V ( /'/ 25 Recognition of P.cturra. Undctanding of »ord.. Dreanung. Birds. 8 monlh- ,; 24 \^\ \ \ /^•/ 24 Communication of ideas. Hymenoptefj S monihs — — 23 21 \ \ \-\ /v Recognition of per«,ns. | ^ ^^^^^ . ^7^ -£i- AITcci.on. \ \ \ \ / V 22 Reason. \ ^^^^^ _-_ _il_ Jealousy. Anger. Play. 21 \ \ A 7 21 Association by similarity Fish and Balnichu. .-week. —;^ -° Parental alTection. Social fecliogs, Se;(ual soleciion. Pugnacity. Indtiittry. Curiosity. 20 ""■^^^^J^iiiai'o* „;r;:-^ — -a v 20 Recognition of offspring. Secondary mstinrts. luMcts ^d Sp.deri. .o,.eel,. '^ IS ■9 ~~~~-~-~^ ^c^^ ) V ^^ t>^ ■9 Association by contiguity. MolLsca. ,weel.. 19 J2^ 17 ^^--^ — I.^ — ^< t^"" — 17 ITeml'^ '"""'" E~ 3 weeks. iS '^ 16 Bmh. -i^ I^ ^ s ^^^ 15 Corlenierata. "7?" uil. 14 t ^^^^ . Nervous .idjustmenls. '->, '' ■ '- i C ■1 „„!,„„„,„ ,„,.„,|, 1^ " n is k. ,, Partly nervous sdjustracnts. probably Cileniersla jj 9 ■ . '° -*-^ ■ 0 perhaps es„„a. . Embryo. ~IO^ S ^S~ 1 kf\ 9 S 9 5 7 S?t^ 7 6 Non. nervous adjustments. ^ 7 _5_ ^ 3 ] i X C 1 T A B M ~r Proioplasui.c movements. Protoplasmtc organ.sms. O.um Jnd 3 INTEODUCTION. In tlie family of tlie sciences Comparative Psychology may claim nearest kinship with Comparative Anatomy ; for just as the latter aims at a scientific comparison of the bodily structures of organisms, so the former aims at a similar com- parison of their mental structures.* Moreover, in the one science as in the other, the first object is to analyze all the complex structures with which each has respectively to deal. "When this analysis, or dissection, has been completed for as great a number of cases as circumstances permit, the next object is to compare with one another all the structures which have been thus analyzed ; and, lastly, the results of such comparison supply, in each case alike, the basis for the final object of these sciences, which is that of classifying, with reference to these results, all the structures which have been thus examined. In actual research these three objects are prosecuted, not successively, but simultaneously. Thus it is not necessary in either case that the final object — that of classification — should wait for its commencement upon the completion of the dissection or analysis of every organism or every mental structure that is to be found upon the earth. On the con- trary, the comparison in each case begins with the facts that are first found to be comparable, and is afterwards pro- gressively extended as knowledge of additional facts becomes more extensive. Now each of the three objects which I have named affords * The word " structure " is used in a metaphorical sense when applied to mind, but the usage is convenient. 6 INTRODUCTION. in its pursuit many and varied points of interest, whicli are quite distinct from any interest tliat may be felt in the attain- ment of the ultimate end — Classification. Thus, for example, the study of the human hand as a mechanism has an interest apart from all considerations touching the comparison of its structure with that of the corresponding member in other animals ; and, similarly, the study of the psychological facul- ties in any given animal has an interest apart from all con- siderations touching their comparison with the corresponding faculties in other animals. Again, just as the comparison of separate bodily members throughout the animal series has an interest apart from any question concerning the classification of animal bodies to which such comparison may ultimately lead, so the study of separate psychical faculties throughout the animal series (including, of course, mankind) has an interest quite distinct from any question concerning the classification of animal minds to which such comparison may ultimately lead. Lastly, around and outside all the objects of these sciences as such, there lies the broad expanse of General Thought, into which these sciences, in all their stages, throw out branches of inference. It is needless to say that of late years the interest with which the unpre- cedented growth of these branches is watched has become so universal and intense, that it may be said largely to have absorbed the more exclusive sources of interest which I have enumerated. With the view of furthering these various lines of interest, I have undertaken a somewhat laborious enquiry, part of which has already been published in the International Scientific Series, and a further instalment of which is con- tained in the present volume. The two works, therefore, " Animal Intelligence " and " Mental Evolution in Animals," although published separately, are really one ; and they have been divided only for the following reasons. In the first place, to have produced the whole as one volume would have INTKODUCTION. 7 been to present a book, if not of inconvenient bulk, at least quite out of keeping with the size of all the other books in the same series. Moreover, the subject-matter of each work, although intimately related to that of the other, is never- theless quite distinct. The first is a compendium of facts relating to Animal Intelligence, which, while necessary as a basis for the present essay, is in itself a separate and distinct treatise, intended to meet the interest already alluded to as attaching to this subject for its own sake ; while the second treatise, although based upon the former, has to deal with a wider range of subject-matter. It is evident that, in entering upon this wider field, I shall frequently have to quit the narrower limits of direct obser- vation within which my former work was confined ; and it is chiefly because I think it desirable clearly to distinguish between the objects of Comparative Psychology as a science, and any inferences or doctrines which may be connected with its study, that I have made so complete a partition of the facts of animal intelligence from the theories which I believe these facts to justify- So much, then, for the reasons which have led to the form of these essays, and the relations which I intend the one to bear to the other. I may now say a few words to indicate the structure and scope of the present essay. Every discussion must rest on some basis of assumption ; every thesis must have some hypothesis. The hypothesis which I shall take is that of the truth of the general theory of Evolution : I shall assume the truth of this theory so far as I feel that all competent persons of the present day will be prepared to allow me. I must therefore first define what degree of latitude I suppose to be thus conceded. I take it for granted, then, that all my readers accept the doctrine of Organic Evolution, or the belief that all species of plants and animals have had a derivative mode of origin by way of natural descent ; and, moreover, that one great law or 8 INTRODUCTION. method of the process has been natural selection, or survival of the fittest. If anyone grants this much, I further assume that he must concede to me the fact, as distinguished from tlie manner and history of Mental Evolution, throughout the whole range of the animal kingdom, with the exception of man. I assume this because I hold that if the doctrine of Organic Evolution is accepted, it carries with it, as a necessary corollary, the doctrine of Mental Evolution, at all events as far as the brute creation is concerned. For throughout the brute creation, from wholly unintelligent animals to the most highly intelligent, we can trace one continuous gradation ; so that if we already believe that all specific forms of animal life have had a derivative origin, we cannot refuse to believe that all the mental faculties which these various forms present must likewise have had a derivative origin. And, as a matter of fact, we do not find anyone so unreasonable as to maintain, or even to suggest, that if the evidimce of Organic Evolution is accepted, the evidence of Mental Evolution, within the limits which I have named, can consistently be rejected. The one body of evidence therefore serves as a pedestal to the other, such that in the absence of the former the latter would have no locus standi (for no one could well dream of Mental Evolution were it not for the evidence of Organic Evolution, or of the transmutation of species) ; while the presence of the former irresistibly suggests the necessity of the latter, as the logical structure for the support of which the pedestal is what it is. It will be observed that in this statement of the case I have expressly excluded the psychology of man, as being a department of comparative psychology with reference to which I am not entitled to assume the principles of Evolu- tion. It seems needless to give my reasons for this exclusion For it is notorious tliat from the hour when Mr. Darwin and Mr. Wallace simultaneously propounded the theory which has exerted so enormous an influence on the thought of the INTRODUCTION". 9 present century, the difference between tlie views of these two joint originators of the theory has since been shared by the ever-increasing host of their disciples. We all know what that difference is. We all know that while Mr. Darwin believed the facts of human psychology to admit of being explained by the general laws of Evolution, Mr. Wallace does not believe these facts to admit of being thus explained. Therefore, while the followers of Mr. Darwin maintain that all organisms whatsover are alike products of a natural genesis, the followers of Mr. Wallace maintain that a distinct exception must be made to this general atement in the case of the human organism ; or at all events in the case of the human mind. Thus it is that the great school of evolutionists is divided into two sects ; according to one the mind of man has been slowly evolved from lower types of psychical exist- ence, and according to the other the mind of man, not having been thus evolved, stands apart, siti generis, from all other types of such existence. Now assuredly we have here a most important issue, and as it is one the discussion of which will constitute a large element of my work, it is perhaps desirable that I should state at the outset the manner in which I propose to deal with it. The question, then, as to whether or not human intelli- gence has been evolved from animal intelligence can only be dealt with scientifically by comparing the one with the other, in order to ascertain the points wherein they agree and the points wherein they differ. Now there can be no doubt that when this is done, the difference between the mental faculties of the most intelligent animal and the mental faculties of the lowest savage is seen to be so vast, that the hypothesis of their being so nearly allied as Mr. Darwin's teaching implies, appears at first sight absurd. And, indeed, it is not until we have become convinced that the theory of Evolution can alone afford an explanation of the facts of human anatomy, 10 INTEODUCTION. that we are prepared to seek for a similar explanation of the facts of human psychology. But wide as is the difference between the mind of a man and the mind of a brute, we must remember that the question is one, not as to degree, but as to kind ; and therefore that our task, as serious enquirers after truth, is calmly and honestly to examine the character of the diiierence which is presented, in order to determine whether it is really beyond the bounds of rational credibility that the enormous interval which now separates these two divisions of mind can ever have been bridged over, by numberless inter- mediate gradations, during the untold ages of the past. AVhile writing the first chapters of the present volume, I intended that the latter half of it should be devoted to a con- sideration of this question, and therefore in " Animal Intelli- gence" I said that such would be the case. But as the work proceeded it soon became evident that a full treat- ment of this question would require more space than could be allowed in a single volume, without seriously curtailing both the consideration of this question itself and also that of Mental Evolution, as this is exhibited in the animal kingdom. I therefore determined on restricting the present essay to a consideration of Mental Evolution in Animals, and on reserv- ing for subsequent publication all the material which I have collected bearing on Mental Evolution in Man. I cannot yet say how long it will be before I can feel that I am justified in publishing my researches concerning this branch of my subject; for the more that I have investigated it, the more have I found that it grows, as it were, in three dimensions — in depth, width, and complexity. But at whatever time I shall be able to publiaJi the third and final instalment of my work, it will of course rest upon the basis supplied by the present essay, as this rests upon the basis supplied by the previous one. It being understood, then, that the present essay is restricted to a consideration of Mental Evolution in Animals INTEODUCTION, 11 I should like to have it also understood that it is further restricted to the psychology as distinguished from the philo- sophy of the subject. In a short and independent essay, published elsewhere,* I have already stated my views con- cerning the more important questions of philosophy into which the subject-matter of psychology is so apt to dip ; but here it is only needful to emphasize the fact that these two strata of thought, although assuredly in juxtaposition, are no less assuredly distinct. My present enquiry belongs only to the upper stratum, or to the science of psychology as dis- tinguished from any theory of knowledge. I am in no wise concerned with " the transition from the object known to the knowing subject," and therefore I am in no wise concerned with any of the philosophical theories which have been pro- pounded upon this matter. In other words, I have every- where to regard mind as an object and mental modifications as phenomena ; therefore I have throughout to investigate the process of Mental Evolution by what is now generally and aptly termed the historical method. I cannot too strongly impress upon the memory of those who from previous reading are able to appreciate the importance of the distinction, that I thus intend everywhere to remain within the borders of psychology, and nowhere to trespass upon the grounds of philosophy. On entering so wide a field of enquiry as that whose limits I have now indicated, it is indispensable to the continuity of advance that we should be prepared, where needful, to supple- ment observation with hypothesis. It therefore seems desira- ble to conclude this Introduction with a few words both to explain and to justify the method which in this matter I intend to follow. It has already been stated that the sole object of this work is that of tracing, in as scientific a manner as possible, the probable history of Mental Evolution, and therefore, of * Nineteenth Century, December, 1S82. 12 INTRODUCTION. course, of enquiring into the causes which have determined it. So far as observation is available to guide us in tliis enquiry, I shall resort to no other assistance. Where, however, from the nature of the case, observation fails us, I shall proceed to inference. But though I shall use this method as sparingly as possible, I am aware that criticism will often find valid ground to object — ' It is all very well to map out the sup- posed genesis of the various mental faculties in this way, but we require some definite experimental or historical proof that the genesis in question actually did take place in the order and manner that you infer.' Now, in answer to this objection, I have only to say that no one can have a more lively appreciation than myself of the supreme importance of experimental or historical veri- fication, in all cases where the possibility of such verification is attainable. But in cases where such verification is not attainable, what are we to do ? "We may clearly do either of two things. We may either neglect to investigate the sub- ject at all, or we may Jo our best to investigate it by employ- ing the only means of investigation which are at our disposal. Of these two courses there can be no doubt which is the one that the scientific spirit prompts. The true scientific spirit desires to examine everything, and if in any case it is refused the best class of instruments wherewith to conduct the examination, it will adopt the next best that are available. In such cases science clearly cannot be forwarded by neglect- ing to use these instruments, while her cause may be greatly advanced by using them with care. This is proved by the fact that, in the science of psychology, nearly all the con- siderable advances which have been made, have been made, not by experiment, but by observing mental phenomena and reasoning from these phenomena deductively. In such cases, therefore, the true scientific spirit prompts us, not to throw away deductive reasoning where it is so frequently the only INTRODUCTION. 13 instrument available, but rather to carry it with us, and to use it as not abusing it. And this, as I have said, is what I shall endeavour to do. No one can regret more than myself that the most interesting of all regions of scientific enquiry should happen to be the one in which experiment, or inductive verification, is least of all applicable ; but such being the case, we must take the case as we find it, use deductive reasoning where we clearly see that it is the only instrument available, but use it to as limited an extent as the nature of our subject permits. MENTAL EVOLUTION IN ANIMALS. CHAPTER I. The Ceiterion of Mind. The subject of our enquiry being Mental Evolution, it is desirable to begin by understanding clearly what we mean by Mind,* and then defining the conditions under which known Mind is invariably found to occur. In this chapter, therefore, I shall deal with what I take to be the Criterion of Mind, and shall then pass on in the next chapter to a consideration of the objective conditions under which alone Mind is observed to exist. It is obvious, then, to start with, that by Mind we may mean two very different things, according as we contemplate it in our own individual selves, or as manifested by other beings. Eor if I contemplate my own mind, I have an imme- diate cognizance of a certain flow of thoughts and feelings, which are the most ultimate things — and, indeed, the only things — of which I am cognizant. But if I contemplate Mind in other persons or organisms, I can have no such immediate cognizance of their thoughts and feelings ; I can only infer the existence of such thoughts and feelings from the activities of the persons or organisms which appear to manifest them. Thus it is that by Mind we may mean either that which is subjective or that wliich is objective. Now throughout the present work we shall have to consider Mind as an object ; and therefore it is well to remember that our only instrument of analysis is the observation of activities * It was necessary in nay -work on Animal Intelligence briefly to touch on this question ; therefore the parts of the analysis which are common to the two works I shall render as much as possible in the same words. 16 MENTAL EVOLUTION IN ANIMALS. which we infer to be prompted by, or associated with, mental antecedents or accompaniments analogous to those of which we are directly conscious in our own subjective experience. That is to say, starting from what I know subjectively of the operations of my own individual mind, and of the activi- ties which in my own organism these operations seem to prompt, I proceed by analogy to infer from the observable activities displayed by other organisms, the fact that certain mental operations underlie or accompany these activities. From this statement of the case it will be apparent that our knowledge of mental activities in any organism other than our own is neither subjective nor objective. That it is not subjective I need not wait to show. That it is not objective may be rendered obvious by a few moments' reflec- tion. For it is evident that mental activities in other organisms can never be to us objects of direct knowledge ; as I have just said, we can only infer their existence from the objective sources supplied by observable activities of such organisms. Therefore all our knowledge of mental activities other than our own really consists of an inferential inter- pretation of bodily activities — this interpretation being founded on our subjective knowledge of our own mental activities. By inference we project, as it were, the known patterns of our own mental chromograph on what is to us the otherwise blank screen of another mind ; and our only knowledge of the processes there taking place is really due to such a projection of our own subjectively. This matter has been well and clearly presented by the late Professor Clifford, who has coined the exceedingly appropriate term eject (in contradistinction to subject and object), whereby to designate the distinctive character of a mind (or mental pro- cess) other than our own in its relation to our own. I shall therefore adopt this convenient term, and speak of all our possible knowledge of other minds as ejective. Now in this necessarily ejective method of enquiry, what is the kind of activities that we are entitled to regard as indicative of Mind ? I certainly do not so regard the flowing of a river or the blowing of a wind. Why ? First, because the subjects are too remote in kind from my own organism to admit of my drawing any reasonable analogy between them and it ; and, secondly, because the activities which they present are invariably of the same kind under the same cir- THE CEITERION OF MIND. 17 cmnstances : they therefore offer no evidence of that which I deem the distinctive character of my own mind as such — Consciousness. In other words, two conditions require to be satisfied before we even begin to imagine that observable activities are indicative of mind ; the activities must be dis- played by a living organism, and they must be of a kind to suggest the presence of consciousness. What then is to be taken as the criterion of consciousness ? Subjectively., no criterion is either needful or possible ; for to me, individually, nothing can be more ultimate than my own consciousness, and, therefore, my consciousness cannot admit of any criterion having a claim to a higher certainty. But, ejectively, some such criterion is required, and as my consciousness cannot come within the territory of a foreign consciousness, I can only appreciate the latter through the agency of ambassadors — these ambassadors being, as I have now so frequently said, the observable activities of an organism. The next question, therefore, is. What activities of an organism are to be taken as indicative of consciousness ? The answer that comes most readily is, — All activities that are indicative of Choice ; wherever we see a living organism apparently exerting inten- tional choice, we may infer that it is conscious choice, and, therefore, that the organism has a mind. But physiology shows that this answer will not do ; for, while not disputing whether there is any mind without the power of conscious choice, physiology, as we shall see in the next chapter, is very firm in denying that all apparent choice is due to mind. The host of reflex actions is arrayed against the proposition, and, in view of such non-mental, though apparently intentional adjustments, we find the necessity for some test of the choice- element as real or fictitious. The only test we have is to ask whether the adjustments displayed are invariably the same under the same circumstances of stimulation. The only dis- tinction between adjustive movements due to reflex action, and adjustive movements accompanied by mental perception, consists in the former depending on inherited mechanisms within the nervous system being so constructed as to effect particular adjustive movements in response to particular stimulations, while the latter are independent of any such inherited adjustment of special mechanisms to the exigencies