WII JAM FEE THE PRINCIPLES OF BIOLOGY BY HERBERT SPENCER IN TWO VOLUMES VOL. I REVISED AND ENLARGED EDITION 1898 NEW YORK D. APPLETON AND COMPANY 1902 ' COPYRIGHT, 1860, 1898, ?Y D. APPLETON AND COMPANY. V, PREFACE TO THE REVISED AND ENLARGED EDITION. RAPID in all directions, scientific progress has during the last generation been more rapid in the direction of Biology than in any other ; and had this work been one dealing with Biology at large, the hope of bringing it up to date could not have been rationally entertained. But it is a work on the Principles of Biology ; and to bring an expo sition of these up to date, seemed not impossible with such small remnant of energy as is left me. Slowly, and often interrupted by ill-health, I have in the course of the last two years, completed this first volume of the final edition. Numerous additions have proved needful. What was originally said about vital changes of matter has been sup plemented by a chapter on " Metabolism." Under the title " The Dynamic Element in Life," I have added a chapter which renders less inadequate the conception of Life pre viously expressed. A gap in preceding editions, which should have been occupied by some pages on " Structure," is now filled up. Those astonishing actions in cell-nuclei which the microscope has of late revealed, will be found briefly set forth under the head of " Cell-Life and Cell- Multiplication." Further evidence and further thought have resulted in a supplementary chapter on " Genesis, Heredity, and Variation " ; in which certain views enun- V vi PREFACE TO THE REVISED EDITION". ciated in the first edition are qualified and developed. Various modern ideas are considered under the title " Ke- cent Criticisms and Hypotheses." And the chapter on " The Arguments from Embryology " has been mainly re written. Smaller increments have taken the shape of new sections incorporated in pre-existing chapters. They are distinguished by the following section-marks : — § 8«, § 4G«, § 87a, § lOOtf, § 113«, § 127«, §§ 130«— 130d. There should also be mentioned a number of foot-notes of some significance not present in preceding editions. Of the three additional appendices the two longer ones have al ready seen the light in other shapes. After these chief changes have now to be named the changes necessitated by revision. In making them assist ance has been needful. Though many of the amendments have resulted from further thought and inquiry, a much larger number have been consequent on criticisms received from gentlemen whose aid I have been fortunate enough to obtain : each of them having taken a division falling within the range of his special studies. The part concerned with Organic Chemistry and its derived subjects, has been looked through by Mr. W. H. Perkin, Ph.D., F.R.S., Professor of Organic Chemistry, Owens College, Manchester. Plant Morphology and Physiology have been overseen by Mr. A. G. Tansley, M.A., F.L.S., Assistant Professor of Bot any, University College, London. Criticisms upon parts dealing with Animal Morphology, I owe to Mr. E. W. Mac- Bride, M.A., Fellow of St. John's College, Cambridge, Pro fessor of Zoology in the McGill University, Montreal, and Mr. J. T. Cunningham, M.A., late Fellow of University PREFACE TO THE REVISED EDITION. yii College, Oxford. And the statements included under Ani mal Physiology have been checked by Mr. W. B. Hardy, M.A., Fellow of Gonville and Caius College, Cambridge, Demonstrator of Physiology in the University. Where the discoveries made since 1864 have rendered it needful to change the text, either by omissions or qualifications or in some cases by additions, these gentlemen have furnished me with the requisite information. Save in the case of the preliminary portion, bristling with the technicalities of Organic Chemistry (including the pages on " Metabolism "), I have not submitted the proofs, either of the new chapters or of the revised chapters, to the gentlemen above named. The abstention has resulted partly from reluctance to trespass on their time to a greater extent than was originally arranged, and partly from the desire to avoid complicating my own work. During the interval occupied in the preparation of this volume the printers have kept pace with me, and 1 have feared adding to the entailed attention the further attention which corre spondence and discussion would have absorbed : feeling that it was better to risk minor inaccuracies than to leave the volume unfinished : an event which at one time appeared probable. I make this statement because, in its absence, one or other of these gentlemen might be held responsible for some error which is not his but mine. Yet another explanation is called for. Beyond the ex position of those general truths constituting the Principles of Biology as commonly accepted, the original edition of this work contained sundry views for which biological opinion did not furnish any authority. Some of these have 1* x PREFACE. the plates. The report commences as follows :— " Dr. Watts, after showing that on his own confession Spencer was indebted for his facts to Huxley and Hooker, who," &c., &c. Wishing in this, as in other cases, to acknowledge indebtedness when con scious of it, I introduced the words referred to, in recognition of the fact that I had repeatedly questioned the distinguished specialists named, on matters beyond my knowledge, which were not dealt with in the books at my com mand. Forgetting the habits of antagonists, and especially theological antag onists, it never occurred to me that my expression of thanks to my friends for " information where my own was deficient," would be turned into the sweep ing statement that I was indebted to them for my facts. Had Professor Watts looked at the preface to the second volume (the two having been published separately, as the prefaces imply), he would have seen a second expression of my indebtedness " for their valuable criticisms, and for the trouble they have taken in checking the numerous statements of fact on which the arguments proceed " — no further indebtedness being named. A moment's comparison of the two volumes in respect of their accumulations of facts, would have shown him what kind of warrant there was for his inter pretation. Doubtless the Rev. Professor was prompted to make this assertion by the desire to discredit the work he was attacking ; and having so good an end in view, thought it needless to be particular about the means. In the art of dealing with the language of opponents, Dr. Watts might give lessons to Monsignor Capcl and Archbishop Manning. December 28lc us better to recognize this necessity. If, in the case supposed, the extra demand for iron ships, after causing ADAPTATION. 241 the erection of some additional ship-yards and the drawing of iron from other manufactures, were to cease; the old dimensions of the ship-building trade would be quickly re turned to : discharged workmen would seek fresh occupa tions, and the new yards would be devoted to other uses. But if the increased need for ships lasted long enough, and became great enough, to cause a flow of capital and labour from other industries into the iron-manufacture, a falling off in the demand for ships, would much less rapidly entail a dwindling of the ship-building industry. For iron being now produced in greater quantity, a diminished consumption of it for ships would cause a fall in its price, and a conse quent fall in the cost of ships : thus enabling the ship builders to meet the competition which we may suppose led to a decrease in the orders they received. And since, when new blast-furnaces and rolling-mills, &c., had been built with capital drawn from other industries, its transference back into other industries would involve great loss; the owners, rather than transfer it, would accept unusually low interest, and an excess of iron would continue to be produced ; resulting in an undue cheapness of ships, and a maintenance of the ship-building industry at a size beyond the need. Eventually, however, if the number of ships required still diminished, the production of iron in excess would become very unremunerative : some of the blast-furnaces would be blown out; and as' much of the capital and labour as remained available would be re-distributed among other occupations. Without repeating the steps of the argument, it will be clear that were the enlargement of the ship-building industry great enough, and did it last long enough to cause an increase in the number of coal-mines, the ship-building industry would be still better able to maintain itself under adverse circum stances; but that it would, though at a more distant period, end by sinking down to the needful dimensions. Thus our conclusions are: — First, that if the extra growth caused by extra activity in a particular industry has lasted long enough 242 THE INDUCTIONS OF BIOLOGY. only to remodel the proximately-affected industries; it will dwindle away again after a moderate period, if the need for it disappears. Second, that a long period must be required before the re-actions produced by an enlarged industry can cause a re-construction of the whole society, and before the countless re-distributions of capital and labour can again reach a state of equilibrium. And third, that only when such a new state of equilibrium is eventually reached, can the adaptive modification become a permanent one. How, in animal organisms the like argument holds, need not be pointed out. The reader will readily follow the parallel. That organic types should be comparatively stable, might be anticipated on the hypothesis of Evolution. The structure of any organism being a product of .the almost infinite series of actions and reactions to which ancestral organisms have been exposed; any unusual actions and reactions brought to bear on an individual, can have but an infinitesimal effect in permanently changing the structure of the organism as a whole. The new set of forces, compounded with all the an tecedent sets of forces, can but inappreciably modify that moving equilibrium of functions which all these antecedent sets of forces have established. Though there may result a considerable perturbation of certain functions — a considerable divergence from their ordinary rhythms — yet the general centre of equilibrium cannot be sensibly changed. On the removal of the perturbing cause the previous balance will be quickly restored : the effect of the new forces being almost obliterated by the enormous aggregate of forces which the previous balance expresses. § 71. As thus understood, the phenomena of adaptation fall into harmony with first principles. The inference that organic types are fixed, because the deviations from them which can be produced within assignable periods are relatively small, and because, when a force producing deviation ceases, there is a return to something like the original state ; proves to ADAPTATION. 243 be an invalid inference. Without assuming fixity of species, we find good reasons for anticipating that kind and degree of stability which is observed. We find grounds for concluding, a priori, that an adaptive change of structure will soon reach a point beyond which further adaptation will be slow; for concluding that when the modifying cause has been but a short time in action, the modification generated will be evanescent; for concluding that a modifying cause acting even for many generations, will do but little towards per manently altering the organic equilibrium of a race ; and for concluding that on the cessations of such cause, its effects will become unapparcnt in the course of a few generations. CHAPTER VI. INDIVIDUALITY. § 72. WHAT is an individual ? is a question which many readers will think it easy to answer. Yet it is a question that has led to much controversy among Zoologists and Botanists, and no quite satisfactory reply to it seems possible. As applied to a man, or to any one of the higher animals, which are all sharply-defined and independent, the word in dividual has a clear meaning: though even here, when we turn from average cases to exceptional cases — as a calf with two heads and two pairs of fore-limbs — we find ourselves in doubt whether to predicate one individuality or two. But when we extend our range of observation to the organic world at large, we find that difficulties allied to this exceptional one meets us everywhere under every variety of form. Each uniaxial plant may perhaps fairly be regarded as a distinct individual; though there are botanists who do not make even this admission. What, however, are we to say of a multiaxial plant? It is, indeed, usual to speak of a tree with its many branches and shoots as singular; but strong reasons may be urged for considering it as plural. Every one of its axes has a more or less independent life, and when cut off and planted may grow into the likeness of its parent; or, by grafting and budding, parts of this tree may be developed upon another tree, and there manifest their specific peculiarities. Shall we regard all the growing axes thus resulting from slips and grafts and buds, as parts of one 244 INDIVIDUALITY. 245 individual or as distinct individuals? If a strawberry-plant sends out runners carrying buds at their ends, which strike root and grow into independent plants that separate from the original one by decay of the runners, must we not say that they possess separate individualities; and yet if we do this, are we not at a loss to say when their separate individu alities were established, unless we admit that each bud was from the beginning an individual? Commenting on such perplexities Schleiden says — " Much has been written and disputed concerning the conception of the individual, without, however, elucidating the subject, principally owing to the misconception that still exists as to the origin of the concep tion. Now the individual is no conception, but the mere subjective comprehension of an actual object, presented to us under some given specific conception, and on this latter it alone depends whether the object is or is not an individual. Under the specific conception of the solar system, ours is an individual : in relation to the specific conception of a planetary body, it is an aggregate of many individuals." ..." I think, however, that looking at the indubitable facts already mentioned, and the relations treated of in the course of these considerations, it will appear most advantageous and most useful, in a scientific point of view, to consider the vegetable cell as the general type of the plant (simple plant of the first order). Under this conception, Protococcus and other plants consisting of only one cell, and the spore and pollen-granule, will appear as individuals. Such individuals may, however, again, with a partial renunciation of their in dividual independence, combine under definite laws into definite forms (somewhat as the individual animals do in the globe of the Volvox globator *). These again appear empiri cally as individual beings, under a conception of a species (simple plants of the second order) derived from the form of * Whether the Volvox is to be classed as animal or vegetal is a matter of dispute ; but its similarity to the blastula stage Of many animals warrants the claim of the zoologists. 246 THE INDUCTIONS OF BIOLOGY. the normal connexion of the elementary individuals. But we cannot stop here, since Nature herself combines these individuals, under a definite form, into larger associations, whence we draw the third conception of the plant, from a connexion, as it were, of the second power (compound plants — plants of the third order). The simple plant proceeding from the combination of the elementary individuals is then termed a bud (gemma), in the composition of plants of the third order." The animal kingdom presents still greater difficulties. When, from sundry points on the body of a common polype, there bud out young polypes which, after acquiring mouths and tentacles and closing up the communications between their stomachs and the stomach of the parent, finally separate from the parent; we may with propriety regard them as distinct individuals. But when in the allied compound Ilydrozoa, we find that these young polypes continue per manently connected with the parent; and when by this continuous budding-out there is presently produced a tree like aggregation, having a common alimentary canal into which the digestive cavity of each polype opens; it is no longer so clear that these little sacs, furnished with mouths and tentacles, are severally to be regarded as distinct indi viduals. We cannot deny a certain individuality to the polypedom. And on discovering that some of the buds, instead of unfolding in the same manner as the rest, are transformed into capsules in which eggs are developed — on discovering that certain of the incipient polypes thus become wholly dependent on the aggregate for their nutrition, and discharge functions which have nothing to do with their own maintenance, we have still clearer proof that the individual ities of the. members are partially merged in the individuality of the group. Other organisms belonging to the same order, display still more decidedly this transition from simple indi vidualities to a complex- individuality. In the Diphyes there INDIVIDUALITY. 247 is a special modification of one or more members of the poly- pcdom into a swimming apparatus which, by its rhythmical contractions, propels itself through the water, drawing the polypedom after it. And in the more differentiated Physalia various organs result from the metamorphosis of parts which are the homologues of individual polypes. In this last instance, the individuality of the aggregate is so pre dominant that the individualities of its members arc practi cally lost. This combination of individualities in such way as to produce a composite individual, meets us in other forms among the ascidians. While in some of these, as -in the Clavelina and in the Botryttidce, the animals associated are but little. subordinated to the community they form, in others they are so combined as to form a compound indi vidual. The pelagic ascidian Doliolum is an example. " Here we find a large individual which swims by contractions of circular muscular bands, carries a train of smaller individuals attached to a long dorsal process of the test. These are arranged in three rows : those constituting the lateral row have wide mouths and no sexual organs or organs of locomo tion — they subserve the nutrition of the colony, a truth which is illustrated by the fact that as soon as they are properly developed the large individual (the mother) loses her alimentary canal ; " while from the median row are eventually derived the sexual zoids. On the hypothesis of Evolution, perplexities of this nature are just such as we might anticipate. If Life in general commenced with minute and simple forms, like those out of which all organisms, however complex, now originate; and if the transitions from these primordial units to organisms made up of groups of such units, and to higher organisms made up of groups of such groups took place by degrees; it is clear that individualities of the first and simplest order would merge gradually in those of a larger and more com plex order, and these again in others of an order having still 17 248 THE INDUCTIONS OF BIOLOGY. greater bulk and organization. Hence it would be impossible to say where the lower individualities ceased and the higher individualities commenced. § 73. To meet these difficulties, it has been proposed that the whole product of a single fertilized germ shall be re garded as a single individual; whether such whole product be organized into one mass, or whether it be organized into many masses that are partially or completely separate. It is urged that whether the development of the fertilized germ be'continuous or discontinuous (§50) is a matter of secondary importance; that the totality of living tissue to which the fertilized germ gives rise in any one case, is the equivalent of the totality to which it gives rise in any other case ; and that we must recognize this equivalence, whether such totality of living tissue takes a concrete or a discrete arrangement. In pursuance of this view, a zoological individual is consti tuted either by any such single animal as a mammal or bird, which may properly claim the title of a zoon, or by any such group of animals as the numerous Medusce that have been developed from the same egg, which are to be severally dis tinguished as zooids. Admitting it to be very desirable that there should be words for expressing these relations and this equivalence, it may be objected that to apply the word individual to a num ber of separate living bodies, is inconvenient : conflicting so much, as it does, with the ordinary conception which this word suggests. It seems a questionable use of language to say that the countless masses of Anacharis Alsinastrum (now Eloidea canadcnsis) which, within these few years, have grown up in our rivers, canals, and ponds, are all parts of one individual: and yet as this plant does not seed in England, these count less masses, having arisen by discontinuous development, must be so regarded if we accept the above definition. It may be contended, too, that while it does violence to our established way of thinking, this mode of interpreting INDIVIDUALITY. 249 the facts is not without its difficulties. Something seems to be gained by restricting the application of the title indi vidual, to organisms which, being in all respects fully devel oped, possess the power of producing their kind after the ordinary sexual method, and denying this title to those in complete organisms which have not this power.* But the definition does not really establish this distinction for us. On the one hand, we have cases in which, as in the working bee, the whole of the germ-product is aggregated into a single organism; and yet, though an individual according to the definition, this organism has no power of reproducing its kind. On the other hand, we have cases like that of the perfect Aphis, where the organism is but an infinitesimal part of the germ product, and yet has that completeness required for sexual reproduction. Further, it might be urged with some show of reason, that if the conception of individuality involves the conception of completeness, then, an organism which possesses an independent power of repro ducing itself, being more complete than an organism in which this power is dependent on the aid of another organism, is more individual. § 74. There is, indeed, as already implied, no definition of individuality that is unobjectionable. All we can do is to make the best practicable compromise. As applied either to an animate or an inanimate object, the word individual ordinarily connotes union among the parts of the object and separateness from other objects. This fundamental clement in the conception of individuality, we cannot with propriety ignore in the biological application of the word. That which we call an individual plant or aniinal must, therefore, be some concrete whole and not a discrete whole. If, however, we say that each concrete living whole is to be regarded as an individual, we are still met by the question — What constitutes a concrete living whole? A young organism arising by internal or external 250 THE INDUCTIONS OP BIOLOGY. ^emmation from a parent organism, passes gradually from a state in which it is an indistinguishable part of the parent organism to a state in which it is a separate organism of like structure with the parent. At what stage does it become an individual? And if its individuality be conceded only when it completely separates from the parent, must we deny indi viduality to all organisms thus produced which permanently retain their connexions with their parents? Or again, what must we say of the Hectocotylus, which is an arm of the Cuttle-fish that undergoes a special development and then, detaching itself, lives independently for a considerable period ? And what must we say of the larval nemertine worm the pilidium of which with its nervous system is left to move about awhile after the developing worm has dropped out of it? To answer such questions we must revert to the definition of Life. The distinction between individual in its biological sense, and individual in its more general sense, must consist in the manifestation of Life, properly so called. Life we have seen to be, " the definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external co-existences and sequences." Hence, a bio logical individual is any concrete whole having a structure which enables it, when placed in appropriate conditions, to continuously adjust its internal relations to external relations, so as to maintain the equilibrium of its functions. In pursuance of this conception, we must consider as individuals all those wholly or partially independent organized masses which arise by mul,ticentral and multiaxial development that is either continuous or discontinuous (§ 50). We must accord the title to each separate aphis, each polype of a polypedom, each bud or shoot of a flowering plant, whether it detaches itself as a bulbil or remains attached as a branch. By thus interpreting the facts we do not, indeed, avoid all anomalies. While, among flowering plants, the power of independent growth and development is usually possessed INDIVIDUALITY. 251 only by shoots or axes ; yet, in some cases, as in that of the Begonia-leaf awhile since mentioned, the appendage of an axis, or even a small fragment of such appendage, is capable of initiating and carrying on the functions of life; and in other cases, as shown by M. Naudin in the Drosera inter media, young plants are occasionally developed from the sur faces of leaves. Nor among forms like the compound Ilydrozoa, does the definition enable us to decide where the line is to be drawn between the individuality of the group and the individualities of the members: merging into each other, as these do, in different degrees. But, as before said, such difficulties must necessarily present themselves if organic forms have arisen by insensible gradations. We must be content with a course which commits us to the smallest number of incongruities; and this course is, to consider as an individual any organized mass which is capable of inde pendently carrying on that continuous adjustment of inner to outer relations which constitutes Life. CHAPTER VIA. CELL-LIFE AND CELL-MULTIPLICATION-. § 74a. THE progress of science is simultaneously towards simplification and towards complication. Analysis simplifies its conceptions by resolving phenomena into their factors, and by then showing how each simple mode of action may be traced under multitudinous forms; while, at the same time, synthesis shows how each factor, by cooperation with various other factors in countless modes and degrees, pro duces different results innumerable in their amounts and varieties. Of course this truth holds alike of processes and of products. Observation and the grouping into classes make it clear that through multitudinous things superficially un like there run the same cardinal traits of structure; while, along with these major unities, examination discloses innu merable minor diversities. A concomitant truth, or the same truth under another aspect, is that Nature everywhere presents us with complexi ties within complexities, which go on revealing themselves as we investigate smaller and smaller objects. In a preceding chapter (§§ 54a, 54&) it was pointed out that each primitive organism, in common with each of the units out of which the higher and larger organisms are built, was found a gene ration ago to consist of nucleus, protoplasm, and cell-wall. This general conception of a cell remained for a time the outcome of inquiry; but with the advance of microscopy it 252 CELL-LIFE AND CELL-MULTIPLICATION. 253 became manifest that within these minute structures pro cesses and products of an astonishing nature are to be seen. These we have now to contemplate. In the passages just referred to it was said that the ex ternal layer or cell-wall is a non-essential, inanimate part pro duced by the animate contents. Itself a product of proto plasmic action, it takes no part in protoplasmic 'changes, and may therefore here be ignored. § 74&. One of the complexities within complexities was disclosed when it was found that the protoplasm itself has a complicated structure. Different observers have described it as constituted by a network or reticulum, a sponge-work, a foam-work. Of these the first may be rejected; since it implies a structure lying in one plane. If we accept the second we have to conceive the threads of protoplasm, corre sponding to the fibres of the sponge, as leaving interstices filled either with liquid or solid. They cannot be filled with a continuous solid, since all motion of the protoplasm would be negatived; and that their content is not liquid seems shown by the fact that its parts move about under the form of granules or microsomes. But the conception of moving granules implies the conception of immersion in a liquid or semi-liquid substance in which they move — not a sponge- work of threads but a foam-work, consisting everywhere of septa interposed among the granules. This is the hypothesis which sundry microscopists espouse, and which seems me chanically the most feasible: the only one which consists with the " streaming " of protoplasm. Ordinarily the name protoplasm is applied to the aggregate mass — the semi-liquid, hyaline substance and the granules or microsomes it con tains. What these granules or microsomes are — whether, as some have contended, they are the essential living elements of the protoplasm, or whether, as is otherwise held, they are nutri tive particles, is at present undecided. But the fact, alleged 254 THE INDUCTIONS OF BIOLOGY. by sundry observers, that the microsomes often form rows, held together by intervening substance, seems to imply that these minute bodies are not inert. Leaving aside unsettled questions, however, one fact of significance is manifest — an immense multiplication of surfaces over which inter-action may take place. Anyone who drops into dilute sulphuric acid a small nail and then drops a pinch of iron filings, will be shown, by the rapid disappearance of the last and the long continuance of the first, how greatly the increasing of sur faces by multiplication of fragments facilitates change. The effect of subdivision in producing a large area in a small space, is shown in the lungs, where the air-cells on the sides of which the blood-vessels ramify, are less than I/I 00th of an inch in diameter, while they number 700,000,000. In the composition of every tissue we see the same principle. The living part, or protoplasm, is divided into innumerable protoplasts, among which are distributed the materials and agencies producing changes. And now we find this principle carried still deeper in the structure of the protoplasm itself. Each microscopic portion of it is minutely divided in such ways that its threads or septa have multitudinous contacts with those included portions of matter which take part in its activities. Concerning the protoplasm contained in each cell, named by some cytoplasm, it remains to say that it always includes a small body called the centrosome, which appears to have a directive function. Usually the centrosome lies outside the nucleus, but is alleged to be sometimes within it. During what is called the " resting stage," or what might more pro perly be called the growing stage (for clearly the occasional divisions imply that in the intervals between them there has been increase) the centrosome remains quiescent, save in the respect that it exercises some coercive influence on the pro toplasm around. This results in the radially-arranged lines constituting an " aster." What is the nature of the coercion exercised by the centrosome — a body hardly distinguishable CELL-LIFE AND CELL-MULTIPLICATION. 255 in size from the microsomes or granules of protoplasm around — is not known. It can scarcely be a repelling force; since, in a substance of liquid or semi-liquid kind, this could not produce approximately straight lines. That it is an attrac tive force seems more probable ; and the nature of the attrac tion would be comprehensible did the centrosome augment in bulk with rapidity. For if integration were in progress, the drawing in of materials might well produce converging lines. But this seems scarcely a tenable interpretation ; since, during the so-called " resting stage," this star-like structure exists — exists, that is, while no active growth of the centro some is going on. Eespecting this small body we have further to note that, like the cell as a whole, it multiplies by fission, and that the bisection of it terminates the resting or growing stage and initiates those complicated processes by which two cells are produced out of one: the first step following the fission being the movement of the halves, with their respective com pleted asters, to the opposite sides of the nucleus. § 74c. With the hypothesis, now general, that the nucleus or kernel of a cell is its essential part, there has not un naturally grown up the dogma that it is always present; but there is reason to think that the evidence is somewhat strained to justify this dogma. In the first place, beyond the cases in which the nucleus, though ordinarily invisible, is said to have been rendered visible by a re-agent, there are cases, as in the already-named Archerina, where no re-agent makes one visible. In the second place, there is the admitted fact that some nuclei are diffused; as in Trachelocerca and some other Infusoria. In (hem the numerous scattered granules are supposed to con stitute a nucleus: an interpretation obviously biassed by the desire to save the generalization. In the third place, the nucleus is frequently multiple in cells of low types; as in some families of Algu3 and predominantly among Fungi. 256 THE INDUCTIONS OF BIOLOGY. Once more, the so-called nucleus is occasionally a branching structure scarcely to be called a " kernel." The facts as thus grouped suggest that the nucleus has arisen in conformity with the law of evolution — that the primitive protoplast, though not homogeneous in the full sense, was homogeneous in the sense of being a uniformly granular protoplasm; and that the protoplasts with diffused nuclei, together with those which are multi-nucleate, and those which have nuclei of a branching form, represent stages in that process by which the relatively homogeneous proto plast passed into the relatively heterogeneous one now almost universal. Concerning the structure and composition of the developed nucleus, the primary fact to be named is that, like the sur rounding granular cytoplasm, it is formed of two distinct elements. It has a groundwork or matrix not differing much from that of the cytoplasm, and at some periods continuous with it; and immersed in this it has a special matter named chromatin, distinguished from its matrix by becoming dyed more or less deeply when exposed to fit re-agents. During the " resting stage," or period of growth and activity which comes between periods of division, the chromatin is dispersed throughout the ground-substance, either in discrete portions or in such way as to form an irregular network or sponge- work, various in appearance. When the time for fission is approaching this dispersed chromatin begins to gather itself together : reaching its eventual concentration through several stages. By its concentration are produced the chromosomes, constant in number in each species of plant or animal. It is alleged that the substance of the chromosomes is not continuous, but consists of separate elements or granules, which have been named chromomeres; and it is also alleged that, whether in the dispersed or integrated form, each chro mosome retains its individuality — that the chromomeres composing it, now spreading out into a network and now uniting into a worm-like body, form a group which never CELL-LIFE AND CELL-MULTIPLICATION. 257 loses its identity. Be this as it may, however, the essential fact is that during the growth-period the chromatin sub stance is widely distributed, and concentration of it is one of the chief steps towards a division of the nucleus and pre sently of the cell. During this process of mitosis or karyokinesis, the dis persed chromatin having passed through the coil-stage, reaches presently the star-stage, in which the chromosomes are arranged symmetrically about the equatorial plane of the nucleus. Meanwhile in each of them there has been a pre paration for splitting longitudinally in such way that the halves when separated contain (or are assumed to contain) equal numbers of the granules or chromomeres, which some think are the ultimate morphological units of the chromo somes. A simultaneous change has occurred : there has been in course of formation a structure known as the amphiaster. The two centrosomes which, as before said, place themselves on opposite sides of the nucleus, become the terminal poles of a spindle-shaped arrangement of fibres, arising mainly from the groundwork of the nucleus, now continuous with the groundwork of the cytoplasm. A conception of this structure may be formed by supposing that the radiating fibres of the respective asters, meeting one another and uniting in the intermediate space, thereafter exercise a trac tive force; since it is clear that, while the central fibres of the bundle will form straight lines, the outer ones, pulling against one another not in straight lines, will form curved lines, becoming more pronounced in their curvatures as the distance from the axis increases. That a tractive force is at work seems inferable from the results. For the separated halves of the split chromosomes, which now form clusters on the two sides of the equatorial plane, gradually part com pany, and are apparently drawn as clusters towards the op posing centrosomes. As this change progresses the original nucleus loses its individuality. The new chromosomes, halves of the previous chromosomes, concentrate to found 258 THE INDUCTIONS OF BIOLOGY. two new nuclei; and, by something like a reversal of the stages above described, the chromatin becomes dispersed throughout the substance of each new nucleus. While this is going on the cell itself, undergoing constriction round its equator, divides into two. Many parts of this complex process are still imperfectly understood, and various opinions concerning them are cur rent. But the essential facts are that this peculiar sub stance, the chromatin, at other times existing dispersed, is, when division is approaching, gathered together and dealt with in such manner as apparently to insure equal quantities being bequeathed by the mother-cell to the two daughter- cells. § 74:d. What is the physiological interpretation of these structures and changes? What function does the nucleus discharge; and, more especially, what is the function dis charged by the chromatin? There have been to these ques tions sundry speculative answers. The theory espoused by some, that the nucleus is the regulative organ of the cell, is met by difficulties. One of them is that, as pointed out in the chapter on " Structure," the nucleus, though morphologically central, is not central geometrically considered ; and that its position, often near to some parts of the periphery and remote from others, almost of itself negatives the conclusion that its function is directive in the ordinary sense of the word. It could not well control the cytoplasm in the sanie ways in all directions and at different distances. A further difficulty is that the cyto plasm when deprived of its nucleus can perform for some time various of its actions, though it eventually dies without reproducing itself. For the hypothesis that the nucleus is a vehicle for trans mit ting hereditary characters, the evidence seems strong. When it was shown that the head of a spermatozoon is simply a detached nucleus, and that its fusion with the CELL-LIFE AND CELL-MULTIPLICATION. 250 nucleus of an ovum is the essential process initiating the development of a new organism, the legitimate inference appeared to be that these two nuclei convey respectively the paternal and maternal traits which arc mingled in the off spring. And when there came to be discerned the karyoki- nesis by which the chromatin is, during cell-fission, exactly halved between the nuclei of the daughter-cells, the conclu sion was drawn that the chromatin is more especially the agent of inheritance. But though, taken by themselves, the phenomena of fertilization seem to warrant this inference, the inference does not seem congruous with the phenomena of ordinary cell-multiplication — phenomena which have noth ing to do with fertilization and the transmission of here ditary characters. No explanation is yielded of the fact that ordinary cell-multiplication exhibits an elaborate process for exact halving of the chromatin. Why should this substance be so carefully portioned out among the cells of tissues which are not even remotely concerned with propagation of the species? If it be said that the end achieved is the convey ance of paternal and maternal qualities in equal degrees to every tissue; then the reply is that they do not seem to- be conveyed in equal degrees. In the offspring there is not a uniform diffusion of the two sets of traits throughout all parts, but an irregular mixture of traits of the one with traits of the other. In presence of these two suggested hypotheses and these respective difficulties, may we not suspect that the action of the chromatin is one which in a way fulfils both functions? Let us consider what action may do this. § 740. The chemical composition of chromatin is highly complex, and its complexity, apart from other traits, implies relative instability. This is further implied by the special natures of its components. Various analyses have shown that it consists of an organic acid (which has been called nucleic acid) rich in phosphorus, combined with an albu- 200 THE INDUCTIONS OF BIOLOGY. minous substance: probably a combination of various pro- teids. And the evidence, as summarised by Wilson, seems to show that where the proportion of phosphorized acid is high the activity of the substance is great, as in the heads of spermatozoa; while, conversely, where the quantity of phos phorus is relatively small, the substance approximates in character to the cytoplasm. Now (like sulphur, present in the albuminoid base), phosphorus is an element which, besides having several allotropic forms, has a great affinity for oxygen; and an organic compound into which it enters, beyond the instability otherwise caused, has a special insta bility caused by its presence. The tendency to undergo change will therefore be great when the proportion of the phosphorized component is great. Hence the statement that " the chemical differences between chromatin and cytoplasm, striking and constant as they are, are differences of degree only ; " and the conclusion that the activity of the chromatin is specially associated with the phosphorus.* What, now, are the implications? Molecular agitation results from decompositon of each phosphorized molecule : shocks are continually propagated around. From the chro matin, units of which are thus ever falling into stabler states, there are ever being diffused waves of molecular motion, setting up molecular changes in the cytoplasm. The chro matin stands towards the other contents of the cell in the same relation that a nerve-element stands to any element of * While the proof was in my hands there was published in Science Pro gress an essay by Dr. T. G. Brodie on " The Phosphorus-containing Substances of the Cell." In this essay it is pointed out that " nucleic acid is particu larly characterized by its instability ... In the process of purification it is extremely liable to decompose, with the result that it loses a considerable part of its phosphorus. In the second place it is most easily split up in another manner in which it loses a considerable part of its nitrogen . . . To avoid the latter source of error he [Miescher] found that it was necessary to keep the temperature of all solutions down to 0° C., the whole time of the preparation." These facts tend strongly to verify the hypothesis that the nucleus is a source of perpetual molecular disturbance — not a regulating centre but a stimulating centre. CELL-LIFE AND CELL-MULTIPLICATION. 201 an organism which it excites : an interpretation congruous with the fact that the chromatin is as near to as, and indeed nearer than, a nerve-ending to any minute structure stimu lated by it. Several confirmatory facts may be named. During the intervals between cell-fissions, when growth and the usual cell-activities are being carried on, the chromatin is dispersed throughout the nucleus into an irregular network : thus greatly increasing the surface of contact between its sub stance and the substances in which it is imbedded. As has been remarked, this wide distribution furthers metabolism — a metabolism which in this case has, as we infer, the func tion of generating, not special matters but special motions. Moreover, just as the wave of disturbance a nerve carries produces an effect which is determined, not by anything which is peculiar in itself, but by the peculiar nature of the organ to which it is carried — muscular, glandular or other; so here, the waves diffused from the chromatin do not de termine the kinds of changes in the cytoplasm, but simply excite it : its particular activities, whether of movement, absorption, or structural excretion, being determined by its constitution. And then, further, we observe a parallelism between the metabolic changes in the two cases; for, on the one hand, " diminished staining capacity of the chromatin [implying a decreased amount of phosphorus, which gives the staining capacity] occurs during a period of intense con structive activity in the cytoplasm; " and, on the other hand, in high organisms having nervous systems, the intensity of nervous action is measured by the excretion of phosphates — by the using up of the phosphorus contained in nerve-cells. For thus interpreting the respective functions of chro matin and cytoplasm, yet a further reason may be given. One of the earliest general steps in the evolution of the Metazoa, is the differentiation of parts which act from parts which make them act. The Ilydrozoa show us this. In the hydroid stage there are no specialized contractile organs : 2G2 THE INDUCTIONS OF BIOLOGY. these are but incipient: individual ectoderm cells have mus cular processes. Nor is there any " special aggregation of nerve-cells." If any stimulating units exist they are scattered. But in the Medusa-stage nerve-matter is collected into a ring round the edge of the umbrella. That is to say, in the undeveloped form such motor action as occurs is not effected by a specialized part which excites another part; but in the developed form a differentiation of the two has taken place. All higher types exhibit this differentia tion. Be it muscle or gland or other operating organ, the cause of its activity lies not in itself but in a nervous agent, local or central, with which it is connected. Hence, then, there is congruity between the above interpretation and certain general truths displayed by animal organization at large. We may infer that in a way parallel to that just indicated, cell-evolution was, under one of its aspects, a change from a stage in which the exciting substance and the substance excited were mingled with approximate uniformity, to a stage in which the exciting substance was gathered together into the nucleus and finally into the chromosomes: leaving behind the substance excited, now distinguished as cytoplasm. § 1-lf. Some further general aspects of the phenomena appear to be in harmony with this interpretation. Let us glance at them. In Chapters III and IIlA of the First Part, reasons were given for concluding that in the animal organism nitroge nous substances play the part of decomposing agents to the carbo-hydrates — that the molecular disturbance set up by the collapse of a proteid molecule destroys the equilibrium of sundry adjacent carbo-hydrate molecules, and causes that evolution of energy which accompanies their fall into mole cules of simpler compounds. Here, if the foregoing argu ment- is valid, we may conclude that this highly complex phosphorized -compound which chromatin contains, plays the CELL-LIFE AND CELL-MITLTIPLTCATION. 2f>3 same part to the adjacent nitrogenous compounds as these play to the carbo-hydrates. If so, we see arising a stage earlier that " general physiological method " illustrated in § 23/. It was there pointed out that in animal organisms the various structures are so arranged that evolution of a small amount of energy in one, sets up evolution of a larger amount of energy in another; and often this multiplied energy undergoes a second multiplication of like kind. If this view is tenable, we may now suspect that this method displayed in the structures of the Metazoa was initiated in the structures of the Protozoa, and consequently characterizes those homologues of them which compose the Metazoa. When contemplated from the suggested point of view, karyokinesis appears to be not wholly incomprehensible. For if the chromatin yields the energy which initiates changes throughout the rest of the cell, we may see why there eventually arises a process for exact halving of the chromatin in a mother-cell between two daughter-cells. To make clear the reason, let us suppose the portioning out of the chromatin leaves one of the two with a sensibly smaller amount than the other. What must result? Its source of activity being relatively less, its rate of growth and its energy of action will be less. If a protozoon, the weaker progeny arising by division of it will originate an inferior stirp, unable to compete successfully with that arising from the sister-cell endowed with a larger portion of chromatin. By continual elimination of the varieties which produce unequal halving, necessarily at a disadvantage if a moiety of their members tend continually to disappear, there will be estab lished a variety in which the halving is exact : the character of this variety being such that all its members aid the per manent multiplication of the species. If, again, the case is that of a metazoon, there will be the same eventual result. An animal or plant in which the chromatin is unequally divided among the cells, must have tissues of uncertain formation. Assume that an organ has, by survival of the 18 264 THE INDUCTIONS OF BIOLOGY. fittest, boon adjusted in the proportions and qualities of its parts to a given function. If the multiplying protoplasts, instead of taking equal portions of chromatin, have some of them smaller portions, the parts of the organ formed of these, developing less rapidly and having inferior energies, will throw the organ out of adjustment, and the individual will suffer in the struggle for life. That is to say, irregular division of the chromatin will introduce a deranging factor and natural selection will weed out individuals in which it occurs. Of course no interpretation is thus yielded of the special process known as karyokinesis. Probably other modes of equal division might have arisen. Here the argu ment implies merely that the tendency of evolution is to establish some mode. In verification of the view that equal division arises from the cause named, it is pointed out to me that amitosis, which is a negation of mitosis or karyo kinesis, occurs in transitory tissues or diseased tissues or where degeneracy is going on. But how does all this consist with the conclusion that the chromatin conveys hereditary traits — that it is the vehicle in which the constitutional structure, primarily of the species and secondarily of recent ancestors and 'parents, is repre sented? To this question there seems to be no definite answer. We may say only that this second function is not necessarily in conflict with the first. While the unstable units of chromatin, ever undergoing changes, diffuse energy around, they may also be units which, under the conditions furnished by fertilization, gravitate towards the organization of the species. Possibly it may be that the complex com bination of proteids, common to chromatin and cytoplasm, is that part in which the constitutional characters inhere; while the phosphorized component, falling from its unstable union and decomposing, evolves the energy which, ordinarily the cause of changes, now excites the more active changes following fertilization. This suggestion harmonizes with the fact that the fertilizing substance which in animals consti- CELL-LIFE AND CELL-MULTIPLICATION. 265 tutes the head of the spermatozoon, and in plants that of the spermatozoid or antherozoid, is distinguished from the other agents concerned by having the highest proportion of the phosphorized element; and it also harmonizes with the fact that the extremely active changes set up by fertilization are accompanied by decrease of this phosphorized element. Spe culation aside, however, we may say that the two functions of the chromatin do not exclude one another, but that the general activity which originates from it may be but a lower phase of that special activity caused by fertilization.* § 74#. Here we come unawares to the remaining topic em braced under the title Cell-Life and Cell-Multiplication. We pass naturally from asexual mutiplication of cells to sexual * The writing of the above section reminded me of certain allied views which I ventured to suggest nearly 50 years ago. They are contained in the Westminster Review for April, 1852, in an article entitled "A Theory of Population deduced from the General Law of Animal Fertility." It is there suggested that the " spermatozoon is essentially a neural element, and the ovum essentially a haemal element," or, as otherwise stated, that the " sperm-cell is co-ordinating matter and the germ-cell matter to be co ordi- nated " (pp. 490-493). And along with this proposition there is given some chemical evidence tending to support it. Now if, in place of " neural " and "haemal," we say — the element that is most highly phosphorized and the element that is phosphorized in a much smaller degree ; or if, in place of co-ordinating matter and matter to be co-ordinated, we say — the matter which initiates action and the matter which is made to act ; there is dis closed a kinship between this early view and the view just, set forth. In the last part of this work, " Laws of Multiplication," which is developed from the essay referred to, I left out the portion containing the quoted sentences, and the evidence supporting the conclusion drawn. Partly I omitted them because the speculation did not form an essential link in the general argument, and partly because I did not see how the suggested interpretation could hold of plants as well as of animals. If, however, the alleged greater staining capac ity of the male generative nucleus in plants implies, as in other cases, that the male cell has a larger proportion of the phosphorized matter than the other elements concerned, then the difficulty disappears. As, along with the idea just named, the dropped portion of the original essay contains other ideas which seem to me worth preserving, I have thought it as \> ell to reproduce it, in company with the chief part of the general argu ment as at first sketched out. It will be found in Appendix A to this volume. 266 THE INDUCTIONS OF BIOLOGY. multiplication — from cell-reproduction to cell-generation. The phenomena are so numerous and so varied that a large part of them must be passed over. Conjugation among the Protophyta and Protozoa., beginning with cases in which there is a mingling of the contents of two cells in no visible respect different from one another, and developing into a great variety of processes in which they differ, must be left aside, and attention limited to the terminal process of fertilization as displayed in higher types of organisms. Before fertilization there occurs in the ovum an incidental process of a strange kind — " strange " because it is a col lateral change taking no part in subsequent changes. I refer to the production and extrusion of the " polar bodies." It is recognized that the formation of each is analogous to cell-formation in general; though process and product are both dwarfed. Apart from any ascribed meaning, the fact itself is clear. There is an abortive cell-formation. Abor- tiveness is seen firstly in the diminutive size of the separated body or cell, and secondly in the deficient number of its chromosomes : a corresponding deficiency being displayed in the group of chromosomes remaining in the egg — remaining, that is (on the hypothesis here to be suggested), in the sister-cell, supposing the polar body to be an aborted cell. It is currently assumed that the end to be achieved by thus extruding part of the chromosomes, is to reduce the re mainder to half the number characterizing the species; so that when, to this group in the germ-cell, the sperm-cell brings a similarly-reduced group, union of the two shall bring the chromosomes to the normal number. I venture to suggest another interpretation. In doing this, however, I must forestall a conclusion contained in the next chapter; namely, the conclusion that gamogenesis begins when agamogenesis is being arrested by unfavourable conditions, and that the failing agamogenesis initiates the gamogenesis. Of numerous illustrations to be presently given I will, to make clear the conception, name only one — the formation of fructifying CELL-LIFE AND CELL-MULTIPLICATION. 267 organs in plants at times when, and in places where, shoots are falling oft' in vigour and leaves in size. Here the suc cessive foliar organs, dccreasingly fitted alike in quality and dimensions for carrying on their normal lives, show us an approaching cessation of asexual multiplication, ending in the aborted individuals we call stamens; and the fact that sudden increase of nutrition while gamogenesis is being thus initiated, causes resumption of agamogenesis, shows that the gamogenesis is consequent upon the failing agamogenesis. See then the parallel. On going back from multicellular organisms to unicellular organisms (or those homologues of them which form the reproductive agents in multicellular organisms), we find the same law hold. The polar bodies are aborted cells, indicating that asexual multiplication can no longer go on, and that the conditions leading to sexual multiplication have arisen. If this be so, decrease in the chromatin becomes an initial cause of the change instead of an accompanying incident; and we need no longer assume that a quantity of precious matter is lost, not by passive incapacity, but by active expul sion. Another anomaly disappears. If from the germ-cell there takes place this extrusion of superfluous chromatin, the implication would seem to be that a parallel extrusion takes place from the sperm-cell. But this is not true. In the sperm-cell there occurs just that failure in the production of chromatin which, according to the hypothesis above sketched out, is to be expected; for, in the process of cell-multiplica tion, the cells which become spermatozoa are left with half the number of chromosomes possessed by preceding cells : there is actually that impoverishment and declining vigour here suggested as the antecedent of fertilization. It needs only to imagine the ovum and the polar body to be alike in size, to see the parallelism; and to see that obscuration of it arises from the accumulation of cytoplasm in the ovum. A test fact remains. Sometimes the first polar body ex truded undergoes fission while the second is being formed. 268 THE INDUCTIONS OF BIOLOGY. This can have nothing to do with reducing the number of chromosomes in the ovum. Unquestionably, however, this change is included with the preceding changes in one trans action, effected by one influence. If, then, it is irrelevant. to the decrease of chromosomes, so must the preceding changes be irrelevant: the hypothesis lapses. Contrariwise this fact supports the view suggested above. That extrusion of a polar body is a process of cell-fission is congruous with the fact that another fission occurs after extrusion. And that this occurs irregularly shows that the vital activities, seen in cell-growth and cell-multiplication, now succeed in producing further fission of the dwarfed cell and now fail : the energies causing asexual multiplication are exhausted and there arises the state which initiates sexual multiplication. Maturation of the ovum having been completed, entrance of the spermatozoon, sometimes through the limiting mem brane and sometimes through a micropyle or opening in it, takes place. This instantly initiates a series of complicated changes : not many seconds passing before there begins the formation of an aster around one end of the spermatozoon- head. The growth of this aster, apparently by linear rangings of the granules composing the reticulum of the germ-cell, progresses rapidly; while the whole structure hence arising moves inward. Soon there takes place the fusion of this sperm-nucleus with the germ-nucleus to form the cleavage-nucleus, which, after a pause, begins to divide and subdivide in the same manner as cells at large : so presently forming a cluster of cells out of which arise the layers originating the embyro. The details of this process do not concern us. It suffices to indicate thus briefly its general nature. And now ending thus the account of genesis under its histological aspect, we pass to the account of genesis under its wider and more significant aspects. CIIArTEB VII. GENESIS. § 75. HAVING, in the last chapter hut one, concluded what constitutes an individual, and having, in the last chapter, contemplated the histological process which initiates a new individual, we are in a position to deal with the multiplica tion of individuals. For this, the title Genesis is here chosen as being the most comprehensive title — the least specialized in its meaning. By some biologists Generation has been used to signify one method of multiplication, and Reproduction to signify another method ; and each of these words has been thus rendered in some degree unfit to signify multiplication in general. Here the reader is indirectly introduced to the fact that the production of new organisms is carried on in fundament ally unlike ways. Up to quite recent times it was believed, even by naturalists, that all the various processes of multi plication observable in different kinds of organisms, have one essential character in common : it was supposed that in every species the successive generations are alike. It has now been proved, however, that in many plants and in numerous animals, the successive generations are not alike; that from one generation there proceeds another whose members differ more or less in structure from their parents; that these produce others like themselves, or like their parents, or like neither; but that eventually, the original form re-appears. 270 THE INDUCTIONS OF BIOLOGY. Instead of there being, as in the cases most familiar to us, a constant recurrence of the same form, there is a cyclical recurrence of the same form. These two distinct processes of multiplication, may be aptly termed homogenesis and hctcro- gcnesis.* Under these heads let us consider them. There arc two kinds of homogcnesis, the simplest of them, probably once universal but now exceptional, being that in which there is no other form of multiplication than one result ing from perpetual spontaneous fission. The rise of distinct sexes was doubtless a step in evolution, and before it took place the formation of new individuals could have arisen only by division of the old, either into two or into many. At present this process survives, so far as appears, among Bacteria, certain Algce, and sundry Protozoa; though it is possible that a rarely-occurring conjugation has in these cases not yet been observed. It is a probable conclusion, how ever, that in the Bacteria at any rate, the once universal mode of multiplication still survives as an exceptional mode. But now passing over these cases, we have to note that the kind of genesis (once supposed to be the- sole kind), in which the successive generations are alike, is sexual genesis, or, as it has been otherwise called — gamo- gcncsis. In every species which multiplies by this kind of homogenesis, each generation consists of males and females; and from the fertilized germs they produce the next generation of similar males and females arises: the only needful qualifi cation of this statement being that in many Protophyta and Protozoa the conjugating cells or protoplasts are not distin guishable in character. This mode of propagation has the further trait, that each fertilized germ usually gives rise to but one individual — the product of development is organized round one axis and not round several axes. Homogenesis in * Unfortunately the word hctcroycnesis has been already used as a synonym for " spontaneous generation." Save by those few who believe in " spontane ous generation," however, little objection will be felt to using the word in a sense that seems much more appropriate. The meaning above given to it covers both Metagenesis and Paithunogeuesiis. GENESIS. 271 contrast with hetcrogenesis as exhibited in species which dis play distinct sexuality, has also the characteristic that each new individual begins as an egg detached from the maternal tissues, instead of being a portion of protoplasm continuous with them, and that its development proceeds independently. This development may be carried on either internally or ex ternally; whence results the division into the oviparous and the viviparous. The oviparous kind is that in which the fertilized germ is extruded from the parent before it has undergone any considerable development. The viviparous kind is that in which development is considerably advanced, or almost completed, before extrusion takes place. This distinction is, however, not a sharply-defined one : there are transitions between the oviparous and the viviparous pro cesses. In ovo-viviparous genesis there is an internal incuba tion ; arid though the young are in this case finally extruded from the parent in the shape of eggs, they do not leave the parent's body until after they have assumed something like the parental form. Looking around, .we find that homogenesis is universal among the Vertcbrala. Every vertebrate animal arises from a fertilized germ, and unites into its single individuality the whole product of this fertilized germ. In the mammals or highest Vcrtebrata, this homogenesis is in every case viviparous; in birds it is uni formly oviparous; and in reptiles and fishes it is always essentially oviparous, though there are cases of the kind above referred to, in which viviparity is simulated. Passing to the Invertebrata, we find oviparous homogenesis universal among the Arachnida (except the Scorpions, which are ovo- viviparous) ; universal among the higher Crustacea, but not among the lower; extremely general, though not universal, among Insects; and universal among the higher Mollusca though not among the lower. Along with extreme inferiority among animals, we find lioinogencsis to be the exception rather than the rule; and in the vegetal kingdom there appear to be no cases, except among the Alyw and a few 272 THE INDUCTIONS OF BIOLOGY. aberrant parasites like the Rafflcsiacece, in which the centre or axis which arises from a fertilized germ becomes the im mediate producer of fertilized germs. In propagation characterized by unlikeness of the succes sive generations, there is asexual genesis with occasionally- recurring sexual genesis ; in other words — agamo genesis inter rupted more or less frequently by gamogenesis. If we set out with a generation of perfect males and females, then, from their ova arise individuals which are neither males nor females, but which produce the next generation from buds. By this method of multiplication many individuals originate from a single fertilized germ. The product of development is organized round more than one centre or axis. The simplest form of heterogenesis is that seen in most uniaxial plants. If, as we find ourselves obliged to do, we regard each separate shoot or axis of growth as a distinct indi vidual, homogenesis is seen in those which have absolutely terminal flowers; but in all other uniaxial plants, the suc cessive individuals are not represented by the series A, A, A, A, &c., but they are represented by the series A, B, A, B, A, B, &c. For in the majority of plants which were classed as uniaxial (§ 50), and which may be conveniently so dis tinguished from other plants, the axis which shoots up from the seed, and substantially constitutes the plant, docs not itself flower but gives lateral origin to flowering axes. Though in ordinary uniaxial plants the fructifying apparatus appears to be at the end of the primary, vertical axis; yet dissection shows that, morphologically considered, each fructifying axis is an offspring from the primary axis. .There arises from the seed a sexless individual, from which spring by gemmation individuals having reproductive organs ; and from these there result fertilized germs or seeds that give rise to sexless indi viduals. That is to say, gamogenesis and agamogenesis alter nate: the peculiarity being that the sexual individuals arise from the sexless ones by continuous development. The Salpce show us an allied form of heterogenesis in the animal GENESIS. 273 kingdom. Individuals developed from fertilized ova, instead of themselves producing fertilized ova, produce, by gemma tion, strings of individuals from which fertilized ova again originate. In multiaxial plants, we have a succession of generations represented by the series A, B, B, B, &c., A, B, B, B, &c. Supposing A to be a flowering axis or sexual indi vidual, then, from any fertilized germ it casts off, there grows up a sexless individual, B; from this there bud-out other sexless individuals, B, and so on for generations more or less numerous, until at length, from some of these sexless indi viduals, there bud-out seed-bearing individuals of the original form A. Branched herbs, shrubs, and trees, exhibit this form of hcterogenesis : the successive generations of sexless individuals thus produced being, in most cases, continuously developed, or aggregated into a compound individual, but being in some cases discontinuously developed. Among animals a kind of heterogenesis represented by the same suc cession of letters, occurs in such compound polypes as the Scrtularia, and in those of the Hydrozoa which assume alter nately the polypoid form and the form of the Medusa. The chief differences presented by these groups arise from the fact that the successive generations of sexless individuals pro duced by budding, are in some cases continuously developed, and in others discontinuously developed; and from the fact that, in some cases, the sexual individuals give off their fertilized germs while still growing on the parent-polypedom, but in other cases not until after leaving the parent-poly pedom and undergoing further development. Where, as in all the foregoing kinds of agamogenesis, the new indi viduals bud out, not from any specialized reproductive organs but from unspecialized parts of the parent, the process has been named, by Prof. Owen, metagenesis. In most instances the individuals thus produced grow from the outsides of the parents — the metagenesis is external. But there is also a kind of metagenesis which we may distinguish as internal. Certain cntozoa of the genus Distoma exhibit it. From the 274 TUE INDUCTIONS OF BIOLOGY. egg of a Distoma there results a rudely-formed creature known as a sporocyst and from this a redia. Gradually, as this divides and buds, the greater part of the inner substance is transformed into young animals called Cercarice (which are the lame of Distomata) ; until at length it becomes little more than a living sac full of living offspring. In the Dis toma pacifica, the brood of young animals thus arising by internal gemmation are not Cercariai, but are like their parent : themselves becoming the producers of Cercarice, after the same manner, at a subsequent period. So that now the succession of forms is represented by the series A, B, A, B, &c., now by the series A, B, B, A, B, B, &c., and now by A, B, B, C, A. Both cases, however, exemplify internal metagenesis in contrast with the several • kinds of external metagenesis described above. That agamogenesis which is carried on in a reproductive organ — either an ovarium or the homo- logue of one — has been called, by Prof. Owen, parthenogenesis. It is the process familiarly exemplified in the Aphides. Here, from the fertilized eggs laid by perfect females there grow up imperfect females, in the ovaria of which are de veloped ova that though unfertilized, rapidly assume the organization of other imperfect females, and are born vivi- parously. From this second generation of imperfect females, there by-and-by arises, in the same manner, a third genera tion of the same kind ; and so on for many generations : the series being thus symbolized by the letters A, B, B, B, B, B, &c., A. Inspecting this kind of heterogenesis it should be added that, in animals as in plants, the number of genera tions of sexless individuals produced before the re-appearance of sexual ones, is indefinite; both in the sense that in the same species it may go on to a greater or less extent accord ing to circumstances, and in the sense that among the genera tions of individuals proceeding from the same fertilized germ, a recurrence of sexual individuals takes place earlier in some of the diverging lines of multiplication than in others. In trees we see that on some branches flower-bearing axes arise GENESIS. 275 while other branches are still producing only leaf-bearing axes; and in the successive generations of Apliides a parallel fact has been observed. Lastly has to be set down that kind of heterogenesis in which, along with gamogenesis, there occurs a form of agamogenesis exactly like it, save in the absence of fecundation. This is called true partheno genesis — reproduction carried on by virgin mothers which are in all respects like other mothers. Among si Ik- worm-moths this parthenogenesis is exceptional rather than ordinary. Usually the eggs of these insects are fertilized; but if they are not they are still laid, and some of them produce larva?. In certain Lcpidoptera, however, of the groups Psychidce and Tineidcc, parthenogenesis appears to be a normal process — indeed, so far as is known, the only process; for of some species the males have never been found. A general conception of the relations among the different modes of Ciencsis, thus briefly described, will be best given by the following tabular statement. f Oviparous or f Homogenesis, which is usually Gamogenesis •{ Ovo-viviparous or Viviparous or ^ f Gamogenesis O I I alternating [ Heterogenesis, which is 1 with f Parthenogenesis [ Agamogenesis -| or f Internal [ Metagenesis -J or [ External This, like all other classifications of such phenomena, pre sents anomalies. It may be justly objected that the pro cesses here grouped under the head agamogenesis, are the same as those before grouped under the head of discontinuous development (§ 50) : thus making development and genesis partially coincident. Doubtless it seems awkward that what are from one point of view considered as structural changes are from another point of view considered as modes of multi- 276 THE INDUCTIONS OF BIOLOGY. plication.* There is, however, nothing for us but a choice of imperfections. We cannot by any logical dichotomies accu rately express relations which, in Nature, graduate into one another insensibly. Neither the above, nor any other scheme, can do more than give an approximate idea of the truth. § 76. Genesis under every form is a process of negative or positive disintegration ; and is thus essentially opposed to that process of integration which is the primary process in individual evolution. Negative disintegration occurs in those cases where, as among the compound Hydrozoa, there is a continuous development of new individuals by budding from the bodies of older individuals; and where the older indi viduals are thus prevented from growing to a greater size, or reaching a higher degree of integration. Positive disintegra tion occurs in those forms of agamogenesis where the produc tion of new individuals is discontinuous, as well as in all cases of gamogenesis. The degrees of disintegration are various. At the one extreme the parent organism is completely broken up, or dissolved into new individuals; and at the other extreme each new individual forms but a small deduction from the parent organism. Protozoa and Protopliyta show us that form of disintegration called spontaneous fission : two or more individuals being produced by the splitting-up of the original one. The Volvox and the Hydrodictyon are plants which, having developed broods within themselves, give them exit by bursting; and among animals the one lately referred to which arises from the Distoma egg, entirely loses its individuality in the individualities of the numerous * Prof. Huxley avoids this difficulty by making every kind of Genesis a mode of development. His classification, which suggested the one given above, is as follows : — f Growth f Continuous •{ (^ Metamorphosis ( Metagenesis f Agamogenesis -| L Discontinuous ^ [ Parthenogenesis L Gamogenesis GENESIS. 277 with which it becomes filled. Speak ing generally, the degree of disintegration becomes less marked as we approach the higher organic forms. Plants of superior types throw off from themselves, whether by gamo- genesis or agamogencsis, parts that are relatively small ; and among superior animals there is no case in which the parent individuality is habitually lost in the production of new individuals. To the last, however, there is of necessity a greater or less disintegration. The seeds and pollen-grains of a flowering plant are disintegrated portions of tissue; as are also the ova and spermatozoa of animals. And whether the fertilized germs carry away from their parents small or large quantities of nutriment, these quanti ties in all cases involve further negative or positive disinte grations of the parents. Except in spore-producing plants, new individuals which result from agamogenesis usually do not separate from the parent-individuals until they have undergone considerable development, if not complete development. The agamo- genetic offspring of those lowest organisms which develop centrally, do not, of course, pass beyond central structure; but the agamogenetic offspring of organisms which develop axial]y, commonly assume an axial structure before they be come independent. The vegetal kingdom shows us this in the advanced organization of detached bulbils, and of buds that root themselves before separating. Of animals, the llydrozoa, the Trematoda, and the Salpw, present us with different kinds of agamogenesis, in all of which the new individuals are organized to a considerable extent before being cast off. This rule is not without exceptions, however. The statoblasts of the Plumatella (which play the part of winter eggs), developed in an unspecialized part of the body, furnish a case of metagenesis in which centres of develop ment, instead of axes, are detached; and in the above-de scribed parthenogenesis of moths and bees, such centres are detached from an ovarium. 278 THE INDUCTIONS OP BIOLOGY. When produced by gamogenesis, the new individuals be come (in a morphological sense) independent of the parents while still in the shape of centres of development, rather than axes of development; and this even where the reverse is apparently the case. The fertilized germs of those inferior plants which are central, or multi central, in their develop ment, are of course thrown off as centres; and the same is usually the case even in those which are uniaxial or multi- axial. In the higher plants, of the two elements that go to the formation of the fertilized germ, the pollen-cell is abso lutely separated from the parent-plant under the shape of a centre, and the egg-cell, though not absolutely separated from the parent, is still no longer subordinate to the organizing forces of the parent. So that when, after the egg-cell has • been fertilized by matter from the pollen-tube, the develop ment commences, it proceeds without parental control : the new individual, though remaining physically united with the old individual, becomes structurally and functionally separate: the old individual doing no more than supply materials. Throughout the animal kingdom, the new individuals produced by gamogenesis are obviously separated in the shape of centres of development wherever the repro duction is oviparous : the only conspicuous variation being in the quantity of nutritive matter bequeathed by the parent at the time of separation. And though, where the reproduc tion is viviparous, the process appears to be different, and in one sense is so, yet, intrinsically, it is the same. For in these cases the new individual really detaches itself from the parent while still only a centre of development ; but instead of being finally cast off in this state it is re-attached, and supplied with nutriment until it assumes a more or less com plete axial structure. § 77. As we have lately seen, the essential act in gamo genesis is the union of two cell-nuclei, produced in the great majority of cases by different parent organisms. Nearly GENESIS. 279 always the containing cells, often called gametes, are unlike : the sperm-cell being the male product, and the germ-cell the female. But among some Protozoa and many of the lower Algce and Fungi, the uniting cells show no differentiation. Sexuality is only nascent. There are very many modes and modifications of modes in which these cells are produced ; very many modes and modifications of modes by which they are brought into contact; and very many modes and modifications of modes by which the resulting fertilized germs have secured to them the fit conditions for their development. But passing over these divergent and re-divergent kinds of sexual multiplica tion, which it would take too much space here to specify, the one universal trait is this coalescence of a detached portion of one organism with a more or less detached portion of another. Such simple Algce as the Desmidiece, which arc sometimes called unicellular plants, show us a coalescence, not of de tached portions of two organisms, but of two entire organ isms: the entire contents of the individuals uniting to form the germ-mass. Where, as among the Confervoidece, we have aggregated cells whose individualities are scarcely at all subordinate to that of the aggregate, the gamogenetic act is often effected by the union " of separate motile protoplasmic masses produced by the division of the contents of any cell of the aggregate. These free-swimming masses of proto plasm, which are quite similar to (but generally smaller than) the agamogenetic ' zoosporcs ' of the same plants, and to the free-swimming individuals of many Protopkyta, are apparently the primitive type of gametes (conjugating cells) ; but it is noteworthy that such a gamete nearly always unites with one derived from another cell or from another indivi dual. The same fact holds with regard to the gametes of the Protophytes themselves, which are formed in the same way from the single cell of the mother individual. In the higher types of Confcrvoidetv, and in Vauchena, we find these equi- 19 280 THE INDUCTIONS OP BIOLOGY. valent, fre'e-swimming, gametes replaced by sexually dif ferentiated sperm- and germ-cells, in some cases arising in different organs set apart for their production, and essentially representing those found in the higher plants. Transitional forms, intermediate between these and the cases where equivalent gametes are formed from any cell of the plant are also known." Recent investigations concerning the conjugation of Pro tozoa have shown that there is not, as was at one time thought, a fusion of two individualities, but a fusion of parts of their nuclei. The macro-nucleus having disappeared, and the micro-nucleus having broken up into portions, each individual receives from the other one of these portions, which becomes fused with its own nuclear matter. So that even in these humble forms, where there is no differentiation of sexes, the union is not between elements that have arisen in the same individual but between those which have arisen in different individuals : the parts being in this case alike. The marvellous phenomena initiated by the meeting of sperm-cell and germ-cell, or rather of their nuclei, naturally suggest the conception of some quite special and peculiar properties possessed by these cells. It seems obvious that this mysterious power which they display of originating a new and complex organism, distinguishes them in the broadest way from portions of organic substance in general. Nevertheless, the more we study the evidence the more are we led towards the conclusion that these cells are not fundamentally different from other cells. The first fact which points to this conclusion is the fact recently dwelt upon ( § 63 ) , that in many plants and inferior animals, a small fragment of tissue which is but little differentiated, is capable of developing into an organism like that from which it was taken. This implies that the component units of tissues have inherent powers of arranging themselves into the forms of the organisms which originated them. And if in these component units, which we distinguished as GENESIS. 2S1 physiological, such powers exist, — if, under fit conditions, and when not much specialized, they manifest such powers in a way as marked as that in which the contents of sperm-cells and germ-cells manifest them; then, it becomes clear that the properties of sperm-cells and germ-cells are not so peculiar as we arc apt to assume. Again, the organs emitting sperm-cells and germ-cells have none of the special ities of structure which might be looked for, did sperm-cells and germ-cells need endowing with properties unlike those of all other organic agents. On the contrary, these reproduc tive centres proceed from tissues characterized by their low organization. In plants, for example, it is not appendages that have acquired considerable structure which produce the fructifying particles: these arise at the extremities of the axes where the degree of structure is the least. The cells out of which come the egg and the pollen-grains, are formed from undifferentiated tissue in the interior of the ovule and of the stamen. Among many inferior animals devoid of special reproductive organs, such as the Hydra, the ova and spermatozoa originate from the interstitial cells of the ecto derm, which lie among the bases of the functional cells — have not been differentiated for function ; and in the Medusae, according to Weismann, they arise in the homologous layer, save where the medusoid form remains attached, and then they arise in the endoderm and migrate to the ectoderm: lack of specialization being in all cases implied. Then in the higher animals these same generative agents appear to be merely modified epithelium-cells — cells not remarkable for their complexity of structure but rather for their sim plicity. If, by way of demurrer to this view, it be asked why other epithelium-cells do not exhibit like properties; there are two replies. The first is that other epithelium-cells are usually so far changed to fit them to their special functions that they are unfitted for assuming the reproductive function. The second is that in some cases, where they are but littlo specialized, they do exhibit the like properties : not, indeed, 282 THE INDUCTIONS OP BIOLOGY. by uniting with other cells to produce new germs but by pro ducing new germs without such union. I learn from Dr. Hooker that the Begonia phyllomaniaca habitually develops young plants from the scales of its stem and leaves — nay, that many young plants arc developed by a single scale. The epidermal cells composing one of these scales swell, here and there, into large globular cells; form chlorophyll in their interiors; shoot out rudimentary axes; and then, by spon taneous constrictions, cut themselves off ; drop to the ground ; and grow into Begonias. Moreover, in a succulent English plant, the Malaxis paludosa, a like process occurs: the self- detached cells being, in this case, produced by the surfaces of the leaves.* Thus, there is no warrant for the assump tion that sperm-cells and germ-cells possess powers funda mentally unlike those of other cells. The inference to which the facts point, is, that they differ from the rest mainly in not having undergone functional adaptations. They are cells which have departed but little from the original and most general type : such specializations as some of them exhibit in the shape of locomotive appliances, being interpretable as ex trinsic modifications which have reference to nothing beyond certain mechanical requirements. Sundry facts tend likewise to show that there does not exist the profound distinction we are apt to assume between the male and female reproductive elements. In the common polype sperm-cells and germ-cells are developed in the same layer of * The implication is that an essentially similar process occurs in those fragments of leaves used for artificial propagation. Besides the Begonias in general, I learn that various other plants are thus multiplied — Citron and orange trees, Hoya carnosa, Aucuba japonica, CUanthus puniceus, etc., etc. Bryophyllum calicinum, Rochea falcata, and Echeveria. I also learn that the following plants, among others, produce buds from their foliage leaves: — Cardamine prateusis, Nasturtium officinale, Roripa palus- tris, jBras.fica oleracea, Arabis pumila, Chelidonium majus, Nymphcea guianen- sis, Episcia bicolor, Chirita sivcnsis, Pinyuicula Backcri, Allium, Gayea, Tolmia, Friiillaria, Ormthogalum , etc. In Cardamine and several others, a complete miniature plant is at once produced ; in other cases bulbils or simi lar detachable buds. GENESIS. 283 indifferent tissue; and in Tetliya, one of the sponges, Prof. Huxley has observed that they occur mingled together in the general parenchyma. The pollen-grains and embryo-cells of plants arise in adjacent parts of the mcristematic tissue of the flower-bud ; and from the description of a monstrosity in the Passion-flower, recently given by Mr. Salter to the Lin- na)an Society, it appears both that ovules may, in -their gen eral structure, graduate into anthers, and that they may produce pollen in their interiors. Moreover, among the lower Algce, which show the beginning of sexual differentiation, the smaller gametes, which we must regard as incipient sperm- cells, are sometimes able to fuse inter sef and give rise to a zygote which will produce a new plant. All which evidence is in perfect harmony with the foregoing conclusion; since, if sperm-cells and germ-cells have natures not essentially un like those of unspecialized cells in general, their natures cannot be essentially unlike each other. The next general fact to be noted is that these cells whose union constitutes the essential act of gamogcnesis, are cells in which the developmental changes have come to a close — cells which are incapable of further evolution. Though they are not, as many cells are, unfitted for growth and meta morphosis by being highly specialized, yet they have lost the power of growth and metamorphosis. They have severally reached a state of equilibrium. And while the internal balance of forces prevents a continuance of constructive changes, it is readily overthrown by external destructive forces. For it almost uniformly happens that sperm-cells and germ- cells which are not brought in contact disappear. In a plant, the egg-cell, if not fertilized, is absorbed or dissipated, while the ovule aborts ; and the unimpregnated ovum eventually decomposes : save, indeed, in those types in which partheno genesis is a part of the normal cycle. Such being the characters of these cells, and such being their fates if kept apart> we have now to observe what happens when they are united. In plants the extremity 284 THE INDUCTIONS OF BIOLOGY. of the elongated pollen-cell applies itself to the surface of the embryo-sac, and one of its nuclei having, with some protoplasm, passed into the egg-cell, there becomes fused with the nucleus of the egg-cell. Similarly in animals, the spermatozoon passes through the limiting membrane of the ovum, and a mixture takes place between the substance of its nucleus and the substance of the nucleus of the ovum. But the important fact which it chiefly concerns us to notice, is that on the union of these re productive elements there begins, either at once or on the return of favourable conditions, a new series of develop mental changes. The state of equilibrium at which each had arrived is destroyed by their mutual influence, and the constructive changes, which had come to a close, recommence. A process of cell-multiplication is set up; and the resulting cells presently begin to aggregate into the rudiment of a new organism. Thus, passing over the variable concomitants of gamo- genesis, and confining our attention to what is constant in it, we see: — that there is habitually, if not universally, a fusion of two portions of organic substance which are either them selves distinct individuals, or are thrown off by distinct in dividuals; that these portions of organic substance, which are* severally distinguished by their low degree of special ization, have arrived at states of structural quiescence or equilibrium; that if they are not united this equilibrium ends in dissolution; but that by the mixture of them this equilibrium is destroyed and a new evolution initiated. § 78. What are the conditions under which Genesis takes place? How does it happen that some organisms multiply by homogenesis and others by hcterogenesis ? Why is it that where agamogcnesis prevails it is usually from time to time interrupted by gamogenesis? A survey of the facts discloses certain correlations which, if not universal, are too !',cneral to be without significance. GENESIS. 285 Where multiplication is carried on by heterogenesis we find, in numerous cases, that agamogenesis continues as long as the forces which result in growth are greatly in excess of the antagonist forces. Conversely, we find that the recur rence of gamogenesis takes place when the conditions are no longer so favourable to growth. In like manner where there is homogenetic multiplication, new individuals are usu ally not formed while the preceding individuals are still rapidly growing — that is, while the forces producing growth exceed the opposing forces to a great extent ; but the f orcna- tion of new individuals begins when nutrition is nearly equalled by expenditure. A few out of the many facts which seem to warrant these inductions must suffice. The relation in plants between fructification and innu trition (or rather, between fructification and such diminished nutrition as makes growth relatively slow) was long ago asserted by a German biologist — Wolff, I am told. Since meeting with this assertion I have examined into the facts for myself. The result has been a conviction, strengthened by every inquiry, that some such relation exists. Uniaxial plants begin to produce their lateral, flowering axes, only after the main axis has developed the great mass of its leaves, and is showing its diminished nutrition by smaller leaves, or shorter internodes, or both. In multiaxial plants two, three, or more generations of leaf-bearing axes, or sex less individuals, are produced before any seed-bearing indi viduals show themselves. When, after this first stage of rapid growth and agamogenetic multiplication, some gamogenetic individuals arise, they do so where the nutrition is least; — not on the main axis, or on secondary axes, or even on tertiary axes, but on axes that are the most removed from the channels which supply nutriment. Again, a flowering axis is commonly less bulky than the others : either much shorter or, if long, much thinner. And further, it is an axis of which the terminal internodes are undeveloped: the foliar organs, which instead of becoming leaves become 286 TEE INDUCTIONS OF BIOLOGY. sepals, and petals, and stamens, follow each other in close succession, instead of being separated by portions of the still- growing axis. Another group of evidences meets us when we observe the variations of fruit-bearing which accom pany variations of nutrition in the plant regarded as a whole. Besides finding, as above, that gamogenesis commences only when growth has been checked by extension of the remoter parts to s6me distance from the roots, we find that gamo genesis is induced at an earlier stage than usual by checking the 'nutrition. Trees are made to fruit while still quite small by cutting their roots or putting them into pots; and luxuriant branches which have had the flow of sap into them diminished, by what gardeners call " ringing," begin to pro duce flower-shoots instead of leaf-shoots. Moreover, it is to be remarked that trees which, by flowering early in the year, seem to show a direct relation between gamogenesis and in creasing nutrition, really do the reverse; for in such trees the flower-buds are formed in the autumn. That structure which determines these buds into sexual individuals is given when the nutrition is declining. Conversely, very high nutrition in plants prevents, or arrests, gamogenesis. It is notorious that unusual richness of soil, or too large a quantity of manure, results in a continuous production of leaf -bearing or sexless shoots; and a like result happens when the cutting down of a tree, or of a large part of it, is followed by the sending out of new shoots : these, supplied with excess of sap, are luxuriant and sexless. Besides being prevented from producing sexual individuals by excessive nutrition, plants are, by excessive nutrition, made to change the sexual individuals they were about to produce, into sexless ones. This, arrest of gamogenesis, may be seen in various stages. The familiar instance of flowers made barren by the transformation of their stamens into petals, shows us the lowest degree of this reversed metamorphosis. Where the petals and stamens are partially changed into green leaves, the return towards the agamogenetic structure is more GENESIS. 287 marked; and it is still more marked when, as occasionally happens in luxuriantly-growing plants, new flowering axes, and even leaf-bearing axes, grow out of the centres of flowers.* The anatomical structure of the sexual axis affords corroborative evidence: giving the impression, as it does, of an aborted sexless axis. Besides lacking those inter- * Among various examples I have observed, the most remarkable were among Foxgloves, growing in great numbers and of large size, in a wood between Whatstandwell Bridge and Crich, in Derbyshire. In one case the lowest flower on the stem contained, in place of a pistil, a shoot or spike of flower-buds, similar in structure to the embryo-buds of the main spike. I counted seventeen buds on it ; of which the first had three stamens, but was otherwise normal ; the second had three ; the third, four ; the fourth, four; &c. Another plant, having more varied monstrosities, evinced excess of nutrition with equal clearness. The following arc the notes I took of its structure: — 1st, or lowest flower on the stem, very large; calyx containing eight divisions, one partly transformed into a corolla, and another trans formed into a small bud with bract (this bud consisted of a five-cleft calyx, four sessile anthers, a pistil, and a rudimentary corolla) ; the corolla of the main flower, which was complete, contained six stamens, three of them bearing anthers, two others being flattened and coloured, and one rudiment ary ; there was no pistil but, in place of it, a large bud, consisting of a three- cleft calyx of which two divisions were tinted at the ends, an imperfect corolla marked internally with the usual purple spots and hairs, three anthers sessile on this mal-formed corolla, a pistil, a seed-vessel with ovules, and. growing to it, another bud of which the structure was indistinct. 2nd flower, large; calyx of seven divisions, one being transformed into a bud with bract, but much smaller than the other ; corolla large but cleft along the top ; six stamens with anthers, pistil, and seed-vessel. 3rd flower, large ; six-cleft calyx, cleft corolla, with six stamens, pistil, and seed-vessel, with a second pisti! half unfolded at its apex. 4th flower, large ; divided along the top, six stamens. 5th flower, large; corolla divided into three parts, six stamens. 6th flower, large; corolla cleft, calyx six cleft, the rest of the flower normal. 7th, and all succeeding flowers, normal. While this chapter is under revision, another noteworthy illustration has been furnished to me by a wall-trained pear tree which was covered in the spring by luxuriant "foreright" shoots. As I learned from the gardener, it was pruned just as the fruit was setting. A large excess of sap was thus thrown into other branches, with the result that in a number of them the young pears were made monstrous by reversion. In some cases, instead of the dried up sepals at the top of the pear, there were produced pood sized leaves ; and in other cases the seed-bearing core of the pear was transformed into a growth which protruded through the top of the pear in the shape of a new shoot. 288 THE INDUCTIONS OF BIOLOGY. nodes which the leaf-bearing axis commonly possesses, the flowering axis differs by the absence of rudimentary lateral axes. In a leaf-bearing shoot the axil of every leaf usually contains a small bud, which may or may not develop into a lateral shoot; but though the petals of a flower are homo logous with leaves, they do not bear homologous buds at their bases. Ordinarily, too, the foliar appendages of sexual axes are much smaller than those of sexless ones — the stamens and pistils especially, which are the last formed, being extremely dwarfed; and it may be that the absence of chlorophyll from the parts of fructification is a fact of like meaning. Moreover, the formation of the seed-vessel appears to be a direct consequence of arrested nutrition. If a gloved- finger be taken to represent a growing shoot, (the finger standing for the pith of the shoot and the glove for the peri pheral layers of meristem and young tissue, in which the process of growth takes place) ; and if it be supposed that there is a diminished supply of material for growth; then, it seems a fair inference that growth will first cease at the apex of the axis, represented by the end of the glove-finger; and supposing growth to continue in those parts of the peripheral layers of young tissue that are nearer to the supply of nutri ment, their further longitudinal extension will lead to the formation of a cavity at the extremity of the shoot, like that which results in a glove-finger when the finger is partially withdrawn and the glove sticks to its end. Whence it seems, both that this introversion of the apical meristem may be considered as due to failing nutrition, and that the ovules growing from its introverted surface (which would have been its outer surface but for the defective nutrition) arc extremely aborted homologues of external appendages : both they and the pollen-grains being either morphologically or literally quite terminal, and the last showing by their dehiscence the exhaustion of the organizing power.* * In partial verification, Mr. Tansley writes: — "Prof. Klebs of Basel has shown that in Ih/drodidyon, gametes can only be produced by the cells of GENESIS. 289 Those kinds of animals which multiply by heterogenesis, present us with a parallel relation between the recurrence of gamogenesis and the recurrence of conditions checking rapid growth: at least, this is shown where experiments have thrown light on the connexion of cause and effect; namely, among the Aphides. These creatures, hatched from eggs in the spring, multiply by agamogenesis, which in this case is parthenogenesis, throughout the summer. When the weather becomes cold and plants no longer afford abundant sap, per fect males and females are produced; and from gamogenesis result fertilized ova. But beyond this evidence we have much more conclusive evidence. For it has been shown, both that the rapidity of the agamogenesis is proportionate to the warmth and nutrition, and that if the temperature and supply of food be artificially maintained, the agamogenesis continues through the winter. Nay more — it not only, under these conditions, continues through one winter, but it has been known to continue for four successive years : some forty or fifty sexless generations being thus produced. And those who have investigated the matter see no reason to doubt the indefinite continuance of this agamogenetic mul tiplication, so long as the external requirements are duly met. Evidence of another kind, complicated by a net when these are above a certain size and age; and then only under conditions unfavourable to growth, such as a feeble light or poverty of nutritive inorganic salts or absence of oxygen, or a low temperature in the water containing the plant. The presence of organic substances, especially sugar, also acts as a stimulus to the formation of gametes, and this is also the case in Vauchcria. Many other Algce produce gametes mainly at the end of the vegetative season, when food is certainly difficult to obtain in their natural habitat, and we may well suppose that their assimilative power is waning. Where, however, as is the case in Vaucheria, the plant depends for propagation mainly on the production of fertilized eggs, we find the sexual organs often produced in conditions very favourable to vegetative growth, in opposition to those cases such as Hydrodictyon, where the chief means of propagation is by zoospores. So that side by side with, and to some extent obscuring, the principle developed above we have a clear adaptation of the production of reproductive cells to the special circumstances of the case." 290 THE INDUCTIONS OP BIOLOGY. special influences, is furnished by the heterogenesis of the Dapknia — a small crustacean commonly known as the Water-flea, which inhabits ponds and ditches. From the nature of its habitat this little creature is exposed to very variable conditions. Besides being frozen in winter, the small bodies of water in which it lives are often unduly heated by the summer Sun, or dried up by continued drought. The circumstances favourable to the Daplmia's life and growth, being thus liable to interruptions which, in our cli mate, have a regular irregularity of recurrence; we may, in conformity with the hypothesis, expect to find both that the gamogenesis recurs along with declining physical prosperity and that its recurrence is very variable. I use the expres sion " declining physical prosperity " advisedly ; since " de clining nutrition," as measured by supply of food, does not cover all the conditions. This is shown by the experiments of Weismann (abstracted for me by Mr. Cunningham) who found that in various Daphnidece which bring forth resting eggs, sexual and asexual reproduction go on simultaneously, as well as separately, in the spring and summer: these variable results being adapted to variable conditions. For not only are these creatures liable to die from lack of food, from the winter's cold, and from the drying up of their ditches, &c., as well as from the over-heating of them, but during this period of over-heating they arc liable to die from that de- oxygenation of the water which heat causes. Manifestly the favourable and unfavourable conditions recurring in com binations that are rarely twice alike, cannot be met by any regularly recurring form of heterogenesis; and it is interest ing to see how survival of the fittest has established a mixed form. In the spring, as well as in the autumn, there is in some cases a formation of resting or winter eggs; and evidently these provide against the killing off of the whole population by summer drought. Meanwhile, by ordinary males and females there is a production of summer egi^s adapted to meet the incident of drying up by drought and GENESIS. 291 subsequent re-supply of water. And all along successive generations of parthenogenetic females effect a rapid multi plication as long as conditions permit. Since life and growth are impeded or arrested not by lack of food only, but by other unfavourable conditions, we may understand how change in one or more of these may set up one or other form of genesis, and how the mixture of them may cause a mixed mode of multiplication which, originally initiated by external causes, becomes by inheritance and selection a trait of the species.* And then in proof that external causes initiate these pecu liarities, we have the fact that in certain Dapknidea? " which live in places where existence and parthenogenesis are pos sible throughout the year, the sexual period has disappeared : " there are no males. Passing now to animals which multiply by homogcnesis — animals in which the whole product of a fertilized germ ag gregates round a single centre or axis instead of round many centres or axes — we see, as before, that so long as the con ditions allow rapid increase in the mass of this germ-product, the formation of new individuals by gamogenesis does not take place. Only when growth is declining in relative rate, do perfect sperm-cells and germ-cells begin to appear; and * This cr-tablishmcnt by survival of the fittest of reproductive processes adapted to variable conditions, is indirectly elucidated by the habits of salmon. As salmon thrive in the sea and fall out of condition in fresh water (bavins during their sea-life not exercised the art of catching fresh-water prey), the implication is that the species would profit if all individuals ran up the rivers just before spawning time in November. Why then do most of them run up during many preceding months? Contemplation of the difficul ties which lie in the way to the spawning grounds, will, I think, suggest nn explanation. There are falls to be leaped and shallow rapids to be ascended. These obstacles cannot be surmounted when the river is low. A fish which starts early in the season has more chances of getting up the falls and the rapids than one which starts later; and, out of condition as it will be, may spawn, though not well. On the other hand, one which starts in October, if floods occur appropriately, may reach the upper waters and then spawn to great advantage; but in the absence of adequate rains it may fail altogether to reach the spawning grounds. Hence the species profits by an irregularity of habits adapted to meet irregular contingencies. 292 THE INDUCTIONS OP BIOLOGY. the fullest activity of the reproductive function arises as growth ceases : speaking generally, at least ; for though this relation is tolcrahly definite in the highest orders of animals which multiply by gamogencsis, it is less definite in the lower orders. This admission does not militate against the hypo thesis, as it seems to do ; for the indefmiteness of the relation occurs where the limit of growth is comparatively indefinite. We saw ( § 46 ) that among active, hot-blooded creatures, such as mammals and birds, the inevitable balancing of assimila tion by expenditure establishes, for each species, an almost uniform adult size; and among creatures of these kinds (birds especially, in which this restrictive effect of expendi ture is most conspicuous), the connexion between cessation of growth and commencement of reproduction is distinct. But we also saw (§4G) that where, as in the Crocodile and the Pike, the conditions and habits of life are such that expenditure does not overtake assimilation as size increases, there is no precise limit of growth; and in creatures thus circumstanced we may naturally look for a comparatively indeterminate relation between declining growth and com mencing reproduction.* There is, indeed, among fishes, at least one case which appears very anomalous. The male parr, or young of the male salmon, a fish of four or five inches in length, is said to produce milt. Having, at this early stage of its growth, not one-hundredth of the weight of a full-grown salmon, how does its production of milt consist with the alleged general law? The answer must be in great measure hypothetical. If the salmon is (as it ap pears to be in its young state) a species of fresh- water trout * I owe to Mr. (now Sir John) Lubbock an important confirmation of this view. After statins: his belief that between Crustaceans and Insects there exists a physiological relation analogous to that which exists between water- vcrtebrata and land-vertebrata, he pointed out to me that while among Insects there is a definite limit of growth, and an accompanying definite com mencement of reproduction, among Crustaceans, where growth has no definite limit, there is no definite relation between the commencement of reproduction and the decrease or arrest of growth. GENESIS. 293 that has contracted the habit of annually migrating to the sea, where it finds a food on which it thrives — if the original size of this species was not much greater than that of the parr (which is nearly as large as some varieties of trout) — and if the limit of growth in the trout tribe is very indefinite, as we know it to be; then we may reasonably infer that the parr has nearly the adult form and size which this species of trout had before it acquired its migratory habit; and that this production of milt is, in such case, a concomitant of the incipient decline of growth naturally arising in the species when living under the conditions of the ancestral species. Should this be so, the immense subsequent growth of the parr into the salmon, consequent on a suddenly-increased ' facility in obtaining food, removes to a great distance the limit at which assimilation is balanced by expenditure; and has the effect, analogous to that produced in plants, of arrest ing the incipient reproductive process. A confirmation of this view may be drawn from the fact that when the parr, after its first migration to the sea, returns to fresh water, having increased in a few months from a couple of ounces to five or six pounds, it no longer shows any fitness for propagation : the grilse, or immature salmon, does not produce milt or spawn. We conclude, then, that the. products of a fertilized germ go on accumulating by simple growth, so long as the forces whence growth results are greatly in excess of the antagonist forces; but that when diminution of the one set of forces or increase of the other, causes a considerable decline in this excess and an approach towards equilibrium, fertilized germs are again produced. Whether the germ-product be organized round one axis or round the many axes that arise by agamogenesis, matters not. Whether, as in the higher animals, this approach to equilibrium results from that dis proportionate increase of expenditure entailed by increase of size; or whether, as in most plants and many inferior animals, it results from absolute or relative decline of nutri tion ; matters not. In any case the recurrence of gamogenesis 294 THE INDUCTIONS OF BIOLOGY. is associated with a decrease in the excess of tissue-producing power. We cannot say, indeed, that this decrease always results in gamogenesis: some organisms multiply for an indefinite period by agamogenesis only. The Weeping Willow, which has been propagated throughout Europe, does not seed in Europe ; and yet, as the Weeping Willow, by its large size and the multiplication of generation upon genera tion of lateral axes, presents the same causes of local innutri tion as other trees, we cannot ascribe the absence of sexual axes to the continued predominance of nutrition. Among ani mals, too, the anomalous case of the Tineidce, a group of moths in which parthenogenetic multiplication goes on for genera tion after generation, seems to imply that gamogenesis does not necessarily result from an approximate balance of assimi lation by expenditure. What we must say is that an approach towards equilibrium between the forces which cause growth and the forces which oppose growth, is the chief condition to the recurrence of gamogenesis; but that there appear to be other conditions, in the absence of which approach to equili brium is not followed by gamogenesis. § 79. The above induction is an approximate answer to the question — When does gamogenesis recur? but not to the question which was propounded — Why does gamogenesis recur? — Why cannot multiplication be carried on in all cases, as it is in many cases, by agamogenesis? As already said, biologic science is not yet advanced enough to reply. Mean while, the evidence above brought together suggests a certain hypothetical answer. Seeing, on the one hand, that gamogenesis recurs only in individuals which are approaching a state of organic equili brium; and seeing, on the other hand, that the sperm-cells and germ-cells thrown off by such individuals are cells in which developmental changes have ended in quiescence, but in which, after their union, there arises a process of active cell-formation ; we may suspect that the approach towards a GENESIS. 295 state of general equilibrium in such gamogcnctic individuals, is accompanied by an approach towards molecular equilibrium in them ; and that the need for this union of sperm-cell and germ-cell is the need for overthrowing this equilibrium, and re-establishing active molecular change in the detached germ — a result probably effected by mixing the slightly different physiological units of slightly different individuals. The several arguments which support this view, cannot be satis factorily set forth until after the topics of Heredity and Variation have been dealt with. Leaving it for the present, I propose hereafter to re-consider it in connexion with sundry others raised by the phenomena of Genesis. But before ending the chapter, it may be well to note the relations between these different modes of multiplication, and the conditions of existence under which they are respectively habitual. While the explanation of the teleologist is untrue, it is often an obverse to the truth; for though, on the hypo thesis of Evolution, it is clear that things are not arranged thus or thus for the securing of special ends, it is also clear that arrangements which do secure these special ends tend to establish themselves — are established by their fulfilment of these ends. Besides insuring a structural fitness between each kind of organism and its circumstances, the working of " natural selection " also insures a fitness between the mode and rate of multiplication of each kind of organism and its circumstances. We may, therefore, without any teleo- logical implication, consider the fitness of homogenesis and heterogenesis to the needs of the different classes of organisms which exhibit them. Heterogenesis prevails among organisms of which the food, though abundant compared with their expenditure, is dis persed in such a way that it cannot be appropriated in a wholesale manner. Protophyta, subsisting on diffused gases and decaying organic matter in a state of minute subdivision, and Protozoa, to which food comes in the shape of extremely small floating particles, are enabled, by their rapid agamo- 296 THE INDUCTIONS OF BIOLOGY. genetic multiplication, to obtain materials for growth better than they would do did they not thus continually divide and disperse in pursuit of it. The higher plants, having for nutriment the carbonic acid of the air and certain mineral components of the soil, show us modes of multiplication adapted to the fullest utilization of these substances. A herb with but little power of forming the woody fibre re quisite to make a stem that can support wide-spreading branches, after producing a few sexless axes produces sexual ones; and maintains its race better, by the consequent early dispersion of seeds, than by a further production of sexless axes. But a tree, able to lift its successive generations of sexless axes high into the air, where each gets carbonic acid and light almost as freely as if it grew by itself, may with advantage go on budding-out sexless axes year after year; since it thereby increases its subsequent power of budding- out sexual axes. Meanwhile it may advantageously trans form into seed-bearers those axes which, in consequence of their less direct access to materials absorbed by the roots, are failing in their nutrition; for it thus throws off from a point at which sustenance is deficient, a migrating group of germs that may find sustenance elsewhere. The hetero- genesis displayed by animals of the Coelenterate type has evidently a like utility. A polype, feeding on minute annelids and crustaceans which, flitting through the water, come in contact with its tentacles, and limited to that quan tity of prey which chance brings within its grasp, buds out young polypes which, either as a colony or as dispersed in dividuals, spread their tentacles through a larger space of water than the parent alone can; and by producing them, the parent .better insures the continuance of its species than it would do if it went on slowly growing until its nutrition was nearly balanced by its waste, and then multiplied by gamogenesis. Similarly with the Aphis. Living on sap sucked from tender shoots and leaves, and able thus to take in but a very small quantity in a given time, this creature's GENESIS. 