of special circumstances. Eeflex actions, imder the influence of their appropriate stimuli, may be compared to the actions 18 MENTAL EVOLUTION IN ANIMALS. of a machine under the manipulations of an operator : when certain springs of action are touched by certain stimuli, the whole machine is thrown into appropriate action ; there is no room for choice, there is no room for uncertainty; but, as surely as any of these inherited mechanisms is affected by the stimulus with reference to which it has been constructed to act, so surely will it act in precisely the same way as it always has acted. But the case with conscious mental adjust- ment is quite different. For, without going into the question concerning the relation of Body and Mind, or waiting to ask whether cases of mental adjustment are not really quite as mechanical in the sense of being the necessary result or correlative of a chain of psychical sequences due to a physical stimulation, it is enough to point to the variable and incalcu- lable character of mental adjustments as distinguished from the constant and foreseeable character of reflex adjustments. All, in fact, that in an objective sense we can mean by a mental adjustment, is an adjustment of a kind that has not been definitely fixed by heredity as the only adjustment possible in the given circumstances of stimulation. Tor, were there no alternative of adjustment, the case, in an animal at least, would be indistinguishable from one of reflex action. It is, then, adaptive action by a living organism in cases where the inherited machinery of the nervous system does not furnish data for our prevision of what the adaptive action must necessarily be — it is only in such cases that we recog- nize the element of mind. In other words, ejectively con- sidered, the distinctive element of mind is consciousness, the test of consciousness is the presence of choice, and the evidence of choice is the antecedent uncertainty of adjustive action between two or more alternatives. To this analysis it is, however, needful to add that, although our only criterion of mind is antecedent uncertainty of adjustive action, it does not follow that all adjustive action in which mind is con- cerned should be of an antecedently uncertain character ; or, which is the same thing, that because some such action may be of an antecedently certain character, we should on this account regard it as non-mental. Many adjustive actions which we recognize as mental are, nevertheless, seen before- hand to be, under the given circumstances, inevitable ; but analysis would show that such is only the case when we have in view agents whom we already, and from independent evidence;, regard as mental. THE CRITERION OF MIND. 19 In positing the evidence of Choice as my objective (or ejective) criterion of Mind, I do not think it necessary to enter into any elaborate analysis of what constitutes this evidence. In a subsequent chapter I shall treat fully of what I call the physiology or objective aspect of choice; and then it will be seen that from the gradual manner in which choice, or the mind-element, arises, it is not practically possible to draw a definite line of demarcation between choosing and non-choosing agents. Therefore, at this stage of the enquiry I prefer to rest in the ordinary acceptation of the term, as implying a distinction which common sense has always drawn, and probably always will draw, between mental and non-mental agents. It cannot be correctly said that a river chooses the course of its flow, or that the earth chooses an ellipse wherein to revolve round the sun. And similarly, however ccmiplex the operations may be of an agent recog- nized as non-mental — such, for instance, as those of a calcu- lating machine — or however impossible it may be to predict the result of its actions, we never say that such operations or actions are due to choice ; we reserve this term for operations or actions, however simple and however easily the result may be foreseen, which are performed, either by agents who in virtue of the non-mechanical nature of these actions prove themselves to be mental, or by agents already recognized as mental — i.e., by agents who have already proved themselves to be mental by performing other actions of such a non- mechanical or unforeseeable nature as we feel assured can only be attributed to choice. And there can be no reasonable doubt that this common-sense distinction between choosing and non-choosing agents is a valid one. Although it may be difficult or impossible, in particular cases, to decide to which of the two categories this or that being should be assigned, this difficulty does not affect the validity of the classification — any more, for instance, than the difficulty of deciding whether Limulus should be classified with the crabs or with the scorpions affects the validity of the classification which marks off the group Crustacea from the group Arachnida. The point is that, notwithstanding special difficulties in assigning this or that being to one or the other class, the psychological classification which I advocate resembles the zoological classification which I have cited ; it is a valid classification, inasmuch as it recognizes a distinction where 20 MENTAL EVOLUTION IN ANIMALS. there is certainly something to distinguish. For even if we take the most mechanical view of mental processes that is possible, and suppose that conscious intelligence plays no part whatever in determining action, there still remains the fact that such conscious intelligence exists, and that prior to certain actions it is always affected in certain ways. There- fore, even if we suppose that the state of things is, so to speak, accidental, and that the actions in question would always be performed in precisely the same way whether or not they were thus connected with consciousness, it would still remain desirable, for scientific purposes, that a marked distinction should be drawn between cases of activity that proceed without, and those that proceed with this remarkable association with consciousness. As the phenomena of sub- jectivity are facts at any rate no less real than those of objectivity, if it is found that some of the latter are invariably and faithfully mirrored in those of the former, such pheno- mena, for this reason alone, deserve to be placed in a distinct scientific category, even though it were proved that the mirror of subjectivity might be removed without affecting any of the phenomena of objectivity. Without, therefore, entertaining the question as to the connexion between Body and Mind, it is enough to say that under any view concerning the nature of this connexion, we are justified in drawing a distinction between activities which are accompanied by feelings, and activities which, so far as we can see, are not so accompanied. If this is allowed, there seems to be no term better fitted to convey the distinction than the term Choice ; agents that are able to choose their actions are agents that are able to feel the stimuli which determine the choice. Such being our Criterion of Mind, it admits of being otherwise stated, and in a more practically applicable manner, in the following words which I quote from " Animal Intelli- gence :" — " It is, then, adaptive action by a living organism in cases where the inlierited machinery of the nervous system does not furnish data for our prevision of what the adaptive action must necessarily be — it is only here that we recognize the objective evidence of mind. The criterion of mind, therefore, which I propose, and to which I shall adhere throughout the present volume, is as follows : — Does the organism learn to make new adjustments, or to modify old THE CRITERTON OF MIND. 21 ones, in accordance with the results of its own individual experience ? If it does so, the fact cannot be merely due to reflex action in the sense above described ; for it is impossible that heredity can have provided in advance for innovations upon or alterations of its machinery during the lifetime of a particular individual." Two points have to be observed with regard to this criterion, in whichever verbal form we may choose to express it. The first is tliat it is not rigidly exclusive either, on the one hand, of a possibly mental character in apparently non- mental adjustments, or, conversely, of a possibly non-mental character in apparently mental adjustments. For it is certain that failure to learn by individual experience is not always conclusive evidence against the existence of mind; such failure may arise merely from an imperfection of memroy, or from there not being enough of the mind-element present to make the adjustments needful to meet the novel circum- stances. Conversely, it is no less certain that some parts of our own nervous system, which are not concerned in the phenomena of consciousness, are nevertheless able in some measure to learn by individual experience. The nervous apparatus of the stomach, for instance, is able in so con- siderable a degree to adapt the movements of that organ to the requirements of its individual experience, that were the organ an organism we might be in danger of regarding it as dimly intelligent. Still there is no evidence to show that non-mental agents are ever able in any considerable measure thus to simulate the adjustments performed by mental ones ; and therefore our criterion, in its practical appKcation, has rather to be guarded against the opposite danger of denying the presence of mind to agents that are really mental. For, as I observed in " Animal Intelligence," " it is clear that long before mind has advanced sufficiently far in the scale of development to become amenable to the test in question, it has probably begun to dawn as nascent subjectivity. In other words, because a lowly organized animal does not learn by its own individual experience, we may not therefore con- clude that in performing its natural or ancestral adaptations to appropiate stimuli, consciousness, or the mind-element, is wholly absent ; we can only say that this element, if present, reveals no evidence of the fact. But, on the other hand, if a lowly organized animal does learn by its own individual 2 22 MENTAL EVOLUTION IN ANIMALS. experience, we are in possession of the best available evi- dence of conscious memory leading to intentional adaptation. Therefore, our criterion applies to the upper limit of non- mental action, not to the lower limit of mental." Or, again adopting the convenient terminology of Clifford, we must always remember that we can never know the mental states of any mental beings other than ourselves as objects ; we can only know them as ejects, or as ideal projections of our own mental states. And it is from this broad fact of psycho- logy that the difficulty arises in applying our criterion of mind to particular cases — especially among the lower animals. For if the evidence of mind, or of being capable of choice, must thus always be ejective as distinguished from objective, it is clear that the cogency of the evidence must diminish as we recede from minds inferred to be like our own, towards minds inferred to be not so like our own, passing in a gradual series into not-minds. Or, otherwise stated, although the evidence derived from ejects is practically regarded as good in the case of mental organizations inferred to be closely analogous to our own, this evidence clearly ceases to be trust- worthy in the ratio in which the analogy fails : so that when we come to the case of very low animals — where the analogy is least — we feel uncertain whether or not to ascribe to them any ejective existence. But I must again insist that this fact — which springs immediately out of the fundamental isolation of the individual mind — is no argument against my criterion of mind as the best criterion available ; it tends, indeed, to show that no better criterion can be found, for it shows the hopelessness of seeking such. The other point which has to be noted with regard to this criterion is as follows. I again quote from " Animal Intelli- gence :" — " Of course to the sceptic this criterion may appear un- satisfactory, since it depends, not on direct knowledge, but on inference. Here, however, it seems enough to point out, as already observed, that it is the best criterion available ; and, further, that scepticism of this kind is logically bound to deny evidence of mind, not only in the case of the lower animals, but also in that of the higher, and even in that of men other than the sceptic himself. For all objections which could apply to the use of this criterion of mind in the animal kingdom, would apply with equal force to the evidence of any THE CEITEKION OF MI^TD. 23 mind other than that of the individual ohjector. This is obvious, because, as I have already observed, the only evi- dence we can have of objective mind is that which is furnished by objective activities ; and, as the subjective mind can never become assimilated with the objective so as to learn by direct feeling the mental processes which there accompany the objective activities, it is clearly impossible to satisfy any one who may choose to doubt the validity of inference, that in any case, other than his own, mental processes ever do accompany objective activities. " Thus it is that philosophy can supply no demonstrative refutation of idealism, even of the most extravagant form. Common-sense, however, universally feels that analogy is here a safer guide to truth than the sceptical demand for impossible evidence; so that if the objective existence of other organisms and their activities is granted — ^without which postulate comparative psychology, like all the other sciences, would be an unsubstantial dream — common sense will always and without question conclude that the activities of organisms other than our own, when analogous to those activities of our own which we know to be accompanied by certain mental states, are in them accompanied by analogous mental states." ^ 24 MENTAL EVOLUTION IN ANIMALS. CHAPTER II. The Structure and Tunctions of Nerve-Tissue. Having thus arrived at the best available Criterion of Mind considered as an eject, we have now to pass on to the topic which has already been propounded, viz., to a consideration of the objective conditions under which known mind is in- variably found to occur. Mind, then, so far as human experience extends, is only certainly known to occur in association with living organisms, and, still more particularly, in association with a peculiar kind of tissue which does not occur in all organisms, and even in those in which it does occur never constitutes more than an exceedingly small percentage of their bulk. This peculiar tissue, so sparingly distributed through the animal kingdom, and presenting the unique characteristic of being associated with mind, is, of course, the nervous tissue. It therefore devolves upon us, first of all, to contemplate the structure and the functions of this tissue, as far as it is needful for the purposes of our subsequent discussion that these should be clearly understood. Throughout the animal kingdom nerve-tissue is invariably present in all species whose zoological position is not below that of the Hydrozoa. The lowest animals in which it has hitherto been detected are the Medusae, or jelly-fishes, and from them upwards its occurrence is, as I have said, invari- able. Wherever it does occur its fundamental structure is very much the same, so that whether we meet with nerve- tissue in a jelly-fish, an oyster, an insect, a bird, or a man, we have no difficulty in recognizing its structural units as everywhere more or less similar. These structural units are microscopical cells and microscopical fibres. (Figs. 1, 2.) The fibres proceed to and from the cells, so serving to THE STRUCTUEE AND FUNCTIONS OF NERVE-TISSUE. 25 Fig. 1. — Motor Nerve Cells connected by intercellular processes {b, b), and giving origin to outgoing fibres (c, c, c, and a). 4. Multipolar cell containing much pig- ment around nucleus. Diagrammatic. (Vogt.) Fig. 2.— Multipolar Ganglion Cell from anterior grey matter of Spinal Cord of Ox, a, Axis cylinder process ; ft, branched processes, magnified 150 dia- meters. (Deiters.) connect tlie cells with one another, and also with distant parts of the animal body. The function of the fibres is that of conducting stimuli or impressions (represented by mole- cular or invisible movements) to and from the nerve-cells, while the function of the cells is that of originating those of the impressions which are conducted by the fibres outwards. Those of the impressions which are conducted by the fibres inwards, or towards the cells, are originated by stimuli affecting the nerve-fibre in any part of its length ; such stimuli may be contact with other bodies or pressure arising therefrom (mechanical stimuli), sudden elevations of temperature (ther- mal stimuli), molecular changes in the nerve-substance pro- 26 MENTAL EVOLUTION IN ANIMALS. duced by irritants (chemical stimuli), effects of electrical disturbance (electrical stimuli), or lastly, the passage of a molecular disturbance from any other nerve- fibre with which the one in question may be connected. Nerve-cells are usually found collected together in aggre- gates, which are called ganglia, to and from which large bundles of nerve-fibres come and go. These rope-like clusters of nerve-fibres constitute the white threads and strings which we recognize as nerves when we dissect an animal, (See Fig. 3.) The relation of the clusters of fibres to the cluster of cells is now such as to supply the anatomical condition to the performance of a physiological Fig. 3. — Small Sympathetic Ganglion (human) with Multipolar Ceils. Magnified about 400 diameters. (Leydig.) process, which is termed Eeflex Action. If we suppose the left-hand bundle of fibres represented in the woodcut to be prolonged and to terminate in a sensory surface, while the other three bundles, when likewise prolonged, terminate in a group of muscles, then a stimulus falling upon the sensory surface would cause a molecular disturbance to travel along the left-hand or in-going nerve to the ganglion; on reaching the ganglion this disturbance would cause the ganglion to discharge its influence into the right-hand or out- going nerves, which would then conduct this disturbance into the group of muscles and cause them to contract. This pro- cess is called reflex action, because the original stimulus falling upon the sensory surface does not pass in a direct line THE STRUCTURE AND FUNCTIONS OF NERVE-TISSUE. 27 to its destination in the muscles, but passes first to tlie ganglion, and is thence reflected from the sensory surface to the muscles.* This, which at first sight appears a round- about or cumbrous sort of process, is really the most economic that is available. For we must remember the enormous number and complexity of the stimuli to which all the higher animals are perpetually exposed, and the consequent neces- sity that arises for there being some system of co-ordination whereby these innumerable stimuli shall be suitably responded to. And such a system of co-ordination is rendered possible, and actually realized, through this principle of reflex action. For the animal body is so arranged that the innumerable nerve-centres, or ganglia, are all more or less in communica- tion one with another, and so receive messages from all parts of the body, to which they respond by sending appropriate messages down the nerve-trunks supplying the particular groups of muscles which under the given circumstances it is desirable to throw into contraction. In other words, when a stimulus falls upon the external surface of an animal, it is not diffused in a general way throughout the whole body of the animal, so causing general and aimless contractions of all the muscles ; but it passes at once to a nerve-centre, and is there centralized; the stimulus is dealt with in a manner which leads to an appropriate response of the organism to that stimulus. For the nerve-centres which receive the stimulus only reflect it to those particular muscle-groups which it is desirable for the organism, under the circumstances, to throw into action. Thus, to take an example, when a small foreign body, such as a crumb of bread, lodges in the windpipe, the stimulus which it there causes is immediately conveyed to a nerve-centre in the spinal cord, and this nerve- centre then originates, by reflex action, a highly complicated series of muscular movements which we call coughing, and which clearly have for their very special object the expul- sion of the foreign body from a position of danger to the organism. Now it is obvious that so complicated a series of muscular movements could not be performed in the absence of a centralizing mechanism ; and this is only one instance among hundreds of others that might be adduced of * The term, however, is not a happy one, because the process is some- thing more than the reflection of the original stimvilus or molecular disturb- ance ; the ganghon adds a new disturbance. 28 MENTAL EVOLUTION IN ANIMALS. the co-ordinating power which is secured by this principle of reflex action. Of course we may wonder how it is that the nerve-centres, which preside over reflex action, not being endowed with consciousness, know what to do with the stimuli which they receive. The explanation of this, however, is that the ana- tomical arrangement of ganglion and nerves in any particular case is such as to leave no choice or alternative of action, if the apparatus is called into action at all. Thus, to begin at the bottom of the series, in the Medusae the simple ganglia are distributed all round the margin of the animal, and respond by reflex action to the stimuli which are applied at any other part of the surface. This has the effect of increas- ing the rate and the strength of the swimming-movements, and so of enabling the animal to escape from the source of danger. Now, although this is a true reflex action, and has an obvious purpose to serve, it does not involve any co-ordi nation of muscular movements. For the anatomical plan of a jelly-fish is so simple, that all the muscular tissue in the body is spread out in the form of one continuous sheet ; so that the only function which the marginal ganglia have to perform when they are stimulated into reflex action, is that of throwing into contraction one continuous sheet of muscular tissue. Hence we may infer that in its earliest stages reflex action is nothing more than a promiscuous discharge of nervous energy by nerve-cells, when they are excited by a stimulus passing into them from their attached nerve-fibres.* But as animals become more highly organized, and distinct muscles are by degrees set apart for the performance of distinct actions, we can readily understand how particular nerve-centres are likewise by degrees set apart to preside over these distinct actions ; the nervous centres then perform the part of trig- gers to the particular muscular mechanisms over which they preside — triggers which can only be loosened by the recep- tion of stimuli along their own particular lines of communi- cation, or nerves. Thus, for instance, in the star- fish — animals which are somewhat higher in the zoological scale than the jelly-fish, and which have a more highly de\'eloped neuro- muscular system — the ganglia are arranged in a ring round * For a full account of reflex action in Medusaj, see Phil. Trans., Croonian Lecture, 1875 ; also Phil. Trans., 1877 and 1880 THE STRUCTURE AND FUNCTIONS OF NERVE-TISSUE. 29 the bases of the five rays, into which they send, and from which they receive, nerve-fibres ; the ganglia are likewise connected with one another by a pentagonal ring of fibres. Now experiment shows that in this simple, and indeed geo- metrical plan of a nervous system, the constituent parts are able, when isolated by section, to preside over the movements of their respective muscles ; for if a single ray be cut off at its base, it will behave in all respects just like the entire star- fish— crawling away from injury, towards light, up perpen- dicular surfaces, and righting itself when turned upon its back. That is to say, the single nerve-centre at the base of a single separated ray is able to do for that ray what the entire pentagonal ring, or central nervous system, is able to do for the entire animal ; it is for that ray the trigger which, when touched by the advent of a stimulus, throws the mus- cular mechanism into appropriate action. Thus it is evident that each of the five nerve-centres stands in such anatomical relation to the muscles of its own ray, that when certain stimuli fall upon the ray, the process of reflex action leaves no choice of response. The beauty and delicacy of this mechanism is shown when in the unmutilated animal all the nerve-centres are in communication as one compound nerve- centre. For now, if one ray is irritated, all the rays will co-operate in making the animal crawl away from the source of irritation; if two opposite rays are simultaneously irri- tated, the star-fish will crawl away in a direction at right angles to an imaginary line joining the two points of irrita- tion. And, more prettily still, in the globular Echinus, or sea-urchin (which is, anatomically considered, a star-fish whose five rays have become doubled over in the form of an orange, soldered together and calcareous so as to make a rigid box), if two equal stimuli be applied simultaneously at any two points of the globe, the direction of escape will be the diagonal between them ; if a number of points be simul- taneously irritated, one effect neutralizes the other, and the animal rotates upon its vertical axis ; if a continuous zone of injury be made all the way round the equator, the same thing happens ; but if the zone be made wider at one hemisphere than the other, the animal will crawl away from the greatest amount of injury. So that in the Echinoderms the geometrical distribution of the nervous system admits of our making ex- periments in reflex action with very precise quantitative 30 MENTAL EVOLUTION IN ANIMALS. results; we can, as it were, play upon this beautifully adjusted mechanism, so as to produce at will the balancing oi this stimulus against that one — the results, as expressed in the movements of the animal, being so many exemplifica- tions of the mechanical principle of the parallelogram of forces.* As we proceed through the animal series we find nervous systems becoming more and more integrated ; nerve-centres multiply, become larger, and serve to innervate more numerous and more complex groups of muscles. It is, however, need- less for me to devote space to describing this advance of structure, because the subject is one belonging to compara- tive anatomy. It is enough to say that everywhere the nervous machinery is so arranged that, owing to the ana- tomical plan of a nerve-centre with its attached nerves, there is no alternative of action presented to the nerve-centre other than that of co-ordinating the group of muscles over the combined contraction of which it presides. The next question, therefore, which arises is — How are we to explain the fact that the anatomical plan of a ganglion, with its attached nerves, comes to be that which is needed to direct the nervous tremours into the particular channels required ? The following is the theory whereby Mr. Herbert Spencer seeks to answer this question, and in order fully to under- stand it we must begin by noticing the effects of stimulation upon undifferentiated protoplasm. A stimulus, then, applied to homogeneous protoplasm, which is everywhere contractile and nowhere presents nerves, has the effect of giving rise to a visible wave of contraction, which spreads in all directions from the seat of stimulation as from a centre. A nerve, on the other hand, conducts a stimulus without undergoing any contraction, or change of shape. Nerves, then, are func- tionally distinguished from undifferentiated protoplasm by the property of conducting invisible or molecular waves of stimvilation from one part of an organism to another, so establishing physiological continuity between such parts without the necessary passage of visible waves of contraction. Now, beginning with the case of undifterentiated proto- plasm, Mr. Spencer starts from thje fact that every portion of the colloidal mass is equally excitable and equally contrac- * For a full account of these experiments, see Croonian Lecture, Phil. Trans., 188:i. THE STRUCTURE AND FUNCTIONS OF NERVE-TISSUE. 31 tile. But soon after protoplasm begins to assume definite shapes, recognized by us as specific forms of life, some of its parts are habitually exposed to the action of forces different from those to which other of its parts are exposed. Conse- quently, as protoplasm continues to assume more and more varied forms, in some cases it must happen that parts thus peculiarly situated with reference to external forces will be more frequently stimulated to contract than are other parts of the mass. Now in such cases the relative frequency with which waves of stimulation radiate from the more exposed parts, will probably have the effect of creating a sort of polar arrangement of the protoplasmic molecules lying in the line through which these waves pass, and for other reasons also will tend ever more and more to convert these lines into passages offering less and less resistance to the flow of such molecular waves, — i.e., waves of stimulation as distinguished from waves of contraction. And lastly, when lines offering a comparatively low resistance to the passage of molecular impulses have thus been organically established, they must then continue to grow more and more definite by constant use, until eventually they become the habitual channels of communication between the parts of the contractile mass through which they pass. Thus, for instance, if such a line has been established between the points A and B of a con- tractile mass of protoplasm, when a stimulus falls upon A, a molecular wave of stimulation will course through that line to B, so causing the tissue at B to contract — and this even though no wave of contraction has passed through the tissue from A to B. Such is a very meagre epitome of Mr. Spencer's theory, the most vivid conception of which may perhaps be conveyed in a few words by employing his own illustration, viz., that just as water continually widens and deepens the channel through which it flows, so molecular waves of the kind we are considering, by always flowing in the same tissue tracts, tend ever more and more to excavate for them- selves functionally differentiated lines of passage. When such a line of passage becomes fully developed, it is a nerve- fibre, distinguishable as such by the histologist ; but before it arrives at this its completed stage, i.e., before it is observable as a distinct structure, Mr. Spencer calls it a " line of dis- charge."* * A certain amount of experimental verification lias been lent to this 32 MENTAL EVOLUTION IN ANIMALS. Such being the manner in which Mr. Spencer supposes nerve-fibres to be evolved, he further supposes nerve-cells to arise in positions where a crossing or confluence of fibres gives rise to a conflict of molecular disturbances ; but it is unnecessary" for our present purposes to enter upon this more elaborate and less satisfactory part of his theory * All I desire now to point out is the a priori probability that nervous channels become developed where they are required simply from the fact of their being required — that is by use. And this d priori probability derives so much confirma- tion from facts that it is scarcely possible to refrain from accepting it as an answer to the question above propounded, namely, How are we to explain the fact that the anatomical plan of a ganglion with its attached nerves comes to be that which is needed to direct the nervous tremours into the par- ticular channels required ? It is a matter of daily observa- tion that " practice makes perfect," and this only means that the co-ordinations of muscular movement which are presided over by this or that nerve-centre admit of more ready performance the more frequently they have been pre- viously performed — which, in turn, only means that the dis- charges taking place in the nerve-centre travel more and more readily through the channels or nerve-fibres which are being rendered more and more permeable by use. So much, indeed, is this the case, that when an associated muscular theory by my own work on the physiology of nerves in Medusae. For a full account of this, I may refer to a lecture published in the Proceedings of the Royal Institution for 1877, on " Evolution of Nerres." The principal facts are that when physiological continuity of a sheet of neuro-muscular tissue is inteiTupted by overlapping or spiral sections, so that the passage both of visible or muscular waves of contraction and invisible or molecular waves of stimulation are blocked, after a long succession of contraction waves are allowed to break upon the shore of the physiological interruption, they at last begin to force a passage, and very soon this passage becomes perfectly free, so that neither the waves of contraction nor those of stimulation are any longer hindered. Whether in such a case a definite nerve-fibre is de- veloped, or only a " line of discharge," I cannot say ; but most probably the passage is effected tlu-ough previously existing fibres of the plexus which become more functionally developed by their increase of activity. * Less satisfactory, not only because more speculative, but because the whole weight of embryological and histological evidence appears to me to be opposed to the speculation. For the whole weight of this evidence goes to show that nerve-cells are the result of the specialization of epithelial or epi- dermal cells— that is, that they arise, not out of undifferentiated protoplasm, but by way of a further differentiation of a particular kind of already dif- ferentiated tissue, where this is exposed to particular kinds of stimulation. THE STRUCTURE AND FUNCTIONS OF NERVE-TISSUE. 33 movement takes place with sufficient frequency, it cannot by any effort of the will become again dissociated ; as is the case, for instance, with the associated movement of the eyeballs, which does not begin to obtain till some days after birth, but which then soon becomes as closely organized as any of the associated movements in the muscles of the limbs.* And if this is the case even in the life-time of individuals, we can scarcely wonder that in the life-time of species heredity with natural selection should still more completely adapt the anatomical plan of ganglia, with their attached nerves, to the performance of the most useful — i.e., the most habitual — actions. Thus we may see in a general way how such nervous machinery may at last come to be differentiated into specially distributed anatomical structures, which, on account of their special distribution, are adapted to minister only to particular co-ordinations of muscular movements. That is to say, we are thus able to understand the rise and development cf Eeflex Action. * Mr. Darwin called my attention to the following passage in the writinga of Lamarck {Phil. Zool., torn, ii, pp. 318-19) : — " Dans toute action, le fluide des nerfs qui la provoque, subit un mouTement de deplacement qui y donne lieu. Or, lorsque cette action a ete plusieurs fois repetee, il n'est pas douteux que le fluide qui I'a executee, ne se soit fraye une route, qui lui devient alors d'autant plus facile a parcourir, qu'il I'a effectivement plus Bouvant franchie, et qu'il n'ait lui-meme une aptitude plus grand ^ suivre cette route frayee que celles qui le sont moins." 34 MENTAL EVOLUTION IN ANIMALS. CHAPTER III. The Physical Basis of Mind. We have already taken it for granted that Mind has a physical basis in the functions of the nervous system, or that every mental process has a corresponding equivalent in some neural process. I shall next endeavour to show how precise this equivalency is. We have seen that ganglionic action consists of waves of nervous tremours originating in the cells, coursing along the attached fibres to other cells, and there arousing fresh impulses of the same kind. Moreover, we have seen that this coursing of nervous impulses through nervous arcs is not, as it were, promiscuous, but that, owing to the anatomical plan of a ganglion, it takes place in certain determinate directions, so that the result, when expressed in muscular movement, shows the function of a ganglion to be that of centraUzing nervous action, or of directing nervous tremours into definite channels. Lastly, we have seen that this directing or centralizing function of ganglia has probably in all cases been due to the principle of use combined with that of natural selection. Now it is known from experiments on the lower animals, as well as from the effects of cerebral disease in man, that the part of the nervous system in all the Vertebrata which appears to be exclusively concerned in all mental operations, is the so-called " large brain," or cerebral hemispheres. This is the convoluted part of the brain which appears imme- diately below the skull, and is above all the series of ganglia or nerve-centres which occupy the rest of the cerebro-spinal tract. As some at least of the bewildering multitude of cells and fibres which constitute the cerebral hemispheres are in connection with these lower ganglia, there is no doubt that the hemispheres are able to " play down " upon these ganglia as upon so many mechanisms, whose function it is to throw THE PHYSICAL BASIS OF MIND. 35 this and that group of muscles into action. Much light is at present being thrown upon this subject by the researches of Hitzig, Fritsch, Terrier, Goltz, and others ; but we must pass on to consider that function of these great nerve-centres with which we shall henceforth be exclusively concerned, the function, namely, of being associated with the phenomena of Mind. As the cerebral hemispheres pretty closely resemble in their intimate structure ganglia in general, there can be no reasonable doubt that the mode of their operation is substan- tially the same ; and as such operation is here attended with the phenomena of subjectivity, there can be equally little doubt that such phenomena must constitute a sort of obverse reflection of ganglionic action. Looking, then, upon this obverse reflection, can we detect any fundamental principles of mental operation which may reasonably be taken to corre- spond with the fundamental principles of ganglionic opera- tion? The most fundamental principle of mental operation is that of memory, for this is the conditio sine qtid non of all mental life. But memory on its obverse side, or the side of physiology, can only mean that a nervous discharge, having once taken place along a certain route, leaves behind it a molecular change, more or less permanent, such that when another discharge afterwards proceeds along the same route, it finds, as it were, the footprints of its predecessor. And this, as we have seen, is no more than we find to be the case with ganglionic action in general. Even long before move- ments involving muscular co-ordination have been repeated with sufficient frequency to become consolidated into one organized and indissoluble act, they become, in virtue of the principle which I have termed the principle of use, more and more easy to repeat ; in all but in the absence of a mental constituent the nerve-centre concerned remembers the pre- vious occurrence of its own discharges ; these discharges have left behind them an impress upon the structure of the ganglion just the same in kind as that which, when it has taken place in the structure of the cerebral hemispheres, we recognize on its obverse side as an impress of memory. The analogy is much too close to be attributed to accident, for it extends into all details. Thus, a ganglion may forget its previous activity if too long an interval is allowed to elapse 36 MENTAL EVOLUTION IN ANIMALS. between the repetitions of its activity, as every one must know who is in the habit of playing on a musical instrument, or performing any other actions entailing the acquirement of dexterity. It may also be observed that when such is the case the particular activity forgotten by the ganglion may be more easily re-acquired than originally it was acquired, which is just what we find to be the case with mental attainments. As particular illustrations of these facts I may state two or three cases, which will also serve to show of how little importance (on the objective side) is the occurrence of con- sciousness to the memory of a ganglion. Eobert Houdin early in life practised the art of juggling with balls in the air, and after a month's practice was able to keep four balls in the air at once. His neuro-muscular machinery was now so well trained, or remembered so well how to perform the series of actions required, that he could afford to withdraw his attention from the performance to the extent of reading a book without hesitation while keeping up the four balls. Thirty years afterwards, on trying the same experiment, having scarcely once handled the balls between times, he found that he could still read with ease while keeping up three balls ; the ganglia concerned had partly forgotten their work, but on the whole remembered it wonderfully well. Again, Lewes gives the case of a waiter asleep at a coffee-house, with much noise of talking around him, who was instantly aroused by a low cry of " Waiter ;" and Dr. Abercrombie gives the case of a man who had long been in the habit of taking down a repeater watch from the head of his bed to make it strike the last hour, and who was observed to do this when otherwise apparently uncon- scious from a fit of apoplexy. But perhaps the most remark- able of all the cases that can be adduced are the most familiar ones of walking and speaking. When we remember the immense amount of neuro-muscular co-ordination that is required for either of these actions, and the laborious steps by which each of them is first acquired in early childhood, it is indeed astonishing that in after life they come to be per- formed without thought of their performance ; the ganglia concerned have fully learned their work. So much for memory. But memory would be a useless faculty of mind if it did not lay the basis for another, and really the most important principle of subjectivity j I mean THE PHYSICAL BASIS OF MIND. 37 the Association of Ideas. This is the root and branch of the whole structure psychological, and therefore, if mind has a physical basis, we should expect to meet with some very general and essential feature of ganglionic action answering to this very general and essential feature of mental action. And this, beyond question, we do find. For the association of ideas is merely a development of simple memory. A mental impression, image, memory, or idea having once occurred in juxtaposition with another, not only are the two memories remembered, but also the fact of their juxtaposition, so that when one memory or idea is aroused, the other is aroused likewise. Let us, then, look at the matter a little more closely, in order to see how this great principle of psychology may receive its explanation, so far as the collateral principle of physiology is concerned. There can be no doubt that in the complex structure of the cerebral hemispheres one nervous arc {i.e., fibres, cells, and fibres) is connected with another nervous arc, and this with another almost ad infinitum ; and there can be equally little doubt that processes of thought are accompanied by nervous discharges taking place, now in this arc, and now in that one, according as the group of nerve-cells in each arc is excited to discharge its influence by receiving a discharge from some of the other nerve-arcs with which it is united. Again, as we have seen, it is practically certain that the more frequently a nervous discharge takes place through a given group of nervous arcs, the more easy will it be for sub- sequent discharges to take place along the same routes — these routes having been thus rendered more permeable to the pas- sage of subsequent discharges. And now a very little reflec- tion will show that in this physiological principle we no doubt have the objective side of the psychological principle of the association of ideas. Eor it may be granted that a series of discharges taking place through the same group of nervous arcs will always be attended with the occurrence of the same series of ideas ; and it may be further granted that the previous passage of a series of discharges through any group of nervous arcs, by making the route more permeable, will have the effect of making subsequent discharges pursue the same course when started from the same origin. And if these two propositions be granted, it follows that the tendency of ideas to recur in the same order as that in which thev 38 MENTAL EVOLUTION IN ANIMALS. have previously occurred, is merely a psycliological expres- sion of the psychological fact that lines of discharge become more and more permeable by use. We thus see that the most fundamental of physiological principles — the association of ideas — is merely an obverse expression of the most fundamental of neurological principles — reflex action ; and that such, in general terms, is the fact, seems to be proved beyond question by such instances as those above given of the sleeping waiter and Dr. Abercrombie's unconscious patient, &c. ; for such cases prove that actions originally due to a conscious association of ideas may, by a sufficiently loug course of ganglionic instruction, cease to be conscious actions, and therefore become in no way distin- guishable from reflex actions.