297 race is more likely to be preserved by a rapid asexual pro pagation of small individuals, wbicb disperse tbemselves over a wide area of nutrition, than it would be did the indi vidual growth continue so as to produce large individuals multiplying sexually. And then when autumnal cold and diminishing supply of sap put a check to growth, the recur rence of gamogenesis, or production of fertilized ova which remain dormant through the winter, is more favourable to the preservation of the race than would be a further con tinuance of agamogenesis. On the other hand, among the higher animals living on food which, though dispersed, is more or less aggregated into large masses, this alternation of gamic and agamic reproduction ceases to be useful. The development of the germ-product into a single organism of considerable bulk, is in many cases a condition without which these large masses of nutriment could not be appro priated ; and here the formation of many individuals instead of one would be fatal. But we still see the beneficial results of the general law — the postponement of gamogenesis until the rate of growth begins to decline. For so long as the rate of growth continues rapid, there is proof that the organism gets food with facility — that expenditure does not seriously check accumulation; and that the size reached is as yet not disadvantageous : or rather, indeed, that it is advantageous. But when the rate of growth is much decreased by the increase of expenditure — when the excess of assimilative power is diminishing so fast as to indicate its approaching disappearance — it becomes needful, for the maintenance of the species, that this excess shall be turned to the production of new individuals; since, did growth continue until there was a complete balancing of assimilation and expenditure, the production of new individuals would be either impossible or fatal to the parent. And it is clear that " natural selec tion " will continually tend to determine the period at whir1! gamogenesis commences, in such a way as most favours the maintenance of the race. 298 THE INDUCTIONS OF BIOLOGY. Here, too, may fitly bo pointed out the fact that, by " natural selection," there will in every case be produced the most advantageous proportion of males and females. If the conditions of life render numerical inequality of the sexes beneficial to the species, in respect either of the number of the offspring or the character of the offspring; then, those varieties of the species which approach more than other varieties towards this beneficial degree of inequality, will be apt to supplant other varieties. And conversely, where equality in the number of males and females is beneficial, the equilibrium will be maintained by the dying out of such varieties as produce offspring among which the sexes are not balanced. NOTE. — Such alterations of statement in this chapter as have been made necessary by the advance of biological know ledge since 1864 have not, I think, tended to invalidate its main theses, but have tended to verify them. Some expla nations to be here added may remove remaining difficulties. Certain types, which are transitional between Protozoa and Metazoa, exhibit under its simplest form the relation between self-maintenance and race-maintenance — the integration primarily effecting the one and the disintegration primarily effecting the other. Among the Mycetozoa a number of amoeba-like individuals aggregate into what is called a plasmodium; and while, in some orders, they become fused into a mass of protoplasm through which their nuclei are dispersed, in other orders (Sorophora) they retain their indi vidualities and simply form a coherent aggregate. These last, presumably the earliest in order of evolution, remain united so long as the plasmodium, having a small power of locomotion, furthers the general nutrition; but when this is impeded by drought or cold, there arise' spores. Each spore contains an amoeboid individual; and this, escaping when favourable conditions return, establishes by fission and by union with others like itself a new colony or plasmodium. GENESIS. 299 Reduced to its lowest terms, we here see the antagonism between that growth of the coherent mass of units which accompanies its physical prosperity, and that incoherence and dispersion of the units which follows unfavourable condi tions and arrest of growth, and which presently initiates new plasmodia. This antagonism, seen in these incipient Metazoa which show us none of that organization characterizing the Metazoa in general, is everywhere in more or less disguised forms exhibited by them — must necessarily be so if growth of the individual is a process of integration while formation of new individuals is a process of disintegration. And, primarily, it is an implication that whatever furthers the one impedes the other. But now while recognizing the truth that nutrition and innutrition (using these words to cover not supply of nutri ment only but the presence of other influences favourable or unfavourable to the vital processes) primarily determine the alternations of these; we have also to recognize the truth that from the beginning survival of the fittest has been shaping the forms and effects of their antagonism. By in heritance a physiological habit which modifies the form of the antagonism in a way favourable to the species, will become established. Especially will this be the case where the lives of the individuals have become relatively definite and where special organs have been evolved for casting off reproductive centres. The resulting physiological rhythm may in such cases become so pronounced as greatly to obscure the primi tive relation. Among plants we sec this in the fact that those which have been transferred from one habitat to another having widely different seasons, long contimic their original time of flowering, though it is inappropriate to the new cir cumstances — the reproductive periodicity has become organic. Similarly in each species of higher animal, development of the reproductive organs and maturation of reproductive cells take place at a settled age, whether the conditions have 300 THE INDUCTIONS OF BIOLOGY. been favourable or unfavourable to physical prosperity. The established constitutional tendency, adapted to the needs of the species, over-rides the constitutional needs of the indi vidual. Even here, however, the primitive antagonism, though greatly obscured, occasionally shows itself. Instance the fact that in plants where gamogenesis is commencing a sudden access of nutrition will cause resumption of agamogenesis ; and I suspect that an illustration may be found among human beings in the earlier establishment of the reproduc tive function among the ill-fed poor than among the well-fed rich. One other qualification has to be added. In plants and animals which have become so definitely constituted that at an approximately fixed stage, the proclivity towards the pro duction of new individuals becomes pronounced, it naturally happens that good nutrition aids it. Surplus nutriment being turned into the reproductive channel, the reproduction is efficient in proportion as the surplus is great. Hence the fact that in fruit trees which have reached the flowering stage, manuring has the effect that though it does not increase the quantity of blossoms it increases the quantity of fruit; and hence the fact that well-fed and easy-living races of men are prolific. CHAPTER VIII. HEREDITY. § 80. ALREADY, in the last two chapters, the law of heredi tary transmission has been tacitly assumed; as, indeed, it unavoidably is in all such discussions. Understood in its entirety, the law is that each plant or animal, if it repro duces, gives origin to others like itself : the likeness consist ing, not so much in the repetition of individual traits as in the assumption of the same general structure. This truth has been rendered so familiar by daily illustration as almost to have lost its significance. That wheat produces wheat — that existing oxen have descended from ancestral oxen — that every unfolding organism eventually takes the form of the class, order, genus, and species from which it sprang; is a fact which, by force of repetition, has acquired in our minds almost the aspect of a necessity. It is in this, however, that Heredity is principally displayed : the manifestations of it commonly referred to being quite subordinate. And, as thus understood, Heredity is universal. The various instances of heterogenesis lately contemplated seem, indeed, to be at variance with this assertion. But they are not really so. Though the recurrence of like forms is, in these instances, not direct but cyclical, still, the like forms do recur; and, when taken together, the group of forms produced during one of the cycles is as much like the groups produced in pre ceding cycles, as the single individual arising by liomo- :,rriH'sis is like ancestral individuals. 301 332 THE INDUCTIONS OF BIOLOGY. While, however, the general truth that organisms of a given type uniformly descend from organisms of the same type, is so well established by infinite illustrations as to have assumed the character of an axiom; it is not universally admitted that non-typical peculiarities are inherited. Many entertain a vague belief that the law of Heredity applies only to main characters of structure and not to details; or, at any rate, that though it applies to such details as constitute differences of species, it does not apply to smaller details. The circumstance that the tendency to repetition is in a slight degree qualified by the tendency to variation (which, as we shall hereafter see, is but an indirect result of the tendency to repetition), leads some to doubt whether Heredity is unlimited. A careful weighing of the evidence, however, and a due allowance for the influences by which the minuter manifestations of Heredity are obscured, may remove this scepticism. First in order of importance comes the fact that not only are there uniformly transmitted from an organism to its off spring, those traits of structure which distinguish the class, order, genus, and species; but also those which distinguish the variety. We have numerous cases, among both plants and animals, where, by natural or artificial conditions, there have been produced divergent modifications of the same species; and abundant proof exists that the members of any one sub-species habitually transmit their distinctive pecu liarities to their descendants. Agriculturists and gardeners can furnish unquestionable illustrations. Several varieties of wheat are known, of which each reproduces itself. Since the potato was introduced into England there have been formed from it a number of sub-species; some of them differing greatly in their forms, sizes, qualities, and periods of ripening. Of peas, also, the like may be said. And the case of the cabbage-tribe is often cited as showing the per manent establishment of races which have diverged widely from a common stock. Among fruits and ilowers the multi- HEREDITY. 303 plication of kinds, and the continuance of each kind with certainty by agamogenesis, and to some extent by gamo- gcnesis, might be exemplified without end. From all sides evidence may be gathered showing a like persistence of varieties among animals. We have our distinct breeds of sheep, our distinct breeds of cattle, our distinct breeds of horses : each breed maintaining its characteristics. The many sorts of clogs which, if we accept the physiological test, we must consider as all of one species, show us in a marked manner the hereditary transmission of small differ ences — each sort, when kept pure, reproducing itself not only in size, form, colour, and quality of hair, but also in disposi tion and speciality of intelligence. Poultry, too, have their permanently-established races. And the Isle of Man sends us a tail-less kind of cat. Even in the absence of other evidence, that which ethnology furnishes would suffice. Grant them to be derived from one stock, and the varieties of man yield proof upon proof that non-specific traits of structure are bequeathed from generation to generation. Or grant only their derivation from several stocks, and we still have, between races descended from a common stock, dis tinctions which prove the inheritance of minor peculiarities. Besides seeing the Negroes continue to produce Negroes, copper-coloured men to produce men of a copper colour, and the fair-skinned races to perpetuate their fair skins — besides seeing that the broad-faced and flat-nosed Calmuck begets children with broad faces and flat noses, while the Jew bequeaths to his offspring the features which have so long characterized Jews; we see that those small unlikenesses which distinguish more nearly-allied varieties of men, are maintained from generation to generation. In Germany, the ordinary shape of skull is appreciably different from that common in Britain: near akin though the Germans are to the British. The average Italian face continues to be unlike the faces of northern nations. The French character is now, as it was centuries ago, contrasted in sundry respects with 304: THE INDUCTIONS OF BIOLOGY. the characters of neighbouring peoples. Nay, even between races so closely allied as the Scotch Celts, the Welsh Celts, and the Irish Celts, appreciable differences of form and nature have become established. The fact that sub-species and sub-sub-species thus exem plify the general law of inheritance which shows itself in the perpetuation of ordinal, generic, and specific peculiarities, is strong reason for the belief that this general lay is unlimited in its application. This has the support of still more special evidences. They are divisible into two classes. In the one come cases where congenital peculiarities, not traceable to any obvious causes, are bequeathed to descendants. In the other come cases where the peculiarities thus bequeathed are not congenital, but have resulted from changes of functions during the lives of the individuals bequeathing them. We will consider first the cases that come in the first class. § 81. Note at the outset the character of the chief testi mony. Excluding those inductions that have been so fully verified as to rank with exact science, there are no inductions so trustworthy as those which have undergone the mercantile test. When we have thousands of men whose profit or loss depends on the truth of their inferences from perpetually- repeated observations ; and when we find that their inferences, handed down from generation to generation, have generated an unshakable conviction ; we may accept it without hesitation. In breeders of animals we have such a class, led by such experiences, and entertaining such a conviction — the convic tion that minor peculiarities of organization are inherited as well as major peculiarities. Hence the immense prices given for successful racers, bulls of superior forms, sheep that have certain desired peculiarities. Hence the careful record of pedigrees of high-bred horses and sporting dogs. Hence the care taken to avoid intermixture with inferior stocks. As quoted by Mr. Darwin, Youatt says the principle of selection " enables the agriculturist not only to modify the character HEREDITY. 305 of his flock but to change it altogether." Lord Somerville, speaking of what breeders have done for sheep, says : — " It would seem that the}' have chalked upon a wall a form per fect in itself and then given it existence." That most skil ful breeder, Sir John Sebright, used to say, with respect to pigeons, that " he would produce any given feather in three years, but it would take him six years to obtain head and beak." In all which statements the tacit assertion is, that individual traits are bequeathed from generation to genera tion, and may be so perpetuated and increased as to become permanent distinctions. Of special instances there are many besides that of the often-cited Otto-breed of sheep, descended from a single short- legged lamb, and that of the six-fingered Gratio Kelleia, who transmitted his peculiarity, in different degrees, to several of his children and to some of his grandchildren. In a paper contributed to the Edinburgh New Philosophical Journal for July, 1863, Dr. (now Sir John) Struthers gives cases of heredi tary digital variations. Esther P — ,who had six fingers on one hand, bequeathed this malformation along some lines of her descendants for two, three, and four generations. A — S — inherited an extra digit on each hand and each foot from his father; and C — G — , who also had six fingers and six toes, had an aunt and a grandmother similarly formed. A collec tion of evidence published by Mr. Sedgwick in the Medico- Chirurgical Review for April and for July, 1863, in two articles on "The Influence of Sex in limiting Hereditary Transmission," includes the following cases: — Augustin Duforet, a pastry-cook of Douai, who had but two instead of three phalanges to all his fingers and toes, inherited this malformation from his grandfather and father, and had it in common with an uncle and numerous cousins. An account has been given by Dr. Lepine, of a man with only three fingers on each hand and four toes on each foot, and whose (grandfather and son exhibited the like anomaly. Bechet describes Victoire Barre as a woman who, like her father and 306 THE INDUCTIONS OF BIOLOGY. sister, had but one developed finger on each hand and but two toes on each foot, and whose monstrosity re-appeared in two daughters. And there is a case where the absence of two distal phalanges on the hands was traced for two genera tions. The various recorded instances in which there has been transmission from one generation to another, of webbed- fingers, of webbed-toes, of hare-lip, of congenital luxation of the thigh, of absent patellae, of club-foot, &c., would occupy more space than can here be spared. Defects in the organs of sense are also not unfrcquently inherited. Four sisters, their mother, and grandmother, are described by Duval as similarly affected by cataract. Prosper Lucas details an example of amaurosis affecting the females of a family for three generations. Duval, Graffe, Dufon, and others testify to like cases coming under their observation.* Deafness, too, is occasionally transmitted from parent to child. There are deaf-mutes whose imperfections have been derived from ancestors; and malformations of the external ears have also been perpetuated in offspring. Of transmitted peculiarities of the skin and its appendages, many cases have been noted. One is that of a family remarkable for enorm ous black eyebrows; another that of a family in which every member had a lock of hair of a lighter colour than the rest on the top of the head; and there are also instances of congenital baldness being hereditary. From one of our lead ing sculptors I learn that his wife has a flat mole under the foot near the little toe, and one of her sons has the same. Entire absence of teeth, absence of particular teeth, and anomalous arrangements of teeth, are recorded as traits that have descended to children. And we have evidence that sound ness and unsoundness of teeth are transmissible. The inheritance of tendencies to such diseases as gout, * While this chapter is passing through the press, I learn from Mr. White Cooper, that not only are near sight, long sight, dull sight, and squinting, hereditary; but that a peculiarity of vision confined to one eye is frequently transmitted : re-appearing ill the same eye in offspring. HEREDITY. 307 con sumption, and insanity is universally admitted. Among the less-common diseases of which the descent has been ob served, are ichthyosis, leprosy, pityriasis, sebaceous tumours, plica polonica, dipsomania, somnambulism, catalepsy, epi lepsy, asthma, apoplexy, elephantiasis. General nervousness displayed by parents almost always re-appears in their chil dren. Even a bias towards suicide appears to be sometimes hereditary. § 82. To prove the transmission of those structural pecu liarities which have resulted from functional peculiarities, is, for several reasons, comparatively difficult. Changes pro duced in the sizes of parts by changes in their amounts of action, are mostly unobtrusive. A muscle which has increased in bulk is usually so obscured by natural or artificial cloth ing, that unless the alteration is extreme it passes without remark. Such nervous developments as are possible in the course of a single life, cannot be seen externally. Visceral modifications of a normal kind are observable but obscurely, or not at all. And if the changes of structure worked in individuals by changes in their habits are thus difficult to trace, still more difficult to trace must be the transmission of them : further hidden, as this is, by the influences of other individuals who are often otherwise modified by other habits. Moreover, such specialities of structure as are duo to specialities of function, are usually entangled with speciali ties of structure which are, or may be, due to selection, natural or artificial. In most cases it is impossible to say that a structural peculiarity which seems to have arisen in offspring from a functional peculiarity in a parent, is wholly inde pendent of some congenital peculiarity of structure in the parent, whence this functional peculiarity arose. We are restricted to cases with which natural or artificial selection can have had nothing to do, and such cases are difficult to find. Some, however, may be noted. A species of plant that has been transferred from one soil 308 THE INDUCTIONS OF BIOLOGY. or climate to another, frequently undergoes what botanists call " change of habit " — a change which, without affecting its specific characters, is yet conspicuous. In its new locality the species is distinguished by leaves that are much larger or much smaller, or differently shaped, or more fleshy; or instead of being as before comparatively smooth, it becomes hairy ; or its stem becomes woody instead of being herbaceous ; or its branches, no longer growing upwards, assume a droop ing character. Now these " changes of habit " are clearly determined by functional changes. Occurring, as they do, in many individuals which have undergone the same transporta tion, they cannot be classed as " spontaneous variations." They are modifications of structure consequent on modifica tions of function that have been produced by modifications in the actions of external forces. And as these modifications re-appear in succeeding generations, we have, in them, ex amples of functionally-established variations that are here ditarily transmitted. Evidence of analogous changes in animals is difficult to disentangle. Only among domesticated kinds have we any opportunity of tracing the results of altered habits; and here, in nearly all cases, artificial selection has obscured them. Still, there are some facts which seem to the point. Mr. Darwin, while ascribing almost wholly to " natural selection " the production of those modifications which eventuate in differences of species, nevertheless admits the effects of use and disuse. He says — " I find in the domestic duck that the bones of the wing weigh less and the bones of the leg more, in proportion to the whole skeleton, than do the same bones in the wild duck; and I presume that this change may be safely attributed to the domestic duck flying much less, and walking more, than its wild parent. The great and inherited development of the udders in cows and goats in countries where they are habitually milked, in comparison with the state of these organs in other countries, is another instance of the effect of use. Not a single domestic animal can be named HEREDITY. 309 which has not in some country drooping cars ; and the view suggested by some authors, that the drooping is due to the disuse of the muscles of the ear, from the animals not being much alarmed by danger, seems probable." Again — " The eyes of moles and of some burrowing rodents are rudimentary in size, and in some cases are quite covered up by skin and fur. This state of the eyes is probably due to gradual reduction from disuse, but aided perhaps by natural selec tion." . . . . " It is well known that several animals belonging to the most different classes, which inhabit the caves of Styria and of Kentucky, arc blind. In some of the crabs the footstalk of the eye remains, though the eye is gone; the stand for the telescope is there, though the tele scope with its glasses has been lost. As it is difficult to imagine that eyes, though useless, could be in any way injurious to animals living in darkness, I attribute their loss wholly to disuse." * The direct inheritance of an acquired peculiarity is sometimes observable. Mr. Lewes gives a case. He " had a puppy taken from its mother at six weeks old, who, although never taught 'to beg' (an accomplishment his mother had been taught), spontaneously took to begging for everything he wanted when about seven or eight months old: he would beg for food, beg to be let out of the room, and one day was found opposite a rabbit hutch begging for rabbits." Instances are on record, too, of * An instance here occurs of the way in which those who are averse to a conclusion will assign the most flimsy reasons for rejecting it. Rather than admit that the eyes of these creatures living in darkness have disappeared from lack of use, some contend that such creatures would be liable to have their eyes injured by collisions with objects, and that therefore natural selec tion would favour those individuals in which the eyes had somewhat dimin ished and were least liable to injury : the implication being that the immunity from the inflammations due to injuries would be so important a factor in life as to cause survival. And this is argued in presence of the fact that one of the most conspicuous among these blind cave-animals is a cray-fish, and that the cray-fish in its natural habitat is in the habit of burrowing in the banks of rivers holes a foot or more deep, and has its eyes exposed to all those possible blows and frictions which the burrowing involves! 310 THE INDUCTIONS OF BIOLOGY. sporting dogs which spontaneously adopted in the field, certain modes of behaviour which their parents had learnt. But the best examples of inherited modifications produced by modifications of function, occur in mankind. To no other cause can be ascribed the rapid metamorphoses under gone by the British races when placed in new conditions. Jn the United States the descendants of the immigrant Irish lose their Celtic aspect, and become Americanized. This cannot be ascribed to mixture, since the feeling with which Irish are regarded by Americans prevents any considerable amount of intermarriage. Equally marked is the case of the immigrant Germans who, though they keep very much apart, rapidly assume the prevailing type. To say that " spon taneous variation " increased by natural selection, can have produced this effect, is going too far. Peoples so numerous cannot have been supplanted in the course of two or three generations by varieties springing from them. Hence the implication is that physical and social conditions have wrought modifications of function and structure, which off spring have inherited and increased. Similarly with special cases. In the Cyclopcedia of Practical Medicine, Vol. II., p. 419, Dr. Brown states that he " has in many instances ob served in the case of individuals whose complexion and general appearance has been modified by residence in hot climates, that children born to them subsequently to such residence, have resembled them rather in their acquired than primary mien." Some visible modifications of organs caused by changes in their functions, may be noted. That large hands are inherited by those whose ancestors led laborious lives, and that those descended from ancestors unused to manual labour com monly have small hands, are established opinions. It seems very unlikely that in the absence of any such connexion, the size of the hand should have come to be generally re garded as some index of extraction. That there exists a like relation between habitual use of the feet and largeness of the HEREDITY. 311 feet, we have strong evidence in the customs of the Chinese. The torturing practice of artificially arresting the growth of the feet, could never have become established among the ladies of China, had they not seen that a small foot was significant of superior rank — that is of a luxurious life — that is of a life without bodily labour. • There is evidence, too, that modifications of the eyes, caused by particular uses of the eyes, are inherited. Short sight appears to be un common among peasants; but it is frequent among classes who use their eyes much for reading and writing, and is often congenital. Still more marked is this relation in Germany. There, the educated are notoriously studious, and judging from the numbers of young Germans who wear spectacles, there is reason to think that congenital myopia is very frequent among them. Some of the best illustrations of functional heredity, are furnished by mental characteristics. Certain powers which mankind have gained in the course of civilization cannot, I think, be accounted for without admitting the inheritance of acquired modifications. The musical faculty is one of these. To say that " natural selection " has developed it by pre serving the most musically endowed, seems an inadequate explanation. Even now that the development and pre valence of the faculty have made music an occupation by which the most musical can get sustenance and bring up families;' it is very questionable whether, taking the musical career as a whole, it has any advantage over other careers in the struggle for existence and multiplication. Still more if we look back to those early stages through which the faculty must have passed before definite perception of melody was arrived at, we fail to see how those possessing the rudi mentary faculty in a somewhat greater degree than the rest, would thereby be enabled the better to maintain themselves and their children. There is no explanation but that the habitual association of certain cadences of speech with certain emotions, has slowly established in the race an 21 312 THE INDUCTIONS OF BIOLOGY. organized and inherited connection between such cadences and such emotions; that the combination of such cadences, more or less idealized, which constitutes melody, has all along had a meaning in the average mind, only because of the meaning which cadences had acquired in the average mind; and that by the continual hearing and practice of melody there has been gained and transmitted an increasing musical sensi bility. Confirmation of this view may be drawn from individual cases. Grant that among a people en dowed with musical faculty to a certain degree, spontaneous variation will occasionally produce men possessing it in a higher degree; it cannot be granted that spontaneous varia tion accounts for the frequent production, by such highly- endowed men, of men still more highly endowed. On the average, the children of marriages with others not similarly endowed, will be less distinguished rather than more distin guished. The most that can be expected is that this unusual amount of faculty shall re-appear in the next generation un- diminished. How then shall we explain cases like those of Bach, Mozart, and Beethoven, all of them sons of men having unusual musical powers who were constantly exercising those powers, and who greatly excelled their fathers in their musical powers ? What shall we say to the facts that Haydn was the son of an organist, that Hummel was born to a music master, and that Weber's father was a distinguished violinist ? The occurrence of so many cases in one nation within a short period of time, cannot rationally be ascribed to the coincidence of " spontaneous variations." It can be ascribed to nothing but inherited developments of structure caused by augmenta tions of function. But the .clearest proof that structural alterations caused by alterations of function are inherited, occurs when the alter ations are morbid. I had originally named in this place the results of M. Brown-Sequard's experiments on guinea-pigs, showing that those which had been artificially made epileptic had offspring which were epileptic ; and I name them again though his inference is by many rejected. For, as exemplified HEREDITY. 313 a few pages back, strong evidence is often disregarded for trivial reasons by those who dislike the conclusion drawn. Just naming this evidence and its possible invalidity, let me pass to some results of experiences recently set forth by Dr. Savage, President of the Neurological Society. In an essay on " Heredity and Neurosis " published in Brain, Parts LXXVII, LXXVIII, 1897, he says:— "We recognise the transmission of a tendency to develop gout, and we recognise that the disease produced by the individual himself differs little from that which may have been inherited." [That is, acquired gout may be transmitted as constitutional gout.] " I have seen several patients whose history I have been able to examine carefully, in whom mental tricks have been trans mitted from one generation to another." In the " musical prodigies " descending from musical parents, " there seemed to be a transmission of a greatly increased aptitude or tendency which is all one is contending for." " Though there is, in my opinion, power to transmit acquired peculiarities, yet the tendency is to transmit a predisposition." (pp.19 — 21.) And an authority on nervous diseases who is second to none — Dr. Hughlings Jackson — takes the same view. The liability to consumption shown by children of consumptive parents, which no one doubts, shows us the same thing. It is admitted that consumption may be produced by condi tions very unfavourable to life ; and unless it is held that the disease so produced differs from the disease when inherited, the conclusion must be that here, too, there is a transmission of functionally-produced organic changes. This holds true whether the production of tubercle is due to innate defect or whether it is due to the invasion of a bacillus. For in this last case the consumptive diathesis must be regarded as a state of body more than usually liable to invasion by the bacillus, and this is the same when acquired as when transmitted. § 83. Two modified manifestations of Heredity remain to be noticed. The one is the re-appearance in offspring of traits not borne by the parents, but borne by the grandparents or 3M THE INDUCTIONS OF BIOLOGY. by remoter ancestors. The other is the limitation of Heredity by sex — the restriction of transmitted peculiarities to off spring of the same sex as the parent possessing them. Atavism, which is the name given to the recurrence of ancestral traits, is proved by many and varied facts. In the picture-galleries of old families, and on the monumental brasses in the adjacent churches, are often seen types of fea ture which are still, from time to time, repeated in members of these families. It is a matter of common remark that some constitutional diseases, such as gout and insanity, after miss ing a generation, will show themselves in the next. Dr. Struthers, in his above-quoted paper " On Variation in the Number of Fingers and Toes, and in the Phalanges in Man," gives cases of malformations common to grandparent and grandchild, but of which the parent had no trace. M. Girou (as quoted by Mr. Sedgwick) says — " One is often surprised to see lambs black, or spotted with black, born of ewes and rams with white wool, but if one takes the trouble to go back to the origin of this phenomena, it is found in the ancestors." Instances still more remarkable, in which the remoteness of the ancestors copied is very great, are given by Mr. Darwin. He points out that in crosses between varieties of the pigeon, there will sometimes re-appear the plumage of the original rock-pigeon, from which these varieties descended; and he thinks the faint zebra-like markings occasionally traceable in horses have probably a like meaning. Theothermodified manifestation of heredity above referred to is the limitation of heredity by sex. In Mr. Sedgwick's essays, already named, will be found evidence implying that there exists some such tendency to limitation, which does or does not show itself distinctly according to the nature of the organic modification to be conveyed. On joining to the evi dence he gives certain bodies of allied evidence we shall, 1 think, find the inconsistcnces comprehensible. Beyond the familiar facts that in ourselves, along with the essential organs of sex there go minor structures and traits HEREDITY. 315 distinctive of sex, such as the beard and the voice in man, we have numerous cases in which, along with different sex- organs there go general differences, sometimes immense and often conspicuous. We have those in which (as in sundry parasites) the male is extremely small compared with the female; we have those in which the male is winged and the female wingless; we have those, as among birds, in which the plumage of males contrasts strongly with that of females ; and among butterflies we have kindred instances in which the wings of the two sexes are wholly unlike — some, indeed, in which there is not simply dimorphism but* polymorphism: two kinds of females both differing from the male. How shall we range these facts with the ordinary facts of inheri tance? Without difficulty if heredity results from the pro clivity which the component units contained in a germ-cell or a sperm-cell have to arrange themselves into a structure like that of the structure from which they were derived. For the obvious corollary is that where there is gamogcnesis there will result partly concurring and partly conflicting proclivities. In the fertilized germ we have two groups of physiological units, slightly different in their structures. These slightly- differcnt units severally multiply at the expense of the nutri ment supplied to the unfolding germ — each kind moulding this nutriment into units of its own type. Throughout the process of development the two kinds of units, mainly agree ing in their proclivities and in the form which they tend to build themselves into, but having minor differences, work in unison to produce an organism of the species from which they were derived, but work in antagonism to produce copies of their respective parent-organisms. And hence ultimately results an organism in which traits of the one are mixed with traits of the other ; and in which, according to the pre- domi nance of one or other group of units, one or other sex with all its concomitants is produced. If so, it becomes comprehensible that witli the predomi nance of either group, and the production of the same sex as 316 THE INDUCTIONS OF BIOLOGY. that of the parent whence it was derived, there will go the repetition not only of the minor sex-traits of that parent but also of any peculiarities he or she possessed, such as monstros ities. Since the two groups are nearly balanced, and since inheritance is never an average of the two parents but a mixture of traits of the one with traits of the other, it is not difficult to see why there should be some irregularity in the transmission of these monstrosities and constitutional tend encies, though they are most frequently transmitted only to those of the same sex.* § 84. Unawares in the last paragraph there has been taken for granted the truth of that suggestion concerning Heredity ventured in § 6G. Anything like a positive explanation is not to be expected in the present stage of Biology, if at all. We can look for nothing beyond a simplification of the problem; and a reduction of it to the same category with certain other problems which also admit of hypothetical solu tions only. If an hypothesis which sundry widespread phe nomena have already thrust upon us, can be shown to render the phenomena of Heredity more intelligible than they at present seem, we shall have reason to entertain it. The ap plicability of any method of interpretation to two different but allied classes of facts, is evidence of its truth. The power which many animals display of reproducing lost parts, we saw to be inexplicable except on the assump tion that the units of which any organism is built have a tendency to arrange themselves into the shape of that organ ism (§65). This power is sufficiently remarkable in cases * In addition to the numerous illustrations given by Mr. Scdgwick, here is one which Colonel A. T. Fraser published in Nature for Nov. 9, 1893, concerning two Hindoo dwarfs : — " In speech and intelligence the dwarfs were indistinguishable from ordinary natives of India. From an interrogation of one of them, it appeared that he belonged to a family all the male members of which have been dwarfs for several generations. They marry ordinary native girls, and the female childreagrow up like those of other people. The males, however, though they develop at the normal rate until they reach the age of six, then cease to grow, and become dwarfs." HEREDITY. 317 where a lost limb or tail is replaced, but it is still more remarkable in cases where, as among some annelids, the pieces into which an individual is cut severally complete themselves by developing heads and tails, or in cases like that of the Holothuria, which having, when alarmed, ejected its viscera, reproduces them. Such facts compel us to admit that the components of an organism have a proclivity towards a special structure — that the adult organism when mutilated exhibits that same proclivity which is exhibited by the young organism in the course of its normal develop ment. As before said, we may, for want of a better name, figuratively call this power organic polarity: meaning by this phrase nothing more than the observed tendency towards a special arrangement. And such facts as those presented by the fragments of a Hydra, and by fragments of leaves from which complete plants are produced, oblige us to recog nize this proclivity as existing throughout the tissues in general — nay, in the case of the Begonia pliyllomaniaca, obliges us to recognize this proclivity as existing in the physiological units contained in each undiffcrentiated cell. Quite in harmony with this conclusion, are certain implications since noticed, respecting the characters of sperm-cells and germ-cells. We saw sundry reasons for rejecting the supposition that these arc highly-specialized cells and for accepting the opposite supposition, that they are cells differing from others rather in being unspecialized. And here the assumption to which we seem driven by the ensemble of the evidence, is, that sperm-cells and germ-cells are essentially nothing more than vehicles in which are con tained small groups of the physiological units in a fit state for obeying their proclivity towards the structural arrange ment of the species they belong to. If the likeness of offspring to parents is thus determined, it becomes manifest, a priori, that besides the transmission of generic and specific peculiarities, there will be a transmis sion of those individual peculiarities which, arising without 318 THE INDUCTIONS OF BIOLOGY. assignable causes, are classed as " spontaneous." For if the assumption of a special arrangement of parts by an organism, is due to the proclivity of its physiological units towards that arrangement; then the assumption of an arrangement of parts slightly different from that of the species, implies physiological units slightly unlike those of the species; and these slightly-unlike physiological units, communicated through the medium of sperm-cell or germ-cell, will tend, in the offspring, to build themselves into a structure similarly diverging from the average of the species. But it is not equally manifest that, on this hypothesis, alterations of structure caused by alterations of function must be transmitted to offspring. It is not obvious that change in the form of a part, caused by changed action, in volves such change in the physiological units throughout the organism that these, when groups of them are thrown off in the shape of reproductive centres, will unfold into organisms that have this part similarly changed in form. Indeed, when treating of Adaptation (§ G'J), we saw that an organ modified by increase or decrease of function, can but slowly re-act on the system at large, so as to bring about those correlative changes required to produce a new equilibrium ; and yet only when such new equilibrium has been established, can we ex pect it to be fully expressed in the modified physiological units of which the organism is built — only then can we count on a complete transfer of the modification to descendants. Nevertheless, that changes of structure caused by changes of action must also be transmitted, however obscurely, ap pears to be a deduction from first principles — or if not a specific deduction, still, a general implication. For if an organism A, has, by any peculiar habit or condition of life, been modified into the form A', it follows that all the func tions of A', reproductive function included, must be in some degree different from the functions of A. An organism being a combination of rhythmically-acting parts in moving equilibrium, the action and structure of any one part cannot HEREDITY. 319 be altered without causing alterations of action and struc ture in all the rest; just as no member of the Solar System could be modified in motion or mass, without producing re arrangements throughout the whole Solar System. And if the organism A, when changed to A', must be changed in all its functions; then the offspring of A' cannot be the same as they would have been had it retained the form A. That the change in the offspring must, other things equal, be in the same direction as the change in the parent, appears implied by the fact that the change propagated throughout the parental system is a change towards a new state of equilibrium — a change tending to bring the actions of all organs, reproductive included, into harmony with these new actions. Or, bringing the question to its ultimate and sim plest form, we may say that as, on the one hand, physiological units will, because of their special polarities, build them selves into an organism of a special structure; so,- on the other hand, if the structure of this organism is modified by modified function, it will impress some corresponding modification on the structures and polarities of its units. The units and the aggregate must act and re-act on each other. If nothing prevents, the units will mould the aggregate into a form in equilibrium with their pre-existing polarities. If, contrariwise, the aggregate is made by incident actions to take a new form, its forces must tend to re-mould the units into harmony with this new form. And to say that the physiological units are in any degree so re-moulded as to bring their polar forces towards equilibrium with the forces of the modified aggregate, is to say that when separated in the shape of reproductive centres, these units will tend to build themselves up into an aggregate modified in the same direc tion. NOTE. — A large amount of additional evidence supporting the belief that functionally produced modifications are in herited, will be found in Appendix B. CHAPTER IX. VARIATION. § 85. EQUALLY conspicuous with the truth that every organism bears a general likeness to its parents, is the truth that no organism is exactly like either parent. Though similar to both in generic and specific traits, and usually, too, in those traits which distinguish the variety, it diverges in numerous traits of minor importance. No two plants are indistinguishable; and no two animals are without differ ences. Variation is co-extensive with Heredity. The degrees of variation have a wide range. There are deviations so small as to be not easily detected; and there are deviations great enough to be called monstrosities. In plants we may pass from cases of slight alteration in the shape of a leaf, to cases where, instead of a flower with its calyx above the seed-vessel, there is produced a flower with its calyx below the seed-vessel; and while in one animal there arises a scarcely noticeable unlikeness in the length or colour of the hair, in another an organ is absent or a supernumerary organ appears. Though small variations are by far the most general, yet variations of considerable magnitude are not uncommon; and even those variations constituted by additions or suppressions of parts, are not so rare as to be excluded from the list of causes by which organic forms are changed. Cattle without horns arc fre quent. Of sheep there are horned breeds and breeds that 320 VARIATION. 321 have lost their horns. At one time there existed in Scot land a race of pigs with solid feet instead of cleft feet. In pigeons, according to Mr. Darwin, " the number of the caudal and sacral vertebra* vary; as does the number of the ribs, together with their relative breadth and the presence of pro cesses." That variations, both small and large, which arise without any specific assignable cause, tend to become hereditary, was shown in the last chapter. Indeed the evidence which proves Heredity in its smaller manifestations is the same evidence which proves Variation ; since it is only when there occur vari ations that the inheritance of anything beyond the structural peculiarities of the species can be proved. It remains here, however, to be observed that the transmission of variations is itself variable; and that it varies both in the direction of decrease and in the direction of increase. An individual trait of one parent may be so counteracted by the influence of the other parent, that it may not appear in the offspring ; or, not being so counteracted, the offspring may possess it, perhaps in an equal degree or perhaps in a less degree; or the off spring may exhibit the trait in even a still higher degree. Among illustrations of this, one must suffice. I quote it from the essay by Sir J. Struthers referred to in the last chapter. " The grcat-great-grandmothcr, Esther P (who mar ried A L ), had a sixth little finger on one hand. Of their eighteen children (twelve daughters and six sons), only one (Charles) is known to have had digital variety. We have the history of the descendants of three of the sons, Andrew, Charles, and James. " (1.) Andrew L had two sons, Thomas and Andrew; and Thomas had two sons all without digital variety. Here we have three successive generations without the variety possessed by the great-grandmother showing itself. " (2.) James L , who was normal, had two sons and seven daughters, also normal. One of the daughters bec;ime Mrs. J (one of the informants), and had three daughters 322 THE INDUCTIONS OF BIOLOGY. and five sons, all normal except one of the sons, James J , now act. 17, who had six fingers on each hand. . . . " In this hranch of the descendants of Esther, we see it passing over two generations and reappearing in one member of the third generation, and now on both hands. " (3.) Charles L , the only child of Esther who had digital variety, had six fingers on each hand. He had threa sons, James, Thomas, and John, all of whom were born with six fingers on each hand, while John has also a sixth toe on one foot. He had also five other sons and four daughters, all of whom were normal. " (a.) Of the normal children of this, the third generation, the five sons had twelve sons and twelve daughters, and the four daughters have had four sons and four daughters, being the fourth generation, all of whom were normal. A fifth generation in this sub-group consists as yet of only two boys and two girls who are also normal. " In this sub-branch, we see the variety of the first gener ation present in the second, passing over the third and fourth, and also the fifth as far as it has yet gone. " (&.) James had three sons and two daughters, who are normal. " (c.) Thomas had four sons and five daughters, who are normal ; and has two grandsons, also normal. " In this sub-branch of the descent, we see the variety of the first generation, showing itself in the second and third, and passing over the fourth, and (as far as it yet exists) the fifth generation. " (d.) John L (one of the informants) had six fingers, the additional finger being attached on the outer side, as in the case of his brothers James and Thomas. All of them had the additional digits removed. John has also a sixth toe on one foot, situated on the outer side. The fifth and sixth toes have a common proximal phalange, and a common integu ment invests the middle and distal phalanges, each having a separate nail. VARIATION. 323 " John L has a son who is normal, and a daughter, Jane, who was born with six fingers on each hand and six toes on each foot. The sixth fingers were removed. The sixth toes arc not wrapped with the fifth as in her father's case, but are distinct from them. The son has a son and daughter, who, like himself, are normal. " In this, the most interesting sub-branch of the descent, we sec digital increase, which appeared in the first generation on one limb, appearing in the second on two limbs, the hands ; in the third on three limbs, the hands and one foot; in the fourth on all the four limbs. There is as yet no fifth generation in uninterrupted transmission of the variety. The variety does not yet occur in any member of the fifth genera tion of Esther's descendants, which consists, as yet, only of three boys and one girl, whose parents were normal, and of two boys and two girls, whose grandparents were normal. It is not known whether in the case of the great-great-grand- mothcr, Esther P , the variety was original or inherited." * § 86. Where there is great uniformity among the members of a species, the divergences of offspring from the average type are usually small; but where, among the members of a species, considerable unlikenesses have once been established, unlikenesses among the offspring are frequent and great. Wild plants growing in their natural habitats are uniform over large areas, and maintain from generation to generation like structures; but when cultivation has caused appreciable differences among the members of any species of plant, ex tensive and numerous deviations are apt to arise. Similarly, between wild and domesticated animals of the same species, we see the contrast that though the homogeneous wild race * This remarkable case appears to militate against the conclusion, drawn a few pages hack, that the increase of a peculiarity by coincidence of " spon taneous variations " in successive generations, is very improbable ; and that the special superiorities of musical composers cannot have thus arisen. The reply is that the extreme frequency of the occurrence among so narrow a class as that of musical composers, forbids the interpretation thus suggested. 324: THE INDUCTIONS OF BIOLOGY. maintains its type with great persistence, the comparatively heterogeneous domestic race frequently produces individuals more unlike the average type than the parents are. Though unlikeness among progenitors is one antecedent of variation, it is by no means the sole antecedent. Were it so, the young ones successively born to the same parents would be alike. If any peculiarity in a new organism were a direct resultant of the structural differences between the two organ isms which produced it; then all subsequent new organisms produced by these two would show the same peculiarity. But we know that the successive offspring have different peculiari ties : no two of them are ever exactly alike. One cause of such structural variation in progeny, is func tional variation in parents. Proof of this is given by the fact that, among progeny of the same parents, there is more differ ence between those begotten under different constitutional states than between those begotten under the same constitu tional state. It is notorious that twins are more nearly alike than children borne in succession. The functional conditions of the parents being the same for twins, but not the same for their brothers and sisters (all other antecedents being constant), we have no choice but to admit that variations in the func tional conditions of the parents, are the antecedents of those greater unlikenesses which their brothers and sisters exhibit. Some other antecedent remains, however. The parents being the same, and their constitutional states the same, vari ation, more or less marked, still manifests itself. Plants grown from seeds out of one pod, or animals produced at one birth, are not alike. Sometimes they differ considerably. In a litter of pigs or of kittens, we rarely see uniformity of markings; and occasionally there are important structural contrasts. I have myself recently been shown a litter of New foundland puppies, some of which had four digits to their feet, while in others there was present, on each hind-foot, what is called the " dew-claw " — a rudimentary fifth digit. Thus, induction points to three causes of variation, all in VARIATION. 325 action together. We have heterogeneity among progenitors, which, did it act uniformly and alone in generating, by com position of forces, new deviations, would impress such new deviations to the same extent on all offspring of the same parents; which it does not. We have functional variation in the parents, which, acting either alone or in combination with the preceding cause, would entail the same structural variations on all young ones simultaneously produced; which it does not. Consequently there is some third cause of varia tion, yet to be found, which acts along with the structural and functional variations of ancestors and parents. § 87. Already, in the last section, there has been implied some relation between variation and the action of external conditions. The above-cited contrast between the uniformity of a wild species and the multiformity of the same species when cultivated or domesticated, thrusts this truth upon us. ^Respecting the variations of plants, Mr. Darwin remarks that " ' sports ' are extremely rare under nature, but far from rare under cultivation." Others who have studied the matter assert that if a species of plant which, up to a certain time, has maintained great uniformity, once has its constitution thoroughly disturbed, it will go on varying indefinitely. Though, in consequence of the remoteness of the periods at which they were domesticated, there is a lack of positive proof that our extremely variable domestic animals have be come variable under the changed conditions implied by domes tication, having been previously constant; yet competent judges do not doubt that this has been the case. Now the constitutional disturbance which precedes varia tion, can be nothing else than an overthrowing of the pre- established equilibrium of functions. Transferring a plant from forest lands to a ploughed field or a manured garden, is altering the balance of forces to which it has been hitherto subject, by supplying it with different proportions of the assimilable matters it requires, and taking away some of the 32G THE INDUCTIONS OF BIOLOGY. positive impediments to its growth which competing wild plants before offered. An animal taken from woods or plains, where it lived on wild food of its own procuring, and placed under restraint while artificially supplied with food not quite like what it had before, is an animal subject to new outer actions to which its inner actions must be adjusted. From the general law of. equilibration we found it to follow that " the maintenance of such a moving equilibrium " as an organism displays, " requires the habitual genesis of interna'l forces corresponding in number, directions, and amounts, to the external incident forces — as many inner functions, single or combined, as there are single or combined outer actions to be met " (First Principles, § 173) ; and more recently (§27), we have seen that Life itself is " the definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external co-existences and sequences." Necessarily, therefore, an organism exposed to a permanent change in the arrangement of outer forces must undergo a permanent change in the arrangement of inner forces. The old equilibrium has been destroyed ; and a new equilibrium must be established. There must be functional perturbations, ending in a re-adjusted balance of functions. If, then, change of conditions is the only known cause by which the original homogeneity of a species is destroyed; and if change of conditions can affect an organism only by altering its functions; it follows that alteration of func tions is the only known internal cause to which the com mencement of variation can be ascribed. That such minor functional changes as parents undergo from year to year are influential on the offspring, we have seen is proved by the greater unlikeness that exists between children born to the same parents at different times, than exists between twins. And here we seem forced to conclude that the larger func tional variations produced by greater external changes, are the initiators of those structural variations which, when once commenced in a species, lead by their combinations and VARIATION. 327 antagonisms to multiform results. Whether they are or are not the direct initiators, they must still be the indirect initiators. § 87a. In the foregoing sentence those pronounced struc tural variations from which may presently arise new varieties and eventually species, are ascribed to " the larger functional variations produced by greater external changes " ; and this limitation is a needful one, since there is a constant cause of minor variations of a wholly different kind. There are the variations arising from differences in the conditions to which the germ is subject, both before detach ment from the parent and after. At first sight it seems that plants grown from seeds out of the same seed-vessel and ani mals belonging to the same litter, ought, in the absence of any differences of ancestral antecedents, to be entirely alike. But this is not so. Inevitably they are subject from the very outset to slightly different sets of agencies. The seeds in a seed-vessel do not stand in exactly the same relations to the sources of nutriment : some are nearer than others. They are somewhat differently exposed to the heat and light pene trating their envelope; and some are more impeded in their growth by neighbours than others are. Similarly with young animals belonging to the same litter. Their uterine lives are made to some extent unlike by unlike connexions with the blood-supply, by mutual interferences not all the same, and even by different relations to the disturbances caused by the mother's movements. So, too, is it after separation from the parent plant or animal. Even the biblical parable reminds us that seeds fall into places -here favourable and there unfavourable in various degrees. In respect of soil, in respect of space for growth, in respect of shares of light, none of them are circumstanced in quite the same ways. With animals the like holds. In a litter of pigs some, weaker than others, do not succeed as often in getting possession of teats. And then in both cases the 328 THK INDUCTIONS OF BIOLOGY. differences thus initiated become increasingly pronounced. Among young plants the smaller, outgrown by their better- placed neighbours, are continually more shaded and more left behind; and among the litter the weakly ones, continually thrust aside by the stronger, become relatively more weakly from deficient nutrition. Differentiations thus arising, both before and after separa tion from parents, though primarily differences of growth, entail structural differences ; for it is a general law of nutri tion that when there is deficiency of food the non-essential organs suffer more than the essential ones, and the unlikc- nesses of proportion hence arising constitute unlikenesses of structure. It may be concluded, however, that variations generated in this manner usually have no permanent results. In the first place, the individuals which, primarily in growth and secondarily in smaller developments of less-important organs, are by implication inferior, are likely to be eliminated from the species. In the second place, differences of struc ture produced in the way shown do not express differences of constitution — are not the effects of somewhat divergent physiological units; and consequently are not likely to be repeated in posterity. § 88. We have still, therefore, to explain those variations which have no manifest causes of the kinds thus far con sidered. These are the variations termed " spontaneous." Not that those who apply to them this word, or some equi valent, mean to imply that they are uncaused. Mr. Darwin expressly guards himself against such an interpretation. He says': — "I have hitherto sometimes spoken as if the varia tions — so common and multiform in organic beings under domestication, and in a lesser degree in those in a state of nature — had been due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation." Not only, however, do I hold, in common with Mr. Darwin, that VARIATION. 329 there must be some cause for these apparently-spontaneous variations, but it seems to me that a definite cause is assign able. I think it may be shown that unlikenesses must neces sarily arise even between the new individuals simultaneously produced by the same parents. Instead of the occurrence of such variations being inexplicable, the absence of them would be inexplicable. In any scries of dependent changes a small initial differ ence often works a marked difference in the results. The mode in which a particular breaker bursts on the beach, may deter mine whether the seed of some foreign plant which it bears is or is not stranded — may cause the presence or absence of this plant from the Flora of the land ; and may so affect, for millions of years, in countless ways, the living creatures throughout the land. A single touch, by introducing into the body some morbid matter, may set up an immensely- involved set of functional disturbances and structural alter ations. The whole tenor of a life may be changed by a word of advice; or a glance may determine an action which alters thoughts, feelings, and deeds throughout a long series of years. In those still more involved combinations of changes which societies exhibit, this truth is still more conspicuous. A hair's-breadth difference in the direction of some soldier's musket at the battle of Arcola, by killing Napoleon, might have changed events throughout Europe ; and though the type of social organization in each European country would have been now very much what it is, yet in countless details it would have been different. Illustrations like these, with which pages might be filled, prepare us for the conclusion that organisms produced by the same parents at the same time, must be more or less differentiated, both by insensible initial differences, and by slight differences in the conditions to which they are subject during their evolution. We need not, however, rest wita assuming such initial differences : the necessity of them is demonstrable. The individual germ-cells which, in succcs- 330 THE INDUCTIONS OF BIOLOGY. sion or simultaneously, arc separated from the same parent, can never be exactly alike; nor can the sperm-cells which fertilize them. When treating of the instability of the homogeneous (First Principles, § 149), we saw that no two parts of any aggregate can be similarly conditioned with re spect to incident forces; and that being subject to forces that are more or less unlike, they must become more or less unlike. Hence, no two ova in an ovarium or ovules in a seed-vessel — no two spermatozoa or pollen-cells, can be identical. Whether or not there arise other contrasts, there are certain to arise quantitative contrasts; since the process of nutrition cannot be absolutely alike for all. The repro ductive centres must begin to differentiate from the very outset. Such being the necessities of the case, what will happen on any successive or simultaneous fertilizations? Inevitably unlikenesses between the respective parental in fluences must result. Quantitative differences among the sperm-cells and among the germ-cells, will insure this. Grant that the number of physiological units contained in any one reproductive cell, can rarely if ever be exactly equal to the number contained in any other, ripened at the same time or at a different time; and it follows that among the fertilized germs produced by the same parents, the physiolo gical units derived from them respectively will bear a dif ferent numerical ratio to each other in every case. If the parents are constitutionally quite alike, the variation in the ratio between the units they severally bequeath, cannot cause unlikenesses among the offspring. But if otherwise, no two of the offspring can be alike. In every case the small initial difference in the proportions of the slightly-unlike units, will lead, during evolution, to a continual multiplication of differ ences. The insensible divergence at the outset will gene rate sensible divergences at the conclusion. Possibly some may hence infer that though, in such case, the off spring must differ somewhat from each other and from both parents, yet that in every one of them there must result a VARIATION. 331 homogeneous mixture of the traits of the two parents. A little consideration shows that the reverse is inferable. If, throughout the proeess of development, the physiological units derived from each parent preserved the same ratio in all parts of the growing organism, each organ would show as much as every other, the influence of either parent. But no such uniform distribution is possible. It has been shown (First Principles, § 163), that in any aggregate of mixed units segregation must inevitably go on. Incident forces will tend ever to cause separation of the two orders of units from each other — will tend to integrate groups of the one order in one place and groups of the other order in another place. Hence there must arise not a homogeneous mean between the two parents, but a mixture of organs, some of which mainly follow the one and some the other. And this is the kind of mixture which observation shows us. Still it may be fairly objected that however the attributes of the two parents are variously mingled in their offspring, they must in all of them fall between the extremes displayed in the parents. In no characteristic could one of the young exceed both parents, were there no cause of " spontaneous variation " but the one alleged. Evidently, then, there is a cause yet unfound. § 89. Thus far we have contemplated the process under its simplest aspect. While we have assumed the two parents to be somewhat unlike, we have assumed that each parent has a homogeneous constitution — is built up of physiological units which arc exactly alike. But in no case can such a homo geneity exist. Each parent had parents who were more or less contrasted — each parent inherited at least two orders of physiological units not quite identical. Here then we have a further cause of variation. The sperm-cells or germ-cells which any organism produces, will differ from each other not quantitatively only but qualitatively. Of the slightly-unlike physiological units bequeathed to it, the reproductive cells it 332 THE INDUCTIONS OF BIOLOGY. casts off cannot habitually contain the same proportions ; and we may expect the proportions to vary not slightly hut greatly. Just as, during the evolution of an organism, the physiological units derived from the two parents tend to segregate, and produce likeness to the male parent in this part and to the female parent in that; so, during the forma tion of reproductive cells, there will arise in one a predomi nance of the physiological units derived from the father, and in another a predominance of the physiological units derived from the mother. Thus, then, every fertilized germ, be sides containing different amounts of the two parental influ ences, will contain different kinds of influences — this having received a marked impress from one grandparent, and that from another. Without further exposition the reader will see how this cause of complication, running back through each line of ancestry, must produce in every germ numerous minute differences among the units. Here, then, we have a clue to the multiplied variations, and sometimes extreme variations, that arise in races which have once begun to vary. Amid countless different combina tions of units derived from parents, and through them from ancestors, immediate and remote — amid the various conflicts in their slightly-different organic polarities, opposing and conspiring with one another in all ways and degrees; there will from time to time arise special proportions causing special deviations. From the general law of probabilities it may be concluded that while these involved influences, derived from many progenitors, must, on the average of cases, ob scure and partially neutralize one another; there must occa sionally result such combinations of them as will produce considerable divergences from average structures; and, at rare intervals, such combinations as will produce very marked divergences. There is thus a correspondence between the inferable results and the results as habitually witnessed. § 90. Still there remains a difficulty. It may be said tliut VARIATION. 333 admitting functional change to be the initiator of variation • — granting that the physiological units of an organism long subject to new conditions, will tend to become modified in Biich way as to cause change of structure in offspring; yet there will still be no cause of the supposed heterogeneity among the physiological units of different individuals. There seems validity in the objection, that as all the members of a species whose circumstances have been altered will be affected in the same manner, the results, when they begin to show themselves in descendants, will show themselves in the same manner: not multiform variations will arise, but deviations all in one direction. The reply is simple. The members of a species thus cir cumstanced will not be similarly affected. In the absence of absolute uniformity among them, the functional changes caused in them will be more or less dissimilar. Just as men of slightly-unlike dispositions behave in quite opposite ways under the sajne circumstances; or just as men of slightly- unlike constitutions get diverse disorders from the same cause, and are diversely acted on by the same medicine; so, the insensibly-differentiated members of a species whose con ditions have been changed, may at once begin to undergo various kinds of functional changes. As we have already seen, small initial contrasts may lead to large terminal con trasts. The intenser cold of the climate into which a species has migrated, may cause in one individual increased con sumption of food to balance the greater loss of heat; while in another individual the requirement may be met by a thicker growth of fur. Or, when meeting with the new foods which a new region furnishes, accident may determine one member of the species to begin with one kind and another member with another kind ; and hence may arise established habits in these respective members and their descendants. Now when the functional divergences thus set up in sundry families of a species have lasted long enough to affect their constitutions, and to modify somewhat the physiological units 334: THE INDUCTIONS OF BIOLOGY. thrown off in their reproductive cells, the divergences pro duced by these in offspring will be of divers kinds. And the original homogeneity of constitution having been thus destroyed, variation may go on with increasing facility. There will result a heterogeneous mixture of modifications of structure caused by modifications of function; and of still more numerous correlated modifications, indirectly so caused. By natural selection of the most divergent forms, the unlike- nesses of parents will be rendered more marked, and the limits of variation wider. Until at length the divergences of constitutions and modes of life, become great enough to lead to segregation of the varieties. § 91. That variations must occur, and that they must ever tend, both directly and indirectly, towards adaptive modifica tions, are conclusions deducible from first principles; apart from any detailed interpretations like the above. That the state of homogeneity is an unstable state we have found to be a universal truth. Each species must pass from the uni form into the more or less multiform, unless the incidence of external forces is exactly the same for all its members, which it never can be. Through the process of differentiation and integration, which of necessity brings together, or keeps to gether, like individuals, and separates unlike ones from them, there must nevertheless be maintained a tolerably uniform species, so long as there continues a tolerably uniform set of conditions in which it may exist. But if the conditions change, either absolutely by some disturbance of the habitat or relatively by spread of the species into other habitats, then the divergent individuals that result must be segregated by the divergent sets of conditions into distinct varieties (First Principles, §166). When, instead of contemplating a species in the aggregate, we confine our attention to a single member and its descendants, we see it to be a corollary from the general law of equilibration that the moving equili brium constituted by the vital actions in each member of VARIATION. 335 this family, must remain constant so long as the external actions to which they correspond remain constant; and that if the external actions are changed, the disturbed balance of internal changes, if not overthrown, cannot cease undergoing modification until the internal changes are again in equi librium with the external actions : corresponding structural alterations having arisen. On passing from these derivative laws to the ultimate law, we sec that Variation is necessitated by the persistence of force. The members of a species inhabiting any area cannot be sub ject to like sets of forces over the whole of that area. And if, in different parts of the area, different kinds or amounts or combinations of forces act on them, they cannot but become different in themselves and in their progeny. To say other wise, is to say that differences in the forces will not produce differences in the effects ; which is to deny the persistence of force. CHAPTER X. GENESIS, HEREDITY, AND VARIATION. § 92. A QUESTION raised, and hypothetically answered, in §§ 78 and 79, was there postponed until we had dealt with the topics of Heredity and Variation. Let us now resume the consideration of this question, in connexion with sundry others which the facts suggest. After contemplating the several methods by which the multiplication of organisms is carried on — after ranging them under the two heads of Homogenesis, in which the succes sive generations are similarly produced, and Heterogenesis, in which they are dissimilarly produced — after observing that Homogenesis is nearly always sexual genesis, while Heteroge nesis is asexual genesis with occasionally-recurring sexual genesis; we came to the questions — why is it that some or ganisms multiply in the one way and some in the other? and why is it that where agamogenesis prevails it is usually, from time to time, interrupted by gamogcnesis? In seeking answers to these questions, we inquired whether there are common to both Homogenesis and Heterogenesis, any condi tions under which alone sperm-cells and germ-cells arise and are united for the production of new organisms; and we reached the conclusion that, in all cases, they arise only when there is an approach to equilibrium between the forces which produce growth and the forces which oppose growth. This answer to the question — when does gamogcnesis recur? 33G GENESIS, HEREDITY, AND VARIATION. 337 still left unanswered the question — why docs gamogenesis recur? And to this the reply suggested was, that the ap proach towards general equilibrium in organisms, "is ac companied by an approach towards molecular equilibrium in them; and that the need for this union of sperm-cell with germ-cell is the need for overthrowing this equilibrium, and re-establishing active molecular change in the detached germ — a result probably effected by mixing the slightly-different physiological units of slightly-different individuals." This is the hypothesis which we have now to consider. Let us first look at the evidences which certain inorganic phenomena furnish. The molecules of any aggregate which have not a balanced arrangement, inevitably tend towards a balanced arrangement. As before mentioned (First Principles, § 100), amorphous wrought iron, when subject to continuous jar, begins to arrange itself into crystals — its atoms assume a condition of polar equilibrium. The particles of unannealed glass, which are so unstably arranged that slight disturbing forces make them separate into small groups, take advantage of that greater freedom of movement given by a raised temperature, to ad just themselves into a state of relative rest. During any such re-arrangement the aggregate exercises a coercive force over its units. Just as in a growing crystal the atoms suc cessively assimilated from the solution, are made by the already crystallized atoms to take a certain form, and even to re-complete that form when it is broken; so in any mass of unstably-arranged atoms which passes into a stable arrange ment, each atom conforms to the forces exercised on it by all the other atoms. This is a corollary from the general law of equilibration. We saw (First Principles, § 170) that every change is towards equilibrium; and that change can never cease until equilibrium is reached. Organisms, above all other aggregates, conspicuously display this progressive equilibration; because their units are of such kinds, and so conditioned, as to admit of easy re-arrangement. Those 338 TITE INDUCTIONS OF BIOLOGY. extremely active changes which go on during the early stages of evolution, imply an immense excess of the mole cular forces over those antagonist forces which the aggregate exercises on the molecules. While this excess continues, it is expended in growth, development, and function: expendi ture for any of these purposes being proof that part of the force constituting molecular tensions remains unbalanced. Eventually, however, this excess diminishes. Either, as in organisms which do not expend much energy, decrease of assimilation leads to its decline; or, as in organisms which expend much energy, it is counterbalanced by the rapidly- increasing reactions of the aggregate (§4G). The cessation of growth when followed, as in some organisms, by death, implies the arrival at an equilibrium between the molecular forces and those forces which the aggregate opposes 'to them. When, as in other organisms, growth ends in the establish ment of a moving equilibrium, there is implied such a decreased preponderance of the molecular forces, as leaves no surplus beyond that which is used up in functions. The declining functional activity characteristic of advancing life, expresses a further decline in this surplus. And ' when all vital movements come to an end, the implication is that the actions of the units on the aggregate and the reactions of the aggregate on the units are completely balanced. Hence, while a state of rapid growth indi cates such a play of forces among the units of an aggregate as will produce active re-distribution, the diminution and arrest of growth shows that the units have fallen into such relative positions that re-distribution is no longer so facile. When, therefore, we see that gamogenesis recurs only when growth is decreasing, or has come to an end, we must say that it recurs only when the organic units are approximating to equilibrium — only when their mutual restraints prevent them from readily changing their arrangements in obedience to incident forces. That units of like forms can be built up into a more stable GENESIS, HEREDITY, AND VARIATION. 339 aggregate than units of slightly unlike forms, is tolerably manifest a priori. And we have facts which prove that mixing allied but somewhat different units, does lead to com parative instability. Most metallic alloys exemplify this truth. Common solder, which is a mixture of lead and tin, melts at a much lower temperature than either lead or tin. The compound of lead, tin, and bismuth, called " fusible metal," becomes fluid at the temperature of boiling water; while the temperatures at which lead, tin, and bismuth be come fluid arc, respectively, 612°, 442°, and 497° F. Still more remarkable is the . illustration furnished by potassium and sodium. These metals are very near akin in all respects — in their specific gravities, their atomic weights, their chemical affinities, and the properties of their compounds. That is to say, all the evidences unite to show that their units, though not identical, have a close resemblance. What now happens when they are mixed? Potassium alone melts at 136°, sodium alone melts at 190°, but the alloy of potassium and sodium is liquid at the ordinary temperature of the air. Observe the meaning of these facts, expressed in general terms. The maintenance of a solid form by any group of units implies among them an arrangement so stable that it is not over thrown by the incident forces. Whereas the assumption of a liquid form implies that the incident forces suffice to destroy the arrangement of the units. In the one case the thermal undulations fail to dislocate the parts; while in the other case the parts are so dislocated by the thermal undulations that they fall into total disorder — a disorder admitting of easy re-arrangement into any other order. For the liquid state is a state in which the units become so far free from mutual restraints, that incident forces can change their relative posi tions very readily. Thus we have reason to conclude that an aggregate of units which, though in the main similar to one another, have minor differences, must be more unstable than an aggregate of homogeneous units. The one will yield to disturbing forces which the other successfully resists. 340 THE INDUCTIONS OF BIOLOGY. Now though the colloidal molecules of which organisms are mainly built, are themselves highly composite; and though the physiological units compounded out of these col loidal molecules must have structures far more involved; yet it must happen with such units, as with simple units, that those which have exactly like forms will admit of ar rangement into a more stable aggregate than those which have slightly-unlike forms. Among units of this order, as among units of a simpler order, imperfect similarity must entail imperfect balance in anything formed of them, and consequent diminished ability to withstand disturbing forces. Hence, given two organisms which, by diminished nutrition or increased expenditure, are being arrested in their growths — given in each an approaching equilibrium between the forces of the units and the forces of the aggregate — given, that is, such a comparatively balanced state among the units that re-arrangement of them by incident forces is no longer so easy; and it will follow that by uniting a group of units from the one organism with a group of slightly-different units from the other, the tendency towards equilibrium will be diminished, and the mixed units will be rendered more modifiable in their arrangements by the forces acting on them : they will be so far freed as to become again capable of that re-distribution which constitutes evolution. And now let us test this hypothesis by seeing what power it gives us of interpreting established inductions. § 93. The majority of plants being hermaphrodites, it has, until quite recently, been supposed that the ovules of each flower are fertilized by pollen from the anthers of the same flower. Mr.. Darwin, however, has shown that the arrange ments are generally such as to prevent this. Either the ovules and the pollen are not ripe simultaneously, or obstacles pre vent access of the one to the other. At the same time he has shown that there exist arrangements, often of a remarkable kind, which facilitate the transfer of pollen by insects from the GENESIS, HEREDITY, AND VARIATION. 341 stamens of one flower to the pistil of another. Simi larly, it has been found that among the lower animals, herma- phrodism does not usually involve the production of fertile ova by the union of sperm-cells and germ-cells developed in the same individual; but that the reproductive centres of one individual are united with those of another to produce fertile ova. Either, as in Pyrosoma, Perophora, and in many higher molluscs, the ova and spermatozoa are matured at different times ; or, as in annelids, they are prevented by their relative positions from coming in contact. Eemembering the fact that among the higher classes of organisms, fertilization is always effected by combining the sperm-cell of one individual with the germ-cell of another; and joining with it the above fact that among hermaphrodite organisms, the germ-cells developed in any individual arc usually not fertilized by sperm-cells developed in the same individual ; we see reason for thinking that the essential thing in fertilization, is the union of specially-fitted portions of different organisms. If fertilization depended on the peculiar properties of sperm-cell and germ-cell, as such ; then, in hermaphrodite organisms, it would be a matter of indiffer ence whether the united sperm-cells and germ-cells were those of the same individual or those of different individuals. But the circumstance that there exist in such organisms elaborate appliances for mutual fertilization, shows that un- likeness of derivation in the united reproductive centres, is the desideratum. Now this is just what the foregoing hypothesis implies. If, as was concluded, fertilization has for its object the disturbance of that approaching equilibrium existing among the physiological units separated from an adult organism ; and if, as we saw reason to think, this object is effected by mixture with the slightly-different physiologi cal units of another organism ; then, we at the same time see that this object will not be effected by mixture with physio logical units belonging to the same organism. Thus, the hypo- tbesis leads us to expect such provisions as we find. 342 THE INDUCTIONS OF BIOLOGY. § 94. But here a difficulty presents itself. These proposi tions seem to involve the conclusion that self-fertilization is impossible. It apparently follows from them, that a group of physiological units from one part of an organism ought to have no power of altering the state of approaching balance in a group from another part of it. Yet self-fertilization does occur. Though the ovules of one plant are generally fer tilized by pollen from another plant of the same kind, yet they may be, some of them, fertilized by pollen of the same plant ; and, indeed, there arc plants in which self-fertilization is the rule : even provision being in some cases made to pre vent fertilization by pollen from other individuals. And though, among hermaphrodite animals, self-fertilization is usually negatived by structural or functional arrangements, yet in certain Entozoa there appear to be special provisions by which the sperm-cells and the germ-cells of the same indi vidual may be united, when not previously united with those of another individual. Kay, it has even been shown that in certain Ascidians the contents of oviduct and spermiduct of the same individual produce, when united, fertile ova whence evolve perfect individuals. Certainly, at first sight, these facts do not consist with the above supposition. Neverthe less there is something like a solution. In the last chapter, when considering the variations caused in offspring from uniting elements representing unlike parental constitutions, it was pointed out that in an unfolding organism, composed of slightly-different physiological units derived from slightly-different parents, there cannot be main tained an even distribution of the two orders of units. We saw that the instability of the homogeneous negatives the uniform blending of them ; and that, by the process of differ entiation and integration, they must be more or less separated ; so that in one part of the body the influence of one parent will predominate, and in another part of the body the influe- ence of the other parent: an inference which harmonizes with daily observation. We also saw that the sperm-cells or GENESIS, HEREDITY, AND VARIATION. 343 germ-cells produced by such an organism must, in virtue of these same laws, be more or less unlike one another. It was shown that through segregation, some of the sperm-cells or germ-cells will get an excess of the physiological units derived from one side, and some of them an excess of those derived from the other side: a cause which accounts for the unlike- ncsses among offspring simultaneously produced. Now from this segregation of the different orders of physiological units, inherited from different parents and lines of ancestry, there arises the possibility of self-fertilization in hermaphrodite organisms. If the physiological units contained in the sperm- cells and germ-cells of the same flower, are not quite homo geneous — if . in some of the ovules the physiological units derived from the one parent greatly predominate, and in some of the ovules those derived from the other parent ; and if the like is true of the pollen-cells; then, some of the ovules may be nearly as much contrasted with some of the pollen-cells in the characters of their contained units, as were the ovules and pollen-cells of the parents from which the plant proceeded. Between part of the sperm-cells and part of the germ-cells, the community of nature will be such that fertilization will not result from their union; but between some of them, the differences of constitution will be such that their union will produce the requisite molecular instability. The facts, so far as they are known, seem in harmony with this deduc tion. Self-fertilization in flowers, when it takes place, is not so efficient as mutual fertilization. Though some of the ovules produce seeds, yet more of them than usual arc abor tive. From which, indeed, results the establishment of varie ties that have structures favourable to mutual fertilization; since, being more prolific, these have, other things equal, greater chances in the " struggle for existence." Further evidence is at hand supporting this interpreta tion. There is reason to believe that self-fertilization, which at the best is comparatively inefficient, loses all efficiency in course of time. After giving an account of the provisions for 23 344 THE INDUCTIONS OP BIOLOGY. an occasional, or a frequent, or a constant crossing between flowers; and after quoting Prof. Huxley to the effect that among hermaphrodite animals, there is no case in which " the occasional influence of a distinct individual can be shown to be physically impossible ; " Mr. Darwin writes — " from these several considerations and from the many special facts which I have collected, but which I am not here able to give, I am strongly inclined to suspect that, both in the vegetable and animal kingdoms, an occasional intercross with a distinct in dividual is a law of nature in none, as I suspect, can self-fertilization go on for perpetuity." This conclusion, based wholly on observed facts, is just the conclusion to which the foregoing argument points. That necessary action and the re-action between the parts of an organism and the organism as a whole — that power of an aggregate to re-mould the units, which is the correlative of the power of the units to build up into such an aggregate ; implies that any differences existing among the units inherited by an organism, must gradually diminish. Being subject in common to the total forces of the organism, they will in common be modified to wards congruity with these forces, and therefore towards like ness with one another. If, then, in a self-fertilizing organism and its self-fertilizing descendants, such contrasts as origi nally existed among the physiological units are progressively obliterated — if, consequently, there can no longer be a segre gation of different physiological units in different sperm- cells and germ-cdls; self-fertilization will become impos sible. Step by step the fertility will diminish, and the series will finally die out. And now observe, in confirmation of this view, that self- fertilization is limited to organisms in which an approximate equilibrium among the organic forces is not long maintained. While growth is actively going on, and the physiological units are subject to a continually-changing distribution of forces, no decided assimilation of the units can be expected: like forces acting on the unlike units will tend to segregate them, GENESIS, HEREDITY, AND VARIATION. 345 so long as continuance of evolution permits further segrega tion; and only when further segregation cannot go on, will the like forces tend to assimilate the units. Hence, where there is no prolonged maintenance of an approximate organic balance, self-fertilization may be possible for some gener ations; hut it will be impossible in organisms distinguished by a sustained moving equilibrium. § 95. The interpretation which it affords of sundry pheno mena familiar to breeders of animals, adds probability to the hypothesis. Mr. Darwin has collected a large " body of facts, showing, in accordance with the almost universal belief of breeders, that with animals and plants a cross between dif ferent varieties, or between individuals of the same variety but of another strain, gives vigour and fertility to the off spring; and on the other hand, that dose interbreeding di minishes vigour and fertility," — a conclusion harmonizing with the current belief respecting family-intermarriages in the human race. Have we not here a solution of these facts? Relations must, on the average of cases, be individuals whose physiological units are more nearly alike than usual. Ani mals of different varieties must be those whose physiological units are more unlike than usual. In the one case, the un- likeness of the units may frequently be insufficient to pro duce fertilization ; or, if sufficient to produce fertilization, not sufficient to produce that active molecular change required for vigorous development. In the other case, both fertiliza tion and vigorous development will be made probable. Nor are we without a cause for the irregular manifestations of these general tendencies. The mixed physiological units composing any organism being, as we have seen, more or less pcgrogatcd in the reproductive centres it throws off; there may arise various results according to the degrees of difference among the units, and the degrees in which the units are segre gated. Of two cousins who have married, the common grand parents may have had either similar or dissimilar constitu- 346 THE INDUCTIONS OF BIOLOGY. tions; and if their constitutions were dissimilar, the proba bility that their married grandchildren will have offspring will be greater than if their constitutions were similar. Or the brothers and sisters from whom these cousins descended, in stead of severally inheriting the constitutions of their parents in tolerably equal degrees, may have severally inherited them in very different degrees : in which last case, intermarriages among the cousins will be less likely to prove infertile. Or the brothers and sisters from whom these cousins descended, may severally have married persons very like, or very unlike, themselves; and from this cause there may have resulted, either an undue likeness, or a due unlikeness, between the married cousins.* These several causes, con spiring and conflicting in endless ways and degrees, will work multiform effects. Moreover, differences of segrega tion will make the reproductive centres produced by the same nearly-related organisms, vary considerably in their amounts of unlikeness; and therefore, supposing their amounts of unlikeness great enough to cause fertilization, this * I omitted to name here a cause which may be still more potent in pro ducing irregularity in the results of cousin-marriages. So far as I can learn, no attempt has been made to distinguish between such results as arise when the related parents from whom the cousins descend are of the same sex and those which arise when they are of different sexes. In the one case two sisters have children who intermarry ; and in the other case a brother and a sister have children who intermarry. The marriages of cousins in these two cases may he quite dissimilar in their results. If there is a tendency to limitation of heredity by sex — if daughters usually inherit more from the mother than sons do, while sons inherit more from the father than from the mother, then two sisters will on the average of cases be more alike in con stitution than a sister and a brother. Consequently the descendants of two sisters will differ less in their constitutions than the descendants of a brother and a sister ; and marriage in the first case will be more likely to prove in jurious from absence of dissimilarity in the physiological units than marriage in the second. My own small circle of friends furnishes evidence tending to verify this conclusion. In one instance two cousins who intermarried are children of two sisters, and they have no offspring. In another the cousins who intermarried are children of two brothers, and they have no offspring. In the third case the cousins were descendants of two brothers and only one child resulted. GENESIS, HEREDITY, AND VARIATION. 347 fertilization will be effective in various degrees. Hence it may happen that among offspring of nearly-related parents, there may be some in which the want of vigour is not marked, and others in which there is decided want of vigour. So that we are alike shown why in-and-in breeding tends to diminish both fertility and vigour : and why the effect cannot be a uniform effect, but only an average effect. § 9G. While, if the foregoing arguments are valid, gamo- genesis has for its main result the initiation of a new develop ment by the overthrow of that approximate equilibrium arrived at among the molecules of the parent-organisms, a fur ther result appears to be subserved by it. Those inferior or ganisms which habitually multiply by agamogenesis, have con ditions of life that are simple and uniform; while those organisms which have highly-complex and variable conditions of life, habitually multiply by gamogcnesis. Now if a species has complex and variable conditions of life, its members must be severally exposed to sets of conditions that are slightly different: the aggregates of incident forces cannot be alike for all the scattered individuals. Hence, as functional deviation must ever be inducing structural deviation, each individual throughout the area occupied tends to become fitted for the particular habits which its particular conditions necessitate; and in so far, unfitted, for the average habits proper to the species. But these undue specializations are continually checked by gamogenesis. As Mr. Darwin remarks, " intercrossing plays a very important part in nature in keeping the individuals of the same species, or of the variety, true and uniform in character : " the idiosyncratic divergences obliterate one another. Gamogenesis, then, is a means of turning to positive advantage the individual differentiations which, in its absence, would result in positive disadvantage. Were it not that individuals are ever being made unlike one another by their unlike conditions, there would not arise in them those contrasts of molecular constitution, which we have 348 THE INDUCTIONS OF BIOLOGY. seen to be needful for producing the fertilized germs of new individuals. And were not these individual differentiations ever being mutually cancelled, they would end in a fatal narrowness of adaptation. This truth will be most clearly seen if we reduce it to its purely abstract form, thus: — Suppose a quite homogeneous species, placed in quite homogeneous conditions ; and suppose the constitutions of all its members in complete concord with their absolutely-uniform and constant conditions; what must happen? The species, individually and collectively, is in a state of perfect moving equilibrium. All disturbing forces have been eliminated. There remains no force which can, in any way, change the state of this moving equilibrium ; either in the species as a whole or in its members. But we have seen (First Principles, § 173) that a moving equilibrium is but a transition towards complete equilibration, or death. The absence of differential or un-equilibrated forces among the members of a species, is the absence of all forces which can cause changes in the conditions of its members — is the ab sence of all forces which can initiate new organisms. To say, as above, that complete molecular homogeneity existing among the members of a species, must render impossible that mutual molecular disturbance which constitutes fertilization, is but another way of saying that the actions and re-actions of each organism, being in perfect balance with the actions and re-actions of the environment upon it, there remains in each organism no force by which it differs from any other — no force which any other does not meet with an equal force — no force which can set up a new evolution among the units of any other. And so we reach the remarkable conclusion that the life of a species, like the life of an individual, is maintained by the unequal and ever-varying actions of incident forces on its different parts.* An individual homogeneous throughout, and * Apropos of this sentence one of my critics writes : — " I cannot find in this book the statement as first made that the ' life of an individual is main- GENESIS, HEREDITY, AND VARIATION. 349 having its substance everywhere continuously subject to like actions, could undergo none of those changes which life con sists of; and similarly, an absolutely-uniform species, having all its members exposed to identical influences, would be deprived of that initiator of change which maintains its exist ence as a species. Just as, in each organism, incident forces constantly produce divergences from the mean state in various directions, which are constantly balanced by opposite diver gences indirectly produced by other incident forces; and just as the combination of rhythmical functions thus maintained, constitutes the life of the organism; so, in a species, there is, through gamogenesis, a perpetual neutralization of those contrary deviations from the mean state which are caused in its different parts by different sets of incident forces; and it is similarly by the rhythmical production and compensation of these contrary deviations, that the species continues to live. The moving equilibrium in a species, like the moving equilibrium in an individual, would rapidly end in complete taincd by the unequal and ever-varying actions of incident forces on its dif ferent parts.' Recent physiological work offers a startling example of the statement." To the question contained in the first sentence the answer is that I have not made the statement in the above words, but that it is implied in the chap ter entitled " The Degree of Life varies as the Degree of Correspondence," and more especially in § 36, which, towards its close, definitely involves the state ment. The verifying evidence my critic gives me is this : — "Prof. Sherrington has shown that if the sensory roots of the spinal nerves are cut one by one there is at first no general effect produced. That is to say, the remainder of the nervous system continues to function as before. This condition (lack of general effect) persists until about six pairs have been cut. With the severance of the seventh pair, however, the whole central nervous system ceases to function, so that stimulation of intact sensory nerves pro duces no reflex action. After a variable period, but one of many hours dura tion, the power of functioning is recovered. That ia to say, if the sensorv impulses (from the skin, &c.) reaching the central nervous system arc rapidly reduced in amount, there comes a point where those remaining do not suffice to keep the structure 'awake.' After a time, however, it adjusts itself to work with the diminished supply. Similarly Strumpell describes the case of a boy ' whose sensory inlets were all paralyzed except one eye and one car.' \Viicu these were closed he instantly fell asleep." 350 THE INDUCTIONS OF BIOLOGY. equilibration, or death, were not its continually-dissipated forces continually re-supplied from without. Besides owing to the external world those energies which, from moment to moment, keep up the lives of its individual members, every species owes to certain more indirect actions of the external Avorld, those energies which enable it to perpetuate itself in successive generations. § 97. What evidence still remains may be conveniently woven up along with a recapitulation of the argument pursued through the last three chapters. Let us contemplate the facts in their synthetic order. That compounding and re-compounding through which we pass from the simplest inorganic substances to the most com plex organic substances, has several concomitants. Each suc cessive stage of composition presents us with molecules that are severally larger or more integrated, that are severally more heterogeneous, that are severally more unstable, and that are more numerous in their kinds (First Principles, § 151). And when we come to the substances of which living bodies are formed, we find ourselves among innumerable divergent groups and sub-groups of compounds, the units of which are large, heterogeneous, and unstable, in high degrees. There is no reason to assume that this process ends with the forma tion of those complex colloids which constitute organic matter. A more probable assumption is that out of the complex col loidal molecules there are evolved, by a still further integra tion, molecules which are still more heterogeneous, and of kinds which are still more multitudinous. What must be their properties? Already the colloidal molecules are ex tremely unstable — capable of being variously modified in their characters by very slight incident forces; and already the complexity of their polarities prevents them from readily falling into such positions of equilibrium as results in crystallization. Now the organic molecules composed of these colloidal molecules, must be similarly characterized in GENESIS, HEREDITY, AND VARIATION. 351 far higher degrees. Far more numerous must be the minute changes that can be wrought in them by minute external forces; far more free must they remain for a long time to obey forces tending to re-distribute them; and far greater must be the number of their kinds. Setting out with these physiological units, the existence of which various organic phenomena compel us to recognize, and the production of which the general law of Evolution thus leads us to anticipate; we get an insight into the phenomena of Genesis, Heredity, and Variation. If each organism is built of certain of these highly-plastic units peculiar to its species — units which slowly work towards an equilibrium of their complex proclivities, in producing an aggregate of the specific structure, and which are at the same time slowly modifiable by the re-actions of this aggregate — we see why the multi plication of organisms proceeds in the several ways, and with the various results, which naturalists have observed. Heredity, as shown not only in the repetition of the specific structure but in the repetition of ancestral deviations from it, becomes a matter of course; and it falls into unison with the fact that, in various inferior organisms, lost parts can be replaced, and that, in still lower organisms, a fragment can develop into a whole. While an aggregate of physiological units continues to grow by the assimilation of matter which it moulds into other units of like type; and while it continues to undergo changes of structure; no equilibrium can be arrived at be tween the whole and its parts. Under these conditions, then, an un-differentiated portion of the aggregate — a group of physiological units not bound up into a specialized tissue — will be able to arrange itself into the structure peculiar to the species; and will so arrange itself, if freed from controlling forces and placed in fit conditions of nutrition and temper ature. Hence the continuance of agamogenesis in little- differentiated organisms, so long as assimilation continues to be greatly in excess of expenditure. 352 THE INDUCTIONS OF BIOLOGY. But let growth be checked and development approach its completion — let the units of the aggregate be severally ex posed to an almost constant distribution of forces ; and they must begin to equilibrate themselves. Arranged, as they will gradually be, into comparatively stable attitudes in relation to one another, their mobility will diminish; and groups of them, partially or wholly detached, will no longer readily re arrange themselves into the specific form. Agamogenesis will be no longer possible; or, if possible, will be no longer easy. When we remember that the force which keeps the Earth in its orbit is the gravitation of each particle in the Earth towards every one of the group of particles existing 92,000,000 of miles off; we cannot reasonably doubt that each unit in an organism acts on all the other units, and is reacted on by them: not by gravitation only but chiefly by other energies. When, too, we learn that glass has its molecular constitution changed by light, and that substances so rigid and stable as metals have their atoms re-arranged by forces radiated in the dark from adjacent objects ; * we are obliged to conclude that the excessively-unstable units of which organisms are built, must be sensitive in a transcendant degree to all the forces pervading the organisms composed of them — must be tending ever to re-adjust, not only their relative attitudes but their molecular structures, into equilibrium with these forces. Hence, if aggregates of the same species are differ ently conditioned, and re-act differently on their component units, their component units will be rendered somewhat dif ferent; and they will become the more different the more widely the re-actions of the aggregates upon them differ, and the greater the number of generations through which these different re-actions of the aggregates upon them are continued. * Fifty years before the discovery of the Rontgen rays .and those habitually emanating from uranium, it had been observed by Moser that under certain conditions the surfaces of metals receive permanent impressions from appro priate objects placed upon them. Such facts show that the molecules of sub stances propagate in all directions special ethereal undulations determined by their special constitutions. GENESIS, HEREDITY, AND VARIATION. 353 If, then, unlikenesses of function among individuals of the same species, produce unlikenesses between the physiological units of one individual and those of another, it becomes com prehensible that when groups of units derived from two indi viduals are united, the group formed will be more unstable than either of the groups was before their union. The mixed units will be less able to resist those re-distributing forces which cause evolution; and may thus have restored to them the capacity for development which they had lost. This view harmonizes with the conclusion, which we saw reason to draw, that fertilization does not depend on any intrinsic peculiarities of sperm-cells and germ-cells, but de pends on their derivation from different individuals. It explains the facts that nearly-related individuals are less likely to have offspring than others, and that their offspring, when they have them, are frequently feeble. And it gives us a key to the converse fact that the crossing of varieties results in unusual vigour. Bearing in mind that the slightly-different orders of phy siological units which an organism inherits from its parents, are subject to the same set of forces, and that when the organism is fully developed this set of forces, becoming con stant, tends slowly to re-mould the two orders of units into the same form; we see how it happens that self-fertilization becomes impossible in the higher organisms, while it remains possible in the lower organisms. In long-lived creatures which have tolerably-definite limits of growth, this assimilation of the somewhat-unlike physiological units is liable to go on to an appreciable extent; whereas in organisms which do not continuously subject their component units to constant forces, there will be much less of this assimilation. And where the assimilation is not considerable, the segregation of mixed units may cause the sperm-cells and germ-cells developed in the same individual, to be sufficiently different to produce, by their union, fertile germs; and several generations of self- fertilizing descendants may succeed one another, before the 354: THE INDUCTIONS OF BIOLOGY. two orders of units have had their unlikenesses so far dimin ished that they will no longer do this. The same principles explain for us the variable results of union between nearly- related organisms. According to the contrasts among the physiological units they inherit from parents and ancestors; according to the unlike proportions of the contrasted units which they severally inherit; and according to the degrees of segregation of such units in different sperm-cells and germ-cells; it may happen that two kindred individuals will produce the ordinary number of offspring or will produce none; or will at one time be fertile and at another not; or will at one time have offspring of tolerable strength and at another time feeble offspring. To the like causes are also ascribable the phenomena of Variation. These are unobtrusive while the tolerably-uni form conditions of a species maintain tolerable uniformity among the physiological units of its members; but they be come obtrusive when differences of conditions, entailing con siderable functional differences, have entailed decided differ ences among the physiological units, and when the different physiological units, differently mingled in every individual, come to be variously segregated and variously combined. Did space permit, it might be shown that this hypothesis is a key to many further facts — to the fact that mixed races arc comparatively plastic under new conditions; to the fact that pure races show predominant influences in the offspring when crossed with mixed races; to the fact that while mixed breeds are often of larger growth, pure breeds are the more hardy — have functions less-easily thrown out of balance. But without further argument it will, I think, be admitted that the power of this hypothesis to explain so many pheno mena, and to bring under a common bond phenomena which seem so little allied, is strong evidence of its truth. And such evidence gains greatly in strength on observing that this hypothesis brings the facts of Genesis, Heredity, and Variation into harmony with first principles. We see that GENESIS, HEREDITY, AND VARIATION. 355 these plastic physiological units, which we find ourselves obliged to assume, are just such more integrated, more hete rogeneous, more unstable, and more multiform molecules, as would result from continuance of the steps through which organic matter is reached. We sec that the differentia tions of them assumed to occur in differently-conditioned aggregates, and the equilibrations of them assumed to occur in aggregates which maintain constant conditions, are but corollaries from those universal principles implied by the persistence of force. We see that the maintenance of life in the successive generations of a species, becomes a con sequence of the continual incidence of new forces on the species, to replace the forces that are ever being rhythmically equilibrated in the propagation of the species. And we thus see that these apparently-exceptional phenomena dis played in the multiplication of organic beings, fall into their places as results of the general laws of Evolution. We have, therefore, weighty reasons for entertaining the hypothesis which affords us this interpretation. CHAPTER XA. GENESIS, HEREDITY, AND VARIATION CONCLUDED. § 97a. SINCE the foregoing four chapters were written, thirty-four years ago, the topics with which they deal have been widely discussed and many views propounded. Ancient hypotheses have been abandoned, and other hypotheses, re ferring tacitly or avowedly to the cell-doctrine, have been set forth. Before proceeding it will be well to describe the chief among these. Most if not all of them proceed on the assumption, shown in § 66 to be needful, that the structural characters of organ isms are determined by the special natures of units which are intermediate between the chemical units and the morphologi cal units — between the invisible molecules of proteid-sub- stances and the visible tissue-components called cells. Four years after the first edition of this volume was published, appeared Mr. Darwin's work, The Variation of Animals and Plants under Domestication; and in this he set forth his doctrine of Fangcnesis. Referring to the doctrine of physiological units which the preceding chapters work out, he at first expressed a doubt whether his own was or was not the same, but finally concluded that it was different. He was right in so concluding. Throughout my argument the im plication everywhere is that the physiological units are all of one kind; whereas Mr. Darwin regards his component units, or " gemmules," as being of innumerable unlike kinds. He supposes that every cell of every tissue gives off gemmules 35G GENESIS, HEREDITY, AND VARIATION. 357 special to itself, and capable of developing into similar cells. We may here, in passing, note that this view implies a funda mental distinction between unicellular organisms and the component cells of multiccllular organisms, which are other wise homologous with them. For while in their essential structures, their essential internal changes, and their essential processes of division, the Protozoa and the component units of the Mctazoa are alike, the doctrine of Pangenesis implies that though the units when separate do not give off invisible gemmules the grouped units do. Much more recently have been enunciated the hypotheses of Prof. Weismann, differing from the foregoing hypotheses in two respects. In the first place it is assumed that the frag ment of matter out of which each organism arises consists of two portions — one of them, the germ-plasm, reserved within the generative organ of the incipient individual, representing in its components the structure of the species, and gives origin to the germs of future individuals; and the other of them, similarly representative of the specific structure, giving origin to the rest of the body, or soma, but contains in its compo nents none of those latent powers possessed by those of the germ-plasm. In the second place the germ-plasm, in com mon with the soma-plasm, consists of multitudinous kinds of units portioned out to originate the various organs. Of these there are groups, sub-groups, and sub-sub-groups. The largest of them, called " idants," are supposed each to contain a number of " ids " ; within each id there are numer ous "determinants" ; and each determinant is made up of many " biophors " — the smallest elements possessing vitality. Passing over details, the essential assumption is that there exists a separate determinant for each part of the organ ism capable of independent variation; and Prof. Weismann infers that while there may be but one for the blood and but one for a considerable area of skin (as a stripe of the zebra) there must be a determinant for each scale on a butter fly's wing: the number 011 the four wings being over two 358 THE INDUCTIONS OF BIOLOGY. hundred thousand. And then each cluster of biophors com posing a determinant has to find its way to the place where there is to be formed the part it represents. Here it is needless to specify the modifications of these hypotheses espoused by various biologists — all of them assum ing that the structural traits of each species are expressed in certain units intermediate between morphological units and chemical units. § 97&. A true theory of heredity must be one which recog nizes the relevant phenomena displayed by all classes of organism. We cannot assume two kinds of heredity, one for plants and another for animals. Hence a theory of heredity may be first tested by observing whether it is equally applicable to both kingdoms of living things. Genesis, he redity, and variation, as seen in plants, are simpler and more accessible than as seen in animals. Let us then note what these imply. Already in § 77 I have illustrated the power which some plants possess of developing new individuals from mere frag ments of leaves and even from detached scales. Striking as are the facts there instanced, they are scarcely more significant than some which are familiar. The formation of cauline buds, presently growing into shoots, shows us a kind of inheritance which a true theory must explain. As de scribed by Kerner, such buds arise in Pimpernel, Toad-flax, etc., below the seed-leaves, even while yet there are no axils in which buds usually grow; and in many plants they arise from intermediate places on the stem : ' that is, without defi nite relations to pre-existing structures. How fortuitous is their origin is shown when a branch is induced to bud by keeping it wrapped round with a wet cloth. Even still better proved is the absence of any relation between cauline buds and normal germs by the frequent growth of them out of " callus " — the tissue which spreads over wounds and the cut ends of branches. It is not easy to reconcile these facts GENESIS, HEREDITY, AND VARIATION. 359 with Mr. Darwin's hypothesis of gemmules. Wo have to assume that where a cauline bud emerges there are present in due proportions gemmules of all the parts which will pres- entty arise from it — leaves, stipules, bracts, petals, stamens, anthers, etc. We have to assume this though, at the time the bud originates,, sundry of these organs, as the parts of flowers, do not exist on the plant or tree. And we have to assume that the gemmules of such parts are duly provided in a portion of adventitious callus, far away from the normal places of fructification. Moreover, the resulting shoot may or may not produce all the parts which the gemmules repre sent; and when, perhaps after years, flowers are produced on its side shoots, there must exist at each point the needful proportion of the required gemmules ; though there have been no cells continually giving them off. Still less docs the hypothesis of Prof.Weismann harmonize with the evidence as plants display it. Plant-embryogeny yields no sign of separation between germ-plasm and soma- plasm; and, indeed, the absence of such separation is ad mitted. After instancing cases among certain of the lower animals, in which no differentiation of the two arises in the first generation resulting from a fertilized ovum, Prof. Weis- mann continues : — "The same is true as regards the higher plants, in which the first shoot arising from the seed never contains germ-cells, or even cells which subsequently become differentiated into germ cells. In all these last-mentioned cases the germ -cells are not present in the first person arising by embryogeny as special cells, but are only formed in much later cell-generations from the offspring of certain cells of which this first person was composed. (Germ-Plasm, p. 185.) How this admission consists with the general theory it is difficult to understand. The units of the soma-plasm are here recognized as having the same generative powers as the units of the germ-plasm. In so far as one organic kingdom and a considerable part of the other are concerned the doctrine is relinquished. Piclinquishment is, indeed, necessitated even by the ordinary facts, and still more by the 24 300 THE INDUCTIONS OF BIOLOGY. facts just instanced. Defence of it involves the assertion that where buds arise, normal or cauline, there exist in due proportion the various ids with their contained determinants — that these are diffused throughout the growing part of the sorna ; and this implies that the somatic tissue does not differ in generative power from the germ-plasm. ' The hypothesis of physiological units, then, remains out standing. For cauline buds imply that throughout the plant- tissue, where not unduly differentiated, the local physiological units have a power of arranging themselves into the structure of the species. But this hypothesis, too, as it now stands, is inadequate. Under the form thus far given to it, it fails to explain some accompanying facts. For if the branch just instanced as producing a cauline bud be cut off and its end stuck in the ground, or if it be bent down and a portion of it covered with earth, there will grow from it rootlets and presently roots. The same portion of tissue which otherwise would have produced a shoot with all its appendages, constituting an individual, now produces only a special part of an individual. § 97c. Certain kindred facts of animal development may now be considered. Similar insufficiencies are disclosed. The often-cited reproduction of a crab's lost claw or a lizard's tail, Mr. Darwin thought explicable by his hypo thesis of diffused gemnmTes, representing all organs or their component cells. But though, after simple amputation, re- growth of the proximate part of the tail is conceivable as hence resulting, it is not easy to understand how the remoter part, the components of which are now absent from the organism, can arise afresh from gemmules no longer origin ated in due proportion. Prof. Weismann's hypothesis, again, implies that there must exist at the place of separation, a ready-provided supply of determinants, previously latent, able to reproduce the missing tail in all its details — nay, even to do this several times over : a strong supposition ! GENESIS, HEREDITY, AND VARIATION. 361 The hypothesis of physiological units, as set forth in preced ing chapters, appears less incompetent : reproduction of the lost part would seem to be a normal result of the proclivity towards the form of the entire organism. But now what are we to say when, instead of being cut off transversely, the tail is divided longitudinally and each half becomes a com plete tail? What are we to say when, if these two tails are similarly dealt with, the halves again complete themselves; and so until as many as sixteen tails have been formed? Here the hypothesis of physiological units appears to fail utterly ; for the tendency it implies is to complete the specific form, by reproducing a single tail only. Various annulose animals display anomalies of develop ment difficult to explain on any hypothesis. We have creatures like the fresh-water Nais which, though it has ad vanced structures, including a vascular system, branchial, and a nervous cord ending with cephalic ganglia, nevertheless shows us an ability like that of the Hydra to reproduce the whole from a small part : nearly forty pieces into which a Nais was cut having severally grown into complete animals. Again we have, in the order PolychcBtce, types like Myrianida, in which by longitudinal budding a string of individuals, sometimes numbering even thirty, severally develop certain segments into heads, while increasing their segments in number. In yet other types there occurs not longitudinal gemmation only, but lateral gemmation : a segment will send out sideways a bud which presently becomes a complete worm. Once more, Syllis ramosa is a species in which Ihe ' individual worms growing from lateral buds, while remaining attached to the parent, themselves give origin to buds; and so produce a branched aggregate of worms. How shall we explain the reparative and reproductive powers thus exempli fied? It seems undeniable that each portion has an ability to produce, according to circumstances, the whole creature or a missing part of the creature. When we read of Sir J. Daly ell that he " cut a Dasyclionc into three pieces ; the 302 THE INDUCTIONS OF BIOLOGY. hindcrmost produced a head, the anterior piece developed an anus, and the middle portion formed both a head and a tail " we are not furnished with an explanation by the hypothesis of gemmules or by the hypothesis of determinants; for we cannot arbitrarily assume that wherever a missing organ has to be produced there exists the needful supply of gemmules or of determinants representing that organ. The hypothesis that physiological units have everywhere a proclivity towards the organic form of the species, appears more congruous with the facts; but even this does not cover the cases in which a new worm grows from a lateral bud. The tendency to com plete the individual structure might be expected rather to restrain this breaking of the lines of complete structure. Still less explicable in any way thus far proposed are certain remedial actions seen in animals. An example of them was furnished in § 67, where " false joints " were de scribed — joints formed at places where the ends of a broken bone, failing to unite, remain moveable one upon the other. According to the character of the habitual motions there results a rudely formed hinge-joint or a ball-and-socket joint, cither having the various constituent parts — periosteum, fibrous tissue, capsule, ligaments. Now Mr. Darwin's hypo thesis, contemplating only normal structures, fails to account for this formation of an abnormal structure. Neither can we ascribe this local development to determinants: there were no appropriate ones in the germ-plasm, since no such structure was provided for. Nor does the hypothesis of physiological units, as presented in preceding chapters, yield an interpretation. These could have no other tendency than to restore the normal form of the limb, and might be expected to oppose the. genesis of these new parts. Thus we have to seek, if not another hypothesis, then some such qualification of an existing hypothesis as will harmonize it with various exceptional phenomena. § 97d. In Part II of the Principles of Sociology, published GENESIS, HEREDITY, AND VARIATION. 303 in 1876, will be found elaborated in detail that analogy be tween individual organization and social organization which was briefly sketched out in an essay on "The Social Organism" published in I860. In §§ 241-3 a parallel is drawn between the developments of the sustaining systems of the two; and it is pointed out how, in the one case as in the other, the com ponents — here organic units and there citizens — have their activities and arrangements mainly settled by local conditions. One leading example is that the parts constituting the alimen tary canal, while jointly fitted to the nature of the food, are severally adapted to the successive stages at which the food arrives in its progress; and that in an analogous way the industries carried on by peoples forming different parts of a society, are primarily determined by the natures of things around — agriculture, pastoral and arable, special manufactures and minings, ship-building and fishing: the respective groups falling into fit combinations and becoming partially modified to suit their work. The implication is that while the organ ization of a society as a whole depends on the characters of its units, in such way that by some types of men despotisms are always evolved while by other types there are evolved forms of government partially free — forms which repeat themselves in colonies — there is, on the other hand, in every case a local power of developing appropriate structures. And it might have been pointed out that similarly in types of creatures not showing much consolidation, as the Annelida, many of the component divisions, largely independent in their vitalities, are but little affected in their structures by the entire aggregate. My purpose at that time being the elucidation of socio logical truths, it did not concern me to carry further the biological half of this comparison. Otherwise there might have been named the case in which a supernumerary finger, beginning to bud out, completes itself as a local organ with bones, muscles, skin, nail, etc., in defiance of central control: even repeating itself when cut oil. There might also have 364 THE INDUCTIONS OF BIOLOGY. been instanced the above-named formation of a false joint with its appurtenances. For the implication in both cases is that a local group of units, determined by circumstances towards a certain structure, coerces its individual units into that structure. Now let us contemplate the essential fact in the analogy. The men in an Australian mining-camp, as M. Pierre Lcroy Beaulieu points out, fall into Anglo-Saxon usages different from those which would characterize a French mining-camp. Emigrants to a far West settlement in America quickly establish post-office, bank, hotel, newspaper, and other urban institutions. We arc thus shown that along with certain traits leading to a general type of social organ ization, there go traits which independently produce fit local organizations. Individuals are led into occupations and official posts, often quite new to them, by the wants of those around — are now influenced and now coerced into social arrangements which, as shown perhaps by gambling saloons, by shootings at sight, and by lynchings, are scarcely at all affected by the central government. Now the physiological units in each species appear to have a similar combination of capacities. Besides their general proclivity towards the specific organization, they show us abilities to organize themselves locally; and these abilities are in some cases dis played in defiance of the general control, as in the super numerary finger or the false joint. Apparently each physio logical unit, while having in a manner the whole organism as the structure which, along with the rest, it tends to form, has also an aptitude to take part in forming any local struc ture, and to assume its place in that structure under the influence of adjacent physiological units. A familiar fact supports this conclusion. Everyone has at hand, not figuratively but literally, an illustration. Let him compare the veins on the backs of his two hands, either with one another or with the veins on another person's hands, and he will see that the branchings and inosculations do not GENESIS, HEREDITY, AND VARIATION. 3C.5 correspond: there is no fixed pattern. But on progressing inwards from the extremities, the distribution of the veins becomes settled — there is a pattern-arrangement common to all persons. These facts imply a predominating control by adjacent parts where control by the aggregate is less easy. A constant combination of forces which, towards the centre, produces a typical structure, fails to do this at the periphery where, during development, the play of forces is less settled. This peripheral vascular structure, not having become fixed because one arrangement is as good as another, is in each determined by the immediately surrounding influences. § 97c. And now let us contemplate the verifications which recent experiments have furnished — experiments made by Prof. G. Born of Breslau, confirming results earlier reached by Vulpian and adding more striking results of kindred nature. They leave no longer doubtful the large share taken by local organizing power as distinguished from central organizing power. The independent vitality shown by separated portions of ventral skin from frog-larvse may be named as the first illus tration. With their attached yolk-cells these lived for days, and underwent such transformations as proved some struc tural proclivity, though of course the product was amorphous. Detached portions of tails of larvae went on developing their component parts in much the same ways as they would have done if remaining attached. More striking still was the evidence furnished by experiments in grafting. These proved that the undiirerentiated rudiment of an organ will, when cut off and joined to a non-homologous place in another individual, develop itself as it would have done if left in its original place. In brief, then, we may say that each part is in chief measure autogenous. These strange facts presented by small aggregates of or ganic matter, which are the seats of extremely complex forces, will seem less incomprehensible if we observe what has taken 3GG TUE INDUCTIONS OF BIOLOGY. place in a vast aggregate of inorganic matter which is the scat of very simple forces — the Solar System. Transcend- ently. different as this is in all other respects, it is analogous in the respect that, as factors of local structures, local influ ences predominate over the influences of the aggregate. For while the members of the Solar System, considered as a whole, are subordinate to the totality of its forces, the arrange ments in each part of it arc produced almost wholly by the play of forces in that part. Though the Sun affects the motions of the Moon, and though during the evolution of the Earth-and-Moon system the Sun exercised an influence, yet the relations of our world and its satellite in respect of masses and motions were in the main locally determined. Still more clearly was it thus with Jupiter and his satellites or Saturn with his rings and satellites. Remembering that the ultimate units of matter of which the Solar System is composed are of the same kinds, and that they act on one another in conformity with the same laws, we see that, re mote as the case is from the one we are considering in all other respects, it is similar in the respect that during organ ization the energies in each locality work effects which are almost independent of the effects worked by the general ener gies. In this vast aggregate, as in the minute aggregates now in question, the parts are practically autogenous. Having thus seen that in a way we have not hitherto recog nized the same general principles pervade inorganic and organic evolution, let us revert to the case of super-organic evolution from which a parallel was drawn above. As anal ogous to the germinal mass of units out of which a new organism is to evolve, let us take an assemblage of colonists not yet socially organized but placed in a fertile region — men derived from a society (or rather a succession of societies) of long-established type, who have in their adapted natures the proclivity towards that type. In passing from its wholly unorganized state to an organized state, what will be the first step? Clearly this assemblage, though it may have GENESIS, HEREDITY, AND VARIATION. 3G7 within the constitutions of its units the potentialities of a specific structure, will not develop forthwith the details of that structure. The inherited natures of its units will first show themselves hy separating into large groups devoted to strongly-distinguished occupations. The great mass, dispers ing over promising lands, will make preparations for farming. Another considerable portion, prompted by the general needs, will begin to form a cluster of habitations and a trading centre. Yet a third group, recognizing the demand for wood, alike for agricultural and building purposes, will betake themselves to the adjacent forests. But in no case will the primary assemblage, before these separations, settle the ar rangements and actions of each group : it will leave each group to settle them for itself. So, too, after these divisions have arisen. The agricultural division will not as a whole prescribe the doings of its members. Spontaneous segrega tion will occur : some going to a pastoral region and some to a tract which promises good crops. Nor within each of these bodies will the organization be dictated by the whole. The pastoral group will separate itself into clusters who tend sheep on the hills and clusters who feed cattle on the plains. Meanwhile those who have gravitated towards urban occu pations will some of them make bricks or quarry stone, while others fall into classes who build walls, classes who prepare fittings, classes who supply furniture. Then along with completion of the houses will go occupation of them by men who bake bread, who make clothing, who sell liquors, and so on. Thus each great group will go on organizing itself irre spective of the rest; the sub-groups within each will do the same; and so will the sub-sub-groups. Quite independently of the people on the hills and the plains and in the town, those in the forest will divide spontaneously into parties who cut down trees, parties who trim and saw them, parties who carry away the timbers; while every party forms for itself an organization of " butty " or " boss," and those who work under him. Similarly with the ultimate divisions — the 368 TIIE INDUCTIONS OF BIOLOGY. separate families : the arrangements and apportionments of duties in each are internally determined. Mark the fact which here chiefly concerns us. This formation of a hetero geneous aggregate with its variously adapted parts, which while influenced by the whole are mainly self-formed, goes on among units of essentially the same natures, inherited from units who belonged to similar societies. And now, carrying this conception with us, we may dimly perceive how, in a developing embryo, there may take place the form ation, first of the great divisions — the primary layers — then of the outlines of systems, then of component organs, and so on continually with the minor structures contained in major structures; and how each of these progressively smaller divisions develops its own organization, irrespective of the changes going on throughout the rest of the embryo. So that though all parts are composed of physiological units of the same nature, yet everywhere, in virtue of local conditions and the influence of its neighbours, each unit joins in forming the particular structure appropriate to .the place. Thus con ceiving the matter, we may in a vague way understand the strange facts of autogenous development disclosed by the above named experiments. § 97/. " But how immeasurably complex must be the physiological units which can behave thus ! " will be remarked by the reader. " To be able to play all parts, alike as mem bers of the whole and as members of this or that organ, they must have an unimaginable variety of potentialities in their natures. Each must, indeed, be almost a microcosm within a microcosm." Doubtless this is true. Still we have a consensus of proofs that the component units of organisms have constitutions of extremely involved kinds. Contemplate the facts and their implications. (1) Here is some large division of the animal kingdom — say the Vertebrata. The component units of all its members have certain fundamental traits in common: all GENESIS, HEREDITY, AND VARIATION. 309 of them have proclivities towards formation of a vertebral column. Leaving behind the great assemblage of Fishes with its multitudinous types, each having special units of composi tion, we pass to the Amphibia, in the units of which there exist certain traits superposed upon the traits they have in common with those of Fishes. Through unknown links we ascend to incipient Mammalian types and then to developed Mammalian types, the units of which must have further superposed traits. Additional traits distinguish the units of each Mammalian order; and, again, those of every genus included in it; while others severally characterize the units of each species. Similarly with the varieties in each species, and the stirps in each variety. Now the ability of any com ponent unit to carry within itself the traits of the sub-king dom, class, order, genus, species, variety, and at the same time to bear the traits of immediate ancestors, can exist only in a something having multitudinous proximate elements arranged in innumerable ways. (2) Again, these units must be at once in sgme respects fixed and in other respects plastic. While their fundamental traits, expressing the structure of the type, must be unchangeable, their superficial traits must admit of modification without much difficulty; and the modi fied traits, expressing variations in the parents and immediate ancestors, though unstable, must be considered as capable of becoming stable in course of time. (3) Once more we have to think of these physiological units (or constitutional units as I would now re-name them) as having such ^natures that while a minute modification, representing some small change of local structure, is inoperative on the proclivities of the units throughout the rest of the system, it becomes operative in the units which fall into the locality where that change occurs. But unimaginable as all this is, the facts may nevertheless in some way answer to it. As before remarked, progressing science reveals complexity within complexity — tissues made up of cells, cells containing nuclei and cytoplasm, cytoplasm 370 THE INDUCTIONS OF BIOLOGY. formed of a protoplasmic matrix containing granules ; and if now we conclude that the unit of protoplasm is itself an inconceivably elaborate structure, we do but recognize the complexity as going still deeper. Further, if we must assume that these component units are in every part of the body acting on one another by extremely complicated sets of forces (ethereal undulations emanating from each of the constituent molecules) determining their relative positions and actions, we are warranted by the discoveries which every day disclose more of the marvellous properties of matter. When to such examples as were given in § 36c we add the example yielded by recent experiments, showing that even a piece of bread, after subjection to pressure, exhibits diarnagnetic properties unlike those it previously exhibited, we cannot doubt that these complex units composing living bodies are all of them seats of energies diffused around, enabling them to act and re-act so as to modify one another's states and positions. We are shown, too, that whatever be the natures of the com plex forces emanating from each, it will, as a matter of course, happen that the power of each will be relatively great in its own neighbourhood and become gradually smaller in parts increasingly remote : making more comprehensible the auto genous character of each local structure. Whatever be their supposed natures we are compelled to ascribe extreme complexity to these unknown somethings which have the power of organizing themselves into a struc ture of this or that species. If gemmules be alleged, then the ability of every organ and part of an organ to vary, implies that the gemmules it gives off are severally capable of receiving minute modifications of their ordinary struc tures: they must have many parts admitting of innumerable relations. Supposing determinants be assumed, then in ad dition to the complexity which each must have to express in itself the structure of the part evolved from it, it must have the further complexity implied by every superposed modification which causes a variation of that part. And, as GENESIS, HEREDITY, AND VARIATION. 371 we have just seen, the hypothesis of physiological units docs not relieve us from the need for kindred suppositions. One more assumption seems necessary if we are to imagine how changes of structure caused by changes of function can be transmitted. Keverting to § 5±d, where an unceasing cir culation of protoplasm throughout an%organism was inferred, we must conceive that the complex forces of which each con stitutional unit is the centre, and by which it acts on other units while it is acted on by them, tend continually to re mould each unit into congruity with the structures around : superposing on it modifications answering to the modifica tions which have arisen in those structures. Whence is to be drawn the corollary that in course of time all the circulating units, — physiological, or constitutional if we prefer so to call them — visiting all parts of the organism, are severally made bearers of traits expressing local modifications; and that those units which are eventually gathered into sperm-cells and germ-cells also bear these superposed traits. If against all this it be urged that such a combination of structures and forces and processes is inconceivably involved, then the reply is that so astonishing a transformation as that which an unfolding organism displays cannot possibly bo effected by simple agencies. § 97«/. But now let it be confessed that none of these hypo theses serves to render the phenomena really intelligible ; and that probably no hypothesis which can be framed will do this. Many problems beyond those which embryology presents have to be solved ; and no solution is furnished. What are we to say of the familiar fact that certain small organs which, with the approach to maturity, become active, entail changes of structure in remote parts — that after the tcstcs have undergone certain final developments, the hairs on the chin grow and the voice deepens?' It has been con tended that certain concomitant modifications in the fluids throughout the body may produce correlated sexual traits; 372 THE INDUCTIONS OF BIOLOGY. and there is proof that in many of the lower animals the period of sexual activity is accompanied by a special bodily state — sometimes such that the flesh becomes unwholesome and even poisonous. But a change of this kind can hardly account for a structural change in the vocal organs in Man. No hypothesis of gemmules or determinants or physiological units enables us to understand how removal of the testes prevents those developments of the larynx and vocal cords which take place if they remain. The inadequacy of our explanations we at once see in presence of a structure like a peacock's tail-feather. Mr. Darwin's hypothesis is that all parts of every organ are con tinually giving off gemmules, which are consequently every where present in their due proportions. But a completed feather is an inanimate product and, once formed, can add to the circulating fluids no gemmules representing all its parts. If we follow Prof. Weismann we are led into an astounding supposition. He admits that every variable part must have a special determinant, and that this results in the assumption of over two hundred thousand for the four wings of a butter fly. Let us ask what must happen in the case of a peacock's feather. On looking at the eye near its end, we see that the minute processes on the edge of each lateral thread must have been in some way exactly adjusted, in colour and posi tion, so as to fall into line with the processes on adjacent threads : otherwise the symmetrical arrangement of coloured rings would be impossible. Each of these processes, then, being an independent variable, must have had its particular determinant. Now there are about 300 threads on the shaft of a large feather, and each of them bears on the average 1,GOO processes, making for the whole feather 480,000 of these pro cesses. For one feather alone there must have been 480,000 determinants, and for the whole tail many millions. And these, along with the determinants for the detailed parts of all the other, feathers, and for the variable components of all organs forming the body at large, must have been contained GENESIS, HEREDITY, AND VARIATION. 373 in the microscopic head of a spermatozoon ! Hardly a credi ble supposition. Nor is it easy to see how we are helped by the hypothesis of constitutional units. Take the feather in its budding state and ask how the group of such units, alike in structure and perpetually multiplying while the unfolding goes on, can be supposed by their mutual actions so to affect one another as eventually to produce the symmetrically-ad justed processes which constitute the terminal eye. Imagina tion, whatever licence may be given, utterly fails us. At last then we are obliged to admit that the actual organ izing process transcends conception. It is not enough to say that we cannot know it; we must say that we cannot even conceive it. And this is just the conclusion which might have been drawn before contemplating the facts. For if, as we saw in the chapter on " The Dynamic Element in Life/' it is impossible for us to understand the nature of this element — if even the ordinary manifestations of it which a living body yields from moment to moment are at bottom incomprehensible; then, still more incomprehensible must be that astonishing manifestation of it which we have in the initiation and unfolding of a new organism. Thus all we can do is to find some way of symbolizing the process so as to enable us most conveniently to generalize its phenomena; and the only reason for adopting the hypothesis of physiological units or constitutional units is that it best serves this purpose. CHAPTEE XL CLASSIFICATION. § 98. THAT orderly arrangement of objects called Classi fication has two purposes, which, though not absolutely distinct, are distinct in great part. It may be employed to facilitate identification, or it may be employed to organize our knowledge. If a librarian places his books in the alpha betical succession of the author's names, he places them in such way that any particular book may easily be found, but not in such way that books of a given nature stand together. When, otherwise, he makes a distribution of books according to their subjects, he neglects various superficial similarities and distinctions, and groups them according to certain pri mary and secondary and tertiary attributes, which severally imply many other attributes — groups them so that any one volume being inspected, the general characters of all the neighbouring volumes may be inferred. He puts together in one great division all works on History; in another all Biographical works; in another all works that treat of Science ; in another Voyages and Travels ; and so on. Each of his great groups he separates into sub-groups; as when he puts different kinds of Literature under the heads of Fiction, Poetry, and the Drama. In some cases he makes sub-sub-groups; as when, having divided his Scientific trea tises into abstract and concrete, putting in the one Logic and Mathematics and in the other Physics, Astronomy, Geology, Chemistry, Physiology, &c. ; he goes on to sub-divide 374 CLASSIFICATION. 375 his books on Physics, into those which treat of Mechanical Motion, those which treat of Heat, those which treat of Light, of Electricity, of Magnetism. Between these two modes of classification note the essential distinctions. Arrangement according to any single con spicuous attribute is comparatively easy, and is the first that suggests itself : a child may place books in the order of their sizes, or according to the styles of their bindings. But ar rangement according to combinations of attributes which, though fundamental, are not conspicuous, requires analysis; and docs not suggest itself till analysis has made some pro gress. Even when aided by the information which the author gives on his title page, it requires considerable know ledge to classify rightly an essay on Polarization ; and in the absence of a title page it requires much more knowledge. Again, classification by a single attribute, which the objects possess in different degrees, may be more or less serial, or linear. Books may be put in the order of their dates, in single file; or if they are grouped as works in one volume, works in two volumes, works in three volumes, &c., the groups may be placed in an ascending succession. But groups severally formed of things distinguished by some common attribute which implies many other attributes, do not admit of serial arrangement. You cannot rationally say either that Historical Works should come before Biographical Works, or Biographical Works before Historical Works ; nor of the sub divisions of creative Literature, into Fiction, Poetry, and the Drama, can you give a good reason why any one should take precedence of the others. Hence this grouping of the like and separation of the un like which constitutes Classification, can reach its complete form only by slow steps. I have shown (Essays, Vol. II., pp. 145-7) that, other things equal, the relations among pheno mena are recognized in the order of their conspicuousness ; and that, other things equal, they are recognized in the order of their simplicity. The first classifications are sure, there- 25 376 THE INDUCTIONS OF BIOLOGY. fore, to bo groupings of objects which resemble one another in external or easily-perceived attributes, and attributes that are not of complex characters. Those likenesses among things which are due to their possession in common of simple obvious properties, may or may not coexist with further likenesses among them. When geometrical figures are classed as curvi linear and rectilinear, or when the rectilinear are divided into trilateral, quadrilateral, &c.,the distinctions made connote various other distinctions with which they are necessarily bound up; but if liquids be classed according to their visible characters — if water, alcohol, sulphurct of carbon, &c., be grouped as colourless and transparent, we have things placed together which are unlike in their essential natures. Thus, where the objects classed have numerous attributes, the probabilities arc that the early classifications, based on simple and manifest attributes, unite under the same head many objects that have no resemblance in the majority of their attributes. As the knowledge of objects increases, it becomes possible to make groups of which the members have more numerous properties in common; and to ascertain what property, or combination of properties, is most characteristic of each group. And the classification eventually arrived at is of such kind that the objects in each group have more attributes in common with one another than they have in common with any excluded objects ; one in which the groups of such groups are integrated on the same principle ; and one in which the degrees of differentiation and integration are proportioned to the degrees of intrinsic unlikeness and like ness. And this ultimate classification, while it serves to iden tify the things completely, serves also to express the greatest amount of knowledge concerning the things — enables us to predicate the greatest number of facts about each thing; and by so doing implies the most precise correspondence between our conceptions and the realities. § 99. Biological classifications illustrate well these phases CLASSIFICATION. 377 through which classifications in general pass. In early attempts to arrange organisms in some systematic manner, we see at first a guidance by conspicuous and simple cha racters, and a tendency towards arrangement in linear order. In successively later attempts, we see more regard paid to combinations of characters which are essential hut often in conspicuous, and an abandonment of a linear arrangement for an arrangement in divergent groups and re-divergent sub groups. In the popular mind, plants are still classed under the heads of Trees, Shrubs, and Herbs; and this serial classing according to the single attribute of magnitude, swayed the earliest observers. They would have thought it absurd to call a bamboo, thirty feet high, a kind of grass; and would have been incredulous if told that the Hart's-tongue should be placed in the same great division with the Tree-ferns. The zoological classifications current before Natural History became a science, had divisions similarly superficial and sim ple. Beasts, Birds, Fishes, and Creeping-things are names of groups marked off from one another by conspicuous differ ences of appearance and modes of life — creatures that walk and run, creatures that fly, creatures that live in the water, creatures that crawl. And these groups were thought of in the order of their importance. The first arrangements made by naturalists were based either on single characters or on very simple combinations of characters; as that of Clusius, and afterwards the more scientific system of Cesalpino, recognizing the importance of inconspicuous structures. Describing plant-classifications, Lindley says : — " Kivinus invented, in 1G90, a system depend ing upon the formation of the corolla; Kamel, in 1693, upon the fruit alone; Magnol, in 1720, on the calyx and corolla; and finally, Linnaeus, in 1731, on variations in the stamens and pistil." In this last system, which has been for so long current as a means of identification (regarded by its author as transitional), simple external attributes are 378 TnE INDUCTIONS OF BIOLOGY. still depended on; and an arrangement, in great measure serial, is based on the degrees in which these attributes are possessed. In 1703, some thirty years before the time of Linnaeus, our countryman Ray had sketched the outlines of a more advanced system. He said that — Plants are either Flowerless, or Flowering ; and these are Dicotyledones, or Monocotyledoncs. Among the minor groups which he placed under these general heads, " were Fungi, Mosses, Ferns, Composites, Cichoracea3, Umbellifers, Papilionaceous plants, Conifers, Labiates, &c., under other names, but with limits not very different from those now assigned to them." Being much in advance of his age, Ray's ideas remained dormant until the time of Jus- sieu; by whom they were developed into what has become known as the Natural System: a system subsequently im proved by De Candolle. Passing through various modifica tions in the hands of successive botanists, the Natural Sys tem is now represented by the following form, which is based upon the table of contents prefixed to Vol. II. of Prof. Oliver's translation of the Natural History of Plants, by Prof. Kerner. His first division, Myxothallophyta (= Myxomy- cetes), I have ventured to omit. The territory it occupies is in dispute between zoologists and botanists, and as I have included the group in the zoological classification, agreeing that its traits are more animal than vegetal, I cannot also include it in the botanical classification. Here, linear arrangement has disappeared: there is a breaking up into groups and sub-groups and sub-sub-groups, which do not admit of being placed in serial order, but only in 'divergent and re-divergent order. Were there space to exhibit the way in which the Alliances are subdivided into Orders, and these into Genera, and these into Species, the same principle of co-ordination would be still further mani- IIYLA. 8UJ}- PHYLA. CLAfWJW. SUH-CLASSES. ALLIANCES. THALLOPHYTA f 2. Cyanophyceno. I. Schizophyta .................. \ Blue -Kreen Algae. [ 3. Schi/omycetes. II. Dinoflagellata Peridineaj ................. 4. III. Bacillariales .................. 5. 6. Protococcoideas. 7. Siphoncse. 8. Confervoideae. IV. Gamophyccac . . I. Chlorophyceas 9. Conjugate}. 10. Charales. 11. Phseophyceee. 12. Dictyotales. 13. Floridese, Red Sea weeds. V. Fungi j II. Mesomycetes j \~- ARCIIEGONIATyE. I. Bryophyta III. Mycomycetes -j ||j- Additional group of Fungi, Lichcnca. f20. Hepaticte, Liver- -j worts. I 21. Musci, Mosses. II. Ptcridophyta, Vus. Cryptogams. PIIANEROGAMIA (Flowering Plains.) I. Cycadales, Cycads II. Coniforae 27. III. Gnetalcs. . . .28. f 22. Filices, Ferns. 23. Hydropterides, Rhizocarpd. 24. Equisetales, Horse-tails. 25. Lycopodiales, Club-mosses. 26. ANGIO- SPEKM.E I. Monocotylcdc I. Monochlamyda? II. Dicotyledons 29. Liliiflora*. 30. Seitamirieas. 31. Gynandraj. 32. Fluviales. 33. Spadiciflorai. 34. Qlumittoraj. 85. Centrosperrna3. 36. Pi-otiales. 37. DaphnalfS. 38. Santalales. 39. Rafflesiales. 40. Asarales. 41. Euphorbiales. 42. Podostenmles. 43. Viridiflora;. 44. Amentales. [45. Balanophorales. f46. Caprifoliales. 47. Asterales. I 48. Campanales. II. MonopctaLf. ... -j 49. Ericales. III. Polypetala;.. 50. Vaccinalos. 51. Prirnulales. 52. TubittorsB. 53. Ranales. 54. Parietales. 55. Malvales. 56. DisciHora3. 57. Crateranthai. 58. Myrtales. 59. Melastomales. 60. Lythrales. 61. Hygrobia*. 62. Passiflora\ 63. Pei>onea. 64. Cactales. 65. Fic-oidales. 1.06. Umbellales. 379 380 TI1E INDUCTIONS OF BIOLOGY. fcsted. On studying the definitions of these primary, sec ondary, and tertiary classes, it will be found that the largest are marked off from one another by some attribute which con notes sundry other attributes ; that each of the smaller classes comprehended in one of these largest classes, is marked off in a similar way from the other smaller classes bound up with it; and that so, each successively smaller class has an in creased number of co-existing attributes. § 100. Zoological classification has had a parallel history. The first attempt which we need notice, to arrange animals in such a way as to display their affinities, is that of Lin- nams. He grouped them thus : * — CL. 1. MAMMALIA. Ord. Primates, Bruta, Ferae, Glires, Pecora, Belluae, Cete. CL. 2. AVES. Ord. Accipitres, Picse, Anseres, Grallae, Gallinse, CL. 3. AMPHIBIA. Ord. Reptiles, Serpentes, Nantes. CL. 4. PISCES. Ord. Apodes, Jugulares, Thoracici, Abdominales. CL. 5. INSECTA. Ord. Coleoptera, Hemiptera, Lepidoptera, Neu- roptera, Diptera, Aptera. CL. 6. VERMES. Ord. Intestina, Mollusca, Testacea, Lithophyta, Zoophyta. This arrangement of classes is obviously based on ap parent gradations of rank; and the placing of the orders similarly betrays an endeavour to make successions, begin ning with the most superior forms and ending with the most inferior forms. While the general and vague idea of perfection determines the leading character of the classifi cation, its detailed groupings are determined by the most conspicuous external attributes. Not only Linnaeus but his opponents, who proposed other systems, were " under the impression that animals were to be arranged together into classes, orders, genera, and species, according to their * This classification, and the three which follow it, I quote (abridging some of them) from Prof. Agassiz's " Essay on Classification." CLASSIFICATION. 381 more or less close external resemblance." This conception survived until the time of Cuvier. " Naturalists," says Agas- siz, " were bent upon establishing one continual uniform series to embrace all animals, between the links of which it was supposed there were no unequal intervals. The watch word of their school was : Natura non facit saltum. They called their system la chaine des etres." The classification of Cuvier, based on internal organization instead of external appearance, was a great advance. He asserted that there are four principal forms, or four general plans, on which animals are constructed; and, in pursuance of this assertion, he drew out the following scheme. First Branch. ANIMALIA VERTEBRATA. Cl. 1. Mammalia. Cl. 2. Birds. Cl. 3. Reptilia. Cl. 4. Fishes. Second Branch. ANIMALIA MOLLUSCA. Cl. 1. Ccphalapoda. Cl. 2. Pteropoda. Cl. 3. Gasteropoda. Cl. 4. Acephala. Cl. 5. Bracliiopoda. Cl. 6. Cirrhopoda. Third Branch. ANIMALIA ARTICULATA. Cl. 1. Annelides. Cl. 2. Crustacea. Cl. 3. Arachnides. CL 4. Insects. Fourth Branch. ANIMALIA RADIATA. Cl. 1. Echinoderrns. Cl. 2. Intestinal Worms. Cl. 3. Acalephse. Cl. 4. Polypi. CJ. 5. Infusoria. 382 THE INDUCTIONS OF BIOLOGY. But though Cuvicr emancipated himself from the concep tion of a serial progression throughout the Animal Kingdom, sundry of his contemporaries and successors remained fet tered by the old error. Less regardful of the differently- combined sets of attributes distinguishing the different sub- kingdoms, and swayed by the belief in a progressive develop ment which was erroneously supposed to imply a linear ar rangement of animals, they persisted in thrusting organic forms into a quite unnatural order. The following classifi cation of Lamarck illustrates this. INVERTEBRATA. I. APATHETIC ANIMALS. Cl. 1. Infusoria. Cl. 2. Polypi. Cl. 3. Radiaria. Cl. 4. Tunicata. Do not feel, and move only by their excited irritability. No brain, no elongated medullary mass ; no senses ; forms varied ; rarely articulations. Cl. 5. Vermes. II. SENSITIVE ANIMALS. Cl. 6. Insects. Cl. 7. Arachnids. Cl. 8. Crustacea. Cl. 9. Annelids. Cl. 10. Cirripcds. Cl. 11. Conchifera. Cl. 12. Mollusks. J Feel, but obtain from their sensa tions only perceptions of objects, a sort of simple ideas, which they are unable to combine to obtain complex ones. No vertebral column ; a brain and mostly an elongated medullary mass; some distinct senses; muscles attached under the skin ; form sym metrical, the parts being in pairs. VERTEBRATA. ( Feel ; acquire preservable ideas ; perform with them operations by which they obtain others ; are intelligent in different degrees. A vertebral column ; a brain and a spinal marrow ; distinct senses; the muscles attached to the internal skeleton; form symmetrical, the parts being in pairs. Passing over sundry classifications in which the serial arrangement dictated by the notion of ascending complexity, is variously modified by the recognition of conspicuous anatomical facts, we come to classifications which recognize III. INTELLIGENT ANIMALS. Cl. 13. Fishes. Cl. 14. Reptiles. Cl. 15. Birds. Cl. 16. Mammalia. CLASSIFICATION. 383 another order of faets — those of development. The embryo- logical inquiries of Von Baer led him to arrange animals as follows : — I. Peripherie Type. (RADIATA.) Evolutio radiata. The development proceeds from a centre, producing identical parts in a radiating order. II. Massive Type. (MOLLUSCA.) Evolutio contorta. The development produces identical parts curved around a conical or other space. III. Longitudinal Type. (ARTICULATA.) Evolutio gemina. The development produces identical parts arising on both sides of an axis, and closing up along a line opposite the axis. IV. Doubly Symmetrical Type. (VEETEBRATA.) Evolutio bigemina. The development produces identical parts arising on both sides of an axis, growing upwards and downwards, and shutting up along two lines, so that the inner layer of the germ is inclosed below, and the upper layer above. The embryos of these animals have a dorsal cord, dorsal plates, and ventral plates, a nervous tube and branchial fissures. Eecognizing these fundamental differences in the modes of development, as answering to fundamental divisions in the animal kingdom, Von Baer shows (among the Vertebrata at least) how the minor differences which arise at successively later embryonic stages, correspond with the minor divisions. Like the modern classification of plants, the modern classi fication of animals shows us the assumed linear order com pletely broken up. In his lectures at the Eoyal Institution, in 1857, Prof. Huxley expressed the relations existing among the several great groups of the animal kingdom, by placing them at the ends of four or five radii, diverging from a centre. The diagram I cannot obtain; but in the pub lished reports of his lectures at the School of Mines the groups were arranged as on the following page. What remnant there may seem to be of linear succession in some of the sub-groups contained in it, is merely an acci dent of typographical convenience. Each of them is to be regarded simply as a cluster. And if Prof. Huxley had fur ther developed the arrangement, by dispersing the sub-groups 384: THE INDUCTIONS OF BIOLOGY. and sub-sub-groups on the same principle, there would result an arrangement perhaps not much unlike that shown on the page succeeding this. VERTEBRATA (Abranchiata) Mammalia Aves Reptilia (Branchiata) Amphibia Pisces. MOLLUSCA ANNULOSA Cephalopoda Heteropoda ~\ Articulate. Gasteropoda- > Insecta Arachnida dioecia ) Myriapoda Crustacea | Pulmonata Gasteropoda- ( Pteropoda monoecia Annuloida. Lamellibranchiata Annellata Scoleidae Echinodermata Trematoda Rotifera Treniadse Turbellaria v Ncmatoidea CCELENTERATA Hydrozoa Actinozoa. PROTOZOA Infusoria Spongiadse Gregarinidse NoctUucidcB Foraminifera ThallassicollidcB In the woodcut, the dots represent orders, the names of which it is impracticable to insert. If it be supposed that when magnified, each of these dots resolves itself into a cluster of clusters, representing genera and species, an ap proximate idea will be formed of the relations among the successively-subordinate groups constituting the animal king dom. Besides the subordination of groups and their general distribution, some other facts arc indicated. By the distances of the great divisions from the general centre, are rudely CLASSIFICATION. 385 symbolized their respective degrees of divergence from the form of simple, undiffercntiated organic matter; which we may regard as their common source. Within each group, the remoteness from the local centre represents, in a rough «* V " . *»*ATV« V E R T E B*'R ATA Vift ^ \ / .'.''Crustace \ ArticMLa-tcL \ A N N U L 9 Sm A \ gcclecida * f s\x A/nnuloida Ptere/ieda * Cr[Juiltfuila. N^ JZchlncdcrmat'a.**,* • '.•$$£12*"*" \ ! / Gasttrfi/ierla. • Putmonata \ / / mcnaci.0. . . \ I ' \ / / \ ' / MOLL US C A .* * 'Poly a oei /PROTOZOA • f i S/itjigida Jnfusoria Sdrneca .* • * • CCE L E N TERATA Aetincxoa* way, the degree of departure from the general plan of the group. And the distribution of the sub-groups within each group, is in most cases such that those which come nearest to neighbouring groups, are those which show the nearest 3SC THE INDUCTIONS OF BIOLOGY. resemblances to them — in their analogies though not in their homologies. No such scheme, however, can give a correct con ception. Even supposing the above diagram expressed the relations of animals to one another as truly as they can be expressed on a plane surface (which of course it does not), it would still be inadequate. Such relations cannot be repre sented in space of two dimensions, but only in space of three dimensions. § lOOfl. Two motives have prompted me to include in its original form the foregoing sketch: the one being that in conformity with the course previously pursued, of giving the successive forms of classifications, it seems desirable to give this form which was approved thirty-odd years ago; and the other being that the explanatory .comments remain now as applicable as they were then. Eeplacement of the diagram by one expressing the relations of classes as they are now conceived, is by no means an easy task; for the conceptions formed of them are unsettled. Concerning the present atti tude of zoologists, Prof. MacBride writes : — " They all recognize a certain number of phyla. Each phylum includes a group of animals about whose relation to each other no one entertains a doubt. Each zoologist, however, has his own idea as to the relationship which the various phyla bear to each other. " The phyla recognized at present are : — " (1) Protozoa. "(2) Porifera (Sponges). " (3) Ccelenterata. " (4) Echinodermata. r Cestodes. " (5) Platyhelminthes 1 Trematodes. ' Turbellaria. "(6) Nemertea. " (7) Ncmatoda. " (8) Acanthocephala (Echinorhyncus). " (9) Chactognatha (Sagitta). "(10) Rotifera. "(11) Annelida (Includes Leeches and Gephyrea, Cruetifera). "(12j Gephyrea, Achaeta. CLASSIFICATION. 387 f Tracheata (Peripatus, Myriapods, Insects). te± [ Pycnogonida. "(14) Mollusca. "(15) Polyzoa (Including Phoronis). "(10) Bruchiopoda. " (17) Chordata (Includes Balanoglossus and Tunicates. Some continental zoologists do not admit Balanoglossus)." [This last phylum of couiee includes the Vertebrata.} Though under present conditions, as above implied, it would be absurd to attempt a definite scheme of relation ships, yet it has seemed to me that the adumbration of a scheme, presenting in a vague way such relationships as are generally agreed upon and leaving others indeterminate, may be ventured; and that a general impression hence resulting may be useful. On the adjacent page I have tried to make a tentative arrangement of this kind. At the bottom of the table I have placed together, under the name " Compound Protozoa," those kinds of aggregated Protozoa which show no differentiations among the members of groups, and are thus distinguished from Metazoa; and I have further marked the distinction by their position, which implies that from them no evolution of higher types has taken place. Respecting the naming of the sub-kingdoms, phyla, classes, orders, &c., I have not maintained entire consistency. The relative values of groups cannot be typographically ex pressed in a small space with a limited variety of letters. The sizes of the letters mark the classificatory ranks, and by the thickness I have rudely indicated their zoological im portance. In fixing the order of subordination of groups I have been aided by the table of contents prefixed to Mr. Adam Sedgwick's Student's Text Book of Zoology and have also made use of Prof. Ray Lankester's classifications of several sub-kingdoms. Let me again emphasize the fact that the relationships of these diverging and re-diverging groups cannot be expressed . •.-,-. f'Avea *', • MasnmaZia f/npltzcenkzl "' " ; Arachnida, Insecta, ••** \ Crustacea -.* •:•• / .. / Amphibia. ' Pisces * Difjljopoda, CcpJialo- f I \« Urocluj7~d& AHH^/***" Echiurowfai A /'' ffij^icdinect Cephalopoda. • ' ArchianneUda BRACH/- / . ^J Scaphopoda. ^ Solenpgastr ^^ N Aster-* video, Enfcrv- V pneusla, AcanfJio* . morpha Tur&eil. aria. CLASSIFICATION. 389 on a flat surface. If we imagine a laurel-bush to be squashed flat by a horizontal plane descending upon it, we shall see that sundry of the upper branches and twigs which were previously close together will become remote, and that the relative positions of parts can remain partially true only with the minor branches. The reader must therefore expect to find some of the zoological divisions which in the order of nature are near one another, shown in the table as quite distant. § 101. While the classifications of botanists and zoologists have become more and more natural in their arrangements, there has grown up a certain artificiality in their abstract nomenclature. When aggregating the smallest groups into larger groups and these into groups still larger, they have adopted certain general terms expressive of the successively more comprehensive divisions; and the habitual use of these terms, needful for purposes of convenience, has led to the tacit assumption that they answer to actualities in Nature. It has been taken for granted that species, genera, orders, and classes, are assemblages of definite values — that every genus is the equivalent of every other genus in respect of its degree of distinctness; and that orders are separated by lines of damarcation which are as broad in one place as another. Though this conviction is not a formulated one, the disputes continually occurring among naturalists on the questions, whether such and such organisms are specifi cally or generically distinct, and whether this or that pecu liarity is or is not of ordinal importance, imply that the conviction is entertained even where not avowed. Yet that differences of opinion like these arise and remain unsettled, except when they end in the establishment of sub-species,' sub-genera, sub-orders, and sub-classes, sufficiently shows that the conviction is ill-based. And this is equally shown by the impossibility of obtaining any definition of the degree of difference which warrants each further elevation in the hierarchy of classes. 390 THE INDUCTIONS OF BIOLOGY. It is, indeed, a wholly gratuitous assumption that organ isms admit of being placed in groups of equivalent values; and that these may be united into larger groups which are also of equivalent values; and so on. There is no a priori reason for expecting this; and there is no a posteriori evi dence implying it, save that which begs the question — that which asserts one distinction to be generic and another to be ordinal, because it is assumed that such distinctions must be either generic or ordinal. The endeavour to thrust plants and animals into these definite partitions is of the same nature as the endeavour to thrust them into linear series. Not that it does violence to the facts in anything like the same degree; but still, it does violence to the facts. Doubt less the making of divisions and sub-divisions, is extremely useful ; or rather, it is necessary. Doubtless, too, in reducing the facts to something like order they must be partially dis torted. So long as the distorted form is not mistaken for the actual form, no harm results. But it is needful for us to remember that while our successively subordinate groups have a certain general correspondence with the realities, they tacitly ascribe to the realities a regularity which does not exist. § 102. A general truth of much significance is exhibited in these classifications. On observing the natures of the attributes which are common to the members of any group of the first, second, third, or fourth rank, we see that groups of the widest generality are based on characters of the greatest importance, physiologically considered; and that the charac ters of the successively-subordinate groups, are characters of successively-subordinate importance. The structural pecu liarity in which all members of one sub-kingdom differ from all members of another sub-kingdom, is a peculiarity that affects the vital actions more profoundly than does the struc tural peculiarity which distinguishes all members of one class from all members of another class. Let us look at a few cases. CLASSIFICATION. 391 We saw (§5(5), that the broadest division among the functions is the division into "the accumulation of energy (latent in food) ; the expenditure of energy (latent in the tissues and certain matters absorbed by them) ; and the transfer of energy (latent in the prepared nutriment or blood) from the parts which accumulate to the parts which expend." Now in the lowest animals, united under the general name Protozoa, there is cither no separation of the parts performing these functions or very indistinct separation : in the Rhizo- poda, all parts are alike accumulators of energy, expenders of energy and transferers of energy; and though in the higher members of the group, the Infusoria, there are some speciali zations corresponding to these functions, yet there are no distinct tissues appropriated to them. Similarly when we pass from simple types to compound types — from Protozoa to Metazoa. The animals known as Coslenterata arc charac terized in common by the possession of a part which accumu lates energy more or less marked off from the part which does not accumulate energy, but only expends it; and the Ilydrozoa and Actinozoa, which are sub-divisions of the Ccelenterata, arc contrasted in this, that in the second these parts are much more differentiated from one another, as well as more complicated. Besides a completer differentiation of the organs respectively devoted to the accumulation of energy and the expenditure of energy, animals next above the Ccelenterata possess rude appliances for the transfer of energy : the peri-visceral sac, or closed cavity between the intestine and the walls of the body, serves as a reservoir of absorbed nutriment, from which the surrounding tissues take up the materials they need. And then out of this sac originates a more efficient appliance for the transfer of ener gy: the more highly-organized animals, belonging to whichever sub-kingdom, all of them possess definitely-con structed channels for distributing the matters containing energy. In all of them, too, the function of expenditure is divided between a directive apparatus and an executive 20 392 THE INDUCTIONS OF BIOLOGY. apparatus — a nervous system and a muscular system. But these higher sub-kingdoms are clearly separated from one another by differences in the relative positions of their com ponent sets of organs. The habitual attitudes of annulose and molluscous creatures, is such that the neural centres are below the alimentary canal and the ha3mal centres above. And while by these traits the annulose and molluscous types are separated from the vertebrate, they are separated from each other by this, that in the one the body is " composed of successive segments, usually provided with limbs," but in the other, the body is not segmented, " and no true articulated limbs are ever developed." The sub-kingdoms being thus distinguished from one an other, by the presence or absence of specialized parts devoted to fundamental functions, or else by differences in the distri butions of such parts, we find, on descending to the classes, that these are distinguished from one another, either by modifications in the structures of fundamental parts, or by the presence or absence of subsidiary parts, or by both. Fishes and Amphibia are unlike higher vertebrates in possess ing branchiae, either throughout life or early in life. And every higher vertebrate, besides having lungs, is characterized by having, during development, an amnion and an allantois. Mammals, again, are marked off from Birds and Keptiles by the presence of mammae, as well as by the form of the occipital condyles. Among Mammals, the next division is based on the presence or absence of a placenta. And divisions of the Placentalia are mainly determined by the characters of the organs of external action. Thus, without multiplying illustrations and without de scending to genera and species, we see that, speaking gener ally, the successively smaller groups are distinguished from one another by traits of successively less importance, physio logically considered. The attributes possessed in common by the largest assemblages of organisms, arc few in number but all-essential in kind. Each secondary assemblage, in- CLASSIFICATION. 393 eluded in one of the primary assemblages, is characterized by further common attributes that influence the functions less profoundly. And so on with each lower grade. § 103. What interpretation is to be put on these truths of classification? We find that organic forms admit of an arrangement everywhere indicating the fact, that along with certain attributes, certain other attributes, which are not directly connected with them, always exist. How are we to account for this fact? And how are we to account for the fact that the attributes possessed in common by the largest assemblages of forms, are the most vitally-important attributes ? No one can believe that combinations of this kind have arisen fortuitously. Even supposing fortuitous combina tions of attributes might produce organisms that would work, we should still be without a clue to this special mode of combination. The chances would be infinity to one against organisms which possessed in common certain fundamental attributes, having also in common numerous non-essential attributes. Nor, again, can any one allege that such combinations are necessary, in the sense that all other combinations are im practicable. There is not, in the nature of things, a reason why creatures covered with feathers should always .have beaks: jaws carrying teeth would, in many cases, have served them equally well or better. The most general characteristic of an entire sub-kingdom, equal in extent to the Vertebrata, might have been the possession of nicti tating membranes ; while the internal organizations through out this sub-kingdom might have been on many different plans. If, as an alternative, this peculiar subordination of traits which organic forms display be ascribed to design, other difficulties suggest themselves. To suppose that a certain plan of organization was fixed on by a Creator for each vast 394 THE INDUCTIONS OF BIOLOGY. and varied group, the members of which were to have many different modes of life, and that he bound himself to adhere rigidly to this plan, even in the most aberrant forms of the group where some other plan would have been more appro priate, is to ascribe a very strange motive. When we dis cover that the possession of seven cervical vertebrae is a gen eral characteristic of mammals, whether the neck be im mensely long as in the giraffe, or quite rudimentary as in the whale, shall we say that though, for the whale's neck, one vertebra would have been equally good, and though, for the giraffe's neck, a dozen would probably have been better than seven, yet seven was the number adhered to in both cases, because seven was fixed upon for the mammalian type? And then, when it turns out that this possession of seven cervical vertebra? is not an absolutely-universal characteristic of mammals (there is one which has eight), shall we conclude that while, in a host of cases, there was a needless adherence to a plan for the sake of consistency, there was yet, in some cases, an inconsistent abandonment of the plan? I think we may properly refuse to draw any such conclusion. What, then, is the meaning of these peculiar relations of organic forms? The answer to this question must be post poned. Having here contemplated the problem as presented in these wide inductions which naturalists have reached ; and having seen what proposed solutions of it are inadmissible; we shall see, in the next division of this work, what is the only possible solution. CHAPTER XII. DISTRIBUTION. § 104. THERE is a distribution of organisms in Space, and there is a distribution of organisms in Time. Looking first at their distribution in Space, we observe in it two different classes of facts. On the one hand, the plants and animals of each species have their habitats limited by external condi tions : they are necessarily restricted to spaces in which their vital actions can be performed. On the other hand, the existence of certain conditions does not determine the pres ence of organisms that are fit for them. There are many spaces perfectly adapted for life of a high order in which only life of a much lower order is found. While, in the inevitable restriction of organisms to environ ments with which their natures correspond we find a negative cause of distribution, there remains to be found that positive cause whence results the presence of organisms in some places appropriate to them and their absence from other places equally appropriate or more appropriate. Let us consider the phenomena as thus classed. § 105. Facts which illustrate the limiting influence of sur rounding conditions are abundant, and familiar to all readers. It will be needful, however, here to cite a few typical ones of each order. The confinement of different kinds of plants and different 398 THE INDUCTIONS OF BIOLOGY. equally common parasitism of the Entozoa — creatures which live within other creatures. Besides being restricted to the bodies of the organisms it infests, each species has usually still narrower limits of distribution; in some cases the in fested organisms furnish fit habitats for the parasites only in certain regions, and in other cases only when in certain constitutional states. There are more indirect modes in which the distributions of organisms affect one another. Plants of some kinds are eaten by animals only in the absence of kinds that are preferred to them ; and hence the prosperity of such plants partly depends on the presence of the preferred plants. Mr. Bates has shown that some South American butterflies thrive in regions where insectivorous birds would destroy them, did they not closely resemble butterflies of another genus which are disliked by those birds. And Mr. Darwin gives cases of dependence still more remote and in volved. Such are the chief negative causes of distribution — the inorganic and organic agencies that set bounds to the spaces which organisms of each species inhabit. Fully to under stand their actions we must contemplate them as working not separately but in concert. We have to regard the physical influences, varying from year to year, as now producing an extension or restriction of the habitat in this direction and now in that, and as producing secondary extensions and re strictions by their effects on other kinds of organisms. We have to regard the distribution of each species as affected not only by causes which favour multiplication of prey or of enemies within its own area, but also by causes which pro duce such results in neighbouring areas. We have to conceive the forces by which the limit is maintained, as including all meteorologic influences, united with the influences, direct or remote, of numerous co-existing species. One general truth, indicated by sundry of the above illus trations, calls for special notice — the truth that all kinds of organisms intrude on one another's spheres of existence. Of DISTRIBUTION. 399 the ways in which they do this the commonest is invasion of territory. That tendency which we see in the human races, to overrun and occupy one another's lands, as well as the lands inhabited by inferior creatures, is a tendency exhibited by all classes of organisms in various ways. Among them, as among mankind, thtfre are permanent conquests, temporary occupations, and occasional raids. Every spring an inroad is made into the area which our own birds occupy, by birds from the South; and every winter the fieldfares of the North come to share the hips and haws of our hedges, and thus entail on our native birds some mortality. Besides these regularly- recurring incursions there arc irregular ones; as of locusts into countries not usually visited by them, or of certain rodents which from time to time swarm into areas adjacent to their own. Every now and then an incursion ends in permanent settlement — perhaps in conquest over indigenous species. Within these few years an American water-weed has taken possession of our ponds and rivers, and to some extent supplanted native water-weeds. Of animals may be named a small kind of red ant, having habits allied to those of tropical ants, which has of late overrun many houses in London. The rat, wKich must have taken to infesting ships within these few centuries, furnishes a good illustration of the readiness of animals to occupy new places that are available. And the way in which vessels visiting India are cleared of the European cockroach by the kindred Blatta oricntalis., shows us how these successful invasions last only until there come more powerful invaders. Animals encroach on one another's spheres of existence in further ways than by trespassing on one another's areas : they adopt one another's modes of life. There are cases in which this usurpation of habits is slight and temporary; and there are cases where it is marked and permanent. Grey crows often join gulls in picking up food between tide-marks; and gulls may occasionally be seen many miles inland, feeding in ploughed fields and on moors. Mr. Darwin has watched a 400 THE INDUCTIONS OF BIOLOGY. fly-catcher catching fish. He says that the greater titmouse sometimes adopts the practices of the shrike, and sometimes of the nuthatch, and that some South American woodpeckers are frugivorous while others chase insects on the wing. Of habitual intrusions on the occupations of other creatures, one case is furnished by the sea-eagle, which* besides hunting the surface of the land for prey, like the rest of the hawk-tribe, often swoops down upon fish. And Mr. Darwin names a species of petrel that has taken to diving, and has a consider ably modified organization. The last cases introduce a still more remarkable class of facts of kindred meaning. This intrusion of organisms on one another's modes of life goes to the extent of intruding on one another's media. The great mass of flowering plants are terrestrial, and (aside from other needs) are required to be so by their process of fructifi cation. But there are some which live in the water, and protrude their flowers above the surface. Nay, there is a still more striking instance. At the sea-side may be found an alga a hundred yards inland, and a phanogam rooted in salt water. Among animals these interchanges of media are numerous. Nearly all coleopterous insects are terrestrial ; but the water- beetle, which like the rest of its order is an air-breather, has aquatic habits. Water appears to be an extremely unfit medium for a fly; and yet Mr. [now Sir John] Lubbock has discovered more than one species of fly living beneath the surface of the water and coming up occasionally for air. Birds, as a class, are specially fitted for an aerial existence; but certain tribes of them have taken to an aquatic existence — swimming on the surface of the water and making continual incursions beneath it, and some kinds have wholly lost the power of flight. Among mammals, too, which have limbs and lungs implying an organization for terrestrial life, may be named kinds living more or less in the water and are more or less adapted to it. We have water-rats and otters which unite the two kinds of life, and show but little modification; hippopotami passing the greater part of their time in the DISTRIBUTION. 401 water, and somewhat more fitted to it; seals living almost exclusively in the sea, and having the mammalian form greatly obscured; whales wholly confined to the sea, and having so little the aspect of mammals as to be mistaken for fish. Conversely, sundry inhabitants of the water make ex cursions on the land. Eels migrate at night from one pool to another. There are fish with specially-modified gills and fin-rays serving as stilts, which, when the rivers they inhabit are partially dried-up, travel in search of better quarters. And while some kinds of crabs do not make land-excursions beyond high-water mark, other kinds pursue lives almost wholly terrestrial. Guided by these two classes of facts, we must regard the bounds to each species' sphere of existence as determined by the balancing of two antagonist sets of forces. The tend ency which every species has to intrude on other areas, other modes of life, and other media, is restrained by the direct and indirect resistance of conditions, organic and inorganic. And these expansive and repressive energies, varying con tinually in their respective intensities, rhythmically equili brate each other — maintain a limit that perpetually oscillates from side to side of a certain mean. § 100. As implied at the outset, the character of a region, when unfavourable to any species, sufficiently accounts for the absence of this species; and thus its absence is not incon sistent with the hypothesis that each species was originally placed in the regions most favourable to it. But the absence of a species from regions that are favourable to it cannot be thus accounted for. Were plants and animals localized wholly with reference to the fitness of their constitutions to surround ing conditions, we might expect Floras to be similar, and Faunas to be similar, where the conditions are similar; and we might expect dissimilarities among Floras and among Faunas, proportionate to the dissimilarities of their conditions. But we do not find such anticipations verified. 400 THE INDUCTIONS OF BIOLOGY. fly-catcher catching fish. He says that the greater titmouse sometimes adopts the practices of the shrike, and sometimes of the nuthatch, and that some South American woodpeckers are frugivorous while others chase insects on the wing. Of habitual intrusions on the occupations of other creatures, one case is furnished by the sea-eagle, which* besides hunting the surface of the land for prey, like the rest of the hawk-tribe, often swoops down upon fish. And Mr. Darwin names a species of petrel that has taken to diving, and has a consider ably modified organization. The last cases introduce a still more remarkable class of facts of kindred meaning. This intrusion of organisms on one another's modes of life goes to the extent of intruding on one another's media. The great mass of flowering plants are terrestrial, and (aside from other needs) are required to be so by their process of fructifi cation. But there are some which live in the water, and protrude their flowers above the surface. Nay, there is a still more striking instance. At the sea-side may be found an alga a hundred yards inland, and a phaenogam rooted in salt water. Among animals these interchanges of media are numerous. Nearly all coleopterous insects are terrestrial; but the water- beetle, which like the rest of its order is an air-breather, has aquatic habits. Water appears to be an extremely unfit medium for a fly; and yet Mr. [now Sir John] Lubbock has discovered more than one species of fly living beneath the surface of the water and coming up occasionally for air. Birds, as a class, are specially fitted for an aerial existence; but certain tribes of them have taken to an aquatic existence — swimming on the surface of the water and making continual incursions beneath it, and some kinds have wholly lost the power of flight. Among mammals, too, which have limbs and lungs implying an organization for terrestrial life, may be named kinds living more or less in the water and are more or less adapted to it. We have water-rats and otters which unite the two kinds of life, and show but little modification; hippopotami passing the greater part of their time in the DISTRIBUTION. 401 water, and somewhat more fitted to it; seals living almost exclusively in the sea, and having the mammalian form greatly obscured; whales wholly confined to the sea, and having so little the aspect of mammals as to be mistaken for fish. Conversely, sundry inhabitants of the water make ex cursions on the land. Eels migrate at night from one pool to another. There are fish with specially-modified gills and fin-rays serving as stilts, which, when the rivers they inhabit are partially dried-up, travel in search of better quarters. And while some kinds of crabs do not make land-excursions beyond high-water mark, other kinds pursue lives almost wholly terrestrial. Guided by these two classes of facts, we must regard the bounds to each species' sphere of existence as determined by the balancing of two antagonist sets of forces. The tend ency which every species has to intrude on other areas, other modes of life, and other media, is restrained by the direct and indirect resistance of conditions, organic and inorganic. And these expansive and repressive energies, varying con tinually in their respective intensities, rhythmically equili brate each other — maintain a limit that perpetually oscillates from side to side of a certain mean. § 10G. As implied at the outset, the character of a region, when unfavourable to any species, sufficiently accounts for the absence of this species; and thus its absence is not incon sistent with the hypothesis that each species was originally placed in the regions most favourable to it. But the absence of a species from regions that are favourable to it cannot be thus accounted for. Were plants and animals localized wholly with reference to the fitness of their constitutions to surround ing conditions, we might expect Floras to be similar, and Faunas to be similar, where the conditions are similar; and we might expect dissimilarities among Floras and among Faunas, proportionate to the dissimilarities of their conditions. But we do not find such anticipations verified. 402 THE INDUCTIONS OF BIOLOGY. Mr. Darwin says that " in the Southern hemisphere, if wo compare large tracts of land in Australia, South Africa, and western South America, between latitudes 25° and 35°, we shall find parts extremely similar in all their conditions, yet it would not be possible to point out three faunas and floras more utterly dissimilar. Or again we may compare the pro ductions of South America south of lat. 35° with those north of 25°, which consequently inhabit a considerably different cli mate, and they will be found incomparably more closely related to each other, than they are to the productions of Australia on Africa under nearly the same climate." Still more striking are the contrasts which Mr. Darwin points out between adjacent areas that arc totally cut off from each other. " No two marine faunas are more distinct, with hardly a fish, shell, or crab in common, than those of the eastern and western shores of South and Central America ; yet these great faunas are separated only by the narrow, but impassable, isthmus of Panama." On opposite sides of high mountain-chains, also, there are marked differences in the organic forms — differ ences not so marked as where the barriers are absolutely im passable, but much more marked than are necessitated by unlikenesses of physical conditions. Not less suggestive is the converse fact that wide geogra phical areas which offer decided geologic and meteorologic contrasts, are peopled by nearly-allied groups of organisms, if there are no barriers to migration. " The naturalist in tra velling, for instance, from north to south never fails to be struck by the manner in which successive groups of beings, specifically distinct, yet clearly related, replace each other. He hears from closely allied, yet distinct kinds of birds, notes nearly similar, and sees their nests similarly constructed, but not quite alike, with eggs coloured in nearly the same manner. The plains near the Straits of Magellan arc inhabit ed by one species of Rhea (American Ostrich), and northward the plains of La Plata by another species of the same genus ; and not by a true ostrich or emu., like those found in Africa DISTRIBUTION. 403 and Australia under the same latitude. On these same plains of La Plata, we see the agouti and bizcacha, animals having nearly the same habits as our hares and rabbits and belonging to the same order of Rodents, but they plainly display an American type of structure. We ascend the lofty peaks of the Cordillera and we find an alpine species of bizcacha; wo look to the waters, and we do not find the beaver or musk- rat, but the coypu and capybara, rodents of the American type. Innumerable other instances could be given. If we look to the islands off the American shore, however much they may differ in geological structure, the inhabitants, though they may be all peculiar species, are essentially American." What is the generalization implied by these two groups of facts? On the one hand, we have similarly-conditioned, and sometimes nearly-adjacent, areas, occupied by quite different Faunas. On the one hand, we have areas remote from one another in latitude, and contrasted in soil as well as climate, occupied by closely-allied Faunas. Clearly then, as like or ganisms are not universally, or even generally, found in like habitats, nor very unlike organisms in very unlike habitats, there is no manifest pre-determined adaptation of the organ isms to the habitats. The organisms do no occur in such and such places solely because they are either specially fit for those places, or more fit for them than all other organisms. The induction under which these facts come, and which unites them with various other facts, is a totally-different one. When we see that the similar areas peopled by dissimilar forms, are those between which there are impassable barriers ; while the dissimilar areas peopled by similar forms, are those between which there are no such barriers; we are at once re minded of the general truth exemplified in the last section — the truth that each species of organism tends ever to expand its sphere of existence — to intrude on other areas, other modes of life, other media. And we are shown that through these perpetually-recurring attempts to thrust itself into every 404 THE INDUCTIONS OF BIOLOGY. accessible habitat, each species spreads until it reaches limits which are for the time insurmountable. § 107. We pass now to the distribution of organic forms in Time. Geological inquiry has established the truth that during a Past of immeasurable duration, plants and animals have existed on the Earth. In all countries their buried remains arc found in greater or less abundance. From com paratively small areas multitudinous different types have been exhumed. Every exploration of new areas, and every closer inspection of areas already explored, brings more types to light. And beyond question, an exhaustive examination of all exposed strata, and of all strata now covered by the sea, would disclose types immensely out-numbering those at present known. Further, geologists agree that even had we before us every kind of fossil which exists, we should still have nothing like a complete index to the past inhabitants of our globe. Many sedimentary deposits have been so altered by the heat of adjacent molten matter, as greatly to obscure the organic remains contained in them. The extensive formations once called " transition," and now re-nained " metamorphic," are acknowledged to be formations of sedimentary origin, from which all traces of such fossils as they probably included have been obliterated by igneous action. And the accepted con clusion is that igneous rock has everywhere resulted from the melting-up of beds of detritus originally deposited by water. How long the reactions of the Earth's molten nucleus on its cooling crust, have been thus destroying the records of Life, it is impossible to say; but there are strong reasons for believing that the records which remain bear but a small ratio to the records which have been destroyed. Thus we have but extremely imperfect data for conclusions respecting the distribution of organic forms in Time. Some few generaliza tions, however, may be regarded as established. One is that the plants and animals now existing mostly differ from the plants and animals which have existed. DISTRIBUTION. 405 Though there are species common to our present Fauna and to past Faunas, yet the fades of our present Fauna differs, more or less, from the fades of each past Fauna. On carry ing out the comparison, we find that past Faunas differ from one another, and that the differences between them arc pro portionate to their degrees of remoteness from one another in Time, as measured by their relative positions in the sediment ary scries. So that if we take the assemblage of organic forms living now, and compare it with the successive assem blages of organic forms which have lived in successive geologic epochs, we find that the farther we go back into the past, the greater does the unlikeness become. The number of species and genera common to the compared assemblages, becomes smaller and smaller; and the assemblages differ more and more in their general characters. Though a species of brachiopod now extant is almost identical with a species found in Silurian strata, though between the Silurian Fauna and our own there are sundry common genera of molluscs, yet it is undeniable that there is a proportion between lapse of time and divergence of organic forms. This divergence is comparatively slow and continuous where there is continuity in the geological formations, but is sudden, and comparatively wide, wherever there occurs a great break in the succession of strata. The contrasts which thus arise, gradually or all at once, in formations that are continuous or discontinuous, are of two" kinds. Faunas of different eras are distinguished partly by the absence from the one of types present in the other, and partly by the unlikenesses between the types common to both. Such con trasts between Faunas as are due to the appearance or disap pearance of types, are of secondary significance : they possibly, or probably, do not imply anything more than migrations or extinctions. The most significant contrasts are those between successive groups of organisms of the same type. And among such, as above said, the differences are, speaking generally, small and continuous where a series of conformable 406 THE INDUCTIONS OF BIOLOGY. strata gives proof of continued existence of the type in the locality ; while they are comparatively large and abrupt where the adjacent formations are shown to have been separated by long intervals. Another general fact, referred to by Mr. Darwin as one which palaeontology has made tolerably certain, is that forms and groups of forms which have once disappeared from the Earth, do not reappear. Passing over the few species which have continued throughout the whole period geologically recorded, it may be said that each species after arising, spread ing for an era, and continuing abundant for an era, eventually declines and becomes extinct ; and that similarly, each genus during a longer period increases in the number of its species, and during a longer period dwindles and at last dies out. After making its exit neither species nor genus ever re-enters. The like is true even of those larger groups called orders. Four types of reptiles which were once abundant have not been found in modern formations, and do not at present exist. Though nothing less than an exhaustive examination of all strata, can prove conclusively that a type of organization when once lost is never reproduced, yet so many facts point to this inference that its truth can scarcely be doubted. To frame a conception of the total amount and general direction of the change in organic forms during the time measured by our sedimentary series, is at present impossible — the data are insufficient. The immense contrast between the few and low forms of the earliest-known Fauna, and the many and high forms of our existing Fauna, has been com monly supposed to prove, not only great change but great progress. Nevertheless, this appearance of progress may be, and probably is, mainly illusive. Wider knowledge has shown that remains of comparatively well-organized creatures really existed in strata long supposed to be devoid of them, and that where they are absent, the nature of the strata often explains their absence, without assuming that they did not exist when these strata were formed. It is a tenable DISTRIBUTION. 407 hypothesis that the successively-higher types fossilized in our successively-later deposits, indicate nothing more than suc cessive migrations from pre-existing continents to continents that were step by step emerging from the ocean — migrations which necessarily began with the inferior orders of organ isms, and included the successively-superior orders as the new lands became more accessible to them and better fitted for them.* While the evidence usually supposed to prove progression is thus untrustworthy, there is trustworthy evidence that there has been, in many cases, little or no progression. Though the orders which have existed from palaeozoic and mcsozoic times down to the present day, are almost universally changed, yet a comparison of ancient and modern members of these orders shows that the total amount of change is not relatively great, and that it is not manifestly towards a higher organization. Though nearly all the living forms which have prototypes in early formations differ from these prototypes specially, and in most cases generically, yet ordinal peculiarities are, in nu merous cases, maintained from the earliest times geologically recorded, down to our own time; and we have no visible evi dence of superiority in the existing genera of these orders. In * For explanations, see " Illogical Geology." Essays, Vol. I. How much we may be misled by assuming that because the remains of creatures of high types have not been found in early strata, such creatures did not exist when those strata were formed, has recently (1897) been shown by the discovery of a fossil Sea-cow in the lower Miocene of Hesse-Darmstadt. The skeleton of this creature proves that it differed from such Sirenian mammals as the existing Manatee only in very small particulars: further dwindling of dis used parts being an evident cause. If, now, we consider that since the beginning of Miocene days this aberrant type of mammal has not much increased its divergence from the ordinary mammalian type ; if we then consider how long it must have taken for this large aquatic mammal (some eight or ten feet long) to be derived by modification from a land-mammal ; and if then we contemplate the probable length of the period required for the evolution of that land-mammal out of a pre-mammalian type ; we seem car ried back in thought to a time preceding any of our geologic records. We are shown that the process of organic evolution has most likely been far slower than is commonly supposed. 27 408 THE INDUCTIONS OF BIOLOGY. his lecture " On the Persistent Types of Animal Life," Prof. Huxley enumerated many cases. On the authority of Dr. Hooker he stated " that there are Carboniferous plants which appear to be generically identical with some now living : that the cone of the Oolitic Araucaria is hardly distinguishable from that of an existing species; that a true Pinus appears in the Purbecks and a Juglans in the chalk." Among animals he named paleozoic and mesozoic corals which are very like certain extant corals ; genera of Silurian molluscs that answer to existing genera; insects and arachnids in the coal-forma tions that are not more than generically distinct from some of our own insects and arachnids. He instanced " the Devonian and Carboniferous PI eur acanthus, which differs no more from existing sharks than these do from one another ; " early mesozoic reptiles " identical in the essential characters of their organization with those now living ; " and Triassic mammals which did not differ "nearly so much from some of those which now live, as these differ from one another." Continu ing the argument in his " Anniversary Address to the Geological Society " in 1862, Prof. Huxley gave many cases in which the changes that have taken place, are not changes towards a more specialized or higher organization — asking " in what sense are the Liassic Chelonia inferior to those which now exist? How are the Cretaceous Ichthyosauria, Plesiosauria, or Pterosauria less embryonic or more differenti ated species than those of the Lias ? " While, however, con tending that in most instances " positive evidence fails to demonstrate any sort of progressive modification towards a less embryonic or less generalized type in a great many groups of animals of long-continued geological existence," Prof. Huxley added that there are other groups, " co-existing with them under the same conditions, in which more or less distinct indications of such a process seem to be traceable." And in illustration of this, he named that better development of the vertebras which characterizes some of the more modern fishes and reptiles, when compared with ancient fishes DISTRIBUTION. 409 and reptiles of the same orders; and the "regularity and evenness of the dentition of the Anoplotherium as contrasting with that of existing Artiodactyles." * The facts thus summed up do not show that higher forms have not arisen in the course of geologic time, any more than the facts commonly cited prove that higher forms have arisen ; nor are they regarded by Professor Huxley as showing this. Were those which have survived from pakeozoic and mesozoic days down to our own day, the only types; and did the modifications, rarely of more than generic value, which these types have undergone, give no better evidences of increased complexity than are actually given by them ; then it would be inferable that there has been no appreciable advance. But there now exist, and have existed during the more recent geologic epochs, various types which are not known to have existed in earlier epochs — some of them widely unlike these persistent types and some of them nearly allied to these persistent types. As yet, we know nothing about the origins of these new types. But it is possible that causes like those which have produced generic differences in the persistent types, have, in some or many cases, produced modifications great enough to constitute ordinal differences. If structural contrasts not exceeding certain moderate limits are held to mark only generic distinctions; and if organisms displaying larger contrasts are regarded as ordinally or typically distinct ; it is obvious that the persistence of a given type through a long geologic period without apparently undergoing devia tions of more than generic value, by no means disproves the occurrence of far greater deviations in other cases; since * Since this passage was written, in 1863, there has come to light much more striking evidence of change from a more generalized to a less general ized type during geologic time. In a lecture delivered by him in 1876, Prof. Huxley gave an account of the successive modifications of skeletal structure in animals allied to the horse. Beginning with the Orohippnx of the Eocene formation, which had four complete toes on the front limb and three toes on the hind limb, he pointed out the successive steps by which in the Mcsohippus, Miohipjms, Protohippus, and Pliohippus, there was a gradual approach to the existing horse. 410 THE INDUCTIONS OF BIOLOGY. the forms resulting from such far greater deviations, being regarded as typically distinct forms, will not be taken as evidence of great change in an original type. That which Prof. Huxley's argument proves, and that only which he considers it to prove, is that organisms have no innate tendencies to assume higher forms; and that " any admissible hypothesis of progressive modification, must be compatible with persistence without progression through indefinite periods." One very significant fact must be added concerning the relation between distribution in Time and distribution in Space. I quote it from Mr. Darwin : — " Mr. Clift many years ago showed that the fossil mammals from the Australian caves were closely allied to the living marsupials of that con tinent. In South America a similar relationship is manifest, even to an uneducated eye, in the gigantic pieces of armour like those of the armadillo, found in several parts of La Plata ; and Professor Owen has shown in the most striking manner that most of the fossil mammals, buried there in such num bers, are related to the South American types. This relation ship is even more clearly seen in the wonderland collection of fossil bones made by MM. Lund and Clausen in the caves of Brazil. I was so much impressed with these facts that I strongly insisted, in 1839 and 1845, on this l law of the suc cession of types,' — on ' this wonderful relationship in the same continent between the dead and the living.' Professor Owen has subsequently extended the same generalization to the Mammals of the Old World. We see the same law in this author's restorations of the extinct and gigantic birds of New Zealand. We see it also in the birds of the caves of Brazil. Mr. Woodward has shown that the same law holds good with sea-shells, but from the wide distribution of most genera of molluscs, it is not well displayed by them. Other cases could be added, as the relation between the extinct and living landshells of Madeira, and between the extinct and living brackish- water shells of the Aralo-Caspian Sea." • DISTRIBUTION. 411 The general results, then, are these. Our knowledge of distribution in Time, being derived wholly from the evidence afforded by fossils, is limited to that geologic time of which some records remain — cannot extend to those remoter times the records of which have been obliterated. From these re maining records, which probably form but a small fraction of the whole, the general facts deducible are these: — That such organic types as have lived through successive epochs, have almost universally undergone modifications of specific and generic values — modifications which have commonly been great in proportion as the period has been long. That besides the types which have persisted from ancient eras down to our own era, other types have from time to time made their ap pearance in the ascending series of strata — types of which some arc lower and some higher than the types previously recorded; but whence these new types came, and whether any of them arose by divergence from the previously-recorded types, the evidence docs not yet enable us to say. That in the course of long geologic epochs nearly all species, most genera, and a few orders, have become extinct; and that a species, genus, or order, which has once disappeared from the Earth never reappears. And, lastly, that the Fauna now occupying each separate area of the Earth's surface is very nearly allied to the Fauna which existed on that area during recent geologic times. § 108. Omitting sundry minor generalizations, the exposi tion of which would involve too much detail, what is to be said of these major generalizations ? The distribution in Space cannot be said to imply that or ganisms have been designed for their particular habitats and placed in them ; since, besides the habitat in which each kind of organism is found there are commonly other habitats, as good or better for it, from which it is absent — habitats to which it is so much better fitted than organisms now occupy ing them, that it extrudes these organisms when allowed the 412 THE INDUCTIONS OF BIOLOG¥. opportunity. Neither can we suppose that the purpose has been to establish varieties of Floras and Faunas; since, if so, why are the Floras and Faunas but little divergent in widely- sundered areas between which migration is possible, while they are markedly divergent in adjacent areas between which migration is impossible ? Passing to distributions in Time, there arise the questions — why during nearly the whole of that vast period geologically recorded have there existed none of those highest organic forms which have now overrun the Earth? — how is it that we find no traces of a creature endowed with large capacities for knowledge and happiness? The answer that the Earth was not, in remote times, a fit habitation for such a creature, besides being unwarranted by the evidence, suggests the equally awkward question — why during untold millions of years did the Earth remain fit only for inferior creatures ? What, again, is the meaning of extinction of types? To conclude that the saurian type was replaced by other types at the beginning of the tertiary period, because it was not adapted to the conditions which then arose, is to conclude that it could not be modified into fitness for the conditions; and this conclusion is at variance with the hypothesis that creative skill is shown in the multiform adaptations of one type to many ends. What interpretations may rationally be put on these and other general facts of distribution in Space and Time, will be seen in the next division of this work. PART III. THE EVOLUTION OF LIFE, CHAPTER I. PRELIMINARY. § 109. IN the foregoing Part, we have contemplated the most important of the generalizations to which biologists have been led by observation of organisms; as well as some others which contemplation of the facts has suggested to me. These Inductions of Biology have also been severally glanced at on their deductive sides; for the purpose of noting the harmony existing between them and those primordial truths set forth in First Principles. Having thus studied the lead ing phenomena of life separately, we arc prepared for study ing them as an aggregate, with the view of arriving at the most general interpretation of them. There is an ensemble of vital phenomena presented by each organism in the course of its growth, development, and decay ; and there is an ensemble of vital phenomena presented by the organic world as a whole. Neither of these can be properly dealt with apart from the other. But the last of them may be separately treated more conveniently than the first. What interpretation we put on the facts of structure and function in each living body, depends entirely on our conception of the mode in which living bodies in general have originated. To form some conclusion respecting this mode — a provisional if not a permanent conclusion — must therefore be our first step. We have to choose between two hypotheses — the hypo thesis of Special Creation and the hypothesis of Evolution. 415 416 TEE EVOLUTION OF LIFE. Either the multitudinous kinds of organisms which now exist, and the far more multitudinous kinds which have existed during past geologic eras, have been from time to time separ ately made; or they have arisen by insensible steps, through actions such as we see habitually going on. Both hypotheses imply a Cause. The last, certainly as much as the first, recognizes this Cause as inscrutable. The point at issue is, how this inscrutable Cause has worked in the production of living forms. This point, if it is to be decided at all, is to be decided only by examination of evidence. Let us inquire which of these antagonist hypotheses is most congruous with established facts. CHAPTER II. GENERAL ASPECTS OF THE SrECIAL-CREATION- HYPOTIIESIS.* § 110. EARLY ideas arc not usually true ideas. Unde veloped intellect, be it that of an individual or that of the race, forms conclusions which require to be revised and re- revised, before they reach a tolerable correspondence with realities. Were it otherwise there would be no discovery, no increase of intelligence. What we call the progress of knowledge, is the bringing of Thoughts into harmony with Things; and it implies that the first Thoughts are either wholly out of harmony with Things, or in very incomplete harmony with them. If illustrations be needed the history of every science furnishes them. The primitive notions of mankind as to the structure of the heavens were wrong; and the notions which replaced them were successively less wrong. The original belief respecting the form of the Earth was wrong; and this wrong belief survived through the first civilizations. The earliest ideas that have come down to us concerning the natures of the elements were wrong; and only in quite recent times has the composition of matter in its various forms been better understood. The interpretations of me chanical facts, of meteorological facts, of physiological facts, were at first wrong. In all these cases men set out with * Several of the arguments used in this chapter and in that which follows it, formed parts of un essay on "The Development Hypothesis," originally published in 1852. 417 418 THE EVOLUTION OF LIFE. beliefs which, if not absolutely false, contained but small amounts of truth disguised by immense amounts of error. Hence the hypothesis that living beings resulted from special creations, being a primitive hypothesis, is probably an untrue hypothesis. It would be strange if, while early men failed to reach the truth in so many cases where it is com paratively conspicuous, they reached it in a case where it is comparatively hidden. § 111. Besides the improbability given to the belief in special creations, by its association with mistaken beliefs in general, a further improbability is given to it by its associa tion with a special class of mistaken beliefs. It belongs to a family of beliefs which have one after another been destroyed by advancing knowledge; and is, indeed, almost the only member of the family surviving among educated people. We all know that the savage thinks of each striking phe nomenon, or group of phenomena, as caused by some separate personal agent; that out of this conception there grows up a polytheistic conception, in which these minor personalities arc variously generalized into deities presiding over different divisions of nature; and that these arc eventually further generalized. This progressive consolidation of causal agencies may be traced in the creeds of all races, and is far from complete in the creed of the most advanced races. The un lettered rustics who till our fields, do not let the conscious ness of a supreme power wholly absorb the aboriginal con ceptions of good and evil spirits, and of charms or secret potencies dwelling in particular objects. The earliest mode of thinking changes only as fast as the constant relations among phenomena are established. Scarcely less familiar is the truth, that while accumulating knowledge makes these conceptions of personal causal agents gradually more vague, as it merges them into general causes, it also destroys the habit of thinking of them as working after the methods of personal agents. We do not now, like Kepler, THE SPECIAL-CREATION-IIYPOTHESIS. 419 assume guiding spirits to keep the planets in their orbits. It is no longer the universal belief that the sea was once for all mechanically parted from the dry land; or that the mountains were placed where we see them by a sudden cre ative act. All but a narrow class have ceased to suppose sunshine and storm to be sent in some arbitrary succession. The majority of educated people have given up thinking of epidemics of punishments inflicted by an angry deity. Nor do even the common people regard a madman as one pos sessed by a demon. That is to say, we everywhere see fading away the anthropomorphic conception of Cause. In one case after another, is abandoned the ascription of phenomena to a will analogous to the human will, working by methods analogous to human methods. If, then, of this once-numerous family of beliefs the im mense majority have become extinct, we may not unrea sonably expect that the few remaining members of the family will become extinct. One of these is the belief we are here considering — the belief that each species of organism was specially created. Many who in all else have abandoned the aboriginal theory of things, still hold this remnant of the aboriginal theory. Ask any well-informed man whether he accepts the cosmogony of the Indians, or the Greeks, or the Hebrews, and he will regard the question as next to an insult. Yet one element common to these cosmogonies he very likely retains : not bearing in mind its origin. For whence did he get the doctrine of special creations ? Catechise him, and he is forced to confess that it was put into his mind in childhood, as one portion of a story which, as a whole, he has long since rejected. Why this fragment is likely to be right while all the rest is wrong, he is unable to say. May we not then expect that the relinquishment of all other parts of this story, will by and by be followed by the relinquish ment of this remaining part of it ? § 112. The belief which we find thus questionable, both 420 TIIE EVOLUTION OP LIFE. as being a primitive belief and as being a belief belonging to an almost-extinct family, is a belief not countenanced by a single fact. No one ever saw a special creation; no one ever found proof of an indirect kind that a special creation had taken place. It is significant, as Dr. Hooker remarks, that naturalists who suppose new species to be miraculously originated, habitually suppose the origination to occur in some region remote from human observation. Wherever the order of organic nature is exposed to the view of zoologists and botanists, it expels this conception; and the conception survives only in connexion with imagined places, where the order of organic nature is unknown. Besides being absolutely without evidence to give it exter nal support, this hypothesis of special creations cannot sup port itself internally — cannot be framed into a coherent thought. It is one of those illegitimate symbolic concep tions which are mistaken for legitimate symbolic concep tions (First Principles, § 9), because they remain untested. Immediately an attempt is made to elaborate the idea into anything like a definite shape, it proves to be a pseud-idea, admitting of no definite shape. Is it supposed that a new organism, when specially created, is created out of nothing? If so, there is a supposed creation of matter; and the crea tion of matter is inconceivable — implies the establishment of a relation in thought between nothing and something — a relation of which one term is absent — an impossible rela tion. Is it supposed that the matter of which the new or ganism consists is not created for the occasion, but is taken out of its pre-existing forms and arranged into a new form? If so, we are met by the question — how is the re-arrangement effected? Of the myriad atoms going to the composition of the new organism, all of them previously dispersed through the neighbouring air and earth, does each, suddenly disen gaging itself from its combinations, rush to meet the rest, unite with them into the appropriate chemical compounds, and then fall with certain others into its appointed place in THE SPECIAL-CREATION-IIYPOTIIESIS. 