* But the proof of the fundamental correlation between ganglioriic action and mental action does not end even here. There is another line of evidence which, although perhaps not quite so definite, nevertheless seems to me most cogent, and even more interesting than the considerations already adduced. If we take ideation to be in the same sense an index of the higher or more complex nervous pro- cesses, as muscular movement is of the lower or less complex, we shall find evidence to show that the development of ideation, or mental evolution, implies a further and continuous development of the corresponding nervous processes, which is precisely the same in kind as that which on the lower plane (that of muscular movement) has led to the advancing development of muscular co-ordination. In other words, if we consent to change the index from muscles to ideas, w^e shall find evidence that the method of nervous evolution has throughout been uniform ; we shall find that the progressive elaboration of nervous structures — which in the one case has found expression in the growing complexity of the muscular system, and in the other case has been reflected in the advancing phases of mental evolution — we shall find that this progressive elaboration has throughout been pervaded by the same principles of development, * A good instance of this may be found in the fact that men always bring their knees together in order to catch a small falling object, such as a coin, while women always spread their knees apart. The reason of course is that the difference of dress has led to a difference of organized habit — the habit in each case having been originally due to intelligent adjustment, but now scarcely distinguishable from a reflex. THE PHYSICAL BASIS OF MIND. 39 Disregarding the philosophical question as to how nervous action is associated with subjective ideation, and concerning ourselves only with the scientific fact that it is thus associated, we may most clearly appreciate the parallel which I am about to draw if we regard the objective processes as the causes of the subjective. Whether or not such is really the case matters nothing to the exposition on which I am about to enter ; for I throughout take it for granted that the association of neurosis and psychosis is as invariable and precise as it would be were it proved to be due to a relation of causality. Placing therefore neurosis for the purposes of my argument as the cause of psychosis, I desire to show that there is a very exact parallel between the ganglionic action which pro- duces subjective ideation and that which produces muscular co-ordination; I desire to show that if we interpret the phenomena of ideation in terms of the nervous activity which is supposed to produce it, we shall find that this activity is just the same in all its laws and principles as that which produces muscular co-ordination. No doubt it sounds absurd, and from a philosophical point of view alone it is absurd, to speak of ideas as the psychological equivalents of muscles. So far as subjective analysis could teach us, it certainly does not seem that an idea presents any further kinship to a muscle than it does to a stone, or to the moon ; but when we look at the matter from the objective side, we perceive that the kinship is most intimate. Taking it for granted that the same idea is only and always aroused during the activity of the same nervous structure, element, or group of cells and fibres, it follows that any particular mental change resembles any particular mus- cular contraction in so far as it is the terminal result of the activity of a particular nervous structure. The incongruity of comparing a mental change to a muscular contraction arises, of course, from the emphatic distinction which must always be felt to exist between mental and dynamical pro- cesses. Physiology, which is concerned only with the dyna- mical processes, can take no cognizance of anything that happens in the region of mind. It can trace nervous action leading to combined muscular movements of greater and greater intricacy as we ascend to more and more elaborated mechanisms; but even when we reach the brain of man, physiology can have nothing to do with the mental side of 40 MENTAL EVOLUTION IN ANIMALS. the nervous processes. All that physiology can see in these processes is a greatly improved power of discriminating between stimuli, and of issuing impulses to a correspondingly greater number and variety of adaptive movements ; the mental changes which accompany these nervous processes are as wholly without the ken of physiology as these nervous processes are without the ken of subjectivity. Therefore it is that when we speak of an idea as the analogue of a muscle, we feel the incongruity of confusing two things which are separated from one another by the whole interval that divides subject from object. But although in speaking of an idea as the analogue of a muscle, we do and ought to feel the incongruity, let it not be supposed that by thus speaking we are allowing ourselves to be betrayed into any confusion of thought. I speak of a mental change as the analogue of a muscular contraction only with reference to its being the ter- minal event invariably associated (whether by way of causality or not) with the activity of a nervous structure. And if we do not seek to press the analogy further than this, there is no fear of our confusing ideas which ought always to be kept fundamentally distinct. So much, then, by way of introduction to the point which I have to make plain. Now it admits of being abundantly proved that throughout the animal kingdom, so long as we regard the muscular system as our index of the structural advances taking place in the nervous system, we find this index to consist in the growing complexity of the muscular system, and the consequent increase in the number and variety of co-ordinated movements which this system is enabled to execute. Therefore the point which I have to prove will be proved if I can make it clear that the process of mental evolution bears some such resemblance to that of muscular evolution as we should expect that it ought to bear, if they are both dependent on a similar process of nervous evolution. In other words, I have to show that the process of mental evolution consists essentially in a progressive co-ordination of progressively developing mental faculties, analogous to that which takes place in muscular movements. Beginning with the faculties of simple sensation, we know, for instance, that when a note of music is struck, it appears to produce a single vibration, and yet physical ana- lysis shows that the sound is not a single vibration, but a THE PHYSICAL BASIS OF MIND. 41 liighly complex structure of vibrations or harmonics, and that the ear takes in all these harmonics by as many separate nervous elements (whatever the elements may be which minister to the perception of pitch), although they are all blended into one compound sensation, which is so well com- pounded that the evidence supplied by it alone would never have led us to suspect that the sensation was other than simple. The same is known to be the case with sensations of colour, taste, and smell ; so that Lewes feels justified in going to the length of saying, " Every sensation is a group of sensible components."* And, taking the same view on the psychological side as I take, he further says in general terms, " The main fact on which our exposition rests is indisputable, namely, that sensation, perception, emotions, conceptions, are not simple undecomposable states, but variously com- pounded." To avoid being tedious, I shall not pursue the analysis through all the grades of the psychological faculties ; but, taking ideation in its widest sense, as including alike the mere memory of a sensation and the most complex process of abstract thought, I shall briefly show that it everywhere displays a grouping and compounding of subjective elements which, if translated into their objective counterparts, display precisely the same method of nervous evolution as that which obtains in the lower ganglia, as expressed by muscular co- ordination. As Bain observes, "Movements frequently conjoined become associated, or grouped, so as to arise in the aggregate at one bidding. Suppose the power of walking attained, and also the power of rotating the limbs, one may then be taught to combine the walking pace with the turning of the toes outward. Two volitions are at first requisite for this act, but after a time the rotation of the limb is combined with the act of walking, and, unless we wish to dissociate the two, they go together as a matter of course ; the one resolution brings on the combined movement Articulate speech largely exemplifies the aggregation of muscular movements and positions. A concurrence of the chest, larynx, tongue, and mouth, in a definite group of exertions, is requisite for each alphabetical letter. These groupings, at first impossible, • Frollems, ^c, p. 260. 42 MENTAL EVOLUTION IN ANIMALS. are, after a time, cemented with all the firmness of tlie strongest instinct." Precisely analogous to this process of blending many- separate muscular movements into one simultaneous and com- pounded movement, is the process of blending many simple ideas into one complex or compounded idea. Just as mus- cular co-ordination is dependent on the simultaneous action of a certain group of nerve-centres for the purpose of securing the combined action of a number of muscles, so we must suppose that a general or a composite idea is dependent on the simultaneous activity of several nerve-centres which riinister to the several component parts of the blended idea. The psychological side of this process has been so well ex- pressed by James Mill, that I cannot do better than render it in his words : — " Ideas which have been so often conjoined that whenever one exists in the mind the other exists along with it, seem to run into one another, to coalesce, as it were, and out of many to form one idea, which idea, however, in reality complex, appears to be no less simple than any one of those of which it is compounded The word ' gold,' for example, or the word ' iron,' appears to express as simple an idea as the word ' colour,' or the word ' sound.' Yet it is immediately seen that the idea of each of those metals is made up of the separate ideas of several sensa- tions : colour, hardness, extension, weight. Those ideas, how- ever, present themselves in such intimate union, that they are constantly spoken of as one, not many. We say, our idea of iron, our idea of gold ; and it is only with an effort that reflecting men perform the decomposition." And simi- larly, of course, with the most highly complex ideas, except that the more complex they become the greater is the diffi- culty of securing the needful composition, and the more easily do they undergo disintegration. Thus it is that, in the words of Mr. Spencer, " In the development of mind there is a pro- gressive consolidation of states of consciousness. States of consciousness once separate become indissoluble. Other states that were originally united with difficulty, grow so coherent as to follow one another without difficulty. And thus there arise large aggregations of states, answering to complex external things — animals, men, buildings — which are so welded together as to be practically single states. But this integration, by uniting a large number of related sensations THE PHYSICAL BASIS OF MIND. 43 into one state, does not destroy them. Though subordinated as parts of a whole, they still exist."* Again, just as the principle of association is exhibited in the case of ideas not only with reference to the simultaneous blending of simple ideas into one complex idea, but also with reference to the successive sequence or concatenation of ideas ; so in the case of muscular co-ordinations we acquire, not only the power of a simultaneous co-operation of muscle- groups, but also that of a successive co-operation. For instance, as Professor Bain observes, " In all manual opera- tions there occur successions of movements so firmly asso- ciated, that when we will to do the first, the rest follow mechanically and unconsciously. In eating, the action of opening the mouth mechanically follows the raising of the morsel Although the learning of successions of movements involves the medium of sensation, in the first instance, yet we must assume that there is a power, in the system, for associating together movements as such." In fact, it might well have been added, there is such a power that manifests itself long before the dawn of any of the powers of the " will " ; it is as true of the polyp as of the man that " in eating, the act of opening the mouth mechanically follows the raising of the morsel." So with the highest or most abstract powers of mind. For abstraction merely means the mental dissociating of qualities from objects, and, in its higher phases, blending these qualities, or conceptions of them, into new ideal com- binations. Lastly, just as innumerable special mechanisms of mus- cular co-ordinations are found to be inherited, innumerable special associations of ideas are found to be the same ; and in one case as in the other, the strength of the organically imposed connection is found to bear a direct proportion to the frequency with which in the history of the species it has occurred. Thus, the simplest, oldest, and most constant ideas relating to time, space, number, sequence, &c., may be compared, in point of organic integrity, with the oldest and most indissolubly associated muscular movements, such as those concerned in breathing, deglutition, and visceral motions. Again, inherited instincts have their counterparts in such inherited muscular co-ordinations as are not abso- * Principles of Psychology, vol. ii, p. 476. 44 MENTAL EVOLUTION IN ANIMALS. lutely indissoluble. And similarly, of course, associations of ideas acquired only during the life-history of the individual need to be more or less constantly maintained by repetition, just as muscular co-ordinations similarly acquired can only be maintained by practice. Upon the whole, therefore, it is impossible that there could be a more precise parallelism between these two manifesta- tions of nervous machinery, and it is one which for recog- nition in a general way does not require scientific analysis ; it has been perceived by the common sense of mankind — witness, for instance, the term " gymnastics " having become applicable to mental no less than to muscular co-ordinations. But, for the sake of systematic completeness, I shall conclude this exposition by briefly pointing out that all those patho- logical derangements which occur in the nervous centres that preside over muscular activities, have their parallels in similar derangements which occur in the nervous centres that are concerned in mental activities. Thus "nervous- ness," or a disturbance of the normal balance of nerve- centres, has a strikingly analogous effect in confusing the ideas and in perturbing muscular co-ordinations. Idiotcy has its parallel in inability to perform complex muscular move- ments, with which inability, indeed, idiotcy is itself almost invariably associated. Lunacy has it counterpart in an un- balanced, or badly correlated power of muscular co-ordina- tion, which in its graver manifestations is known as ataxy ; while mania is mental convulsion, and unconsciousness mental paralysis. I must not, however, take leave of this branch of our subject without briefly alhiding to a difl&culty which may occur to some minds, and which has been well stated by Professor Calderwood in his recently published work.* The difficulty to which I allude arises from there being an absence of such a constant relationship between the size or mass of the brain, and the degree of intelligence displayed by it, as the foregoing teaching would reasonably lead us to expect. Now, I do not deny that the relation of intelligence to size, mass, or weight of brain is a perplexing matter when we look to the animal kingdom as a whole ; for although there is unquestionably a general relation of a quantitative * Pp. 211—216. A . THE PHYSICAL BASIS OF IiIIND. 45 kind, it is not a constant relation. Even within the limits of the hnman species this relation is not so precise as is usually- supposed ; for, neglecting particular cases that might be quoted of men of genius not having particularly large or heavy brains, the converse cases are perhaps in this connec- tion more remarkable — viz., those of feeble-minded persons having large and apparently well-formed brains. I am indebted to Dr. I'rederick Bateman of the Eastern Counties' Asylum for directing my attention to the observations of Dr. Mierzejewskis, which were published at the international congress of psychologists held in Paris in 1878. These observations, which appear to have been carefully made, seeing that casts of the brains were exhibited, went to show that idiotcy is compatible with large and apparently well- developed brains — the amount of grey matter in one instance being " enormous," And, if we turn to the animal kingdom, we find in a still larger measure that the mere amount of cerebral substance furnishes but a very uncertain index of the level of intelli- gence which is attained by the animal. This is the case even when we eliminate the element of complexity that is introduced by the differences which obtain in different animals between the bulk of the brain and the bulk of the body — small animals requiring a greater proportional bulk of brains than large ones, because the nervous machinery which ministers to muscular movement and co-ordination has in. both cases to be accommodated. But this element of com- plexity may be removed by considering the cases in which small animals exhibit remarkable intelligence ; and in this respect no animals are so remarkable as the more intelligent species of ants alluded to in my former work. As Mr. Darwin has observed, the brain of such an insect deserves to be regarded as perhaps the most wonderful piece of matter in the world. But if this whole question touching the relation between the mass of brain and degree of intelligence is felt to lie as a difficulty in the way of evolutionary theory, I should reply to it by the following considerations. In the first place, that there is a general relation between size of brain and degree of intelligence, both in the case of man and in that of animals, is unquestionable. It is, there- fore, only with the more special exceptions that we have to 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 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 plus 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 multum in parvo, 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 KOOT-PKINCIPLES OF MIND. 47 CHAPTER IV. The Eoot-peinciples of Mind. Ai-THOUGH the phenomena of Mind, and so of Choice, are both complex, and as to their causation obscure, I think we have now seen that we are justified in beheving 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 which we 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 we are agreed that every psychical change of which we have any experience is invariably associated with a definite phvsical change, whatever we 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 indifferently call it, a physiological side, I shall endeavour to point out what I con- ceive to be the most iiltimate principle of physiology which analysis shows to be common to them all. On the mental side, as we have already seen, we have no difficulty in dis- tinguishing this ultimate principle, or common characteristic, as that which we designate by the term 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- logical development than in the functions of the human brain. For not only do the lower animals manifest, in a long descending scale, powers of choice which gradually fade away into greater and greater simplicity ; but we should be led a priori 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 a priori 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 u]3on one side of the tank near the surface of the water, and if a jet of sea water is made to play continuously and forcibly upon the 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 tliat it will expand its tentacles in search oi 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-PKINCIPLES 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 Math 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 the most carefully observed facts with regard to this interesting subject are those which we owe to the later researches of Mr. 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 tlie 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 ^^^y 7^740 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 50 MENTAL EVOLUTION IN ANIMALS. extremely doubtful wliether 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 sprmg-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 2>ressitre that is so delicately perceived, while the stimulus supplied by impact 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 wholly 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 the 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 Avhich 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 tlie 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 vji^pi^ ^e6retion] and /the slight, though prolonged pressure V, LIB v.- ^ THE ROOT-PEINCIPLES 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 those 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 o£the most artificial construction . . . From the same sandy hottotn, 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-grain 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 the 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 * Contem'porary 'Review, April, 1873 62 MENTAL EVOLUTION IN ANIMALS. responses are appropriate. In order to see this, let lis take the principal faculties of mind in their ascending order, and consider Avhat 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. Again, many of the nervous mechanisms which minister to various Eeflex 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 call 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 ROOT-PKINCIPLES OF MIND 53 pliysiologically considered, the emotions are the activities of highly wrought nervous mechanisms, and these activities are only excited by the 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 tlie 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 which 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 which, 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 we 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 difi'erent kinds of stimuli, irrespective of their degrees of mechanical intensity. But, before giving a brief 54 MENTAL EVOLUTION IN ANIMALS. 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 wait 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 with 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 choosing 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 tliey refer to things which are the product of a gradual evolution — things which came from other tilings 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 EOOT-PKINCIPLES OF MIND. 55 Peeling 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 which 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 which 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 betAveen light and darkness, and to adapt their movements to seek the 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 dijfferent kinds of contact ; and, in correspondence with this advance in receptive power, w^e observe a commensurate 56 MENTAL EVOLUTION IN ANIMALS. advance in tlie 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 ai-e able to distinguish quickly and accurately between moving and not moving objects coming upon them from various sides, as w^ell 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, swimming 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 which 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 ninnerous 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 antennas and highly perfected organs of special sense, is also greater. And the same principles hold throughout the Vertebrated series. It has already been THE ROOT-PEINCIPLES 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 Elephant 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 correlated 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, hps, and jaws, as well as to some extent in the paws. I think the superior intelligence of the Octopus, among moUusks, is to be attributed to the exceptional advantages which are rendered by its large and flexible, sensitive and powerful arms. 58 MENTAL EVOLUTION IN ANIMALS. the 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 to study the effects of these finer mechanisms. 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-PKINCIPLES OF MIND. 69 Thus the two faculties are, as it were, necessarily hound together. But here another consideration arises. They are thus bound together only up to the point at which the adap- 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 ina^^gurated. 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 between 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 compared with the co-ordinated movements of a spinning- 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 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 powers of adjustive movement have been emancipated from their necessary alliance with his powers of muscular co-ordination. I say, from his powers of muscular co-ordination, because it is evident that our powers of adjustive movement, and so of adaptation in general, have never been, and can never he, 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 of 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 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 probable 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 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 imderstand 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-PEINCIPLES OF MIND. 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 with 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. More 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 EVOLUTION 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-siglited of actions, adapted to meet the most remote contingencies of stinmlation, 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 DIAGEAM. 63 CHAPTER 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 Mind. 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 diagram embodies the results of my analysis throughoiit, 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 have 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 everywhere 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 furnish upon the subject ; and although it is no doubt true that the progress of science may affect the diagram 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 sufficiently coherent 64 MENTAL EVOLUTION IN ANIMALS. to render it highly 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. Erom 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, only 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 DIAGRAIL C5 ception, 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 exhibit 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 bra,nches 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 sundry 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 a^es 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 columns, 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 higher faculties as they occur in animals and the same faculties as they occur in man. Confining, then, our attention to the first twenty-eight 66 MENTAL EVOLUTION IN 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 outhne 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 wliich 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, branches, and the two parallel coUmms 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 the faculties of nutrition, excita'oility, 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 DIAGEAIL 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 development — 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 I have either a priori reasons or actual evidence to conclude that they first definitely appear in the growing structure of Miud ; 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 hypo- 68 MENTAL EVOLUTION IN ANIMALS. thesis ; and, 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 accept 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 hk 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 the 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 Neurility, or the stem of Mind ; in these levels occur the EXPLANATION OF THE DIAGKAM. 69 Non-nervous Adjustments, Unicellular Organisms, ana 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 Ccelenterata, 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 whether 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. Seliiifcr on Nervous System of Aurelia Auriia, Phil. Trans., 1878, and Profs. O. and H. Hei'Lwig on Das Nerceiisi/ntem und die Sinnesorgane der Meduseii. 70 MENTAL EVOLUTION IN ANILIALS. CHAPTEE 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 prominent attention to the fact that from 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 proce,jSes, it is impossible to avoid a certain amount of over- lapping witli 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 tlieir probable evolution, it may often appear that 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, have 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 through- out— viz., that all mental processes must be regarded as pre- senting physical counterparts.* 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 this 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 " Nervous 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 tlie impossibility of entirely sepa- rating psychology from physiology for the purposes of exposition will, mutatis mutandis, 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 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 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 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 aniesthetic, will remember the peculiar experience of feeling consciousness becoming obliterated by stages CONSCIOUSNESS, 73 Tor in our own organisms we know tliat 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 with 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 subsequently 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 "taking in" the situation. And any 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 MENTAL EVOLUTION IN ANIMALS. response (liowever complex tliis 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 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 many stimuli without some ganglion through which they are all brought into relation. In the pro- cess of bringing them into relation, this ganghon 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 perpetual 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 Psychologi/, vol. i, p. 435. I thint, 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 bave anything to do with the rise of consciousness, except in so far as it may be conducive to what we may term tlie ganglionic friction, which is expressed by delay of response. CONSCIOUSNESS. 75 tliem 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 changes into con- centrated serial changes. Whether 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 aU 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 ItlENTAL EVOLUTION IN ANIMALS. tlie 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 briefly 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 sufiiciently 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 Ccelenterata 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 reflex 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 riiil. Trans,, Croonian Lecture, 1881. CONSCIOUSNESS. 77 place upon a still higher 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-born 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 MoUusca — 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 unques- tionably intelligent, • See his work on Earlkworms, 1S81. V8 MENTAL EVOLUTION IN ANIMALS. CHAPTEE VII. 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 Reflex 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. When 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 faculties ; it only has to do with the 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 with 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; we 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 somewhere 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 Coelenterata. In doing this, it is needless to observe, I am drawing the line quite arbitrarily. On the one hand, for anything that is known to the contrary, not only the sensitive plant which responds to a mechanical stimulus, but even the 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 whether 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 validity of such inference clearly diminishes with 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 Lewes, 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 Englena viridis. After precautions had been taken to eliminate causes 1 and 2, it was 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 whether 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 viridis prefers the blue.* The remarkable observation recorded by Mr. H. J. Carter, r.R.S., and quoted from him in my previous work,t seems to display almost incredible powers of special sense among the * For f uU account of tliese experiments, see PJliiger^s Archiv.f. d.ges. rhifsiologie, 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 ar(; some that love light, and some that 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 ^ 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 Medusae, it is among them also that we first meet with organs of special sense. I have myseK observed that several species of Medusae seek the 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 polydiademata, 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 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 light requires to fall in order to constitute an adequate stimulus ; just as a photographic plate requu-es 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- organ. 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 Medusse 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 Medusse 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 Meduste, 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 other species of Medusse, 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 manubrmm 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 longer able to localize the seat of contact. Nevertheless it feels that con- tact is taking place someivhere, 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 the 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 Actiniae Mr. Walter Pollock and myself have ob- tained conclusive evidence of the sense of smell. Por 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. 84 MENTAL EVOLUTION IN ANIMALS. with unmistakeable evidence of the occurrence of all the five senses — or, more correctly, with unmistakeable 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 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 corresponding 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 smeU 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 tliis 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 see things, not in the position in which they are 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, while 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 Heeckelf — ^"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 Alcipidae, which are highly organized Annelidse 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." Further, 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 will suddenly withdraw their expanded tufts when a shadow falls upon them ; but the shadow must be that of an object moving with some rapidity.-f* 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.^ 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 liis position, upon which the female approached him.|| I have myself published observations proving the occurrence of a sense of hearing among the Lepidoptera.H Turning to the morphological side of the subject, it is remarkable that in the Articulata the * See JEarthivorms, pp. 19-45. t -Z^^^ thierische Wille, s. 194, % Earthworms have no ears and are totally deaf, altliough very sensitive to vibrations eommunicated through contact with solid bodies. (See Darwin, loc. cit., pp. 26-7.) § Hseckel, 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. if See Nature, vol. xv, p. 177. SENSATION. 87 auditory organs occur among different members of the group in widely different parts of the body. Thus in the 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 tibige 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 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 smeU 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 moans of their antennae. 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 Eje among Vermes, and also, as we shall presently see, among MoUusca. t Darwin, loo. cif., 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 the 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 MoUusca, 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 siipplementary 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- SENSATION. 89 goiis 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. Tor 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 sj)ecies {e.g., the Skate) being of enormous size in relation to the other parts of the brain. The sense of touch is provided for in many species by tentaculse 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 there 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 part of the animal. I say over any other part of the animal (and not only in the nasal fossae), 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. Hseckel, 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 * Marsliall, Outlines of Physiology, voL i, p. 603. SENSATION. 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 depth of many fathoms in the water ; or the eye of a Swift, which is able so suddenly to form its adjustments ; 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 visual 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 protection at the present day. In other words, the evolution of the eyes of birds and of the protective coloration of their prey must be supposed to have progressed pari passu, 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 sight, 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 EVOLUTION 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 Eep tiles, 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 readies its greatest supremacy in Birds, all 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, where also see in more detail my observations on the feeding habits of the curlew. t See Animal Intelligence, pp. 28G-7. SENSATION. 93 tory sense ; and it is not until he has himself seen the 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 Eegent'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, then 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 that 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 degTee 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. With the exception of the singing monkey {Hylobates agilis), there is no evidence of any mammal other than man 5 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 mastift" " 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 Mustelidse 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 witli cotton- wool, it is stni 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 SENSATION. 95 sense-organs as it occurs in the sight of the vulture or the smell of the dog. Indeed, Heeckel 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 Hseckel in his view that the " homing " faculty of certain animals is due to some additional and inexplicable sense, and therefore I shall reserve my treatment of this topic for my chapters on Instinct. After this rapid survey of the powers 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-fibres 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 the 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 96 MENTAL EVOLUTION IN ANIMALS. extent of the receiving surface, the greater is the impression ; so that if the 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 with which the special mechanism we are considering is not concerned) ; and there- fore we have to contemplate the probable cause of its origin and 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 SENSATION. 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 baths. 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 ar.tonishing 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. Moreover, 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. 98 MENTAL EVOLUTION IN ANIMALS. in those parts to be more sensitive to changes of temperature. But 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 which 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- 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, and 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 e%ddence 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 chcu- rneleo) is known to change 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 analogous facts occur among the Cephalopoda {e.g., octopus), Batrachia {e.g.. Common Frog), Eeptilia {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 Pleuronectidae 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. jM. Fredericq afterwards found the same thing to be true of the Octopus, and in conjunction with Professors Burdon- • Journ. Linn. Soc, 1881. These observations have been adversely criti- cized by Mereikowsky (Comptes Rendus, xciii, pp. 160-1), but his criticisms have been fully met by further experiments recently published by Sir John {■Tourn. 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 fm'ther proof that a well-developed sense of colour occurs in some of the Articulata, 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. N. Moseley to the efiect 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 attein 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 Anfs, Bees, and Wasps, and in Animal Intelligence. t Quarterli/ Journ, Micro. Science, New Series, vol. xtU, pp. 19-22. 100 MENTAL EVOLUTION 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 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 Hseckel 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 green. 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 enqui;re, by means of a table of questions addressed to educated Europeans in all parts of the world, whether 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 which is at once trust- worthy and available. But in saying this I do not intend to • Coluu7--sense, Chapter X. SENSATION. 101 dispute tlie 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 aesthetic 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 harmony 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 M^ay 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 seme 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-effect of warming or cooling a portion of the skin remains, the temperature-sense of that portion is altered in 102 MENTAL EVOLUTION IN ANIMALS. sucli 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 coloars, and vice versd. So, too, it is with simultaneous contrasts. It is well known that if a small colourless 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 temperature, 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 different 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 blind 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 this 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 having the lowest and not the highest 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 growth 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 walls. 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, again, the earliest sign of commencement consists in a similar pitting of the general integument, but 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 Hseckel, " the general conclusion has been reached that in man, and in all other animals, the sense-organs as a whole arise in essentially the same way, viz., as parts of the external integument or epidermis. The external integument is the original 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 differentiations of the general sense of touch. • Science and CuUure, &c., p. 271. PLEASURES AND PAINS. 105 CHAPTER VIII. Pleasures and Pains, Memory, and Association of Ideas. In the diagram I have represented Pleasures and Pains as occupying in their first 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 of 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 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 stimulation. 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 Pnychology and Physiological Esthetics, in both cases the chapter on " Pleasures and Pains." 106 MENTAL 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 organism," 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 wherein 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 PLEASURES 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 hurtftdness, as well as between the amount of pleasure and tlie degree of wJiolesomeness.* As Mr. Allen observes, *•' nothing can more thoroughly mihtate against the efficiency 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 painfulness 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 those 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 cravinos 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 put it in a simple form, * I use these antithetical words because their etjmology alone suggests forcibly the doctrine in question. 108 MENTAL EVOLUTION IN ANIMALS. the 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 tas^te 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 then being actually disintegrated by the direct or indirect action of the irritant." Now if the doctrine before us is found to apply generally 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 tlie 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 pleasure, 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 "uidance." PLEASURES AND PAINS. 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 this adjustment or corre- spondence, the zoological principle of the survival of the fittest 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 harmful 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, when 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 long 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 tlie 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 disagreeable to consciousness, although 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 rationaU 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. Tlie latter consideration disarms any criti- cism which 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 d'etre 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 diasrram 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 written, M. Kibot has published his excel- * On "the Physical Basis of Mind." 112 MENTAL EVOLUTION IN ANIMALS. lent work on the " Diseases of Memory," which has now been translated, and forms a member of the International Scientific Series. In this work M. Eibot deals fnlly with 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 sliould 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 xnj chapter above alluded to with the first chapter of M. Eibot'a work. MEMORY AND ASSOCIATION OF IDEAS. 113 curious fact to hold in the case of muscular tissues of various animals, from the Medusae upM'ards.* Ap;ain, I concur with M. liibot in his opinion that the 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, but the formation among them of deter7ni- nate associations 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." Profound, how^ever, as our ignorance unquestionably is concerning the physical substratum of memory, I think we 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 ganglionic friction. And this view is confirmed by the large and general fact noted in * See " Concluding Obserrations on the Locomotor System of Medusse," Thil. Trans., Pt. I, 1880; and on "Modification of Excitability," &e., Froc. Hoy. Soc, Nos. 171 and 211. Also, Journal of Anatomy and Physio- logy, vol. X. Another equally good instance of what may be termed proto- plasmic memoi-y 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., wherever 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 memory of its occiuTence. 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-efi'ect 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 tlie 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, Qrundzlicje der philosophiseJien Fsycliologie, 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 E^aumur, ' Entomology,' vol. i, p. 391) that larvae 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 the 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 fiUed 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 116 MENTAL 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 difficulty 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 talces its place, this emerges into consciousness as a feeling that is not familiar. And whether such feelings of familiarity or unfamiliarity arise in the exj^erience of the individual or in that of the species, makes, as I have said, no essential difference either in the pliysiolo- gical or in the psychological aspect of the case. As showing how close is tlie connection between here- ditary memory, or instinct, andmeniory individually acquired, I sliall briefly state some very interesting experiments which were made by Professor Preyer on newly-hatched cliickens. He laid before a newly-liatched 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 the 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 three substances, and after the lapse of an hour replaced them. The chick 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 Memory — for the chickens which first pecked at inedible objects in the 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, whether 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. 