421 the aggregate of complex tissues and organs? Surely thus to assume a myriad supernatural impulses, differing in their directions and amounts, given to as many different atoms, is a multiplication of mysteries rather than the solution of a mystery. For every one of these impulses, not being the result of a force locally existing in some other form, implies the creation of force; and the creation of force is just as inconceivable as the creation of matter. It is thus with all attempted ways of representing the process. The old Hebrew idea that God takes clay and moulds a new creature, as a potter moulds a vessel, is probably too grossly an thropomorphic to be accepted by any modern defender of the special-creation doctrine. But having abandoned this crude belief, what belief is he prepared to substitute? If a new organism is not thus produced, then in what way is one produced? or rather — in what way does he conceive a new organism to be produced? We will not ask for the ascer tained mode, but will be content with a mode which can be consistently imagined. No such mode, however, is assign able. Those who entertain the proposition that each kind of organism results from a divine interposition, do so because they refrain from translating words into thoughts. They do not really believe, but rather believe they believe. For belief, properly so called, implies a mental representation of the thing believed, and no such mental representation is here possible. §113. If we imagine mankind to be contemplated by* some being as short-lived as an ephemeron, but possessing intelligence like our own — if we imagine such a being study ing men and women, during his few hours of life, and speculating as to the mode in which they came into existence ; it is manifest that, reasoning in the usual way, he would suppose each man and woman to have been separately created. No appreciable changes of structure occurring in any of them during the time over which his observa- 422 THE EVOLUTION OF LIFE. tions extended, this being would probably infer that no changes of structure were taking place, or had taken place; and that from the outset each man and woman had pos sessed all the characters then visible — had been originally formed with them. The application is obvious. A human life is ephemeral compared with the life of a species; and even the period over which the records of all human lives extend, is ephemeral compared with the life of a species. There is thus a parallel contrast between the im mensely-long series of changes which have occurred during the life of a species, and that small portion of the series open to our view. And there is no reason to suppose that the first conclusion drawn by mankind from this small part of the series visible to them, is any nearer the truth than would be the conclusion of the supposed ephemeral being respecting men and women. This analogy, suggesting as it does how the hypothesis of special creations is merely a formula for our ignorance, raises the question — What reason have we to assume special crea tions of species but not of individuals; unless it be that in the case of individuals we directly know the process to be otherwise, but in the case of species do not directly know it to be otherwise? Have we any ground for concluding that species were specially created, except the ground that we have no immediate knowledge of their origin? And does our ignorance of the manner in which they arose warrant us in asserting that they arose by special creation? Another question is suggested by this analogy. Those who, in the absence of immediate evidence of the way in which species arose, assert that they arose not in a natural way allied to that in which individuals arise, but in a super natural way, think that by this supposition they honour the Unknown Cause of things; and they oppose any antagonist doctrine as amounting to an exclusion of divine power from the world. But if divine power is demonstrated by the separate creation of each species, would it not have been still THE SPECIAL-CREATION-HYPOTHESIS. 423 better demonstrated by the separate creation of each indivi dual? Why should there exist this process of natural gene sis? Why should not omnipotence have been proved by the supernatural production of plants and animals everywhere throughout the world from hour to hour? Is it replied that the Creator was able to make individuals arise from one another in a natural succession, but not to make species thus arise? This is to assign a limit to power instead of magni fying it. Either it was possible or not possible to create species and individuals after the same general method. To say that it was not possible is suicidal in those who use this argument; and if it was possible, it is required to say what end is served by the special creation of species which would not have been better served by the special creation of individuals. Again, what is to be thought of the fact that the immense majority of these supposed special creations took place before mankind existed? Those who think that divine power is demonstrated by special creations, have to answer the question — to whom demonstrated? Tacitly or avowedly, they regard the demonstrations as being for the benefit of mankind. But if so, to what purpose were the millions of these demonstrations which took place on the Earth when there were no intelligent beings to contemplate them? Did the Unknowable thus demonstrate his power to himself ? Few will have the hardihood to say that any such demonstration was needful. There is no choice but to regard them, either as superfluous exercises of power, which is a derogatory supposition, or as exercises of power that were necessary because species could not be otherwise produced, which is also a derogatory supposition. § 113a. Other implications concerning the divine character must be recognized by those who contend that each species arose by divine fiat. It is hardly supposable that Infinite Power is exercised in trivial actions effecting trivial changes. Yet the organic world in its hundreds of thousands of species 4-24 THE EVOLUTION OP LIFE. shows in each sub-division multitudinous forms which, though unlike enough to be classed as specifically distinct, diverge from one another only in small details which have no signifi cance in relation to the life led. Sometimes the number of specific distinctions is so great that did they result from human agency we should call them whimsical. For example, in Lake Baikal are found 115 species of an amphipod, Gammarus; and the multiplicity becomes start ling on learning that this number exceeds the number of all other species of the genus : various as are the conditions to which, throughout the rest of the world, the genus is subject. Still stranger seems the superfluous exercise of power on examining the carpet of living forms at the bottom of the ocean. Not dwelling on the immense variety of creatures unlike in type which live miles below the surface in absolute darkness, it will suffice to instance the Polyzoa alone: low types of animals so small that a thousand of them would not cover a square inch, and on which, nevertheless, there has been, according to the view we are considering, an exercise of creative skill such that by small variations of structure more than 350 species have been produced ! Kindred illustrations are furnished by the fauna of caverns. Are we to suppose that numerous blind creatures — crusta ceans, myriapods, spiders, insects, fishes — were specially made sightless to fit them for the Mammoth Cave? Or what shall we say of th.9 Proteus, a low amphibian with rudimentary eyes, which inhabits certain caves in Carniola, Carinthia and Dalmatia and is not found elsewhere. Must we conclude that God went out of his way to devise an animal for these places ? More puzzling still is a problem presented to the special- creationist by a batrachian inhabiting Central Australia. In a region once peopled by numerous animals but now made unfit by continuous droughts, there exists a frog which, when the pools arc drying up, fills itself with water and burrowing in the mud hibernates until the next rains ; which may come in a year or may be delayed for two years. What is to be THE SPECIAL-CREATION-nYPOTTIESIS. 425 thought of this creature ? Were its structure and the accom panying instinct divinely planned to fit it to this particular habitat ? Many such questions might be asked which, if answered as the current theory necessitates, imply a divine nature hardly like that otherwise assumed. § 114. Those who espouse the aboriginal hypothesis en tangle themselves in yet other theological difficulties. This assumption that each kind of organism was specially de signed, carries with it the implication that the designer intended everything which results from the design. There is no escape from the admission that if organisms were severally constructed with a view to their respective ends, then the character of the constructor is indicated both by the ends themselves, and the perfection or imperfection with which the organisms are fitted to them. Observe the consequences. Without dwelling on the question recently raised, why during untold millions of years there existed on the Earth no beings endowed with capacities for wide thought and high feeling, we may content ourselves with asking why, at present, the Earth is largely peopled by creatures which inflict on one another so much suffering? Omitting the human race, whose defects and miseries the current theology professes to account for, and limiting ourselves to the lower creation, what must we think of the countless different pain- inflicting appliances and instincts with which animals are endowed? Not only now, and not only ever since men have lived, has the Earth been a scene of warfare among all sentient creatures; but palaeontology shows us that from the earliest eras geologically recorded, there has been going on this universal carnage. Fossil structures, in common with the structures of existing animals, show us elaborate weapons for destroying other animals. We have unmistakable proof that throughout all past time, there has been a ceaseless devouring of the weak by the strong. How is this to 426 . TIIE EVOLUTION OF LIFE. bo explained? How happens it that animals were so designed as to render this bloodshed necessary? How happens it that in almost every species the number of individuals annually born is such that the majority die by starvation or by violence before arriving at ma turity? Whoever contends that each kind of animal was specially designed, must assert either that there was a deli berate intention on the part of the Creator to produce these results, or that there was an inability to prevent them. Which alternative does he prefer? — to cast an imputation on the divine character or to assert a limitation of the divine power ? It is useless for him to plead that the destruction of the less powerful by the more powerful, is a means of pre venting the miseries of decrepitude and incapacity, and therefore works beneficently. For even were the chief mor tality among the aged instead of among the young, there would still arise the unanswerable question — why were not animals constructed in such ways as to avoid these evils? why were not their rates of multiplication, their degrees of intelligence, and their propensities, so adjusted that these sufferings might be escaped ? And if decline, of vigour was a necessary accompaniment of age, why was it not provided that the organic actions should end in sudden death, when ever they fell below the level required for pleasurable exist ence? Will any one who contends that organisms were specially designed, assert that they could not have been so designed as to prevent suffering? And if he admits that they could have been made so as to prevent suffering, will he assert that the Creator preferred making them in such ways as to inflict suffering ? Even as thus presented the difficulty is sufficiently great ; but it appears immensely greater when we examine the facts more closely. ' So long as we contemplate only the preying of the superior on the inferior, some good appears to be extracted from the evil — a certain amount of life of a higher order, is supported by sacrificing a great deal of life of a THE SPECIAL-CREATION-HYPOTIIESIS. 427 lower order. So long, too, as we leave out all mortality but that which, by carrying off the least perfect members of each species, leaves the most perfect members to survive and multiply; we see some compensating benefit reached through the suffering inflicted. But what shall we say on finding innumerable cases in which the suffering inflicted brings no compensating benefit? What shall we say when we see the inferior destroying the superior? What shall we say on finding elaborate appliances for furthering the multiplication of organisms incapable of feeling, at the expense of misery to organisms capable of happiness ? Of the animal kingdom as a whole, more than half the species are parasites. " The number of these parasites," says Prof. Owen, " may be conceived when it is stated that almost every known animal has its peculiar species, and generally more than one, sometimes as many as, or even more kinds than, infest the human body." This parasitism begins among the most minute creatures and pervades the entire animal kingdom from the lowest to the highest. Even Protozoa, made visible to us only by the microscope, are infested, as is Paramcecium by broods of Spli(Broplirya; while in large and complex animals parasites are everywhere present in great variety. More than this is true. There are para sites upon parasites — an arrangement such that those which are torturing the creatures they inhabit are themselves tor tured by indwelling creatures still smaller: looking like an ingenious accumulation of pains upon pains. But passing over the evils thus inflicted on animals of in ferior dignity, let us limit ourselves to the case of Man. The Bothriocephalus latus and the Ttjcnia solium, are two kinds of tape-worm, which flourish in the human intestines; produc ing great constitutional disturbances, sometimes Bending in insanity; and from the germs of the Tcctiia, when carried into other parts of the body, arise certain partially-developed forms known as Ci/sticerci, Echinococci, and Ccenuri, which cause disorganization more or less extensive in the brain, the 428 THE EVOLUTION OF LIFE. lungs, the liver, the heart, the eye, &c., often ending fatally after long-continued suffering. Five other parasites, belong ing to a different class, arc found in the viscera of man — the Trichoccplialus, the Oxyurls, the Stroncjylus (two species), the Ancylostomum and the Ascaris; which, beyond that defect of nutrition which they necessarily cause, sometimes induce certain irritations that lead to complete demoraliza tion. Of another class of cntozoa, belonging to the sub division Trematoda, there are five kinds found in different organs of the human body — the liver and gall-duct, the portal vein, the intestine, the bladder, the eye. Then we have the Trichina spiralis, which passes through one phase of its existence imbedded in the muscles and through another phase of its existence in the intestine; and which, by the induced disease Trichinosis, has lately committed such ra vages in Germany as to cause a panic. To these we must add the Guinea-worm, which in some part of Africa and India makes men miserable by burrowing in their legs; and the more terrible African parasite the Bilharzia, which affects 30 per cent, of the natives on the east coast with bleeding of the bladder. From entozoa, let us pass to epizoa. There are two kinds of Acari, one of them inhabiting the follicles of the skin and the other producing the itch. There are crea tures that bury themselves beneath the skin and lay their eggs there; and there are three species of lice which infest the surface of the body. Nor is this all. Besides animal parasites there are sundry vegetal parasites, which grow and multiply at our cost. The Sarcina vcntriculi inhabits the stomach, and produces gastric disturbance. The Leptothrix luccalis is extremely general in the mouth, and may have something to do with the decay of teeth. And besides these there are jnicroscopic fungi which produce ringworm, porrigo, pityriasis, thrush, £c. Thus the human body is the habitat of parasites, internal and external, animal and ve getal, numbering, if all are set down, between two and three dozen species; sundry of which are peculiar to Man, and THE SPECIAL-CREATION-HYPOTIIESIS. 429 many of which produce great suffering and not unfrequently death. What interpretation is to be put on these facts by those who espouse the hypothesis of special creations? Ac cording to this hypothesis, all these parasites were designed for their respective modes of life. They were endowed with constitutions fitting them to live by absorbing nutriment from the human body; they were furnished with appliances, often of a formidable kind, enabling them to root themselves in and upon the human body; and they were made prolific in an almost incredible degree, that their germs might have a sufficient number of chances of finding their way into the human body. In short, elaborate contrivances were com bined to insure the continuance of their respective races; and to make it impossible for the successive generations of men to avoid being preyed on by them. What shall we say to this arrangement ? Shall we say that " the head and crown of things," was provided as a habitat for these para sites? Shall we say that these degraded creatures, incapable of thought or enjoyment, were created that they might cause human misery? One or other of these alternatives must be chosen by those who contend that every kind of organism was separately devised by the Creator. Which do they prefer? With the conception of two antagonist powers, which severally work good and evil in the world, the facts are congruous enough. But with the conception of a supreme beneficence, this gratuitous infliction of pain is absolutely incompatible. § 115. Sec then the results of our examination. The belief in special creations of organisms arose among men during the era of profoundest darkness ; and it belongs to a family of beliefs which have nearly all died out as enlighten ment has increased. It is without a solitary established fact on which to stand ; and when the attempt is made to put it into definite shape in the mind, it turns out to be only a pseud-idea. This mere verbal hypothesis, which men idly 430 THE EVOLUTION OF LIFE. accept as a real or thinkable hypothesis, is of the same nature as would he one, based on a day's observation of human life, that each man and woman was specially created • — an hypothesis not suggested by evidence but by lack of evidence — an hypothesis which formulates ignorance into a semblance of knowledge. Further, we see that this hypo thesis, failing to satisfy men's intellectual need of an inter pretation, fails also to satisfy their moral sentiment. It is quite inconsistent with those conceptions of the divine nature which they profess to entertain. If infinite power was to be demonstrated, then, either by the special creation of every individual, or by the production of species by some method of natural genesis, it would be better demonstrated than by the use of two methods, as assumed by the hypothesis. And if infinite goodness was to be demonstrated, then, not only do the provisions of organic structure, if they are specially devised, fail to demonstrate it, but there is an enormous mass of them which imply malevolence rather than bene volence. Thus the hypothesis of special creations turns out to be worthless by its derivation; worthless in its intrinsic in coherence; worthless as absolutely without evidence; worth less as not supplying an intellectual need; worthless as not satisfying a moral want. We must therefore consider it as counting for nothing, in opposition to any other hypothesis respecting the origin of organic beings. CHAPTER III. GENERAL ASPECTS OF THE EVOLUTION-HYPOTHESIS. § 116. JUST as the supposition that races of organisms have been specially created, is discredited by its origin; so, conversely, the supposition that races of organisms have been evolved, is credited by its origin. Instead of being a conception suggested and accepted when mankind were profoundly ignorant, it is a conception born in times of com parative enlightenment. Moreover, the belief that plants and animals have arisen in pursuance of uniform laws, instead of through breaches of uniform laws, is a belief which has come into existence in the most-instructed class, living in these better-instructed times. Not among those who have disregarded the order of Nature, has this idea made its appearance; but among those who have familiarized them selves with the order of Nature. Thus the derivation of this modern hypothesis is as favourable as that of the ancient hypothesis is unfavourable. § 117. A kindred antithesis exists between the two fami lies of beliefs, to which the beliefs we are comparing severally belong. While the one family has been dying out the other family has been multiplying. As fast as men have ceased to regard different classes of phenomena as caused by special personal agents, acting irregularly; so fast have they come to regard these different classes of phenomena as caused by a general agency acting uniformly — the two changes being 431 432 THE EVOLUTION OF LIFE. correlatives. And as, on the one hand, the hypothesis that each species resulted from a supernatural act, having lost nearly all its kindred hypotheses, may be expected soon to die; so, on the other hand, the hypothesis that each species resulted from the action of natural causes, being one of an increasing family of hypotheses, may be expected to survive. Still greater will the probability of its survival and estab lishment appear, when we observe that it is one of a particular genus of hypotheses which has been rapidly ex tending. The interpretation of phenomena as results of Evolution, has been independently showing itself in various fields of inquiry, quite remote from one another. The sup position that the Solar System has been evolved out of dif fused matter, is a supposition wholly astronomical in its origin and application. Geologists, without being led thereto by astronomical considerations, have been step by step ad vancing towards the conviction that the Earth has reached its present varied structure by modification upon modifica tion. The inquiries of biologists have proved the falsity of the once general belief, that the germ of each organism is a minute repetition of the mature organism, differing from it only in bulk; and they have shown, contrariwise, that every organism advances from simplicity to complexity through insensible changes. Among philosophical politicians, there has been spreading the perception that the progress of society is an evolution: the truth that "constitutions arc not made but grow," is seen to be a part of the more general truth that societies are not made but grow. It is now universally admitted by philologists that languages, instead of being arti ficially or supernaturally formed, have been developed. And the histories of religion, of science, of the fine arts, of the industrial arts, show that these have passed through stages as unobtrusive as those through which the mind of a child passes on its way to maturity. If, then, the recognition of evolution as the law of many diverse orders of phenomena, has been spreading; may we not say that there thence arises TUE EVOLUTION-HYPOTHESIS. 433 the probability that evolution will presently be recognized as the law of the phenomena we are considering? Each further advance of knowledge confirms the belief in the unity of Nature; and the discovery that evolution has gone on, or is going on, in so many departments of Nature, becomes a reason for believing that there is no department of Nature in which it does not go on. § 118. The hypotheses of Special Creation and Evolution, are no less contrasted in respect of their legitimacy as hy potheses. While, as we have seen, the one belongs to that order of symbolic conceptions which are proved to be illusive by the impossibility of realizing them in thought; the other is one of those symbolic conceptions which are more or less fully realizable in thought. The production of all organic forms by the accumulation of modifications and of diver gences by the continual addition of differences to differences, is mentally representable in outline, if not in detail. Various orders of our experiences enable us to conceive the process. Let us look at one of the simplest. There is no apparent similarity between a straight line and a circle. The one is a curve; the other is defined as without curvature. The one encloses a space; the other will not enclose a space though produced for ever. The one is finite ; the other may be infinite. Yet, opposite as the two are in their characters, they may be connected together by a series of lines no one of which differs from the adjacent ones in any appreciable degree. Thus, if a cone be cut by a plane at right angles to its axis we get a circle. If, instead of being perfectly at right angles, the plane subtends with the axis an angle of 89° 59', we have an ellipse which no human eye, even when aided by an accurate pair of compasses, can distinguish from a circle. Decreasing the angle minute by minute, this closed curve becomes perceptibly eccentric, then manifestly so, and by and by acquires so immensely elongated a form so as to bear no recognizable resemblance to a circle. 434 THE EVOLUTION OF LIFE. By continuing this process the ellipse changes insensibly into a parabola. On still further diminishing the angle, the para bola becomes an hyperbola. And finally, if the cone be made gradually more obtuse, the hyperbola passes into a straight line as the angle of the cone approaches 180°. Here then we have five different species of line — circle, ellipse, parabola, hyperbola, and straight line — each having its pecu liar properties and its separate equation, and the first and last of which are quite opposite in nature, connected together as members of one scries, all producible by a single process of insensible modification. But the experiences which most clearly illustrate the pro cess of general evolution, are our experiences of special evolution, repeated in every plant and animal. Each organ ism exhibits, within a short time, a series of changes which, when supposed to occupy a period indefinitely great, and to go on in various ways instead of one way, give us a tolerably clear conception of organic evolution at large. In an indi vidual development, we see brought into a comparatively infinitesimal time, a scries of metamorphoses equally great with each of those which the hypothesis of evolution assumes to have taken place during immeasurable geologic epochs. A tree differs from a seed in every respect — in bulk, in struc ture, in colour, in form, in chemical composition. Yet is the one changed in the course of a few years into the other: changed so gradually, that at no moment can it be said — Now the seed ceases to be and the tree exists. What can be more widely contrasted than a newly-born child and the small, semi-transparent, gelatinous spherule constituting the human ovum? The infant is so complex in structure that a cyclopaedia is needed to describe its constituent parts. The germinal vesicle is so simple that it may be defined in a line. Nevertheless, nine months suffice to develop the one out of the other; and that, too, by a series of modifications so small, that were the embryo examined at successive minutes, even a microscope would not disclose any sensible changes. TIIE EVOLTJTION-IIYrOTnESTS. 435 Aided by such facts, the conception of general evolution may be rendered as definite a conception as any of our complex conceptions can be rendered. If, instead of the successive minutes of a child's foetal life, we take the lives of successive generations of creatures — if we regard the successive genera tions as differing from one another no more than the foetus differs in successive minutes; our imaginations must indeed be feeble if we fail to realize in thought, the evolution of the most complex organism out of the simplest. If a single cell, under appropriate conditions, becomes a man in the space of a few years ; there can surely be no difficulty in understanding how, under appropriate conditions, a cell may, in the course of untold millions of years, give origin to the human race. Doubtless many minds are so unfurnished with those ex periences of Nature out of which this conception is built, that they find difficulty in forming it. Looking at things rather in their statical than in their dynamical aspects, they never realize the fact that, by small increments of modifica tion, any amount of modification may in time be generated. The surprise they feel on finding one whom they last saw as a boy, grown into a man, becomes incredulity when the degree of change is greater. To such, the hypothesis that by any series of changes a protozoon can give origin to a mam mal, seems grotesque — as grotesque as Galileo's assertion of the Earth's movement seemed to his persecutors; or as grotesque as the assertion of the Earth's sphericity seems now to the New Zealanders. But those who accept a literally- unthinkable proposition as quite satisfactory, may not un naturally be expected to make a converse mistake. § 119. The hypothesis of evolution is contrasted with the hypothesis of special creations, in a further respect. It is not simply legitimate instead of illegitimate, because repre- sentable in thought instead of unrepresentable; but it has the support of some evidence, instead of being absolutely un supported by evidence. Though the facts at present assign- 436 THE EVOLUTION OF LIFE. able in direct proof that by progressive modifications, races of organisms which are apparently distinct from antecedent races have descended from them, are not sufficient ; yet there are numerous facts of the order required. Beyond all ques tion unlikenesses of structure gradually arise among the members of successive generations. We find that there is going on a modifying process of the kind alleged as the source of specific differences : a process which, though slow, does, in time, produce conspicuous changes — a process which, to all appearance, would produce in millions of years, any amount of change. In the chapters on "Heredity" and "Variation," contained in the preceding Part, many such facts were given, and more might be added. Although little attention has been paid to the matter until recent times, the evidence already collected shows that there take place in successive generations, altera tions of structure quite as marked as those which, in succes sive short intervals, arise in a developing embryo — nay, often much more marked; since, besides differences due to changes in the relative sizes or parts, there sometimes arise differ ences due to additions and suppressions of parts. The struc tural modification proved to have taken place since organisms have been observed, is not less than the hypothesis demands — bears as great a ratio to this brief period, as the total amount of structural change seen in the evolution of a com plex organism out of a simple germ, bears to that vast period during which living forms have existed on the Earth. We have, indeed, much the same kind and quantity of direct evidence that all organic beings have arisen through the actions of natural causes, which we have that all the structural complexities of the Earth's crust have arisen through the actions of natural causes. Between the known modifications undergone by organisms, and the totality of modifications displayed in their structures, there is no greater disproportion than between the observed geological changes, and the totality of geological changes supposed to have been THE EVOLUTION-HYPOTHESIS. 4P>? similarly caused. Here and there are sedimentary deposits now slowly taking place. At this place a shore has been greatly encroached on by the sea during recorded times; and at another place an estuary has become shallower within some generations. In one region an upheaval is going on at the rate of a few feet in a century; while in another region occasional earthquakes cause slight variations of level. Ap preciable amounts of denudation by water are visible in some localities; and in other localities glaciers arc detected in the act of grinding down the rocky surfaces over which they glide. But these changes arc infinitesimal compared with the aggregate of changes to which the Earth's crust testifies, even in its still extant systems of strata. If, then, the small changes now being wrought on the Earth's crust by natural agencies, yield warrant for concluding that by such agencies acting through vast epochs, all the structural complexities of the Earth's crust have been produced; do not the small known modifications produced in races of organisms by natu ral agencies, yield warrant for concluding that by natural agencies have been produced all those structural complexities which we see in them ? The hypothesis of Evolution then, has direct support from facts which, though small in amount, arc of the kind required ; and the ratio which these facts bear to the generalisation based on them, seems as great as is the ratio between facts and generalization which, in another case, produces conviction. § 120. Let us put ourselves for a moment in the position of those who, from their experiences of human modes of action, draw differences respecting the mode of action of that Ulti mate Power manifested to us through phenomena. We shall find the supposition that each kind of organism was separately designed and put together, to be much less consistent witli their professed conception of this Ultimate Power, than is the supposition that all kinds of organisms have resulted from one unbroken process. Irregularity of method is a mark of 438 THE EVOLUTION OF LIFE. weakness. Uniformity of method is a mark of strength. Con tinual interposition to alter a pre-arranged set of actions, implies defective arrangement in those actions. The main tenance of those actions, and the working out by them of the highest results, implies completeness of arrangement. If human workmen, whose machines as at first constructed re quire perpetual adjustment, show their increasing skill by making their machines self-adjusting ; then, those who figure to themselves the production of the world and its inhabitants by a " Great Artificer," must admit that the achievement of this end by a persistent process, adapted to all contingencies, implies greater skill than its achievement by the process of meeting the contingencies as they severally arise. So, too, it is with the contrast under its moral aspect. We saw that to the hypothesis of special creations, a difficulty is presented by the absence of high forms of life during im measurable epochs of the Earth's existence. But to the hypothesis of evolution, absence of them is no such obstacle. Suppose evolution, and this question is necessarily excluded. Suppose special creations, and this question can have no satisfactory answer. Still more marked is the con trast between the two hypotheses, in presence of that vast amount of suffering entailed on all orders of sentient beings by thoir imperfect adaptations to their conditions of life, and the further vast amount of suffering entailed on them by enemies and by parasites. We saw that if organisms were severally designed for their respective places in Nature, the inevitable conclusion is that these innumerable kinds of in ferior organisms which prey on superior organisms, were in tended to inflict all the pain and mortality which results. But the hypothesis of evolution involves us in no such dilemma. Slowly, but surely, evolution brings about an in creasing amount of happiness. In all forms of organization there is a progressive adaptation, and a survival of the most adapted. If, in the uniform working out of the process, there are evolved organisms of low types which prey on THE EVOLUTION-HYPOTHESIS. 439 those of higher types, the evils inflicted form but a deduction from the average benefits. The universal multiplication of the most adapted must cause the spread of those superior organisms which, in one way or other, escape the invasions of the inferior; and so tends to produce a type less liable to the invasions of the inferior. Thus the evils accompanying evolution arc ever being self-eliminated. Though there may arise the question — Why could they not have been avoided? there docs not arise the question — Why were they deliber ately inflicted? Whatever may be thought of them, it is clear that they do not imply gratuitous malevolence. § 121. In all respects, then, the hypothesis of evolution contrasts favourably with the hypothesis of special creation. It has arisen in comparatively-instructed times and in the most cultivated class. It is one of those beliefs in the uni form concurrence of phenomena, which are gradually sup planting beliefs in their irregular and arbitrary concurrence; and it belongs to a genus of these beliefs which has of late been rapidly spreading. It is a definitely-conceivable hypo thesis; being simply an extension to the organic world at large, of a conception framed from our experiences of indi vidual organisms; just as the hypothesis of universal gravi tation was an extension of the conception which our experi ences of terrestrial gravitation had produced. This definitely- conceivable hypothesis, besides the support of numerous analogies, has the support of direct evidence. We have proof that there is going on a process of the kind alleged; and though the results of this process, as actually witnessed, are minute in comparison with the totality of results ascribed to it, yet they bear to such totality a ratio as great as that by which an analogous hypothesis is justified. Lastly, that sentiment which the doctrine of special creations is thought necessary to satisfy, is much better satisfied by the doctrine of evolution; since this doctrine raises no contradictory impli- 440 THE EVOLUTION OF LIFE. cations respecting the Unknown Cause, such as are raised by the antagonist doctrine. And now, having observed how, under its most general aspects, the hypothesis of organic evolution commends itself to us by its derivation, by its coherence, by its analogies, by its direct evidence, by its implications; let us go on to con sider the several orders of facts which yield indirect support to it. We will begin by noting the harmonies between it and sundry of the inductions set forth in Part II. CHAPTER IV. THE ARGUMENTS FROM CLASSIFICATION". § 122. IN § 103, we saw that the relations which exist among the species, genera, orders, and classes of organisms, are not interpretable as results of any such causes as have usually been assigned. We will here consider whether they are interpretable as the results of evolution. Let us first con template some familiar facts. The Norwegians, Swedes, Danes, Germans, Dutch, and Anglo-Saxons, form together a group of Scandinavian races, which are but slightly divergent in their characters. Welsh, Irish, and Highlanders, though they have differences, have not such differences as hide a decided community of nature: they are classed together as Celts. Between the Scandi navian race as a whole and the Celtic race as a whole, there is a distinction greater than that between the sub-divisions which make up the one or the other. Similarly, the several peoples inhabiting Southern Europe are more nearly allied to one another, than the aggregate they form is allied to the aggregates of Northern peoples. If, again, we compare these European varieties of Man, taken as a group, with that group of Eastern varieties which had a common origin with it, we see a stronger contrast than between the groups of Euro pean varieties themselves. And once more, ethnologists find differences of still higher importance between the Aryan stock as a whole and the Mongolian stock as a whole, or the 441 442 TnE EVOLUTION OF LIFE. Negro stock as a whole. Though these contrasts are partially obscured by intermixtures, they are not so much obscured as to hide the truths that the most-nearly-allied varieties of Man are those which diverged from one another at com paratively-recent periods; that each group of nearly-allied varieties is more strongly contrasted with other such groups that had a common origin Avith it at a remoter period; and so on until we come to the largest groups, which are the most strongly contrasted, and of whose divergence no trace is extant. The relations existing among the classes and sub-classes of languages, have been briefly referred to by Mr. Darwin in illustration of his argument. We know that languages have arisen by evolution. Let us then see what grouping of them evolution has produced. On comparing the dialects of adja cent counties in England, we find that their differences are so small as scarcely to distinguish them. Between the dialects of the Northern counties taken together, and those of the Southern counties taken together, the contrast is stronger. These clusters of dialects, together with those of Scotland and Ireland, are nevertheless so similar that we regard them as one language. The several languages of Scandinavian Europe, including English, are much more unlike one another than are the several dialects which each of them includes; in cor respondence with the fact that they diverged from one another at earlier periods than did their respective dialects. The Scandinavian languages have nevertheless a certain com munity of character, distinguishing them as a group from the languages of Southern Europe; between which there are general and special affinities that similarly unite them into a group formed of sub-groups containing sub-sub-groups. And this wider divergence between the order of languages spoken in Northern Europe and the order of languages spoken in Southern Europe, answers to the longer time that has elapsed since their differentiation commenced. Further, these two orders of modern European languages, as well as Latin and THE ARGUMENTS FROM CLASSIFICATION. 443 Greek and certain extinct and spoken languages of the East, are shown to have traits in common which unite them into one great class known as Aryan languages; radically dis tinguished from the classes of languages spoken by the other main divisions of the human race. § 123. Now this kind of subordination of groups which we see arises in the course of continuous descent, multiplication, and divergence, is just the kind of subordination of groups which plants and animals exhibit : it is just the kind of subordination which has thrust itself on the attention of naturalists in spite of pre-conceptions. The original idea was that of arrangement in linear order. We saw that even after a considerable acquaintance with the structures of organisms had been acquired, naturalists con tinued their efforts to reconcile the facts with the notion of a uni-serial succession. The accumulation of evidence necessi tated the breaking up of the imagined chain into groups and sub-groups. Gradually there arose the conviction that these groups do not admit of being placed in a line. And the con ception finally arrived at, is that of certain great sub-king doms, very widely divergent, each made up of classes much less divergent, severally containing orders still less divergent ; and so on with genera and species. Hence this " grand fact in natural history of the subordi nation of group under group, which from its familiarity does not always sufficiently strike us," is perfectly in harmony with the hypothesis of evolution. The extreme significance of this kind of relation among organic forms is dwelt on by Mr. Darwin, who shows how an ordinary genealogical tree represents, on a small scale, a system of grouping analogous to that which exists among organisms in general, and which is explained on the supposition of a genealogical tree by which all organisms are affiliated. If, wherever we can trace direct descent, multiplication, and divergence, this formation of groups within groups takes place; there results a strong pre- 444: THE EVOLUTION OF LIFE. sumption that the groups within groups which constitute the animal and vegetal kingdoms, have arisen by direct descent, multiplication, and divergence — that is, by evolution. § 124. Strong confirmation of this inference is yielded by the fact, that the more marked differences which divide groups are, in both cases, distinguished from the less marked differences which divide sub-groups, by this, that they are not simply greater in degree, but they are more radical in kind. Objects, as the stars, may present themselves in small clusters, which are again more or less aggravated into clusters of clusters, in such manner that the individuals of each simple cluster are much closer together than are the simple clusters gathered into a compound cluster : in which case, the trait that unites groups of groups differs from the trait that unites groups, not in nature but only in amount. But this is not so either with the groups and sub-groups which we know have resulted from evolution, or with those which we here infer have resulted from evolution. In both cases the highest or most general classes, are marked off from one another by fundamental differences that have no common measure with the differences that mark off small classes. Observe the parallelism. We saw that each sub-kingdom of animals is distinguished from other sub-kingdoms, by some unlikeness in its main plan of organization; such as the presence or absence of a peri-visceral cavity. Contrariwise, the members of the smallest groups are united together, and separated from the members of other small groups, by modifications which do not affect the relations of essential parts. That this is just the kind of arrangement which results from evolution, the case of languages will show. On comparing the dialects spoken in different parts of England, we find scarcely any difference but those of pro nunciation: the structures of the sentences are almost uni form. Between English and the allied modern languages THE ARGUMENTS FROM CLASSIFICATION. 445 there are divergences of structure : there are some unlike- nesses of idiom; some unlikenesses in the ways of modifying the meanings of verbs; and considerable unlikenesses in the uses of genders. But these unlikenesses are not sufficient to hide a general community of organization. A greater con trast of structure exists between these modern languages of Western Europe, and the classic languages. Differentiation into abstract and concrete elements, which is shown by the substitution of auxiliary words for inflections, has produced a higher specialization, distinguishing these languages as a group from the older languages. Nevertheless, both the ancient and modern languages of Europe, together with some Eastern languages derived from the same original, have, under all their differences of organization, a fundamental like ness; since in all of them words are formed by such a coal escence and integration of roots as destroys the independent meanings of the roots. These Aryan languages, and others which have the amalgamate character, are united by it into a class distinguished from the aptotic and agglutinate lan guages ; in which the roots are either not united at all, or so incompletely united that one of them still retains its inde pendent meaning. And philologists find that these radical traits which severally determine the grammatical forms, or modes of combining ideas, characterize the primary divisions among languages. So that among languages, where we know that evolution has been going on, the greatest groups are marked off from one another by the strongest structural contrasts ; and as the like holds among groups of organisms, there results a further reason for inferring that these have been evolved. § 125. There is yet another parallelism of like meaning. We saw (§ 101) that the successively-subordinate groups — classes, orders, genera, and species — into which zoologists and botanists segregate animals and plants, have not, in reality, those definite values conventionally given to them. There 446 THE EVOLUTION OF LIFE. arc well-marked species, and species so imperfectly marked that some systematists regard them as varieties. Between genera strong contrasts exist in many cases, and in other cases contrasts so much less decided as to leave it doubt ful whether they imply generic distinctions. So, too, is it with orders and classes: in some of which there have been introduced sub-divisions, having no equivalents in others. Even of the sub-kingdoms the same truth holds. The con trast between the Ccelenterata and the Mollusca, is far less than that between the Ccelenterata and the Vertebrata. Now just this same indefiniteness of value, or incomplete ness of equivalence, is observable in those simple and com pound and re-compound groups which we see arising by evolution. In every case the endeavour to arrange the divergent products of evolution, is met by a difficulty like that which would meet the endeavour to classify the branches of a tree, into branches of the first, second, third, fourth, &c., orders — the difficulty, namely, that branches of intermediate degrees of composition exist. The illustration furnished by languages will serve us once more. Some dialects of English are but little contrasted ; others are strongly contrasted. The alliances of the several Scandinavian tongues with one another are different in degree. Dutch is much less distinct from German than Swedish is; while between Danish and Swedish there is so close a kinship that they might almost be regarded as widely-divergent dialects. Similarly on com paring the larger divisions, we sec that the various languages of the Aryan stock have deviated from their original to very unlike distances. The general conclusion is manifest. While the kinds of human speech fall into groups, and sub-groups, and sub-sub-groups; yet the groups are not equal to one another in value, nor have the sub-groups equal values, nor the sub-sub-groups. If, then, when classified, organisms fall into assemblages such that those of the same grade are but indefinitely equiva lent ; and if, where evolution is known to have taken place, THE ARGUMENTS FROM CLASSIFICATION. 447 there have arisen assemblages between which the equivalence is similarly indefinite; there is additional reason for in ferring that organisms are products of evolution. § 126. A fact of much significance remains. If groups of organic forms have arisen by divergence and re-divergence; and if, while the groups have been developing from simple groups into compound groups, each group and sub-group has been giving origin to more complex forms of its own type; then it is inferable that there once existed greater structural likenesses between the members of allied groups than exists now. This, speaking generally, proves to be so. Between the sub-kingdoms the gaps are extremely wide; but such distant kinships as may be discerned, bear out anti cipation. Thus in the formation of the germinal layers there is a general agreement among them; and there is a further agreement among sundry of them in the formation of a gastrula. This simplest and earliest likeness, significant of primitive kinship, is in most cases soon obscured by divergent modes of development; but sundry sub-kingdoms continue to show relationships by the likenesses of their larval forms; as we see in the trochophores of the Polyzoa, Annelida, and Mollusca — sub-kingdoms the members of which by their later structural changes are rendered widely unlike. More decided approximations exist between the lower members of classes. In tracing down the Crustacea and the Aracknida from their more complex to their simpler forms, zoologists meet with difficulties: respecting some of these simpler forms, it becomes a question which class they belong to. The Lepidosircn, about which there have been disputes whether it is a fish or an amphibian, is inferior, in the organi zation of its skeleton, to the great majority of both fishes and amphibia. Widely as they differ from them, the lower mam mals have some characters in common with birds, which the higher mammals do not possess. Now since this kind of relationship of groups is not ac- 448 TI1E EVOLUTION OF LIFE. counted for by any other hypothesis, while the hypothesis of evolution gives us a clue to it; we must include it among the supports of this hypothesis which the facts of classifica tion furnish. § 127. What shall we say of these leading truths when taken together? That naturalists have been gradually com pelled to arrange organisms in groups within groups, and that this is the arrangement which we see arises by descent, alike in individual families and among races of men, is a striking circumstance. That while the smallest groups are the most nearly related, there exist between the great sub-kingdoms, structural contrasts of the profoundest kind, cannot but im press us as remarkable, when we see that where it is known to take place evolution actually produces these feebly-distin guished small groups, and these strongly-distinguished great groups. The impression made by these two parallelisms, which add meaning to each other, is deepened by the third parallel ism, which enforces the meaning of both — the parallelism, namely, that as, between the species, genera, orders, classes, &c., which naturalists have formed, there are transitional types ; so between the groups, sub-groups, and sub-sub-groups, which we know to have been evolved, types of intermediate values exist. And these three correspondences between the known results of evolution and the results here ascribed to evolution, have further weight given to them by the fact, that the kinship of groups through their lowest members is just the kinship which the hypothesis of evolution implies. Even in the absence of these specific agreements, the broad fact of unity amid multiformity, which organisms so strik ingly display, is strongly suggestive of evolution. Freeing ourselves from pre-conceptions, we shall see good reason to think with Mr. Darwin, " that propinquity of descent — the only known cause of the similarity of organic beings — is the bond, hidden as it is by various degrees of modification, which is partly revealed to us by our classifications." When THE ARGUMENTS FROM CLASSIFICATION. 449 we consider that this only known cause of similarity, joined with the only known cause of divergence (the influence of conditions), gives us a key to these likenesses obscured by unlikenesses ; we shall see that were there none of those remarkable harmonies above pointed out, the truths of classi fication would still yield strong support to our conclusion. CHAPTER V. THE ARGUMENTS FROM EMBRYOLOGY. § 127a. ALREADY I have emphasized the truth that Nature is always more complex than we suppose (§ 74a) — that there are complexities within complexities. Here we find illus trated this truth under another aspect. When seeking to formulate the arguments from Embryology, we are shown that the facts as presented in Nature are not to he expressed in the simple generalizations we at first make. While we recognize this truth we must also recognize the truth that only by enunciation and acceptance of imperfect generalizations can we progress to perfect ones. The order of Evolution is conformed to by ideas as by other things. The advance is, and must be, from the indefinite to £he definite. It is impossible to express the totality of any natural pheno menon in a single proposition. To the primary statement expressing that which is most dominant have to be added secondary statements qualifying it. We see this even in so simple a case as the flight of a projectile. The young artillery officer is first taught that a cannon-shot describes a curve treated as a parabola, though literally part of an extremely eccentric ellipse not distinguishable from a parabola. Pre sently he learns that atmospheric resistance, causing a con tinual decrease of velocity, entails a deviation from that theoretical path which is calculated on the supposition that the velocity is uniform; and this incorrectness he has to 450 THE ARGUMENTS FROM EMBRYOLOGY. 451 allow for. Then, further, there comes the lateral deviation due to wind, which may be appreciable if the wind is strong and the range great. To introduce him all at once to the correct conception thus finally reached would be impossible : it has to be reached through successive qualifications. And that which holds even in this simple case necessarily holds more conspicuously in complex cases. The title of the chapter suggests a metaphor, which is, indeed^ something more than a metaphor. There is an em bryology of conceptions. That this statement is not wholly a figure of speech, we shall see on considering that cerebral organization is a part of organization at large; and that the evolving nervous plexus which is the correlative of an evolv ing conception, must conform to the general law of change conformed to in the evolution of the whole nervous structure as well as in the evolution of the whole bodily structure. As the body has at first a rude form, very remotely suggesting that which is presently developed by the superposing of modi fications on modifications; so the brain as a whole and its con tained ideas together make up an inner world answering with extreme indefiniteness to that outer world to which it is brought by successive approximations into tolerable corre spondence ; and so any nervous plexus and its associated hypo thesis, which refer to some external group of phenomena under investigation, have to reach their final developments by successive corrections. This being the course of discovery must also be the course of exposition. In pursuance of this course we may there fore fitly contemplate that early formula of embryological development which we owe to von Bacr. § 128. Already in § 52, where the generalization of von Baer respecting the relations of embryos was set forth, there was given the warning, above repeated with greater distinct ness, that it is only an adumbration. In the words of his translator, he "found that in its earliest 452 THE EVOLUTION OP LIFE. stage, every organism has the greatest number of characters in common with all other organisms in their earliest stages; that at a stage somewhat later, its structure is like the struc tures displayed at corresponding phases by a less extensive multitude of organisms; that at each subsequent stage, traits are acquired which successively distinguished the de veloping embryo from groups of embryos that it previously resembled — thus step by step diminishing the class of embryos which it still resembles; and that thus the class of similar forms is finally narrowed to the species of which it is a member." Assuming for a moment that this generalization is true as it stands, or rather, assuming that the qualifications needed are not such as destroy its correspondence with the average facts, we shall see that it has profound significance. For if we follow out in thought the implications — if we conceive the germs of all kinds of organisms simultaneously develop ing, and imagine that after taking their first step together, at the second step one half of the vast multitude diverges from the other half; if, at the next step, we mentally watch the parts of each great assemblage beginning to take two or more routes of development; if we represent to ourselves such bifurcations going on, stage after stage, in all the branches; we shall see that there must result an aggregate analogous, in its arrangement of parts, to a tree. If this vast genealogical tree be contemplated as a Whole, made up of trunk, main branches, secondary branches, and so on as far as the terminal twigs; it will be perceived that all the various kinds of organisms represented by these terminal twigs, forming the periphery of the tree, will stand related to one another in small groups, which are united into groups of groups, and so on. The embryological tree, expressing the developmental relations of organisms, will be similar to the tree which symbolizes their classificatory relations. That subordination of classes, orders, genera, and species, to which naturalists have been gradually led, is just that subordination THE ARGUMENTS PROM EMBRYOLOGY. 453 which results from the divergence and re-divergence of embryos, as they all unfold. On the hypothesis of evolution this parallelism has a meaning — indicates that primordial kinship of all organisms, and that progressive differentiation of them, which the hypothesis alleges. But on any other hypothesis the parallelism is meaningless ; or rather, it raises a difficulty; since it implies either an effect without a cause or a design without a purpose. § 129. This conception of a tree, symbolizing the relation ships of types and a species derived from the same root, has a concomitant conception. The implication is that each organism, setting out from the simple nucleated cell, must in the course of its development follow the line of the trunk, some main branch, some sub-branch, some sub-sub-branch, &c., of this embryological tree; and so on till it reaches that ultimate twig representing the species of which it is a member. It must in a general way go through the particular line of forms which preceded it in all past times : there must be what has been aptly called a " recapitulation " of the suc cessive ancestral structures. This, at least, is the conclusion necessitated by the generalization we arc considering under its original crude form. Von Baer lived in the days when the Development Hypo thesis was mentioned only to be ridiculed, and he joined in the ridicule. What he conceived to be the meaning of these groupings of organisms and these relations among their embryological histories, is not obvious. The only alternative to the hypothesis of Evolution is the hypothesis of Special Creation ; and as he did not accept the one it is inferable that he accepted the other. But if he did this he must in the first place have found no answer to the inquiry why organisms specially created should have the embryological kinships he described. And in the second place, after discovering that his alleged law was traversed by many and various noncon formities, he would have been without any explanation of 454 THE EVOLUTION OF LIFE. these. Observe the positions which were open to him and the reasons which show them to be untenable. If it be said that the conditions of the case necessitated the derivation of all organisms from simple germs, and there fore necessitated a morphological unity in their primitive states ; there arises the obvious answer, that the morphologi cal unity thus implied, is not the only morphological unity to be accounted for. Were this the only unity, the various kinds of organisms, setting out from a common primordial form, should all begin from the first to diverge individually, as so many radii from a centre ; which they do not. If, other wise, it be said that organisms were framed upon certain types, and that those of the same type continue developing together in the same direction, until it is time for them to begin putting on their specialities of structure; then the answer is, that when they do finally diverge they ought severally to develop in direct lines towards their final forms. No reason can be assigned why, having parted company, some should progress towards their final forms by irregular or cir cuitous routes. On the hypothesis of design such deviations are inexplicable. The hypothesis of evolution, however, while it pre-supposes those kinships among embryos in their early forms which are found to exist, also leads us to expect nonconformities in their courses of development. If, as any rational theory of evolution implies, the progressive differentiations of types from one another during past times, have resulted from the direct and indirect effects of external conditions — if races of organisms have become different, either by imme diate adaptations to unlike habits of life, or by the mediate adaptations resulting from preservation of the individuals most fitted for such habits of life, or by both; and if most embryonic changes are significant of changes that were undergone by ancestral races; then these irregularities must be anticipated. For the successive changes in modes of life pursued by successive ancestral races, can have had no THE ARGUMENTS FROM EMBRYOLOGY. 455 regularity of sequence. In some cases they must have been more numerous than in others; in some cases they must have been greater in degree than in others; in some cases they must have been to simpler modes, in some cases to more complex modes, and in some cases to modes neither higher nor lower. Of two cognate races which diverged in the remote past, the one may have had descendants that have remained tolerably constant in their habits, while the other may have had descendants that have passed through widely-aberrant modes of life; and yet some of these last may have eventually taken to modes of life like those of the other races derived from the same stock. And if the meta morphoses of embryos indicate, in a general way, the changes of structure undergone by ancestors; then, the later embryo- logic changes of such two allied races will be somewhat different, though they may end in very similar forms. An illustration will make this clear. Mr. Darwin says: " Petrels are the most aerial and oceanic of birds, but in the quiet sounds of Tierra del Fuego, the Puffinuria berardi, in its general habits, in its astonishing power of diving, its manner of swimming, and of flying when unwillingly it takes flight, would be mistaken by any one for an auk or grebe; nevertheless, it is essentially a petrel, but with many parts of its organization profoundly modified." Now if we suppose these grebe-like habits to be continued through a long epoch, the petrel-form to be still more obscured, and the approxi mation to the grebe-form still closer; it is manifest that while the chicks of the grebe and the Puffinuria will, during their early stages of development, display that likeness in volved by their common derivation from some early type of bird, the chick of the Puffinuria will eventually begin to show deviations, representative of the ancestral petrel-struc ture, and will afterwards begin to lose these distinctions and assume the grebe-structure. Hence, remembering the perpetual intrusions of organisms on one another's modes of life, often widely different; and 456 THE EVOLUTION OF LIFE. remembering that these intrusions have been going on from the beginning; we shall be prepared to find that the general law of embryonic parallelism is qualified by irregularities which are mostly small, in many cases considerable, and occa sionally great. The hypothesis of evolution accounts for these : it does more — it implies the necessity of them. § 130. The substitutions of organs and the suppressions of organs, are among those secondary embryological phenomena which harmonize with the belief in evolution but cannot be reconciled with any other belief. Some embryos, during early stages of development, possess organs that afterwards dwindle away, as there arise other organs to discharge the same functions. And in other embryos organs make their appearance, grow to certain points, have no functions to dis charge, and disappear by absorption. We have a remarkable instance of substitution in the temporary appliances for respiration, which some embryos exhibit. During the first phase of its development, the mam malian embryo possesses a system of blood-vessels distributed over what is called the area vasculosa — a system of vessels homologous with one which, among fishes, serves for aerating the blood until the permanent respiratory organs come into play. Now since this system of blood-vessels, not being in proximity to an oxygenated medium, cannot be serviceable to the mammalian embryo during development of the lungs, as it is serviceable in the embryo-fish during development of the gills, this needless formation of it is unaccountable as a result of design. But it is quite congruous with the sup position that the mammalian type arose out of lower verte brate types. For in such case the mammalian embryo, pass ing through states representing in a general way those which its remote ancestors had in common with the lower Verte- ~braia, develops this system of vessels in like manner with them. An instance more significant still is furnished by certain Amphibia. One of the facts early made familiar THE ARGUMENTS PROM EMBRYOLOGY. 4f,7 to the natural-history student is that the tadpole breathes hy external branchiae, and that these, needful during its aquatic life, dwindle away as fast as it develops the lungs fitting it for terrestrial life. But in one of the higher Amphibia, the viviparous Salamander, these transformations ordinarily undergone during the free life of the larva, are undergone by the embryo in the egg. The branchiae are developed though there is no use for them : lungs being sub stituted as breathing appliances before the creature is born. Even more striking than the substitutions of organs are the suppressions of organs. Mr. Darwin names some cases as " extremely curious ; for instance, the presence of teeth in foetal whales, which when grown up have not a tooth in their heads; ... It has even been stated on good authority that rudiments of teeth can be detected in the beaks of certain embryonic birds." Irreconcilable with any teleological theory, these facts do not even harmonize with the theory of fixed types which are maintained by the development of all the typical parts, even where not wanted; seeing that the dis appearance of these incipient organs during foetal life spoils the typical resemblance. But while to other hypotheses these facts are stumbling-blocks, they yield strong support to the hypothesis of evolution. Allied to these cases, are the cases of what has been called retrograde development. Many parasitic creatures and creatures which, after leading active lives for a time, become fixed, lose, in their adult states, the limbs and senses they had when young. It may be alleged, however, that these creatures could not secure the habitats needful for them, without possessing, during their larval stages, eyes and swim ming appendages which eventually become useless; that though, by losing these, their organization retrogresses in one direction, it progresses in another direction; and that, there fore, they do not exhibit the needless development of a higher type on the way to a lower type. Nevertheless there are instances of a descent in organization, following an appa- 458 THE EVOLUTION OF LIFE. rcntly-superfluous ascent. Mr. Darwin says that in some genera of cirripedes, "the Iarva3 become developed either into hermaphrodites having the ordinary structure, or into what I have called complemental males, and in the latter, the development has assuredly been retrograde; for the male is a mere sack, which lives for a short time, and is destitute of mouth, stomach, or other organ of importance, excepting for reproduction." § 130a. But now let us contemplate more closely the energies at work in the unfolding embryo, or rather the energies which the facts appear to imply. Whatever natures we ascribe to the hypothetical units proper to each kind of organism, we must conclude that from the beginning of embryonic development, they have a pro clivity towards the structure of that organism. Because of their phylogenetic origin, they must tend towards the form of the primitive type; but the superposed modifications, con flicting with their initial tendency, must cause a swerving towards each successively higher type. To take an illustra tion : — If in the germ-plasm out of which will come a verte brate animal there is a proclivity towards the primitive piscine form, there must, if the germ-plasm is derived from a mammal, be also from the outset a proclivity towards the mammalian form. While the initial type tends continually to establish itself the terminal type tends also to establish itself. The intermediate structures must be influenced by their conflict, as well as by the conflict of each with the pro clivities towards the amphibian and reptilian types. This complication of tendencies is increased by the intervention of several other factors. There is the factor of economy. An embryo in which the transformations have absorbed the smallest amount of energy and wasted the smallest amount of matter, will have an advantage over embryos the transformations of which have cost more in energy and matter : the young animal will set THE ARGUMENTS FROM EMBRYOLOGY. 459 out with a greater surplus of vitality, and will be more likely than others to live and propagate. Again, in the embryos of its descendants, inheriting the tendency to economical trans formation, those which evolve at the least cost will thrive more than the rest and be more likely to have posterity. Thus will result a continual shortening of the processes. We can see alike that this must take place and that it does take place. If the whole series of phylogenctic changes had to be repeated — if the embryo mammal had to become a complete fish, and then a complete amphibian, and then a complete reptile, there would be an immense amount of surperfluous building up and pulling down, entailing great waste of time and of materials. Evidently these abridgments which econo my entails, necessitate that unfolding embryos bear but rude resemblances to lower types ancestrally passed through — vaguely represent their dominant traits only. From this principle of economy arise several derivative principles, which may be best dealt with separately. § 130&. In some cases the substitution of an abridged for an unabridged course of evolution causes the entire disappear ance of certain intermediate forms. Structural arrangements once passed through during the unfolding are dropped out of the series. In the evolution of these embryos with which there is not laid up a large amount of food-yolk there occurs at the outset a striking omission of this kind. When, by successive fissions, the fertilized cell has given rise to a cluster of cells constituting a hollow sphere, known as a blastula, the next change under its original form is the introversion of one side, so as to produce two layers in place of one. An idea of the change may be obtained by taking an india-rubber ball (hav ing a hole through which the air may escape) and thrusting in one side until its anterior surface touches the interior surface of the other side. If the cup-shaped structure resulting be supposed to have its wide opening gradually narrowed,, until it 460 THE EVOLUTION OF LIFE. becomes the mouth of an internal chamber, it will represent what is known as a gastrula — a double layer of cells, of which the outer is called epiblast and the inner hypoblast (answering to ectoderm and endoderm) inclosing a cavity known as the archenteron,, or primitive digestive sac. But now in place of this original mode of forming the gastrula, there occurs a mode known as delamination. Throughout its whole extent the single layer splits so as to become a double layer — one sphere of cells inclosing the other; and after this direct for mation of the double layer there is a direct formation of an opening through it into the internal cavity. There is thus a shortening of the primitive process: a number of changes are left out. Often a kindred passing over of stages at later periods of development may be observed. In certain of the Mollusca, as the Patella chiton, the egg gives origin to a free-swimming larva known as a trochosphere, from which presently comes the ordinary molluscous organization. In the highest division of the Molluscs, however, the Cephalopods, no trochosphere is formed. The nutritive matter laid up in the egg is used in building up the young animal without any indication of an ancestral larva. § 130c. Among principles derived from the principle of economy is the principle of pre-adaptation — a name which we may appropriately coin to indicate an adaptation made in advance of the time at which it could have arisen in the course of phylogenetic history. How pre-adaptation may result from economy will be shown by an illustration which human methods of con struction furnish. Let us assume that building houses of a certain type has become an established habit, and that, as a part of each house, there is a staircase of given size. And suppose that in consequence of changed conditions — say the walling in of the town, limiting the internal space and in creasing ground-rents — it becomes the policy to build houses TIIE ARGUMENTS PROM EMBRYOLOGY. 4G1 of many stories, let out in flats to different tenants. For the increased passing up and down, a staircase wider at its lower part will be required. If now the builder, when putting up the ground floor, follows the old dimensions, then after all the stories are built, the lower part of the staircase, if it is to yield equal facilities for passage, must be reconstructed. Instead of a staircase adapted to those few stories which the original type of house had, economy will dictate a pro-adapta tion of the staircase to the additional stories. On carrying this idea with us, we shall see that if from some type of organism there is evolved a type in which enlargement of a certain part is needed to meet increased functions, the greater size of this part will begin to show itself during early stages of unfolding. That unbuilding and rebuilding which would be needful were it laid down of its original size, will be made needless if from the beginning it is laid down of a larger size. Hence, in successive genera tions, the greater prosperity and multiplication of individuals in which this part is at the outset somewhat larger than usual, must eventually establish a marked excess in its development at an early stage. The facts agree with this inference. Referring to the contrasts between embryos, Mr. Adam Sedgwick says that " a species is distinct and distinguishable from its allies from the very earliest stages." Whereas, according to the law of von Baer, " animals so closely allied as the fowl and duck would be indistinguishable in the early stages of development," " yet I can distinguish a fowl and a duck embryo on the second day by the inspection of a single transverse section through the trunk." This experience harmonizes with the statement of the late Prof. Agassiz, that in some cases traits characterizing the species appear at an earlier period than traits characterizing the genus. Similar in their implications are the facts recently pub lished by Dr. E. Mehnert, concerning the feet of pentadactyle vertebrates. A leading example is furnished by the foot in 462 THE EVOLUTION OF LIFE. the struthious birds. Out of the original five digits the two which eventually become large while the others disappear, soon give sign of their future predominance : their early sizes being in excess of those required for the usual functional re quirements in birds, and preparing the way for their special requirements in the struthious birds. Dr. Mehnert shows that a like lesson is given by the relative developments of legs and wings in these birds. Ordinarily in vertebrates the fore limbs grow more rapidly than the hind limbs ; but in the ostrich, in which the hind limbs or legs have to become so large while the wings are but little wanted, the leg develop ment goes in advance of the wing-development in early embryonic stages: there is a pre-adaptation. Much more striking are examples furnished by creatures whose modes of existence require that they shall have enormous fertility — require that the generative system shall be very large. Ordinarily the organs devoted to maintenance of the race develop later than the organs devoted to main tenance of the individual. But this order is inverted in certain Entozoa. To these creatures, imbedded in nutritive matters, self-maintenance cost nothing, and the structures devoted to it are relatively of less importance than the struc tures devoted to race-maintenance, which, to make up for the small chance any one germ has of getting into a fit habitat, have to produce immense numbers of germs. Here the rudi ments of the generative systems are the first to become visible — here, in virtue of the principle of pre-adaptation, a struc ture belonging to the terminal form asserts itself so early in the developmental process as almost to obliterate the struc ture of the initial form. It may be that in some cases where the growth of certain organs goes in advance of the normal order, the element of time comes into play — the greater time required for con struction. To elucidate this let us revert to our simile. Suppose that the staircase above instanced, or at any rate its lower part, is required to be of marble with balusters finely THE ARGUMENTS FROM EMBRYOLOGY. 4G3 carved. If this piece of work is not promptly commenced and pushed on fast, it will not be completed when the rest of the house is ready: workmen and tools will still block it up at a time when it should be available. Similarly among the parts of an unfolding embryo, those in which there is a great deal of constructive work must early take such shape as will allow of this. Now of all the tissues the nervous tissue is that which takes longest to repair when injured; and it seems a not improbable inference that it is a tissue which is slower in its histological development than others. If this be so, we may see why, in the embryos of the higher vertebrates, the central nervous system quickly grows large in comparison to the other systems — why by pre-adaptation the brain of a chick develops in advance of other organs so much more than the brain of a fish. § I3Qd. Yet another complication has to be noted. From the principle of economy, it seems inferable that decrease and disappearance of organs which were useful in ancestral types but have ceased to be useful, should take place uniformly; but they do not. In the words of Mr. Adam Sedgwick, " some ancestral organs persist in the embryo in a function- less rudimentary (vestigial) condition and at the same time without any reference to adult structures, while other an cestral organs have disappeared without leaving a trace." * This anomaly is rendered more striking when joined with the fact that some of the structures which remain con spicuous are relatively ancient, while some which have been obliterated are relatively modern — e.g., "gill slits [which date back to the fish-ancestor], have been retained in embryology, whereas other organs which have much more recently disap peared, c. g. teeth of birds, fore-limbs of snakes [dating back to the reptile ancestor], have been entirely lost." f Mr. Sedg wick ascribes these anomalies to the difference between larval * Studies from the Morphological Laboratory in the University of Cam bridge, vol. vi, p. 84. f Ibid., p. 81. 404' THE EVOLUTION OF LIFE. development and embryonic development, and expresses his general belief thus : — "The conclusion here reached is that, whereas larval development must retain traces (it may be very faint) of ancestral stages of struc ture because they are built out of ancestral stages, embryonic develop ment need not necessarily do so, and very often does not; that embryonic development in so far as it is a record at all, is a record of structural features of previous larval stages. Characters which dis appear during free life disappear also in the embryo, but characters which though lost by the adult are retained in the larva may ulti mately be absorbed into the embryonic phase and leave their traces in embryonic development." * To set forth the evidence justifying this view would en cumber too much the general argument. Towards elucidation of such irregularities let me name two factors which should I think be taken into account. Abridgment of embryonic stages cannot go on uniformly with all disused organs. Where an organ i& of such size that progressive diminution of it will appreciably profit the young animal, by leaving it a larger surplus of unused material, we may expect progressive diminution to occur. Contrariwise, if the organ is relatively so small that each decrease will not, by sensibly increasing the reserve of nutriment, give the young animal an advantage over others, decrease must not be looked for: there may be a survival of it even though of very ancient origin. Again, the reduction of a superfluous part can take place only on condition that the economy resulting from each de scending variation of it, is of greater importance than are the effects of variations simultaneously occurring in other parts. If by increase or decrease of any other parts of the embryo, survival of the animal is furthered in a greater degree than by decrease of this superfluous part, then such decrease is unlikely; since it is illegitimate to count upon the repeated concurrence of favourable variations in two or more parts which are independent. So that if changes of an * Stitdi^s from the Morphological Laboratory in tlie University of Cam bridge, vol. vi, p. 89. THE ARGUMENTS FROM EMBRYOLOGY. 405 advantageous kind are going on elsewhere in the embryo a useless part may remain long undiminished. Yet another cause operates, and perhaps cooperates. Em bryonic survival of an organ which has become functionless, may readily happen if, during subsequent stages of develop ment, parts of it are utilized as parts of other organs. In the words of Mr. J. T. Cunningham : — "It seems to be a general fact that a structure which in meta morphosis disappears completely may easily be omitted altogether in embryonic development, while one which is modified into something else continues to passfnore or less through its original larval condi tion." (Science Progress, July, 1897, p. 488.) One more factor of considerable importance should be taken into account. A disused organ which entails evil because construction of it involves needless cost, may entail further evil by being in the way. This, it seems to me, is the reason why the fore-limbs of snakes have disappeared from their embryos. When the long-bodied lizard out of which the ophidian type evolved, crept through stiff herbage, and moved its head from side to side to find openings, there re sulted alternate bends of its body, which were the beginnings of lateral undulations ; and we may easily see that in propor tion as it thus progressed by insinuating itself through inter stices, the fore-limbs, less and less used for walking, would be more and more in the way; and the lengthening of the body, increasing the undulatory motion and decreasing the use of the fore-limbs, would eventually make them absolute impediments. Hence besides the benefit in economy of con struction gained by embryos in which the fore-limbs were in early stages a little less developed than usual, they would gain an advantage by having, when mature, smaller fore- limbs than usual, leading to greater facility of locomotion. There would be a double set of influences causing, through selection, a comparatively rapid decrease of these appendages. And we may I think see also, on contemplating the kind of movement, that the fore-limbs would be more in the way than the hind limbs, which would consequently dwindle with 466 THE EVOLUTION OF LIFE. such smaller rapidity as to make continuance of the rudi ments of them comprehensible. § 131 — 132. So that while the embryonic law enunciated by von Baer is in harmony with the hypothesis of evolu tion, and is, indeed, a law which this hypothesis implies, the nonconformities to the law are also interpretable by this hypothesis. Parallelism between the courses of development in species allied by remote ancestry, is liable to be variously modi fied in correspondence with the later ancestral forms passed through after divergence of such species. The substitution of a direct for an indirect process of formation, which we have reason to believe will show itself, must obscure the embryonic history. And the principle of economy which leads to this substitution produces effects that are very irregu lar and uncertain in consequence of the endlessly varied con ditions. Thus several causes conspire to produce deviations from the general law. Let it be remarked, finally, that the ability to trace out cmbryologic kinships and the inability to do this, occur just where, according to the hypothesis of Evolution, they should occur. We saw in § lOOa that zoologists are agreed in group ing animals into some 17 phyla — Mollusca, Arthropoda, Echinodermata, &c. — each of which includes a number of classes severally sub-divided into orders, genera, species. All the members of each phylum are so related embryologically, that the existence of a common ancestor of them in the remote past is considered certain. But when it comes to the relations among the archaic ancestors, opinion is unsettled. Whether, for instance, the primitive Chordata, out of which the V 'ertcbrata emerged, have molluscan affinities or anne- lidan affinities, is still a matter in dispute. With regard to the origins of various other types no settled conclusions are held. Now it is clear that on tracing down each branch of the great t genealogical tree, kinships would be much more THE ARGUMENTS FROM EMBRYOLOGY. 4f>7 manifest among the recently-differentiated forms than among those forms which diverged from one another in the earliest stages of organic life, and had separated widely before any of the types we now know had come into existence. CHAPTER VI. THE ARGUMENTS PROM MORPHOLOGY. § 133. LEAVING out of consideration those parallelisms among their modes of development which characterize organisms belonging to each group, that community of plan which exists among them when mature is extremely remarkable and extremely suggestive. As before shown (§ 103), neither the supposition that these combinations of attributes which unite classes are fortuitous, nor the supposi tion that no other combinations were practicable, nor the supposition of adherence to pro-determined typical plans, suffices to explain the facts. An instance will best prepare the reader for seeing the true meaning of these fundamental likenesses. Under the immensely-varied forms of insects, greatly elongated like the dragon-fly or contracted in shape like the lady-bird, winged like the butterfly or wingless like the flea, we find this character in common — there are primarily seventeen segments.* These segments may be distinctly * Early in our friendship (about 1855) Prof. Huxley expressed to me his conviction that all the higher articulate animals have twenty segments or somites. That he adhered to this view in 1880, when his work on The Crayfsh was published, is shown by his analysis there given of the twenty segments existing in this fluviatile crustacean; and adhesion to it had been previously shown in 1877, when his work on The Anatomy of Invertebrated Animals was published. On p. 398 of that work he writes :— " In the abdo men there are, at most, eleven somites, none of which, in the adult, bear ambulatory limbs. Thus, assuming the existence of six somites in the head, THE ARGUMENTS FROM MORPHOLOGY. 409 marked or they may be so fused as to make it difficult to find the divisions between them, but they always exist. What now can be the meaning of this community of structure throughout the hundred thousand kinds of insects filling the air, burrowing in the earth, swimming in the water? Why under the down-covered body of a moth and under the hard wing-cases of a beetle, should there be discovered the same number of divisions? Why should there be no more somites in the Stick-insect, or other Phasmid a foot long, than there arc in a small creature like the louse? Why should the inert Aphis and the swift-flying Emperor-butterfly bo con structed on the same fundamental plan? It cannot be by chance that there exist equal numbers of segments in all these multitudes of species. There is no reason to think it was necessary., in the sense that no other number would have made a possible organism. And to say that it is the result of design — to say that the Creator followed this pattern throughout, merely for the purpose of maintaining the pat tern — is to assign an absurd motive. No rational interpre tation of these and countless like morphological facts, can be given except by the hypothesis of evolution; and from the hypothesis of evolution they are corollaries. If organic forms have arisen from common stocks by perpetual divergences and re-divergences — if they have continued to inherit, more or less clearly, the characters of ancestral races; then there the normal number of somites in the body of insects will be twenty, as in the higher Crustacea and Araclinida" To this passage, however, he puts the note : — " It is open to question whether the podical plates represent a somite; and therefore it must be recollected that the total number of somites, the existence of which can be actually demonstrated in insects, is only seventeen, viz., four for the head, three for the thorax, and ten for the abdomen." I have changed the number twenty, which in the original edition occurred in the text, to the number seventeen in deference to sug gestions made to me ; though I find in Dr. Sharp's careful and elaborate work on the Insecta, that Viallancs and Cholodkovsky agree with Huxley in believing that there are six somites in the insect-head. The existence of a doubt on this point, however, docs not essentially affect the argument, since there is agreement among rnorphologists respecting the constancy of the total number of somites in insects. 470 THE EVOLUTION OF LIFE. will naturally result these communities of fundamental structure among creatures which have severally become modified in multitudinous ways and degrees, in adaptation to their respective modes of life. To this let it be added that while the belief in an intentional adhesion to a p re-deter mined pattern throughout a whole group, is nega tived by the occurrence of occasional deviations from the pattern; such deviations are reconcilable with the belief in evolution. As pointed out in the last chapter, ancestral traits will be obscured more or less according as the super posed modifications of structure, have or have not been fur thered by the conditions of life and development to which the type has been subjected. § 134. Besides these wide-embracing and often deeply- hidden homologies, which hold together different animals, there are the scarcely-less significant homologies between dif ferent organs of the same animal. These, like the others, are obstacles to the supernatural interpretations and sup ports of the natural interpretation. One of the most familiar and instructive examples is furnished by the vertebral column. Snakes, which move sinuously through and over plants and stones, obviously need a segmentation of the bony axis from end to end ; and inas much as flexibility is required throughout the whole length of the body, there is advantage in the comparative uniformity of this segmentation. The movements would be impeded if, instead of a chain of vertebrae varying but little in their lengths, there existed in the middle of the series some long bony mass that would not bend. But in the higher Verte- brata, the mechanical actions and reactions demand that while some parts of the vertebral column shall be flexible, other parts shall be inflexible. Inflexibility is specially requi site in that part of it called the sacrum ; which, in mammals and birds, forms a fulcrum exposed to the greatest strains the skeleton has to bear. Now in both mammals and birds, THE ARGUMENTS FROM MORPHOLOGY. 471 this rigid portion of the vertebral column is not made of one long segment or vertebra, but of several segments fused together. In man there are five of these confluent sacral vertebra}; and in the ostrich tribe they number from seven teen to twenty. Why is this? Why, if the skeleton of each species was separately contrived, was this bony mass made by soldering together a number of vertebras like those forming the rest of the column, instead of being made out of one single piece? And why, if typical uniformity was to be maintained, does the number of sacral vertebra vary within the same order of birds? Why, too, should the development of the sacrum be by the round-about process of first forming its separate constituent vertebra?, and then destroying their separateness ? In the embryo of a mammal or bird, the central element of the vertebral column is, at the outset, continuous. The segments that are to become vertebra}, arise gradually in the adjacent mesoderm, and enwrap this originally-homogeneous axis or notochord. Equally in those parts of the spine which are to remain flexible, and in those parts which are to grow rigid, these segments are formed; and that part of the spine which is to compose the sacrum, having acquired this segmental structure, loses it again by coalescence of the segments. To what end is this construc tion and re-construction? If, originally, the spine in verte brate animals consisted from head to tail of separate move- able segments, as it does still in fishes and some reptiles — if, in the evolution of the higher Vertebrata, certain bf these moveable segments were rendered less movcablc with respect to one another, by the mechanical conditions they were exposed to, and at length became relatively immovable; it is comprehensible why the sacrum formed out of them, should continue ever after to show its originally-segmented structure. But on any other hypothesis this segmented structure is inexplicable. " We see the same law in comparing the wonderfully complex jaws and legs in crus taceans," says Mr. Darwin : referring to the fact that those 472 THE EVOLUTION OF LIFE. numerous lateral appendages which, in the lower crustaceans, most of them serve as legs, and have like shapes, are, in the higher crustaceans, some of them represented by enormously- developed claws, and others by variously-modified foot-jaws. " It is familiar to almost every one," he continues, " that in a flower the relative position of the sepals, petals, stamens, and pistils, as well as their intimate structure, are intelli gible on the view that they consist of metamorphosed leaves arranged in a spire. In monstrous plants we often get direct evidence of the possibility of one organ being transformed into another; and we can actually see in embryonic crustaceans and in many other animals, and in flowers, that organs, which when mature become extremely different, are at an early stage of growth exactly alike." . . . " Why should one crustacean, which has an ex tremely complex mouth formed of many parts consequently always have fewer legs; or conversely, those with many legs have simpler mouths? Why should the sepals, petals, stamens, and pistils in any individual flower, though fitted for such widely-different purposes, be all constructed on the same pattern ? " To these and countless similar questions, the theory of evolution furnishes the only rational answer. In the course of that change from homogeneity to heterogeneity of struc ture displayed in evolution under every form, it will neces sarily happen that from organisms made up of numerous like parts, there will arise organisms made up of parts more and more unlike: which unlike parts will nevertheless continue to bear traces of their primitive likeness. § 135. One more striking morphological fact, near akin to some of the facts dwelt on in the last chapter, must be here set down — the frequent occurrence, in adult animals and plants, of rudimentary and useless organs, which are homologous with organs that are developed and useful in allied animals and plants. In the last chapter we saw that THE ARGUMENTS FROM MORPHOLOGY. 473 during the development of embryos, there often arise organs which disappear on being replaced by other organs dis charging the same functions in better ways ; find that in some cases, organs develop to certain points and are then re-absorbed without performing any functions. Very gene rally, however, the partially-developed organs are retained throughout life. The osteology of the higher Vertebrata supplies abundant examples. Vertebral processes which, in one tribe, are fully formed and ossified from independent centres, are, in other tribes, mere tubercles not having independent centres of ossification. While in the tail of this animal the vertebra? are severally composed of centrum and appendages, in the tail of that animal they are simple osseous masses without any appendages; and in another animal they have lost their individualities by coalescence with neighbouring vertebra? into a rudimentary tail. From the structures of the limbs analogous facts are cited by comparative anatomists. The undeveloped state of certain metacarpal bones, characterizes whole groups of mammals. In one case we find the normal number of digits; and, in another case, a smaller number with an atrophied digit to make out the complement. Here is a digit with its full number of phalanges ; and there a digit of which one phalange has been arrested in its growth. Still more remarkable are the instances of entire limbs being rudi mentary; as in certain snakes, which have hind legs hidden beneath the integument. So, too, is it with dermal appendages. Some of the smooth-skinned amphibia have scales buried in the skin. The seal, which is a mammal con siderably modified in adaptation to an aquatic life, and which uses its feet mainly as paddles, has toes that still bear ex ternal nails; but the manatee, which is a much more trans formed mammal, has nailless paddles which, when the skin is removed, are said, by Humboldt, to display rudimentary nails at the ends of the imbedded digits. Nearly all birds are covered with developed feathers, severally composed of a shaft 474 THE EVOLUTION OF LIFE. bearing fibres, each of which, again, bears a fringe of down. But in some birds, as in the ostrich, various stages of arrested development of the feathers may be traced : be'tween the umisually-elaborated feathers of the tail, and those about the beak which are reduced to simple hairs, there arc transi tions. Nor is this the extreme case. In the Apteryx we see the whole of the feathers reduced to a hair-like form. Again, the hair which commonly covers the body in mammals is, over the greater part of the human body almost rudimentary, and is in some parts reduced to mere down — down which nevertheless proves itself to be homologous with the hair of mammals in general, by occasionally developing into the original form. Numerous cases of aborted organs are given by Mr. Darwin, of which a few may be here added. " No thing can be plainer," he remarks, "than that wings are formed for flight, yet in how many insects do we see wings so reduced in size as to be utterly incapable of flight, and not rarely lying under wing-cases, firmly soldered together ? " . . . " In plants with separated sexes, the male flowers often have a rudiment of a pistil; and Kolreuter found that by crossing such male plants with an hermaphrodite species, the rudi ment of the pistil in the hybrid offspring was much increased in size; and this shows that the rudiment and the perfect pistil are essentially alike in nature." And then, to complete the proof that these undeveloped parts are marks of descent from races in which they were developed, there are not a few direct experiences of this relation. " We have plenty of cases of rudimentary organs in our domestic productions — as the stump of a tail in tailless breeds — the vestige of an ear in earless breeds — the re-appearance of minute dangling horns in hornless breeds of cattle." (Origin of Species, 1859, pp. 451,454.) Here, as before,' the teleological doctrine fails utterly ; for these rudimentary organs are useless, and occasionally even detrimental; as is the appendix vermiformis, in Man — a part of the caecum which is of no value fpr the purpose of ubsorp- THE ARGUMENTS FROM MORPHOLOGY. 475 tion but which, by detaining small foreign bodies, often causes severe inflammation and death. The doctrine of typical plans is equally out of court; for while, in some members of a group, rudimentary organs completing the general type are traceable, in other members of the same group such organs are unrepresented. There remains only the doctrine of evolu tion; and to this, these rudimentary organs offer no diffi culties. On the contrary, they are among its most striking evidences. § 136. The general truths of morphology thus coincide in their implications. Unity of type, maintained under extreme dissimilarities of form and mode of life, is explicable as re sulting from descent with modification; but is otherwise in explicable. The likenesses disguised by unlikenesses, which the comparative anatomist discovers between various organs in the same organism, are worse than meaningless if it be supposed that organisms were severally framed as we now see them; but they fit in quite harmoniously with the belief that each kind of organism is a product of accumulated modi fications upon modifications. And the presence, in all kinds of animals and plants, of functionally-useless parts corre sponding to parts that are functionally-useful in allied ani mals and plants, while it is totally incongruous with the belief in a construction of each organism by miraculous interposi tion, is just what we are led to expect by the belief that organ isms have arisen by progression. CHAPTER VII. THE ARGUMENTS FROM DISTRIBUTION. § 137. IN §§ 105 and 106, we contemplated the phenomena of distribution in Space. The general conclusions reached, in great part based on the evidence brought together by Mr. Darwin, were that, " on the one hand, we have similarly-con ditioned, and sometimes nearly-adjacent, areas, occupied by quite different Faunas. On the other hand, we have areas remote from each other in latitude, and contrasted in soil as well as climate, which are occupied by closely-allied Faunas." Whence it was inferred that " as like organisms are not uni versally, or even generally, found in like habitats; nor very unlike organisms, in very unlike habitats ; there is no manifest pro-determined adaptation of the organisms to the habitats." In other words, the facts of distribution in Space do not conform to the hypothesis of design. At the same time we saw that " the similar areas peopled by dissimilar forms, are those between which there are impassable barriers ; while the dissimilar areas peopled by similar forms, are those between which there are no such barriers ; " and these generalizations appeared to harmonize with the abundantly- illustrated truth, "that each species of organism tends ever to expand its sphere of existence — to intrude on other areas, other modes of life, other media." By way of showing still more clearly the effects of com petition among races of organisms, let me here add some 476 .'THE ARGUMENTS FROM DISTRIBUTION. 477 recently-published instances of the usurpations of areas, and changes of distribution hence resulting. In the Natural His tory Review for January, 1864, Dr. Hooker quotes as follows from some New Zealand naturalists : — " You would be sur prised at the rapid spread of European and other foreign plants in this country. All along the sides of the main lines of road through the plains, a Polygonum (aviculare), called ' Cow Grass,' grows most luxuriantly, the roots sometimes two feet in depth, and the plants spreading over an area from four to five feet in diameter. The dock (Rumex obtusifolius or R. crispus) is to be found in every river bed, extending into the valleys of the mountain rivers, until these become mere tor rents. The sow-thistle is spread all over the country, growing luxuriantly nearly up to 0000 feet. The water-cress increases in our still rivers to such an extent, as to threaten to choke them altogether ... I hav.e measured stems twelve feet long and three-quarters of an inch in diameter. In some of the mountain districts, where the soil is loose, the white clover is completely displacing the native grasses, forming a close sward In fact, the young native vegetation appears to shrink from competition with these more vigorous in truders." "The native (Maori) saying is 'as the white man's rat has driven away the native rat, so the European fly drives away our own, and the clover kills our fern, so will the Maoris disappear before the white man himself.' " Given this universal tendency of the superior to over run the habitats of the inferior,* let us consider what, on the hypothesis of evolution, will be the effects on the geo graphical relationships of species. § 138. A race of organisms cannot expand its sphere of existence without subjecting itself to new external conditions. Those of its members which spread over adjacent areas, * To avoid circumlocution I let these words stand, though they are not truly descriptive; for the prosperity of imported species is largely, if not mainly, caused by the absence of those natural enemies which kept them dowu at home. 478 THE EVOLUTION OP LIFE. inevitably come in contact with circumstances partially different from their previous circumstances; and such of them as adopt the habits of other organisms, necessarily experience re-actions more or less contrasted with the re actions before experienced. Now if changes of organic structure are caused, directly or indirectly, by changes in the incidence of forces; there must result unlikenesses of structure between the divisions of a race which colonizes new habitats. Hence, in the absence of obstacles to migra tion, we may anticipate manifest kinships between the ani mals and plants of one area, and those of areas adjoining it. This inference corresponds with an induction before set down (§ 106). In addition to illustrations of it already quoted from Mr. Darwin, his pages furnish others. One is that species which inhabit islands are allied to species which inhabit neighbouring main lands; and another is that the faunas of clustered islands show marked similari ties. " Thus the several islands of the Galapagos Archi pelago arc tenanted," says Mr. Darwin, " in a quite marvellous manner, by very closely related species; so that the inhabitants of each separate island, though mostly dis tinct, are related in an incomparably closer degree to each other than to the inhabitants of any other part of the world." Mr. Wallace has traced " variation as specially influenced by locality " among the Papilionidce inhabiting the East Indian Archipelago : showing how " the species and varieties of Celebes possess a striking character in the form of the an terior wings, different from that of the allied species and varieties of all the surrounding islands ; " and how " tailed species in India and the western islands lose their tails as they spread eastward through the archipelago." During his travels on the Upper Amazons, Mr. Bates found that " the greater part of the species of Ithomice changed from one locality to another, not further removed than 100 to 200 miles;" that "many of these local species have the appear ance of being geographical varieties ; " and that in some THE ARGUMENTS FROM DISTRIBUTION. 479 species " most of the local varieties are connected with their parent form by individuals exhibiting all the shades of variation." Further general relationships are to be inferred. If races of organisms, ever being thrust by pressure of popula tion into new habitats, undergo modifications of structure as they diverge more and more widely in Space, it follows that, speaking generally, the widest divergences in Space Avill indicate the longest periods during which the descendants from a common stock have been subject to modifying con ditions; and hence that, among organisms of the same group, the smaller contrasts of structure will be limited to the smaller areas. This we find : " varieties being," as Dr. Hooker says in his Flora of Tasmania, " more re stricted in locality than species, and these again than genera." Again, if races of organisms spread, and as they spread are altered by changing incident forces; it follows that where the incident forces vary greatly within given areas, the alterations will be more numerous than in equal areas which are less-variously conditioned. This, too, proves to be the fact. Dr. Hooker points out that the rela tively uniform regions have the fewest species; while in the most multiform regions the species are the most numerous. § 139. Let us consider next, how the hypothesis of evo lution corresponds with the facts of distribution, not over different areas but through different media. If all forms of organisms have descended from some primordial form, it follows that since this primordial form must have inhabited some one medium out of the several media now inhabited, the peopling of other media by its descendants implies migration from one medium to others — implies adaptations to media quite unlike the original medium. To speak speci fically — water being the medium in which the lowest living forms exist, the implication is that the earth and the air have been colonized from the water. Great dilliculties 480 THE EVOLUTION OF LIFE. appear to stand in the way of this assumption. Ridiculing those who alleged the uniserial development of organic forms, who, indeed, laid themselves open to ridicule by their many untenable propositions, Von Baer writes — " A fish, swimming towards the shore desires to take a walk, but finds his fins useless. They diminish in breadth for want of use, and at the same time elongate. This goes on with children and grandchildren for a few millions of years, and at last who can be astonished that the fins become feet? It is still more natural that the fish in the meadow, finding no water, should gape after air, thereby, in a like period of time developing lungs; the only difficulty being that in the meanwhile, a few generations must manage without breath ing at all." Though, as thus presented, the belief in a transition looks laughable; and though such deriva tion of terrestrial vertebrates by direct modification of piscine vertebrates, is untenable; yet we must not conclude that no migrations of the kind alleged can have taken place. The adage that " truth is stranger than fiction," applies quite as much to Nature in general as to human life. Besides the fact that certain fish actually do " take a walk " without any obvious reason; and besides the fact that sundry kinds of fish ramble about on land when prompted by the drying-up of the waters they inhabit ; there is the still more astounding fact that one kind of fish climbs trees. Few things seem more manifestly impossible, than that a water-breathing creature without efficient limbs, should ascend eight or ten feet up the trunk of a palm ; and yet the Anabas scandens does as much. To previous testimonies on this point Capt. Mitchell has recently added others. Such remarkable cases of temporary changes of media, will prepare us for conceiving how, under special conditions, permanent changes of media may have taken place; and for considering how the doctrine of evolu tion is elucidated by them. Inhabitants of the sea, of rivers, and of lakes, are many of them left from time to time partially or completely with- THE ARGUMENTS FROM DISTRIBUTION. 481 out water; and those which show the power to change their media temporarily or permanently, are in very many cases of the kinds most liable to be thus deserted by their medium. Let us consider what the sea-shore shows us. Twice a day the rise and the fall of the tide covers and uncovers plants and animals, fixed and moving; and through the alternation of spring and neap tides, it results that the exposure of the organisms living low down on the beach, varies both in frequency and duration: while some of them are left dry only once a fortnight for a very short time, others, a little higher up, are left dry during two or three hours at several ebb tides every fortnight. Then by small gradations we come to such as, living at the top of the beach, are bathed by salt-water only at long intervals; and still higher to some which are but occasionally splashed in stormy weather. What, now, do we find among the organisms thus subject to various regular and irregular alterations of media? Besides many plants and many fixed animals, we find moving animals of numerous kinds; some of which are confined to the lower zones of this littoral region, but others of which wander over the whole of it. Omitting the humbler types, it will suffice to observe that each of the two great sub-kingdoms, Mollusca and Arthropoda, supplies examples of creatures having a wide excursiveness within this region. We have gasteropods which, when the tide is down, habitu ally creep snail-like over sand and sea-weed, even up as far as high-water mark. We have several kinds of crustaceans, of which the crab is the most conspicuous, running about on the wet beach, and sometimes rambling beyond the reach of the water. And then note the striking fact that each of the forms thus habituated to changes of media, is allied to forms which arc mainly or wholly terrestrial. On the West Coast of Ireland marine gasteropods are found on the rocks three hundred feet above the sea, where they are only at long in tervals wetted by the spray ; and though between gasteropods of this class and land-gasteropods the differences are con- 482 THE EVOLUTION OF LIFE. siderable, yet the land-gasteropods are more closely allied to them than to any other Mollusca. Similarly, the two highest orders of crustaceans have their species which live occasion ally, or almost entirely, out of the water: there is a kind of lobster in the Mauritius which climbs trees; and there is the land-crab of the West Indies, which deserts the sea when it reaches maturity and re-visits it only to spawn. Seeing, thus, how there are many kinds of marine creatures whose habitats expose them to frequent changes of media; how some of the higher kinds so circumstanced, show a consider able adaptation to both media; and how these amphibious kinds are allied to kinds that are mainly or wholly terres trial; we shall see that the migrations from one medium to another, which evolution pre-supposcs, are by no means im practicable. With such evidence before us, the assumption that the distribution of the Vertebrata through media so dif ferent as air and water, may have been gradually effected in some analogous manner, would not be altogether unwarranted even had we no clue to the process. We shall find, however, a tolerably distinct clue. Though rivers, and lakes, and pools, have no sensible tidal variations, they have their rises and falls, regular and irregular, moderate and extreme. Especially in tropical climates, we see them annually full for a certain number of months, and then dwindling away and drying up. The drying up may reach various degrees and last for various periods. It may go to the extent only of producing a liquid mud, or it may reduce the mud to a hardened, fissured solid. It may last for a few days or for months. That is to say, aquatic forms which are in one place annually subject to a slight want of water for a short time, are elsewhere subject to greater wants for longer times : we have gradations of transition, analogous to those which the tides furnish. Now it is well known that creatures in habiting such waters have, in various degrees, powers of meeting these contingencies. The contained fish either bury themselves in the mud when the dry season cornea, or ramble THE ARGUMENTS FROM DISTRIBUTION. 483 in search of other waters. This is proved by evidence from India, Guiana, Siam, Ceylon; and some of these fish, as the Anabas scandens, are known to survive for days out of the water. But the facts of greatest significance are furnished by an allied class of Vertebrata, almost peculiar to habitats of this kind. The Amphibia are not, like fish, usually found in waters that are never partially or wholly dried up; but they nearly all inhabit waters which, at certain seasons, evaporate, in great measure or completely — waters in which most kinds of fish cannot exist. And what are the leading structural traits of these Amphibia? They have two respiratory systems — pulmonic and branchial — variously developed in different orders; and they have two or four limbs, also variously developed. Further, the class Amphibia consists of two groups, in one of which this duality of the respiratory system is permanent, and the development of the limbs always incomplete; and in the other of which the branchiaa disappear as the lungs and limbs become fully developed. The lowest group, the Percnnibranchiata, have internal organs for aerating the blood which approach in various degrees to lungs, until " in the Siren, the pulmonic respira tion is more extensive and important than the branchial ; " and to these creatures, having a habitat partially aerial and partially aquatic, there are at the same time supplied, in the shallow water covering soft mud, the mechanical conditions which render swimming difficult and rudimentary limbs use ful. In the higher group, the Caducibranchiata, we find still more suggestive transformations. Having at first a structure resembling that which is permanent in the perennibranchiate amphibian, the larva of the caducibranchiate amphibian pursues for a time a similar life ; but, eventually, while the branchial appendages dwindle the lungs grow : the respiration of air, originally supplementary to the respiration of water, predominates over it more and more, till it replaces it entirely ; and an additional pair of legs is produced. This |iaving been done, the creature either becomes, like the Triton., one which 484 THE EVOLUTION OF LIFE. quits the water only occasionally; or, like the Frog, one which pursues a life mainly terrestrial, and returns to the water now and then. Finally, if we ask under what condi tions this metamorphosis of a water-breather into an air- breather completes itself, the answer is — it completes itself at the time when the shallow pools inhabited by the larvae are being dried up, or in danger of being dried up, by the summer's sun.* Sec, then, how significant are the facts when thus brought together. There are particular habitats in which animals are subject to changes of media. In such habitats exist animals having, in various degrees, the power to live in both media, consequent on various phases of transitional organization. Near akin to these animals there are some that, after passing their early lives in the water, acquire more completely the structures fitting them to live on land, to which they then migrate. Lastly, we have closely-allied creatures, like the Surinam toad and the terrestrial salamander, which, though they belong by their structures to the class Amphibia, are not amphibious in their habits — creatures the larvae of which do not pass their early lives in the water, and yet go through these same metamorphoses ! Must we then think, like Von Baer, tha*, the distribution of kindred organisms through different media presents an insurmountable difficulty? On the contrary, with facts like these before us, the evolution- hypothesis supplies possible interpretations of many phe nomena that are else unaccountable. After seeing the ways in which such changes of media are in some cases gradually * While these pages arc passing through the press (in 1864), Dr. Hooker has obliged me by pointing out that "plants afford many excellent examples" of analogous transitions. He says that among true "water plants," there are found, in the same species, varieties which have some leaves submerged and some floating ; other varieties in which they are all floating ; and other varieties in which they are all submerged. Further, that many plants characterized by floating leaves, and which have all their leaves floating when they grow in deeper water, are found with partly aerial leaves when they grow in shallower water ; and that elsewhere they occur in almost dry soil with all their leaves aerial. THE ARGUMENTS FROM DISTRIBUTION. 485 imposed by physical conditions, and in other cases voluntarily commenced and slowly increased in the search after food; we shall begin to understand how, in the course of evolution, there have . arisen strange obscurations of one type by the externals of another type. When we see land-birds occa sionally feeding by the water-side, and then learn that one of them, the water-ouzel, an " anomalous member of the strictly terrestrial thrush family, wholly subsists by diving — grasp ing the stones with its feet and using its wings under water " — we are enabled to comprehend how, under pressure of population, aquatic habits may be acquired by creatures organized for aerial life ; and how there may eventually arise an ornithic type in which the traits of the bird are very much disguised. On finding among mammals some that, in search of prey or shelter, have taken to the water in various degrees, we shall cease to be perplexed on discovering the mammalian structure hidden under a fish-like form, as it is in the Cetacea and the Sirenia: especially on finding that in the sea-lion and. the seals there are transitional forms. Grant that there has ever been going 011 that re-distribution of organisms which we see still resulting from their intrusions on one another's areas, media, and modes of life; and we have an explanation of those multitudinous cases in which homologies of structure are complicated with analogies. And while it accounts for the occurrence in one medium of organic types fundamentally organized for another medium, the doc trine of evolution accounts also for the accompanying unfit- nesses. Either the seal has descended from some mammal which little by little became aquatic in its habits, in which case the structure of its hind limbs has a meaning ; or else it was specially framed for its present habitat, in which case the structure of its hind limbs is incomprehensible. § 140. The facts respecting distribution in Time, which have more than any others been cited both in proof and in disproof of evolution, are too fragmentary to be conclusive 480 THE EVOLUTION OF LIFE. cither way. Were the geological record complete, or did it, as both Uniformitarians and Progressionists have commonly assumed, give us traces of the earliest organic forms; the evidence hence derived, for or against, would have had more weight than any other evidence. As it is, all we can do is to see whether such fragmentary evidence as remains, is con gruous with the hypothesis. Paleontology has shown that there is a " general relation between lapse of time and divergence of organic forms " (§ 107) ; and that " this divergence is comparatively slow and continuous where there is continuity in the geological forma tions, but is sudden and comparatively wide wherever there occurs a great break in the succession of strata." Now this is obviously what we should expect. The hypothesis implies structural changes that arc not sudden but gradual. Hence, where conformable strata indicate a continuous record, we may anticipate successions of forms only slightly different from one another; while we may rationally look for marked contrasts between the groups of forms fossilized in adjacent strata, where there is evidence of a great blank in the record. The permanent disappearances of species, of genera, and of orders, which we saw to be a fact tolerably-well established, is also a fact for which the belief in evolution prepares us. If later organic forms have in all cases descended from earlier organic forms, and have diverged during their descent, both from their prototypes and from one another; then it follows that such of them as become extinct at any epoch, will never re-appear at a subsequent epoch; since there can never again arise a concurrence and succession of conditions such as those under which each type was evolved. Though comparisons of ancient and modern organic forms, prove that many types have persisted through enormous periods of time, without undergoing great changes; it was shown that such comparisons do not disprove the occurrence in other organic forms, of changes great enough to produce what are called different types. The result of inductive in- THE ARGUMENTS FROM DISTRIBUTION. 487 quiry we saw to be, that while a few modern higher types yield signs of having been developed from ancient lower types; and that while there are many modern types which may have been thus developed, though we are without evidence that they have been so ; yet that " any admissible hypothesis of progressive modiiication must be compatible with persistence without progression through indefinite periods." Now these results are quite congruous with the hypothesis of evolution. As rationally interpreted, evolution must in all cases be under stood to result, directly or indirectly, from the incidence of forces. If there are no changes of conditions entailing organic changes, organic changes are not to be expected. Only in organisms which fall under conditions leading to additional modifications answering to additional needs, will there be that increased heterogeneity which characterizes higher forms. Hence, though the facts of palaeontology cannot be held con clusive proof of evolution, yet they are congruous with it; and some of them yield it strong support. § 141. One general truth respecting distribution in Time, is profoundly significant. If, instead of contemplating the relations among past forms of life taken by themselves, we contemplate the relations between them and the forms now existing, we find a connexion which is in harmony with the belief in evolution but irreconcilable with any other belief. Note, first, how full of meaning is the close kinship existing between the aggregate of organisms now living, and the aggregate of organisms which lived in the most recent geologic times. In the last-formed strata, nearly all the imbedded remains are those of species which still flourish. Strata a little older contain a few fossils of species now ex tinct, though, usually, species greatly resembling extant ones. Of the remains found in strata of still earlier date, the ex tinct species form a larger percentage ; and the differences be tween them and the allied species now living are more marked. That is to say, the gradual change of organic types in Time, 33 488 THE EVOLUTION OF LIFE. which we before saw is indicated by the geological record, is equally indicated by the relation between existing organic types and organic types of the epochs preceding our own. The evidence completely accords with the belief in a descent of present life from past life. Doubtless such a kinship is not incongruous with the doctrine of special crea tions. It may be argued that the introduction, from time to time, of new species better fitted to the somewhat changed conditions of the Earth's surface, would result in an apparent alliance between our living Flora and Fauna, and the Floras and Faunas that lately lived. No one can deny it. But on passing from the most general aspect of the alliance to its more special aspects, we shall find this interpretation com pletely negatived. For besides a close kinship between the aggregate of sur viving forms and the aggregate of forms which have died out in recent geologic times; there is a peculiar connexion of like nature between present and past forms in each great geographical region. The instructive fact, before cited from Mr. Darwin, is the " wonderful relationship in the same con tinent between the dead and the living." This relationship is not explained by the supposition that new species have been at intervals supernaturally placed in each habitat, as the habitat became modified; since, as we saw, species are by no means uniformly found in the habitats to which they are best adapted. It cannot be said that the marsupials imbedded in recent Australian strata, having become extinct because of unfitness to some new external condition, the existing mar supials were then specially created to fit the modified en vironment; since sundry animals found elsewhere are so much more in harmony with these new Australian condi tions that, when taken to Australia, they rapidly extrude the marsupials. While, therefore, the similarity between the existing Australian Fauna and the Fauna which immediately preceded it over the same area, is just that which the belief in evolution leads us to expect; it is a similarity which THE ARGUMENTS FROM DISTRIBUTION. 489 cannot be otherwise accounted for. And so is it with parallel relations in New England, in South America, and in Europe. § 142. Given, then, that pressure which species exercise on one another, in consequence of the universal overfilling of their respective habitats — given the resulting tendency to thrust themselves into one another's areas, and media, and modes of life, along such lines of least resistance as from time to time are found — given besides the changes in modes of life, hence arising, those other changes which physical alterations of habitats necessitate — given the structural modi fications directly or indirectly produced in organisms by modi fied conditions; and the facts of distribution in Space and Time are accounted for. That divergence and re-divergence of organic forms, which we saw to be shadowed forth by the truths of classification and the truths of embryology, we see to be also shadowed forth by the truths of distribution. If that aptitude to multiply, to spread, to separate, and to dif ferentiate, which the human races have in all times shown, be a tendency common to races in general, as we have ample reason to assume ; then there will result those kinds of spacial relations and chronological relations among the species, and genera, and orders, peopling the Earth's ^ur face, which we find exist. The remarkable identities of type discovered between organisms inhabiting one medium, and strangely modified organisms inhabiting another medium, are at the same time rendered comprehensible. And the appear ances and disappearances of species which the geological record shows us, as well as the connexions between succes sive groups of species from early eras down to our own, cease to be inexplicable. CHAPTER VIII. HOW IS ORGANIC EVOLUTION CAUSED? § 143. ALREADY it has been necessary to speak of the causes of organic evolution in general terms; and now wo are prepared for considering them specifically. The task before us is to affiliate the leading facts of organic evolu tion, on those same first principles conformed to by evolution at large. Before attempting this, however, it will be instructive to glance at the causes of organic evolution which have been from time to time alleged. § 144. The theory that plants and animals of all kinds were gradually evolved, seems to have been at first accom panied only by the vaguest conception of cause — or rather, by no conception of cause properly so called, but only by the blank form of a conception. One of the earliest who in modern times (1735) contended that organisms are indefi nitely modifiable, and that through their modifications they have become adapted to various modes of existence, was De Maillot. But though De Maillet supposed all living beings to have arisen by a natural, continuous process, he does not appear to have had any definite idea of that which determines this process. In 1794, in his Zoonomia, Dr. Erasmus Darwin gave reasons (sundry of them valid ones) for believing that organized beings of every kind, have 490 HOW IS ORGANIC EVOLUTION CAUSED? 491 descended from one, or a few, primordial germs; and along with some observable causes of modification, which he points out as aiding the developmental process, he apparently ascribes it, in part, to a tendency given to such germ or germs when created. He suggests the possibility " that all warm-blooded animals have arisen from one living filament, which THE GREAT FIRST CAUSE endued with animality, with the power of acquiring new parts, attended with new pro pensities, directed by irritations, sensations, volitions, and associations; and thus possessing the faculty of continuing to improve by its own inherent activity." In this passage we see the idea to be, that evolution is pre-determined by some intrinsic proclivity. " It is curious," says Mr. Charles Darwin, " how largely my grandfather, Dr. Erasmus Darwin, anticipated the erroneous grounds of opinion, and the views of Lamarck." One of the anticipa tions was this ascription of development to some inherent tendency. To the " plan general de la nature, et sa marche uniforme dans ses operations," Lamarck attributes " la progression evidente qui existe dans la composition de Torganisation des animaux ; " and " la gradation reguliere qu'ils devroient offrir dans la composition de leur organ isation," he thinks is rendered irregular by secondary causes. Essentially the same in kind, though some what different in form, is the conception put forth in the Vestiges of Creation; the author of which contends " that the several series of animated beings, from the simplest and oldest up to the highest and most recent, are, under the pro vidence of God, the results, first, of an impulse which has been imparted to the forms of life, advancing them, in defi nite times, by generation, through grades of organization terminating in the highest dicotyledons and vertebrata;" and that the progression resulting from these impulses, is modified by certain other causes. The broad contrasts be tween lower and higher forms of life, are regarded by him as implying an innate aptitude to give birth to forms of 492 THE EVOLUTION OF LIFE. more perfect structures. The last to re-enunciate this doctrine has been Prof. Owen ; who asserts " the axiom of the continuous operation of creative power, or of the ordained becoming of living things." Though these words do not suggest a very definite idea, yet they indicate the belief that organic progress is a result of some in-dwelling tendency to develop, supernaturally impressed on living matter at the outset — some ever-acting constructive force which, independently of other forces, moulds organisms into higher and higher forms. In whatever way it is formulated, or by whatever language it is obscured, this ascription of organic evolution to some aptitude naturally possessed by organisms, or miraculously imposed on them, is unphilosophical. It is one of those ex planations which explain nothing — a shaping of ignorance into the semblance of knowledge. The cause assigned is not a true cause — not a cause assimilable to known causes — not a cause that can be anywhere shown to produce analogous effects. It is a cause unrepresentable in thought: one of those illegitimate symbolic conceptions which cannot by any mental process be elaborated into a real conception. In brief, this assumption of a persistent formative power in herent in organisms, and making them unfold into higher types, is an assumption no more tenable than the assump tion of special creations : of which, indeed, it is but a modi fication; differing only by the fusion of separate unknown processes into a continuous unknown process. § 145. Besides this intrinsic tendency to progress which Dr. Darwin ascribes to animals, he says they have a capacity for being modified by processes which their own desires initiate. He speaks of powers as " excited into action by the necessities of the creatures which possess them, and on which their existence depends ; " and more specifically he says that " from their first rudiment or primordium, to the termination of their lives, all animals undergo perpetual HOW IS ORGANIC EVOLUTION CAUSED? 493 transformations; which arc in part produced by their own exertions, in consequence of their desires and aversions, of their pleasures and their pains, or of irritations, or of associa tions; and many of these acquired forms or properties are transmitted to their posterity." While it embodies a belief for which much may be said, this passage involves the assumption that desires and aversions, existing before ex periences of the actions to which they are related, wore the originators of the actions, and therefore of the structural modifications caused by them. In his Philosophic, Zooloyique, Lamarck much more specifically asserts " le sentiment intericur" to be in all creatures that have developed nervous systems, an independent cause of those changes of form which are due to the exercise of organs : distinguishing it from that simple irritability possessed by inferior animals, which cannot produce what we call a desire or emotion ; and holding that these last, along with all " qui manquent de systeme nerveux, ne vivent qu'a 1'aide des excitations qu'ils regoivent de 1'extericur." Afterwards he says — " je reconnus quo la nature, obligee d'abord d'emprunter des milieux en- vironnans la puissance cxcitatrice des mouvemens vitaux et des actions des animaux imparfaits, sut, en composaiit de plus en plus 1'organisation animale, transporter cette puis sance dans 1'interieur meme de ces etres, et qu'a la fin, elle parvint a mettre cette meme puissance a la disposition de 1'individu." And still more definitely he contends that if one considers " la progression qui se montre dans la com position de 1'organisation," ..." alors on eut pu aperce- voir comment les besoins, d'abord reduits a nullite, et dont le nombre ensuite s'est accru graduellement, ont amene le penchant aux actions propres a y satisf aire : comment les actions devenues habituelles et energiqucs, ont occasionne le developpement des organes qui les cxecutcnt." Now though this conception of Lamarck is more precisely stated, and worked out with much greater elaboration and wider knowledge of the facts, it is essentially the same as 494 THE EVOLUTION OF LIFE. that of Dr. Darwin; and along with the truth it contains, contains also the same error more distinctly pronounced. Merely noting that desires or wants, acting directly only on the nervo-muscular system, can have no immediate in fluence on very many organs, as the viscera, or such external appendages as hair and feathers; and observing, further, that even some parts which belong to the apparatus of ex ternal action, such as the bones of the skull, cannot be made to grow by increase of function called forth by desire; it will suffice to point out that the difficulty is not solved, but simply slurred over, when needs or wants are introduced as independent causes of evolution. True though it is, as Dr. Darwin and Lamarck contend, that desires, by leading to increased actions of motor organs, may induce further de velopments of such organs; and true, as it probably is, that the modifications hence arising are transmissible to offspring ; yet there remains the unanswered question — Whence do these desires originate? The transference of the exciting power from the exterior to the interior, as described by Lamarck, begs the question. How comes there a wish to perform an action not before performed? Until some beneficial result has been felt from going through certain movements, what can suggest the execution of such movements? Every desire consists primarily of a mental representation of that which is desired, and secondarily excites a mental representation of the actions by which it is attained; and any such mental representations of the end and the means, imply antecedent experience of the end and antecedent use of the means. To assume that in the course of evolution there from time to time arise new kinds of actions dictated by new desires, is simply to remove the difficulty a step back. § 146. Changes of external conditions are named, by Dr. Darwin, as causes of modifications in organisms. Assigning as evidence of original kinship, that marked similarity of type which exists among animals, he regards their devia- HOW IS ORGANIC EVOLUTION CAUSED? 495 tions from one another, as caused by differences in their modes of life: such deviations being directly adaptive. After enumerating various appliances for procuring food, he says they all " seem to have been gradually produced during many generations by the perpetual endeavour of the creatures to supply the want of food, and to have been delivered to their posterity with constant improvement of them for the purposes required." And the creatures possessing these various appliances are considered as having been rendered unlike by seeking for food in unlike ways. As illustrating the alterations wrought by changed circumstances, he names the acquired characters of domestic animals. La marck has elaborated the same view in detail : using for the purpose, with great ingenuity, his extensive knowledge of the animal kingdom. From a passage in the Avertiissement it would at first sight seem that he looks upon direct adapt ation to new conditions as the chief cause of evolution. He says — " Je regardai comme certain que le mouvement des fluidcs dans 1'interieur des animaux, mouvement qui c'est progressivement accelere avec la composition plus grande de 1'organisation ; et que rinftuence des circonstances nouvelles, a mesure que les animaux s'y exposerent en so repandant dans tous les lieux habitables, furent les deux causes gene- rales qui ont amene les differens animaux a 1'etat ou nous les voyons actuellement." But elsewhere the view he expresses appears decidedly different from this. He asserts that " dans sa marche, la nature a commence, et recommence encore tous les jours, par former les corps organises les plus simples ; " and that " les premieres ebauchcs de 1'animal et du vegetal etant formees dans les lieux et les circonstances convenables, les facultes d'une vie commenc,ante et d'un mouvement or- ganique etabli, ont necessairement developpe pcu a peu les organes, et qu'avec le temps elles les ont diversifies ainsi que les parties." And then, further on, he puts in italics this proposition : — " La progression dans la composition de I 'or ganisation subit, ga et la, dans la serie gctierale des animaux, 496 THE EVOLUTION OF LIFE. des anomalies operees par I'influence des circonstanccs d'liali- tation, et par celle des habitudes contractees." These, and sundry other passages, joined with his general scheme of classification, make it clear that Lamarck conceived adaptive modification to be, not the cause of progression, hut the cause of irregularities in progression. The inherent tendency which organisms have to develop into more perfect forms, would, according to him, result in a uniform series of forms; hut varieties in their conditions work divergences of struc ture, which break up the series into groups: groups which he nevertheless places in uni-serial order, and regards as still substantially composing an ascending succession. § 147. These speculations, crude as they may be con sidered, show much sagacity in their respective authors, and have done good service. Without embodying the truth in definite shapes, they contain adumbrations of it. Not directly, but by successive approximations, do mankind reach correct conclusions; and those who first think in the right direction, loose as may be their reasonings, and wide of the mark as their inferences may be, yield indispensable aid by framing provisional conceptions and giving a bent to inquiry. Contrasted with the dogmas of his age, the idea of De Maillet was a great advance. Before it can be ascertained how organized beings have been gradually evolved, there must be reached the conviction that they have been gradu ally evolved; and this conviction he reached. His wild notions about the way in which natural causes acted in the production of plants and animals, must not make us forget the merit of his intuition that animals and plants were pro duced by natural causes. In Dr. Darwin's brief expo sition, the belief in a progressive genesis of organisms is joined with an interpretation having considerable definite- ness and coherence. In the space of ten pages he not only indicates several of the leading classes of facts which support HOW IS ORGANIC EVOLUTION CAUSED! 497 the hypothesis of development, but he docs something towards suggesting the process of development. His reasonings show an unconscious mingling of the belief in a supernaturally- impressed tendency to develop, with the belief in a develop ment arising from the changing incidence of conditions. 1'robably had he pursued the inquiry further, this last belief would have grown at the expense of the first. La marck, in elaborating this general conception, has given greater precision both to its truth and to its error. Assert ing the same imaginary factors and the same real factors, he has traced out their supposed actions in detail; and has, in consequence, committed himself to a greater number of untenable positions. But while, in trying to reconcile the facts with a theory which is only an adumbration of the truth, he laid himself open to the criticisms of his con temporaries; he proved himself profounder than his con temporaries by seeing that natural genesis, however caused, has been going on. If they were wise in not indorsing a theory which fails to account for a great part of the facts; they were unwise in ignoring that degree of congruity with the facts, which shows the theory to contain some funda mental verity. Leaving out, however, the imaginary factors of evolution which these speculations allege, and looking only at the one actual factor which Dr. Darwin and Lamarck assign as ac counting for some of the phenomena; it is manifest, from our present stand-point, that this, so far as it is a cause of evolution, is a proximate cause and not an ultimate cause. To say that functionally-produced adaptation to conditions originates either evolution in general, or the irregularities of evolution, is to raise the further question — why is there a functionally-produced adaptation to conditions? — why do use and disuse generate appropriate changes of structure? Neither this nor any other interpretation of biologic evolu tion which rests simply on the basis of biologic induction, is an ultimate interpretation. The biologic induction must 498 TIIJS EVOLUTION OF LIFE. itself be interpreted. Only when the process of evolution of organisms is affiliated on the process of evolution in general, can it be truly said to be explained. The thing required is to show that its various results are corollaries from first principles. We have to reconcile the facts with the universal laws of the re-distribution of matter and motion. CHAPTER IX. EXTERNAL FACTORS. § 148. WHEN illustrating the rhythm of motion (First Principles, § 83) it was pointed out that besides the daily and annual alternations in the quantities of light and heat which any portion of the Earth's surface receives from the Sun, there are alternations which require immensely-greater periods to complete. Reference was made to the fact that " every planet, during a certain long period, presents more of its northern than of its southern hemisphere to the Sun at the time of its nearest approach to him ; and then again, during a like period, presents more of its southern hemisphere than of its northern — a recurring coincidence which, though it causes in some planets no sensible alterations of climate, in volves, in the case of the Earth, an epoch of 21,000 years during which each hemisphere goes through a cycle of tem perate seasons, and seasons that are extreme in their heat and cold." Further, we saw that there is a variation of this variation. The slow rhythm of temperate and intemperate climates, which takes 21,000 years to complete itself, under goes exaggeration and mitigation during epochs that are far longer. The Earth's orbit slowly alters in form : now ap proximating to a circle, and now becoming more eccentric. During the period in which the Earth's orbit has least eccentricity, the temperate and intemperate climates which repeat their cycle in 21,000 years, are severally less tem- 499 500 TIIR EVOLUTION OF LIFE. pcrate and less intemperate, than when, some one or two millions of years later, the Earth's orhit has reached its ex treme of eccentricity. Thus, besides those daily variations in the quantities of light and heat received by organisms, and responded to by variations in their functions; and besides the annual variations in the quantities of light and heat which organisms receive, and similarly respond to by variations in their functions; there are variations that severally complete themselves in 21,000 years and in some millions of years — variations to which there must also be responses in the changed functions of organisms. The whole vegetal and animal kingdoms, are subject to quadruply-compounded rhythms in the inci dence of the forces on which life primarily depends — rhythms so involved in their slow working round that at no time during one of these vast epochs, can the incidence of these various forces be exactly the same as at any other time. To the direct effects so produced on organ isms, have to be added much more important indirect effects. Changes of distribution must result. Certain redistributions are occasioned even by the annual variations in the quantities of the solar rays received by each part of the Earth's surface. The migrations, of birds thus caused are familiar. So, too, are the migrations of certain fishes : in some cases from one part of the sea to another; in some cases from salt water to fresh water; and in some cases from fresh water to salt water. Now just as the yearly changes in the amounts of light and heat falling on each locality, yearly extend and restrict the habitats of many organisms which are able to move about with some rapidity; so must the alterations of temperate and intemperate climates produce extensions and restrictions of habitats. These, though slow, must be uni versal — must affect the habitats of stationary organisms as well as those of locomotive ones. For if, during an astro nomic era, there is going on at any limit to a plant's habitat, a diminution of the winter's cold or summer's heat, which EXTERNAL FACTORS. 501 had before stopped its spread at that limit ; then, though the individual plants are fixed, yet the species will move : the seeds of plants living at the limit, will produce individuals which survive beyond the limit. The gradual spread so effected, having gone on for souie ten thousand years, the opposite change of climate will begin to cause retreat. The tide of each species will, during one half of a long epoch, slowly flow into new regions, and then will slowly ebb away from them. Further, this rise and fall in the tide of each species will, during far longer intervals, undergo increasing rises and falls and then decreasing rises and falls. There will be an alteration of spring tides and neap tides, answer ing to the changing eccentricity of the Earth's orbit. These astronomical rhythms, therefore, entail on organisms unceasing changes in the incidence of forces in two ways. They directly subject them to variations of solar influences, in such a manner that each generation is somewhat differently affected in its functions; and they indirectly bring about complicated alterations in the environing agencies, by carry ing each species into the presence of new physical conditions, new soil and surface. § 149. The power of geological actions to modify every where the circumstances in which plants and animals are placed, is conspicuous. In each locality denudation slowly uncovers different deposits, and slowly changes the exposed areas of deposits already uncovered. Simultaneously, the alluvial beds in course of formation, arc qualitatively affected by these progressive changes in the natures and proportions of the strata denuded. The inclinations of surfaces and their directions with respect to the Sun, arc at the same time modi fied; and the organisms existing on them are thus having their thermal conditions continually altered, as well as their drainage. Igneous action, too, complicates these gradual modifications. A flat region cannot be step by step thrust up into a protuberance without unlike climatic changes 502 THE EVOLUTION OF LIFE. being produced in its several parts, by their exposures to different aspects. Extrusions of trap, wherever they take place, revolutionize the localities ; both over the areas covered and over the areas on to which their detritus is carried. And where volcanoes are formed, the ashes they occasionally send out modify the character of the soil throughout large sur rounding tracts. In like manner alterations in the Earth's crust cause the ocean to be ever subjecting the organisms it contains to new combinations of conditions. Here the water is being deep ened by subsidence, and there shallowed by upheaval. While the falling upon it of sediment brought down by neighbour ing large rivers, is raising the sea-bottom in one place, in another the habitual rush of the tide is carrying away the sediment deposited in past times. The mineral character of the submerged surface on which sea-weeds grow and molluscs crawl, is everywhere occasional]y changed; now by the bringing away from an adjacent shore some previously un touched strata; and now by the accumulation of organic remains, such as the shells of pteropods or of foraminifera. A further series of alterations in the circumstances of marine organisms, is entailed by changes in the movements of the water. Each modification in the outlines of neighbouring shores makes the tidal streams vary their directions or velocities or both. And the local temperature is from time to time raised or lowered, because some far-distant change of form in the Earth's crust has wrought a divergence in those circulating currents of warm and cold water which pervade the ocean. These geologically-caused changes in the physical charac ters of each environment, occur in ever-new combinations, and with ever-increasing complexity. As already shown (First Principles, § 158), it follows from the law of the mul tiplication of effects, that during long periods each tract of the Earth's surface increases in heterogeneity of both form and substance. So that plants and animals of all kinds are, EXTERNAL FACTORS. 503 in the course of generations, subjected by alterations in the crust of the Earth, to sets of incident forces differing from previous sets, both by changes in the proportions of the factors and, occasionally, by the addition of new factors. § 150. Variations in the astronomical conditions joined with variations in the geological conditions, bring about variations in the meteorological conditions. Those slow alternations of elevation and subsidence which take place over immense areas, here producing a continent where once there was a fathomless ocean, and there causing wide seas to spread where in a long past epoch there stood snow capped mountains, gradually work great atmospheric changes. While the highest parts of an emerging surface of the Earth's crust exist as a cluster of islands, the plants and animals which in course of time migrate to them have climates that are peculiar to small tracts of land surrounded by large tracts of water. As, by successive upheavals, greater areas are exposed, there begin to arise sensible con trasts between the states of their peripheral parts and their central parts. The breezes which daily moderate the extremes of temperature near the shores, cease to affect the interiors; and the interiors, less qualified too in their heat and cold by such ocean-currents as approach the coast, acquire more decidedly the characters due to their latitudes. Along with the further elevations which unite the members of the archipelago into a continent, there come new meteoro- logic changes, as well as exacerbations of the old. The winds, which were comparatively uniform in their directions and periods when only islands existed, grow involved in their distribution, and widely-different in different parts of the continent. The quantities of rain which they discharge and of moisture which they absorb, vary everywhere according to the proximity to the sea and to surfaces of land having special characters. Other complications result from variations of height above 3U 504: THE EVOLUTION OP LIFE. the sea: elevation producing a decrease of heat and conse quently an increase in the precipitation of water — a precipit ation which takes the shape of snow where the elevation ia very great, and of .rain where it is not so great. The gather ings of clouds and descents of showers around mountain tops, are familiar to every tourist. Inquiries in the neigh bouring valleys prove that within distances of a mile or two the recurring storms differ in their frequency and violence. Nay, even a few yards off, the meteorological conditions vary in such regions : as witness the way in which the condensing vapour keeps eddying round on one side of some high crag, while the other side is clear; or the way in which the snow- line runs irregularly to different heights, in all the hollows and ravines of each mountain side. As climatic variations thus geologically produced, are compounded with those which result from slow astronomical changes; and as no correspondence exists between the geologic and the astronomic rhythms ; it results that the same plexus of actions never recurs. Hence the incident forces to which the organisms of every locality are exposed by atmos pheric agencies, are ever passing into unparalleled combina tions; and these are on the average ever becoming more complex. § 151. Besides changes in the incidence of inorganic forces, there are equally continuous, and still more involved, changes in the incidence of forces which organisms exercise on one another: As before pointed out (§ 105), the plants and animals inhabiting each locality are held together in so entangled a web of relations, that any considerable modifica tion which one species undergoes, acts indirectly on many other species, and eventually changes, in some degree, the circumstances of nearly all the rest. If an increase of heat, or modification of soil, or decrease of humidity, causes a par ticular kind of plant either to thrive or to dwindle, an unfavourable or favourable effect is wrought on all such EXTERNAL FACTORS. 505 competing kinds of plants as are not immediately influenced in the same way. The animals which eat the seeds or browse on the leaves, cither of the plant primarily affected or those of its competitors, are severally altered in their states of nutri tion and in their numbers; and this change presently tells on various predatory animals and parasites. And since each of these secondary and tertiary changes becomes itself a centre of others, the increase or decrease of each species produces waves of influence which spread and reverberate and re- reverberate throughout the whole Flora and Fauna of the locality. More marked and multiplied still, are the ultimate effects of those causes which make possible the colonization of neigh bouring areas. Each intruding plant or animal, besides the new inorganic conditions to which it is subject, is subject to organic conditions different from those to which it has been accustomed. It has to compete with some organisms unlike those of its preceding habitat. It must preserve itself from enemies not before encountered. Or it may meet with a species over which it has some advantage greater than any it had over the species it was previously in contact with. Even where migration does not bring it face to face with new competitors or new enemies or new prey, it inevitably experiences new proportions among these. Further, an ex panding species is almost certain to invade more than one adjacent region. Spreading both north and south, or east and west, it will come among the plants and animals, here of a level district and there of a hilly one — here of an inland tract and there of a tract bordered by the sea. And while different groups of its members will thus expose themselves to the actions and reactions of different Floras and Faunas, these different Floras and Faunas will simultaneously have their organic conditions changed by the intruders. This process becomes gradually more active and more complicated. Though, in particular cases, a plant or animal may fall into simpler relations with the living things around 506 THE EVOLUTION OF LIFE. than those it was before placed in, yet it is manifest that, on the average, the organic environments of organisms have been advancing in heterogeneity. As the number of species with which each species is directly or indirectly implicated, multiplies, each species is oftencr subject to changes in the organic actions which influence it. These more frequent changes severally grow more involved. And the correspond ing reactions affect larger Floras and Faunas, in ways increas ingly complex and varied. § 152. When the astronomic, geologic, meteorologic, and organic agencies which are at work on each species of plant and animal are contemplated as becoming severally more complicated in themselves, and as co-operating in ways that are always partially new; it will be seen that throughout all time there has been an exposure of organisms to endless successions of modifying causes which gradually acquire an intricacy scarcely conceivable. Every kind of plant and animal may be regarded as for ever passing into a new environment — as perpetually having its relations to external circumstances altered, either by their changes with respect to it when it remains stationary, or by its changes with respect to them when it migrates, or by both. Yet a further cause of progressive alteration and compli cation in the incident forces, exists. All other things con tinuing the same, every additional faculty by which an organism is brought into relation with external objects, as well as every improvement in such faculty, becomes a means of subjecting the organism to a greater number and variety of external stimuli, and to new combinations of external stimuli. So that each advance in complexity of organization, itself becomes an added source of complexity in the incidence of external forces. Once more, every increase in the locomotive powers of animals, increases both the multiplicity and the multiformity of the actions of things upon them, and of their reactions EXTERNAL FACTORS. 507 upon things. Doubling a creature's activity quadruples the area that comes within the range of its excursions; thus augmenting in number and heterogeneity, the external agencies which act on it during any given interval. By compounding the actions of these several orders of factors, there is produced a geometric progression of changes, increasing with immense rapidity. And there goes on an equally rapid increase in the frequency with which the com binations of the actions are altered, and the intricacies of their co-operations enhanced. CHAPTER X. INTERNAL FACTORS. §153. WE saw at the outset (§§10—16), that organic matter is built up of molecules so unstable, that the slightest variation in their conditions destroys their equilibrium, and causes them either to assume altered structures or to decom pose. But a substance which is beyond all others changeable by the actions and reactions of the forces liberated from instant to instant within its own mass, must be a substance which is beyond all others changeable by the forces acting on it from without. If their composition fits organic aggregates for undergoing with special facility and rapidity those re-dis tributions of matter and motion whence result individual organization and life ; then their composition must make them similarly apt to undergo those permanent re-distributions of matter and motion which are expressed by changes of struc ture, in correspondence with permanent re-distributions of matter and motion in their environments. In First Principles,, when considering the phenomena of Evolution at large, the leading characters and causes of those changes which constitute organic evolution were briefly traced. Under each of the derivative laws of force to which the passage from an incoherent, indefinite homogeneity to a coherent, definite heterogeneity, conforms, were given illustra tions drawn from the metamorphoses of living bodies. Here 508 INTERNAL FACTORS. 509 it will be needful to contemplate the several resulting pro cesses as going on at once, in both individuals and species. § 154. Our postulate being that organic evolution in gen eral commenced with homogeneous organic matter, we have first to remember that the state of homogeneity is an un stable state (First Principles, §149). In any aggregate " the relations of outside and inside, and of comparative nearness to neighbouring sources of influence, imply the re ception of influences that arc unlike in quantity, or quality, or both; and it follows that unlike changes will be produced in the parts thus dissimilarly acted upon." Further, " if any given whole, instead of being absolutely uniform through out, consists of parts distinguishable from one another — if each of these parts, while somewhat unlike other parts, is uniform within itself; then, each of them being in unstable equilibrium, it follows that while the changes set up within it must render it multiform, they must at the same time render the whole more multiform than before ; " and hence, " whether that state with which we commence be or be not one of perfect homogeneity, the process must equally be towards a relative heterogeneity." This loss of homogeneity which the special instability of organic aggre gates fits them to display more promptly and variously than any other aggregates, must be shown in more numerous ways in proportion as the incident forces are more numerous. Every differentiation of structure being a result of some difference in the relations of the parts to the agencies acting on them, it follows that the more multiplied and more unlike the agencies, the more varied must be the differentiations wrought. Hence the change from a state of homogeneity to a state of heterogeneity, will be marked in proportion as the environing actions to which the organism is exposed are complex. This transition from a uniform to a mul tiform state, must continue through successive individuals. Given a series of organisms, each of which is developed from 510 THE EVOLUTION OF LIFE. a portion of a preceding organism,, and the question is whether, after exposure of the series for a million years to changed in cident forces, one of its members will be the same as though the incident forces had only just changed. To say that it will, is implicitly to deny the persistence of force. In relation to any cause of divergence, the whole series of such organisms may be considered as fused together into a continuously- existing organism ; and when so considered, it becomes mani fest that a continuously-acting cause will go on working a continuously-increasing effect, until some counteracting cause prevents any further effect. But now if any primordial organic aggregate must, in it self and through its descendants, gravitate from uniformity to multiformity, in obedience to the more or less multiform forces acting on it; what must happen if these multiform forces are themselves undergoing slow variations and compli cations? Clearly the process, ever-advancing towards a tem porary limit but ever having its limit removed, must go on unceasingly. On those structural changes wrought in the once homogeneous aggregate by an original set of incident forces, will be superposed further changes wrought by a modi fied set of incident 'forces; and so on throughout all time. Omitting for the present those circumstances which check and qualify its consequences, the instability of the homo geneous must be recognized as an ever-acting cause of organic evolution, as of all other evolution. While it follows that every organism, considered as an in dividual and as one of a series, tends thus to pass into a more heterogeneous state; it also follows that every species, con sidered as an aggregate of individuals, tends to do the like. Throughout the area it inhabits, the conditions can never be absolutely uniform : its members must, in different parts of the area, be exposed to different sets of incident forces. Still more decided must this difference of exposure be when its members spread into other habitats. Those expansive and repressive energies which set to each species a limit that INTERNAL FACTORS. 511 perpetually oscillates from side to side of a certain mean, are, as we lately saw, frequently changed by new combinations of the external factors — astronomic, geologic, meteorologic, and organic. Hence there from time to time arise lines of di minished resistance, along which the species flows into new localities. Such portions of the species as thus migrate, are subject to circumstances unlike its previous average circum stances. And from multiformity of the circumstances, must come multiformity of the species. Thus the law of the instability of the homogeneous has here a three-fold corollary. As interpreted in connexion with the ever-progressing, ever-complicating changes in external factors, it involves the conclusion that there is a prevailing tendency towards greater heterogeneity in all kinds of organisms, considered both individually and in successive generations ; as well as in each assemblage of organisms con stituting a species ; and, by consequence, in each genus, order, and class. § 155. When considering the causes of evolution in general, we further saw (First Principles., § 156), that the multiplication of effects aids continually to increase that heterogeneity into which homogeneity inevitably lapses. It was pointed out that since "the several parts of an aggre gate are differently modified by any incident force ; " and since " by the reactions of the differently modified parts the incident force itself must be divided into differently modi fied parts ; " it follows that " each differentiated division of the aggregate thus becomes a centre from which a differ entiated division of the original force is again diffused. And since unlike forces must produce unlike results, each of these differentiated forces must produce, throughout the aggregate, a further series of differentiations." To this it was added that, in proportion as the heterogeneity increases, the compli cations arising from this multiplication of effects grow more marked; because the more strongly contrasted the parts of 512 THE EVOLUTION OF LIFE. an aggregate become, the more different must.be their reac tions on incident forces, and the more unlike must be the secondary effects which these initiate; and because every increase in the number of unlike parts adds to the number of such differentiated incident forces, and such secondary effects. How this multiplication of effects conspires, with the in stability of the homogeneous, to work an increasing multi formity of structure in an organism, was shown at the time; and the foregoing pages contain further incidental illustra tions. In § 69 it was pointed out that a change in one function must produce ever-complicating perturbations in other functions; and that, eventually, all parts of the organism must be modified in their states. Suppose that the head of a bison becomes much heavier, what must be the indirect results ? The muscles of the neck are put to greater exertions; and its vertebra have to bear additional tensions and pressures, caused both by the increased weight of the head, and by the stronger contractions of the muscles that support and move it. These muscles also affect their special attachments: several of the dorsal spines suffer augmented strains; and the vertebra? to which they are fixed are more severely taxed. Further, this heavier head and the more massive neck it necessitates, require a stronger fulcrum: the whole thoracic arch, and the fore-limbs which support it, are subject to greater continuous stress and more violent occasional shocks. And the required strengthening of the fore-quarters cannot take place without the centre of gravity being changed, and the hind limbs being differently reacted upon during locomotion. Any one who compares the out line of the bison with that of its congener, the ox, will see how profoundly a heavier head affects the entire osseous and muscular systems. Besides this multiplica tion of mechanical effects, there is a multiplication of physiological effects. The vascular apparatus is modified throughout its whole structure by each considerable modifi- INTERNAL FACTORS. 513 cation in the proportions of the body. Increase in the size of any organ implies a quantitative, and often a qualitative, reaction on the blood; and thus alters the nutrition of all other organs. Such physiological correlations are exemplified in the many differences which accompany difference of sex. That the minor sexual peculiarities are brought about by the physiological actions and reactions, is shown both by the fact that they are commonly but faintly marked until the fundamentally distinctive organs are developed, and that when the development of these is prevented, the minor sexual peculiarities do not arise. No further proof is, I think, needed, that in any individual organism or its de scendants, a new external action must, besides the primary internal change which it works, work many secondary changes, as well as tertiary changes still more multiplied. That tendency towards greater heterogeneity which is given to an organism by disturbing its environment, is helped by the tendency which every modification has to produce other modifications — modifications which must become more nu merous in proportion as the organism becomes more com plex. Lastly, among the indirect and involved manifesta tions of this tendency, we must not omit the innumerable small irregularities of structure which result from the cross ing of dissimilarly-modified individuals. It was shown (§§89, 90) that what are called "spontaneous variations," are interprctable' as results of miscellaneously compounding the changes Avrought in different lines of ancestors by differ ent conditions of life. These still more complex and multi-- tudinous effects so produced, are further illustrations of the multiplication of effects. Equally in the aggregate of individuals constituting a species, does multiplication of effects become the continual cause of increasing multiformity. The lapse of a species into divergent varieties, initiates fresh combinations of forces tending to work further divergences. The new varieties compete with the parent species in new ways; and so add 514: THE EVOLUTION OF LIFE. new elements to its circumstances. They modify somewhat the conditions of other species existing in their habitat, or in the habitat they have invaded; and the modifications wrought in such other species become additional sources of influence. The Flora and Fauna of every region are united by their entangled relations into a whole, of which no part can be affected without affecting the rest. Hence, each dif ferentiation in a local assemblage of species, becomes the cause of further differentiations. § 156. One of the universal principles to which we saw that the re-distribution of matter and motion conforms, is that in any aggregate made up of mixed units, incident forces produce segregation — separate unlike units and bring together like units ; and it was shown that the increasing in tegration and definiteness which characterizes each part of an evolving organic aggregate, as of every other aggregate, results from this (First Principles., § 166). It remains here to say that while the actions and reactions between organ isms and their changing environments, add to the hetero geneity of organic structures, they also give to the heterogeneity this growing distinctness. At first sight the reverse might be inferred. It might be argued that any new set of effects wrought in an organism by some new set of external forces, must tend more or less to obliterate the effects previously wrought — must produce confusion or in- definiteness. A little consideration, however, will dissipate this impression. Doubtless the condition under which alone increasing de- finiteness of structure can be acquired by any part of an or ganism, either in an individual or in successive generations, is that such part shall be exposed to some set of tolerably-con stant forces; and doubtless, continual change of circum stances interferes with this. But the interference can never be considerable. For the pre-existing structure of an organ ism prevents it from living under any new conditions except INTERNAL FACTORS. 515 such as arc congruous with the fundamental characters of its organization — such as subject its essential organs to actions substantially the same as before. Great changes must kill it. Hence, it can continuously expose itself and its descendants, only to those moderate changes which do not destroy the general harmony between the aggregate of incident forces and the aggregate of its functions. That is, it must remain under influences calculated to make greater the defmiteness of the chief differentiations already produced. If, for ex ample, we set out with an animal in which a rudimentary vertebral column with its attached muscular system has been established; it is clear that the mechanical arrange ments have become thereby so far determined, that subse quent modifications are extremely likely, if not certain, to be consistent with the production of movement by the actions of muscles on a flexible central axis. Hence, there will con tinue a general similarity in the play of forces to which the flexible central axis is subject; and so, notwithstanding the metamorphoses which the vertebrate type undergoes, there will be a maintenance of conditions favourable to increasing defmitencss and integration of the vertebral column. More over, this maintenance of such conditions becomes secure in proportion as organization advances. Each further com plexity of structure, implying some further complexity in the relations between an organism and its environment, must tend to specialize the actions and reactions between it and its environment — must tend to increase the stringency with which it is restrained within such environments as admit of those special actions and reactions for which its structure fits it; that is, must further guarantee the continuance of those actions and reactions to which its essential organs respond, and therefore the continuance of the segregating process. How in each species, considered as an aggregate of indi viduals, there must arise stronger and stronger contrasts among those divergent varieties which result from the in stability of the homogeneous and the multiplication of effects, 510 THE EVOLUTION OF LIFE. need only be briefly indicated. It has already been shown (First Principles., § ICG), that in conformity to the universal law that mixed units are segregated by like incident forces, there are produced increasingly-definite distinctions among varieties, wherever there occur definitely-distinguished sets of conditions to which the varieties are respectively subject. § 157. Probably in the minds of some, the reading of this chapter has been accompanied by a running commentary, to the effect that the argument proves too much. The apparent implication is, that the passage from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity in organic aggregates, must have been going on universally; whereas we find that in many cases there has been persistence with out progression. This apparent implication, however, is not a real one. For though every environment on the Earth's surface undergoes changes; and though usually the organisms which each environment contains, cannot escape certain resulting new influences; yet occasionally such new influences are escaped, by the survival of species in the unchanged parts of their habitats, or by their spread into neighbouring habitats which the change has rendered like their original habitats, or by both. Any alteration in the temperature of a climate or its degree of humidity, is unlikely to affect simultaneously the whole area occupied by a species; and further, it can scarcely fail to happen that the addition or subtraction of heat or moisture, will give to a part of some adjacent area, a climate like that to which the species has been habituated. If, again, the circumstances of a species are modified by the intrusion of some foreign kind of plant or animal, it follows that since the intruders will probably not spread throughout its whole habitat, the species will, in one or more localities, remain unaffected by them. Especially among marine crea tures, must there frequently occur cases in which modifying causes are continually eluded. Comparatively uniform as INTERNAL FACTORS. 517 arc the physical conditions to which the sea exposes its in habitants, it becomes possible for such of them as live on widely-diffused food, to be widely distributed; and wide dis tribution generally prevents the members of a species from being all subject to the same cause. Our commonest cirr- iped, for instance, subsisting on minute creatures every where dispersed through the water; needing only to have some firm surface on which to build up its shell; and in scarcely any danger from surrounding animals; is able to exist on shores so widely remote from one another, that nearly every change in the incident forces must fall within narrower areas than that which the species occupies. Nearly always, therefore, a portion of the species will survive un modified. Its easily-transported germs will take possession of such new habitats as have been rendered fitter by the change that has unfitted some parts of its original habitat. Hence, on successive occasions, while some parts of the species are slightly transformed, another part may continu ally escape transformation by migrating hither and thither, where the simple conditions needed for its existence recur in nearly the same combinations as before. And it will so become possible for it to survive, with insignificant structural changes, throughout long geologic periods. § 158. The results to which we find ourselves led, are these. In subordination to the different amounts and kinds of forces to which its different parts are exposed, every indi vidual organic aggregate, like all other aggregates, tends to pass from its original indistinct simplicity towards a more distinct complexity. Unless we deny the persistence of force, we must admit that the lapse of an organism's struc ture from an indefinitely homogeneous to a definitely hetero geneous state, must be cumulative in successive generations, if the forces causing it continue to act. And for the like reasons, the increasing assemblage of individuals arising from 518 THE EVOLUTION OF LIFE. a common stock, is also liable to lose its original uniformity; and, in successive generations, to grow more pronounced in its multiformity. These changes, which would go to but a comparatively small extent were organisms exposed to constant external conditions, are kept up by the continual changes in external conditions, produced by astronomic, geologic, meteorologic, and organic agencies: the average result being, that on previous complications wrought by previous incident forces, new complications are continually superposed by new inci dent forces. And hence simultaneously arises increasing heterogeneity in the structures of individuals, in the struc tures of species, and in the structures of the Earth's Flora and Fauna. But while, in very many or in most cases, the ever- changing incidence of forces is ever adding to the complexity of organisms, and to the complexity of the organic world as a whole; it does this only where its action cannot be eluded. And since, by migration, it is possible for a species to keep itself under conditions that are tolerably constant, there must be a proportion of cases in which greater heterogeneity of structure is not to be expected. To show, however, that there must arise a certain average tendency to the production of greater heterogeneity is not sufficient. Aggregates might be rendered more heterogeneous by changing incident forces, without having given to them that kind of heterogeneity required for carrying on life. Hence it remains now to inquire how the production and maintenance of this kind of heterogeneity is insured. CHAPTER XL DIRECT EQUILIBRATION. § 159. EVERY change is towards a balance of forces; and of necessity can never cease until a balance of forces is reached. When treating of equilibration under its general aspects (First Principles, Part II., Chap, xxii.), we saw that every aggregate having compound movements tends continu ally towards a moving equilibrium; since any unequilibrated force to which such an aggregate is subject, if not of a kind to overthrow it altogether, must continue modifying its state until an equilibrium is brought about. And we saw that the structure simultaneously reached must be " one presenting an arrangement of forces that counterbalance all the forces to which the aggregate is subject ; " since, " so long as there remains a residual force in any direction — be it excess of a force exercised by an aggregate on its environment, or of a force exercised by its environment on the aggregate, equi librium does not exist; and therefore the re-distribution of matter must continue." It is essential that this truth should here be fully compre hended; and to the end of insuring clear comprehension of it, some re-illustration is desirable. The case of the Solar System will best serve our purpose. An assemblage of bodies, each of which has its simple and compound motions that severally alternate between two extremes, and the whole of which has its involved perturbations, that now increase 34 519 520 THE EVOLUTION OP LIFE. and now decrease, is here presented to us. Suppose a new factor were brought to 'bear on this moving equilibrium — say by the arrival of some wandering mass, or by an additional momentum given to one of the existing masses — what would be the result? If the strange body or the extra energy were very large, it might so derange the entire system as to cause its collapse. But what if the incident energy, falling on the system from without, proved insufficient to overthrow it? There would then arise a set of perturbations which would, in the course of an enormous period, slowly work round into a modified moving equilibrium. The effects primarily im pressed on the adjacent masses, and in a smaller degree on the remoter masses, would presently become complicated with the secondary effects impressed by the disturbed masses on one another ; and these again with tertiary effects. Waves of perturbation would continue to be propagated throughout the entire system; until, around a new centre of gravity, there had been established a set of planetary motions different from the preceding ones. The new energy must gradually be used up in overcoming the energies resisting the divergence it generates; which antagonizing energies, when no longer opposed, set up a counter-action, ending in a compensating divergence in the opposite direction, followed by a re-com pensating divergence, and so on. Now though instead of being, like the Solar System, in a state of independent moving equilibrium, an organism is in a state of dependent moving equilibrium (First Principles, § 170) ; yet this does not prevent the manifestation of the same law. Every animal daily obtains from without, a supply of energy to replace the energy it expends; but this continual giving to its parts a new momentum, to make up for the momentum con tinually lost, docs not interfere with the carrying on of actions and reactions like those just described. Here, as before, we have a definitely-arranged aggregate of parts, called organs, having their definitely-established actions and reactions, called functions. These rhythmical actions or DIRECT EQUILIBRATION. 521 functions, and the various compound rhythms resulting from their combinations, are so adjusted as to balance the actions to which the organism is subject: there is a constant or periodic genesis of energies which, in their kinds, amounts, and directions, suffice to antagonize the energies the organism has constantly or periodically to bear. If, then, there exists this moving equilibrium among a set of internal actions, exposed to a set of external actions, what must result if any of the external actions are changed? Of course there is no longer an equilibrium. Some energy which the organism habitually generates, is too great or too small to balance some incident energy; and there arises a residual energy exerted by the environment on the organism, or by the organism on the environment. This residual or unbalanced energy, of necessity expends itself in producing some change of state in the organism. Acting directly on some organ and modify ing its function, it indirectly modifies dependent functions and remotely influences all the functions. As we have already seen (§§ 68, 69), if this new energy is permanent, its effects must be gradually diffused throughout the entire sys tem; until it has come to be equilibrated in producing those structural rearrangements whence result a counter-balancing energy. The bearing of this general truth on the question we are now dealing with is obvious. Those modifications upon modifications, which the unceasing mutations of their en vironments have been all along generating in organisms, have been in each case modifications involved by the estab lishment of a new balance with the new combination of actions. In every species throughout all geologic time, there has been perpetually going on a rectification of the equilibrium, which has been perpetually disturbed by the alteration of its circumstances; and every further hetero geneity has been the addition of a structural change entailed by a new equilibration, to the structural changes entailed by previous equilibrations. There can .be no other ultimate in- 522 THE EVOLUTION OF LIFE. tcrpretation of the matter, since change can have no other goal. This equilibration between the functions of an organism and the actions in its environment, may be either direct or indirect. The new incident force may either immediately call forth some counteracting force, and its concomitant structural change; or it may be eventually balanced by some otherwise-produced change of function and structure. These two processes of equilibration are quite distinct, and must be separately dealt with. We will devote this chapter to the first of them. § 160. Direct equilibration is that process currently known as adaptation. We have already seen (Part II., Chap. v.), that individual organisms become modified when placed in new conditions of life — so modified as to re-adjust the powers to the requirements; and though there is great difficulty in disentangling the evidence, we found reason for thinking (§82) that structural changes thus caused by functional changes are inherited. In the last chapter, it was argued that if, instead of the succession of individuals constituting a species, there were a continuously-existing individual, any functional and structural divergence produced by a new inci dent action, would increase until the new incident action was counterpoised ; and that the replacing of a continuously- existing individual by a succession of individuals, each formed out of the modified substance of its predecessor, will not pre vent the like effect from being produced. Here we further find that this limit towards which any such organic change advances, in the species as in the individual, is a new moving equilibrium adjusted to the new arrangement of external forces. But now what are the conditions under which alone, direct equilibration can occur ? Are all the modifications that serve to re-fit organisms to their environments, directly adaptive modifications? And if otherwise, which are the directly DIRECT EQUILIBRATION. 523 adaptive and which are not? How are we to distinguish between them? There can be no direct equilibration with an external agency which, if it acts at all, acts fatally ; since the organism to be adapted disappears. Conversely, some inaccessible benefit which a small modification in the organism would make accessible, cannot by its action tend to produce this modification: the modification and the benefit do not stand in dynamic relation. The only new incident forces which can work the changes of function and structure required to bring any animal or plant into equilibrium with them, are such incident forces as operate on this animal or plant, either continuously or frequently. They must be capable of appreciably changing that set of complex rhythmical actions and reactions constituting the life of the organism; and yet must not usually produce perturbations that are fatal. Let us see what are the limits to direct equilibration hence arising. § 161. In plants, organs engaged in nutrition, and exposed to variations in the amounts and proportions of matters and forces utilized in nutrition, may be expected to undergo cor responding variations. We find evidence that they do this. The " changes of habit " which are common in plants, when taken to places unlike in climate or soil to those before in habited by them, are changes of parts in which the modified external actions directly produce modified internal actions. The characters of the stem and shoots as woody or succulent, erect or procumbent; of the leaves in respect of their sizes, thicknesses, and textures; of the roots in their degrees of development and modes of growth; are obviously in imme diate relation to the characters of the environment. A per manent difference in the quantity of light or heat affects, day after day, the processes going on in the leaves. Habitual rain or drought alters all the assimilative actions, and appre ciably influences 'the organs that carry them on. Some par- 524 THE EVOLUTION OF LIFE. ticular substance, by its presence in the soil, gives new quali ties to some of the tissues; causing greater rigidity or flexi^ bility, and so affecting the general aspect. Here then we have changes towards modified sets of functions and struc tures, in equilibrium with modified sets of external forces. But now let us turn to other classes of organs possessed by plants — organs which are not at once affected in their actions by variations of incident forces. Take first the organs of defence. Many plants are shielded against animals that would else devour them, by formidable thorns; and others, like the nettle, by stinging hairs. These must be counted among the appliances by which equilibrium is maintained between the actions in the organism and the actions in its environment; seeing that were these defences absent, the destruction by herbivorous animals would be so much in-, creased, that the number of young plants annually produced would not suffice, as it now does, to balance the mortality, and the species would disappear. But these defensive appliances, though they aid in maintaining the balance between inner and outer actions, cannot have been directly called forth by the outer actions which they serve to neutra lize; for these outer actions do not continuously affect the functions of the plant even in a general way, still less in the special way required. Suppose a species of nettle bare of poison-hairs, to be habitually eaten by some mammal in truding on its habitat. The actions of this mammal would have no direct tendency to develop poison-hairs in the plant; since the individuals devoured could not bequeath changes of structure, even were the actions of a kind to pro duce fit ones ; and since the individuals which perpetuated themselves would be those on which the new incident force had not fallen. Organs of another class, similarly cir cumstanced, are those of reproduction. Like the organs of defence these are not, during the life of the individual plant, variably exercised by variable external actions ; and there* fore do not fulfil those conditions under 'which structural DIRECT EQUILIBRATION. 525 changes may bo directly caused by changes in the environ ment. The generative apparatus contained in every flower acts only once during its existence ; and even then, the parts subserve their ends in a passive rather than an active way. Functionally-produced modifications are therefore out of the question. If a plant's anthers are so placed that the insect which most commonly frequents its flowers, must come in contact with the pollen, and fertilize with it other flowers of the same species; and if this insect, dwindling away or dis appearing from the locality, leaves behind no insects having such shapes and habits as cause them to do the same thing efficiently, but only some which do it inefficiently; it is clear that this change of its conditions has no immediate tendency to work in the plant any such structural change as shall bring about a new balance with its conditions. For the anthers, which, even when they discharge their functions, do it simply by standing in the way of the insect, are, under the supposed circumstances, left untouched by the insect; and this remaining untouched cannot have the effect of so modifying the stamens as to bring the anthers into a position to be touched by some other insect. Only those individuals whose parts of fructification so far differed from the average form that some other insect could serve them as pollen- carrier, would have good chances of perpetuating themselves. And on their progeny, inheriting the deviation, there would act no external force directly tending to make the deviation greater ; since the new circumstances to which re-adaptation is required, are such as do not in the least alter the equilibrium of functions constituting the life of the individual plant. § 162. Among animals, adaptation by direct equilibration is similarly traceable wherever, during the life of the indi vidual, an external change generates some constant or re peated change of function. This is conspicuously the case with such parts of an animal as are immediately exposed to diffused influences, like those of climate, and with such parts 526 THE EVOLUTION OF LIFE. of an animal as are occupied in its mechanical actions on the environment. Of the one class of cases, the darkening of the skin which follows exposure to one or other extreme of temperature, may be taken as an instance; and with the other class of cases we are made familiar by the increase and decrease which use and disuse cause in the organs of motion. It is needless here to exemplify these: they were treated of in the Second Part of this work. But in animals, as in plants, there are many indispensable offices fulfilled by parts between which and the external con ditions they respond to, there is no such action and reaction as can directly produce an equilibrium. This is especially manifest with dermal appendages. Some ground exists for the conclusion that the greater or less development of hairs, is in part immediately due to increase or decrease of demand on the passive function, as forming a non-conducting coat; but be this as it may, it is impossible that there can exist an}? such cause for those immense developments of hairs which we sec in the quills of the porcupine, or those complex de velopments of them known as feathers. Such an enamelled armour as is worn by Lcpidosteus, is inexplicable as a direct result of any functionally-worked change. For purposes of defence, such an armour is as needful, or more needful, for hosts of other fishes; and did it result from any direct re action of the organism against any offensive actions it was subject to, there seems no reason why other fishes should not have developed similar protective coverings. Of sundry reproductive appliances the like may be said. The secretion of an egg-shell round the substance of an egg, in the oviduct of a bird, is quite inexplicable as a consequence of some functionally-wrought modification of structure, im mediately caused by some modification of external con ditions. The end fulfilled by the egg-shell, is that of protecting the contained mass against certain slight pres sures and collisions, to which it is liable during incubation. How, by any process of direct equilibration, could it come to DIRECT EQUILIBRATION. 527 have the required thickness ? or, indeed, how could it come to exist at all? Suppose this protective envelope to be too weak, so that some of the eggs a bird lays are broken or cracked. In the first place, the breakages or crackings are actions which cannot react on the maternal organism in such ways as to cause the secretion of thicker shells for the future : to suppose that they can, is to suppose that the bird understands the cause of the evil, and that the secre tion of thicker shells can be effected by its will. In the second place, such developing chicks as are contained in the shells which crack or break, are almost certain to die; and cannot, therefore, acquire appropriately-modified constitu tions : even supposing any relation could exist between the impression received and the change required. Meanwhile, such eggs as escape breakage arc not influenced at all by the requirement; and hence, on the birds developed from them, there cannot have acted any force tending to work the need ful adjustment of functions. In no way, therefore, can a direct equilibration between constitution and conditions be here produced. Even in organs that can be modified by certain incident actions into correspondence with such in cident actions, there are some re-adjustments which cannot be effected by direct balancing. It is thus with the bones. The majority of the bones have to resist muscular strains; and variations in the muscular strains call forth, by reaction, variations in the strengths of the bones. Here there is direct equilibration. But though the greater massiveness acquired by bones subject to greater strains, may be ascribed to counter-acting forces evoked by forces brought into action; it is impossible that the acquirement of greater lengths by bones can be thus accounted for. It has been supposed that the elongation of the metatarsals in wading birds, has resulted from direct adaptation to conditions of life. To justify this supposition, however, it must be shown that the mechanical actions and reactions in the legs of a wading bird, differ from those in the legs of other birds; and that the differential actions arc equilibrated by the extra 528 THE EVOLUTION OF LIFE. lengths. There is not the slightest evidence of this. The metatarsals of a hird have to bear no appreciable strains but those due to the superincumbent weight. Standing in the water docs not appreciably alter such strains; and even if it did, an increase in the lengths of these bones would not fit them any better to meet the altered strains. § 163. The conclusion at which we arrive is, then, that there go on in all organisms, certain changes of function and structure that are directly consequent on changes in the inci dent forces — inner changes by which the outer changes are balanced, and the equilibrium restored. Such re-equi librations, which are often conspicuously exhibited in in dividuals, we have reason to believe continue in successive generations ; until they are completed by the arrival at struc tures fitted to the modified conditions. But, at the same time, we see that the modified conditions to which organ isms may be adapted by direct equilibration, are conditions of certain classes only. That a new external action may be met by a new internal action, it is needful that it shall either continuously or frequently be borne by the individuals of the species, without killing or seriously injuring them; and shall act in such way as to affect their functions. And we find that many of the environing agencies — evil or good — to which organisms have to be adjusted, are not of these kinds : being agencies which either do not immediately affect the functions at all, or else affect them in ways that prove fatal. Hence there must be at work some other process which equilibrates the actions of organisms with the actions they are exposed to. Plants and animals that continue to exist, are necessarily plants and animals whose powers balance the powers acting on them; and as their environments change, the changes which plants and animals undergo must necessarily be changes towards re-establishment of the balance. Besides direct equilibration, there must therefore be an indirect equilibration. How this goes on we have now to inquire. CHAPTER XII. INDIRECT EQUILIBRATION. § 1 G4. BESIDES those perturbations produced in any organ ism by special disturbing forces, there are ever going on many others — the reverberating effects of disturbing forces pre viously experienced by the individual, or by ancestors; and the multiplied deviations of function so caused imply multiplied deviations of structure. In § 155 there was re-illustrated the truth, set forth at length when treating of Adaptation (§69), that an organism in a state of moving equilibrium, cannot have extra function thrown on any organ, and extra growth produced in such organ, without correlative changes being entailed throughout all other functions, and eventually throughout all other organs. And when treating of Variation (§ 5)0), we saw that individuals which have been made, by their different circumstances, to deviate functionally and structurally from the average type in different directions, will bequeath to their joint offspring, compound perturbations of function and compound deviations of structure, endlessly varied in their kinds and amounts. Now if the individuals of a species are thus necessarily made unlike in countless ways and degrees — if in one in dividual the amount of energy in a particular direction is greater than in any other individual, or if here a peculiar combination gives a resulting action which is not found else where; then, among all the individuals, some will be less liable than others to have their equilibria overthrown by 530 THE EVOLUTION OF LIFE. a particular incident force previously unexperienced. Unless the change in the environment is so violent as to be univer sally fatal to the species,, it must affect more or less differently the slightly-different moving equilibria which the members of the species present. Inevitably some will be more stable than others when exposed to this new or altered factor. That is to say, those individuals whose functions are most out of equilibrium with the modified aggregate of external forces, will be those to die; and those will survive whose functions happen to be most nearly in equilibrium with the modified aggregate of external forces. But this survival of the fittest * implies multiplication of the fittest. Out of the fittest thus multiplied there will, as before, be an overthrowing of the moving equilibrium wher ever it presents the least opposing force to the new incident force. And by the continual destruction of the individuals least capable of maintaining their equilibria in presence of this new incident force, there must eventually be reached an altered type completely in equilibrium with the altered con ditions. § 1G5. This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called " natural selection, or the preservation of * It will be seen that the argument naturally leads up to this expression — Survival of the Fittest — which was here used for the first time. Two years later (July, 1866) Mr. A. R. Wallace wrote to Mr. Darwin contending that it should be substituted for the expression ''Natural Selection." Mr. Darwin demurred to this proposal. Among reasons for retaining his own expression he said that I had myself, in many cases, preferred it — " continually using the words Natural Selection." (Life and Letters, &c., vol. Ill, pp. 45-6.) Mr. Darwin was quite right in his statement, but not right in the motive he ascribed to me. My reason for frequently using the phrase " Natural Selec tion," after the date at which the phrase " Survival of the Fittest " was first used above, was that disuse of Mr. Darwin's phrase would have seemed like an endeavour to keep out of sight my own indebtedness to him, and the indebtedness of the world at large. The implied feeling has led me ever since to use the expressions Natural Selection and Survival of the Fittest with some thing like equal frequency. INDIRECT EQUILIBRATION. 531 favoured races in the struggle for life." That there goes on a process of this kind throughout the organic world, Mr. Darwin's great work on the Origin of Species has shown to the satisfaction of nearly all naturalists. Indeed, when once enunciated, the truth of his hypothesis is so obvious as scarcely to need proof. Though evidence may be required to show that natural selection accounts for everything ascribed to it, yet no evidence is required to show that natural selec tion has always been going on, is going on now, and must ever continue to go on. Kecognizing this as an a priori cer tainty, let us contemplate it under its two distinct aspects. That organisms .which live, thereby prove themselves fit for living, in so far as they have been tried, while organisms which die, thereby prove themselves in some respects unfitted for living, are facts no less manifest than is the fact that this self- purification of a species must tend ever to insure adaptation between it and its environment. This adaptation may be either so maintained or so produced. Doubtless many who have looked at Nature with philosophic eyes, have ob served that death of the worst and multiplication of the best, tends towards maintenance of a constitution in harmony with surrounding circumstances. That the average vigour of any race would be diminished did the diseased and feeble habitually survive and propagate; and that the destruction of such, through failure to fulfil some of the conditions to life, leaves behind those which are able to fulfil the conditions to life, and thus keeps up the average fitness to the conditions of life; are almost self-evident truths. But to recognize " Natural Selection " as a means of preserving an already- established balance between the powers of a species and the forces to which it is subject, is to recognize only its simplest and most general mode of action. It is the more special mode of action with which we are here concerned. This more special mode of action, Mr. Darwin has been the first to recognize as an all-important factor, though, besides his co-discoverer Mr. A. R. Wallace, some others have perceived 532 THE EVOLUTION OF LIFE. that such a factor is at work. To him we owe due appreciation of the fact that natural selection is capable of producing fit ness between organisms and their circumstances. He has worked up an enormous mass of evidence showing that this " preservation of favoured races in the struggle for life," is an ever-acting cause of divergence among organic forms. He has traced out the involved results of the process with marvellous subtlety. He has shown how hosts of otherwise inexplicable facts, are accounted for by it. In brief, he has proved that the cause he alleges is a true cause; that it is a cause which we see habitually in action; and that the results to be in ferred from it are in harmony with the phenomena which the Organic Creation presents, both as a whole and in its details. Let us glance at a few of the more important inter pretations which the hypothesis furnishes. A soil possessing some ingredient in unusual quantity, may supply to a plant an excess of the matter required for certain of its tissues; and may cause all the parts formed of such tissues to be abnormally developed. Suppose that among these are the hairs clothing its surfaces, including those which grow on its seeds. Thus furnished with some what longer fibres, its seeds, when shed, are carried a little further by the wind before they fall to the ground. The plants growing from them, being rather more widely dis persed than those produced by other individuals of the same species, will be less liable to smother one another; and a greater number may therefore reach maturity and fructify. Supposing the next generation subject to the same peculiarity of nutrition, some of the seeds borne by its members will not simply inherit this increased development of hairs, but will carry it further; and these, still more advantaged in the same way as before, will, on the average, have still more numerous chances of continuing the race. Thus, by the sur vival, generation after generation, of those possessing these longer- hairs, and the inheritance of successive increments of growth in the hairs, there may result a seed deviating greatly INDIRECT EQUILIBRATION. 533 from the original. Other individuals of the same species, subject to the different physical conditions of other localities, may develop somewhat thicker or harder coatings to their seeds : so rendering their seeds less digestible by the birds which devour them. Such thicker-coated seeds, by escaping undigested more frequently than thinner-coated ones, will have additional chances of growing and leaving offspring; and this process, acting in a cumulative manner season after season, will produce a seed diverging in another direction from the ancestral type. Again, elsewhere, some modification in the physiologic actions of the plant may lead to an un usual secretion of an essential oil in the seeds; rendering them unpalatable to creatures which would otherwise feed on them : so giving an advantage to the variety in its rate of multiplication. This incidental peculiarity, proving a preservative, will, as before, be increased by natural selection until it constitutes another divergence. Now in such cases, we see that plants may become better adapted, or re-adapted, to the aggregate of surrounding agencies, not through any direct action of such agencies on them, but through their indirect action — through the destruction by them of the indi viduals least congruous with thorn, and the survival of those most congruous with them. All these slight variations of function and structure, arising among the members of a species, serve as so many experiments; the great majority of which fail, but a few of which succeed. Just as each plant bears a multitude of seeds, out of which some two or three happen to fulfil all the conditions required for reaching maturity and continuing the race; so each species is ever producing numerous slightly-modified forms, deviating in all directions from the average, out of which most fit the sur rounding conditions no better than their parents, or not so well, but some few of which fit the conditions better; and, doing so, are enabled the better to preserve themselves, and to produce offspring similarly capable of preserving them selves. Among animals the like process results in 534 THE EVOLUTION OP LIFE. the like development of various structures which cannot have been affected by the performance of functions — their functions being purely passive. The thick shell of a mollusk cannot have arisen from direct reactions of the organism against the external actions to which it is exposed; but it is quite explicable as an effect of the survival, generation after generation, of individuals whose thicker coverings protected them against enemies. Similarly with such dermal struc ture as that of the tortoise. Though we have evidence that, the skin, where it is continually exposed to pressure and fric tion, may thicken, and so re-establish the equilibrium by opposing a greater inner force to a greater outer force; yet we have no evidence that a coat of armour like that of the tortoise can be so produced. Nor, indeed, are the conditions under which alone its production in such a manner could be accounted for, fulfilled; since the surface of the tortoise is not exposed to greater pressure and friction than the surfaces of other creatures. This massive carapace, and the strangely- adapted osseous frame-work which supports it, are inexplic able as results of evolution, unless through the process of natural selection. So, too, is it with the formation of odori ferous glands in some mammals, or the growth of such ex crescences as those of the camel. Thus, in short, is it with all those organs of animals which do not play active parts. Besides giving us explanations of structural characters that are otherwise unaccountable, Mr. Darwin shows how natural selection explains peculiar relations between indi viduals in certain species. Such facts as the dimorphism of the primrose and other flowers, he proves to be in harmony with his hypothesis, though stumbling-blocks to all other hypotheses. The various differences which accompany differ ence of sex, sometimes slight, sometimes very great, are similarly accounted for. As before suggested (§ 79), natural selection appears capable of producing and maintaining the right proportion of the sexes in each species; and it requires but to contemplate the bearings of the argument, to see that INDIRECT EQUILIBRATION. 535 the formation of different sexes may itself have been deter mined in the same way. To c-onvey here an adequate idea of Mr. Darwin's doctrine, throughout the immense range of its applications, is of course impossible. The few illustrations just given, are intended simply to remind the reader what Mr. Darwin's hypothesis is, and what are the else insoluble problems which it solves for us. § 166. But now, though it seems to me that we are thus supplied with a key to phenomena which are multitudinous and varied beyond all conception; it also seems to me that there is a moiety of the phenomena which this key will not unlock. Mr. Darwin himself recognizes use and disuse of parts, as causes of modifications in organisms ; and does this, indeed, to a greater extent than do some who accept his general conclusion. But I conceive that he does not recog nize them to a sufficient extent. While he shows that the inheritance of changes of structure caused by changes of function, is utterly insufficient to explain a great mass — probably the greater mass — of* morphological phenomena; I think he leaves unconsidered a mass of morphological pheno mena which are explicable as results of functionally-produced modifications, and are not explicable as results of natural selection. By induction, as well as by inference from the hypothesis of natural selection, we know that there exists a balance among the powers of organs which habitually act together — such proportions among them that no one has any consider able excess of efficiency. We see, for example, that through out the vascular system there is maintained an equilibrium of the component parts: in some cases, under continued excess of exertion, the heart gives way, and we have enlarge ment; in other cases the large arteries give way, and we have aneurisms; in other cases the minute blood-vessels give way — now bursting, now becoming chronically congested. 536 THE EVOLUTION OF LIFE. That is to say, in the average constitution, no superfluous strength is possessed by any of the appliances for circulating the blood. Take, again, a set of motor organs. Great strain here causes the fibres of' a muscle to tear. There the muscle does not yield but the tendon snaps. Elsewhere neither muscle nor tendon is damaged, but the bone breaks. Joining with these instances the general fact that, under the same adverse conditions, different individuals show their slight differences of constitution by going wrong some in one way and some in another; and that even in the same individual, similar adverse conditions will now affect one viscus and now another; it becomes manifest that though there cannot be maintained an accurate balance among the powers of the organs composing an organism, yet their excesses and de ficiencies of power are extremely slight. That they must be extremely slight, is, as before said, a deduction from the hypothesis of natural selection. Mr. Darwin himself argues " that natural selection is continually trying to economise in every part of the organization. If under changed conditions of life a structure before useful becomes less useful, any diminution, however slight, iirits development, will be seized on by natural selection, for it will profit the individual not to have its nutriment wasted in building up an useless struc ture." In other words, if any muscle has more fibres than are required, or if a bone is stronger than needful, no advant age results but rather a disadvantage — a disadvantage which will decrease the chances of survival. Hence it follows that among any organs which habitually act in con cert, an increase of one can be of no service unless there is a concomitant increase of the rest. The co-operative parts must vary together; otherwise variation will be detrimental. A stronger muscle must have a stronger bone to resist its contractions; must have stronger correlated muscles and ligaments to secure the neighbouring articulations; must have larger blood-vessels to bring it supplies; must have a more massive nerve to transmit stimulus, and some extra INDIRECT EQUILIBRATION 537 development of a nervous centre to supply the extra stimu lus. The question arises, then, — do variations of the appro priate kinds occur simultaneously in all these co-operative parts? Have we any reason to think that the parts spon taneously increase or decrease together? The assumption that they do seems to me untenable; and its untenability will, I think, become conspicuous if we take a case, and observe how .extremely numerous and involved are the varia tions which must be supposed to occur together. In illustration of another point, we have already considered the modifications required to accompany increased weight of the head (§155). Instead of the bison, the moose deer, or the extinct Irish elk, will here best serve our purpose. In this last species the male has enormously-developed horns, used for purposes of offence and defence. These horns, weighing upwards of a hundred-weight, are carried at great mechanical disadvantage : supported as they are, along with the massive skull which bears them, at the extremity of the outstretched neck. Further, that these heavy horns may be of use in fighting, the supporting bones and muscles must be strong enough, not simply to carry them, but to put them in motion with the rapidity needed for giving blows. Let us, then, ask how, by natural selection, this complex apparatus of bones and muscles can have been developed, pari passu with the horns? If we suppose the horns to have been originally of like size with those borne by other kinds of deer; and if we suppose that in some individual they became larger by spontaneous variation; what would be the concomitant changes required to render their greater size useful? Other things equal, the blow given by a larger horn would be a blow given by a heavier mass moving at a smaller velocity: the momentum would be the same as before; and the area of contact with the body struck being somewhat increased, while the velocity was decreased, the injury done would be less. That horns may become better weapons, the whole apparatus concerned in moving them must be so strength- 538 THE EVOLUTION OF LIFE. ened as to impress more force on them, and to bear the more violent reactions of the blows given. The bones of the skull on which the horns are seated must be thickened; otherwise they will break. The vertebras of the neck must be further developed; and unless the ligaments which hold together these vertebra?, and the muscles which move them, are also enlarged, nothing will be gained. Again the upper dorsal vertebra? and their spines must be strengthened, that they may withstand the stronger contractions of the neck-muscles ; and like changes must be made on the scapular arch. Still more must there be required a simultaneous development of the bones and muscles of the fore-legs; since these extra growths in the horns, in the skull, in the neck, in the shoulders, add to the burden they have to bear; and without they are strengthened the creature will not only suffer from loss of speed but will fail in fight. Hence, to make larger horns of use, additional sizes must be acquired by numerous bones, muscles, and ligaments, as well as by the blood-ves sels and nerves on which their actions depend. On call ing to mind how the spraining of a single small muscle in the foot incapacitates for walking, or how permanent weak ness in a knee-ligament will diminish the power of the leg, it will be seen that unless all these many changes are simul taneously made, they may as well be none of them made — or rather, they would better be none of them made; since the enlargements of some parts, by putting greater strains on connected parts, would render them relatively weaker if they remained unenlarged. Can we with any propriety assume that these many enlargements duly proportioned will be simultaneously effected by spontaneous variations? I think not. It would be a strong supposition that the verte bra? and muscles of the neck suddenly became bigger at the same time as the horns. It would be a still stronger sup position that the upper dorsal vertebra? not only at the same time became more massive, but appropriately altered their proportions^ by the development of their immense neural INDIRECT EQUILIBRATION. 539 spines. And it would be an assumption still more straining our powers of belief, that along with heavier horns there should spontaneously take place the required strengthenings in the bones, muscles, arteries, and nerves of the scapular and the fore-legs. Besides the multiplicity of directly-cooperative organs, the multiplicity of organs which do not cooperate, save in the degree implied by their combination in the same organism, seems to me a further hindrance to the development of special structures by natural selection alone. Where the life is simple, or where circumstances render some one function supremely important, survival of the fittest may readily bring about the appropriate structural change, without aid from the transmission of functionally-caused modifications. But in proportion as the life grows complex — in proportion as a healthy existence cannot be secured by a large endow ment of some one power, but demands many powers; in the same proportion do there arise obstacles to the increase of any particular power by " the preservation of favoured races in the struggle for life." As fast as the faculties are multi plied, so fast does it become possible for the several members of a species to have various kinds of superiorities over one another. While one saves its life by higher speed, another does the like by clearer vision, another by keener scent, another by quicker hearing, another by greater strength, another by unusual power of enduring cold or hunger, another by special sagacity, another by special timidity, another by special courage; and others by other bodily and mental attributes. Conditions being alike, each of these life- saving attributes is likely to be transmitted to posterity. But we may not assume that it will be increased in subse quent generations by natural selection. Increase of it can result only if individuals possessing average endowments of it are more frequently killed off than individuals highly endowed with it ; and this can happen only when the attri bute is one of greater importance, for the time being, than 540 THE EVOLUTION OF LIFE. most of the other attributes. If those members of the species which have but ordinary shares of it, nevertheless survive by virtue of other superiorities which they severally possess; then it is not easy to see how this particular attri bute can be developed by natural selection in subsequent generations. The probability seems rather to be that, by gamogenesis, this extra endowment will, on the average, be diminished in posterity — just serving in the long run to make up for the deficient endowments of those whose special powers lie in other directions ; and so to keep up the normal structure of the species. As fast as the number of bodily and mental faculties increases, and as fast as maintenance of life comes to depend less on the amount of any one and more on the combined actions of all; so fast does the production of specialities of character by natural selection alone, become difficult. Particularly does this seem to be so with a species so multitudinous in its powers as mankind; and above all does it seem to be so with such of the human powers as have but minor shares in aiding the struggle for life — the aesthetic faculties, for example. It by no means follows, however, that in cases of this kind, and cases of the preceding kind, natural selection plays no part. Wherever it is not the chief agent in working organic changes, it is still, very generally, a secondary agent. The survival of the fittest must nearly always further the produc tion of modifications which produce fitness, whether they be incidental modifications, or modifications caused by direct adaptation. Evidently, those individuals whose constitu tions have facilitated the production in them of any struc tural change consequent on any functional change demanded by some new external condition, will be the individuals most likely to live and to leave descendants. There must be a natural selection of functionally-acquired peculiarities, as well as of spontaneously-acquired peculiarities; and hence such structural changes in a species as result from changes of habit necessitated by changed circumstances, natural selec tion will render more rapid than they would otherwise be. INDIRECT EQUILIBRATION. 541 There are, however, some modifications in the sizes and forms of parts, which cannot have been aided by natural selection; but which must have resulted wholly from the inheritance of functionally-caused alterations. The dwind ling of organs of which the undue sizes entail no appreciable evils, furnishes the best evidence of this. Take, for an example, that diminution of the jaws and teeth which characterizes the civilized races, as contrasted with the savage races.* How can the civilized races have been bene- * I am indebted to Mr. [now Sir W.] Flower for the opportunity of ex amining the many skulls in the Museum of the College of Surgeons for verifi cation of this. Unfortunately the absence, in most cases, of some or many teeth, prevented me from arriving at that specific result which would have been given by weighing a number of the under jaws in each race. Simple inspection, however, disclosed a sufficiently-conspicuous difference. The under jaws of Australians and Negroes, when collated with those of English men, were visibly larger, not only relatively but absolutely. One Australian jaw only seemed about of the same size as an average English jaw; and this (probably the jaw of a woman), belonging as it did to a smaller skull, bore a greater ratio to the whole body of which it formed part, than did an English jaw of the same actual size. In all the other cases, the under jaws of these inferior races (containing larger teeth than our own) were absolutely more massive than our own — often exceeding them in all dimensions ; and relative?// to their smaller skeletons were much more massive. Let me add that the Australian and Negro jaws are thus strongly contrasted, not with all British jaws, but only with the jaws of the civilized British. An ancient British skull in the collection possesses a jaw almost or quite as massive as those of the Australian skulls. All this is in harmony with the alleged relation between greater size of jaws and greater action of jaws, involved by the habits of savages. [In 1891 Mr. F. Howard Collins carefully investigated this matter: meas uring ten Australian, ten Ancient British, and ten recent English skulls in the College of Surgeons Museum. The result proved an absolute difference of the kind above indicated, and a far greater relative difference. To ascertain this last a common standard of comparison was established — an equal size of skull in all the cases ; and then when the relative masses or cubic sizes of the jaws were calculated, the result which came out was this: — Australian jaw, 1948; Ancient British jaw, 1135; Recent English jaw, 1030. "Hence," in the words of Mr. Collins, " the mass of the Recent English jaw is, roughly speak ing, half that of the Australian relatively to that of the skull, and a ninth less than that of the Ancient British." He adds verifying evidence from witnesses who have no hypothesis to support — members of the Odontological Society. The Vice President, Mr. Mummery, remarks of the Australians that "the 5i2 THE EVOLUTION OF LIFE. filed in the struggle for life, by the slight decrease in these comparatively-small bones? No functional superiority pos sessed by a small jaw over a large jaw in civilized life, can be named as having caused the more frequent survival of small-jawed individuals. The only advantage accompanying smallness of jaw, is the advantage of economized nutrition; and this cannot be great enough to further the preservation of those distinguished by it. The decrease of weight in the jaw and co-operative parts, which has arisen in the course of thousands of years, does not amount to more than a few ounces. This decrease has to be divided among the many generations which have lived and died in the interval. Let us admit that the weight of these parts diminished to the extent of an ounce in a single generation (which is a large admission) ; it still cannot be contended that the having to carry an ounce less in weight, and to keep in repair an ounce less of tissue, could sensibly affect any man's fate. And if it never did this — nay, if it did not cause a frequent survival of small-jawed individuals where large-jawed individuals died; natural selection could neither cause nor aid diminution of the jaw and its appendages. Here, therefore, the decreased action which has accompanied the growth of civilized habits (the use of tools and the disuse of coarse food), must have been the sole cause at work. Through direct equilibration, diminished external stress on these parts has resulted in diminution of the internal forces by which this stress is met. From generation to generation, this lessening of the parts consequent on functional decline has been inherited. And since the survival of individuals must always have been determined by more important structural traits, this tr.iit can have neither been facilitated nor retarded by natural selection. § 167. Returning from these extensive classes of facts for jaw-bones are powerfully developed, and large in proportion to the cra nium."] INDIRECT EQUILIBRATION. 