6 118 MENTAL 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 shall do so now, notwithstanding the disadvantage 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 difliculty in dealing with the faculties of Mind in the probable order of their evolution, 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 sliall 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 convenientadjectives. 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 Mind) 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 cohere 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 the 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 perceived ; 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 he 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 heing 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 have been written backwards by the left hand, and even the hand-writing can be recognized on holding the paper before a mirror. As the left hand may never have performed this feat before, an,d cannot perform it unless the right hand is working simultaneously, the case looks Uke 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 mind 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 off 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 InteJlect, 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 from 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, would 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 classify 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 when 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.f 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,]: we must conclude that a dim power * Loc. cit., p. 42. t Animal IntelUgence, pp. 28-9. J Ibid., p. 25. 122 MENTAL EVOLUTION IN ANIMALS. of memory is also present iu the division of the MoUusca. 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 MoUusca 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.^ Seeing that memory in various stages of development thus unquestionably occurs among the MoUusca, 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 sheU 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 the 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 Hjid., p. 27. J 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. ISTevertheless, 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 where 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- wasps carefully teach- ing themselves (by taking mental notes of landmarks) the localities to which 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 work — viz., for Beetles, pp. 227 — 9, for Earwigs, p. 229, and for the common House- fly, 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 " Memorj," 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 Reptiles 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,1[ and the sound of a clinking collar after an interval of three years ;ir 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. t Hid-, pp. 254-C2. X Ibid., p. 266. § For all these facts, see ibid., pp. 266-70. II Ibid., p. 330. % Ibid., p. 438. ** Ibid., p. 387. +t Ibid., pp. 485-98. PERCEPTION. 125 CHAPTER IX. Perception. At the level marked 18 I represent tlie rise from Sensa- tion to Perception. By this term I mean, in accordance with general usage, the faculty of cognition. " The contrast between Sensation and Perception is the contrast between 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 distincfuished 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, which 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 Perception, 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 uii 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. AU 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, tlie 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 j;7/2ts 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 that 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 sufficiently 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 allude. 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 morpliological 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 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 ; 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, whether 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 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 123 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 perceptive 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 development 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 tilled 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 tliis, 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 PEKCEPTION. 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 past sen- sation. Again, the power of discerning a change of milk impKes 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 we have seen the next phase of memory to depend. And, lastly, from tliis 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 tliat the sun shines ; yet we speak of perceiving that the sun shines. As a matter of fact, however, we do remember that the sun 130 MENTAL EVOLUTION IN ANIMALS. shines, and in all the habitual phenomena of experience such memoiies as this become so blended with our perceptions of the 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 higher 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 changes) are completely auto- matic, they are on this account precluded from being regarded 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 recocjnition as distinguished from rejlex 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 wliich heredity has played in forming the perceptive faculty PERCEPTION. 131 of the individual prior to its own experience. We have already 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. This 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 which 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 " putt' and spit."* Birds come into the world with better endowments of perception than animals of any other class. For they are in fuU 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,t 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. f See Animal Intelligence, pp. 256-7. 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 signalhng the perception. That is to say, an electrical shock being administered to one hand, and as quicldy 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 part in a reflex action.-|- Acts of perception in which different senses are concerned occupy different 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 ^, * Arch.f. d. ffex. Physiol., xliii, 526 (1874). t Ibid., vii, p. 610. " X Sco Herumn, Eandb. d. rhjsioL, Bd. II, Th. 3, 8. 264. PERCEPTION. 133 and for sight -I- of a second,* The observations of Von Wit- tichf, Vintschgau, and Honig-Schnied;!: show that the reaction- time for taste varies between 0'1598''' to 0"2351" 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"167'^ 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 sight, 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 Electrical shock on left hand Sudden sound Electric shock on forehead. . Electric shock on right hand Visual impression from electric spark Electric shock on toe of left foot . . 01139" 01276 01360 0-1370 01390 01506 01749§ 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 to 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 shows, 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 Physiol., 1868, p. 657. t Qt. Ret. Med. (3), xxxi, p. 113. X Arch.f. Anat. und Phi/siol., x, p. 1. § PJliiger's Archiv., Bd.VII, p. 620. 134 MENTAL EVOLUTION IN ANIMALS. ception.* The last-named author found that an exposure of ^ 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 the skin, right or left foot stimulated by an electric shock ; signal to be made in one case only 0-066" Dilemma of visual perceptions between two colours, 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 the 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 thus be seen that the time required for the act of meeting a dilemma is from ^ to J^- 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. Physiol., Bd. IV, p. 329 ; Monaf.sher. d. Ber. Acad., June, 1871. t For Donders' investigations, see Archiv. f. Anat. und Fhysiol., 1868, pp. 657-81. I Archiv. f. d. ges. Physiol., 1877, pp. 293-380. PERCEPTION. 13i Localization by sight . . . . . . Distinguishing colour . . Localization by hearing (least interval) Distingmshing pitch (high notes) Localization by touch , . Distinguishing pitch (low notes) Localization by hearing (greatest intei-val) 0011" 0-012 0-015 0019 0-021 0-034 0-062 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. Reaction-time. Eemarks. 26 23 76 24 20 22 35 0 -1337 0 -3311 0-9952 0 -1751 0 -2562 0 1295 0-1381 Rough, lively labouring-man. Lively in movements, but rather slow^ in apprehen- sion. Infirm and not intelligent. Slow and deliberate in movements. Slow and somewhat uncertain in movements. Slow and very precise in movements. 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 shootiDg 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 Lot; cit., 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 tlie 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 slieet of paper what part of the underlying page the marked paragraph occupied, I suddenly removed the sh6et 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 before. Meanwhile the first reader, the moment after the book had been removed, wrote down aU 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 I 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 between slowness of reading and power of assimilation ; on the con- trary, when all the efforts are directed to assimilating as PERCEPTION. 137 much as possible in a given time, tlie 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 shows that the 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 reducing the reaction-time. The degree of reduction which might thus be produced was itself made the subject of experiment by Exner, who chose the old man already mentioned in one of tlie above quoted tables as having the unusually long reaction-time of 0"9952''''. 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 multitudinous and complex kind, is proved in every-day life by the acquired rapidity with which bankers' clerks are able to add up 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 fashion 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.| 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 Robert Houdin, vol. ii, p. 9. Professor Preyer has also published some observations on this snliject. f Ibid., p. 7. X La durata del disceraimento e dcUa detenninazione volition, Rivisti di Fdus. iScientlf., I, p. 2. § Mind, No. XXX. PERCErXION. 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 * Problems of Life and Mind, 3rd ser., p. 107. See also Dr. J. Hugh- lings Jackson in Brain, Nos. Ill and IV j and Mr. Sully, in Illusions, pp. 27-30. 140 MENTAL EVOLUTION IN ANIMALS. Perception arises out of Eeflex Action, Keflex Action out of Perception, or whether there 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 operation 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 * Pnnciplcs of Pisjcholocjy, vol. i, p. 416. 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 light which is given out when such heat rises to redness. Presumably, therefore, 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 Donders 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 general fact, that throughout the animal kingdom 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 defining 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- 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 wliich 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 Chap'ucx's II and III. IMAGINATION. 143 Bain, and others, wno 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 seasation,* 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 comes in. Later on there arises association by similarity, and from this point onwards Ideation advances by abstrac- tion, generalization, and symboKc 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 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 higher phases of the idea-forming powers which we may conveniently in- clude under the general term Imagination. Kow, 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 * Thus, Mr. Spencer says, " Tlie idea is an imperfect and feeble repetition of the original impression . . . There is first a presented manifestation of the vivid 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 occupies 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 which I disagree with him touching the earliest stages of memory — or those before the advent of the association of ideas. Only I may point out that 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, .. - - 143: 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 have 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 run§ on in a continuous stream when all the 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 the diagram which 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 Eeflection. 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 witli another, and there can be no harm in adopting it if we remember, what I desire always 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 Eealism. Such, however, is not the case. For, although it is true that, if we were able to imagine every abstraction, Eealism 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 Eeflection, I am careful to keep well within the lines of Nominalism. Turning now to the lateral columns, it wiU be seen that 1 place upon a level with the rise of imagination the classes MoUusca, Insecta, Arachnida, Crustacea, Cephalopoda, and the cold-blooded Yertebrata. My justification for assigning to these animals the first manifestation of tliis faculty wiU be found, as in other cases, in " Animal Intelligence." Thus 146 MENTAL EVOLUTION m ANIMALS. the octopus which followed a lobster with which it had been fighting into an adjacent tank, by laboriously climbing np the perpendicular partition between the 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 IntelKgence " 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 plate, 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 time 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 IniclUgence, pp. 122 dO, and 181-19. IMAGINATION. 147 appetite ; the animal then becomes bold by necessity. He even runs to meet danger, knowing [i.e., forecasting by 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 suificient number of objects, he becomes the sport of an illusory system, which may lead him into infinite mistakes although perfectly consistent with the principles which have taken root in his mind. He will 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 awaiting 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 the fox and wolf in eluding the hounds is also evi- dence of a vivid imagination. In addition to the cases of this given in Animal 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 : — " Near the south coast of San Fi-ancisco a farmer had been much annoyed by the loss of his chickens. His hounds had svxcceeded 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 obUterated by the swell. When, finally, he had gone far enough, as he supposed, to destroy the scent, he turned inland." 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 but still more deadly pain which it fears at the hands of the man. Coming now to Imagination of the third degree, or that wliich 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 higher animals. 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 Loiver 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 Cuvier, Jerdon, Houzeau, Bechstein, Bennet, Thompson, Lindsay, and Dar- win.* Tliompson 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 Mammalia 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 swimming ; 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 that occur in other animals as in man, in canine rabies, for instance, as in human hydrophobia. "J On this subject Fleming writes : — " It (i.e., a rabid dog) appeared as if it was haunted by some horrid phantoms. ... 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 ; Facultes-Mentales des Animaux, Sfc., tome ii, p. 183 ; Mind in the Lotcer Animals, vol. ii, p. 96; JPassions of Animals, p. 60; and Descent of Man, p. 74. t According to Pierguin, Guar, Elam, and Lindsay, dreaming in animals may be so vivid as to kad to somnambulism (see Lindsay, loc. cit., p. 97, et seq.). Thus Gruer 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 EVOLUTION IN ANIMALS. at the vacant air, as if pursuing something against which it had an enmity." And, indeed, this peculiarity of being 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 effect 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." Pierquin 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 slie 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 onimals present Imagination of what I have called the third order. This class of facts consists of * See Youat, On the Dog, under Rabies. t Traite de la Folic des Aiiimaux, difc, tome i, y. 93, IMAGINATION". 151 animals showing by their actions that they have in their " 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 w^ith the sluggishness and lack of energy on their 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, the 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 dangers and fatigues of hundreds of miles of travel for the sole purpose of returning to the scenes which occupy their 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 the 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 w^hich the animal is strongly attached. I have myself known a case in which a terrier of my own household, on the * Thompson, Passions of Animals, pp. 6i-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 cause 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 through what I have called the first three stages, so as to ari'ive 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 proved 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 absurd to accredit a moUusk with imagination, 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 liabitual 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 which 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 image, 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.) With a still 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 Eeptiles, 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 thu-d degree — it being I think higlily 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 that in the soul Are many lesser faculties that 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. Before taking leave of Imagination there are two branches of the subject which I should like briefly to consider. One 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, el scq. IMAGINATION. 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 the 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 m 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 obviously 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 grinning, 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 object, and would bring it with renewed manifestations of friendliness. Some kindred state of mind it is which, 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. The 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 worrying 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. " Now in this and all my other experiments I have no doubt that the behaviour of the terrier arose from his seiise 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 the same oppressive and alarming sense of the mysterious which uncultured 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 that the sense of the mysterious in this animal was sufficiently 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 w^as 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 which 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 with 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 after 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 with 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 whining 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, when 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 behaviour. 158 MENTAL EVOLUTION IN ANIMALS. i.e., by tlie violation of his 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 was at a distance from home. But the keeper, Vv'ho had a large experience in the training of dogs, assured me if I allowed this one to be taken to tlie 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 th^e 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 such would have been the case, however, I have little doubt, for on one occasion when a number of apples were being shot out of bags upon th ! wooden floor of an apple-room, the sound in the house as each bag was shot closely resembled that of distant thxmder. 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 liim, and on again returniag to the house be listened to the riunbling with all cheerfulness. INSTINCT. 1C9 CHAPTEE XL Instinct. Definition. 1 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 I 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 circumstaDces by all the individuals of the same species." Eeferring 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. 10-17. t I say "at most," because such a stimulus may be less than a sensation, in that it may never cross the field of consciousness. 160 MENTAL EVOLUTION IN ANIMALS. stimulus to an action apparently instinctive, ex hypotliesi tlie 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, and 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. Eefiex 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. IGl 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 by 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 giasp 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 wMeh 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. 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 between 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 single 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 within 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 twelve days old one of my little proteges, while running about beside me, gave the peculiar chirr whereby they announce the approach of danger. I looked PERFECTION OF INSTINCT. 163 Up, and behold 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, which, if anything, might be acquired by imitation — for a hen with 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 when 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.R.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 dexteiity, I may mention that on placing four ducklings a day old in the open air for 164 MENTAL EVOLUTION IN ANIMALS. the first time, one of tliem almost immediately snapped at and caught a fly on the wing. More interesting, however, is the deliberate art of catching flies practised by the turkey. 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 tliem. In doing this, its head could be seen to shake like a hand that is attempted to be held steady by a visible effort. 