543 which Mr. Darwin's hypothesis does not account, to the still more extensive classes of facts for which it does account, and which are unaccountable on any other hypothesis; let us consider in what way this hypothesis is expressible in terms of the general doctrine of evolution. Already it has been pointed out that the evolving of modified types by "' natural selection or the preservation of favoured races in the struggle for life/' must be a process of equilibration; since it results in the production of organisms which are in equilibrium with their environments. At the outset of this chapter, something was done towards showing how this continual survival of the fittest may be understood as the progressive establishment of a balance between inner and outer forces. Here, however, we must consider the matter more closely. On previous occasions we have contemplated the assem blage of individuals composing a species, as an aggregate in a state of moving equilibrium. We have seen that its powers of multiplication give it an expansive energy which is antagonized by other energies; and that through the rhyth mical variations in these two sets of energies there is main tained an oscillating limit to its habitat, and an oscillating limit to its numbers. On another occasion (§ 9G) it was shown that the aggregate of individuals constituting a species, has a kind of general life which, " like the life of an individual, is maintained by the unequal and ever-varying actions of incident forces on its different parts." We saw that " just as, in each organism, incident forces constantly produce divergences from the mean state in various direc tions, which are constantly balanced by opposite divergences indirectly produced by other incident forces; and just as the combination of rhythmical functions thus maintained, con stitutes the life of the organism ; so, in a species there is, through gamogenesis, a perpetual neutralization of those con trary deviations from the mean state, which are caused in its different parts by different sets of incident forces; and it is similarly by the rhythmical production and compensation of 544: THE EVOLUTION OF LIFE. these contrary deviations that the species continues to live." Hence, to understand how a species is affected by causes which destroy some of its units and favour the multiplication of others, we must consider it as a whole whose parts are held together by complex forces that are ever re-balancing themselves — a whole whose moving equilibrium is continu ally disturbed and continually rectified. Thus much premised, let us next call to mind how moving equilibria in general are changed. In the first place, a new incident force falling on any part of an aggregate with balanced motions, produces a new motion in the direction of least resistance. In the second place, the new incident force is gradually used up in overcoming the opposing forces, and when it is all expended the opposing forces produce a recoil — a reverse deviation which counter-balances the original deviation. Consequently, to consider whether the moving equilibrium of a species is modified in the same way as moving equilibria in general, is to consider whether, when exposed to a new force, a species yields in the direction of least resistance; and whether, by its thus yielding, there is generated in the species a compensating change in the opposite direction. We shall find that it does both these things. For what, expressed in mechanical terms, is the effect wrought on a species by some previously-unknown enemy, that kills such of its members as fail in defending them selves? The disappearance of those individuals which meet the destroying forces by the smallest preserving forces, is tantamount to the yielding of the species as a whole at the places where the resistances are the least. Or if by some general influence, such as alteration of climate, the members of a species are subject to increase of external actions which are ever tending to overthrow their equilibria, and which they are ever counter-balancing by certain physiolo gical actions, which are the first to die? Those least able to generate the internal energies which antagonize these external energies. If the change be an increase of the INDIRECT EQUILIBRATION. 545 winter's cold, then such members of the species as have unusual powers of getting food or of digesting food, or such as are by their constitutional aptitude for making fat, fur nished with reserve stores of force, available in times of scarcity, or such as have the thickest coats and so lose least heat by radiation, survive; and their survival implies that in each of them the moving equilibrium of functions presents such an adjustment of internal forces, as prevents over throw by the modified aggregate of external forces. Con versely, the members which die are, other things equal, those deficient in the power of meeting the new action by an equi valent counter-action. Thus, in all cases, a species con sidered as an aggregate in a state of moving equilibrium, has its state changed by the yielding of its fluctuating mass wherever this mass is weakest in relation to the special forces acting on it. The conclusion is, indeed, a truism. But now what must follow from the de struction of the least-resisting individuals and survival of the most-resisting individuals? On the moving equilibrium of the species as a whole, existing from generation to gener ation, the effect of this deviation from the mean state is to produce a compensating deviation. For if all such as are deficient of power in a certain direction are destroyed, what must be the effect on posterity? Had they lived and left offspring, the next generation would have had the same average powers as preceding generations : there would have been a like proportion of individuals less endowed with the needful power, and individuals more endowed with it. But the more-endowed individuals being alone left to continue the race, there must result a new generation characterized by a larger average endowment of this power. That is to say, on £he moving equilibrium of a species, an action pro ducing change in a given direction is followed, in the next generation, by a reaction producing an opposite change. Observe, too, that these effects correspond in their degrees of violence. If the alteration of some external factor is so 546 THE EVOLUTION OP LIFE. great that it leaves alive only the few individuals possessing extreme endowments of the power required to antagonize it; then, in succeeding generations, there is a rapid multiplica tion of individuals similarly possessing extreme endowments of this power — the force impressed calls out an equivalent conflicting force. Moreover, the change is temporary where the cause is temporary, and permanent where the cause is permanent. All that are deficient in the needful attribute having been killed off, and the survivors having the needful attribute in a comparatively high degree, there will descend from them, not only some possessing equal amounts of this attribute with themselves, but also some possessing less amounts of it. If the destructive agency has not continued in action, such less-endowed individuals will multiply; and the species, after sundry oscillations, will return to its pre vious mean state. But if this agency be a persistent one, such less endowed individuals will be continually killed off, and eventually none but highly-endowed individuals will be produced — a new moving equilibrium, adapted to the new environing conditions, will result. It may be objected that this mode of expressing the facts does not include the cases in which a species becomes modified in relation to surrounding agencies of a passive kind — cases like that of a plant which acquires hooked seed-vessels, by which it lays hold of the skins of passing animals, and makes them the distributors of its seeds — cases in which the outer agency has no direct tendency at first to affect the species, but in which the species so alters itself as to take advantage of the outer agency. To cases of this kind, however, the same mode of interpretation applies on simply changing the terms. While, in the aggregate of influences amid which a species exists, there are some which tend to ovcrfhrow the moving equilibria of its members, there are others which facilitate the maintenance of their moving equilibria, and some which are capable of giving their moving equilibria increased stability: instance the spread into their habitat of INDIRECT EQUILIBRATION. 547 some new kind of prey, which is abundant at seasons when other prey is scarce. Xow what is the process by which the moving equilibrium in any species becomes adapted to some additional external factor furthering its maintenance? In stead of an increased resistance to be met and counter balanced, there is here a diminished resistance; and the diminished resistance is equilibrated in the same way as the increased resistance. As, in the one case, there is a more frequent survival of individuals whose peculiarities enable them to resist the new adverse factor; so, in the other case, there is a more frequent survival of individuals whose pecu liarities enable them to take advantage of the new favourable factor. In each member of the species, the balance of func tions and correlated arrangement of structures, differ slightly from those existing in other members. To say that among all its members, one is better fitted than the rest to benefit by some before-unused agency in the environment, is to say that its moving equilibrium is, in so far, more stably adjusted to the sum of surrounding influences. And if, consequently, this individual maintains its moving equilibrium when others fail, and has offspring which do the like — that is, if indivi duals thus characterized multiply and supplant the rest; there is, as before, a process which effects equilibration be tween the organism and its environment, not immediately but mediately, through the continuous intercourse between the species as a whole and the environment. § 1G8. Thus we sec that indirect equilibration docs what ever direct equilibration cannot do. All these processes by which organisms are re-fitted to their ever-changing environ ments, must be equilibrations of one kind or other. As authority for this conclusion, we have not simply the uni versal truth that change of every order is towards equili brium; but we have also the truth that life itself is a moving equilibrium between inner and outer actions — a con tinuous adjustment of internal relations to external relations; 548 THE EVOLUTION OF LIFE. or the maintenance of a balance between the forces to which an organism is subject and the forces which it evolves. Hence all changes which enable a species to live under altered con ditions, are changes towards equilibrium with the altered conditions; and therefore those which do not come within the class of direct equilibrations, must come within the class of indirect equilibrations. And now we reach an interpretation of Natural Selection regarded as a part of Evolution at large. As understood in First Principles, Evolution is a continuous redistribution of matter and motion; and a process of evolution which is not expressible in terms of matter and motion has not been reduced to its ultimate form. The conception of Natural Selection is manifestly one not known to physical science: its terms are not of a kind physical science can take cognis ance of. But here we have found in what manner it may be brought within the realm of physical science. Eejecting metaphor we see that the process called Natural Selection is literally a survival of the fittest; and the outcome of the above argument is that survival of the fittest is a maintenance of the moving equilibrium of the functions in presence of outer actions : implying the possession of an equilibrium which is relatively stable in contrast with the unstable equilibria of those which do not survive. CHAPTER XIII. THE CO-OPERATION OF THE FACTORS. § 1G9. THUS the phenomena of Organic Evolution may be interpreted in the same way as the phenomena of all other Evolution. Fully- to see this, it will be needful for us to con template in their ensemble, the several processes separately described in the four preceding chapters. If the forces acting on any aggregate remain the same, the changes produced by them will presently reach a limit, at which the outer forces are balanced by the inner forces; and thereafter no further metamorphosis will take place. Hence, that there may be continuous changes of structure in organ isms, there must be continuous changes in the incident forces. This condition to the evolution of animal and vegetal forms, we find to be fully satisfied. The astronomic, geologic, and meteorologic changes that have been slowly but inces santly going on, and have been increasing in the complexity of their combinations, have been perpetually altering the circumstances of organisms; and organisms, becoming more numerous in theii kinds and higher in their kinds, have been perpetually altering one another's circumstances. Thus, for those progressive modifications upon modifications which or ganic evolution implies, we find a sufficient cause. The increasing inner changes for which we thus find a cause in the perpetual outer changes, conform, so far as we can trace them, to the universal law of the instability of the homo- 549 550 THE EVOLUTION OF LIFE. gcncous. In organisms, as in all other things, the exposure of different parts to different kinds and amounts of incident forces, has necessitated their differentiation; and, for the like reason, aggregates of individuals have been lapsing into varieties, and species, and genera, and orders. Further, in each type of organism, as in the aggregate of types, the mul tiplication of effects has continually aided this transition from a more homogeneous to a more heterogeneous state. And yet again, that increasing segregation and concomitant in creasing defmiteness, associated with the growing hetero geneity of organisms, has been aided by the continual de struction of those which expose themselves to aggregates of external actions markedly incongruous with the aggregates of their internal actions, and the survival of those subject only to comparatively small incongruities-. Finally, we have found that each change of structure, superposed on preceding changes, has been a re-equilibration necessitated by the disturbance of a preceding equilibrium. The mainte nance of life being the maintenance of a balanced combina tion of functions, it follows that individuals and species that have continued to live, are individuals and species in which the balance of functions has not been overthrown. Hence survival through successive changes of conditions, implies successive adjustments of the balance to the new conditions. The actions that are here specified in succession, are in' reality simultaneous; and they must be so conceived before organic evolution can be rightly understood. Some aid towards so conceiving them will be given by the annexed table, representing the co-operation of the factors. § 170. Eespecting this co-operation, it remains only to point out the respective shares of the factors in producing the total result; and the way in which the proportions of their respective shares vary as evolution progresses. At first, changes in the amounts and combinations of inor ganic forces, astronomic, geologic, and meteorologic, were the THE CO-OPERATION OP THE FACTORS. 551 ill;! sll'li! •tJoi' Soiej •-.S1- S'" ig^e III!! Hit!! lillll Mllll Ifi li? • immediately through their functions; -j aS.5 j§ ° « ° a « - al c£J'o II II tjgl its aggregate J I of individuals, byactjnsd.ffei lyouslightly-ui individuals in I same locality; 1 i _g 1 1 , It! II! 1 h I! Oft W O O P-i W O 552 THE EVOLUTION OP LIFE. only causes of the successive modifications; and these changes have continued to be causes. But as, through the diffusion of organisms and consequent differential actions of inorganic forces, there arose unlikenesses among them, pro ducing varieties, species, genera, orders, classes, the actions of organisms on one another became new sources of organic modifications. And as fast as types have multiplied and become more complex, so fast have the mutual actions of organisms come to be more influential factors in their re spective evolutions : eventually becoming the chief factors. Passing from the external causes of change to the internal processes of change entailed by them, we see that these, too, have varied in their proportions : that which was originally the most important and almost the sole process, becoming gradually less important, if not at last the least important. Always there must have been, and always there must con tinue to be, a survival of the fittest; natural selection must have been in operation at the outset, and can never cease to operate. While yet organisms had small abilities to co ordinate their actions, and adjust them to environing actions, natural selection worked almost alone in moulding and re moulding organisms into fitness for their changing environ ments; and natural selection has remained almost the sole agency by which plants and inferior orders of animals have been modified and developed. The equilibration of organisms that are almost passive, is necessarily effected in directly, by the action of incident forces on the species as a whole. But along with the evolution of organisms having some activity, there grows up a kind of equilibration which is in part direct. In proportion as the activity increases direct equilibration plays a more important part. Until, when the nervo-muscular apparatus becomes greatly deve loped, and the power of varying the actions to fit the varying requirements becomes considerable, the share taken by direct equilibration rises into co-ordinate importance or greater importance. As fast as essential faculties multiply, and as THE CO-OPERATTON OP THE FACTORS. 553 fast as the number of organs which co-operate in any given function increases, indirect equilibration through natural selection becomes less and less capable of producing specific adaptations; and remains capable only of maintaining the general fitness of constitution to conditions. The production of adaptations by direct equilibration then takes the first place : indirect equilibration serving to facilitate it. Until at length, among the civilized human races, the equilibration becomes mainly direct : the action of natural selection being limited to the destruction of those who are constitutionally too feeble to live, even with external aid. As the preserva tion of incapables is secured by our social arrangements; and as very few save incarcerated criminals are prevented by their inferiorities from leaving Ihe average number of off spring ; it results that survival of the fittest can scarcely at all act in such way as to produce specialities of nature, either bodily or mental. Here the specialities of nature, chiefly mental, which we see produced, and which are so rapidly produced that a few centuries show a considerable change, must be ascribed almost wholly to direct equilibration.* * As bearing on the question of the varieties of Man, let me here refer to a paper on " The Origin of the Human Races " read before the Anthro* political Society. March 1st, 1864, by Mr. Alfred Wallace. In this paper, Mr. Wallace shows that along with the attainment of that intelligence implied by the use of implements, clothing, &c., there arises a tendency for modifications of brain to take the place of modifications of body : still, how. ever, regarding the natural selection of spontaneous variations as the cause of the modifications. But if the foregoing arguments be valid, natural selection here plays but the secondary part of furthering the adaptations otherwise caused. It is true that, as Mr. Wallace argues, and as I have myself briefly indicated (sec Westminster Review, for April, 1852, pp. 490— 601), the natural selection of races leads to the survival of the more cerebrally-devcloped, while the less ccrebrally-developed disappear. lint though natural selection acts freely in the struggle of one society with another; yet, among the units of each society, its action is so interfered with that there remains no adequate cause for the acquirement of mental superiority by one race over another, except the inheritance of functionally- produced modifications. CHAPTER XIY. THE CONVERGENCE OF THE EVIDENCES. § 171. OF the three classes of evidences that have been assigned in proof of Evolution, the a priori, which we took first, were partly negative, partly positive. On considering the " General Aspects of the Special-crea tion hypothesis," we discovered it to be worthless. Dis credited by its origin, and wholly without any basis of observed fact, we found that it was not even a thinkable hypothesis; and, while thus intellectually illusive, it turned out to have moral implications irreconcilable with the pro fessed beliefs of those who hold it. Contrariwise, the " General Aspects of the Evolution- hypothesis " begot the stronger faith in it the more nearly they were considered. By its lineage and its kindred, it was found to be as closely allied with the proved truths of modern science, as is the antagonist hypothesis with the proved errors of ancient ignorance. We saw that instead of being a mere pseud-idea, it admits of elaboration into a definite conception : so showing its legitimacy as an hypothesis. In stead of positing a purely fictitious process, the process which it alleges proves to be one actually going on around us. To which add that, morally considered, this hypothesis presents no radical incongruities. Thus, even were we without further means of judging, 554 THE CONVERGENCE OP THE EVIDENCES. 555 there could be no rational hesitation which of the two views should be entertained. § 172. Further means of judging, however, we found to be afforded by bringing the two hypotheses face to face with the general truths established by naturalists. These induc tive evidences were dealt with in four chapters. "The Arguments from Classification" were these. Organ isms fall into groups within groups; and this is the arrange ment which we see results from evolution, where it is known to take place. Of these groups within groups, the great or primary ones are the most unlike, the sub-groups are less unlike, the sub-sub-groups still less unlike, and so on; and this, too, is a characteristic of groups demonstrably produced by evolution. Moreover, indefiniteness of equivalence among the groups is common to those which we know have been evolved, and those here supposed to have been evolved. And then there is the further significant fact, that divergent groups are allied through their lowest rather than their high est members. Of " the Arguments from Embryology," the first is that when developing embryos arc traced from their common starting point, and their divergences and re-divergences symbolized by a genealogical tree, there is manifest a general parallelism between the arrangement of its primary, second ary, and tertiary branches, and the arrangement of the di visions and sub-divisions of our classifications. Nor do the minor deviations from this general parallelism, which look like difficulties, fail, on closer observation, to furnish addi tional evidence; since those traits of a common ancestry which embryology reveals, are, if modifications have resulted from changed conditions, liable to be disguised in different ways and degrees in different lines of descendants. We next considered "the Arguments from Morphology." Apart from those kinships among organisms disclosed by their developmental changes, the kinships which their adult 556 THE EVOLUTION OF LIFE. forms show arc profoundly significant. The unities of type found under such different externals, are inexplicable except as results of community of descent with non-community of modification. Again, each organism analyzed apart, shows, in the likenesses obscured by unlikenesses of its component parts, a peculiarity which can be ascribed only to the formation of a more heterogeneous organism out of a more homogeneous one. And once more, the existence of rudimentary organs, homologous with organs that are developed in allied animals or plants, while it admits of no other rational interpretation, is satisfactorily interpreted by the hypothesis of evolution. Last of the inductive evidences, came " the Arguments from Distribution." While the facts of distribution in Space are unaccountable as results of designed adaptation of organ isms to their habitats, they are accountable as results of the competition of species, and the spread of the more fit into the habitats of the less fit, followed by the changes which new conditions induce. Though the facts of distribution in Time are so fragmentary that no positive conclusion can be drawn, yet all of them are reconcilable with the hypothesis of evolution, and some of them yield it strong support: especially the near relationship existing between the living and extinct types in each great geographical area. Thus of these four groups, each furnished several argu ments which point to the same conclusion; and the conclu sion pointed to by the arguments of any one group, is that pointed to by the arguments of every other group. This coincidence of coincidences would give to the induction a very high degree of probability, even were it not enforced by deduction. But the conclusion deductively reached, is in harmony with the inductive conclusion. § 173. Passing from the evidence that evolution has taken place, to the question — How has it taken place? we find in known agencies and known processes, adequate causes of its phenomena. THE CONVERGENCE OP THE EVIDENCES. 557 In astronomic, geologic, and mcteorologic changes, ever in progress, ever combining in new and more involved ways, we have a set of inorganic factors to which all organisms are exposed; and in the varying and complicating actions of organisms on one another, we have a set of organic factors that alter with increasing rapidity. Thus, speaking generally, all members of the Earth's Flora and Fauna experience per petual re-arrangements of external forces. Each organic aggregate, whether considered individually or as a continuously-existing species, is modified afresh by each fresh distribution of external forces. To its pre-existing differentiations new differentiations are added ; and thus that lapse to a more heterogeneous state, which would have a fixed limit were the circumstances fixed, has its limit perpetually removed by the perpetual change of the circumstances. These modifications upon modifications which result in evolution structurally considered, arc the accompaniments of those functional alterations continually required to re- equilibrate inner with outer actions. That moving equi librium of inner actions corresponding with outer actions, which constitutes the life of an organism, must cither be overthrown by a change in the outer actions, or must undergo perturbations that cannot end until there is a re-adjusted balance of functions and correlative adaptation of structures. But where the external changes are either such as are fatal when experienced by the individuals, or such as act on the individuals in ways that do not affect the equilibrium of their functions; then the re-adjustment results through the effects produced on the species as a whole — there is indirect equilibration. By the preservation in successive generations of those whose moving equilibria are least at variance with the requirements, there is produced a changed equilibrium completely in harmony with the requirements. § 174. Even were this the whole of the evidence assign able for the belief that organisms have been gradually evolved, 558 THE EVOLUTION OF LIFE. it would have a warrant higher than that of many beliefs which are regarded as established. But the evidence is far from exhausted. At the outset it was remarked that the phenomena pre sented by the organic world as a whole, cannot be properly dealt with apart from the phenomena presented by each organism, in the course of its growth, development, and decay. The interpretation of either implies interpretation of the other; since the two are in reality parts of one process. Hence, the validity of any hypothesis respecting the one class of phenomena, may be tested by its congruity with phenomena of the other class. We are now about to pass to the more special phenomena of development, as displayed in the structures and functions of individual organisms. If the hypothesis that plants and animals have been progres sively evolved be true, it must furnish us with keys to these phenomena. We shall find that it does this; and by doing it gives numberless additional vouchers for its truth. CHAPTER XIVA. RECENT CRITICISMS AND HYPOTHESES. § 174fl. SINCE the first edition of this work was published, and more especially since the death of Mr. Darwin, an active discussion of the Evolution hypothesis has led to some sig nificant results. That organic evolution has been going on from the dawn of life down to the present time, is now a belief almost universally accepted by zoologists and botanists — " almost universally," 1 say, because the surviving influence of Cuvier prevents acceptance of it by some of them in France. Omit ting the ideas of these, all biological interpretations, specu lations, and investigations, tacitly assume that organisms of every kind in every era and in every region have come into existence by the process of descent with modifica tion. But while concerning the fact of evolution there is agree ment, concerning its causes there is disagreement. The ideas of naturalists have, in this respect, undergone a dif ferentiation increasingly pronounced; which has ended in the production of two diametrically opposed beliefs. The cause which Mr. Darwin first made conspicuous has come to be regarded by some as the sole cause; while, on the part of others there has been a growing recognition of the cause which he at first disregarded but afterwards admitted. Prof. Weismann and his supporters contend that natural selection suffices to explain everything. Contrariwise, among 559 560 THE EVOLUTION OP LIFE. many who recognize the inheritance of functionally-produced changes, there are a few, like the Ecv. Prof. Henslow, who regard it as the sole factor. The foregoing chapters imply that the beliefs of neither extreme are here adopted. Agreeing with Mr. Darwin that both factors have been operative, I hold that the inheritance of functionally-caused alterations has played a larger part than he admitted even at the close of his life; and that, coming more to the front as evolution has advanced, it has played the chief part in producing the highest types. I am not now about to discuss afresh these questions, but to deal with certain further questions. For while there has been taking place in the biological world the major differentiation above indicated, there have been taking place certain minor differentiations — there have been arising special views respecting the process of organic evolution. Concerning each of these it is needful to say something. § 1746. Among the implied controversies the most con spicuous one has concerned the alleged process called by Prof. Weismann Panmixia — a process which Dr. Eomanes had foreshadowed under the name of " the Cessation of Selection." Dr. Eomanes says : — " At that time it appeared to me, as it now appears to Weismann, entirely to supersede the necessity of supposing that the effect of disuse is ever inherited in any degree at all." * The alleged mode of action is exemplified by Prof. Weismann as follows : — ''A goose or a duck must possess strong powers of flight in the natural state, but such powers are no longer necessary for obtaining food when it is brought into the poultry-yard, so that a rigid selection of individuals with well-developed wings, at once ceases among its descendants. Hence in the course of generations, a deterioration of the organs of flight must necessarily ensue, and the other members and organs of the bird will be similarly affected." t * Darwin and after Darwin, Part II, p. 99. f J&says upon Heredity, vol. i, p. V'O. RECENT CRITICISMS AND HYPOTHESES. 561 Here, and throughout the arguments of those who accept the hypothesis of Panmixia, there is an unwarranted assump tion — nay, an assumption at variance with the doctrine in support of which it is made. It is contended that in such cases as the one given there will, apart from any effects of disuse, be decrease in the disused organs because, not being kept by Natural Selection up to the level of strength pre viously needed, they will vary in the direction of decrease; and that variations in the direction of decrease, occurring in some individuals, will, by interbreeding, produce an average decrease throughout the species. But why will the disused organs vary in the direction of decrease more than in the direction of increase? The hypothesis of Natural Selection postulates indeterminate variations — deviations no more in one direction than in the opposite direction: implying that increases and decreases of size will occur to equal extents and with equal frequencies. With any other assumption the hypothesis lapses; for if the variations in one direction exceed those in another the question arises — What makes them do this? And whatever makes them do this become? the essential cause of the modification: the selection of favourable variations is tacitly admitted to be an insufficient explanation. But if the hypothesis of Natural Selection itself implies the occurrence of equal variations on all sides of the mean, how can Panmixia produce decrease? Plus deviations will cancel minus deviations, and the organ will remain where it was.* * In a letter published by Dr. Romanes in Nature, for April 26, 1894, he alleges three reasons why " as soon as selection is withdrawn from an organ the minus variations of that organ outnumber the plus variations." The first is that " the survival-mean must descend to the birth-mean." The interpre tation of this is that if the members of a species are on the average born with an organ of the required size, and if they are exposed to natural selec tion, then those in which the organ is relatively small will some of them die, and consequently the mean size of the organ at adult age will be greater than at birth. Contrariwise, if the organ becomes useless and natural selec tion does not operate on it, this difference between the birth-mean and the survival-mean disappears. Now here, again, the plus variations and their 502 THE EVOLUTION OF LIFE. " But you have forgotten the tendency to economy of growth/' will be the reply — " you have forgotten that in Mr. Darwin's words 'natural selection is continually trying to economize in every part of the organization ; ' and that this is a constant cause favouring minus variations." I have not forgotten it; but have remembered it as showing how, to support the hypothesis of Panmixia, there is invoked the aid of that very hypothesis which it is to replace. For this principle of economy is but another aspect of the principle of functionally-produced modifications. Nearly forty years ago I contended that " the different parts of ... an individual organism compete for nutriment; and severally obtain more or less of it according as they are discharging more or less duty : " * the implication being that as all other organs are demanding blood, decrease of duty in any one, entailing de creased supply of blood, brings about decreased size. In other words, the alleged economy is nothing else than the abstrac tion, by active parts, of nutriment from an inactive part ; and is merely another name for functionally-produced decrease. So that if the variations are supposed to take place pre- effects are ignored. Supposing the organ to be useful, it is tacitly assumed that while minus variations are injurious, plus variations are not injurious. This is untrue. Superfluous size of an organ implies several evils: — Its original cost is greater than requisite, and other organs suffer; the con tinuous cost of its nutrition is unduly great, involving further injury; it adds needlessly to the weight carried and so again is detrimental ; and there is in some cases yet a further mischief — it is in the way. Clearly, then, those in which plus variations of the organ have occurred are likely to be killed off as well as those in which minus variations have occurred; and hence there is no proof that the survival-mean will exceed the birth-mean. Moreover the assumption has a fatal implication. To say that the survival- mean of an organ is greater than the birth- mean is to say that the organ is greater in proportion to other organs than it was at birth. What happens if instead of one organ we consider all the organs ? If the survival-mean of a particular organ is greater than its birth-mean, the survival mean of each other organ must also be greater. Thus the proposition is that every organ has become larger in relation to every other organ ! — a marvellous proposi tion. I need only add that Dr. Romanes1 inferences with respect to the two other causes— atavism and failing heredity — are similarly vitiated by ignoring the plus variations and their effects. * Westminster Review, January, 18GO. See also Essays, &c., vol. i, p. 290. RECENT CRITICISMS AND HYPOTHESES. 563 dominantly in the direction of decrease, it can only be by silently assuming the cause which is overtly denied. But now we come to the strange fact that the particular case in which panmixia is assigned in disproof of alleged inheritance of functionally-produced modifications, is a case in which it would be inapplicable even were its assumption legitimate — the case of disused organs in domestic animals. For since nutrition is here abundant, the principle of economy under the form alleged does not come into play. Contrari wise, there even occurs a partial re-development of rudi mentary organs : instances named by Mr. Darwin being the supplementary mammae in cows, fifth toes on the hind feet of dogs, spurs and comb in hens, and canine teeth in mares. Now clearly, if organs disused for innumerable generations may thus vary in the direction of increase, it must, a fortiori, be so with recently disused organs, and there disappears all plea (even the illegitimate plea) for assuming that in the wing of a wild duck which has become domesticated, the minus variations will exceed the plus variations : the hypothesis of panmixia loses its postulate. If it be said that Mr. Darwin's argument is based on the changed ratio between the weights of log-bones and wing- bones, and that tin's changed ratio may result not from de crease of the wing-bones but from increase of the leg-bones, then there comes a fatal reply. Such increase cannot be ascribed to selection of varieties, since there is no selec tive breeding to obtain larger legs, and as it is not pretended that panmixia accounts for increase the case is lost: there remains no cause for such increase save increase of function. § 174c. The doctrine of determinate evolution or definitely- directed evolution, which appears to be in one form or other entertained by sundry naturalists, has been set forth by the late Prof. Eimer under the title " Orthogenesis." A distinct statement of his conception is not easily made for the reason that, as I think, the conception itself is indistinct. Here are some extracts from a translation of his paper published at CCi THE EVOLUTION OF LIFE. Chicago. Out of these the reader may form a notion of the theory : "Orthogenesis shows that organisms develop in definite directions without the least regard for utility through purely physiological causes as the result of organic growth, as I term the process." " I am concerned in this paper with definitely directed evolution as the cause of transmutation, and not with the effects of the use and activity of organs which with Lamarck I adopted as the second main explanatory cause thereof." " The causes of definitely directed evolution are contained, accord ing to my view, in the effects produced by outward circumstances and influences such as climate and nutrition upon the constitution of a given organism." "At variance with all the facts of definitely directed evolution ... is also the contention of my opponent [Weismann] . . . that the variations demonstrably oscillate to and fro in the most di verse directions about a given zero-point. There is no oscillation in the direction of development, but simply an advance forwards in a straight line with occasional lateral divergences whereby the forkings of the ancestral tree are produced. " * These sentences contain one of those explanations which explain nothing; for we are not enabled to see how the " outward circumstances and influences " produce the effects ascribed to them. We are not shown in what way they cause organic evolution in general, still less in what way they cause the infinitely-varied forms in which organic evo lution results. The assertion that evolution takes definitely- directed lines is accompanied by no indication of the reasons why particular lines are followed rather than others. In short, we are simply taken a step back, and for further in terpretation referred to a cause said to be adequate, but the operations of which we are to imagine as best we may. This is a re-introduction of supernaturalism under a dis guise. It may pair off with the conception made popular by the Vestiges of the Natural History of Creation, in which it was contended that there exists a persistent tendency towards the birth of a higher form of creature ; or it may be bracketed * " On Orthogenesis and the Impotence of Natural Selection in Species- Formation," pp. 2, 19, 22, 24. RECENT CRITICISMS AND HYPOTHESES. 505 with the idea entertained by the late Prof. Owen, who alleged an " ordained becoming " of living things. § 174^. An objection to the Darwinian doctrine which has risen into prominence, is that Natural Selection does not explain that which it professes to explain. In the words of Mr. J. T. Cunningham : — "Everybody knows that the theory of natural selection was put for ward by Darwin as a theory of the origin of species, and yet it is only a theory of the origin of adaptations. The question is: Are the dif ferences between species differences of adaptation ? If so, then the origin of species and the origin of adaptations are equivalent terms. But there is scarcely a single instance in which a specific character has been shown to be useful, to be adaptive." * To illustrate this last statement Mr. Cunningham names the plaice, flounder, and dab as three flat fishes in which, along with the adaptive characters related to the mode of life com mon to them all, each has specific characters which are not adaptive. No evidence is forthcoming that these in any way conduce to the welfare of the species. Two propositions are here involved which should be separately dealt with. The first is that the adaptive modifications which survival of the fittest is able to produce, do not become specific traits: they are traits separate in kind from those which mark off groups proved to be specifically distinct by their inability to breed together. Such evidence as we at present have seems to warrant this statement. Out of the many varieties of dogs most, if not all, have been rendered distinct by adaptive modifications, mostly produced by selection. But, notwith standing the immense divergences of structure so produced, the varieties inter-breed. To this, however, it may be replied that sufficient time has not elapsed — that the process by which a structural adaptation so reacts on the constitution as to make it a distinct one, possibly, or probably, takes many thousands of years. Let us accept for the moment Lord Kelvin's low estimate of the geologic time during which * Address to Plymouth Institution, at opening of Session 1895-6. 560 THE EVOLUTION OF LIFE. life has existed — one hundred million years. Suppose we divide that time into as many parts as there are hours occu pied in the development of a human foetus. And suppose that during these hundred million years there has been going on with some uniformity the evolution of the various organic types now existing. Then the amount of change undergone by the foetus in an hour, will be equivalent to the amount of change undergone by an evolving organic form in fifteen thousand years. That is to say, during general evolution it may have taken fifteen thousand years to establish, as dis tinct, two species differing from one another no more than the foetus differs from itself after the lapse of an hour. Hence, though we lack proof that adaptive modifications be come specific traits, it is quite possible that they are in course of becoming specific traits. The converse proposition, that the traits by which species are ordinarily distinguished are non-adaptive traits is well sustained; and the statement that, if not themselves useful they are correlated with those which are useful, is, to say the least, unproved. For the instances given by Mr. Darwin of correlated traits are not those between adaptive traits and the traits regarded as specific, but between traits none of which are specific; as between skull and limbs in swine, tusks and bristles in swine, horns and wool in sheep, beak and feet in pigeons. If we seek a clue in those processes by which correlations are brought about — the physiological actions and reactions — we may at once see that any organic modification, be it adaptive or not, must entail secondary modifications through out the rest of the organism, most of them insensible but some of them sensible. The competition for blood among organs, referred to above, necessitates that, other things re maining the same, the extra growth of any one tells on all others, in variable degrees according to conditions, and may cause appreciable diminutions of some. This is not all. While the quantity of blood supplied to other organs is RECENT CRITICISMS AND HYPOTHESES. 507 affected, its quality also is in some cases affected. Each organ, or at any rate each class of organs, has special nutri tion — abstracts from the blood a proportion of ingredients different from that abstracted by other organs or classes of organs. Hence may result a deficiency or a surplus of some element: instance the change in the blood which must be caused by growth of a stag's antlers. Now if such effects are always produced., and if, further, a change of general nutri tion caused by a new food or by a difference of ability to utilize certain components of food, similarly operates (in stance the above named correlation between horns and wool), then every modification must entail throughout the organism multitudinous alterations of structure. Such alterations will ordinarily be neither in themselves useful nor necessarily correlated with those which are useful; since they must arise as concomitants of any change, whether adaptive or not. There will consequently arise the innumerable minute differ ences presented by allied species in addition to the differences called specific. On joining with recognition of this general process a recog nition of the tendency towards localization of deposit, one possible origin of specific marks is suggested. When in an organism the circulating fluids contain useless matter, normal or abnormal, the excretion of it, once determined towards a certain place, continues at that place. Trees furnish examples in the casting out of gums and resins. Animal life yields evidence in gouty concretions and such morbid products as tubercle. A place of enfeebled nutrition is commonly chosen — not unfrequently a place where a local injury has occurred. Now if we extend this principle, well recognized in pathological processes, to physiological processes, we may infer that where an adaptive modification has so reacted on the blood as to leave some matter to be got rid of, the deposit of this, initiated at some place of least resistance, may pro duce a local structure which eventually becomes a species- mark. A relevant inquiry suggests itself — What proportion o7 568 THE EVOLUTION OF LIFE. of species-marks are formed out of inanimate tissue or tissue of low vitality — tissue which, like hair, feathers, horns, teeth, is composed of by-products unfit for carrying on vital actions. '§ 174e. In the days when, not having been better in structed by Mr. Darwin, I believed that all changes of struc ture in organisms result from changes of function, I held that the cause of such changes of function is migration. As suming as the antecedent of migration a great geologic change, such as upheaval of the East Indian Archipelago step by step into a continent, it was argued, in an essay I then, wrote, that, subjected primarily to new influences in its original habitat, each kind of plant and animal would sec ondarily be subjected to the altered conditions consequent on spreading over the upheaved regions. "Each species being distributed over an area of some extent, and tending continually to colonize the new area exposed, its different members would be subject to different sets of changes. Plants and animals spreading towards the equator would not be affected in the same way with others spreading from it. Those spreading towards the new shores would undergo changes unlike the changes undergone by those spreading into the mountains. Thus, each original race of organisms would become the root from which diverged several races differing more or less from it and from one another." It was further argued that, beyond modifications caused 'by change of physical conditions and food, others would be caused by contact of the Flora and Fauna of each island with the Floras and Faunas of other islands: bringing experience of animals and plants before unknown.* While this conception was wrong in so far as it ascribed the production of new species entirely to inheritance of functionally-wrought alterations (thus failing to recognize Natural Selection, which was not yet enunciated), it was right in so far as it ascribed organic changes to changes of condi tions. And it was, I think, also right in so far as it implied * Westminster Review, April, 1857. "Progress: its Law and Cause." See also Essom, vol. i. RECENT CRITICISMS AND HYPOTHESES. 5f,9 that isolation is a condition precedent to such changes. Ap parently it did not occur to me as needful to specify this iso lation as making possible the differentiation of species; since it goes without saying that members of a species spreading east, west, north, south, and forming groups hundreds of miles apart, must, while breeding with those of the same group be prevented from breeding with those of other groups — prevented from having their locally-caused modifications mutually cancelled. The importance of isolation has of late been emphasized by Dr. Eomanes and others, who, to that isolation conse quent on geographical diffusion, have added that isolation which results from difference of station in the same habitat, and also that due to differences in the breeding periods arising in members of the same species. Doubtless in what ever way effected, the isolation of a group subject to new conditions and in course of being changed, is requisite as a means to permanent differentiation Doubtless also, as con tended by Mr. Gulick and Dr. Eomanes, there is a difference between the case in which an entire species being subject to the same conditions is throughout modified in character, thus illustrating what Mr. Gulick calls "monotypic evolution," and the case in which different parts of the species, leading different lives, will, if they are by any means prevented from inter-breeding with other parts, form divergent varieties : thus illustrating " polytypic evolution." , § 174/. Beyond geographical and topographical isolation, there is an isolation of another kind regarded by some as having had an important share in organic evolution. Fore- shadcwed by Mr. Belt, subsequently enunciated by Mr. Catch- pool, fully thought out by Mr. Gulick, and more recently elaborated by Dr. Romanes, " Physiological Selection " is held to account for the genesis of marked varieties side by side with their parents. It is contended that without the kind of isolation implied by it, variations will be swamped by inter- 570 THE EVOLUTION OF LIFE. crossing, and divergence prevented; but that by tbe aid of this kind of isolation, a uniform species may be differentiated into two or more species, though its members continue to live in the same area. Facts are assigned to show that slightly unlike varieties may become unable to inter-breed either with the parent- species or with one another. This mutual inferiority is not of the kind we might expect. We might reasonably suppose that when varieties had diverged widely, crossing would be impracticable, because their constitutions had become so far unlike as to form an unworkable mixture. But there seems evidence that the infertility arises long before such a cause could operate, and that instead of failure to produce a work able constitution, there is failure to produce any constitution at all — failure to fertilize. Some change in the sexual system is suggested as accounting for this. That a minute difference in the reproductive elements may suffice, plants prove by the fact that when two members of slightly-diver gent varieties arc fertilized by each other's pollen, the fer tility is less than if each were fertilized by the pollen of its own variety; and where the two kinds of pollen are both used, that derived from members of the same variety is pre potent in. its effect over that derived from members of the other variety. The writers above named contend that variations must occur in the reproductive organs as well as in other organs; that such variations may produce relative infertility in par ticular directions; and that such relative infertility may be the first step towards prevention of crossing and estab lishment of isolation : so making possible the accumulation of such differences as mark off new species. Without doubt we have here a legitimate supposition and a legitimate infer ence. Necessarily there must happen variations of the kind alleged, and considering how sensitive the reproductive sys tem is to occult influences (witness among ourselves the fre quent infertility of healthy people while feeble unhealthy RECEXT CRITICISMS AND HYPOTHESES. 571 ones arc fertile), it is reasonable to infer that minute and obscure alterations of this kind may make slightly-different varieties unable to inter-breed. Granting that there goes on this " physiological selection," we must recognize it as one among the causes by which isola tion is produced, and the differentiating influence of natural selection in the same locality made possible. § 174gr. The foregoing criticisms and hypotheses do not, however, affect in any essential way the pre-existing concep tions. If, as in the foregoing chapters, we interpret the facts in terms of that redistribution of matter and motion consti tuting Evolution at large, we shall see that the general theory, as previously held, remains outstanding. It is indisputable that to maintain its life an organism must maintain the moving equilibrium of its functions in presence of environing actions. This is a truism : overthrow of the equilibrium is death. It is a corollary that when the environment is changed, the equilibrium of functions is dis turbed, and there must follow one of two results — either the equilibrium is overthrown or it is re-adjusted : there is a re-equilibration. Only two possible ways of effecting the re-adjustment exist — the direct and the indirect. In the one case the changed outer action so alters the moving equili brium as to call forth an equivalent reaction which balances it. If re-equilibration is not thus effected in the individual it is effected in the succession of individuals. Either the species altogether disappears, or else there disappear, genera tion after generation, those members of it the equilibria of whose functions are least congruous with the changed actions in the environment; and this is the survival of the fittest or natural selection. If now we persist in thus contemplating the problem as a statico-dynamical one, we shall see that much of the discus sion commonly carried on is beside the question. The centre around which the collision of arguments has taken place, is 572 THE EVOLUTION OF LIFE. the question of the formation of species. But here we sec that this question is a secondary and, in a sense, irrelevant one. We are concerned with the production of evolving and diverging organic forms; and whether these are or are not marked off by so-called specific traits, and whether they will or will not breed together, matters little to the general argu ment. If two divisions of a species, falling into unlike con ditions and becoming re-equilibrated with them, eventually acquire the differences of nature called specific, this is but a collateral result. The essential result is the formation of divergent organic forms. The biologic atmosphere, so to speak, has been vitiated by the conceptions of past natural ists, with whom the identification and classification of species was the be-all and end-all of their science, and who regarded the traits which enabled them to mark off their specimens from one another, as the traits of cardinal importance in Nature. But after ignoring these technical ideas it becomes manifest that the distinctions, morphological or physiological, taken as tests of species, are merely incidental phenomena. Moreover, on continuing thus to look at the facts, we shall better understand the relation between adaptive and specific characters, and between specific characters and those many small differences which always accompany them. For during re-equilibration there must, beyond those changes of struc ture required to balance outer actions by inner actions, be numerous minor changes. In any complex moving equi librium alterations of larger elements inevitably cause altera tions of elements immediately dependent on them, and these again of others: the effects reverberate and re-reverberate throughout the entire aggregate of actions down to the most minute. Of resulting structural changes a few will be con spicuous, more will be less conspicuous, and so on continu ously multiplying in number and decreasing in amount. Here seems a fit place for remarking that there are certain processes which do not enter into these re-equilibrations but in a sense interfere with them. One example must sufficu. RECENT CRITICISMS AND HYPOTHESES. 573 Among dogs may be observed the trick of rolling on some mass having a strong animal smell : commonly a decaying carcase. This trick has probably been derived from the trick of rolling on the body of an animal caught and killed, and so gaining a tempting odour. A male dog which first did this, and left a trail apt to be mistaken for that of prey, would be more easily found by a female, and would be more likely than others to leave posterity. Now such a trick could have no relation to better maintenance of the moving equilibrium, and might very well arise in a dog having no superiority. If it arose in one of the worst it would be eliminated from the species, but if it arose in one of medium constitution, fairly capable of self-preservation, it would tend to produce survival of certain of the less fit rather than the fittest. Probably there are many such minor traits which are in a sense accidental, and are neither adaptive nor specific in the ordinary sense. § 1747i. But now let it be confessed that though all pheno mena of organic evolution must fall within the lines above indicated, there remain many unsolved problems. Take as an instance the descent of the tcstes in the Mam malia. Neither direct nor indirect equilibration accounts for this. We cannot consider it an adaptive change, since there seems no way in which the production of sperm-cells, internally carried on in a bird, is made external by adjust ment to the changed requirements of mammalian life. Nor can we ascribe it to survival of the fittest ; for it is incredible that any mammal was ever advantaged in the struggle for life by this changed position of these organs. Contrariwise, the removal of them from a place of safety to a place of danger, would seem to be negatived by natural selection. Nor can we regard the transposition as a concomitant of re-equili bration; since it can hardly be due to some change in the general physiological balance. An example of another order is furnished bv the mason- 574: THE EVOLUTION OF LIFE. wasp. Several instincts, capacities, peculiarities, which are in a sense independent though they cooperate to the same end, are here displayed. There is the instinct to build a cell of grains of sand, and the ability to do this, which though in a sense separate may be regarded as an accompaniment; and there is the secretion of a cement — a physiological pro cess not directly connected with the psychological process. After oviposition there comes into play the instinct to seek, carry home, and pack into the cell, the small caterpillars, spiders, &c., which are to serve as food for the larva; and then there is the instinct to sting each of them at a spot where the injected hypnotic poison keeps the creature insen sible though alive till it is wanted. These cannot be regarded as parts of a whole developed in simultaneous coordination. There is no direct connexion between the building instinct and the hypnotizing instinct; still less between these in stincts and the associated appliances. What were the early stages they passed through imagination fails to suggest. Their usefulness depends on their combination; and this combination would seem to have been useless until they had all reached something like their present completeness. Nor can we in this case ascribe anything to the influence of teach ing by imitation, supposed to explain the doings of social in sects ; for the mason-wasp is solitary. Thus the process of organic evolution is far from being fully understood. We can only suppose that as there are devised by human beings many puzzles apparently unan swerable till the answer is given, and many necromantic tricks which seem impossible till the mode of performance is shown; so there are apparently incomprehensible results which are really achieved by natural processes. Or, other wise, we must conclude that since Life itself proves to be in its ultimate nature inconceivable, there is probably an incon ceivable element in its ultimate workings. END OF VOL. I. APPENDICES. APPENDIX A. THE GENERAL LAW OF ANIMAL FERTILITY. [In the Westminster Eeview for April, 1852, / published an essay under the title " A Theory of Population deduced from the General Law of Animal Fertility" That essay was the germ of Part VI of this work, " The Laws of Multiplication" in which its essential theses are fully developed. When developing them, I omitted some portions of the original essay — one which was not di rectly relevant, and another which contained a speculation open to criticism. As indicated in § 74_/, I find that this speculation has an unexpected congruity with recent results of inquiry. I therefore decide to reproduce it here along with the definition of Life pro pounded in that essay, which, though subsequently replaced by the definition elaborated in Part /. contains an element of truth.! * # * * * Some clear idea of the nature of Life itself, must, indeed, form a needful preliminary. We may be sure that a search for the influences determining the maintenance and multiplication of living organisms, cannot be successfully carried out unless we understand what is the peculiar property of a living organism — what is the widest generalization of the phenomena that indicate life. By way of preparation, therefore, for the Theory of Popu lation presently to be developed, we propose devoting a brief space to this prior question. ***** Employing the term, then, in its usual sense, as applicable only to organisms, Life may be defined as — the co-ordination of actions. The growth of a crystal, which is the highest inorganic process we are acquainted with, involves but one action — that of accre tion. The growth of a cell, which is the lowest organic process, involves two actions — accretion and disintegration — repair and waste — assimilation and oxidation. Wholly deprive a cell of oxygen, and it becomes inert — ceases to manifest vital phe nomena ; or, as we say, dies. Give it no matter to assimilate, and it wastes away and disappears, from continual oxidation. Evidently, then, it is in the balance of these two actions that the life consists. It is not in the assimilation alone ; for the crystal 57? 578 APPENDIX A. assimilates : neither is it in the oxidation alone ; for oxidation is common to inorganic matter : but it is in the joint maintenance of these — the co-ordination of them. So long as the two go on together, life continues : suspend either of them, and the result is — death. The attribute which thus distinguishes the lowest organic from the highest inorganic bodies, similarly distinguishes the higher organisms from the lower ones. It is in the greater complexity of the co-ordination — that is, in the greater number and variety of the co-ordinated actions — that every advance in the scale of being essentially consists. And whether we regard the numerous vital processes carried on in a creature of complex structure as so many additional processes, or whether, more philosophically, we regard them as subdivisions of the two fundamental ones — oxida tion and accretion — the co-ordination of them is still the life. Thus turning to what is physiologically classified as the vegetative system, we see that stomach, lungs, heart, liver, skin, and the rest, must work in concert. If one of them does too much or too little — that is, if the co-ordination be imperfect — the life is dis turbed ; and if one of them ceases to act — that is, if the co-ordi nation be destroyed — the life is destroyed. So likewise is it with the animal system, which indirectly assists in co-ordinating the actions of the viscera by supplying food and oxygen. Its com ponent parts, the limbs, senses, and instruments of attack or defence must perform their several offices in proper sequence ; and further, must conjointly minister to the periodic demands of the viscera, that these may in turn supply blood. How completely the several attributes of animal life come within the definition, we shall best see on going through them seriatim. Thus Strength results from the co-ordination of actions ; for it is produced by the simultaneous contraction of many muscles and many fibres of each muscle ; and the strength is great in propor tion to the number of these acting together — that is, in propor tion to the co-ordination. Swiftness also, depending partly on strength, but requiring also the rapid alternation of movements, equally comes under the expression ; seeing that, other things equal, the more quickly sequent actions can be made to follow each other, the more completely are they co-ordinated. So, too, is it with Agility ; the power of a chamois to spring with safety from crag to crag implies accurate co-ordination in the movements of manv different muscles, and a due subordination of them all to the perceptions. The definition similarly includes Instinct, which consists in the uniform succession of certain actions or series of actions after certain sensations or groups of sensations ; and that which surprises us in instinct is the accuracy with which these compound actions respond to these compound sensations ; that is GENERAL LAW OP ANIMAL FERTILITY. 579 — the completeness of their co-ordination. Thus, likewise, is it with Intelligence, even in its highest manifestations. That which we call rationality is the power to combine, or co-ordinate a great number and a great variety of complex actions for the achieve ment of a desired result. The husbandman has in the course of years, by drainage and manuring, to bring his ground into a fer tile state ; in the autumn he must plough, harrow, and sow, for his next year's crop ; must subsequently hoe and weed, keep out cattle, and scare away birds ; when harvest comes, must adapt the mode and time of getting in his produce to the weather and the labour market ; he must afterwards decide when, and where, and how to sell to the best advantage ; and must do all this that he may get food and clothing for his family. By properly co ordinating these various processes (each of which involves many others) — by choosing right modes, right times, right quantities, right qualities, and performing his acts in right order, he attains his end. But if he have done too little of this, or too much of that ; or have done one thing when he should have done another — if his proceedings have been badly co-ordinated — that is, if he have lacked intelligence — he fails. We find, then, that the co-ordination of actions is a definition of Life, which includes alike its highest and its lowest manifesta tions ; and not only so, but expresses likewise the degree of Cife, seeing that the Life is high in proportion as the co-ordination is great. Proceeding upwards, from the simplest organic cell in which there are but two interdependent actions, on through the group in which many such cells are acting in concert, on through the higher group in which some of these cells assume mainly the respiratory and others the assimilative function — proceeding still higher to organisms in which these two functions are subdivided into many others, and in which some cells begin to act together as contractile fibres; next to organisms in which the visceral divi sion of labour is carried yet further, and in which many contrac tile fibres act together as muscles — ascending again to creatures that combine the movements of several limbs and many bones and muscles in one action ; and further, to creatures in which complex impressions are followed by the complex acts we term instinctive — and arriving finally at man, in whom not only are the separate acts complex, but who achieves his ends by com bining together an immense number and variety of acts often extending through years — we see that the progress is uniformly towards greater co-ordination of actions. Moreover, this co-ordi nation of actions unconsciously constitutes the essence of our common notion of life ; for we shall find, on inquiry, that when we infer the death of an animal, which does not move on being touched, we infer it because we miss the usual co-ordination of a 5SO APPENDIX A. sensation and a motion : and we shall also find, that the test by which wo habitually rank creatures high or low in the scale of vitality is the decree of co-ordination their actions exhibit. * * * * * There remains but to notice the objection which possibly may be raised, that the co-ordination of actions is not life, but the ability to maintain life. Lack of space forbids going into this at length. It must suffice to say, that life and the ability to main tain life will be found the same. We perpetually expend the vitality we have that we may continue our vitality. Our power to breathe a minute hence depends upon our breathing now. We must digest during this week that we may have strength to digest next. That we may get more food, we must use the force which the food we have eaten gives us. Everywhere vigorous life is the strength, activity, and sagacity whereby life is maintained ; and equally in descending the scale of being, or in watching the decline of an invalid, we see that the ebbing away of life is the ebbing away of the ability to preserve life.* [Only on now coining to re-read the definition of Life enun ciated at the commencement of this essay with the arguments \ised in justification of it, does it occur to me that its essential thought ought to have been incorporated in the definition of Life given in Part I. The idea of co-ordination is there implied in the idea of correspondence, but the idea of co-ordination is so cardi nal a one that it should be expressed not by implication but overtly. It is too late to make the required amendment in the proper place, for the first part of this work is already stereotyped and printed. Being unable to do better I make the amendment here. The formula as completed will run : — The definite combi nation of heterogeneous changes, both simultaneous and succes sive, co-ordinated into correspondence with external co-existences and sequences.] Ending here this preliminary dissertation, let us now proceed to our special subject. § 1. On contemplating its general circumstances, we perceive that any race of organisms is subject to two sets of conflicting influences. On the one hand by natural death, by enemies, by lack of food, by atmospheric changes, &c., it is constantly being * Tt may be needful to remark, that by the proposed expression it is intended to define — not Life in its essence ; but, Life as manifested to us — not Life as a noumcnon : but, Life as a phenomenon. The ultimate mystery is as great as ever: seeing that there remains unsolved the question — What determines the co-ordination of actions ? GENERAL LAW OF ANIMAL FERTILITY. 581 destroyed. On the other hand, partly by the strength, swiftness and sagacity of its members, and partly by their fertility, it is constantly being- maintained. These conflicting sets of influences may be conveniently generalized as — the forces destructive of race, and the forces preservative of race. § 2. Whilst any race continues to exist, the forces destructive of it and the forces preservative of it must perpetually tend towards equilibrium. If the forces destructive of it decrease, the race must gradually become more numerous, until, either from lack of food or from increase of enemies, the destroying forces again balance the preserving forces. If, reversely, the forces destructive of it increase, then the race must diminish, until, either from its food becoming relatively more abundant, or from its enemies dying of hunger, the destroying forces sink to the level of the preserving forces. Should the destroying forces be of a kind that cannot be thus met (as great change of climate), the race, by becoming extinct, is removed out of the category. Hence this is necessarily the law of maintenance of all races ; seeing that when they cease to conform to it they cease to be. Now the forces preservative of race are two — ability in each member of the race to preserve itself, and ability to produce other members — power to maintain individual life, and power to propagate the species. These must vary inversely. When, from lowness of organization, the ability to contend with external dangers is small, there must be great fertility to compensate for the consequent mortality ; otherwise the race must die out. When, on the contrary, high endowments give much capacity of self-preservation, there needs a correspondingly low degree of fertility. Given the dangers to be met as a constant quantity ; then, as the ability of any species to meet them must be a con stant quantity too, and as this is made up of the two factors — power to maintain individual life and power to multiply — these cannot do other than vary inversely. § 3. To show that observed phenomena harmonise with this a priori principle seems scarcely needful. But, though axiomatic in its character, and therefore incapable of being rendered more certain, yet illustrations of the conformity to it which nature everywhere exhibits, will facilitate the general apprehension of it. In the vegetable kingdom we find that the species consisting of simple cells, exhibit the highest reproductive power. The yeast fungus, which in a few hours propagates itself throughout a large mass of wort, offers a familiar example of the extreme rapidity with which these lowly organisms multiply. In the Protococcus nivalis, a microscopic plant which in the course of a night reddens 582 APPENDIX A. many square miles of snow, we have a like example ; as also in the minute Algce, which colour the waters of stagnant pools. The sudden appearance of green films on damp decaying surfaces, the spread of mould over stale food, and the rapid destruction of crops by mildew, afford further instances. If we ascend a step to plants of appreciable size, we still find that in proportion as the organization is low the fertility is great. Thus of the com mon puff-ball, which is little more than a mere aggregation of cells, Fries says, " in a single individual of Reticularia maxima, I have counted (calculated ?) 10,000,000 sporules." From this point upwards, increase of bulk and greater complexity of structure are still accompanied by diminished reproductive power ; instance the Macrocystis pyrifera, a gigantic sea-weed, which sometimes attains a length of 1500 feet, of which Carpenter remarks, " This development of the nutritive surface takes place at the expense of the fructifying apparatus, which is here quite subordinate." * And when we arrive at the highly-organized exogenous trees, we find that not only are they many years before beginning to bear with any abundance, but that even then they produce, at the out side, but a few thousand seeds in a twelvemonth. During its centuries of existence, an oak does not develop as many acorns as a fungus does spores in a single night. Still more clearly is this truth illustrated throughout the animal kingdom. Though not so great as the fertility of the Protophyta, which, as Prof. Henslow says, in some cases passes comprehension, the fertility of the Protozoa is yet almost beyond belief. In the polyga^tric animalcules spontaneous fission takes place so rapidly that " it has been calculated by Prof. Ehren- berg that no fewer than 268 millions might be produced in a month from a single Paramecium ; " f and even this astonishing rate of increase is far exceeded in another species, one individual of which, " only to be perceived by means of a high magnifying power, is calculated to generate 170 billions in four days." J Amongst the larger organisms exhibiting this lowest mode of reproduction under a modified form — that of gemmation — we see that, though not nearly so rapid as in the Infusoria, the rate of multiplication is still extremely high. This fact is well illus trated by the polypes ; and in the apparent suddenness with which whole districts are blighted by the Aphis (multiplying by internal gemmation), we have a familiar instance of the startling results which the parthenogenetic process can achieve. Where reproduction becomes occasional instead of continuous, as it does amongst higher creatures, the fertility equally bears an inverse ratio to the development. " The queen ant of the African * Prin. ofPhys., 2nd edit., p. 77. f Ibid., 3rd edit., p 249. \ Ibid., p. 124. GENERAL LAW OF ANIMAL FERTILITY. 583 Termites lays 80,000 eggs in twenty-four hours ; and the common hairworm (Gordius) as many as 8,000,000 in less than one day." * Amongst the Vertebrata the lowest are still the most prolih'c. " It has been calculated," says Carpenter, " that above a million of eggs are produced at once by a single codfish." \ In the strong and sagacious shark comparatively few are found. Still less fertile are the higher reptiles. And amongst the Mammalia, beginning with small Rodents, which quickly reach maturity, produce large litters, and several litters in the year; advancing step by step to the higher mammals, some of which are long in attaining the reproductive age, others of which produce but one litter in a year, others but one young one at a time, others who unite these peculiarities; and ending with the elephant and man, the least prolific of all, we find that throughout this class, as throughout the rest, ability to multiply decreases as ability to maintain individual life increases. § 4. The a priori principle thus exemplified has an obverse of a like axiomatic character. We have seen that for the continu ance of any race of organisms it is needful that the power of self- preservation and the power of reproduction should vary inversely. We shall now see that, quite irrespective of such an end to be subserved, these powers could not do otherwise than vary in versely. In the nature of things species can subsist only by con forming to this law ; and equally in the nature of things they can not help conforming to it. Reproduction, under all its forms, may be described as the separation of portions of a parent plant or animal for the purpose of forming other plants or animals. Wh ether it be by sponta neous fission, by gemmation, or by gemmules ; whether the detached products be bulbels, spores or seeds, ovisacs, ova or spermatozoa ; or however the process of multiplication be modi fied, it essentially consists in the throwing off of parts of adult organisms for the purpose of making new organisms. On the other hand, self preservation is fundamentally a maintenance of the organism in undiminished bulk. Amongst the lowest forms of life, aggregation of tissue is the only mode in which the self- preserving power is shown. Even in the highest, sustaining the body in its integrity is that in which self-preservation most truly consists — is the end which the widest intelligence is indirectly made to subserve. Whilst, on the one side, it cannot be denied that the increase of tissue constituting growth is self-preservation both in essence and in result ; neither can it, on the other side, be denied that a diminution of tissue, either from injury, disease, or old age, is in both essence and result the reverse. * Agassiz -id Gould, p. 274. f Pri:i. of Phys., 3rd edit, p. 964. 38 584 APPENDIX A. Hence the maintenance of the individual and the propagation of the race being respectively aggregative and separative, necessarily vary inversely. Every generative product is a deduction from the parental life ; and, as already pointed out, to diminish life is to diminish the ability to preserve life. The portion thrown off is organised matter ; vital force has been expended in the organ isation of it, and in the assimilation of its component elements ; which vital force, had no such portion been made and thrown oil, would have been available for the preservation of the parent. Neither of these forces, therefore, can increase, save at the expense of the other. The one draws in and incorporates new material ; the other throws off material previously incorporated. The one adds to ; the other takes from. Using a convenient expression for describing the facts (though one that must not be construed into an hypothesis), we may say that the force which builds up and repairs the individual is an attractive force, whilst that which throws off germs is a repulsive force. But whatever may turn out to be the true nature of the two processes, it is clear that they are mutually destructive ; or, stating the proposition in its briefest form — Individuation and Keproduction are antagonistic. Again, illustrating the abstract by reference to the concrete, let us now trace throughout the organic world the various phases of this antagonism. § 5. All the lowest animal and vegetable forms — Protozoa and Protophyta — consist essentially of a single cell containing fluid, and having usually a solid nucleus. This is true of the Infu soria, the simplest Entozoa, and the microscopic Algae and Fungi. The organisms so constituted uniformly multiply by spontaneous fission. The nucleus, originally spherical, becomes elongated, then constricted across its smallest diameter, and ultimately separates, when " its divisions," says Prof. Owen, describing the process in the Infusoria, " seem to repel each other to positions equidistant from each other, and from the pole or end of the body to which they are nearest. The influence of these distinct centres of assimilation is to divert the flow of the plasmatic fluid from a common course through the body of the polygastrian to two special courses about those centres. So much of the primary developmental process is renewed, as leads to the insulation of the sphere of the influence of each assimilative centre from that of the other by the progressive formation of a double party wall of integument, attended by progressive separation of one party wall from the other, and by concomitant constriction of the body of the polygastrian, until the vibratile action of the superficial cilia of each separating moiety severs the narrowed neck of union, and they become two distinct individuals." * Similar in * " Parthenogenesis," p. 8. GENERAL LAW OP ANIMAL FERTILITY. 585 its general view is Dr. Carpenter's description of the multiplica tion of vegetable cells, which he says divide, " in virtue, it may be surmised, of a sort of mutual repulsion between the two halves of the endochrome (coloured cell-contents) which leads to their spontaneous separation." * Under a modified form of this process, the cell-contents, instead of undergoing bisection, divide into numerous parts, each of which ultimately becomes a separate individual. In some of the Alga3 " a whole brood of young cells may thus be at once generated in the cavity of the parent-cell, which subsequently bursts and sets them free." j- The Achlya prolifera multiplies after this fashion. Amongst the Fungi, too, the same mode of increase is exemplified by the Protococcus nivalis. And " it would appear that certain Infusoria, especially the Kolpodince, propagate by the breaking-up of their own mass into reproductive particles." J Now in this fissiparous mode of multiplication, which "is amazingly productive, and indeed surpasses in fertility any other with which we are acquainted," § we see most clearly the anta gonism between individuation and reproduction. We see that the reproductive process involves destruction of the individual ; for in becoming two, the parent fungus or polygastrian must be held to lose its own proper existence ; and when it breaks up into a numerous progeny, does so still more completely. More over, this rapid mode of multiplication not only destroys the in dividuals in whom it takes place, but also involves that their in dividualities, whilst they continue, shall be of the lowest kind. For assume a protozoon to be growing by imbibition at a given rate, and it follows that the oftener it divides the smaller must be the size it attains to ; that is, the smaller the development of its individuality. And a further manifestation of the same truth is seen in the fact that the more frequent the spontaneous fission the shorter the existence of each individual. So that alike by preventing anything beyond a microscopic bulk being attained, by ijreventing the continuance of this in its integrity beyond a few aours, and by be.ng fatal when it occurs, this most active mode of reproduction shows the strongest antagonism to individual life. § 6. Whether or not we regard reproduction as resulting from a repulsive force (and, as seen above, both Owen and Carpenter lean to some such view), and whether or not we consider the formation of the individual as due to the reverse of this — an attractive force — we cannot, on studying the phenomena, help admitting that two opposite activities ithus generalized arc at * Pri.ii. of Phi/s., p. O'J. f Ibid, p. 93. \ ft>id., p. 91 7. § " A Ocncrui Outline of the Animal Kingdom." By Trof. T. R. Jones, F. (}. S , p. 01. 586 APPENDIX A. work ; we cannot help admitting that the aggregative and sepa rative tendencies do in each case determine the respective de velopments of the individual and the race. On ascending one degree in the scale of organic life, we shall find this truth clearly exemplified. For if these single-celled organisms which multiply so rapidly be supposed to lose some of their separative tendency, what must be the result ? They now not only divide frequently, but the divided portions fly apart. How, then, will a diminution of this separative tendency first show 'itself? May we not expect that it will show itself in the divided portions not flying apart, but remaining near each other, and forming a group ? This we find in nature to be the first step in advance. The lowest com pound organisms are " simple aggregations of vesicles without any definite arrangement, sometimes united, but capable of existing sepa rately" * In these cases, " every component cell of the aggre gate mass that springs from a single germ, being capable of existing independently of the rest, may be regarded as a distinct individual." f The several stages of this aggregation are very clearly seen in both the animal and vegetable kingdoms. In the Hcematococcus binalis, the plant producing the reddish slime seen on damp surfaces, not only does each of the cells retain its original sphericity, but each is separated from its neighbour by a wide interval filled with mucus ; so that it is only as being diffused through a mass of mucus common to them all, that these cells can be held to constitute one individual. We find, too, that " the component cells, even in the highest Algae, are generally separated from each other by a large quantity of mucilaginous intercellular substance." \ And, again, the tissue of the simpler Lichens, " in consequence of the very slight adhesion of its component cells, is said to be pulverulent." § Similarly the Protozoa, by their feeble union, constitute the organisms next above them. Amongst the Polygastrica there are many cases " in which the individuals produced by fission or gemmation do not become completely detached from each other." || The Oph- rydium, for instance, " exists under the form of a motionless jelly- like mass . . . made up of millions of distinct and similar individuals imbedded in a gelatinous connecting substance ; " ^f and again, the Uvella, or " grape monad," 'consists of a cluster " which strongly resembles a transparent mulberry rolling itself across the field of view by the ciliary action of its component individuals." ** The parenchyma of the Sponge, too, is made * Carpenter. f Prin. of Phys., p. 873. \ Ibid, p. 203. § Ibid., p. 209. I Ibid., p. 249. II Ibid., p. 249. ** Ibid., p. 250. GENERAL LAW OF ANIMAL FERTILITY. 587 up of cells " each of which has the character of a distinct ani malcule, having a certain power of spontaneous motion, obtaining and assimilating its own food, and altogether living by and for itself ; " and so small is the cohesion of these individual cells, that the tissue they constitute " drains away when the mass is removed from the water, like white of egg." * Of course in proportion as the aggregate tendency leading to the formation of these groups of monads is strong, we may expect that, other things equal, the groups will be large. Proceeding upwards from the yeast fungus, whose cells hold together in groups of four, five, and six,f there must be found in each species of these composite organisms a size of group determined by the strength of the aggregative tendency in that species. Hence we may expect that, when this limit is passed, the group no longer remains united, but divides. Such we find to be the fact. These groups of cells undergo the same process that the cells themselves do. They increase up to a certain point, and then multiply either by simple spontaneous fission or by that modification of it called gemmation. The Volvox globator, which is made up of a number of monads associated together in the form of a hollow sphere, develops within itself a number of smaller spheres similarly constituted ; and after these, swimming freely in its interior, have reached a certain size, the parent group of animalcules bursts and sets the interior groups free. And here we may observe how this compound individuality of the Volvox is destroyed in the act of reproduction as the simple individuality of the monad is. Again, in the higher forms of grouped cells, where something like organisation begins to show itself, the aggregations are not only larger, but the separative process, now carried on by the method of gemmation, no longer wholly destroys the individual. And in fact, this gemination may be regarded as the form which spontaneous fission must assume in ceasing to be fatal ; seeing that gemmation essentially consists in the separation, not into halves, but into a larger part and a smaller part ; the larger part continuing to represent the original individual. Thus in the common Hydra or fresh-water polype, " little bud-like processes are developed from the external surface, which are soon observed to resemble the parent in character, possessing a digestive sac, mouth, and teritacula ; for a long time, however, their cavity is connected with that of the parent ; but at last the communication is cut off, and the young polype quits its attachment, and goes in quest of its .own main tenance." I § 7. Progress from these forms of organisation to still higher * Prln. ofPhys., p. 256. f Ibid., p. 212. $ Ibid., p. 266. 588 APPENDIX A. • forms is similarly characterized by increase of the aggregative tendency or diminution of the separative, and similarly exhibits the necessary antagonism between the development of the in dividual and the increase of the race. That process of grouping which constitutes the first step towards the production of complex organisms, we shall now find repeated in the formation of series of groups. Just as a diminution of the separative tendency -is shown in the aggregation of divided monads, so is a further diminution of it shown in the aggregation of the divided groups of monads. The first instance that occurs is att'orded by the compound polypes. " Some of the simpler forms of the com posite ffydroida," says Carpenter, " may be likened to a Hydra, whose gemmao, instead of becoming detached, remain perma nently connected with the parent ; and as these in their turn may develop gemmae from their own bodies, a structure of more or less arborescent character may be produced." * A similar species of combination is observable amongst the Sryozoa, and the com pound Tunicata. Every degree of union may be found amongst these associated organisms ; from the one extreme in which the individuals can exist as well apart as together, to the other extreme in which the individuals are lost in the general mass. Whilst each Bryozoon is tolerably independent of its neighbour, " in the compound Hydroida, the lives of the polypes are sub ordinate to that of the polypdom." f Of the Salpidce and Pyrosomidce, Carpenter says : — " Although closely attached to one another, these associated animals are capable of being separated by a smart shock applied to the sides of the vessel in which they are swimming. ... In other species, however, the sepa rate animals are imbedded in a gelatinous mass," and in one kind " there is an absolute union between the vascular systems of the different individuals." \ In the same manner that with a given aggregative tendency there is a limit to the size of groups, so is there a similarly- determined limit to the size of series of groups ; and that spontaneous fission which we have seen in cells and groups of cells we here find repeated. In the lower Annelida, for example, " after the number of segments in the body has been greatly multiplied by gemmation, a separation of those of the posterior portion begins to take place ; a constriction forms itself about the beginning of the posterior third of the body, in front of which the alimentary canal undergoes a dilatation, whilst on the seg ment behind it a proboscis and eyes are developed, so as to form the head of the young animal which is to be budded off; and in due time, by the narrowing of the constriction, a complete sepa- * Prin. of Phys., p. 267. f /&«*•, P- 276. % Ibid., 2nd edit, p. 115. GENERAL LAW OP ANIMAL FERTILITY. 589 ration is effected." * Not unfrequently in the Nais this process is repeated in the young one before it becomes independent of the parent. The higher Annelida are distinguished by the greater number of' segments held in continuity ; an obvious result of comparatively infrequent fission. In the class Myriapoda, which stands next above, " there is no known instance of multiplication by fission." f Yet even here the law may be traced both in the number and structure of the segments. The length of the body is still increased after birth " by gemmation from (or partial fission of) the penultimate segment." The lower members of the class are distinguished from the higher by the greater extent to which this gemmation is carried. Moreover, the growing aggre gative tendency is seen in the fact, that each segment of the Julus " is formed by the coalescence of two original segments," J whilst in the Scolopendridce, which are the highest of this class, " the head, according to Mr. Newport, is composed of eight segments, which are often consolidated into one piece ; " § both of which phenomena may be understood as arrests of that process of fission, which, if allowed to go a little further, would have produced dis tinct segments; and, if allowed to go further still, would have separated these segments into groups. § 8. Remarking, first, how gradually this mode of multiplica tion disappears — how there are some creatures that spontaneously divide or not according to circumstances ; others that divide when in danger (the several parts being capable of growing into complete individuals) ; others which, though not self -dividing, can live on in each half if artificially divided ; and others in which only one of the divided halves can live — how, again, in the Crus taceans the power is limited to the reproduction of lost limbs ; how there are certain reptiles that can re-supply a lost tail, but only imperfectly ; and how amongst the higher Vertebrata the ability to repair small injuries is all that remains — remarking thus much, let us now, by way of preparation for what is to follow, consider the significance of the foregoing facts taken in connec tion with the definition of Life awhile since given. This spontaneous fission, which we have seen to be, in all cases, more or less destructive of individual life, is simply a cessation in the co-ordination of actions. From the single cell, the halves of whose nucleus, instead of continuing to act together, begin to repel each other, fly apart, establish distinct centres of assimilation, and finally cause the cell to divide ; up to the Anne- lidan, whose string of segments separates, after reaching a certain length ; we everywhere see the phenomenon to be fundamentally * Prin. r>fP7i>/s., p. 954. -f- /&«/., p. 958. t/J.;if,p. 086. % Ibid., p. 058. 590 APPENDIX A. this. The tendency to separate is the tendency not to act together, probably arising from inability to act together any longer ; and the process of separation is the process of ceasing to act together. How truly non-co-ordination is the essence of the matter will be seen on observing that fission takes place more or less rapidly, according as the co-ordinating apparatus is less or more developed. Thus, "the capability of spontaneous division is one of the most distinctive attributes of the acrite type of structure ; " * the acrite type of structure being that in which the neurine or nervous matter is supposed to be diffused through the tissues in a molecular state, and in which, therefore, there exists no distinct nervous or co-ordinating system. From this point upwards the gradual disappearance of spontaneous fission is clearly related to the gradual appearance of nerves and ganglia — a fact well exemplified by the several grades of Annelida and Myriapoda. And when we remember that in the embryotic development of these classes, the nervous system does not make its appearance until after the rest of the organism has made great progress, we may even suspect that that coalescence of segments characteristic of the Hyriapoda, exhibits the co-ordi nating power of the rapidly-growing nervous system overtaking and arresting the separative tendency ; and doing this most where it (the nervous system) is most developed, namely, in the head. And here let us remark, in passing, how7, from this point of view, we still more clearly discern the antagonism of individuation and reproduction. We before saw that the propagation of the race is at the expense of the individual : in the above facts we may contemplate the obverse of this — may see that the formation of the individual is at the expense of the race. This combination of parts that are tending to separate and become distinct beings — this union qf many incipient minor individualities into one large individuality — is an arrest of reproduction — a diminution in the number produced. Either these units may part and lead inde pendent lives, or they may remain together and have their actions co-ordinated. Either they may, by their diffusion, form a small, simple, and prolific race, or, by their aggregation, a large, com plex, and infertile one. But manifestly the aggregation involves the infertility ; and the fertility involves the smallness. § 9. The ability to multiply by spontaneous fission, and the ability to maintain individual life, are opposed in yet another mode. It is not in respect of size only, but still more in respect of structure, that the antagonism exists. * " A General Outline of the Animal Kingdom." By Professor T. R. Jones, p. Gl. GENERAL LAW OF ANIMAL FERTILITY. 591 Higher organisms are distinguished from lower ones partly by bulk, and partly by complexity. This complexity essentially consists in the mutual dependence of numerous different organs, each subserving the lives of the rest, and each living by the help of the rest. Instead of being made up of many like parts, per forming like functions, as the Crinoid, the Star-fish, or the Milli pede, a vertebrate animal is made up of many unlike parts, performing unlike functions. From that initial form of a com pound organism, in which a number of minor individuals are simply grouped together, we may, more or less distinctly, trace not only the increasing closeness of their union, and the gradual disappearance of their individualities in that of the mass, but the gradual assumption by them of special duties. And this " physiological division ofc labour," as it has been termed, has the same effect as the division of labour amongst men. As the preservation of a number of persons is better secured when, uniting into a society, they severally undertake different kinds of work, than when they are separate and each performs for him self every kind of work ; so the preservation of a congeries of parts, which, combining into one organism, respectively assume nutrition, respiration, circulation, locomotion, as separate func tions, is better secured than when those parts are independent, and each fulfils for itself all these functions. But the condition under which this increased ability to main tain life becomes possible is, that the parts shall cease to separate. While they are perpetually separating, it is clear that they cannot assume mutually subservient duties. And it is further clear that the more the tendency to separate diminishes, that is, the larger the groups that remain connected, the more minutely and perfectly can that subdivision of functions which, we call organization be car ried out. Thus we see that in its most active form the ability to multiply is antagonistic to the ability to maintain individual life, not only as preventing increase of bulk, but also as preventing organiza tion — not only as preventing homogeneous co-ordination, but as preventing heterogeneous co-ordination. § 10. To establish the unbroken continuity of this law of fertility, it will be needful, before tracing its results amongst the higher animals, to explain in what manner spontaneous fission is now understood, and what the cessation of it essentially means. Originally, naturalists supposed that creatures which multiply by self-division, under any of its several forms, continue so to multiply perpetually. In many cases, however, it has latterly been shown that they do not do this ; and it is now becoming a received opinion that they do not, and cannot, do this, in any 502 APPENDIX A. case. A fertilised germ appears here, as amongst higher organ isms, to be the point of departure ; and that constant formation of new tissue implied in the production of a great number of individuals by fission, seems gradually to exhaust the germinal capacity in the same way that the constant formation of new tissue, during the development of a single mammal, exhausts it. The phenomena classified by Steenstrup as " Alternate Genera tion," and since generalised by Professor Owen in his work " On Parthenogenesis," illustrate this. The egg of a Medusa (jelly fish) develops into a polypoid animal called the Strobila. This Strobila lives as the polype does, and, like it, multiplies rapidly by gemmation. After a great number of individuals has been thus produced, and when, as we must suppose, the germinal capacity is approaching exhaustion, eacfc Strobila begins to exhibit a series of constrictions, giving it some resemblance to a rouleau of coin or a pile of saucers. These constrictions deepeii ; the segments gradually develop tentacula ; the terminal segment finally separates itself, and swims away in the form of a young Medusa • the other segments, in succession, do the same ; and from the eggs which these Medusa? produce, other like series of polypoid animals, multiplying by gemmation, originate. In the compound Polypes, in the Tunicata, in the Trematoda, and in the Aphis, we find repeated, under various modifications, the same phenomenon. Understanding then, this lowest and most rapid mode of multiplication to consist essentially in the production of a great number of individuals from a single germ — perceiving, further, that diminished activity of this mode of multiplication consists essentially in the aggregation of the germ-product into larger masses — and seeing, lastly, that the disappearance of this mode of multiplication consists essentially in the aggregation of the germ-product into one mass — we shall be in a position to com prehend, amongst the higher animals, that new aspect of the law, under which increased individuation still involves diminished reproduction. Progressing from those lowest forms of life in which a single ovum originates countless organisms, through the successive stages in which the number of organisms so originated becomes smaller and smaller ; and finally arriving at a stage in which one ovum produces but one organism ; we have now, in our further ascent, to observe the modified mode in which this same necessary antagonism between the ability to multiply, and the ability to preserve individual life, is ex hibited. § 11. Throughout both the animal and vegetable kingdoms, generation is effected " by the union of the contents of a GENERAL LAW OF ANIMAL FERTILITY. 593 ' sperm-cell ' with those of a ' germ-cell ; ' the latter being that from within which the embryo is evolved, whilst the former supplies some material or influence necessary to its evolution." * Amongst the lowest vegetable organisms, as in the Desmidece, the DiatomacecB, and other families of the inferior Algce, these cells do not appreciably differ ; and the application to them of the terms " sperm-cell " and " germ-cell " is hypothetical. From this point upwards, however, distinctions become visible. As we advance to higher and higher types of structure, marked differences arise iu the character of these cells, in the organs evolving them, and in the position of these organs, which are finally located in separate sexes. Doubtless a separation in the functions of " sperm-cell " and " germ-cell " has simultaneously arisen. That change from homogeneity of function to hetero geneity of function which essentially constitutes progress in organization may be assumed to take place here also ; and, indeed, it is probable that the distinction gradually established between these cells, in origin and appearance, is merely significant of, and consequent upon, the distinction that has arisen between them in constitution and office. Let us now inquire in what this distinction consists. If the foundation of every new organism be laid bv the com bination of two elements, we may reasonably suspect that these two elements are typical of some two fundamental divisions of which the new organism is to consist. As nothing iu nature is without meaning and purpose, we may be sure that the universality of this binary origin, signifies the universality of a binary structure. The simplest and broadest division of which an organism is capable must be that signified. What, then, must this division be ? The proposed definition of organic life supplies an answer. If organic life be the co ordination of actions, then an organism may be primarily divided into parts whose* actions are co-ordi nated, and parts which co-ordinate them — organs which are made to work in concert, and the apparatus which makes them (jo work — or, in other words, the assimilative, vascular, excretory, and muscular systems on the one hand, and the nervous svstcm on the other. The justness of this classification will become further apparent, when it is remembered that by the nervous «ystem alone is the individuality established. By it all parts are made one in purpose, instead of separate ; by it the organism is rendered a conscious whole — is enabled to recognise its own extent and limits ; and by it are all injuries notified, repairs directed, and the general conservation secured. The more the nervous system is developed, the more reciprocally subservient do * Prin. o/Phys., p. 907. 594 APPENDIX A. the components of the body become — the less can they bear separating. And that which thus individuates many parts into one whole, must be considered as more broadly distinguished from the parts individuated, than any of these parts from each other. Further evidence in support of this position may be drawn from the fact, that as we ascend in the scale of animal life, that is, as the co-ordination of actions becomes greater, we find the co-ordinating or nervous system becoming more and more definitely separated from the rest ; and in the vertebrate or highest type of structure we find the division above insisted on distinctly marked. The co-ordinating parts and the parts co ordinated are placed on opposite sides of the vertebral column. With the exception of a few ganglia, the whole of the nervous masses are contained within the neural arches of the vertebrae ; whilst all the viscera and limbs are contained within, or appended to, the hsemal arches — the terms neural and haemal having, in deed, been chosen to express this fundamental division. If, then, there be truth in the assumption that the two elements, which, by their union, give origin to a new organism, typify the two essential constituents of such new organism, we must infer that the sperm-cell and germ-cell respectively consist of co-ordinating matter and matter to be co-ordinated — neurine and nutriment. That apparent identity of sperm-cell and germ- cell seen in the lowest forms of life may thus be understood as significant to the fact that no extended co-ordination of actions exists in the generative product — each cell being a separate indi vidual ; and the dissimilarity seen in higher organic types may, conversely, be understood as expressive of, and consequent upon, the increasing degree of co-ordination exhibited." * That the sperm-cell and germ-cell are thus contrasted in nature and function may further be suspected on considering the distinctive characteristics of the sexes. Of the two elements they respectively contribute to the formation of a fertile germ, it may be reasonably supposed that each furnishes that which it possesses in greatest abundance and can best spare. "Well, in the greater size of the nervous centres in the male, as well as in the fact that during famines men succumb sooner than women, we see that in the male the co-ordinating system is relatively predominant. From the same evidence, as well as from the greater abundance of the cellular and adipose tissues in women, we may infer that the nutritive system predominates in the female, f Here, then, is additional support for the hypothesis * Should it he objected that in the higher plants the sperm-cell and germ- ccll differ, though no distinct co-ordinating system exists, it is replied that there is co ordination of actions, though of a i'eeble kind, and that there must be some agency by which this is carried 071. •j- It is a significant fact thai amongst the dicueious invcrtcbrata, where the GENERAL LAW OF ANIMAL FERTILITY. 595 that the sperm-cell, which is supplied by tne male, contains co ordinating matter, and the germ-cell, which is supplied by the female, contains matter to be co-ordinated. The same inference may, again, be drawn from a general view of the maternal function. For if, as we see, it is the office of the mother to afford milk to the infant, and during a previous period to afford blood to the foatus, it becomes probable that during a yet earlier stage it is still the function to supply nutri ment, though in another form. Indeed when, ascending gradually the scale of animal life, we perceive that this supplying of rnilk, and before that of blood, is simply a continuation of the previous process, we may be sure that, with Nature's usual consistency, this process is essentially one from the beginning. Quite in harmony with this hypothesis concerning the respec tive natures of the sperm-cell and germ-cell is a remark of Car penter's on the same point : — " Looking," lie says, " to the very equal mode in which the characters of the two parents are mingled in hybrid offspring, and to the certainty that the material conditions which determine the development of the germ are almost exclusively female, it would seem probable that the dynamical conditions arc, in great part, furnished by the male." * § 12. Could nothing but the foregoing indirect evidence be adduced in proof of the proposition that the spermatozoon is essentially a neural element, and the ovum essentially a haemal element, we should scarcely claim for it anything more than plausibility. On finding, however, that this indirect evidence is merely introductory to evidence of a quite direct nature, its significance will become apparent. Adding to their weight taken separately the force of their mutual confirmation, these two series of proofs will be seen to give the hypothesis a high degree of probability. The direct evidence now to be considered is of several kinds. On referring to the description of the process of multiplication in monads, quoted some pages back (§ 5), from Professor Owen, the reader will perceive that it is by the pellucid nucleus that the growth and reproduction of these single-celled creatures are regu lated. The nucleus controls the circulation of the plasrnatic fluid ; the fission of the nucleus is the first step towards the formation of another cell ; each half of the divided nucleus estab lishes round itself an independent current ; and, apparently, it ics by the repulsion of the nuclei that the separation into two indi- nutritive system greatly exceeds the other systems in development, the female is commonly the largest, and often greatly" so. In sonic of the Ilotifera the male has no nutritive svstem at all. Bee Prin. of P/i>/s.. p. 95 1. * Prin. ofPhys., p. 908. 590 APPENDIX A. viduals is finally effected. All -which facts, when generalised, imply that the nucleus is the governing or co-ordinating part. Now, Professor Owen subsequently points out that the matter of the sperm-cell performs in the fertilised germ-cell just this same function which the nucleus performs in a single-celled animal. We find the absorption by a germ-cell of the contents of a sperm- cell "followed by the appearance of a pellucid nucleus in the centre of the opaque and altered germ-cell ; we further see its successive fissions governed by the preliminary division of the pellucid centre ; " and, led by these and other facts, Professor Owen thinks that " one cannot reasonably suppose that tho nature and properties of the nucleus of the impregnated germ-cell and that of the monad can be different." * And hence he further infers that " the nucleus of the monad is of a nature similar to, if not identical with," the matter of the spermatozoon. But we have seen that in the monad the nucleus is the co-ordinating part ; and hence to say that the sperm-cell is, in nature, identical with it, is to say that the sperm-cell consists of co-ordinating matter. Chemical analysis affords further evidence, though, from the imperfect data at present obtained, less conclusive evidence than could be wished. Partly from the white and gray nervous sub stances having been analysed together instead of separately, and partly from the difficulty of isolating the efficient contents of the sperm-cells, a satisfactory comparison cannot be made. Never theless, possessing in common, as they do, one element, by which they arc specially characterised, the analysis, as far as it goes, supports our argument. The following table, which has been made up from data given in the Cyclopaedia of Anatomy and Physi ology, Art. NERVOUS SYSTEM, gives the proportion of this ele ment in the brain in different conditions, and shows how impor tant is its presence. In Infauts. In Youth. In Adults. In Old Men. In Idiots. Solid constituents in a hundred parts of bruin 17.21 25 . 74 27.49 26.15 29.07 Of these solid constituents the phosphorus amounts to. . ... Which gives a percentage of 0.8 1.65 1.80 1.00 0.85 phosphorus in the solid con stituents of 4.65 6.41 6 54 3.82 2.92 This connection between the quantity of phosphorus present and the degree of mental power exhibited, is sufficiently signiii- * " Parthenogenesis," pp. 66, 67. GENERAL LAW OF ANIMAL FERTILITY. 597 cant; and the fact that in the same individual the varying degrees of cerebral activity are indicated by the varying quanti ties of alkaline phosphates excreted by the kidneys,* still more clearly shows the essentialness of phosphorus as a constituent of nervous matter. Respecting the constitution of sperm-cells chemists do not altogether agree. One thing, however, is certain — that they contain unoxidixed phosphorus ; and also a fatty acid, that is not improbably similar to the fatty acid contained in ncurine.f' In fact, there would seem to be present the con stituents of that oieophosphoric acid which forms so distinctive an element of the brain. That a large quantity of binoxide of protein is also present, may be ascribed to the fact that a great part of the sperm-cell consists merely of the protective membrane and its locomotive appendage ; the really eflicient portion being but the central contents.^ Evidence of a more conclusive nature — evidence, too, which will show in what direction our argument tends — is seen in the marked antagonism of the nervous and generative systems. Thus, the fact that intense mental application, involving great waste of the nervous tissues, and a corresponding consumption of nervous matter for their repair, is accompanied by a cessation in the production of sperm-cells, giv.es strong support to the hypo thesis that the sperm-cells consist essentially of neurine. And this becomes yet clearer on finding that the converse fact is true — that undue production of sperm-cells involves cerebral inac tivity. The first result of a morbid excess in this direction is headache, which may be taken to indicate that the brain is out of repair ; this is followed by stupidity ; should the disorder con tinue, imbecility supervenes, ending occasionally in insanity. That the sperm-cell is co-ordinating matter, and the germ- cell matter to be co-ordinated, is, therefore, an hypothesis not only having much a priori probability, but one supported by nu merous facts. § 13. This hypothesis alike explains, and is confirmed by, the truth, that throughout the vertebrate tribes the degree of fertility varies inversely as the development of the nervous system. * "Lectures on Animal Chemistry." By Dr. Bencc Jones. Medical Times, Sept. 13th, 1851. Sec also Pri'n. of Phi/.t., p. 171. •f Cyclopaedia of Anatomy and Physiology^ Vol. IV, p. 50f>.'* | From ;i remark of Drs. Wagner and Leuckart this chemical evidence seems to have already suggested the idea that the sperm-cell becomes " metamorphosed into the central parts of the nervous system." But though they reject this assumption, and though the experiments of Mr. Newport clearly render it untenable, yet none of the facts latterly brought to litrht conflict with the hypothesis that the sperm-cell contains unorganized co-ordinating matter. 598 The necessary antagonism of Individuation and Reproduction docs indeed show itself amongst the higher animals, in some degree in the manner hitherto traced ; namely, as determining the total bulk. Though the parts now thrown off, being no longer segments or gemmao, are not obvious diminutions of the parent, yet they must be really such. Under the form of in ternal fission, the separative tendency is as much opposed to the aggregative tendency as ever ; and, other things equal, the greater or less development of the individual depends upon the less or greater production of new individuals or germs of new indi viduals. As in groups of cells, and series of groups of cells, we saw that there was in each species a limit, passing which, the germ product would not remain iinited ; so in each species of higher animal there is a limit, passing which, the process of cell- multiplication results in the throwing off of cells, instead of re sulting in the formation of more tissue. Hence, taking an aver age view, we see why the smaller animals so soon arrive at a reproductive age, and produce large and frequent broods ; and why, conversely, increased size is accompanied by retarded and diminished fertility. But, as above implied, it is not so much to the bulk of the body as a whole, as to the bulk of the nervous system, that fertility stands related amongst the higher animals. Probably, indeed, it stands thus related in all cases ; the difference simply arising from the fact, that whereas in the lower organisms, where the nervous system is not concentrated, its bulk varies as the bulk of the body, in the higher organisms it does not do so. Be this as it may, however, we see clearly that, amongst the verte- brata, the bodily development is not the determining circum stance. In a fish, a reptile, a bird, and a mammal cf the same weight, there is nothing like equality of fecundity. Cattle and horses, arriving as they do so soon at a reproductive age, are much more prolific than the human race, at the same lime that they are much larger. And whilst, again, the difference in size between the elephant and man is far greater, their respective powers of multiplication are less unlike. Looking in these cases at the nervous systems, however, we find no such discrepancy. On learning that the average ratio of the brain to the body is — in fishes, 1 to 5668 ; in reptiles, 1 to 1321 ; in birds, 1 to 212 ; and in mammals, 1 to 186;* their different degrees of fecundity are accounted for. Though an ox will outweigh half-a-dozen men, yet its brain and spinal cord are far less than those of one man ; and though in bodily development the elephant so im mensely exceeds the human being, yet the elephant's cerebro- spinal system is only thrice the size attained by that of civilized * Quain's Elements of Anatomy, p. G72. GENERAL LAW OF ANIMAL FERTILITY. 599 men.* Unfortunately, it is impossible to trace throughout the animal kingdom this inverse relationship between the nervous and reproductive systems with any accuracy. Partly from the fact that, in each case, the degree of fertility depends on three variable elements — the age at which reproduction begins, the number produced at a birth, and the frequency of the births; partly from the fact that, in respect to most animals, these data are not satisfactorily attainable, and that, when they are attain able, they are vitiated by the influence of domesticity ; and partly from the fact that no precise measurement of the respective nervous systems has been made, we are unable to draw any but general and somewhat vague comparisons. These, however, as far as they go, are in our favour. Ascending from beings of the acrite nerveless type, which are the most prolific of all, through the various invertebrate sub-kingdoms, amongst which spontane ous fission disappears as the nervous system becomes developed ; passing again to the least nervous and most fertile of the verte brate series — Fishes, of which, too, the comparatively large- brained cartilaginous kinds multiply much less rapidly than the others ; progressing through the more highly endowed and less prolific Reptiles to the Mammalia, amongst wyhich the Rodents, with their unconvoluted brains, are noted for their fecundity ; and ending with man and the elephant, the least fertile and largest- brained of all — there seems to be throughout a constant relation ship between these attributes. And indeed, on turning back to our a priori principle, no other relationship appears possible. We found it to be tne necessary law of maintenance of races, that the abilitv to maintain indi vidual life and the ability to multiply vary inversely. But the ability to maintain individual life is in all cases measured by the development of the nervous system. If it be in good visceral organi zation that the power of self-preservation is shown, this implies some corresponding nervous apparatus to secure sufficient food. If it be in strength, there must be a provision of nerves and nervous centres answering to the number and size of the muscles. If it be in swiftness and agility, a proportionate development of the cerebellum is presupposed. If it be in intelligence, this varies * The maximum weight of the horse's brain is 1 Ib. 7 ozs. ; the human brain weighs 3 Ibs., and occasionally as much as 4 Ibs. ; the brain of a whale, 75 feet long, weighed 5 Ibs. 5 ozs. ; and the elephant's brain reaches from 8 Ibs. to 10 Ibs. Of the whale's fertility we know nothing; but the elephant's quite agrees with the hypothesis. The elephant does not attain its full size until it is thirty years old, from which we may infer that it arrives at a reproductive age later than man does ; its period of gestation is two years, and it produces one at a birth. Evidently, therefore, it is much less prolific than man. Sec Miiller'a Pht/tdoloyy (Baly's translation), p. 815, and Quain's Elements of Anatomy, p. 671. ,59 COO APPENDIX A. with the size of the cerebrum. As in all cases co-ordination cf actions constitutes the life, or, what is the same thing, the ability to maintain life ; and as throughout the animal kingdom this co ordination, under all its forms, is effected by nervous agents of some kind or other ; and as each of these nervous agents per forms but one function ; it follows that in proportion to the number of the actions co-ordinated must be the number of nervous agents. Hence the nervous system becomes the universal measure of the degree of co-ordination of actions; that is, of the life, or ability to maintain life. And if the nervous system varies directly as the ability to maintain life, it must vary inversely as the ability to multiply.* And here, assuming the constitution of the sperm-cell above inferred to be the true one, we see how the obverse a priori prin ciple is fulfilled. Where, as amongst the lowest organisms, bulk is expressive of life, the antagonism of individuation and re production was broadly exhibited in the fact that the making of two or more new individuals was the wwmaking of the original individual. And now, amongst the higher organisms, where bulk is no longer the measure of life, we see that this antagonism is between the neural elements thrown off, and that internal neural mass whose bulk is the measure of life. The production of co ordinating cells must be at the expense of the co-ordinating appa ratus ; and the aggregation of the co-ordinating apparatus must be at the expense of co-ordinating cells. How the antagonism affects the female economy is not so clear. Possibly the provision required to be made for supplying nervous as well as other nutri ment to the embryo, involves an arrest in the development of the nervous system ; and if so, probably this arrest takes place early in proportion as the number of the coming offspring makes the required provision great: or rather, to put the facts in their right sequence, an early arrest renders the production of a numerous offspring possible. § 14. The law which we have thus traced throughout the ani- * That the size of the nervous system is the measure of the ability to maintain life, is a proposition that must, however, be taken with some qualifications. The ratio between the amounts of gray and white matter present in each ease is probably a circumstance of moment. Moreover, the temperature of the blood may have a modifying influence; seeing that small nervous centres exposed to rapid oxidation will be equivalent to larger ones more slowly oxidized. Indeed, we see amongst mankind, that though, in the main, size of brain determines mental power, yet temperament exercises some control. There is reason to think, too, that certain kinds of nervous action involve greater consumption of nervous tissue than others ; and this will somewhat complicate the comparisons. Nevertheless, these admissions do not affect the generalization as a whole, but merely prepare us to meet with minor irregularities. GENERAL LAW -OP ANIMAL FERTILITY. 001 tnal kingdom, and which must alike determine the different fer tilities of different species, and the variations of fertility in the same species, we have now to consider in its application to man kind. [ The remainder of the essay, which as implied, deals with the ap plication of this general principle to the multiplication of the human race, need not be here reproduced. The subject is treated in full in Part VL] APPENDIX B. in THE INADEQUACY OF NATURAL SELECTION, ETC., ETC. [In this Appendix are included four essays originally published in the Contemporary Review and subsequently republished as pam phlets. The first appeared under the above title in February and March, 1893; the second in May of that year under the title " Prof. Weismanrfs Theories ; " the third in December of that year under the title "A Rejoinder to Prof. Wcismann ; " and the fourth in October, 1894, under the title " Weismannism Once More" As these successive essays practically form parts of one whole, I have thought it needless to keep them separate by repeating their titles, and have simply marked them off from one another by the numbers I, II, III, IV. Of course, as they are components of a controversy, some incompleteness arises from the absence of the essays to which portions of them were replies ; but in each the course of the argu ment sufficiently indicates the counter-arguments which were metA I. STUDENTS of psychology are familiar with the experiments of Weber on the sense of touch. ITe found that different parts of the surface differ widely in their ability to give information concerning the things touched. Some parts, which yielded vivid sensations, yielded little or no knowledge of the sizes or forms of the things exciting them ; whereas other parts, from which there came sensations much less acute, furnished clear impressions respecting the tangible characters, even of relatively small objects. These unlikenesses of tactual discriminativeness he ingeniously expressed by actual measurements. Taking a pair of compasses, he found that if they were closed so nearly that the points were less than one-twelfth of an inch apart, the end of the forefinger could not perceive that there were two points : the two points seemed one. But when the compasses were opened so that the points were one-twelfth of an inch apart, then the end of the forefinger distinguished the two points. At the same time, he found that the compasses must be opened to the extent of two and a half inches, before the middle of the back could distinguish between two points and one. That is to say, as thus INADEQUACY OP NATURAL SELECTION, ETC. G03 measured, the end of the forefinger has thirty times the tactual discriminativeness which the middle of the back has. Between these extremes he found gradations. The inner surfaces of the second joints of the fingers can distinguish separateness of positions only half as well as the tip of the forefinger. The innermost joints are still less discriminating, but have powers of discrimination equal to that of the tip of the nose. The end of the great toe, the palm of the hand, and the cheek, have alike one-fifth of the perceptiveness which the tip of the forefinger has ; and the lower part of the forehead has but one-half that possessed by the cheek. The back of the hand and the crown of the head are nearly alike in having but a four teenth or a fifteenth of the ability to perceive positions as dis tinct, which is possessed bv the finger-end. The thigh, near the knee, has rather less, and the breast less still ; so that the com passes must be opened more than an inch and a half before the breast distinguishes the two points from one another. What is the meaning of these differences ? How, in the course of evolution, have they been established ? If " natural selec tion," or survival of the fittest, is the assigned cause, then it is required to show in what way each of these degrees of endow ment has advantaged the possessor to such extent that not infre quently life has been directly or indirectly preserved by it. We might reasonably assume that in the absence of some differentiat ing process, all parts of the surface would have like powers of perceiving relative positions. They cannot have become widely unlike in perceptiveness without some cause. And if the cause alleged is natural selection, then it is necessary to show that the greater degree of the power possessed by this part than by that, has not only conduced to the maintenance of life, but has con duced so much that an individual in whom a variation has pro duced better adjustment to needs, thereby maintained life when some others lost it; and that among the descendants inheriting this variation, there was a derived advantage such* as enabled them to multiply more than the descendants of individuals not possessing it. Can this, or anything like this, be shown ? That the superior perceptiveness of the forefinger-tip has thus arisen, might be contended with some apparent reason. Such perceptiveness is an important aid to manipulation, and may have sometimes given a life-saving advantage. In making arrows or fish-hooks, a savage possessing some extra amount of it may have been thereby enabled to get food where another failed. In civilized life, too, a sempstress with well-endowed finger-ends might be expected to gain a better livelihood than one with finger-ends which were obtuse ; though this advantage would not be yo great as appears. I have found that two ladies whose 604 APPENDIX B. finger-ends were covered with glove-tips, reducing their sensitive ness from one-twelfth of an. inch between compass-points to one- seventh, lost nothing appreciable of their quickness and goodness in sewing. An experience of my own here comes in evidence. Towards the close of my salmon-fishing davs I used to observe what a bungler I had become in putting on and taking off arti ficial flies. As the tactual discriminativeness of my finger-ends, recently tested, comes up to the standard specified by Weber, it is clear that this decrease of manipulative power, accompanying increase of age, was due to decrease in the delicacy of muscular co-ordination and sense of pressure — not to decrease of tactual discriminativeness. But not making much of these criticisms, let us admit the conclusion that this high perceptive power possessed by the forefinger-end may have arisen by survival of the fittest ; and let us limit the argument to the other differences. How about the back of the trunk and its face ? Is any advan tage derived from possession of greater tactual discriminativeness by the last than the first ? The tip of the nose has more than three times the power of distinguishing relative positions which the lower part of the forehead has. Can this greater power be shown to have any advantage ? The back of the hand has scarcely more discriminative ability than the crown of the head, and has only one-fourteenth of that which the finger-tip has. Why is this ? Advantage might occasionally be derived if the back of the hand could tell us more than it does about the shapes of the surfaces touched. Why should the thigh near the knee be twice as perceptive as the middle of the thigh ? And, last of all, why should the middle of the forearm, middle of the thigh, middle of the back of the neck, and middle of the back, all stand on the lowest level, as having but one-thirtieth of the perceptive power which the tip of the forefinger has ? To prove that these differences have arisen by natural selection, it has to be shown that such small variation in one of the parts as might occur in a generation — say one-tenth extra amount — has yielded an appre ciably greater power of self-preservation ; and that those inherit ing it have continued to be so far advantaged as to multiply more than those who, in other respects equal, were less endowed with this trait. Does any one think he can show this ? But if this distribution of tactual perceptiveness cannot be explained by survival of the fittest, how can it be explained ? The reply is that, if there has been in operation a cause which it is now the fashion among biologists to ignore or deny, these various differences are at once accounted for. This cause is the inheritance of acquired characters. As a preliminary to setting forth the argument showing this, I have made some experiments. It is a current belief that the fingers of the blind, more prac- INADEQUACY OF NATURAL SELECTION, ETC. G05 tised in tactual exploration than the fingers of those who can see, acquire greater discriminativeness : especially the fingers of those blind who have been taught to read from raised letters. Not wishing to trust to this current belief, I recently tested two youths, one of fifteen and the other younger, at the School for the Blind in Upper Avenue Road, and found the belief to be correct. I found that instead of being unable to distinguish between points of the compasses until they were opened to one- twelfth of an inch apart, both of them could distinguish between points when only one-fourteenth of an inch apart. They had thick and coarse skins ; and doubtless, had the intervening obstacle, so produced, been less, the discriminative power would have been greater. It afterwards occurred to me that a better test would be furnished by those whose finger-ends are exercised in tactual perceptions, not occasionally, as by the blind in read ing, but all day long in pursuit of their occupations. The facts answered expectation. Two skilled compositors, on whom I experimented, were both able to distinguish between points when they were only one-seventeenth of an inch apart. Thus we have clear proof that constant exercise of the tactual nervous struc ture leads to further development.* Now if acquired structural traits are inheritable, the various contrasts above set down are obvious consequences ; for the gradations in tactual perceptiveness correspond with the grada tions in the tactual exercises of the parts. Save by contact with clothes, which present only broad surfaces having but slight and indefinite contrast, the trunk has scarcely any converse with * Let me here note in passing a highly significant implication. The development of nervous structures which in such cases take place, cannot be limited to the linker-ends. If we figure to ourselves the separate sensi tive areas which severally yield independent feelings, as constituting a net work (not, indeed, a network sharply marked out, but probably one such that the ultimate fibrils in each area intrude more or less into adjacent areas, so that the separations arc indefinite), it is manifest that when, with exercise, the structure has become further elaborated, and the meshes of the network smaller, there must be a multiplication of fibres communicating with the cen tral nervous system. If two adjacent areas were supplied by branches of one fibre, the touching of either would yield to consciousness the same sensation: there could be no discrimination between points touching the two. That there may be discrimination, there must be a distinct connection between each area and the tract of grey matter which receives the impressions. Nav more, there must be, in this central recipient-tract, an added number of the separate elements which, by their excitements, yield separate feelings. So that this in creased power of tactual discrimination implies a peripheral development, a multiplication of fibres in the trunk-nerve, and a complication of the nerve- centre. It can scarcely be doubted that analogous changes occur under analogous conditions throughout all parts of the nervous system — not in its sensory appliances only, but in all its higher co-ordinating appliances, up to the highest. 606 APPENDIX B. external bodies, and it has but small discriminative power ; but what discriminative power it has is greater on its face than on its back, corresponding to the fact that the chest and abdomen are much more frequently explored by the hands : this differ ence being probably in part inherited from inferior creatures ; for, as we may see in dogs and cats, the belly is far more accessible to feet and tongue than the back. No less obtuse than the back are the middle of the back of the neck, the middle of the fore arm, and the middle of the thigh ; and these parts have but rare experiences of irregular foreign bodies. The crown of the head is occasionally felt by the fingers, as also the back of one hand by the fingers of the other ; but neither of these surfaces, which are only twice as perceptive as the back, is used with any frequency for touching objects, much less for examining them. The lower part of the forehead, though more perceptive than the crown of the head, in correspondence with a somewhat greater converse with the hands, is less than one-third as perceptive as the tip of the nose ; and manifestly, both in virtue of its relative prominence, in virtue of its contacts with things smelt at, and in virtue of its frequent acquaintance with the handkerchief, the tip of the nose has far greater tactual experience. Passing to the inner surfaces of the hands, which, taken as wholes, are more constantly occupied in touching than are the back, breast, thigh, forearm, forehead, or back of the hand, Weber's scale shows that they are much more perceptive, and that the degrees of percep- tiveness of different parts correspond with their tactual activities. The palms have but one-fifth the perceptiveness possessed by the forefinger-ends ; the inner surfaces of the finger-joints next the palms have but one-third; while the inner surfaces of the second joints have but one-half. These abilities correspond with the facts that whereas the inner parts of the hand are used only in grasping things, the tips of the fingers come into play not only when things are grasped, but when such things, as well as smaller things, are felt at or manipulated. It needs but to observe the relative actions of these parts in writing, in sewing, in judging textures, &c., to see that above all other parts the finger-ends, and especially the forefinger-ends, have the most multiplied expe riences. If, then, it be that the extra perceptiveness acquired from actual tactual activities, as in a compositor, is inheritable, these gradations of tactual perceptiveness are explained. Doubtless some of those who remember Weber's results, have had on the tip of the tongue the argument derived from the tip of the tongue. This part exceeds all other parts in power of tactual discrimination : doubling, in that respect, the power of the forefinger-tip. It can distinguish points that are only one- twenty-fourth of an inch apart. Why this unparalleled perceptive- INADEQUACY OF NATURAL SELECTION, ETC. CUT ness ? If survival of the fittest be the ascribed cause, then it lias to be shown what the advantages achieved have been ; and, fur ther, that those advantages have been sufficiently great to have had effects on the maintenance of life. Besides tasting, there are two functions conducive to life, which the tongue performs. It enables us to move about food during mastication, and it enables us to make many of the articulations constituting speech. But how does the extreme discriminative- ness of the tongue-tip aid these functions ? The food is moved about, not by the tongue-tip, but by the body of the tongue ; and even were the tip largely employed in this process, it would still have to be shown that its ability to distinguish between points one-twenty-fourth of an inch apart, is of service to that end, which cannot be shown. It may, indeed, be said that the tactual perceptiveness of the tongue-tip serves for detection of foreign bodies in the food, as plum-stones or as fish-bones. But such extreme perceptiveness is needless for the purpose. A perceptive- ness equal to that of the finger-ends would suffice. And further, even were such extreme perceptiveness useful, it could not have caused survival of individuals who possessed it in slightly higher degrees than others. It needs but to observe a dog crunching small bones, and swallowing with impunity the sharp-angled pieces, to see that but a very small amount of mortality would be prevented. But what about speech ? Well, neither here can there be shown any advantage derived from this extreme perceptiveness. ' For making the s and z, the tongue has to be partially applied to a portion of the palate next the teeth. Not only, however, must the contact be incomplete, but its place is indefinite — may be half an inch further back. To make the sh and zA, the contact has to be made, not with the tip, but with the upper surface of the tongue ; and must be an incomplete contact. Though, for making the liquids, the tip of the tongue and the sides of the tongue are used, yet the requisite is not any exact adjustment of the tip, but an imperfect contact with the palate. For the th, the tip is used along with the edges of the tongue ; but no perfect adjust ment is required, either to the edges of the teeth, or to the junc tion of the teeth with the palate, where the sound may equally well be made. Though for the t and d complete contact of the tip and edges of the tongue with the palate is required, yet the place of contact is not definite, and the tip takes no more import ant share in the action than the sides. Any one who observes the movements of his tongue in speaking, will find that there occur no cases in which the adjustments must have an exactness corresponding to the extreme power of discrimination which the tip possesses : for speech, this endowment is useless. Even were 608 APPENDIX B. it useful, it could not be shown that it has been developed by survival of the fittest ; for though perfect articulation is an aid, yet imperfect articulation has rarely such an eifect as to impede a man in the maintenance of his life. If he is a good workman, a German's interchanges of 6's and pjs do not disadvantage him. A Frenchman who, in place of the sound of /A, always makes the sound of 2, succeeds as a teacher of music or dancing, no lees than if he achieved the English pronunciation. Nay, even such an imperfection of speech as that which arises from cleft palate, does not prevent a man from getting on if he is capable. Tiue, it may go against him as a candidate for Parliament, or as an " orator " of the unemployed (mostly not worth employing). But in the struggle for life he is not hindered by the effect to the extent of being less able than others to maintain himself and his offspring. Clearly, then, even if this unparalleled perceptive- ness of the tongue-tip is required for perfect speech, such use is not sufficiently important to have been developed by natural selection. How, then, is this remarkable trait of the tongue-tip to be accounted >for ? Without difficulty, if there is inheritance of acquired characters. For the tongue-tip has, above all other parts of the body, unceasing experiences of small irregularities of surface. It is in contact with the teeth, and either consciously or unconsciously is continually exploring them. There is hardly a moment in which impressions of adjacent but different positions are not being yielded to it by either the surfaces of the teeth or their edges ; and it is continually being moved about from some of them to others. No advantage is gained. It is simply that the tongue's position renders perpetual exploration almost inevit able ; and by perpetual exploration is developed this unique power of discrimination. Thus the law holds throughout, from this highest degree of perceptivencss of the tongue-tip to its lowest degree on the back of the trunk ; and no other explanation of the facts seems possible. " Yes, there is another explanation," I hear some one say : " they may be explained by panmixia." Well, in the first place, as the explanation by panmixia implies that these gradations of perceptivcness have been arrived at by the dwindling of nervous structures, there lies at the basis of the explanation an unproved and improbable assumption ; and, in the second place, even were there no such difficulty, it may with certainty be denied that panmixia can furnish an explanation. Let us look at its preten sions. It was not without good reason that Bentham protested against metaphors. Figures of speech in general, valuable as they INADEQUACY OP NATURAL SELECTION, ETC. (Jo'j are in poetry and rhetoric, cannot be used without danger in science and philosophy. ** The title of Mr. Darwin's great work furnishes us with an instance of the misleading effects produced by them. It runs : — The Origin of Species by means of Natural Selection, or the Preservation of favoured Races in the Struggle for Life. Here are two figures of speech which conspire to produce an impression more or less erroneous. The expression " natural selection " was chosen as serving .to indicate some parallelism with artificial selection — the selection exercised by breeders. Now selection connotes volition, and thus gives to the thoughts of readers a wrong bias. Some increase of this bias is produced by the words in the second title, " favoured races ; " for anything which is favoured implies the existence of some agent conferring a favour. * I do not mean that Mr. Darwin himself failed to recognize the mis leading connotations of his words, or that he did not avoid being misled by them. In chapter iv of the Origin of Species, he says that, considered literally, " natural selection is a false term," and that the personification of Nature is objectionable ; but he thinks that readers, and those who adopt his views, will soon learn to guard themselves against the wrong implications. Here I venture to think that he was mistaken. For thinking this, there is the reason that even his disciple, Mr. Wallace — no, not his disciple, but his co-discoverer, ever to be honoured — has apparently been influenced by them. When, for example, in combating a view of mine, he says that " the very thing said to be impossible by variation and natural selection has been again and again effected by variation and artificial selection," he seems clearly to imply that the processes are analogous, and operate in the same way. Now this is untrue. They are analogous only within certain narrow limits ; and, in the great majority of cases, natural selec tion is utterly incapable of doing that which artificial selection does. To see this it needs only to de-personalise Nature, and to re member that, as Mr. Darwin says, Nature is " only the aggregate action and product of many natural laws [forces]." Observe its relative shortcomings. Artificial selection can pick out a par ticular trait, and, regardless of other traits of the individuals displaying it, can increase it by selective breeding in successive generations. For, to the breeder or fancier, it matters little whether such individuals are otherwise well constituted. They may be in this or that way so unfit for carrying on the struggle for life, that were they without human care, they would disappear forthwith. On the other hand, if we regard Nature as that which it is, an assemblage of varilus forces, inorganic and organic, some favourable to the maintenance of life and many at variance with its maintenance — forces whi|h operate blindly— we see that CIO APPENDIX B. there is no such selection of this or that trait ; but that there is a selection only of individuals which are, by the aggregate of their traits, best fitted for living. And here I may note an advantage possessed by the expression " survival of the fittest ; " since this does not tend to raise the thought of any one character which, more than others, is to be maintained or increased ; but tends rather to raise the thought of a general adaptation for all purposes. It implies the process which Nature can alone carry on — the leaving alive of those which are best able to utilize sur rounding aids to life, and best able to combat or avoid surround ing dangers. And while this phrase covers the great mass of cases in which there are preserved well-constituted individuals, it also covers those special cases which are suggested by the phrase u natural selection," in which individuals succeed beyond others in the struggle for life, by the help of particular characters which conduce in important ways to prosperity and multiplication. For now observe the fact which here chiefly concerns us, that survival of the fittest can increase any serviceable trait, only if that trait conduces to prosperity of the individual, or of posterity, or of both, in an important degree. There can be no increase of any structure by natural selection unless, amid all the slightly vary ing structures constituting the organism, increase of this particu lar one is so advantageous as to cause greater multiplication of the family in which it arises than of other families. Variations which, though advantageous, fail to do this, must disappear again. Let us take a case. Keenness of scent in a deer, by giving early notice of approach ing enemies, subserves life so greatly that, other things equal, an individual having it in an unusual degree is more likely than others to survive ; and, among descendants, to leave some simi larly endowed or more endowed, who again transmit the variation with, in some cases, increase. Clearly this highly useful power may be developed by natural selection. So also, for like reasons, may quickness of vision and delicacy of hearing ; though it may be remarked in passing that since this extra sense-endowment, serving to give early alarm, profits the herd as a whole, which takes the alarm from one individual, selection of it is not so easy, unless it occurs in a conquering stag. But now suppose that one member of the herd — perhaps because of more efficient teeth, perhaps by greater muscularity of stomach, perhaps by secretion of more appropriate gastric juices — is enabled to eat and digest a not uncommon plant which the others refuse. This peculiarity may, if food is scarce, conduce to better self-maintenance, and better fostering of young if the individual is a hind. But unless this plant is abundant, and the advantage consequently great, the advantages which other members of the herd gain from other INADEQUACY OF NATURAL SELECTION, ETC. Oil slight variations may be equivalent. This one has unusual agility, and leaps a chasm which others balk at. That one de velops longer hair in winter, and resists the cold better. Another has a skin less irritated by Hies, and can graze without so much interruption. Here is one which has an unusual power of detect ing food under the snow ; and there is one which shows extra sagacity in the choice of a shelter from wind and rain. That the variation giving ability to eat a plant before unutilized, may become a trait of the herd, and eventually of a variety, it is need ful that the individual in which it occurs shall have more de scendants, or better descendants, or both, than have the various other individuals severally having their small superiorities. If these other individuals severally profit by their small superiori ties, and transmit them to equally large numbers of offspring, no increase of the variation in question can take place : it must soon be cancelled. Whether in the Origin of Species Mr. Darwin has recognized this fact, I do not remember, but he has certainly done it by implication in his Animals and Plants under Domestica tion. Speaking of variations in domestic animals, he there says that " any particular variation would generally be lost by crossing, reversion, and the accidental destruction of the varying individu als, unless carefully preserved by man." (Vol. II, p. 292.) That which survival of the fittest docs in cases like the one I have instanced, is to keep all faculties up to the mark, by destroying such individuals as have faculties in some respect below the mark ; and it can produce development of some one faculty only if that faculty is predominantly important. It seems to me that many naturalists have practically lost sight of this, and assume that natural selection will increase any advantageous trait. Certainly a view now held by some assumes as much. The consideration of this view, to which the foregoing para graph is introductory, may now be entered upon. This view con cerns, not direct selection, but what has been called, in question able logic, " reversed selection " — the selection which effects, not increase of an organ, but decrease of it. For as, under some con ditions, it is of advantage to an individual and its descendants to have some structure of larger size, it may be, under other condi tions — namely, when the organ becomes useless — of advantage to have it of smaller size ; since, even if it is not in the way, its weight and the cost of its nutrition are injurious taxes on the organism. But now comes the truth to be emphasized. Just as direct selection can increase an organ only in certain cases, so can reversed selection decrease it only in certain cases. Like the increase produced by a variation, the decrease produced by one must be such as will sensibly conduce to preservation and multi plication. It is, for instance, conceivable that were the long and 612 APPENDIX B. massive tail of the kangaroo to become useless (say by the forcing of the species into a mountainous and rocky habitat filled with brushwood), a variation which considerably reduced the tail might sensibly profit the individual in which it occurred ; and, in seasons when food was scarce, might cause survival when indi viduals with large tails died. But the economy of nutrition must be considerable before any such result could occur. Suppose that in this new habitat the kangaroo had no enemies ; and sup pose that, consequently, quickness of hearing not being called for, large ears gave no greater advantage than small ones. Would an individual with smaller ears than usual, survive and propagate better than other individuals, in consequence of the economy of nutrition achieved ? To suppose this is to suppose that the sav ing of a grain or two of protein per day would determine the kangaroo's fate. Long ago I discussed this matter in the Principles of Biology (§ 166), taking as an instance the decrease of the jaw implied by the crowding of the teeth, and now proved by measurement to have taken place. Here is the passage : — " No functional superiority possessed by a small jaw over a large jaw, in civilized life, can be named as having caused the more frequent survival of small-jawed individuals. The only advantage which smallness of jaw might be supposed to give, is the advantage of economized nutrition ; and this could not be great enough to further the preservation of men possessing it. The decrease of weight in the jaw and co operative parts that has arisen in the course of many thousands of years, does not amount to more than a few ounces. This decrease has to be divided among the many generations that have lived and died in the interval. Let us admit that the weight of these parts diminished to the extent of an ounce in a single generation (which is a large- admission); it still cannot be contended that the having to carry an ounce less in weight, or having to keep in repair an ounce less of tissue, could sensibly affect any man's fate. And if it never did this — nay, if it did not cause a frequent survival of small-jawed individuals where large-jawed indi viduals died, natural selection could neither cause nor aid diminution of the jaw and its appendages." When writing this passage in 1864, I never dreamt that a quarter of a century later, the supposable cause of degeneration here examined and excluded as impossible, would be enunciated as an actual cause and named " reversed selection." One of the arguments used to show the adequacy of natural selection under its direct or indirect form consists of a counter argument to the effect that inheritance of functionally-wrought changes, supposing it to be operative, does not explain certain of the facts. This is alleged by Prof. Wcismann as a part justification for his doctrine of Panmixia. Concerning the " blind fish and amphibia" found in dark places, which have but rudimentary eyes " liiddcn under the skin," he argues that " it is difficult to reconcile the facts of the case with the ordinary theory that the eyes of these INADEQUACY OF NATURAL SELECTION, ETC. G13 animals have simply degenerated through disuse." After giving instances of rapid degeneration of disused organs, he argues that if " the effects of disuse are so striking in a single life, we should certainly expect, if such effects can be transmitted, that all traces of an eye would soon disappear from a species which lives in the dark." Doubtless this is a reasonable conclusion. To explain the facts on the hypothesis that acquired characters are inheri table, seems very difficult. One possible explanation may, in deed, be named. It appears to be a general law of organization that structures are stable in proportion to their antiquity — that while organs of relatively modern origin have but a comparatively superficial root in the constitution, and readily disappear if the conditions do not favour their maintenance, organs of ancient origin have deep-seated roots in the constitution, and do not readily disappear. Having been early elements in the type, and having continued to be reproduced as parts of it during a period extending throughout many geological epochs, they are compara tively persistent. Now the eye answers to this description as being a very early organ. But waiving possible explanations, let us take the particular instance cited by Prof. Weismann and sec what is to be made of it. lie writes : — " The caverns in Carniola and Carintliia, in which the blind Proteus and so many other blind animals live, belong geologically to the Jurassic formation ; and although we do not exactly know when for example the Proteus first entered them, the low organization of this amphibian certainly indicates that it has been sheltered there for a very long period of time, and that thousands of generations of this species have succeeded one another in the caves. " Hence there is no reason to wonder at the extent to which the degene ration of the eyo has been already carried in the Proteus ; even if we assume that it is merely due to the cessation of the conserving influence of natural selection." * Let me first note a strange oversight on the part of Prof. JWeismann. Jle points out that the caverns in question belong to the Jurassic formation : apparently intending to imply that they have an antiquity related to that of the formation. But there is no such relation, except that the caverns cannot be older than the formation. They may have originated at any period since the containing strata were deposited ; and they may be therefore relatively modern. But passing over this, and admit ting that the Proteus has inhabited the caverns for an enormous period, what is to be said of the fact that their eyes have not disappeared entirely, as Prof. Weismann contends they should have done had the inheritance of the effects of disuse been all along operative ? There is a very sufficient answer — the rudi mentary eyes arc not entirely useless. It seems that when the * Essays upon Heredity, p. 87. f,14 APPENDIX B. underground streams it inhabits are unusually swollen, some in dividuals of the species are carried out of the caverns into the open (being then sometimes captured). It is also said that the creatures shun the light ; this trait being, I presume, observed when it is in captivity. Now obviously, among individuals carried out into the open, those which remain visible are apt to be carried off by enemies ; whereas, those which, appreciating the difference between light and darkness, shelter themselves in dark places, survive. Hence the tendency of natural selection is to prevent the decrease of the eyes beyond that point at which they can distinguish between light and darkness. Thus the apparent anomaly is explained. Let me suggest, as another possible reason for persistence of rudimentary organs, that the principle of economy of growth will cause diminution of them only in proportion as their constituents are of value for other uses in the organism ; and that in many cases their constituents are practically valueless. Hence prob ably the reason why, in the case of stalk-eyed crustaceans, the eye is gone but the pedicle remains, or to use Mr. Darwin's simile, the telescope has disappeared but not its stand. Along with that inadequacy of natiiral selection to explain changes of structure which do not aid life in important wavs, alleged in § 160 of The Principles of Biology, a further inadequacy was alleged. It was contended that the relative powers of co operative parts cannot be adjusted solely by survival of the fittest ; and especially where the parts are numerous and the co operation complex. In illustration it was pointed out that im mensely developed horns, such as those of the extinct Irish elk, weighing over a hundred-weight, could not, with the massive skull bearing them, be carried at the extremity of the out stretched neck without many and great modifications of adjacent bones and muscles of the neck and thorax ; and that without strengthening of the fore-legs, too, there would be failure alike in fighting and in locomotion. And it was argued that while we cannot assume spontaneous increase of all these parts propor tionate to the additional strains, we cannot suppose them to in crease by variations, one at once, without supposing the creature to be disadvantaged by the weight and nutrition of parts that were for the time useless — parts, moreover, which would revert to their original sizes before the other needful variations occurred. When, in reply to me, it was contended that co-operative parts vary together, I named facts conflicting with this assertion — the fact that the blind cray-fish of the Kentucky caves have lost their eyes but not the foot stalks carrying them ; the fact that the normal proportion between tongue and beak in certain INADEQUACY OP NATURAL SELECTION, ETC. fi 1 T> selected varieties of pigeons is lost ; the fact that lack of con comitance in decrease of jaws and teeth in sundry kinds of pet dogs, has caused great crowding of the teeth (" The Factors of Organic Evolution, Essays, i, 401—40^). And I then argued that if co-operative parts, small in number and so closely associated as these are, do not vary together, it is unwarrantable to allege that co-operative parts which are very numerous and remote from one another vary together. After making this rejoinder I enforced mv argument by a further example — that of the giraffe. Tacitly recognizing the truth that the unusual structure of this creature must have been, in its most conspicuous traits, the result of sur vival of the fittest (since it is absurd to suppose that efforts to reach high brandies could lengthen the legs), I illustrated afresh the obstacles to co-adaptation. Not dwelling on the objection that increase of any components of the fore-quarters out of adjustment to the others, would cause evil rather than good, I went on to argue that the co-adaptation of parts required to make the giraffe's structure useful, is rnucli greater than at first appears. This animal has a grotesque gallop, necessitated by the great difference in length between the fore and the hind limbs. I pointed out that the mode of action of the hind limbs shows that the bones and muscles have all been changed in their propor tions and adjustments ; and I contended that, difficult as it is to believe that all parts of the fore -quarters have been co-adapted by the appropriate variations, now of this part now of that, it becomes impossible to believe that all the parts in the hind quarters have been simultaneously co-adapted to one another and to all the parts of the fore-quarters : adding that want of co- adaptation, even in a single muscle, would cause fatal results when high speed had to be maintained while escaping from an enemy. Since this argument, repeated with this frcsli illustration, was published in 1886, I have met with nothing to be called a reply ; and might, I think, if convictions usually followed proofs, leave the matter as it stands. It is true that, in his Darwinism, Mr. Wallace has adverted to my renewed objection, and, as already said, contended that changes such as those instanced can be ef fected by natural selection, since such changes can be effected by artificial selection : a contention which, as I have pointed out, assumes a parallelism that does not exist. But now, instead of pursuing the argument further along the same line, let me take a somewhat different line. If there occurs some change in an organ, say by increase of its size, which adapts it better to the creature's needs, it is admitted that when, as commonly happens, the use of the organ demands the co-operation of other organs, the change in it will general Iv 40 616 APPENDIX B. be of no service unless the co-operative organs are changed. If, for instance, there takes place such a modification of a rodent's tail as that which, by successive increases, produces the trowel- shaped tail of the beaver, no advantage will be derived unless there also take place certain modifications in the bulks and shapes of the adjacent vertebrae and their attached muscles, as well as, probably, in the hind limbs ; enabling them to withstand the reactions of the blows given by the tail. And the question is, by what process these many parts, changed in different degrees, are co-adapted to the new requirements — whether variation and natural selection alone can effect the readjustment. There are three conceivable ways in which the parts may simultaneously change : — (1) they may all increase or decrease together in like degree ; (2) they may all simultaneously increase or decrease in dependently, so as not to maintain their previous proportions, or assume any other special proportions ; (.3) they may vary in such ways and degrees as to make them jointly serviceable for the new end. Let us consider closely these several conceivabilities. And first of all, what are we to understand by co-operative parts ? In a general sense, all the organs of the body are co operative parts, and are respectively liable to be more or less changed by change in any one. In a narrower sense, more directly relevant to the argument, we may, if we choose to multiply difficulties, take the entire framework of bones and muscles as formed of co-operative parts ; for these are so related that any considerable change in the actions of some entails change in the actions of most others. It needs only to observe how, when putting out an effort, there goes, along with a deep breath, an expansion of the chest and a bracing up of the abdo men, to see that various muscles beyond those directly concerned are strained along with them. Or, when suffering from lumbago, an effort to lift a chair will cause an acute consciousness that not the arms only arc brought into action, but also the muscles of the back. These cases show how the motor organs are so tied to gether that altered actions of some implicate others quite remote from them. But without using the advantage which this interpretation of the words would give, let us take, as co-operative organs, those which are obviously such — the organs of locomotion. What, then, shall we say of the fore limbs and hind limbs of terrestrial mammals, which co-operate closely and perpetually ? Do they vary together ? If so, how have there been produced such con trasted structures as that of the kangaroo, with its large hind limbs and small fore limbs, and that of the giraffe, in which the hind limbs are small and the fore limbs large — how does it happen that, descending from the same primitive mammal, these INADEQUACY OF NATURAL SELECTION, ETC. C17 creatures have diverged in the proportions of their limbs in opposite directions ? Take, again, the articulate animals. Com pare one of the lower types, with its rows of almost equal-sized limbs, and one of the higher types, as a crab or a lobster, with limbs some very small and some very large. How came this contrast to arise in the course of evolution, if there was the equality of variation supposed ? But now let us narrow the meaning of the phrase still further, giving it a more favourable interpretation. Instead of con sidering separate limbs as co-operative, let us consider the com ponent parts of the same limb as co-operative, and ask what would result from varying together. It would in that case happen that, though the fore and hind limbs of a mammal might become different in their sizes, they would not become different in their structures. If so, how have there arisen the unlikenesscs between the hind legs of the kangaroo and those of the elephant ? Or if this comparison is objected to, because the creatures belong to the widely different divisions of implacental and placenta! mammals, take the cases of the rabbit and the elephant, both belonging to the last division. On the hypothesis of evolution these are both derived from the same original form ; but the pro portions of the parts have become so widely unlike that the corresponding joints are scarcely recognized as such by the un observant : at what seem corresponding places the legs bend in opposite ways. Equally marked, or more marked, is the parallel fact among the Articulata. Take that limb of the lobster which bears the claw and compare it with the corresponding limb in an inferior articulate animal, or the corresponding limb of its near ally, the rock lobster, and it becomes obvious that the component segments of the limb have come to bear to one another in the one case, proportions immensely different from those they bear in the other case. Undeniably, then, on contemplating the general facts of organic structure, we see that the concomitant variations in the parts of limbs, have not been of a kind to pro duce equal amounts of change in them, but quite the opposite — have been everywhere producing inequalities. Moreover, we are reminded that this production of inequalities among co-opera tive parts, is ari essential principle of development. Had it not been so, there could not have been that progress from homoge neity of structure to heterogeneity of structure which constitutes evolution. We pass now to the second supposition : — that the variations in co-operative parts occur irregularly, or in such independent ways that they bear no definite relations to one another — miscel laneously, let us say. This is the supposition which best corre sponds with the facts. Glances at the faces around yield 618 APPENDIX B. conspicuous proofs. Many of the muscles of the face and some of the bones, are distinctly co-operative ; and these respectively vary in such ways as to produce in each person a different com bination. What we see in the face we have reason to believe holds in the limbs and in all other parts. Indeed, it needs but to compare people whose arms are of the same lengths, and observe how stumpy are the fingers of one and how slender those of another ; or it needs but to note the unlikcnesses of gait of passers-by, implying small unlikenesses of structure ; to be con vinced that the relations among the variations of co-operative parts are anything but fixed. And now, confining our attention to limbs, let us consider what must happen if, by variations taking place miscellaneously, limbs have to be partially changed from fitness for one function to fitness for another function — have to be re-adapted. That the reader may fully comprehend the argument, he must here have patience while a good many ana tomical details are set down. Let us suppose a species of quadruped of which the members have, for immense past periods, been accustomed to locomotion over a relatively even surface, as, for instance, the " prairie-dogs " of North America ; and let us suppose that increase of numbers has driven part of them into a region full of obstacles to easy locomotion — covered, say, by the decaying stems of fallen trees, such as one sees in portions of primeval forest. Ability to leap must then become a useful trait ; and, according to the hypo thesis we are considering, this ability will be produced by the selection of favourable variations. What are the variations required ? A leap is effected chiefly by the bending of the hind limbs so as to make sharp angles at the joints, and then suddenly straightening them ; as any one may see on watching a cat leap on to the table. The first required change, then, is increase of the large extensor muscles, by which the hind limbs are straightened. Their increases must be duly proportioned ; for if those which straightened one joint become much stronger than those which straightened the other joint, the result must be collapse of the other joint when the muscles are contracted together. But let us make a large admission, and suppose these muscles to vary together ; what further muscular change is next required ? In a plantigrade mammal the metatarsal bones chiefly bear the reac tion of the leap, though the toes may have a share. In a digiti- grade mammal, however, the toes form almost exclusively the fulcrum, and if they are to bear the reaction of a higher leap, the flexor muscles which depress and bend them must be pro portionately enlarged : if not, the leap will fail from want of a firm point d'appui. Tendons as well as muscles must be modified ; and, among others, the many tendons which go to the digits and INADEQUACY OF NATURAL SELECTION, ETC. G19 their phalanges. Stronger muscles and tcndona imply greater strains on the joints ; and unless these are strengthened, one or other, dislocation will be caused by a more vigorous spring. Not only the articulations themselves must be so modified as to bear greater stress, but also the numerous ligaments which hold the parts of each in place. Nor can the bodies of the bones remain unstrengthened ; for if they have no more than the strengths needed for previous movements they will fail to bear more violent movements. Thus, saying nothing of the required changes in the pelvis, as well as in the nerves and blood-vessels, there arc, counting bones, muscles, tendons, ligaments, at least fifty differ ent parts in each hind leg which have to be enlarged. More over they have to be enlarged in unlike degrees. The muscles and tendons of the outer toes, for example, need not be added to so much as those of the median toes. Now, throughout their successive stages of growth, all these parts have to be kept fairly well balanced ; as any one may infer on remembering sundry of the accidents he has known. Among my own friends I could name one who, when playing lawn-tennis, snapped the Achilles tendon ; another who, while swinging his children, tore some of the muscular fibres in the calf of his leg ; another who, in getting over a fence, tore a ligament of one knee. Such facts, joined with every one's experience of sprains, show that during the .extreme exertions to which limbs are now and then subject, there is a giving way of parts not quite up to the required level of strength. How, then, is this balance to be maintained ? Suppose the extensor muscles have all varied appropriately ; their varia tions are useless unless the other co-operative parts have also varied appropriately. Worse than this. Saying nothing of the dis advantage caused by extra weight and cost of nutrition, they will be causes of mischief — causes of derangement to the rest by con tracting with undue force. And then, how long will it take for the rest to be brought into adjustment ? As Mr. Darwin says concerning domestic animals : — " Any particular variation would generally be lost by crossing, reversion, &c. . . . unless care fully preserved by man." In a state of nature, then, favourable variations of these muscles would disappear again long before one or a few of the co-operative parts could be appropriately varied, much more before all of them could. With this insurmountable difficulty goes a difficulty still more insurmountable — if the expression may be allowed. It is not a question of increased sizes of parts only, but of altered shapes of parts, too. A glance at the skeletons of mammals shows how unlike are the forms of the corresponding bones of their limbs; and shows that they have been severally re-moulded in each species to the different requirements entailed by its different 620 APPENDIX B. habits. The change from the structures of hind limbs fitted only for walking and trotting to hind limbs fitted also for leaping, implies, therefore, that, along with strengthenings of bones there must go alterations in their forms. Now the fortuitous altera tions of form which may take place in any bone are countless. How long, then, will it be before there takes place that particu lar alteration which will make the bone fitter for its new action ? And what is the probability that the many required changes of shape, as well as of size, in bones will each of them be effected before all the others are lost again ? If the probabilities against success are incalculable, when we take account only of changes in the sizes of parts, what shall we say of their incalculableness when differences of form also are taken into account ? " Surely this piling up of difficulties has gone far enough"; the reader will be inclined to say. By no means. There is a difficulty immeasurably transcending those named. We have thus far omitted the second half of the leap, and the provisions to be made for it. After ascent of the animal's body comes descent ; and the greater the force writh which it is projected up, the greater is the force with which it comes down. Hence, if the supposed creature has undergone such changes in the hind limbs as will enable them to propel it to a greater height, without having undergone any changes in the fore limbs, the result will be that on its descent the fore limbs will give way, and it Avill come down on its nose. The fore limbs, then, have to be changed simultaneously with the hind. How changed ? Con trast the markedly bent hind limbs of a cat with its almost straight fore limbs, or contrast the silence of the spring on to the table with the thud which the fore paws make as it jumps off the table. See how unlike the actions of the hind and fore limbs are, and how unlike their structures. In what way, then, is the required co-adaptation to be effected ? Even were it a question of relative sizes only, there would be no answer ; for facts already given show that we may not assume simultaneous increases of size to take place in the hind and fore limbs ; and, indeed, a glance at the various human races, which differ considerably in the ratios of their legs to their arms, shows us this. But it is not simply a question of sizes. To bear the increased shock of descent the fore limbs must be changed throughout in their structures. Like those in the hind limbs, the changes must be of many parts in many proportions ; and they must be both in sizes and in shapes. More than this. The scapular arch and its attached muscles must also be strengthened and re-moulded. See, then, the total requirements. We must suppose that by natural selection of miscellaneous variations, the parts of the hind limbs will be co-adapted to one another, in sizes, shapes, and ratios ; INADEQUACY OF NATURAL SELECTION, ETC. G21 that those of the fore limbs will undergo co-adaptation similar in their complexity, but dissimilar in their kinds ; and that the two sets of co-adaptations will be effected pari passu. If, as may be held, the probabilities are millions to one against the first set of changes being achieved, then it may be held that the probabilities are billions to one against the second being simultaneously achieved, in progressive adjustment to the first. There remains only to notice the third conceivable mode of adjustment. It may. be imagined that though, by the natural selection of miscellaneous variations, these adjustments cannot be effected, they may nevertheless be made to take place appro priately. How made ? To suppose them so made is to suppose that the prescribed end is somewhere recognized ; arid that the changes are step by step simultaneously proportioned for achiev ing it — is to suppose a designed production of these changes. In such case, then, we have to fall back in part upon the primitive hypothesis ; and if we do this in part, we may as well do it wholly — may as well avowedly return to the doctrine of special creations. What, then, is the only defensible interpretation ? If such modifications of structure produced by modifications of function as we see take place in each individual, are in any measure transmissible to descendants, then all these co-adaptations, from the simplest up to the most complex, are accounted for. In some cases this inheritance of acquired characters suffices by itself to explain the facts ; and in other cases it suffices when taken in combination with the selection of favourable variations. An example of the first class is furnished by the change just con sidered ; and an example of the second class is furnished by the case, before named, of development in a deer's horns. If, by some extra massivencss spontaneously arising, or by formation of an additional " point," an advantage is gained either for attack or defence, then, if the increased muscularity and strengthened structure of the neck and thorax, which wielding of these some what heavier horns produces, are in a greater or less degree inherited, and in several successive generations are by this process brought up to the required extra strength, it becomes possible and advantageous for a further increase of the horns to take place, and a further increase in the apparatus for wielding them, and so on continuously. By such processes only, in which each part gains strength in proportion to function, can co-opera tive parts be kept in adjustment, and be re-adjusted to meet new requirements. Close contemplation of the facts impresses me more strongly than ever with the two alternatives — either there lias been inheritance of acquired characters, or there has been no evolution. 622 APPENDIX B. This very pronounced opinion will be met, on the part of some, \>y a no less pronounced demurrer, which involves a denial of possibility. It has been of late asserted, and by many believed, that inheritance of acquired characters cannot occur. Weisinann, they say, has shown that there is early established in the evolu tion of each organism such a distinctness between those compo nent units which carry on the individual life and those which are devoted to maintenance of the species, that changes in the one cannot affect the other. We will look closely into his doctrine. Basing his argument on the principle of the physiological division of labour, and assuming that the primary division of labour is that between such part of an organism as carries on individual life and such part as is reserved for the production of other lives, Weisinann, starting with " the first multicellular organism," says that — " Hence the single group would come to be divided into two groups of cells, which may be called somatic and reproductive — the cells of the body as opposed to those which are concerned with reproduction." (JHssays upon Heredity, i, p. 27.) Though he admits that this differentiation " was not at first absolute, and indeed is not always so to-day," yet he holds that the differentiation eventually becomes absolute in the sense that the somatic cells, or those which compose the body at large, come to have only a limited power of cell-division, instead of an un limited power which the reproductive cells have ; and also in the sense that eventually there ceases to be any communication between the two further than that implied by the supplying of nutriment to the reproductive cells by the somatic cells. The outcome of this argument is that, in the absence of communica tion, changes induced in the somatic cells, constituting the indi vidual, cannot influence the natures of the reproductive cells, and cannot therefore be transmitted to posterity. Such is the theory. Now let us look at a few facts — some familiar, some unfamiliar. His investigations led Pasteur to the positive conclusion that the silkworm diseases are inherited. The transmission from parent to offspring resulted, not through any contamination of the surface of the egg by the body of the parent while being deposited, but resulted from infection of the egg itself — intrusion of the parasitic organism. Generalized observations concerning the disease called pebrine, enabled him to decide, by inspection of the eggs, which were infected and which were not : certain modi fications of form distinguishing the diseased ones. More than this ; the infection was proved by microscopical examination of the contents of the egg ; in proof of which he quotes as follows from Dr. Carlo Vittadini : — " II resultc ile mes reeherclics sur Ics graiucs, & 1'epoquc ou commence le INADEQUACY OP NATURAL SELECTION, ETC. 623 developpement du gcrme, quo Ics corpuscules, unc fois apparus dans 1'ceuf, auginentcnt graducllcment en nombrc, a mcsurc quc 1'embryon sc developpe ; (jue, dans Ics dernicrs jours dc I'incubution, IVuf en cst plein, au point de fairc croire quo la inajcure partic des granules du jaune se sont transform^ en corpuscules. " line autre observation importonte cst quc 1'ernbryon aussi cst souille de corpuscules, ct il un degre tcl qu'on pcut soupconner quc 1'infection du jaune tire son orij/inc du pcrme lui-merne ; en d'autrcs tcrmes que le germe cst pii- inordialcmcnt infectc, et portc en lui-meme ces corpuscules tout connne les vcrs adultcs, frappes du mcmc mal." * Thus, then the substance of the egg and even its innermost vital part, is permeable by a parasite sufficiently large to be microscopically visible. It is also of course permeable by the invisible molecules of protein, out of which its living tissues are formed, and by absorption of which they subsequently grow. But, according to Weismann, it is not permeable by those invisible units of protoplasm out of which the vitally active tissues of the parent are constituted : units composed, as we must assume, of variously arranged molecules of protein. So that the big thing may pass, and the little thing may pass, but the inter mediate thing may not pass ! A fact of kindred nature, unhappily more familiar, may be next brought in evidence. It concerns the transmission of a disease not infrequent among those of unregulated lives. The highest authority concerning this disease, in its inherited form, is Mr. Jonathan Ilutchinson ; and the following are extracts from a letter I have received from him, and which I publish with his assent : — " I do not think that there can be any reasonable doubt that a very large majority of those who suffer from inherited syphilis take the taint from the male parent. ... It is the rule when a man marries who has no remaining local lesion, but in whom the taint is not eradicated, for his wife to remain apparently well, whilst her child may suifer. No doubt the child infects its mother's blood, but this does not usually evoke any obvious symptoms of syphilis. ... 1 am sure I have seen hundreds of syphilitic infants whose mothers had not, so far as I could ascertain, ever displayed a single symptom." See, then, to what we are committed if we accept Weismann's hypothesis. We must conclude, that whereas the reproductive cell may be effectually invaded by an abnormal living element in the parental organism, those normal living elements which constitute the vital protoplasm of the parental organism, cannot invade it. Or if it be admitted that both intrude, then the implication is that, whereas the abnormal element can so modify the development as to cause changes of structure (as of the teeth), the normal element can cause no changes of structure ! f * Lm Mul.itHcx tfm IVr.s- 33 degrees, directly or indirectly, to the multiplication of the stirp ; whence failure to account for various changes ascribed to it. And we have seen that it yields no explanation of the co-adapta tion of co-operative parts, even when the co-operation is rela tively simple, and still less when it is complex. On the other hand, we see that if, along with the transmission of generic and specific structures, there tend to be transmitted modifications arising in a certain way, there is a strong a priori probability that there tend to be transmitted modifications arising in all ways. We have a number of facts confirming this inference, and show ing that acquired characters are inherited — as large a number as can be expected, considering the difficulty of observing them and the absence of search. And then to these facts may be added the facts with which this essay set out, concerning the distribu tion of tactual discriminativeness. While we saw that these are inexplicable by survival of the fittest, we saw that they are clearly explicable as resulting from the inheritance of acquired characters. And here let it be added that this conclusion is con spicuously warranted by one of the methods of inductive logic, known as the method of concomitant variations. For throughout the whole series of gradations in perceptive power, we saw that the amount of the effect is proportionate to the amount of the alleged cause. II. Apart from those more special theories of Professor Weismann I lately dealt with, the wide acceptance of which by the biological world greatly surprises me, there are certain more general theo ries of his — fundamental theories — the acceptance of which surprises me still more. Of the two on which rests the vast superstructure of his speculations, the first concerns the distinc tion between the reproductive elements of each organism and the non-reproductive elements. He says : — " Let us now consider how it happened that the multicellular animals and plants, which arose from unicellular forms of life, came to lose this power of living for ever. " The answer to this question is closely bound np with the principle of division of labour which appeared among multicellular organisms at a very early stage. . . . " The first multicellular organism was probably a cluster of similar cells, but these units soon lost their original homogeneity. As the result of mere relative position, some of the cells were especially fitted to provide for the nutrition of the colony, while others undertook the work of reproduction." (Kssafis upon Heredity, i, p. 27) Here, then, we have the great principle of the division of labour, which is the principle of all organization, taken as prima- 634 APPENDIX B. rily illustrated in the division between the reproductive cells and the non-reproductive or somatic cells — the cells devoted to the continuance of the species, and the cells which subserve the life of the individual. And the early separation of reproductive cells from somatic cells, is alleged on tiie ground that this primary division of labour is that which arises between elements devoted to species-life and elements devoted to individual life. Let us not be content with words but look at the facts. When Milne-Edwards first used the phrase " physiological division of labour," he was obviously led to do so by perceiving the analogy between the division of labour in a society, as described by political economists, and the division of labour in an organism. Every one who reads has been familiarized with the first as illustrated in the early stages, when men were warriors while the cultivation and drudgery were done by slaves and women ; and as illustrated in the later stages, when not only are agriculture and manufactures carried on by separate classes, but agriculture is carried on by landlords, farmers, and labourers, while manufactures, multitudinous in their kinds, severally in volve the actions of capitalists, overseers, workers, &c., and while the great function of distribution is carried on by whole sale and retail dealers in different commodities. Meanwhile students of biology, led by Milne-Edwards's phrase, have come to recognize a parallel arrangement in a living creature ; shown, primarily, in the devoting of the outer parts to the general business of obtaining food and escaping from enemies, while the inner parts are devoted to the utilization of food, and supporting themselves and the outer parts ; and shown, secondarily, bv the subdivision of these great functions into those of various limbs and senses in the one case, and in the other case into those of organs for digestion, respiration, circulation, excretion, &c. But now let us ask what is the essential nature of this division of labour. In both cases it is an exchange of services — an arrange ment under which, while one part devotes itself to one kind of action and yields benefits to all the rest, all the rest, jointly and severally performing their special actions, yield benefits to it in exchange. Otherwise described, it is a system of mutual depen dence : A depends for its welfare upon B, C, and D ; B upon A, C, and D ; and so with the rest : all depend upon each and each upon all. Now let us apply this true conception of the division of labour, to that which Professor Weismann calls a division of labour. Where is the exchange of services between somatic cells and reproductive cells ? There is none. The somatic cells render great services to the reproductive cells, by furnishing them with materials for growth and multiplication; but the reproductive cells render no services at all to the somatic cells. -If we look INADEQUACY OF NATURAL SELECTION, ETC. £35 for the mutual dependence we look in vain. We find entire dependence on the one side and none on the other. Between the parts devoted to individual life and the part devoted to species- life, there is no division of labour whatever. The individual works for the species ; but the species works not for the indivi dual. Whether at the stage when the species is represented by reproductive cells, or at the stage when it is represented by eggs, or at the stage when it is represented by young, the parent does everything for it, and it docs nothing for the parent. The essential part of the conception is gone : there is no giving and receiving, no exchange, no mutuality. But now suppose we pass over this fallacious interpretation, and grant Professor Weismann his fundamental assumption and his fundamental corollary. Suppose we grant that because the primary division of labour is that between somatic cells and reproductive cells, these two groups are the first to be differen tiated. Having granted this corollary, let us compare it with the facts. As the alleged primary division of labour is universal, so the alleged primary differentiation should be universal too. Let us see whether it is so. Already, in the paragraph from which I have quoted above, a crack in the doctrine is admitted : it is said that " this differentiation was not at first absolute, and indeed it is not always so to-day."* And then, on turning to page 74, we find that the crack has become a chasm. Of the reproductive cells it is stated that — " In Vertebrata they do not become distinct from the other cells of the body until the embryo is completely formed." That is to say, in this large and most important division of the animal kingdom, the implied universal law does not hold. Much 'more than this is confessed. Lower down the page we read — " There may be in fact cases in which such separation does not take place until after the animal is com pletely formed, and others, as I believe that I have shown, in which it first arises one or more generations later, viz., in the buds produced by the parent." So that in other great divisions of the animal kingdom the alleged law is broken ; as among the Ccelenterata by the Hi/drozoa, as among the Mollusca by the Ascidians, and as among the Platyhdminthes by the Trematode worms. Following this admission concerning the Vertebrata^ come certain sentences which I partially italicize : — "Thus, as their development shows, a marked antithesis exists between the substance of the undying reproductive cells and that of the perishable body-cells. Wo cannot explain this fact except by the sujf/xmitioH that each reproductive cell potentially contains two kinds of substance, which at a variable tinr.' alter the commencement of embryonic development, separate from one another, and linalls' produce two sharply contrasted groups of cells." (p. 74) 636 APPENDIX B. And a little lower down the page we meet with the lines : — "It is therefore quite conceivable that the reproductive cells might sepa rate from the somatic cells much later than in the examples mentioned above, without changing the hereditary tendencies of which they are the bearers." That is to say, it is " quite conceivable " that after sexless Cercarice have gone on multiplying by internal gemmation for generations, the "two kinds of substance" have, notwithstanding innumerable cell-divisions, preserved their respective natures, and finally separate in such ways as to produce reproductive cells. Here Professor Weismann does not, as in a case before noted, assume something which it is " easy to imagine," but he assumes something which it is difficult to imagine ; and apparently thinks that a scientific conclusion may be thereon safely based. Associated with the assertion that the primary division of labour is between the somatic cells and the reproductive cells, and associated with the corollary that the primary differentiation is that which arises between them, there goes another corollary. It is alleged that there exists a fundamental distinction of nature between these two classes of cells. They are described as respec tively mortal and immortal, in the sense that those of the one class are limited in their powers of multiplication, while those of the other class are unlimited. And it is contended that this is due to inherent unlikeness of nature. Before inquiring into the truth of this proposition, I may fitly remark upon a preliminary proposition set down by Professor Weismann. Referring to the hypothesis that death depends " upon causes which lie in the nature of life itself," he says : — " I do not however believe in the validity of this explanation : I consider that death is not a primary necessity, but that it has been secondarily acquired as an adaptation. I believe that life is endowed with a fixed duration, not because it is contrary to its nature to be unlimited, but because the unlimited existence of individuals would be a luxury without any corresponding advan tage." (p. 24) This last sentence has a teleological sound which would be appropriate did it come from a theologian, but which seems strange as coming from a man of science. Assuming, however, that the implication was not intended, I go on to remark that Professor Weismann has apparently overlooked a universal law of evolution — not organic only, but inorganic and super-organic — which implies the necessity of death. The changes of every aggregate, no matter of what kind, inevitably end in a state of equilibrium. Suns and planets die, as well as organisms. The process of integration, which constitutes the fundamental trait of all evolution, continues until it has brought about a state which INADEQUACY OP NATURAL SELECTION, ETC. G37 negatives further alterations, molar or molecular — a state of balance among the forces of the aggregate and the forces which oppose them.* In KO far, therefore, as Professor Weisrnann's conclusions imply the non-necessity of death, they cannot be sustained. But now let us consider the above-described antithesis be tween the immortal Protozoa and the mortal Mctazoa. An essen tial part of the theory is that the Protozoa can go on dividing and subdividing without limit, so long as the fit external condi tions are maintained. But what is the evidence for this ? Even by Professor Weismann's own admission there is no proof. On p. 285 he says : — "I could only consent to adopt the hypothesis of rejuvenescence [achieved by conjugation], if it were rendered absolutely certain that reproduction by division could never under any circumstances persist indefinitely. But this cannot be proved with any greater certainty than the converse proposition, and hence, as far as direct proof is concerned, the facts are equally uncertain on both sides." But this is an admission which seems to be entirely ignored when there is alleged the contrast between the immortal Protozoa and the mortal Metazoa. Following Professor Weismann's method, it would be " easy to imagine " that occasional conjugation is in all cases essential ; and this easily imagined conclusion might fitly be used to bar out his own. Indeed, considering how commonly conjugation is observed, it may be held difficult to imagine that it can in any cases be dispensed with. Apart from imaginations of either kind, however, here is an acknowledgment that the immortality of Protozoa is not proved ; that the allegation has no better basis than the failure to observe cessation of fission ; and that thus one term of the above antithesis is not a fact, but is only an assumption. And now what about the other term of the antithesis — the alleged inherent mortality of the somatic cells ? This we shall, I think, find is no more defensible than the other. Such plausi bility as it possesses disappears when, instead of contemplating the vast assemblage of familiar cases which animals present, we contemplate certain less familiar and unfamiliar cases. By these we are shown that the usual ending of multiplication among somatic cells is due, not to an intrinsic cause, but to extrinsic causes. Let us, however, first look at Professor Weismann's own statements : — " I have endeavoured to explain death as the result of restriction in the powers of reproduction possessed by the somatic cells, and I have suggested that such restriction may conceivably follow from a limitation in the * Sec First 1'rincijtli's, Part II, Chap. XXII, " Equilibration." G38 APPENDIX B. number of cell-generations possible for the cells of each organ and tissue." (P- 28) " The above-mentioned considerations show us that the degree of repro ductive activity present in the tissues is regulated by internal causes while the natural death of an organism is the termination — the hereditary limitation — . of the process of cell-division, which began in the segmentation of the ovum." (p. 30) Now, though, in the above extracts there is mention of " in ternal causes" determining "the degree of reproductive activity" of tissue cells, and though, on page 28, the "causes of the loss" of the power of unlimited cell-production " must be sought out side the organism, that is to say, in the external conditions of life," yet the doctrine is that somatic cells have become consti tutionally unfitted for continued cell-multiplication. " The somatic cells have lost this power to a gradually increasing extent, so that at length they became restricted to a fixed, though perhaps very large, number of cell-generations." (p. 28) Examination will soon disclose good reasons for denying this in- honmt restriction. We will look at the various causes which affect their multiplication, and usually put a stop to increase after a certain point is reached. There is first the amount of vital capital given by the parent ; partly in the shape of a more or less developed structure, and partly in the shape of bequeathed nutriment. Where this vital capital is small, and the young creature, forthwith obliged to carry on physiological business for itself, has to expend effort in obtaining materials for daily consumption as well as for growth, a rigid restraint is put on that cell-multiplication required for a large size. Clearly, the young elephant, starting with a big and well-organized body, and supplied gratis with milk during early stages of growth, can begin physiological business on his own account on a great scale ; and by its large transactions his system is enabled to supply nutriment to its multiplying somatic cells until they have formed a vast aggregate — an aggregate such as it is impossible for a young mouse to reach, obliged as it is to begin physiological business in a small way. Then there is the character' of the food in respect of its digestibility and its nutri- tiveness. Here, that which the creature takes in requires much grinding-up, or, when duly prepared, contains but a small amount of available matter in comparison with the matter that has to be thrown away ; while there, the prey seized is almost pure nutri ment, and requires but little trituration. Hence, in some cases, an unprofitable physiological business, and in other cases a profit able one ; resulting in small or large supplies to the multiplying somatic cells. Further, there has to be noted the grade of visceral development, which, if low, yields only crude nutriment slowly distributed, but which, if high, serves by its good appli- INADEQUACY OF NATURAL SELECTION, ETC. 039 anccs for solution, depuration, absorption, and circulation, to yield to the multiplying somatic cells a rich and pure blood. Then we come to an all-important factor, the cost of obtaining food. Here large expenditure of energy in locomotion is necessi tated, and there but little — here great efforts for small portions of food, and there small eiforts for great portions : again result ing in physiological poverty or physiological wealth. Next, beyond the cost of nervo-muscular activities in foraging, there is the cost of maintaining bodily heat. So much heat implies so much consumed nutriment, and the loss by radiation or conduc tion, which has perpetually to be made good, varies according to many circumstances — climate, medium (as air or water), covering, size of body (small cooling relatively faster than large) ; and in proportion to the cost of maintaining heat is the abstraction from the supplies for cell-formation. Finally, there are three all- important co-operative factors, or rather laws of factors, the effects of which vary with the size of the animal. The first is that, while the mass of the body varies as the cubes of its dimen sions (proportions being supposed constant), the absorbing surface varies as the squares of its dimensions ; whence it results that, other things equal, increase of size implies relative decrease of nutrition, and therefore increased obstacles to cell-multiplication.* The second is a further sequence from these laws — namely, that while the weight of the body increases as the cubes of the dimen sions, the sectional areas of its muscles and bones increase as their squares ; whence follows a decreasing power of resisting strains, and a relative weakness of structure. This is implied in the ability of a small animal to leap many times its own length, while a great animal, like the elephant, cannot leap at all : its bones and muscles being unable to bear the stress which would be required to propel its body through the air. What increasing cost of keeping together the bodily fabric is thus entailed, we cannot say ; but that there is an increasing cost, which diminishes the available materials for increase of size, is beyond question.f And then, in the third place, we have augmented expense of distribution of nutriment. The greater the size becomes, the more force must be exerted to send blood to the periphery ; and this once more entails deduction from the cell- forming matters. * Principles of Biohyii, § 46, (No. 8. April, 18f>3). f Ibid. This must not be understood as implying that while the mass increases as the cubes, the quantity of motion which can be generated increases only as the squares ; for this would not be true. The quantity of motion is obviously measured, not by the sectional areas of the muscles alone, but by these multiplied into their lengths, and therefore increases as the cubes. Hut this admission leaves untouched the conclusion that the ability to b«ir .sm.w increases only as the squares; and thub limits the ability to generate motion, by relative incoherence of materials. 640 APPENDIX B. Here, then, we have nine factors, several of them involving subdivisions, which co-operate in aiding or restraining cell- multiplication. They occur in endlessly varied proportions and combinations ; so that every species differs more or less from every other in respect of their effects. But in all of them the co-operation is such as eventually arrests that multiplication of cells which causes further growth ; continues thereafter to entail slow decrease in cell-multiplication, accompanying decline of vital activities ; and eventually brings cell-multiplication to an end. Nowr a recognized principle of reasoning — the Law of Parsimony— forbids the assumption of more causes than are needful for explanation of phenomena ; and since, in all such living aggregates as those above supposed, the causes named inevitably bring about arrest of cell-multiplication, it is illegiti mate to ascribe this arrest to some inherent property in the cells. Inadequacy of the other causes must be shown before an inherent property can be rightly assumed. For this conclusion we find ample justification when we con template types of animals which lead lives that do not put such decided restraints on cell-multiplication. First let us take an instance of the extent to which (irrespective of natures of cells as reproductive or somatic) cell-multiplication may go, where the conditions render nutrition easy and reduce expenditure to a minimum. 1 refer to the case of the Aphides. Though it is early in the season (March), the hothouses at Kew have furnished a sufficient number of these to show that twelve of them weigh a grain — a larger number than would be required were they full- sized. Citing Professor Owen, who adopts the calculations of Tougard to the effect that by agamic multiplication " a single impregnated ovum of Aphis may give rise, without fecundation, to a quintillion of Aphides," Professor Huxley says : — " I will assume that an Aphis weighs -n^ of a grain, which is certainly vastly under the mark. A quintillion of Aphides will, on this estimate, weigh a quatrillion of grains. He is a very stout man who weighs two million grains; consequently the tenth brood alone, if all its members survive the perils to which they are exposed, contains more substance than 500,- 000,000 stout men — to say the least, more than the whole population of China ! " * And had Professor Huxley taken the actual weight, one-twelfth of a grain, the quintillion of Aphides would evidently far out weigh the whole human population of the globe : five billions of tons being the weight, as brought out by my own calculation ! Of * The Transactions of the Linnrean Society of London, Vol. XXII, p. 215. The estimate of Reaumur, cited by Kirby and Spcnce, is still higher — " in five generations one Aphis may be the progenitor of 5,904,900,000 descendants ; and that it is supposed that in one year there may be twenty generations." (Introduction to Entomology, Vol. I, p. 175) INADEQUACY OF NATURAL SELECTION, ETC. 041 course I do not cite this in proof of the extent to which multipli cation of somatic cells, descending from a single ovum, may go ; because it will be contended, with some reason, that each of the sexless Aphides, viviparously produced, arose by fission of a cell which had descended from the original reproductive cell. 1 cite it merely to show that when the cell-products of a fertilized ovum are perpetually divided and subdivided into small groups, distributed over an unlimited nutritive area, so that they can get materials for growth at no cost, and expend nothing appre ciable in motion or maintenance of temperature, cell-production may go on without limit. For the agamic multiplication of Aphides has been shown to continue for four years, and to all appearance would be ceaseless were the temperature and supply of food continued without break. But now let us pass to analo gous illustrations of cause and consequence, open to no criticism of the kind just indicated. They are furnished by various kinds of Entozoa, of which take the Trematoda, infesting molluscs and fishes. Of one of them we read : — " Gyrodactylus multiplies agamically by the development of a young Trematode within the body, as a sort of internal bud. A second generation appears within the first, and even a third within the second, before the young Gyrodactylus is born." * And the drawings of Steenstrup, in \nsAlternation of Generations, show us, among creatures of this group, a sexless individual the whole interior of which is trans formed into smaller sexless individuals, which severally, before or after their emergence, undergo similar transformations— a multi plication of somatic cells without any sign of reproductive cells. Under what circumstances do such modes of agamic multiplica tion, variously modified among parasites, occur ? They occur where there is no expenditure whatever in motion or maintenance of temperature, and where nutriment surrounds the body on all sides. Other instances are furnished by groups in which, though the nutriment is not abundant, the cost of living is almost un- appreciable. Among the Ccelenterata there are the Hydroid Polyps, simple and compound ; and among the Mollusca we have various types of Ascidians, fixed and floating, Botryllidce and Salpce. But now from these low animals in which sexless reproduction, and continued multiplication of somatic cells, is common, and one class of which is named " zoophytes," because its form of life simulates that of plants, let us pass to plants themselves. In these there is no expenditure in effort, there is no expenditure in maintaining temperature, and the food, some of it supplied by the earth, is the rest of it supplied by a medium which every - * ,1 Manual of the Anatomy of Invcrtd/ratcd Animals, by T. II. Huxley, p. 'JOG. C-12 APPENDIX B. where bathes the outer surface : the utilization of its contained material being effected gratis by the Sun's rays. Just as was to be expected, we here find that agamogenesis may go on without end. Numerous plants and trees are propagated to an unlimited extent by cuttings and buds ; and we have sundry plants which cannot be otherwise propagated. The most familiar are the double roses of our gardens j these do not seed, and yet have been distributed everywhere by grafts and buds. Hothouses furnish many cases, as I learn from an authority second to none. Of " the whole host of tropical orchids, for instance, not one per cent, has ever seeded, and some have been a century under culti vation." Again, we have the Acorus calamus, " that has hardly been known to seed anywhere, though it is found wild all over the north temperate hemisphere." And then there is the con spicuous and conclusive case of Eloidea Canadensis (alias An- acharis,} introduced no one knows how (probably with timber), and first observed in 1847, in several places ; and which, having since spread over nearly all England, now everywhere infests ponds, canals, and slow rivers. The plant is dioecious, and only the female exists here. Beyond all question, therefore, this vast progeny of the first slip or fragment introduced, sufficient to cover many square miles were, it put together, is constituted entirely of somatic cells. Hence, as far as we can judge, these somatic cells are immortal in the sense given to the word by Professor Weismann ; and the evidence that they are so is im measurably stronger than the evidence which leads him to assert immortality for the fissiparously-multiplyirig Protozoa. This endless multiplication of somatic cells has been going on under the eyes of numerous observers for forty odd years. What observer has watched for forty years to see whether the fissi- parous multiplication of Protozoa does not cease ? What ob server has watched for one year, or one month, or one week ? * Even were not Professor Weismann's theory disposed of by this evidence, it might be disposed of by a critical examination of his own evidence, using his own tests. Clearly, if we are to * Respecting the JSloidea I learn that in 1879 — thirty years after it had become a pest — one solitary male plant was found in a pond near Edin burgh; but "in an exhaustive inquiry on the plant made by Dr. Groenland, of Copenhagen, he could find no trace of any male specimens having been found in Europe other than the Scotch." In waters from which the Eloidea has disappeared, it seems to have done so in consequence of the growth of an A Iga, which has produced tnrbid water unfavourable to it. That is to say, the decreased multiplication of somatic cells in some cases, is not due to any exhaustion, but is caused by the rise of enemies or adverse conditions ; as happens generally with introduced species of plants and animals which multiply at first enormously, and then, without any loss (if reproductive power, begin to decrease under the antagonizing influences which grow up. INADEQUACY OF NATURAL SELECTION, ETC. C43 measure relative mortalities, we must assume the conditions to be the same and must use the same measure. Let us do this with some appropriate animal — say Man, as the most open to observa tion. The mortality of the somatic cells constituting the mass of the human body, is, according to Professor Weismann, shown by the decline and final cessation of cell-multiplication in its various organs. Suppose we apply this test to all the organs : not to those only in which there continually arise bile-cells, epithelium- cells, &c., but to those also in which there arise reproductive cells. What do we find ? That the multiplication of these last comes to an end long before the multiplication of the first. In a healthy woman, the cells which constitute the various active tis sues of the body, continue to grow and multiply for many years after germ-cells have died out. If similarly measured, then, these cells of the last class prove to be more mortal than those of the first. But Professor Weismann uses a different measure for the two classes of cells. Passing over the illegitimacy of this pro ceeding, let us accept his other mode of measurement, and see what comes of it. As described by him, absence of death among the Protozoa is implied by that unceasing division and subdivision of which they are said to be capable. Fission continued without end, is the definition of the immortality he speaks of. Apply this conception to the reproductive cells in a Metazoon. That the immense majority of them do not multiply without end, we have already seen : with very rare exceptions they die and disappear without result, and they cease their multiplication while the body as a whole still lives. But wnat of those extremely exceptional ones which, as being actually instrumental to the maintenance of the species, are alone contemplated by Professor Weismann ? Do these continue their fissiparous multiplications without end ? By no means. The condition under which alone they preserve a qualified form of existence, is that, instead of one becoming two, two become one. A member of series A and a member of series B, coalesce ; and so lose their individualities. Now, obviously, if the immortality of a series is shown if its members divide and sub divide perpetually, then the opposite of immortality is shown when, instead of division, there is union. Each series ends, and there is initiated a new series, differing more or less from both. Thus the assertion that the reproductive cells are immortal, can be defended only by changing the conception of immortality other wise implied. Even apart from these last criticisms, however, we have clear disproof of the alleged inherent difference between the two classes of cells. Among animals, the multiplication of somatic cells is brought to an end by sundry restraining conditions ; but in various plants, where these restraining conditions are absent, the inulli- 044 APPENDIX B. Slication is unlimited. It may, indeed, be said that the alleged istinction should be reversed ; since the fissiparous multiplication of reproductive cells is necessarily interrupted from time to time by coalescence, while that of the somatic cells may go on for a century without being interrupted. In the essay to which this is a postscript, conclusions were drawn from the remarkable case of the horse and the quagga, there narrated, along with an analogous case observed among pigs. These conclusions have since been confirmed. I am much indebted to a distinguished correspondent who has drawn my attention to verifying facts furnished by the offspring of whites and negroes in the United States. Referring to information given him many years ago, he says : — " It was to the effect that the children of white women by a white father, had been repeatedly observed to show traces of black blood, in cases when the woman had previous connection with [i.e. a child by] a negro." At the time I received this information, an American was visiting me ; and, on being appealed to, answered that in the United States there was an established belief to this effect. Not wishing, how ever, to depend upon hearsay, I at once wrote to America to make inquiries. Professor Cope of Philadelphia has written to friends in the South, but has not yet sent me the results. Pro fessor Marsh, the distinguished paleontologist, of Yale, New Haven, who is also collecting evidence, sends a preliminary letter in which he says : — " I do not myself know of such a case, but have heard many statements that make their existence probable. One instance, in Connecticut, is vouched for so strongly by an acquaintance of mine, that I have good reason to believe it to be authentic." That cases of the kind should not be frequently seen in the North, especially nowadays, is of course to be expected. The first of the above quotations refers to facts observed in the South during slavery days ; and even then, the implied conditions were naturally very infrequent. Dr. W. J. Youmans of New York has, on my behalf, interviewed several medical professors, who, though they have not themselves met with instances, say that the alleged result, described above, " is generally accepted as a fact." But he gives me what I think must be regarded as authoritative tes timony. It is a quotation from the standard work of Professor Austin Flint, and runs as follows : — " A peculiar and, it seems to me, an inexplicable fact is, that previous pregnancies have an influence upon offspring. This is well known to breeders of animals. If pure-blooded mares or bitches have been once covered by an inferior male, in subsequent fecundations the young arc likely to partake of the character of the first male, even if they be afterwards bred with males of unimpeachable pedigree. What the mechanism of the influence of the first INADEQUACY OF NATURAL SELECTION, ETC. 645 conception is, it is impossible to say ; but the fact is incontestable. The same influence is observed in the human subject. A woman may have, by a second husband, children who resemble a former husband, and this is particularly well marked in certain instances by the colour of the hair and eyes. A white woman who has had children by a negro may subsequently bear children to a white man, these children presenting some of the unmistakable peculiarities of the negro raco." * Dr. Youmans callsd on Professor Flint, who remembered " investi gating the subject at the time his larger work was written [the above is from an abridgment], and said that he had never heard the statement questioned." Some days before I received this letter and its contained quo tation, the remembrance of a remark I heard many years ago con cerning dogs, led to the inquiry whether they furnished analogous evidence. It occurred to me that a friend who is frequently appointed judge of animals at agricultural shows, Mr. Fookes, of Fairlield, Pewsey, Wiltshire, might know something about the matter. A letter to him brought various confirmatory state ments. From one " who had bred dogs for many years " he learnt that — " It is a well known and admitted fact that if a bitch has two litters by two different dogs, the character of the first father is sure to be perpetuated in any litters she may afterwards have, no matter how pure-bred a dog may be the begetter." After citing this testimony, Mr. Fookes goes on to give illus trations known to himself. " A friend of mine near this had a very valuable Dachshund bitch, which most unfortunately had a litter by a stray sheep-dog. The next year her owner sent her on a visit to a pure Dachshund dog, but the produce took quite as much of the first father as the second, and the next year he sent her to another Dachshund with the same result. Another case : — A friend of mine in Devizes had a litter of puppies, unsought for. by a setter from a favourite pointer bitch, and after this she never bred any true pointers, no matter of what the paternity was." [Since the publication of this article, additional evidences have come to hand. One is from the late Prof. Rilcy, State Entomologist at Washington, who says that telegony is an "established principle among well-educated farmers" in the United States, and who gives me a case in horse-breeding to which he was himself witness. Mr. W. P. Smith, writing from Stoughton (Grange, Guildford, but giving the results of his experiences in America, says that " the fact of a previous conception influencing subsequent offspring was so far recognised among American cattle-breeders" that it was proposed to raise the rank of any heifer that had borne a first calf by a thoroughbred bull, and though this resolution when brought before one of the chief societies was not carried, yet on all sides it was admitted that previous conceptions had effects of the kind alleged. Mr. Smith in another letter says: — "When I had a large mule and horse ranche in America I noticed that the foals of mares * A Text Book of Human Ph'/siohyy. By Austin Flint, M.D., LL.D. Fourth edition. New York: D. Appleton ft Co. 1888. Page 797. 64:6 APPENDIX B. by horse stallions had a mulish appearance in those cases where the marc had previously given birth to a mule foal. Common heifers who have had calves by a thoroughbred bull are apt thereafter to have well-bred calves even from the veriest scrubs." Yet another very interesting piece of evidence is furnished by Mr. W. Scdgwick, M.R.C.S., in an article on "The Influence of Heredity in Disease," published in the British Medical Journal for Feb. 22, 1896, pp. 4(>0-2. It concerns the transmission of a malformation known among medical men as hypospadias. Referring to a man belonging to a family in which this defect prevailed, he writes : — " The widow of the man from whom these throe generations of hypospadians were descended married again, after an interval of eighteen months ; and in this instance the second husband was not only free from the defect, but there was no history of it in his family. By this second marriage she had four hypospadiac sons and four hypospadiac grandsons ; whilst there were seven grandsons and three great-grandsons who were not mal-formed."] Coming from remote places, from those who have no theory to support, and who are some of them astonished by the unex pected phenomena, the agreement dissipates all doubt. In four kinds of mammals, widely divergent in their natures — man, horse, dog, and pig — ;we have this same seemingly-anomalous kind of heredity, made visible under analogous conditions. We must take it as a demonstrated fact that, during gestation, traits of constitution inherited from the father produce effects upon the constitution of the mother ; and that these communicated effects are transmitted by her to subsequent offspring. We are supplied with an abso lute disproof of Professor Weismann's doctrine that the repro ductive cells are independent of, and uninfluenced by, the somatic cells ; and there disappears absolutely the alleged obstacle to the transmission of acquired characters. Notwithstanding experiences showing the futility of contro versy for the establishment of truth, I am tempted here to answer opponents at some length. But even could the editor allow me the needful space, I should be compelled, both by lack of time and by ill-health, to be brief. I must content myself with notic ing a few points which most nearly concern me. Referring to my argument respecting tactual discriminative- ness, Mr. WTa]lace thinks that I — " afford a glaring example of taking the unessential in place of the essential, and drawing conclusions from a partial and altogether insufficient survey of the phenomena. For this 'tactual discriminativcness,' which is alone dealt with by Mr. Spencer, forms the least important, and probably only an inci dental portion of the great vital phenomenon of skin-sensitiveness, which is at once the watchman and the shield of the organism against imminent external dangers." (Fortnightly Review, April, 1893, p. 497) Here Mr. Wallace assumes it to be self-evident that skin-sensi tiveness is due to natural selection, and assumes that this must be admitted by me. lie supposes it is only the unequal distribution INADEQUACY OF NATURAL SELECTION, ETC. G47 of skin-discriminativeness which I contend is not thus accounted for. Hut 1 deny that either the general sensitiveness or the special sensitiveness results from natural selection ; and I have years ago justified the first disbelief as I have recently the second. In " The Factors of Organic Evolution " (Essays, 454 — 8), I have given various reasons for inferring that the genesis of the nervous system cannot be due to survival of the fittest ; but that it is due to the direct effects of converse between the surface and the environment ; and that thus only is to be explained the strange fact that the nervous centres are originally superficial, and migrate inwards during development. These conclusions I have, in the essay Mr. Wallace criticizes, upheld by the evidence which blind boys and skilled compositors furnish ; proving, as this does, that increased nervous development is peripherally initiated. Mr. Wallace's belief that skin-sensitiveness arose by natural selection, is unsupported by a single fact. He assumes that it must have been so produced because it is all-important to self-preservation. My belief that it is directly initiated by converse with the environ ment, is supported by facts ; and I have given proof that the assigned cause is now in operation. Am I called upon to abandon my own supported belief and accept Mr. Wallace's unsupported belief ? I think not. Referring to my argument concerning blind cave-animals, Professor Lankester, in Nature of February 23, 1893, writes : — " Mr. Spencer shows that the saving of ponderable material in the sup pression of an eye is but a small economy : he loses sight of the fact, however, that possibly, or even probably, the saving to the organism in the reduction of an eye to a rudimentary state is not to be measured by mere bulk, but by the non-expenditure of special materials and special activities which are con cerned in the production of an organ so peculiar and elaborate as is the verte brate eye." It seems to me that a supposition is here made to do duty as a fact ; and that I might with equal propriety say that " possibly, or even probably," the vertebrate eye is physiologically cheap : its optical part, constituting nearly its whole bulk, consisting of a low order of tissue. There is, indeed, strong reason for con sidering it physiologically cheap. If any one remembers how relatively enormous are the eyes of a fish just out of the egg — a pair of eyes with a body and head attached ; and if he then remembers that every egg contains material for such a pair of eyes ; he will see that eye-material constitutes a very considerable part of the fish's roe ; and that, since the female fish provides this quantity every year, it cannot be expensive. My argument against Weismann is strengthened rather than weakened by con templation of these facts. Professo- Lankcster asks my attention to a hypothesis of his 42 048 APPENDIX B. own, published in the Encyclopedia Britannica, concerning the production of blind cave-animals. lie thinks it can — " be fully explained by natural selection acting on congenital fortuitous varia tions. Many animals are thus born with distorted or defective eyes whose parents have not had their eyes submitted to any peculiar conditions. Sup posing a number of some species of Arthropod or Fish to be swept into a cavern or to be carried from less to greater depths in the sea, those individu als with perfect eyes would follow the glimmer of light and eventually escape to the outer air or the shallower depths, leaving behind those with imperfect eyes to breed in the dark place. A natural selection would thus be effected " in successive generations. First of all, I demur to the words " many animals." Under the abnormal conditions of domestication, congenitally defective eyes may be not very uncommon ; but their occurrence under natural conditions is, I fancy, extremely rare. Supposing, however, that in a shoal of young fish, there occur some with eyes seriously defective. What will happen ? Vision is all-important to the young fish, both for obtaining food and for escaping from enemies. This is implied by the immense development of eyes just referred to ; and the obvious conclusion to be drawn is that the partially blind would disappear. Considering that out of the enormous number of young fish hatched with perfect eyes, not one in a hundred reaches maturity, what chance of surviving would there be for those with imperfect eyes ? Inevitably they would be starved or be snapped up. Hence the chances that a matured or partially matured semi-blind fish, or rather two such, male and female, would be swept into a cave and left behind are extremely remote. Still more remote must the chances be in the case of cray-fish. Sheltering themselves as these do under stones, in crevices, and in burrows which they make in the banks, and able quickly to anchor themselves to weeds or sticks by their claws, it seems scarcely supposable that any of them could be carried into a cave by a flood. What, then, is the probability that there will be two nearly blind ones, and that these will be thus carried ? Then, after this first extreme improbability, there comes a second, which we may, I think, rather call an impossibility. How would it be possible for creatures subject to so violent a change of habitat to survive ? Surely death would quickly follow the sub jection to such utterly unlike conditions and modes of life. The existence of these blind cave- animals can be accounted for only by supposing that their remote ancestors began making excursions into the cave, and, finding it profitable, extended them, genera tion after generation, further in : undergoing the required adapta tions little by little.* * This supposition I find verified by Mr. A. S. Packard in his elaborate monograph on "The Cave Fauna of North America, &c.," as also in his article published in the American Naturalist, September, 1S88; for he there men- INADEQUACY OP NATURAL SELECTION, ETC. G49 Between Dr. Romanes and myself the first difference concerns the interpretation of " Panmixia." Clearer conceptions of these matters would be reached if, instead of thinking in abstract terms, the physiological processes concerned were brought into the fore ground. Beyond the production of changes in the sizes of parts by the selection of fortuitously-arising variations, I can see but one other cause for the production of them — the competition among the parts for nutriment. This has the effect that active parts are well-supplied and grow, while inactive parts arc ill- supplied and dwindle.