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 sufficiently 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 mammals. He found, for instance, that new-born pigs seek to suck almost immediately after birth. If removed twenty feet from the mother, they wriggle 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 distinguisliable 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 kittens 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 " Nature." " Apropos to what Mr. Spalding says about the early age at which the instinctive antipathy of the cat to the dog becomes apparent, 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- * Nature, vol. xi, p. 507. PERFECTION OF INSTINCT. 165 house wliich contained a doe rabbit with a very young family, I turned loose a ferret. The doe rabbit left her young ones, and the latter, as soon as they smelled the ferret, began to crawl about in so energetic a manner as to leave no doubt that the cause of the commotion was fear, and not merely the discomfort arising from the temporary absence of the mother."* With reference to the instinctive endowments of this kind in kittens, I may also quote the following, which I find among Mr. Darwin's MS S : — "The many cases of inborn fear or ferocity in young animals directed towards particular objects, as well as the loss of these individualized passions, seems to me extremely curious. Let any one who doubts their existence give a mouse to a kitten taken early from its mother, and which has never before seen one, and observe how soon the kitten growls with hair erect, in a manner wholly different from when at play or when fed with ordinary food. We cannot suppose that the kitten has an inborn picture of a mouse graven in its mind. But, as when an old hunter snorts with eagerness at the very first sound of the horn, we must sup- pose the old associations excite him almost as instantly as when a sudden noise makes him start, so I imagine, with the difference that the imagination has become hereditary instead of being only fixed by habit, the kitten without any definite anticipation trembles with excitement at the smell of the mouse." The only other observations made by Mr. Spalding which it is desirable to quote are those by which he proved experi- mentally that young birds do not require, as was ordinarily supposed, to be taught to fly, but fly instinctively. This fact was proved by keeping young swallows caged until they were fledged, and then allowing them to escape. When we con- sider the complicated muscular co-ordination required for flight, the fact that young birds when fledged should be able to fly at the first attempt constitutes another remarkable instance of the perfection of instinct. Of course it is true that under ordinary circumstances the parent birds encourage their progeny to fly, but the experiments in question show that such encouragement, or tuition, is not necessary to enable the young birds to practise the art. But it is among insects that we meet with the most re- * Nature, vol. xi, p. 554. 166 MENTAL EVOLUTION IN ANIMALS. markable cases. Thus, to give only a few. Keaumur and Swanderdam assert that a young Bee, as soon as its wings are dry, will 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, which 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 offspring. 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 space 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 time." J 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 fully- * Kirby and Spencc, loc. cit., vol. ii, p. 470. t Ihid., i, p. 357. J Sir J. Lubbock, Address to Entomol. Soc, 1882. IMPEEFECTION 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 life as a larva and its new life as an imago, is as great as the difference between the 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 quite as remarkable 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 tliis 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 carnaria) deposits its eggs in the flowers of the " carrion plant " {Stapclia hirsuta), the smell of wdiich resembles that of putrid meat, and so deceives the fly.* Similarly, the house-fly has been observed to deposit eggs in snufi'.f Again, the Eev. Mr. Bevan and Miss C. Shuttleworth, write me independently that they have seen wasps and bees visiting representations of flowers upon the wall-paper of rooms ; and Trevellian saw the same mistake made by the sphinx-moth.^ 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, E.E.S., informs me that he has noticed honey-seeking insects mistake for flowers the bright coloured salmon flies stuck in his hat while fishing ; and Mr. F. M. Burton, writing to " Nature " (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 naturalist Couch observed a * E. Darwin, Zoonomia, i, § 16, art. 11. Also Kirby and Spence, loc. cit., ii, 469, who state the fact on the authoi-ity of Dr. Zinken. t Zinken, in Germar. Mag. der Ento., Bd. I, abth. 4, § 189. X See Houzeau, loc. cit., I, 210. 168 MENTAL EVOLUTION IN ANIMALS. bee mistake a sea-anemone {Tealia crassicornis), w^iicli was " covered merely by a rim of M'ater," for a flower— darting into the centre of the disk, " and though it struggled a good 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.f " 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. rufa) carrying pupa skins, with a great and apparently useless expenditure 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 first 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.^ 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 iu 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 Rarvesting Ants and Trap-door Spiders, p. 37, et seq. IMPERFECTION OF INSTINCT. 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 escaiDe 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 enough in the case of tamed animals (which when agaiu " 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, hut 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 which 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 unhooded 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 IMPEKFECTION OF INSTINCT. 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 connection, 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 hatching, took to the eggs, sat on them, and brought out chicks.' Says Willoughby (in ' Pay'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 ofl&ce,' says Baptista Rosa (' Magi a 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.' Keaumur (' Art de Paire Eclore.' torn, ii, p. 8) 172 MENTAL EVOLUTION 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 was confounded, and became mixed with reason or experience : for it tried repeatedly to suck three or four other Idttens 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 OHrich ''S. Breutnall, Port Elizabeth, 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 had 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 singular aberration of instinct had become a fixed delusion, whenever the bottle was thrown or placed in the yard — no matter whether it lay horizontally or was placed upright — the same ridiculous scene was enacted ; at that moment the pigeon came flying down v/ith 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. •we so regard the exhibitions of erotomania, infanticidal mania, &c., which occur 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 which 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 they 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 which 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. Probably this is the explanation, although I 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 (chiefly domestic work, for which they are fed by their foraging sisters) ; so it is possible that in the hive-bee the drones were originally useful members of the community, and that they have lost their primitively useful instincts. But whatever 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 flagrant 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 during 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 eflbrts, 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 sa5''s 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 occur, 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. Now 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 race — 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 clcs Kmdes, Leipzig, 1882, pp. 166-7. t ^f^^<^-> I'P- 107-75. OKIGIN AND DEVELOPMENT OF INSTINCTS. 177 CHAPTER XII. Instinct (contimced). 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 intelligent, 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 foT any other purpose, adopted a similar habit, the 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 effects of habit in successive generations, actions which were originally intelligent become, as it were, stereotyped into per- * Quoted from my own article ou "Instinct," in tlie Encyclopaedia Bri- tannica. 178 MENTAL EVOLUTION IN 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 sj'^stem 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 way 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 cb 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, tlien 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 a 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 time, 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 right within before dragging 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 again 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. Nat, 4 ser., tome vi, p. 148. With respect to Bees, see 180 MENTAL EVOLUTIOX IN ANIMALS. " In another way we perhaps see tlie 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 that 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, toI. i, p. 497. For tlio hammock caterpillar, Bee Mem. Hoc. Pliys. de Oenbve, tome vii, p. 154. * Zoonomia, p. 140. t 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 schoolroom, 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, imless 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 well 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 v,^onderfully 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 " rliythmical 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 {Menial Physiology, p. 373), " Wliat 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. altliougli every dog adheres to his particular attitude through life. Nearly all domestic animals exhibit slight but indi- vidually constant differences of movement w^hen 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 avidity, 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, whicli is referred to in this connection in Mr. Darwin's MSS. + For example, the Nut-hate li 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 desci'ibes 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 Golden Eagle builds in precipitous crags of rock ; but Mr. D. E. Knox {Antumns on the Spey, 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 Bometimes 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 wliich 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 the twigs and lichens outside and the fine grasses which invariably constitute the lining ; this lias been more especially the case when th 6 bird has select-ed 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 OEIGIN AND DEVELOPMENT OF INSTINCTS. 183 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, Eiichner observes, " one ant will let herself be killed rather than let go the pupa which 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 v/idgeon 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 herself down upon the ground just observed in the text, sucli instaneea might be multiplied indefinitely ; 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 H'*-^' ORIGIN AND DEVELOPMENT OF INSTINCTS. 185 tinder the same roof, and in the same straw bed kept each other warm ; and when the dog was taken to the field, the lamentations of the goose 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- tridges and landrails. Such unusual cases among 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 tliat " bands of tlie Grolden-crested Wren may frequently be observed in winter consorting with bands of the Coal-Titmouse, and in a less degree with those of the Long-tailed Titmouse ; "while parties of Redpoles 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 ANIMALS. same trick under the same frame of mind, and which 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 Piev. 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 purely 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 different words in Variation of Animals and Flanls, &c., vol. i, pp. 450-1. t Here, however, I may remark that I have noticed several Syke terriers perforin these movements while begging, so that the action seems to be due to some race-distinction of a psycliological 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 thoroughly sense- less psychological peculiarity. I refer to the instance "which was communicated some years ago to Mr. Darwin by Dr. Huggins, r.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 brought the dog, 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 him. 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. NichoUs, 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 would 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 (though 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 all 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 Malle asserts that these different paces have been acquired since the time of the Roman 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. t After giving numerous references on this point in a footnote, Mr. Darwin concludes the latter thus : — " I may add that I was formerly struck by no horse on the grassy plains of La Plata havinfj the natural high action of some P2nglish 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. Sec. 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 fev/ 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 chapter, 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. This 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 would 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 fX the biscacha, which " almost invariably collects all sorts of * For further particulars on the instinct of tumbling, see Variation of Animals and Plants, vol. i, p. 219, and 230. I Some years ago the Eatels 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 pi-obably develope a true instinct of turning somersaults analogous to that of the tumbler- pigeon. X I have frequently no'dL'ed a siiiiilar 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 IV, — viz., that such habits may vary, and that vjhen they vary the variations may be 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 undergoes the variation of becoming 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. From 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 we 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 way of proof. If among a number of meaningless habits, all more or less hereditary and more or less varial^le, 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 this instinct began in habits adapted to the protection of the eggs, it is certain that it cannot have begun with any intelligent reference to hatch- ing them ; and it is no less certain that before the instinct attained its present degree of perfection, it must have passed 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 fly 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. Tabre has observed that Bembex inclica lays an egg in a chamber, * A Movographic Revision and Si/nopsis of the Trichoj^tera of the European Fauna, 1881, by Eobert M'Lachlan, F.E.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. Numerous 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 proj)ositions, 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, vjhen frequently performed hy 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. 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, although 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 our dis- cussion, therefore, we shall now pass.f Accepting, then. Proposition VI as beyoncl dispute, we have here to substantiate Proposition VII, viz., That automatic actions and conscious habits may he inherited, Now we have already seen that this is certainly the case * Article "Instinct," Todd's Cyclo. of Anat., vol. iii, 1839. t Mr. Darwin's MS points out that persons of weak intellect are very apt to fall into habitual or automatic actions, ai^d 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, they are found to resemble automatic habits in showiug most unrestricted play when intelligence is enfeebled or idiotic. 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 wliich 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 .... Hofacker, in Germany, remarks on the inheritance of hand -writing ; and it has been even asserted that English boj's, 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 eases of hereditary aptitude for music and painting. Also Galton's ITerediiary Genivs, for high mental qualities running in families, either in the same or in analogous Uncs of activity ; and Spencer (Psychology, i, p. 422) for race-characteristics of psychology in man. The effects of " good breeding " or " blood" in bequeathing hcredit&ry disposition and refinement have already OEIGIN AND DEVELOPMENT OF INSTINCTS. 195 now to the more important case of animals, I shall give only a few examples among almost any number that 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 instance 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 show that the same applies to the sense of modesty. * Phil. Trans., 1839, p. 369. + Inasmuch as the action of " begging " is so unusual in the Cat, the above case of its hereditary transmission is more remarkable than the similar cases which occur in the Dog ; see Lewes, Problems of Life and Mijid. vol. i, p. 229, and Fiske, Cosmic Philosophy, vol. ii, p. 150, and more especially a case recorded by Mr. L. Hurt, in Nature (Aug. 1, 1872) of a Skye terrier 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 Sulivau, R.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 haa 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 otliers 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 IBritish 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. Eae, F.K.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.' " OKIGIN AND DEVELOPMENT OF INSTINCTS. 197 played an important part, and at present we are confining 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- cated 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. Pages might 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 development of 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 with 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, wdiich dropped upon crossing the track of a Partridge, as its male parent would 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 them 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 gxeat-grandfather was 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."J 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. f Blaine, Rural Sports, p. 8G3, quoted by Darwin. X Ori. 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. Gr., 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. Bull, 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 J 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 ; under- 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 Ger- many, 232 ; sucking bones, 247 ; sense of direction in, 290. Causation, appreciated by animals, 155-8. 388 MENTAL EVOLUTION IN ANIMALS. Cephalopoda, intelligence of related to organs of touch, 57 ; eyes of, 88 ; ears of, 89 ; tactile organs of, 89 ; colour-sense in, 98 ; memory 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 rostratus, 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 handwriting, 194. Ccelenterata, consciousness in, 76, 348 ; special sense of, 83-4 ; emotions of, 342 ; grade of mental evolution of, 348. CoUett, E.., on migration of the lemming, 283-5. Colour-sense, 98-104. Comparative Psychology in relation to comparative anatomy, 5 ; objects of, as a science, 6-7. Comte, on Fetishism in animals, 154. ConceptuaUsm, 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 tho 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 psycliology 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-pai-asitic habits or the, 251-2 ; parallelism of instincts of the, with those of Molothrus, 273-4 ; migration of the young, 289. CuciiliitcB. 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 ants 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 vdldness 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, 215 ; on local variations of instinct in birds, 245-6 ; on the hysena not burrowing in South Africa, 249 ; on specific variations of instinct as difficulties against the theory of natural selection, 251 ; on parasitic habits of Molothrus, 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 theory 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 effects 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 J on the incorrigibly wild instincts of sundry 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 artificially 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. DioncBa, discrimination shown by, 50-1. Direction, sense of, 289-94. Discrimination, in relation to clioice, 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 upon 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 showing fear of water, 188 ; natural wilduess 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 Odjjnerus, 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, nervous 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. Edward, 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 wounded 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 Englena 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 Octojpus, 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. P. Fabre, J., on instincts of Bembex, 166, and of Sphex, 179, 2S9-303 ; on sense of direction in bees, 293-4. Fear in animals, 341 ; in young children and low animals, 342-3. Eeeling. See Sensation. Feelings, logic of, 325. Feigning death, 303-16 ; injury, 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 functions 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 the subordinate part played by natural selection in the development of instinct, 256. ritch, Oswald, on benevolence shown by a cat, 345-6. FitzRoy, 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 Rev. 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. Galen, on instinct of a kid, 115. Oallus hankiva, wildness of chickens reared from wild stock of, 232. Galton, Francis, on hereditary genius, 194. Ganglia, structure and functions of, 26-33 ; Mr. Spencer's theory of genesis of, 32. Gardener, J. S., on moths flying into a waterfall, 280. Gardner, on intelligence of a crab, 336. Garnett, on instincts of crossed ducks, 199. Gasteropoda, eyes of, 88 ; memory in, 121. See Mollusca. Generalization, 145. Gentry, W. K. G., on carnivorous habits of herbivorous rodent, 248. Gladstone, W. E., on colour-sense, 100. Goatsucker, 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. Haeckel, Professor, on sense - organs, 81, 85-6 ; on supposed unknown sense pobsessed by Fish, 90 j on supposed unknown senses possessed INDEX. 393 by Mammals, 95 ; 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. Handwriting, inheritance of, 194. Hate, in animals, 341, 345. Haust, on ducks building in trees, 211. Hawfinch, learning the song of a blackbird, 222. Hawk, eye of, 91 ; old, teacLing young to capture prey, 226 ; changed in- stincts of Swallow-tailed, 254. Hearing, sense of, in Medusae, 82 ; in Articulata, 86-7 ; in MoUusca, 88-9 ; in Fish, 90 ; in Amphibia and Reptiles, 90 ; in Birds, 91-2 ; in Mam- mals, 93-4 ; reaction-time of, 132. Helix 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 incvibating and natural instincts of the, 213-17 ; drinking move- ments of the, not instinctive, 229 ; loss of incubating instinct of tbe 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 ; to 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. Seteropoda, eyes of, 88. Hertwist, Professors O. and R., on nervous system of llediisce, 69. Hewetson, on variation in the nest of the nuthatch, 182. Hewett, on wildness of hybrids between fowls and pheasants, 199. Hill, Richard, on gregarious habits in nidification, 253. Hitzig, on functions of the cerebrum, 35. Hofaeker, on inheritance of handwriting, 194. HoflPmann, Professor, on a puppy learning to imitate a cat, 224. Hogg, on instincts of a sheep-dog, 240-1. Holiman, 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 acquired 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 bankiva, 232 ; on migration, 288. Huxley, Professor T. H., on evolution of sense-organs, 104. Hydrozoa, nerve-tissues in, 24. Hyaena, not burrowing in South Africa, 244. Sylohates 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 ia 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 different 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; instincts of, 165-8, 179, 201-2, 203-9, 220-1, 246, 277-81, 285-6, 290, 293-5, 297-309 ; emotions of, 344. INDEX. 395 Instinct, physiological aspect of, 52 ; as hereditary memory, 115-17, 131 ; definition of, 159; involres a mental element, 160; perfection of, 160-7 ; in youn^ birds and mammals, 161-5 ; in insects, 165-8, 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 fossilized, 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 difii- 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 j of feigning injury, 316-17; in relation to reason, 338-9. 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. K. 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 instincts 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 vai-iation 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 ANBIALS. Lamarct, his tlieory of evolution of nerves by use, 33. Lamellibranchiata, 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. Leptdoptera, 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 a8 groups of components, 41 ; his definition of Sensation, 78 ; on pre- perception, 139 ; on instincts of duckUngs, 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 Californian 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 Hymenoptera, 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. MacFarlane, 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. Macroglos/sa stellatariim, 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 imitating the songs of other birds, 222 ; on a terrier imitating a cat, 233-4 ; on old birds educating young, 226 ; on instinct of burying Buporfluous food, 233. INDEX. 397 Manimals, special senses of, 57 ; siglit, 92 ; hearing, 93-4 ; taste and touch, 94 ; coloui', 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, 144, 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 convulsion, 44. Marshall, Professor John, on sense of smell in Octopus, 89 ; on sense of sight in Surinam Sprat, 90. Martins, nidification of, 210-11 ; warning chickens against hawks, 221-2. McCready, on larvae of a Medusa sucking their parent, 259-60. MeduscB, larvae of, sucking parent, 259-60 ; following light not instinctive, 258 ; nervous system of, 24, 28 ; special sensation in, 56, 81-83. Melanerpes formicivorus, peculiar instinct of, 255. Memory, of ganglia without consciousness, 35-6 ; analysis of, 111-17; of infant, 114-16, 120-1; in MoUusca, 121-2; in Echinodermata and Crustacea, 122 ; in Insects, 123 ; in Fish, 123 ; in other Vertebrata, 124 ; as involved in perception, 129-30. Merejkowsky, on colour-ssnse of Daphnea 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. G., on reason, 325, 335-40. M'Lachlan, R., 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. MoUusca, 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 beaver, 329. Morgan, Professor Lloyd, on alleged instinct of the scorpion to commit suicide, 278. Moseley, Professor H. N"., on colour-sense of marine animals, 99; on imper- fection of instinct in honey-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, 38-4i4. Mysis, ear of, 87 ; colour-sense of, 98. Mysteriousness, sense of, in animals, 155-8. N. 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 HornbiUs, 255. Nightingale, midnight singing of, inlierited, 246. Noulet, on nidification of swallows, 211. Nuthatch, variation in nest-building of the, 182. o. 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. Orthoptera, ears of, 87. Osmia aurulenta, 208. Osmia bicolor, 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, Sir 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 Ground, 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 affected by heredity, 130-1 ; in Mammals, Birds, Reptiles, 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 j 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 j 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, appi'cciated by birds, 91 ; by Si/looates agilis, 93 j and by dogs, 94. Play, 341, 345. Pleasures, 105-11. JPleuronectidce, 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 actinitB, 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 preferring sweet tastes, 114, and remembering taste of milk, 115 ; on instinct of chickens, 116-17 ; on I'apidity of perception acquired by training, 138 ; on infant learning to balance the head, &c., 175-6 ; on imitative move- ments and dreaming shown by the infant, 225 ; on kataplexy of animals, 308-11 ; on emotions of the infant, 342, 344. Prichard, on a puppy reared by a cat, 217, 224. Pride, 341, 345. Progeny, yearning for, 212-13. 400 MENTAL EVOLUTION IN AMIMALS. Protista as affected by light, 80-1. Protozoa as affected by light, 80-1 ; chasing one another, 81. Pteropoda, eyes of, 88. Pugnacity, 341, 344. Pierguin on somnambulism in animals, 149 ; on delusions o£ an ape, 150. Psychology, relation of Comparative to Comparative Anatomy, 5 ; distinction between, and Philosophy, 11. R. Eabbit, 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 burrowing in Sor, 248. Kae, 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. Kats, understanding of mechanisms by, 351. Eattle-snake, tail of the, 277. Eazor-fish, memory in the, 122. Reaction-time, in perception, 132-5. Reason, 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. Reaumur, on larvse remembering the taste of particular leaves, 115 ; on instincts of bees, 166 ; on instincts of the capon, 171-2. Recognition of offspring, 3 19. Recollection, 120. Reflection, 145, Reflex 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. Regret, in animals, 347. Rhea, mistaken instinct of the, 168. Remorse, in animals, 341. Rengger, on changed instincts of a wild cat in confinement, 172 ; on attach- ment of a monkey to a dog, 184. Reptiles, sense of sight in, 90; hearing, smell, taste, and touch of, 90; colour 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. Resentment, 341, 345. Retriever. See Dog. Revenge, in animals, 341, 346. lihizopoda, powers of special sense in, 80. Ribot, on memory, 111-13. King-plovers, continuing to build where sea has retired, 246. Romanes, G-. J., observations on lledttseB, 31-2; on sea-anemones, 48, 83; on JEchinodermala, 8i, 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 coloui'-sense of Octopus, 98-9; oa INDEX, 401 earliest age at wliicli an infant is able to associate ideas, 120-1 ; on inability of hermit-crab to associate simple ideas, 122-3 j on time-rela- tions iu perception, 136-7 ; on sense of mysterious in, and appreci ition of cause by dogs, 155-8; on instinctive antipathy of young rabbits to ferrets, 164-5 ; on handwriting, 194 ; 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, 171. 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. Saint-Hilaire, GeofFroy, on intelligence of an orang-outang, 328. Salmon. See Fish. Satiety, sense of, 95. Savages, sense of direct.'on 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 Serpulte, 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 Australian puppy, 232 j on love of man as in- stinctive in domestic dogs, 239. Seeboum, on migration of birds, 289. Scinus htidsonitts, 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 j 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 wasps, 167. Sight, sense of, in Protista, 81 ; in Medusse, 81-2 ; in Echinodermata, 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 j reaction- time of, 133 ; in young animals, 161-4. Sigismund, on infants remembering the taste of milk, 114 402 MENTAL EVOLUTION IN ANIMALS. Signs, logic of, 325. Skate, olfactory organs of the, 90. Skylark, feigning death, 304. Smith, Adam, on a case of couching for cataract, 323-4. Smith, Dr. Andrew, on hyjenas not burrowing in South Africa, 249. Smith, F., on instinct of bees, 20S. Smith, Col. H., on instincts of wild dogs under 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 Reptiles, 90 ; in Birds, 92 ; in Mammals, 92-3. Snipe, sense of touch in the, 92. Social feelings, in animals, 341, 344. Solen Groose, 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, eye of the, 90. Squirrel, a, dying of terror, 307. Star-fish. See Echinodermata. Starlings, associating with rooks, 185. Starling, 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 natural 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. Surprise, 341, 34 i. Swallow, plasticity and local variation of instincts of the, 210, 246-7; migra- tion of the, 296. Swallows, nidification of, 210-11. Svvainson, on mistaken instinct of the Australian parrot, 167. Svvandcrdam, on instincts of beeB, 166. INDEX. 403 Swift, eye of the, 91. See Swallow. Sympathy, 341, 345. Sparrow, nidification of the, 210 ; changed instincts of a, 213 ; learning song of a linnet, 222 ; local yariations of instinct of the, 247. TacJiornis pTioenicohea, 21 2. Tailor-bird, modified instincts of the, 210. Tait, Lawson, on hereditary transmission of hogging in a cat, 195. Tameness. See Wildness. Taste, sense of, in Protista, 81 ; in Articnlata, 88 ; in Fish, 90 ; in Amphibia and Keptiles, 90 ; in Birds, 92 ; in Mammals, 94, Temmick, on migration of birds, 289. 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 attached to dogs and cats, 184 ; on efTects of domestication in modifying instinct, 242 ; on a monkey feign- ing death, 311-12. Thompson, Eev. 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. Tiaropsis 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 Medusoe, Echinodermata, MoUiisca, and Articulata, 56 ; in Vertebrata, 58 ; in Fish, Amphibia, and Reptiles, 90 ; in Birds, 92 ; in Mammals, 94 j as origin of all special senses, 103-4 ; reaction-time of, 132. Trevellian, on mistaken instinct of a sphinx moth, 167. 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. Ulloa, on dogs not barking in Juan Fernandez, 250, Venus' Fly-trap. See Dionaa. Venn, on association of ideas by talking birds, 124. Villiers, De, on instincts of the processional caterpillar, 312. 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 evolution 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 crossed ducks, 199. Wasps. See Insects. Weasel, feigning death, 307. Weber, on sense of temperature, 96. Wedderburn, Sir 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 Rev. G., 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, 124. 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. Wolfl", Madame de Meuron, on a migration of but) erflies, 285. Wolverine, 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 Ground, 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. Wundt, on analogy between conscious and unconscious memory, 114. Yarrel, on Birds, 222, 247. Youatt, on the Dog, 150, 198, 211 ; on the Sheep, 224, 2L7. z. Zinken, Dr., on mistaken instinct of flies, 1G7. INDEX. 405 INDEX TO Mr. DARWIN'S POSTHUMOUS ESSAY. A. Alison, on instinct, 357, 367, 370, 375. Amhlyrhynchus, tameness of, 361. Angoumois moth, double instincts of the, 373. Antelopes, migi-ations of, 381. Ants, ceasing to move eggs when heat is supplied to them, 368 ; instincts of white, 376. Artamus sordidus, variations in nest-building instincts of, 372. Audubon, on nidification of Gulls, 369, and of Sterna minuta, 372. B. Bachman, on migrations of the bison and Canada geese, 356 ; on migrations of squin-els, 380. Banks, Sir J., an changed instincts of a spider, 373. Barrington, Hon. Daines, on wildness of large birds, 362. Beaver, habitations of the, 372. Bechstein, on migratory and non-migratory thrushes, 355; on varialions in the singing of nightingales, 374. Bees, instincts of, in making queens, 376 ; in ventilatinsr hives, 378-9 ; mis- taken instincts of, 382-3 ; variation in instinct of, 372-3 ; pillaging each other, 375. Birds, migratory habits of, 355-9 ; tameness of, in islands unfrequented by man, 360-63 ; nidification of, 364-72 ; variation of instinct in, 374 j instincts of small in mobbing hawks, 382. Bison, migrations of the, 355, 381. Bizcacha, instincts of the, 379. Blackbirds, nidification of a pair of, 371. Blackwall, on nidification, 371 ; on magpies not imitating sounds when in a state of nature, 374-5 ; on nidification of a yellow bunting, 371. Blyth, on instincts of removing mutings, &c., fi'om nests, 379 ; on the wild hen cackling over her eggs, 381. Bonnet, on double instincts, 373-4; on instincts of ants, 368. Botton, on nidification, 369. Bourgoanne, on migratory instinct of sheep in Spain, 358. Brent goose, migratory impulse of a worn out, 356. Brougham, Lord, on instincts of chickens, 374. Bruce, on instincts of the Bee-cuckoo, 382 ; on instincts of the Abyssinian pigeon, 379. Buch, von, on animals dying in the Solfortara of Java, 380. Bufialo, migration of the, 355-6. Burrowing, instinct of, 372. Butcher-bird, nidification of the, 382. 18 406 MENTAL EVOLUTION IN ANIMALS. c. Carmichael, Capt., on tameness of birds at Tristan d'Acunlia, 361. Caterpillar. See Insects. Chaffinch, nldification of a, 371. Chickens, instincts of, 374. Chrysomela, feigning death, 364, Clarke, on migration of the bison, 381. Cluiscus, feigning death, 364. Colenso, on a migratory cuckoo in New Zealand, 360. Collocalia, nidification of, 365-6. Couch, on animals feigning death, 363 ; on nidification, 369, 370, 371. Corse, on elephants attacking companions escaped from captivity, 381. Crow, hooded, fearlessness of, in Egypt, 363. Cuckoo, mistaken instincts of the, 382 j instincts of the Bee, 382. Cu7'Chlis, feigning death, 364. Cuvier, on Tocal organs of Passeres, 375. D. B'Arbigny, on knowledge of time shown by a hawk, 357. [Darwin, Charles, on tameness of animals in islands unfrequented by man, 360-62 ; on a lizard feigning death, 363-4 ; on nidification of Collo- calia, 365-6 ; on stupidity of Furnarius cunicularius, 371 ; on the in- stinct of burrowing, 872 ; on instincts of the Guanaco and Bizcacha, 379 ; on the nidification of Furnarius, 382. Death, feigning of by animals, 363-4. Deer, expelling wounded companions from herd, 376. De Greer, on insects feigning death, 364. Direction, sense of, shown by animals and men, 357-9. Dog, instincts of, with regard to excrement, 379. Du Bois, on tameness of birds at Bourbon, 361. Duck, fearlessness shown by wild, of railway-trains, 362 ; a logger-headed, defending a goose from a hawk, 381. Duges, on double instincts of spiders, 374 ; on maternal instincts of spider, 382. E. Elephants, attacking companions escaped from captivity, 381. Elk, migrations of the, 360. F. Eischcr, Professor, on a hen incubating her eggs in a hot-bed, 367. Ely -catcher, a, building nest upon a hot-house, 367. Fox, wariness and tameness of the, 361. Fox, the Eev. W. D., on the nidification of a pair of blackbirds, and a pair of redstarts, 371. Fremont, Col., on migrations of the bison, 356. Furnarius cunicularius, stupidity of, 371 ; nidification of, 381-2. G. Gad fly, instincts of the, 375. INDEX. 407 Golden -plover, fearlessness shown by the, of fire-arms, 363. Gold-finch, nidification of the, 369. Goodsir, on fearlessness shown by wild ducks of railway trains, 362. Goose, migratory impulse of a Brent, worn out, 356 ; the Siberian feigning death, 363. Goring, instinct of, 381. Gould, on migration of birds, 355 ; on nidification of Megapodidm, 367 ; of Artamus sordidus, 372. Graber, on migratory birds of Faroe, 360. Grey, Sir G., on sense of direction shown by native Australians, 357. Gulls, nidification of, 369 ; parasitic instincts of, 373. Guanacoes, instincts of, 379. Harcourt, E, V., on non-migratory habits of woodcoct, 356 ; on absence of migratory birds in Madeira, 359. Hare, alleged burrows of the, 372. Hawk, knowledge of time shown by a, 357; tameness of a, at Galapagos Islands, 361. Hearne, on habitation of the beaver, 372. Heineken, Dr., on non-migratory habits of woodcock, 356. Hen, wild cackling over her eggs, 381. Herbert, Thos., on tameness of birds at Mauritius, 361. Heron, wildness of the, 362 ; nidification of the, 369. Hewitson, C, on tameness of magpies in Norway, 363 ; on nidification of a chaffinch, 371. Sirundo, migration of, 358 ; nidification of, 365-6, 369-70. Histers, feigning death, 364. Hogg, on migratory instinct of sheep, 358. Home, on structure of the proventriculus of Collocalia, 366. Homing faculty in animals, 358. Hogstrom, on migration of ermines, 380. Horse, instincts of the, with regard to excrement, 379. House-fly, instincts of the, with regard to excrement, 379. House-martin, nidification of the, 365. See Martin. Huber, on bees pillaging each other, 375 ; on mistaken instincts of bees, 382-3. Huber, P., on double instincts of a beetle larva, 373. Hunt, Consul C, on birds visiting the Azores, 358, 359-60. Hull, the Rev. J., on nidification of the magpie, 370. Hyaenas, not burrowing in S. Africa, 372. ^ Hyrax, instincts of the, with regard to excrement, 379. Icterus haltimore, nidification of, 372. Insects, feigning death, 363-4 ; varied instincts of, 372-3 ; double instincts of, 373-4 ; hatched in human body, 375 ; instincts of, exliibited only once, 377 ; instincts of, with regard to excrement, 379 ; migrations of, 378 ; mistaken instincts of, 382-3. Instinct, of migration, 355-60 ; of fear, 360-64 ; of nidification, 364-72 ; double in certain birds, 371-73, and in certain insects, 373-4 ; of mam- mals in forming habitations, 372-3; of beaver and musk rat, 372; of 408 MENTAL EVOLUTION IN ANIMALS. buiTOwing, 372 ; variations in, of bees, 372-3 ; of chickens pecking fheir way out of eggs, 374 ; of gad-fly, 375; of parasitism, 375-6; of bees, 375-6 ; of Molothrus and white ants, 376 ; of digging pitfalls, 376-7 ; alleged to be detrimental to the species exliibiting it, 377; only once exhibited, 377-8; differences of, in related forms, 378; small and trivial, 378-9 ; of removing broken eggs and mutings, 379 ; of Abys- sinian pigeon, Lagostomus, and Guanacoes, 379 ; with regard to excre- ment, 379 ; imperfect and mistaken, 380 ; social, 381 ; apparently detrimental, 381-83 ; of attacking wounded companions, 381 ; of cock pheasants crowing and wild hens cackling, 381 ; of shrew-mouse scream- ing, ostrich scattering eggs, 382 ; at fault in sundry animals, 182-3. Ireland, habits of animals in. See W. Thompson. Ischndi, on migratory instincts of Alpine cattle, 358. lulus, feigning death, 364. J. Jackdaw, nidification of a, 370 ; stupidity of a, 371. Jenyns, the Kev. L., on habitations of rats, 372 ; on insects hatched within the human body, 375 ; on crowing of the cock pheasant, 381. Jesse, on the nidification of a jackdaw, 370. Kangaroo, regm-gitation of food by the, 374. Kirby and Spence, on instincts of insects, 364, 368, 374, 375, 376, 377, 378, 379, 383. Knapp, on nidification of the butcher-bird, 382. L. Lagostmmis, instincts of, 401. Lamarck, on co-operation of swallows, 375. Larvse. See Insects. Lloyd, L., on migration of the lemming, 380. Le Roy, on wariness of foxes and wolves, 361. Lewis, on migration of the bison, 381. Le Vaillant, on migratory and non-migratory habits of quail, 355. Linneus, on instinct, 377. Livingstone, on instincts of hyrax, 379. Lizards, wildness and tameness of, 356 ; feigning death, 363-4. M. Macgillivray, on nests of swifts, 365-6, of kitty-wrens, 368 and 370, of herons, 369 ; on cooperation in martins, 375 ; ou parasitism in gulls, 375. Magpie, fearlessness of the, in Norway, 362 ; nidification of the, 370 ; powers of the, in imitating various sounds, 394-.'). Mammals, migrations of, 355-6, 358 -9 ; instinctive fear shown by, 361 j habitations of, 372-3. INDEX. 409 Martin, nidificat-on of the, 364, 3fi9, 370. Martins, cooperation shown bj, 375. Martin, W. C, on regurgitation of food by the Kangaroo, 374. Megapodidm, nidification of, 367-8. Mice, wariness of, 362. Migration, 355-60; of young birds, 355; of quail, 355; of buffalo, 355 fi; theory of, 359 ; of elk and reindeer, 360 ; of lemming, squirrel, and ermine, 380 ; of insects, 380 ; of pigeons, antelopes, and bisons, 381. Molothrus, instincts of, S76. Montague, on nidification of sparrows, 369. Moresby, Capt., on tameness of birds at Providence Islands, 361. Mosto, Cada, on tameness of C. de Verde Island pigeons, 361. Musk-rat, habitation of, 372. N. Nidification, 364-72 ; of swallows, 365-6 ; of MegapodidcB, 367-8 j varia- tions in instinct of, 369-73 ; double instinct of, 371-72. "Nightingale, variations in singing of the, 374. / o. Osmia, variation in instincts of, 372-3. Ostrich, scattering her eggs, 382. P. Partridge, variation in instincts of the, 373. Peabody, on nidification of Cypelus pelasgius, 365 ; of kitty-wrens, 368 ; of herons, 369 ; of Totanus macularius, 371 ; of Icterus baltimore, 372. Pheasant, maternal instincts of the hen, 379; crowing instincts of cock, 381. Pigeon, fearlessness of the, at C. de Verde Islands, 361, and at Galapagos, 363 ; instincts of the Abyssinian, 379 ; migration of the Passenger, 381 j instinct of the, in attacking wounded companions, 380. Ptinus, feigning death, 364. Pulex, variations of pupa of, 374. Q. Q.uail, migration of the, 355. R. Eae, Dr. J., on feai'lessness shown by birds of railway trains, 362 j and of firearms, 363. Eat, musk, habitation of the, 372. Eat, wariness of the, 362. Eeaumur, on instincts of ants, 368. Eedstarts, nidification of a pair of, 371. Eeindeer, migrations of the, 360. 410 MENTAL EVOLUTION IN ANIMALS. Reinwardts, on animals dying in the Solfortara of Java, 3S0. Eichardson, on nidification of American swallows, 369-80. Eoberts, M. E., on nidification of Sirundo riparia, 365. Kobin, fainting from fright, 363 ; nidification of the, 369. s. Salmon, migrations of the, 355, 358. Savi, Dr, P., on the double instinct of nidification shown by Sylvia cisticola-, 371. Scope, on migration of salmon, 358. Scrope, W., on deer expelling wounded companions from herd, 381. Sheep, homing faculty of Highland, 358 ; migratory instinct of Spanish, 358-9. Sheppard, on the nidiGcation of a golden-crested wren, 371. Shrew-mouse, instinct of a, in screaming when approached, 382. Smith, Dr. Andrew, on migrations of quail, 355 j on hysenas not burrowing in S. Africa, 372. Smith, F., on variations in instincts of bees, 372-3. Snake, incubating eggs in a hot-bed, 367. Sparrow, nidification of the, 369. Spence, on migration of insects, 380. Spider, feigning death, 364 ; changed instincts of a, 373 ; double instincts of the hunting, 374 ; maternal instincts of the, mistaken, 382 ; instinct of the female to devour male, 383. Sterna minuta, variations in nest-building instincts of, 372. St. Hilaire, Geoffry, on tameness of hooded crows in Egypt, 363. St. John, on non-migratory habits of woodcock, 356. Sullivan, Captain, on a duck defending a goose from a hawk, 381. Swallows, migration of, 358 ; nidification of, 365-6, 369-80 ; cooperation of, 375. Swans, nidification of, 370. Swift, non-migratory habits of the, 356 ; nidification of the, 365-6. Sylvia cisticola, double instinct of nidification shown by, 371. T. Taylor-bird, nidification of the, 369. Thompson, E. 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