* This competition is the cause of " economy of growth " ; this is the cause of decrease from disuse ; and this is the only conceivable cause of that decrease which Dr. Romanes contends follows the cessation of selection. The three things are aspects of the same thing. And now, before leaving this question, let me remark on the strange proposition which has to be defended by those who deny the dwindling of organs from disuse. Their proposition amounts to this : — that for a hundred generations an inactive organ may be partially denuded of blood all through life, and yet in the hundredth generation will be produced of just the same size as in the first ! There is one other passage in Dr. Romanes' criticism — that concerning the influence of a previous sire on progeny — which calls for comment. He sets down what he supposes Weismann will say in response to my argument. " First, he may question the fact." Well, after the additional evidence given above, I think he is not likely to do that ; unless, indeed, it be that along with readiness to base conclusions on things " it is easy to imagine " there goes reluctance to accept testimony which it is difficult to doubt. Second, he is supposed to reply that " the Germ-plasm of the first sire has in some way or another become partly commingled with that of the immature ova " ; and Dr. Romanes goes on to describe how there may be millions of spermatozoa and " thousands of millions " of their contained " ids " around the ovaries, to which these secondary effects are tions "variations in Pscudrtrcmia cavcrnarnm and Tomoccnut plumbcus, found living near the entrance to caves in partial daylight." The fact;', :;:; accumulated by Mr. Packard, furnished a much more complete answer to Prof. Lankcstcr than is above given, as, for example, the " blindness of Ncotoma, or the Wood- Hat of Mammoth Cave." It seems that there are a'eo "cave beetles, with or without rudimentary eyes," and "eyeless spiders" and Myriapods. And there are insects, as some "species of Anophthalmus and j\delops, whose larvae are lacking in all traces of eyes and optic nerves and Ipbes." These instances cannot be explained as sequences of an inrush of water carrying with it the remote ancestors, some of which' did not find their •way out ; nor can others of them be explained by supposing an inrush of air, which did the like. *See"Socinl Organism" in Westminster Review for January, 1860; also Pri.iciples of Sociology, § 247. 650 APPENDIX B. due. But, on the one hand, he does not explain why in such cases each subsequent ovum, as it becomes matured, is not fer tilized by the sperm-cells present, or their contained germ-plasm, rendering all subsequent fecundations needless ; and, on the other hand, he does not explain why, if this does not happen, the potency of this remaining germ-plasm is nevertheless such as to affect not only the next succeeding offspring, but all subsequent offspring. The irreconcilability of these two implications would, I think, sufficiently dispose of the supposition, even had we not daily multitudinous proofs that the surface of a mamnialian ovarium is not a spermatneca. The third reply Dr. Romanes urges, is the inconceivability of the process by which the germ-plasm of a pre ceding male parent affects the constitution of the female and her subsequent offspring. In response, I have to ask why he piles up a mountain of difficulties based on the assumption that Mr. Darwin's explanation of heredity by " Pangenesis " is the only available explanation preceding that of Weismann ? and why he presents these difficulties to me, more especially ; deliberately ignoring my own hypothesis of physiological units ? It cannot be that he is ignorant of this hypothesis, since the work in which it is variously set forth (Principles of Biology, §§ 66 — 97) is one with which he is well acquainted : witness his Scientific Evidences of Organic Evolution ; and he has had recent reminders of it in Weismann's Germ-plasm, where it is repeatedly referred to. Why, then, does he assume that I abandon my own hypothesis and adopt that of Darwin ; thereby entangling myself in difficulties which my own hypothesis avoids ? If, as I have argued, the germ-plasm consists of substantially similar units (having only those minute differences expressive of individual and ancestral differences of structure), none of the complicated requirements which Dr. Romanes emphasizes exist ; and the alleged incon ceivability disappears. Here I must end: not intending to say more, unless for some very urgent reason ; and leaving others to carry on the discus sion. 1 have, indeed, been led to suspend for a short time my proper work, only by consciousness of the transcendent import ance of the question at issue. As I have before contended, a right answer to the question whether acquired characters are or are not inherited, underlies right beliefs, not only in Biology and Psychology, but also in Education, Ethics, and Politics. III. As a species of literature, controversy is characterised by a terrible fertility. Each proposition becomes the parent of half a INADEQUACY OF NATURAL SELECTION, ETC. G51 dozen ; so that a few replies and rejoinders produce an un manageable population of issues, old and new, which end in being a nuisance to everybody. Remembering this, I shall re frain from dealing with all the points of Professor Weismann's answer. I must limit myself to a part ; and that there may be no suspicion of a selection convenient to myself, I will take those contained in his first article. Before dealing with his special arguments, let me say some thing about the general mode of argument which Professor Weis- mann adopts. The title of his article is "The All-Sufficiency of Natural Selection." * Very soon, however, as on p. 322, we come to the admission, which he has himself italicised, "that it is really very difficult to imagine this process of natural selection in its details ; and to this day it is impossible to demonstrate it in any one point." Elsewhere, as on pp. 327 and 336 a propos of other cases, there are like admissions. But now if the sufficiencv of an assigned cause cannot in any case be demonstrated, and if it is " really very difficult to imagine " in what way it has produced its al leged effects, what becomes of the " all-sufficiency " of the cause ? How can its all-sufficiency be alleged when its action can neither be demonstrated nor easily imagined ? Evidently to fit Professor Weismann's argument the title of the article should have been " The Doubtful Sufficiency of Natural Selection." Observe, again, how entirely opposite are the ways in which he treats his own interpretation and the antagonist interpreta tion. He takes the problem presented by certain beautifully adapted structures on the anterior legs of " very many insects," which they use for cleansing their antennae. These, he argues, cannot have resulted from the inheritance of acquired characters ; since any supposed changes produced by function would be changes in the chitinous exo-skeleton, which, being a dead sub stance, cannot have had its changes transmitted. He then pro ceeds, very candidly, to point out the extreme difficulties which lie in the way of supposing these structures to have resulted from natural selection : admitting that an opponent might " say that it was absurd " to assume that the successive small variations im plied were severally life-saving in their effects. Nevertheless, he holds it unquestionable that natural selection has been the cause. See then the difference. The supposition that the apparatus has been produced by the inheritance of acquired characters is rejected because it presents insuperable difficulties. But the supposition that the apparatus has been produced by natural selection is accepted, thouyh it presents insuperable difficulties. * Contemporary Review, September, 1893. 052 APPENDIX B. If this mode of reasoning is allowable, no fair comparison be tween diverse hypotheses ean be made. With these remarks on Professor Weismann's method at large, let me now pass to the particular arguments he uses, taking them seriatim. The first case he deals with is that of the progressive degra dation of the human little toe. This he considers a good test case ; and he proceeds to discuss an assigned cause — the inherited and accumulated effects of boot-pressure. Without much diffi culty he shows that this interpretation is inadequate ; since fusion of the phalanges, which constitutes in part the progressive degradation, is found among peoples who go barefoot, and has been found also in Egyptian mummies. Having thus disposed of Mr. Buckman's interpretation, Professor Weismann forthwith concludes that the ascription of this anatomical change to the inheritance of acquired characters is disposed of, and assumes, as the only other possible interpretation, a dwindling " through pan mixia " : " the hereditary degeneration of the little toe is thus quite simply explained from my standpoint." It is surprising that Professor Weismann should not have seen that there is an explanation against which his criticism does not tell. If we go back to the genesis of the human type from some lower type of primates, we see that while the little toe has ceased to be of any use for climbing purposes, it has not come into any considerable use for walking and running. A glance at the feet of the sub-human primates in general, shows that the inner digits are, as compared with those of men, quite small, have no such relative length and massiveness as the human great toes. Leav ing out the question of cause, it is manifest that the great toes have been immensely developed, since there took place the change from arboreal habits to terrestrial habits. A study of the mechanics of walking shows why this has happened. Stability requires that the " line of direction " (the vertical line let fall from the centre of gravity) shall fall within the base, and, in walking, shall be brought at each step within the area of support, or so near it that any tendency to fall may be checked at the next step. A necessary result is that if, at each step, the chief stress of support is thrown on the outer side of the foot, the body must be swayed so that the " line of direction" may fall within the outer side of the foot, or close to it; and when the next step is taken it must be similarly swayed in an opposite way, so that the outer side of the other foot may bear the weight. That is to say, the body must oscillate from side to side, or waddle. The movements of a duck when walking or running show what hap pens when the points of support are wide apart. Clearly this INADEQUACY OF NATURAL SELECTION, ETC. 653 kind of movement conflicts with efficient locomotion. There is a waste of muscular energy in making these lateral movements, and they are at variance with the forward movement. We may infer, then, that the developing man profited by throwing the stress as much as possible on the inner sides of the feet ; and was especially led to do this when going fast, which enabled him to abridge the oscillations : as indeed we now see in a drunken man. Thus there was thrown a continually increasing stress upon the inner digits as they progressively developed from tha effects of use ; until now that the inner digits, so large compared with the others, bear the greater part of the weight, and being relatively near one another, render needless any marked sway- ings from side to side. But what has meanwhile happened to the outer digits ? Evidently as fast as the great toes have come more and more into play and developed, the little toes have gone more and more out of play and have been dwindling for — how long shall we say ? — perhaps a hundred thousand years. So far, then, am J from feeling that Professor Weismann lias here raised a difficulty in the way of the doctrine I hold, that I feel indebted to him for having drawn attention to a very strong evidence in its support. This modification in the form of the foot, which has occurred since arboreal habits have given place to terrestrial habits, shows the effects of use and disuse simultaneously. The inner digits have increased by use while the outer digits have decreased by disuse. Saying that he will not " pause to refute other apparent proofs of the transmission of acquired characters," Professor Weismann proceeds to deal with the argument which, with various illustrations, I have several times urged — the argument that the natural selection of fortuitously-arising variations cannot account for the adjustment of co-operative parts. Very clearly and very fairly he summarises this argument as used in The Principles of Biology in 1864. Admitting that in this case there are " enormous difficulties " in the way of any other interpreta tion than the inheritance of acquired characters, Professor AYeismann before proceeding to assault this " last bulwark of the Lamarckian principle," premises that the inheritance of ac quired characters cannot be a cause of change because inactive as well as active parts degenerate when they cease to be of use : instancing the " skin and skin-armature of crabs and insects." On this I may remark in the first place that an argument derived from degeneracy of passive structures scarcely meets the case of development of active structures ; and I may re mark in the second place that 1 have never dreamt of denying the elliciency of natural selection as a cause of degeneracy in G54 APPENDIX B. passive structures when the degeneracy is such as aids the pro sperity of the stirp. Making this parenthetical reply to his parenthetical criticism I pass to his discussion of this particular argument which he un dertakes to dispose of. His cheval dc bataille is furnished him by the social insects — not a fresh one, however, as might be supposed from the way in which he mounts it. From time to time it has carried other riders, who have couched their lances with fatal effects, as they supposed. But I hope to show that no one of them has unhorsed an antagonist, and that Professor Weismann fails to do this just as completely as his predecessors. I am, indeed, not sorry that he has afforded me the opportunity of criticising the general discussion concerning the peculiarities of these interesting crea tures, which it has often seemed to me sets out with illegitimate assumptions. The supposition always is that the specialities of structures and instincts in the unlike classes of their communities, have arisen during the period in which the communities have existed in something like their present forms. This cannot be. It is doubtless true that association without differentiations of classes may pre-exist for co-operative purposes, as among wolves, and as among various insects which swarm under certain circum stances. Hence we may suppose that there arise in some cases permanent swarms — that survival of the fittest will establish these constant swarms where they are advantageous. But admitting this, we have also to admit a gradual rise of the associated state out of the solitary state. Wasps and bees present us with grada tions. If, then, we are to understand how the organized societies have arisen, either out of the solitary state or out of undifferen- tiatcd swarms, we must assume that the differences of structure and instinct among the members of them arose little by little, as the social organization arose little by little. Fortunately we are able to trace the greater part of the process in the annually- formed communities of the common wasp ; and we shall recognize in it an all-important factor (ignored by Professor Weismann) to which the phenomena, or at any rate the greater part of them, are due. But before describing the Avasp's annual history, let me set down certain observations made when, as a boy, 1 was given to angling, and, in July or August, sometimes used for bait " wasp- grubs," as they were called. After having had two or three days the combs or " cakes " of these, full of unfed larvae in all stages of growth, I often saw some of them devouring the edges of their cells to satisfy their appetites ; and saw others, probably the most advanced in growth, which were spinning the little covering caps to their cells, in preparation for assuming the pupa INADEQUACY OF NATURAL SELECTION, ETC. 655 state. It is to be inferred that if, after a certain stage of growth has been reached, the food-supply becomes inadequate or is stopped altogether, the larva undergoes its transformation pre maturely ; and, as we shall presently see, this premature traiis- formation has several natural sequences. Let us return now to the wasp's family history. In the spring, a queen-wasp or mother-wasp which has survived the winter, begins to make a small nest containing four or more cells in which she lays eggs, and as fast as she builds additional cells, she lays an egg in each. Presently, to these activities, is added the feeding of the larvje : one result being that the multiplication of larvae involves a restriction of the food that can be given to each. If we suppose that the mother-wasp rears no more larvse than she can fully feed, there will result queens or mothers like herself, relatively few in number. But if we suppose that, laying more numerous eggs she produces more larvae than she can fully feed, the result will be that when these have reached a certain stage of growth, inadequate supply of food will be followed by pre mature retirement and transformation into pupae. What will be the characters of the developed insects? The ^ first effect of arrested nutrition will be smaller size. This we find. A second effect will be defective development of parts that are latest formed and least important for the survival of the individual. Hence we may look for arrested development of the reproductive organs — non-essential to individual life. And this expectation is in accord with what we see in animal development at large ; for (passing over entirely sexless individuals) we see that though the repro ductive organs may be marked out early in the course of develop ment, they are not made fit for action until after the structures for carrying on individual life are nearly complete. The implica tion is, then, that an inadequately-fed and small larva will become a sterile imago. Having noted this, let us pass to a remarkable concomitant. In the course of development, organs are formed not alone in the order of their original succession, but partly in the. order of importance and the share they have to take in adult activities — a change of order called by Haeckel " heterochrony." Hence the fact that we often see the maternal instinct precede the sexual instinct. Every little girl with her doll shows us that the one may become alive while the other remains dormant. In the case of wasps, then, premature arrest of development may result in incompleteness of the sexual traits, along with complete ness of the maternal traits. What happens ? Leave out the lay ing of eggs, and the energies of the mother-wasp are spent wholly in building cells and feeding larva?, and the worker-wasp forth with begins to spend its life in building cells and feeding larvae. Thus interpreting the facts, we have no occasion to assume any 656 APPENDIX B. constitutional difference between the eggs of worker-wasps and the eggs of queens ; and that their eggs are not different we see, first, in the fact that occasionally the worker-wasp is fertile and lays drone-producing eggs, and we see secondly that (if in this respect they are like the bees, of which, however, we have no proof) the larva of a woiker-wasp can be changed into the larva of a queen-wasp by special feeding. But be this as it may, we have good evidence that the feeding determines everything. Says l)r. Orinerod, in his British Social Wasps : — "When the swarm is strong and food plentiful ... the well fed larvae develop into females, full, large, and overflowing with fat. There are all gradations of size, from the large fat female to the smallest worker. The larger the wasp, the larger and better developed, as the rule, are the female organs, in all their details. In the largest wasps, which are to be the queens of another year, the ovaries differ to all appearances in nothing but their size from those of the larger worker wasps. . . . Small feeble swarms produce few or no perfect females ; but in large strong swarms they are found by the score." (pp. 248-9) To this evidence add the further evidence that queens and workers pass through certain parallel stages in respect of their maternal activities. At first the queen, besides laying eggs, builds cells and feeds larvae, but after a time ceases to build cells, and feeds larvae only, and eventually doing neither one nor the other, only lays eggs, and is supplied with food by the workers. So it is in part with the workers. While the members of each succes sive brood, when in full vigour, build cells and feed larva?, by- and-by they cease to build cells, and only feed larva? : the ma ternal activities and instincts undergo analogous changes. In this case, then, we are not obliged to assume that only by a pro cess of natural selection can the differences of structure and in stinct between queens and workers be produced. The only way in which natural selection here comes into play is in the better survival of the families of those queens which made as many cells, and laid as many eggs, as resulted in the best number of half-fed larvre, producing workers ; since by a rapid multiplica tion of workers the family is advantaged, and the ultimate p_ro- duction of more queens surviving into the next year insured. « The differentiation of classes does not go far among the wasps, because the cycle of processes is limited to a year, or rather to the few months of the summer. It goes further among the hive- bees, which, by storing food, survive from one }ear into the next. Unlike the queen-wasp, the queen-bee neither builds cells nor gathers food, but is fed by the workers : egg laying has become her sole business. On the other hand the workers, occupied ex clusively in building and nursing, have the reproductive organs more dwarfed than they are in wasps. Still we see that the worker-bee occasionally lays drone-producing eggs, and that, by INADEQUACY OP NATURAL SELECTION, ETC. 657 giving extra nutriment and the required extra space, a worker- larva can be developed into a queen-larva. In respect to the leading traits, therefore, the same interpretation holds. Doubt less there are subsidiary instincts which are apparently not thus interpretable. But before it can be assumed that an interpreta tion of another kind is necessary, it must be shown that these instincts cannot be traced back to those pre-social types and semi- social types which must have preceded the social types we now see. For unquestionably existing bees must have brought with them from the pre-social state an extensive endowment of in stincts, and, acquiring other instincts during the unorganized social state, must have brought these into the present organized social state. It is clear, for instance, that the cell-building in stinct in all its elaboration was mainly developed in the pre-social stage ; for the transition from species building solitary cells to those building combs is traceable. We are similarly enabled to account for swarming as being an inheritance from remote ances tral types. For just in the same way that, with under-feeding of larvae, there result individuals with imperfectly developed repro ductive systems, so there will result individuals with imperfect sexual instincts ; and just as the imperfect reproductive system partially operates upon occasion, so will the imperfect sexual in stinct. Whence it will result that on the event which causes a queen to undertake a nuptial flight which is effectual, the workers may take abortive nuptial flights : so causing a swarm. And here, before going further, let us note an instructive class of facts related to the class of facts above set forth. Summing up, in a chapter on "The Determination of Sex," an induction from many cases, Professor Geddes and Mr. Thompson remark that "such conditions as deficient or abnormal food," and others causing " preponderance of waste over repair .... tend to result in production of males ; " while " abundant and rich nutri tion " and other conditions which " favour constructive processes result in the production of females." * Among such evidences of this as immediately concern us, are these : — J. II. Fabre found that in the nests of Osmia tricornis, eggs at the bottom, first laid, and accompanied by much food, produced females, while those at the top, last laid, and accompanied by one- half or one-third the quantity of food, produced males.f Huber's observations on egg-laying by the honey-bee, show that in the normal course of things, the queen lays eggs of workers for eleven months, and only then lays eggs of drones : that is, when de clining nutrition or exhaustion has set in. Further, we have the above-named fact, shown by wasps and bees, that when workers * Evolution of Sex, p. 50. f /Souvenirs Entoinohyiijucs, 3mc Scric, p. 328. 058 APPENDIX B. l?.y eggs these produce drones only.* Special evidence, harmon izing with general evidence, thus proves that among the social insects the sex is determined by degree of nutrition while the egg is being formed. See then how congruous this evidence is with the conclusion above drawn ; for it is proved that after an egg, predetermined as a female, has been laid, the character of the produced insect as a perfect female or imperfect female is deter mined by the nutrition of the larva. That is, one set of differences in structures and instincts is determined by nutrition before the egg is laid, and a further set of differences in structures and instincts is determined by nutrition after the egg is laid. We come now to the extreme case — that of the ants. Is it not probable that the process of differentiation has been similar ? There are sundry reasons for thinking so. With ants as with wasps and bees — the workers occasionally lay eggs ; and an ant- community can, like a bee-community, when need be, produce queens out of worker-larvrc : presumably in the same manner by extra feeding. But here we have to add special evidence of great significance. For observe that the very facts concerning ants, which Professor Weismann names as exemplifying the formation of the worker type by selection, serve, as in the case of wasps, to exemplify its formation by arrested nutrition. He says that in several species the egg-tubes in the ovaries show progressive decrease in number; and this, like the different degrees of arrest in the ovaries of the worker-wasps, indicates arrest of larva- feeding at different stages. He gives cases showing that, in different degrees, the eyes of workers are less developed in the number of their facets than those of the perfect insects ; and he also refers to the wings of workers as not being developed : remarking, however, that the rudiments of their wings show that the ancestral forms had wings. Are not these traits also results of arrested nutrition ? Generally among insects the larvse are either blind or have but rudimentary eyes ; that is to say, visual organs are among the latest organs to arise in the genesis of the perfect organism. Hence early arrest of nutrition will stop formation of these, while various more ancient structures have become tolerably complete. Similarly with wings. Wings are late organs in insect phylogeny, and therefore will be amor.g those most likely to abort where development is prematurely arrested. And both these traits will, for the same reason, natu rally go along with arrested development of the reproductive system. Even more significant, however, is some evidence as signed by Mr. Darwin respecting the caste-gradations among the driver ants of West Africa. He says : — * Natural History of Bf>3 of this supposed cause, but will leave it to be dealt with by im plication a few pages in advance, where the general hypothesis of panmixia will be reconsidered. And now, at length, we are prepared for dealing with Professor Weismann's crucial case — with his alleged disproof that co-adapta tion of co-operative parts results from inheritance of acquired characters, because in the case of the Amazon-ants, it has arisen where the inheritance of acquired characters is impossible. For after what has been said, it will be manifest that the whole ques tion is begged when it is assumed that this co-adaptation has arisen since there existed among these ants an organized social state. Unquestionably this organized social state pre-supposes a series of modifications through which it has been reached. It follows, then, that there can be no rational interpretation without a preceding inquiry concerning that earlier state in which there were no castes, but only males and females. What kinds of individuals were the ancestral ants — at first solitary, and then semi-social ? They must have had marked powers of offence and defence. Of predacious creatures, it is the more powerful which form societies, not the weaker. Instance human races. Nations originate from the relatively warlike tribes, not from the rela tively peaceful tribes. Among the several types of individuals forming the existing ant community, to which, then, did the ancestral ants bear the greatest resemblance ? They could not have been like the queens, for these, now devoted to egg-laying, are unfitted for conquest. They could not have been like the inferior class of workers, for these, too, are inadequately armed and lack strength. Hence they must have been most like these Amazon-ants or soldier-ants, which now make predatory excur sions — which now do, in fact, what their remote ancestors did. What follows ? Their co-adapted parts have not been produced by the selection of variations within the ant-community, such as we now see it. They have been inherited from the pre-social and early social types of ants, in which the co-adaptation of parts had been effected by inheritance of acquired characters. It is not that the soldier-ants have gained these traits ; it is that the other castes have lost them. Early arrest of development causes ab sence of them in the inferior workers ; and from the queens they have slowly disappeared by inheritance of the effects of disuse. For, in conformity with ordinary facts of development, we may conclude that in a larva which is being so fed as that the development of the reproductive organs is becoming pronounced, there will simultaneously commence arreet in the development of those organs which are not to be used. There arc abundant proofs that along with rapid growth of some organs others abort. And if these inferences are true, ihen Professor Weismann's aiyu- 43 664: APPENDIX B. ment falls to the ground. Nay, it falls to the ground even if con clusions so definite as these be not insisted upon ; for before he can get a basis for his argument he must give good reasons for concluding that these traits of the Amazon-ants have not been inherited from remote ancestors. One more step remains. Let us grant him his basis, and let us pass from the above negative criticism to a positive criticism. As before, I decline to follow the practice of talking in abstracts instead of in concretes, and contend that, difficult as it may be to see how natural selection has in all cases operated, we ought, at any rate, to trace out its operation whenever we can, and see where the hypothesis lands us. According to Professor Weis- mann's admission, for production of the Amazon-ant by natural selection, "many parts must have varied simultaneously and in harmony with one another • " * and he names as such, larger jaws, muscles to move them, larger head, and thicker chitin for it, bigger nerves for the muscles, bigger motor centres in the brain, and, for the support of the big head, strengthening of the thorax, limbs, and skeleton generally. As lie admits, all these parts must have varied simultaneously in due proportion to one another. What must have been the proximate causes of their variations ? They must have been variations in what he calls the " determinants." He says : — " We have, however, to deal with the transmission of parts which are variable and this necessitates the assumption that just as many independent and variable parts exist in the germ-plasm as are present in the fully formed organism." f Consequently to produce simultaneously these many variations of parts, adjusted in their sizes and shapes, there must have simultaneously arisen a set of corresponding variations in the " determinants " composing the germ-plasm. AA hat made them simultaneously vary in the requisite ways ? Professor Weismann will not say that there was somewhere a foregone intention. This would imply supernatural agency. He makes no attempt to assign a physical cause for these simultaneous appropriate variations in the determinants : an adequate physical cause being inconceivable. What, then, remains as the only possible inter pretation ? Nothing but a fortuitous concourse of variations ; re minding us of the old " fortuitous concourse of atoms." Nay, indeed, it is the very same thing. For each of the " determinants," made up of "biophors," and these again of protein-molecules, and these again of simpler chemical molecules, must have had its molecular constitution changed in the required way ; and the molecular constitutions of all the " determinants," severally modi- lied differently, but in adjustment to one another, must have been * Loc. cit., p. 318. f The Germ Plasm, p. 54. INADEQUACY OF NATURAL SELECTION, ETC. 665 thus modified by " a fortuitous concourse of atoms." Now if this is an allowable supposition in respect of the " determinants," and the varying organs arising from them, why is it not an allow able supposition in respect of the organism as a whole ? Why not assume " a fortuitous concourse of atoms " in its broad, simple form ? Nay, indeed, would not this be much the easier ? For observe, this co-adaptation of numerous co-operative parts is not achieved by one set of variations, but is achieved gradually by a series of such sets. That is to say, the " fortuitous concourse of atoms " must have occurred time after time in appropriate ways. We have not one miracle, but a series of miracles ! Of the two remaining points in Professor Weismann's first article which demand notice, one concerns his reply to my argu ment drawn from the distribution of tactual discriminativeness. In what way does he treat this argument ? lie meets it by an argu ment derived from hypothetical evidence — not actual evidence. Taking the case of the tongue-tip, I have carefully inquired whether its extreme power of tactual discrimination can give any life-saving advantage in moving about the food during mastica tion, in detecting foreign bodies in it, or for purposes of speech ; and have, I think, shown that the ability to distinguish between points one twenty-fourth of an inch apart is useless for such pur poses. Professor Weismann thinks he disposes of this by observ ing that among the apes the tongue is used as an organ of touch. But surely a counter-argument equivalent in weight to mine should have given a pase in which power to discriminate between points one twenty-fourth of an inch apart instead of one-twentieth of an inch apart (a variation of one-sixth) had a life-saving efficacy ; or, at any rate, should have suggested such a case. Nothing of the kind is done or even attempted. But now note that his reply, accepted even as it stands, is suicidal. For what has the trusted process of panmixia been doing ever since the human being began to evolve from the ape ? Why during thou sands of generations has not the nervous structure giving this extreme discriminativeness dwindled away ? Even supposing it had been proved of life-saving efficacy to our simian ancestors, it ought, according to Professor Weismann's own hypothesis, to have disappeared in us. Either there was none of the assumed special capacity in the ape's tongue, in which case his reply fails, or panmixia has not operated, in which case his theory of degene racy fails. All this, however, is but preface to the chief answer. The argument drawn from the case of the tongue-tip, with which alone Professor Weismann deals, is but a small part of my aro-n- ment, the remainder of which he does not attempt to touch — 606 APPENDIX B. docs not even mention. Had I never referred to the tongue-tip at all, the various contrasts in discriminativeness which I have named, between the one extreme of the forefinger-tip and the other extreme of the middle of the back, would have abundantly sufficed to establish my case — would have sufficed to show the in adequacy of natural selection as a key and the adequacy of the inheritance of acquired characters. It seems to me, then, that judgment must go against him by default. Practically he leaves the matter standing just where it did.* * While Professor Weismann has not dealt with my argument derived from the distribution of discriminativeness on the skin, it has been criticized by Mr. McKeen Cattcll, in the last number of Mind (October, 1893). His general argument, vitiated by extreme misconceptions, I need not deal with. He says : — " Whether changes acquired by the individual are hereditary, and if so to what extent, is a question of great interest for ethics no less than for biology. But Mr. Spencer's application of this doctrine to account for the origin of species [!] simply begs the question. He assumes useful variations [!] — whether of structure or habit is immaterial — without attempting to explain their origin " : two absolute misstatemcnts in two sentences ! The only part of Mr. Cattell's criticism requiring reply is that which concerns the " sensation-areas " on the skin. He implies that since Weber, experimental psychologists have practically set aside the theory of sensation areas: showing, among other things, that relatively great accuracy of discrimination can be quickly acquired by " increased interest and attention. . . . Practice for a few minutes will double the accuracy of discrimination, and practice on one side of the body is carried over to the other." To me it seems manifest that " increased interest and attention " will not enable a patient to discriminate two points where a few minutes before he could perceive only one. That which he can really do in this short time is to learn to discriminate between the massivcncss of a sensation produced by two points and the massiveness of that produced by one, and to infer one point or two points accordingly. Respecting the existence of sensation-areas marked off from one another, I may, in the first place, remark that since the eye originates as a dermal sac, and since its retina is a highly developed part of the sensitive surface at large, and since the discriminative power of the retina depends on the division of it into numerous rods and cones, each of which gives a separate sensation- area, it would be strange were the discriminative power of the skin at large achieved by mechanism fundamentally different. In the second place I may remark that if Mr. Cattdl will refer to Professor Gustav Rctzius's Biologischc [fnfersuchungcn, New Series, vol. iv (Stockholm, 1892), he will sec elaborate diagrams of superficial nerve-endings in various animals show ing many degrees of separateness. I guarded myself against being supposed to think that the sensation-areas are sharply marked off from one another ; and suggested, contrariwise, that probably the branching nerve-terminations intruded among the branches of adjacent nerve-terminations. Here let me add that the intrusion may vary greatly in extent ; and that where the intrud ing fibres run far among those of adjacent areas, the discriminativeness will be but small, while it will be great in proportion as each set of branching fibres is restricted more nearly to its own area. All the facts are explicable on this supposition. INADEQUACY OF NATURAL SELECTION, ETC. 667 The other remaining point concerns the vexed question of panmixia. Confirming the statement of Dr. Romanes, Professor Weismann says that I have misunderstood him. Already (Con temporary Review, May, 1893, p. 758, and Reprint, p. 66) I have quoted passages which appeared to justify my interpretation, arrived at after much seeking.* Already, too, in this review (July, 1893, p. 54) I have said why I did not hit upon the inter pretation now said to be the true one : I never supposed that any one would assume, without assigned cause, that (apart from the excluded influence of disuse) the minus variations of a disused organ are greater than the plus variations. This was a tacit challenge to produce reasons for the assumption. Professor Weismann does not accept the challenge, but simply says : — " In my opinion all organs are maintained at the height of their de velopment only through uninterrupted selection" (p. 332): in the absence of which they decline. Now it is doubtless true that as a naturalist he may claim for his " opinion " a relatively great weight. Still, in pursuance of the methods of science, it seems to me that something more than an opinion is required as the basis of a far-reaching theory, f * To save space and exclude needless complication I have omitted these passages from the preceding divisions of this appendix. \ Though Professor Weismann docs not take up the challenge, Dr. Romanes does. He says : — " When selection is withdrawn there will be no excessive plus variations, because so long as selection was present the efficiency of the organ was maintained at its highest level : it was only the tninus variations which were then eliminated" (Contemporary Revieio, p. 611). In the first place, it seems to me that the phrases used in this sentence beg the question. It says that " the efficiency of the organ was maintained at its highest level"; which implies that the highest level (tacitly identified with the greatest size) is the best and that the tendency is to fall below it. This is the very thing I ask proof of. Suppose I invert the idea and say that the organ is maintained ai its right size by natural selection, because this prevents increase beyond the size which is best for the organism. Every organ should be in due proportion, and the welfare of the creature as a whole is interfered with by excess as well as by defect. It may be directly interfered with — as for instance by too big an eyelid ; and it may be indi rectly interfered with, where the organ is large, by needless weight and cost of nutrition. In the second place the question which here concerns us is not what natural selection will do with variations. We are concerned with the previous question — What variations will arise ? An organ varies in all ways ; and, unless reason to the contrary is shown, the assumption must be that variations in the direction of increase are as frequent and as great as those in the direction of decrease. Take the case of the tongue. Certainly there arc tongues inconveniently large, and probably tongues inconveniently small. What reason have we for assuming that the inconveniently small tongues occur more frequently than the inconveniently large ones? None that I can see. Dr. Romanes has not shown that when natural selection ceases to act on an organ the minus variations in each new generation will exceed the/>/«.s variations. Uut if they are equal the alleged process of pan mixia has no place. 668 APPENDIX B. Though the counter-opinion of one who is not a naturalist (as Professor Weismann points out) may be of relatively small value, yet I must here again give it, along with a final reason for it. And this reason shall be exhibited, not in a qualitative form, but in a quantitative form. Let us quantify the terms of the hypothesis by weights ; and let us take as our test case the rudi mentary hind-limbs of the whale. Zoologists are agreed that the whale has been evolved from a mammal which took to aquatic habits, and that its disused hind-limbs have gradually disappeared. When they ceased to be used in swimming, natural selection played a part — probably an important part — in decreas ing them ; since, being then impediments to movement through the water, they diminished the attainable speed. It may be, too, that for a period after disappearance of the limbs beneath the skin, survival of the fittest had still some effect. But during the bitter stages of the process it had no effect ; .since the rudiments caused no inconvenience and entailed no appreciable cost. Here, therefore, the cause, if Professor Weismann is right, must have been panmixia. Dr. Struthers, Professor of Anatomy at Aber deen, whose various publications show him to be a high, if not the highest, authority on the anatomy of these great cetaceans, has kindly taken much trouble in furnishing me with the need ful data, based upon direct weighing and measuring and estima tion of specific gravity. In the Black Whale (Balcenoptcra borealis) there are no rudiments of hind-limbs whatever : rudiments of the pelvic bones only remain. A sample of the Greenland Right Whale, estimated to weigh 44,800 Ibs., had femurs weighing together 3^ ozs. ; while a sample of the Razor-back Whale (Balcenoptera musculus), 50 feet long, and estimated to weigh 56,000 Ibs., had rudimentary femurs weighing together one ounce ; so that these vanishing remnants of hind-limbs weighed but one- 896,000th part of the animal. Now in considering the alleged degeneration by panmixia, we have first to ask why these femurs must be supposed to have varied in the direction of decrease rather than in the direction of increase. During its evolution from the original land-mammal, the whale has grown enormously, implying habitual excess of nutrition. Alike in the embryo and in the growing animal, there must have been a chronic plethora. Why, then, should we suppose these rudiments to have become smaller ? Why should they not have enlarged by deposit in them of superfluous materials ? But let us grant the unwarranted assumption of predominant minus variations. Let us say that the last variation was a reduction of one-half — that in some in dividuals the joint weight of the femurs was suddenly reduced from two ounces to one ounce — a reduction of one-900, 000th of the creature's weight. By inter-crossing with those inheriting INADEQUACY OP NATURAL SELECTION, ETC. 009 the variation, the reduction, or a part of the reduction, was made a trait of the species. Now, in the first place, a necessary im plication is that this minus variation was maintained in posterity. So far from having reason to suppose this, we have reason to suppose the contrary. As before quoted, Mr. Darwin says that " unless carefully preserved by man," " any particular varia tion would generally be lost by crossing, reversion, and the acci dental destruction of the varying individuals." * And Mr. Galton, in his essay on •' Regression towards Mediocrity," f contends that not only do deviations of the whole organism from the mean size tend to thus disappear, but that deviations in its components do 80. Hence the chances are against such minus variation being so preserved as to affect the species by panmixia. In the second place, supposing it to be preserved, may we reasonably assume that, by inter-crossing, this decrease, amounting to about a millionth part of the creature's weight, will gradually affect the constitutions of all Razor-back Whales distributed over the Arctic seas and the North Atlantic Ocean, from Greenland to the Equa tor ? Is this a credible conclusion ? For three reasons, then, the hypothesis must be rejected. Thus, the only reasonable interpretation is the inheritance of acquired characters. If the effects of use and disuse, which are known causes of change in each individual, influence succeeding individuals — if functionally-produced modifications of structure are transmissible, as well as modifications of structure otherwise arising — then this reduction of the whale's hind limbs to minute rudiments is accounted for. The cause has been unceasingly operative on all individuals of the species ever since the trans formation began. In one case see all. If this cause has thus operated on the limbs of the whale, it lias thus operated in all creatures on all parts having active functions. At the outset I intimated that I must limit my replies to those arguments of Professor Weismann which are contained in his first article. That those contained in his second might be dealt with no less effectually, did time and space permit, is mani fest to me ; but about the probability of this the reader must form his own judgment. My replies thus far may be summed up as follows : — Professor Weismann says he has disproved the conclusion that degeneration of the little toe has resulted from inheritance of ac quired characters But his reasoning fails against an interpre tation he overlooks. A profound modification of the hind limbs * The Variation of Ann/mix ut as the primary variations in the phyletic metamor phosis occurred little by little, the secondary adaptations would probably as a rule be able to keep pace with them. Time would thus be gained till, in the course of generations, by constant selection of those germs the primary constituents of which are best suited to one another, the greatest possible degree of harmony may be reached, and consequently a definitive metamor phosis of the species involving all the parts of the individual may occur '' (p. 19). The connecting sentences, along with those which precede and succeed, would not, if quoted, give to the reader clearer conceptions than these by themselves give. But when dis entangled from Professor Weismann's involved statements, the essential issues are, T think, clear enough. In the case of the stag, that daily working together of the numerous nerves, muscles, and bones concerned, by which they are adjusted to the carrying and using of somewhat heavier horns, produces on them effects which, as I hold, are inheritable, but which, as Professor Weis- mann holds, are not inheritable. If they are not inheritable, what must happen ? A fawn of the next generation is born witli no such adjustment of nerves, muscles and bones as had been produced by greater exercise in the parent, and with no tendency to such adjustment. Consequently if, in successive generations, the horns go on enlarging, all these nerves, muscles, and bones, remaining of the original sixes, become utterly inadequate. The result is loss of life : the process of adaptation fails. " No," says Professor Weismann, " we inust conclude that the germ-plasm has varied in the needful manner." How so ? The process of " intra-individual selection," as he calls it, can have had no effect, since the cells of the soma cannot influence the reproductive cells. In what way, then, has the germ-plasm gained the characters required for producing simultaneously all these modified co operative parts. Well, Professor Weismann tells us merely that we must suppose that the germ-plasm acquires a certain sensitive ness such as gives it a proclivity to development in the requisite ways. How is such proclivity obtainable ? Only by having a multitude of its "determinants" simultaneously changed in fit modes. Emphasi/ing the fact that even a small failure in any 678 APPENDIX B. one of the co-operative parts may be fatal, as the sprain of an over-taxed muscle shows us, I alleged that the chances are infinity to one against the needful variations taking place at the same time. Divested of its elaboration, its abstract words and tech nical phrases, the outcome of Professor Weismann's explanation is that he accepts this, and asserts that the infinitely improbable thing takes place ! Either his argument is a disguised admission of the inheritable- ness of acquired characters (the effects of " intra-selcction ") or else it is, as before, the assumption of a fortuitous concourse of favourable variations in the determinants — " a fortuitous con course of atoms." Leaving here this main issue, I return now to that collateral issue named on a preceding page as being postponed — whether the neuters among social insects result from specially modified germ-plasms or whether they result from the treatment received during their larval stages. For the substantiation of his doctrine Professor Weismann is obliged to adopt the first of these alternatives; and in his Komancs Lecture he found it needful to deal with the evidence 1 brought in support of the second alternative. He says that " poor feeding is not the causa efficiens of sterility among bees, but is merely the stimulus which not only results in the formation of rudimentary ovaries, but at the same time calls forth all the other distinctive characters of the workers" (pp. 29—30); and he says this although he has in preceding lines admitted that it is " true of all animals that they reproduce only feebly or not at all when badly and insufficiently nourished : " a known cause being thus displaced by a supposed cause. But Professor Weismann pro ceeds to justify his interpretation by experimentally-obtained evidence. He " reared large numbers of the eggs of a female blow-fly " ; the larvffi of some he fed abundantly, but the larvae of others sparingly ; and eventually he obtained from the one set flies of full size, and from the other small flies. Nevertheless the small flies were fertile, as well as the others. Here, then, was proof that innutrition had not produced infertility ; and he contends that therefore among the neuter social insects, infertility has not resulted from innutrition. The argument seems strong, and to many will appear conclusive ; but there are two differences which entirely vitiate the comparison Professor Weismann institutes. One of them has been pointed out by Mr. Cunningham. In the case of the blow-fly the food supplied to the larvae though different in quantity was the same in quality ; in the case of the social insects the food supplied, whether or not different in INADEQUACY OF NATURAL SELECTION, ETC. 679 quantity, differs in quality. Among bees, wasps, ants, &c., the larvae of the reproductive forms are fed upon a more nitrogenous food than are the larvae of the workers ; whereas the two sets of larvae of the blow-fly, as fed by Professor Weismann, were alike supplied with highly nitrogenous food. Hence there did not exist the same cause for non-development of the reproductive organs. Here, then, is one vitiation of the supposed parallel. There is a second. While the development of an embryo follows in a rude way the phyletic metamorphoses passed through by its ancestry, the order of development of organs is often gradually modified by the needs of particular species : the structures being developed in such order as conduces to self-sustentation and the welfare of offspring. Among other results there arise differences in the relative dates of maturity of the reproductive system and of the other systems. It is clear, a priori, that it must be fatal to a species if offspring are habitually produced before the conditions requisite for their survival are fulfilled. And hence, if the life is a complex one, and the care taken of offspring is great, repro duction must be much longer delayed than where the life is simple and the care of offspring absent or easy. The contrast between men and oxen sufficiently illustrates this truth. Now the sub ordination of the order of development of parts to the needs of the species, is conspicuously shown in the contrast between these two kinds of insects which Professor Weismann compares as though their requirements were similar. What happens with the blow fly ? If it is able to suck up some nutriment, to fly toler ably, and to scent out dead flesh, various of its minor organs may be more or less imperfect without appreciable detriment to the species : the eggs can be laid in a fit place, and that is all that is wanted. Hence it profits the species to have the repro ductive system developed comparatively early — in advance, even, of various less essential parts. Quite otherwise is it with social insects, which take such remarkable care of their young ; or rather to make the case parallel — quite otherwise is it with those types from which the social insects have descended, bringing into the social state their inherited instincts and constitutions. Con sider the doings of the mason-wasp, or mason-bee, or those of the carpenter-bee. What, in these cases, must the female do that she may rear members of the next generation ? There is a fit place for building or burrowing to be chosen ; there is the collecting together of grains of sand and cementing them into a strong and water-proof cell, or there is the burrowing into wood and there building several cells ; there is the collecting of food to place along with the eggs deposited in these cells, solitary or associated, including that intelligent choice of small caterpillars which, dis- 44 680 APPENDIX B. covered and carried home, are carefully packed away and hypno tized by a sting, so that they may live until the growing larva hashed of them. For all these proceedings there have to be provided the n't external organs — cutting instruments, &c., and the tit internal organs — complicated nerve-centres in which are located these various remarkable instincts, and ganglia by which these delicate operations have to be guided. And these special structures have, some if not all of them, to be made perfect and brought into efficient action before egg-laying takes place. Ask what would happen if the reproductive system were active in advance of these ancillary appliances. The eggs would have to be laid without protection or food, and the species would forth with disappear. And if that full development of the reproduc tive organs which is marked by their activity, is not needful until these ancillary organs have come into play, the implication, in conformity with the general law above indicated, is that the per fect development of the reproductive organs will take place later than that of these ancillary organs, and that if innutrition checks the general development, the reproductive organs will be those which chiefly suffer. Hence, in the social types which have descended from these solitary types, this order of evolution of parts will be inherited, and will entail the results I have inferred. If only deductively reached, this conclusion would, I think, be fully justified. But now observe that it is more than deductively reached. It is established by observation. Professor Riley, Ph.D., late Government Entomologist of the United States, in his annual address as President of the Biological Society of Wash ington,* on January 29, 1894, said : — " Among the more curious facts connected with these Termites, because of their exceptional nature, is the late development of the internal sexual organs in the reproductive forms." (p. 34.) Though what has been shown of the Termites has not been shown of the other social insects, which belong to a different order, yet, considering the analogies between their social states and between their constitutional requirements, it is a fair infer ence that what holds in the one case holds partially, if not fully, in the other. Should it be said that the larval forms do not pass into the pupa state in the one case as they do in the other, the answer is that this does not affect the principle. The larva carries into the pupa state a fixed quantity of tissue-forming material for the production of the imago. If the material is sufficient, then a complete imago is formed. If it is not sufficient, then, while the earlier formed organs are not affected by the deficiency, the deficiency is felt when the latest formed organs , come to be developed, and they are consequently imperfect. * Procccdiiiys of the Uiologica1 Socicfy of Washington, vol. ix. INADEQUACY OF NATURAL SELECTION, ETC. 681 Even if left without reply, Professor Weismann's interpreta tion commits him to some insuperable difficulties, which I must now point out. Unquestionably lie has " the courage of his opinions ; " and it is shown throughout this collateral discussion as elsewhere. He is compelled by accumulated evidence to admit " that there is only one kind of egg from which queens and workers as well as males arise." * But if the production of one or other form from the same germ does not result from speciality of feeding, what does it result from ? Here is his reply : — " We must rather suppose that the primary constituents of two distinct reproductive systems — eg, those of the queen and worker — are contained in the germ-plasm of the egg." f " The courage of his opinions," which Professor Weismann shows in this assumption, is, however, quite insufficient. For since he himself has just admitted that there is only one kind of egg for queens, workers, and males, he must at any rate assume three sets of " determinants." (1 find that on a subsequent page he does so.) But this is not enough, for there are, in many cases, two if not more kinds of workers, which implies that four sets of determinants must co-exist in the same egg. Even now we have not got to the extent of the assumption required. In the address above referred to on " Social Insects from Psychical and Evolutional Points of View," Professor Riley gives us (p. 33) the— Forms in a Termca Colony under Normal Conditions. 1. Youngest larvae. 2. Larvae [of those] unfit 3. Larv;e [that will be] fit for reproduction. for reproduction. 4. Larva; of 5. Larva? of 8. Nymphs of 1st 9. Nymphs of 2nd workers. soldiers. form. form. 6. Workers. 7. Soldiers. 10. Winged forms. 11. True royal pairs. Hence as, in this family tree, the royal pair includes male and female, it results that there are jive different adult forms (Grass! says there are two others) arising from like eggs or larvie ; and Professor Weismann's hypothesis becomes proportionately com plicated. Let us observe what the complications are. It often happens in controversy — metaphysical controversy more than any other — that propositions are accepted without their terms having been mentally represented. In public pro ceedings documents are often " taken as Tead," sometimes with mischievous results ; and in discussions propositions arc often * Iloma:ies Lecture, p. 2'J. f Ibid., p. 35. 682 APPENDIX B. taken as thought when they have not been thought and cannot be thought. It sufficiently taxes imagination to assume, as Pro fessor Weismann does, that two sets of " ids " or of " determi nants " in the same egg are, throughout all the cell-divisions which end in the formation of the morula, kept separate, so that they may subsequently energize independently ; or that if they are not thus kept separate, they have the power of segregating in the required ways. But what are we to say when three, four, and even five sets of " ids " or bundles of " determinants " are present ? How is dichotomous division to keep these sets dis tinct ; or if they are not kept distinct, what shall we say to the chaos which must arise after many fissions, when each set in con flict with the others strives to produce its particular structure ? And how are the conquering determinants to find they ways out of the melee to the places where they are to fulfil their organizing functions ? Even were they all intelligent beings and each had a map by which to guide his movements, the problem would be sufficiently puzzling. Can we assume it to be solved by uncon scious units ? Thus even had Professor Weismann shown that the special structures of the different individuals in an insect-community are not due to differences in the nurtures they receive, which he has failed to do, he would still be met by this difficulty in the way of his own view, in addition to the three other insuperable difficul ties grouped together in a preceding section. The collateral issue, which has occupied the largest space in the controversy, has, as commonly happens, begotten a second generation of collateral issues. Some of these are embodied in the form of questions put to me, which I must here answer, lest it should be supposed that they are unanswerable and my view therefore untenable. In the notes he appends to his Romanes Lecture, Professor Weismann writes : — " One of the questions put to Spencer by Ball is quite sufficient to show the utter weakness of the position of tiamarckism : — if their characteristics did not arise among the workers themselves, but were transmitted from the pre-social time, how does it happen that the queens and drones of every generation can give anew to the workers the characteristics which they them selves have long ago lost ? " (p. 68). It is curious to see put forward in so triumphant a manner, by a professed naturalist, a question so easily disposed of. I answer it by putting another. How does it happen that among those moths of which the female has but rudimentary wings, she con tinues to endow the males of her species with wings ? How does it happen, for example, that among the Geomctridcc, the peculiar INADEQUACY OF NATURAL SELECTION, ETC. 683 structures and habits of which show that they have all descended from a common ancestor, some species have winged females and some wingless females; and that though they have' lost the wings the ancestral females had, these wingless females convey to the males the normal developments of wings ? Or, still better, how is it that in the Psychidce there are apterous worm-like females, which lay eggs that bring forth winged males of the ordinary imago form ? If for males we read workers, the case is parallel to the cases of those social insects, the queens of which bequeath characteristics they have themselves lost. The ordinary facts of embryonic evolution yield us analogies. What is the most com mon trait in the development of the sexes ? When the sexual organs of either become pronounced, the incipient ancillary organs belonging to the opposite sex cease to develop and remain rudi ments, while the organs special to the sex, essential and non- essential, become fully developed. What, then, must happen with the queen-ant, which, through countless generations, has ceased to use certain structures and has lost them from disuse ? If one of the eggs which she lays, capable, as Professor Weis- mann admits, of becoming queen, male, or worker of one or other kind, does not at a certain stage begin actively to develop its re productive system, then those organs of the ancestral or pre-social tvpe which the queen has lost begin to develop, and a worker results. Another difficulty in the way of my view, supposed to be fatal, is that presented by the Iloney-ants — aberrant members of certain ant-colonies which develop so enormously the pouch into which the food is drawn, that the abdomen becomes little else than a great bladder out of which the head, thorax, and legs protrude. This, it is thought, cannot be accounted for otherwise than as a consequence of specially endowed eggs, which it has become profitable to the community for the queen to produce. But the explanation fits in quite easily with the view I have set forth. No one will deny that the taking in of food is the deepest of vital requirements, and the correlative instinct a dominant one ; nor will any one deny that the instinct of feeding young is less deeply seated — comes later in order of time. So, too, every one will admit that the worker-bee or worker-ant before regurgitat ing food into the mouth of a larva must first of all take it in. Hence, alike in order of time and necessity, it is to bo assumed that development of the nervous structures which guide self- nutrition, precedes development of the nervous structures which guide the feeding of larvae. What, then, will in some cases happen, supposing there is an arrested development consequent on innutrition ? It will in some cases happen that while the nervous centres prompting and regulating deglutition are fully 684 APPENDIX B. formed, the formation of those prompting and regulating the regurgitation of the food into the mouths of larvae are arrested. What will be the consequence ? The life of the worker is mainly passed in taking in food and putting it out again. If the putting out is stopped its life will be mainly passed in taking in food. The receptacle will go on enlarging and it will eventually assume the monstrous form that we see.* Here-, however, to exclude misinterpretations, let me explain. I by no means deny that variation and selection have produced, in these insect-communities, certain effects such as Mr. Darwin suggested. Doubtless ant-queens vary ; doubtless there are varia tions in their eggs ; doubtless differences of structure in the re sulting progeny sometimes prove advantageous to the stirp, and originate slight modifications of the species. But such changes, legitimately to be assumed, arc changes in single parts — in single organs or portions of organs. Admission of this does not in volve admission that there can take place numerous correlated variations in different and often remote parts, which must take place simultaneously or else be useless. Assumption of this is what Professor Weismann's argument requires, and assumption of this we have seen to be absurd. Before leaving the general problem presented by the social insects, let me remark that the various complexities of action not explained by inheritance from pre-social or semi-social types, are probably due to accumulated and transmitted knowledge. I recently read an account of the education of a butterfly, carried to the extent that it became quite friendly with its protector and would come to be fed. If a non-social and relatively unin telligent insect is capable of thus far consciously adjusting its actions, then it seems a reasonable supposition that in a com munity of social insects there has arisen a mass of experience and usage into which each new individual is initiated ; just as happens among ourselves. We have only to consider the chaos which would result were we suddenly bereft of language, and if the young were left to grow up without precept and example, to see that very probably the polity of an insect community is made possible by the addition of intelligence to instinct, and the trans mission of information through sign-language. There remains now the question of panmixia, which stands exactly where it did when I published the "Eejoinder to Pro fessor Weismann." * This interpretation harmonizes with a fact which I learn from Prof. Kiley, that there are gradations in this development, and that in some species the ordinary neuters swell their abdomens so greatly with food that they can hardly get home. INADEQUACY OP NATURAL SELECTION, ETC. 685 After showing that the interpretation I put upon his view was justified by certain passages quoted ; and after pointing out that one of his adherents had set forth the view which I, combated — if 'not as his view yet as supplementary to it ; I went on to criti cize the view as set forth afresh by Professor Weismann himself. 1 showed that as thus set forth the actuality of the supposed cause of decrease in disused organs, implies that minus variations habitually exceed plus variations — in degree or in number, or in both. Unless it can be proved that such an excess ordinarily occurs, the hypothesis of panmixia has no place ; and I asked, where is the proof that it occurs. No reply. Not content with this abstract form of the question I put it also in a concrete form, and granted for the nonce Professor Weismann's assumption : taking the case of the rudimentary hind limbs of the whale. I said that though, during those early stages of decrease in which the disused limbs were external, natural selection probably had a share in decreasing them, since they were then impediments to locomotion, yet when they became internal, and especially when they had dwindled to nothing but remnants of the femurs, it is impossible to suppose that natural selection played any part : no whale could have survived and initiated a more prosperous stirp in virtue of the economy, achieved by such a decrease. The operation of natural selection being out of the question, I inquired whether such a decrease, say of one-half when the femurs weighed a few ounces, occurring in one individual, could be supposed in the ordinary course of reproduction to affect the whole of the whale species inhabiting the Arctic Seas and the North Atlantic Ocean ; and so on with successive diminutions until the rudiments had reached their present minuteness. Tasked whether such an interpretation could be rationally entertained. No reply. Now in the absence of replies to these two questions it seems to me that the verdict must go against Professor Weismann by default. If he has to surrender the hypothesis of panmixia, what results? All that evidence collected by Mr. Darwin and others, regarded by them as proof of the inheritance of acquired charac ters, which was cavalierly set aside on the strength of this alleged process of panmixia, is reinstated. And this reinstated evidence, joined with much evidence since furnished, suffices to establish the repudiated interpretation. In the printed report of his Romanes Lecture, after fifty pages of complicated speculations which we are expected to accept as proofs, Professor Weismann ends by saying, in reference to thu case of the neuter insects : — 686 APPENDIX B. " This case is of additional interest, as it may serve to convince those naturalists who are still inclined to maintain that acquired characters are inherited, and to support the Lamarckian principle of development, that their view cannot be the right one. It has not proved tenable in a single instance " (p. 54). Most readers of the foregoing pages will think that since Pro fessor Weismann has left one after another of ray chief theses without reply, this is rather a strong assertion ; and they will still further raise their eyebrows on remembering that, as I have shown, where he has given answers his answers are invalid. And now we come to the additions which I indicated at the outset as having to be made — certain evidences which have come to light since this controversy commenced. When, by a remenrbered observation made in boyhood, joined with the familiar fact that worker-larvae can be changed into the larvae of queens by feeding, I was led to suggest that probably all the variations of form in the social insects are consequent on differences of nurture, I was unaware that observations and experiments were being made which have justified this suggestion. Professor Grassi has recently published accounts of the food- habits of two European species of Termites, shewing that the various forms are due to feeding, lie is known to be a most careful observer, and some of the most curious of his facts are confirmed by the collection of white ants exhibited by Dr. David Sharp, F.R.S., at the soiree of the Royal Society in May last. He has favoured me with the following account of Grassi's results, which I publish with his assent : — "There is great variety as to the constituents of the community and economy of the species in White Ants. One of the simplest conditions known is that studied by Grassi in the case of the European species Calotermes flavi- collis. In this species there is no worker caste ; the adult forms are only of two kinds, viz., soldiers, and the males and females ; the sexes are externally almost indistinguishable, and there are males and females of soldiers as well as of the winged forms, though the sexual organs do not undergo their full development in any soldier whether male or female. " The soldier is not however a mere instance of simple arrested develop ment. It is true that there is in it arrested development of the sexual organs, but this is accompanied by change of form of other parts — changes so extreme that one would hardly suppose the soldier to have any connection with either the young or the adult of the winded forms. " Now according to Grassi the whole of the individuals when born are undifferentiated forms (except as to sex), and each one is capable of going on the natural course of development and thus becoming a winged insect, or can be deviated from this course and made into a soldier ; this is accomplished by the White Ants by special courses of feeding. " The evidence given by Grassi is not conclusive as to the young beincc all born alike ; and it may be that there are some individuals born that could not be deviated from the natural course and made into soldiers. But there is one case which seems to show positively that the deviation Grassi believes INADEQUACY OF NATURAL SELECTION, ETC. G87 X to occur is real, and not due to the selection by the ants of an individual that though appearing to our eyes undifferentiated is not really so. This is that an individual can be made into a soldier after it has visibly undergone one half or more of the development into a winged form. The Termites can in fact operate on an individual that has already acquired the rudi ments of wings and whose head is totally destitute of any appearance of the shape of the armature peculiar to the soldier, and can turn it into a soldier ; the rudiments of the wings being in such a case nearly entirely re-absorbed." Grass! has been for many years engaged in investigating these phenomena, and there is no reason for rejecting his statement. We can scarcely avoid accepting it, and if so, Professor Weis- mann's hypothesis is conclusively disposed of. Were there different sets of " determinants " for the soldier-form and for the winged sexual form, those " determinants " which had gone a long way towards producing the winged sexual form, would in evitably go on to complete that form, and could not have their proclivity changed by feeding. [Yet more evidence to the like effect has since become known. At the meeting of the Entomological Society, on March 14, 1894 (reported in Nature, March 29) : — "Dr. ]). Sharp, F.K.S., exhibited a collection of white ants ( Termites), formed by Mr. G. D. Ilaviland in Singapore, whieh comprised about twelve species, of most of which the various forms were obtained. Lie said that Prof. Grassi had recently made observations on the European species, and had brought to light some important particulars ; and also that in the discussion that had recently been carried on between Mr. Herbert Spencer and Prof. Weismann, the former had stated that in his opinion the different forms of social insects were produced by nutrition. Prof. Grassi's observations showed this view to be correct, and the specimens now exhibited confirmed one of the most important points in his observations. Dr. Sharp also stated that Mr. Haviland found in one nest eleven neotcinic queens — that is to say, individu als having the appearance of the queen in some respects, while in others they are still immature." Another similarly conclusive verification I published in Nature for December 6, 1894, under the title "The Origin of Classes among the ' Parasol ' Ants." The letter ran as follows : — "Mr. J. H. Hart is Superintendent of the Royal Botanic Gardens in Trini dad. He has sent me a copy of his report presented to the Legislative Coun cil in March, 1893, and has drawn my attention to certain facts contained in it concerning the 'Parasol' ants — the leaf-cutting ants which feed on the i'ungi developed in masses of the cut leaves carried to their nests. Both Mr. » Bates and Mr. Belt described these ants, but described, it seems, different, though nearly allied, species, the habits of which are partially unlike. As they are garden-pests, Mr. Hart was led to examine into the development and social arrangements of these :n\t<; establishing, to that end, artificial nests, after the manner adopted by Sir John Luhboek. Several of the facts set down have an important bearing on a question now under discussion. The following extracts, in which they are named, I abridge by omitting passages not relevant to the issue : " ' The history of my uc^tj is as follows : Nos. 1 and 2 were both takeii 688 APPENDIX B. (August 0) on the same day, while destroying nests in the Gardens, and were portions of separate nests but of the same species. No. 3 was procured ou September 5, and is evidently a different although an allied species to Nos. 1 and 2. " ' Finding neither of my nests had a queen, I procured one from another nest about to be destroyed, and placed it with No. 1 nest. It was received by the workers, and at once attended by a numerous retinue in royal style. On August 30 I removed the queen from No. 1 and placed it with No. 2, when it was again received in a most loyal manner. . . ' . " 'Ants taken from Nos. 1 and 2 and placed with No. 3 were immediately destroyed by the latter, and even the soldiers of No. 3, as well as workers or nurses, were destroyed when placed with Nos. 1 and 2. " ' In nest No. 2, from which I removed the queen on August 30, there arc now in the pupa stage several queens and several males. The forms of ant in nests Nos. 1 and 2 are as follows : (a) queen, (b) male (both winged, but the queen loses its wings after marital flight), (c) large workers, (d) small workers, and (c) nurses. In nest No. 3 I have not yet seen the queen or male, but it possesses— (a) soldier, (7>) larger workers, (c) smaller workers, and (d) nurses; but these are different in form to those of nests No. 1 and No. 2. Probably we might add a third form of worker, as there are several sizes in the nest. . . . '"It is curious that in No. 1 nest, from which the queen was removed on August 30, new queens and mal.es are now being developed, while in No. 2 nest, where the queen is at present, nothing but workers have been brought out, and if a queen larva or pupa is placed there it is at once destroyed, while worker larvae or pupae are amicably received. In No. 3 all the eg^s, larvae, and pupae collected with the nest have been hatched, and no eggs have since made their appearance to date. There is no queen with this nest. . . . On November 14 I attempted to prove by experiment how small a number of " parasol " ants it required to form a new colony. I placed two dozen of ants (one dozen workers and one dozen nurses) in two separate nests, No. 4 and No. 5. With No. 4 I placed a few larvae with a few rose petals for them to manipulate. With No. 5 I gave a small piece of nest covered with mycelium. On the 16th these nests were destroyed by small foraging ants, known as the " sugar " or " meat " ant, and I had to remove them and replace with a new colony. My notes on these are not sufficiently lengthy to be of much im portance. But I noted four eggs laid on the "l6th, or two days after being placed in their new quarters ; no queen being present. The experiment is bc'ing continued. I may mention that in No. 4 nest, in which no fungus was present, the larvae of all sizes appeared to change into the pupa) stage at once for want of food [a fact corresponding with the fact I have named as observed by myself sixty years ago in the case of wasp larvae]. The circumstance tends to show that the development of the insect is influenced entirely by the feed ing it gets in the larva stage. " ' In nest No. 2 before the introduction of a queen there were no eggs or larvae. The first worker was hatched on October 27, or fifty-seven days after wards, and a continual succession has since been maintained, but as yet (November 19) no males or queens have made their appearance.' " In a letter accompanying the report, Mr. Hart says : — " ' Since these were published, my notes go to prove that ants can practi cally manufacture at will, male, female, soldier, worker, or nurse. Some of the workers are capable of laying eggs, and from these can be produced all the various forms as well as from a queen's egg. "'There does not, however, appear to be any difference in the character of the food ; as I cannot find that the larger larvae are fed with anything differ ent to thai given to the smaller.' INADEQUACY OP NATURAL SELECTION, ETC. 689 " These results were obtained before the recent discussion of the question commenced, and joined with the other evidence entirely dispose of those arguments which Prof. Weismann bases on i'acts furnished by the social insects."] The other piece of additional evidence I have referred to, is furnished by two papers contributed to The Journal of Anatomy and Physiology for October 1893 and April 1894, by K. Havelock Charles, M. D., &c. &c., Professor of Anatomy in the Medical College, Lahore. These papers set forth the differences between the leg-bones of Europeans and those of the Punjaub people — differences caused by their respective habits of sitting in chairs and squatting on the ground, lie enumerates more than twenty such differences, chiefly in the structures of the knee-joint and ankle-joint. From the resume of his second paper I quote the following passages, which sufficiently show the data and the in ferences : — " 7. The habits as to sitting postures of Europeans differ from those of their prehistoric ancestors, the Cave-dwellers, &c., who probably squatted on the ground. " 8. The sitting postures of Orientals are the same now as ever. They have retained the habits of their ancestors. The Europeans have not done so. " 9. Want of use would induce changes in form and size, and so, gradually, small differences would be integrated till there would be total disappearance of the markings on the European skeleton, as no advantage would accrue to him from the possession of facets on his bones fitting them for postures not practised by him. " 10. The facets seen on the bones of the Panjabi infant or footus have been transmitted to it by the accumulation of peculiarities gained by habit in the evolution of its racial type— in which an acquisition having become a per manent possession, ' profitable to the individual under its conditions of life,' is transmitted as a useful inheritance. " 11. These markings are due to the influence of certain positions, which are brought about by the use of groups of muscles, ami they are the definite results produced by actions of these muscles. " 12. The effects of the use of the muscles mentioned in No. 11 are trans mitted to the offspring, for the markings are present in the fcelm-in-utero, in the child at birth, and in the infant. "13. .The markings arc instances of the transmission of acquired charac ters, which heritage in the individual, function subsequently develops." No other conclusion appears to me possible. Panmixia, even were it not invalidated by its unwarranted assumption as above shown, would be out of court : the case is not a case of either increase or decrease, of size but of numerous changes of form. Simultaneous variation of co-operative parts cannot be alleged, since these co-operative parts have not changed in one way but in various ways and degrees. And even were it permissible to suppose that the required different variations had taken place simultaneously, natural selection cannot be supposed to have operated. The assumption would imply that in the struggle for 690 APPENDIX B. existence, individuals of the European races who were less capable than others of crouching and squatting, gained by those minute changes of structure which incapacitated them, such advantages that their stirps prevailed over other stirps — an absurd suppo sition. And now I must once more point out that a grave responsi bility rests on biologists in respect of the general question ; since wrong answers lead, among other effects, to wrong beliefs about social affairs and to disastrous social actions. In me this convic tion has unceasingly strengthened. Though The Origin of Species proved to me that the transmission of acquired characters cannot be the sole factor in organic evolution, as I had assumed in So cial Statics and in The Principles of Biology, published in pre- Darwinian days, yet I have never wavered in the belief that it is a factor and an all-important factor. And 1 have felt more and more that since all the higher sciences are dependent on the science of life, and must have their conclusions vitiated if a fun damental datum given to them by the teachers of this science is erroneous, it behoves these teachers not to let an erroneous datum pass current : they are called on to settle this vexed question one way or other. The times give proof. The work of Mr. Benjamin Kidd on Social Evolution, which has been so much lauded, takes Weismannism as one of its data ; and if Weismannism be untrue, the conclusions Mr. Kidd draws must be in large measure erro neous and may prove mischievous. POSTSCRIPT. — Since the foregoing pages have been put in type there has appeared in Natural Science for September, an abstract of certain parts of a pamphlet by Professor Oscar Hertwig, set ting forth facts directly bearing on Professor Weismann's doctrine respecting the distinction between reproductive cells and somatic cells. In The Principles of Biology, § 77, I contended that repro ductive cells differ from other cells composing the organism, only in being unspecialized. And in support of the hypothesis that tissue-cells in general have a reproductive potentiality, I instanced the cases of the Begonia, phyllomaniaca and Malaxis paludosa. In the thirty years which have since elapsed, many facts of like sig nificance have been brought to light, and various of these are given by Professor Hertwig. Here are some of them : — " Galls are produced under the stimulus of the insect almost anywhere on the surface of a plant. Yet in most cases these galls, in a sense grown at random on the surface of a plant, when placed in damp earth will give rise to a young plant. In the hydroid Tubularia mescmbri/anthcmum, when the polyp-heads are cut off, new heads arise. But if both head and root be cut off, and the upper end be inserted in the mud, then from the original upner end not head-polyps but root filaments will arise, while from the original lower end iiot root filaments but head-polyps will grow. . . . INADEQUACY OF NATURAL SELECTION, ETC. 691 Dricsch, by separating the first two and the first four segmentation spheres of an EcMnu* ovum, obtained two or four normal plutei, respectively one half and a quarter of the normal size. ... So, also, in the case of Amphioxuft, Wilson obtained a normal, but proportionately diminished embryo with complete nervous system from a separated sphere of a two- or four- or eight celled stage. . . . Gliabry obtained noriral embryos in cases where some of the segmentation-spheres had been artificially de stroyed." These evidences, furnished by independent observers, unite in showing, firstly, that all the multiplying cells of the developing embryo are alike ; and, secondly, that the soma-cells of the adult severally retain, in a latent form, all the powers of the original embryo- cell. If these facts do not disprove absolutely Professor Weismann's hypothesis, we may wonderingly ask what facts would disprove it ? Since Hertwig holds that all the cells forming an organism of any species primarily consist of the same components, I at first thought that his hypothesis was identical with my own hypothesis of " physiological units," or, as 1 would now call them, constitu tional units. It seems otherwise, however ; for he thinks that each cell contains " only those material particles which are bearers of cell-properties," and that organs " are the functions of cell- complexes." To this it may be replied that the ability to form the appropriate cell-complexes, itself depends upon the constitu tional units contained in the cells. APPENDIX C. THE INHERITANCE OF FUNCTIONALLY-WROUGHT MODIFI CATIONS: A SUMMARY. THE assertion that changes of structure caused by changes of function are transmitted to descendants is continually met by the question — Where is the evidence ? When some facts arc assigned in proof, they are pooh-poohed as insufficient. If after a time the question is raised afresh and other facts are named, there is a like supercilious treatment of them. Successively rejected in this way, the evidences do not accumulate in the minds of opponents ; and hence produce little or no effect. When they are brought together, however, it turns out that they are numerous and weighty. We will group them into negative and positive. Negative evidence is furnished by those cases in which traits otherwise inexplicable are explained if the structural effects of use and disuse are transmitted. In the foregoing chapters and appendices three have been given. (1) Co-adaptation of co-operative parts comes first. This has been exemplified by the case of enlarged horns in a stag J" by the case of an animal led into the habit of leaping, and in the case of the giraffe (cited in " The Factors of Organic Evolution ") ; and it has been shown that the implied co-adaptations of parts cannot possibly have been effected by natural selection. (2) The possession of unlike powers of discrimination by dif ferent parts of the human skin, was named as a problem to be solved on the hyuothesis of natural selection or the hypothesis of panmixia; and it was shown that neither of these can by any twisting yield a solution. But the facts harmonize with the hypothesis that the effects of use are inherited. (3) Then come the cases of those rudimentary organs which, like the hind limbs of the whale, have nearly disappeared. Dwindling by natural selection is here out of the question ; and dwindling by panmixia, even were its assumptions valid, would be incredible. But as a sequence of disuse the change is clearly explained. Failure to solve any one of these three problems would, I think, INHERITANCE OF FUNCTIONALLY- WROUGHT CHANGES. 693 alone prove the Neo-Darwinian doctrines untenable ; and the fact that we have three unsolved problems seems to me fatal. From this negative evidence, turn now to the posith dence. This falls into several groups. There are first the facts collected by Mr. Darwin, implying functionally- altered structures in domestic animals. The hypo thesis of panmixia is, as we have seen, out of court ; and there fore Mr. Darwin's groups of evidences are reinstated. There is the changed ratio of wing-bones and leg-bones in the duck ; there are the drooping ears of cats in China, of horses in Russia, of sheep in Italy, of guinea-pigs in Germany, of goats and cattle in India, of rabbits, pigs, and dogs in all long-civilized countries. Though artificial selection has come into play where drooping has become a curious trait (as in rabbits), and has probably caused the greater size of ears which has in some cases gone along with diminished muscular power over them ; yet it could not have been the initiator, and has not been operative on animals bred for profit. Again there are the changes produced by climate ; as instance, among plants, the several varieties of maize estab lished in Germany and transformed in the course of a few gene rations. Facts of another class are yielded by the blind inhabitants of caverns.. One who studies the memoir by Mr. Packard on The Cave Fauna of North America, &c , will be astonished at the variety of types in which degeneration or loss of the eyes has become a concomitant of life passed in darkness. A great increase in the force of this evidence will be recognized on learn ing that absence or extreme imperfection of visual organs is found also in creatures living in perpetual night at the bottoms of deep oceans. Endeavours to account for these facts otherwise than by the effects of disuse we have seen to be futile. Kindred evidence is yielded by decrease of the jaws in those races which have had diminished use of them — mankind and certain domestic animals. Relative smallness in the jaws of civilized men, manifest enough on comparison, has been proved by direct measurement. In pet dogs — pugs, household spaniels — we find associated the same cause with the same effect. Though there has been artificial selection, yet this did not operate until the diminution had become manifest. Moreover there has been diminution of the other structures concerned in biting : there are smaller muscles, feeble zygomata, and diminished, areas for inser tion of muscles — traits which cannot have resulted from selec tion, since they are invisible in the living animal. In abnormal vision produced by abnormal use of the eyes we have evidence of another kind. That the Germans, among 694 APPENDIX C. whom congenital short sight is notoriously prevalent, have been made shortsighted by inheritance of modifications due to con tinual reading of print requiring close attention, is by some disputed. It is strange, however, that if there exists no causal connexion between them, neither trait occurs without the other elsewhere. But for the belief that there is a causal connexion we have the verifying testimony of oculists. From Dr. Lindsay Johnson I have cited cases within his professional experience of functionally-produced myopia transmitted to .children ; and he asserts that other oculists have had like experiences. Development of the musical faculty in the successive members of families from which the great composers have come, as well as in the civilized races at large, is not to be explained by natural selection. Even when it is great, the musical faculty has not a life-saving efficiency as compared with the average of faculties ; for the most highly gifted have commonly passed less prosperous lives and left fewer offspring than have those possessed of ordi nary abilities. Still less can it be said that the musical faculty in mankind at large has been developed by survival of the fittest. No one will assert that men in general have been enabled to survive and propagate in proportion as their musical appreciation was great. The transmission of nervous peculiarities functionally pro duced is alleged bv the highest authorities — Dr. Savage, presi dent of the Neurological Society, and Dr. Hughlings Jackson. The evidence they assign confirms, and is confirmed- by, that which the development of the musical faculty above named supplies. Here, then, we have sundry groups of facts directly support ing the belief that functionally-wrought modifications descend from parents to offspring. Now let us consider the position of those Darwinians who dis sent from Darwin, and who make light of all this evidence. We might natural] v suppose that their own hypothesis is unassailable. Yet, strange to say, they admit that there is no direct proof that any species has been established by natural selection. The proof is inferential only. The certainty of an axiom does not give certainty to the deductions drawn from it. That natural selection is, and always has been, operative is incontestable. Obviously I should" be the last person to .deny that survival of the fittest is a necessity : its negation is inconceivable. The Neo-Darwinians, however, judging from their attitude, apparently assume that firmness of the basis implies firmness of the superstructure. But however high may be the probability of some of the conclusions drawn, INHERITANCE OF FUNCTIONALLY-WROUGHT CHANGES. 095 none of them can have more than probability ; while some of them remain, and are likely to remain, very questionable. Ob serve the difficulties. (1) The general argument proceeds upon the analogy between natural selection and artificial selection. Yet all know that the first cannot do what the last does. Natural selection can do nothing more than preserve those of which the aggregate charac ters are most favourable to life. It cannot pick out those possessed of one particular favourable character, unless this is of extreme importance. (2) In many cases a structure is of no service until it has reached a certain development ; and it remains to account for that increase of it by natural selection which must be supposed to take place before it reaches the stage of usefulness. (3) Advantageous variations, not preserved in nature as they are by the breeder, are liable to be swamped by crossing or to disappear by atavism. Now whatever replies are made, their component propositions cannot be necessary truths. So that the conclusion in each case, however reasonable, cannot claim certainty : the fabric can have no stability like that of its foundation. When to uncertainties in the arguments supporting the hypo thesis we add its inability to explain facts of cardinal significance, as proved above, there is I think ground for asserting that natural selection is less clearly shown to be a factor in the origin ation of species than is the inheritance of functionally-wrought changes. If, finally, it is said that the mode in which functionally- wrought changes, especially in small parts, so affect the reproduc tive elements as to repeat themselves in offspring, cannot be imagined — if it be held inconceivable that those minute changes in the organs of vision which cause myopia can be transmitted through the appropriately-modified sperm-cells or germ-cells ; then the reply is that the opposed hypothesis presents a corre sponding inconceivability. Grant that the habit of a pointer was produced by selection of those in which an appropriate variation in the nervous system had occurred ; it is impossible to imagine how a slightly-different arrangement of a few nerve-cells and fibres could be conveyed by a spermatozoon. So too it is im possible to imagine how in a spermatozoon there can be conveyed the 480,000 independent variables required for the construction of a single peacock's feather, each having a proclivity towards its proper place. Clearly the ultimate process by which inheritance is effected in either case passes comprehension ; and in this respect neither hypothesis has an advantage over the other. 45 APPENDIX I). ON ALLEGED "SPONTANEOUS GENERATION," AND ON TEE HYPOTHESIS OF PHYSIOLOGICAL UNITS. [The following letter, originally written for publication in the North American Review, but declined by the Editor in pursuance of a general rule, and eventually otherwise published in the United States, / have thought well to append to this first volume of the Prin ciples of Biology. / do this because the questions which it discusses are dealt with in this volume ; and because the further explanations it furnishes seem needful to prevent misapprehensions.] The Editor of the North American Review. SIR, It is in most cases unwise to notice adverse criticisms. Either they do not admit of answers or the answers may be left to the penetration of readers. When, however, a critic's allegations touch the fundamental propositions of a book, and especially when they appear in a periodical having the position of the North Ameri can Review, the case is altered. For these reasons the article on " Philosophical Biology," published in your last number, demands from me an attention which ordinary criticisms do not. It is the more needful for me to notice it, because its two leading objections have the one an actual fairness and the other an apparent fairness ; and in the absence of explanations from me, they will be considered as substantiated even by many, or perhaps most, of those who have read the work itself — much more by those who have not read it. That to prevent the spread of misapprehensions I ought to say something, is further shown by the fact that the same two ob jections have already been made in England — the one by Dr. Child, of Oxford, in his Essays on Physiological Subjects, and the other by a writer in the Westminster Review for July, 1865. In the note to which your reviewer refers, I have, as he says, tacitly repudiated the belief in "spontaneous generation ;" and that I have done this in such a way as to leave open the door for the interpretation given by him is true. Indeed the fact that Dr. Child, whose criticism is a sympathetic one, puts the same con struction on this note, proves that your reviewer has but drawn what seems to be a necessary inference. Nevertheless, the infer ence is one which 1 did not intend to be drawn. In explanation, let me at the outset remark that I am placed at a disadvantage in having had to omit that part of the System of Phi losophy which deals with Inorganic Evolution. In the original pro gramme will be found a parenthetic reference to this omitted part, which should, as there stated, precede the Principles of Biology. ALLEGED SPONTANEOUS GENERATION, ETC. 697 Two volumes are missing. The doling chapter of the second, were it written, would deal with the evolution of organic matter — the step preceding the evolution of living forms. Habitually carrying^ with me in thought the contents of this unwritten chapter, I have, in some cases, expressed myself as though the reader had it before him ; and have thus rendered some of my statements liable to mis constructions. Apart from this, however, the explanation of the ap parent inconsistency is very simple, if not very obvious. In the first place, I do not believe in the "spontaneous generation " commonly alleged, and referred to in the note ; and so little have I associated in thought this alleged " spontaneous generation " which I disbe lieve, with the generation by evolution which I do believe, that the repudiation of the one never occurred to me as liable to be taken for repudiation of the other. That creatures having quite specific struc tures are evolved in the course of a few hours, without antecedents calculated to determine their specific forms, is to me incredible. Not onlv the established truths of Biology, but the established truths of science in general, negative the supposition that organisms having structures definite enough to identify them as belonging to known genera and species, can be produced in the absence of germs derived from antecedent organisms of the same genera and species. If there can suddenly be imposed on simple protoplasm the organi zation which constitutes it a Paramcecium, I see no reason why animals of greater complexity, or indeed of any complexity, may not be constituted after the same manner. In brief, I do not accept these alleged facts as exemplifying Evolution, because they imply something immensely beyond that which Evolution, as I understand it, can achieve. In the second place, my disbelief extends not only to the alleged cases of " spontaneous generation," but to every case akin to them. The very conception of spontaneity is wholly incon gruous with the conception of Evolution. For this reason I regard as objectionable Mr. Darwin's phrase "spontaneous variation" (as indeed he does himself) ; and I have sought to show that there are always assignable causes of variation. No form of Evolution, inorganic or organic, can be spontaneous ; but in every instance the antecedent forces must be adequate in their quantities, kinds, and distributions, to work the observed effects. Neither the al leged cases of " spontaneous generation," nor any imaginable cases in the least allied to them, fulfil this requirement. If, accepting these alleged cases of " spontaneous generation," I had assumed, as your reviewer seems to do, that the evolution of organic life commenced in an analogous way ; then, indeed, I should have left myself open to a fatal criticism. This supposed " spon taneous generation " habitually occurs in menstrua that contain either organic matter, or matter originally derived from organisms ; and such organic matter, proceeding in all known cases from or ganisms of a higher kind, implies the pre-existence of such higher 698 APPENDIX D. organisms. By what kind of logic, then, is it inferrible that organic life was initiated after a manner like that in which Infusoria are 4paid to be now spontaneously generated ? Where, before life com menced, were the superior organisms from which these lowest or ganisms obtained their organic matter ? Without doubting that there are those who, as the reviewer says, " can penetrate deeper than Mr. Spencer has done into the idea of universal evolution," and who, as he contends, prove this by accepting the doctrine of " spontaneous generation " ; I nevertheless think that I can pene trate deep enough to see that a 'tenable hypothesis respecting the origin of organic life must he reached by some other clue than that furnished by experiments on decoction of hay and extract of beef. From what I do not believe, let me now pass to what I do be lieve. Granting that the formation of organic matter, and the evo lution of life in its lowest forms, may go on under existing cos- mical conditions ; but believing it more likely that the formation of such matter and such forms, took place at a time when the heat of the Earth's surface was falling through those ranges of tempera ture at which the higher organic compounds are unstable ; I con ceive that the moulding of such organic matter into the simplest types, must have commenced with portions of protoplasm more minute, more indefinite, and more inconstant in their characters, than the lowest Rhizopods — less distinguishable from a mere frag ment of albumen than even the Protogenes of Professor Haeckel. The evolution of specific shapes must, like all other organic evolu tion, have resulted from the actions and reactions between such in cipient types and their environments, and the continued survival of those which happened to have specialities best fitted to the specialities of their environments. To reach by this process the comparatively well-specialized forms of ordinary Infusoria, must, I conceive, have taken an enormous period of time. To prevent, as far as may be, future misapprehension, let me elaborate this conception so as to meet the particular objections raised. The reviewer takes for granted that a " first organism " must be assumed by me, as it is by himself. But the conception of a " first organism," in anything like the current sense of the words, is wholly at variance with conception of evolution ; and scarcely less at variance with the facts revealed by the microscope. The lowest living things are not properly speaking organisms at all ; for they have no distinctions of parts — no traces of organization. It is al most a misuse of language to call them " forms" of life : not only are their outlines, when distinguishable, too unspecific for description, but they change from moment to moment and are never twice alike, either in two individuals or in the same individual. Even the word " type " is applicable in but a loose way ; for there is little constancy in their generic characters : according as the surrounding conditions determine, they undergo transformations now of one kind and now of ALLEGED SPONTANEOUS GENERATION, ETC. 699 another. And the vagueness, the inconstancy, the want of appre ciable structure, displayed by the simplest of living things as we now see them, are characters (or absences of characters) which, on the hypothesis of Evolution, must have been still more decided when, as at first, no "forms," no "types," no " specific shapes," had been moulded. That " absolute commencement of organic life on the globe," which the reviewer says I " cannot evade the admission of," 1 distinctly deny. The affirmation of universal evolution is in itself the negation of an " absolute commencement " of anything. Construed in terms of evolution, every kind of being is conceived as a product of modifications wrought by insensible gradations on a pre-existing kind of being ; and tliis holds as fully of the supposed " commencement of organic life" as of all subsequent developments of organic life. It is no more needful to suppose an " absolute commencement of organic life " or a " first organism," than it is needful to suppose an absolute commencement of social life and a first social organism. The assumption of such a necessity in this last case, made by early speculators with their theories of "social contracts" and the like, is disproved by the facts; and the facts, so far as they are ascertained, disprove the assumption of such a necessity in the first case. That organic matter was not produced all at once, but was reached through steps, we are well warranted in believing by the experiences of chemists. Organic matters are produced in the laboratory by what we may literally call artificial evolution. Chemists find themselves unable to form these complex combinations directly from their elements ; but they succeed in form ing them indirectly, by successive modifications of simpler combina tions. In some binary compound, one element of which is present in several equivalents, a change is made by substituting for one of these equivalents an equivalent of some other element ; so producing a ternary compound. Then another of the equivalents is replaced, and so on. For instance, beginning with ammonia, N II3, a higher form is obtained by replacing one of the atoms of hydrogen by an atom of methyl, so producing methyl-amine, N (C H3 IL) ; and then, under the further action of methyl, ending in a further substitution, there is reached the still more compound substance dimethyl-amine, N (C II3) (C 1I3) II. And in this manner highly complex substances are eventually built up. Another character istic of their method is no less significant. Two complex com pounds are employed to generate, by their action upon one an other, a compound of still greater complexity : different hetero geneous molecules of one stage, become parents of a molecule a stage higher in heterogeneity. Thus, having built up acetic acid out of its elements, and having by the process of substitution de scribed above, changed the acetic acid into propionic acid, and pro- ...,,..'",. , ,, , , . ( C (C H.,) (C II,) II ) piomc into butyric, or which the formula is •< ,-, x /TT K\ r I 700 APPENDIX D. this complex compound, by operating on another complex compound, such as the dimethyl- arnine named above, gene rates one of still greater complexity, butyrate of dimethyl-amine | C (0(LIO) R*} K | N (C HS) (C na) H. See, then, the re- markable parallelism. The progress towards higher types of or ganic molecules is effected by modifications upon modifications ; as throughout Evolution in general. Each of these modifications is a change of the molecule into equilibrium with its environment — an adaptation, as it were, to new surrounding conditions to which it is subjected ; as throughout Evolution in general. Larger, or more integrated, aggregates (for compound molecules are such) are suc cessively generated ; as throughout Evolution in general. More complex or heterogeneous aggregates are so made to arise, one out of another ; as throughout Evolution in general. A geometrically- increasing multitude of these larger and more complex aggregates so produced, at the same time results ; as throughout Evolution in general. And it is by the action of the successively higher forms on one another, joined with the action of environing conditions, that the highest forms are reached ; as throughout Evolution in general. When we thus see the identity of method at the two extremes — when we see that the general laws of evolution, as they are exem plified in known organisms, have been unconsciously conformed to by chemists in the artificial evolution of organic matter; we can scarcely doubt that these laws were conformed to in the natural evolution of organic matter, and afterwards in the evolution of the simplest organic forms. In the early world, as in the modern laboratory, inferior types of organic substances, by their mutual actions under fit conditions, evolved the superior types of organic substances, ending in organizable protoplasm. And it can hardly be doubted that the shaping of organizable protoplasm, which is a substance modifiable in multitudinous ways with extreme facility, went on after the same manner. As I learn from one of our first chemists, Prof. Frankland, protein is capable of existing under probably at least a thousand isomeric forms ; and, as we shall presently see, it is capable of forming, with itself and other elements, substances yet more intricate in composi tion, that are practically infinite in their varieties of kind. Exposed to those innumerable modifications of conditions which the Earth's surface afforded, here in amount of light, there in amount of heat, and elsewhere in the mineral quality of its aqueous medium, this extremely changeable substance must have undergone now one, now another, of its countless metamorphoses. And to the mutual influences of its metamorphic forms under favouring con ditions, we may ascribe the production of the still more composite, still more sensitive, still more variously-changeable portions of organic matter, which, in masses more minute and simpler than ALLEGED SPONTANEOUS GENERATION, ETC. 701 existing Protozoa, displayed actions verging little by little into those called vital — actions which protein itself exhibits in a certain degree, and which the lowest known living things exhibit only in a greater degree. Thus, setting out with inductions from the experiences of organic chemists at the one extreme, and with inductions from the observations of biologists at the other extreme, we are enabled deductively to bridge the interval — are enabled to conceive how organic compounds were evolved, and. how, by a continuance of the process, the nascent life displayed in thsse became gradually more pronounced. And this it iy which has to be explained, and which the alleged cases of " spontaneous generation " would not, were they substantiated, help us in the least to explain. It is thus manifest, T think, that I have not fallen into the alleged inconsistency. Nevertheless, I admit that your reviewer was justified in inferring this inconsistency ; and 1 take blame to my self for not having seen that the statement, as 1 have left it, is open to misconstruction. I pass now to the second allegation — that in ascribing to certain specific molecules, which I have called " pkysiological units," the aptitude to build themselves into the structure of the organism to which they are peculiar, I have abandoned my own principle, and have assumed something beyond the re-distribution of Matter and Motion. As put by the reviewer, his case appears to be well made out ; and that he is not altogether unwarranted in so putting it, may be admitted. Nevertheless, there does not in reality exist the supposed incongruity. Before attempting to make clear the adequacy of the conception which I am said to have tacitly abandoned as insufficient, let me remove that excess of improbability the reviewer gives to it, by the extremely-restricted meaning with which he uses the word mechani cal. In discussing a proposition of mine he says : — " He then cites certain remarks of Mr. Paget on the permanent effects wroujrht in the blood by the poison of scarlatina and smal!-pox, as justifying the belief that such a ' power ' exists, and attributes the repair of a wasted tissue to ' forces analogous to those by which a crystal reproduces its lost mex.' (Neither of which phenomena, however, is explicable by mechanical causes.)" Were it not for the deliberation with which this last statement is made, I should take it for a slip of the pen. As it is, however, I have no course left but to suppose the reviewer unaware of the fact that molecular actions of all kinds arc now not only conceived as mechanical actions, but that calculations based on this conception of them, bring out the results that correspond with observation. There is no kind of re-arrangement among molecules (crystallization being one) which the modern physicist does nut think of. 702 APPENDIX D. and correctly reason upon, in terms of forces and motions like those of sensible masses. Polarity is regarded as a resultant of such forces and motions ; and when, as happens in many cases, light changes the molecular structure of a crystal, and alters its polarity, it does this by impressing, in conformity with mechanical laws, new motions on the constituent molecules. That the reviewer should present the mechanical conception under so extremely limited a form, is the more surprising to me because, at the outset of the very work he reviews, I have, in various passages, based inferences on those immense extensions of it which he ignores ; indicating, for example, the interpretation it yields of the inorganic chemical changes effected by heat, and the organic chemical changes effected by light (Principles of Biology, § 13). Premising, then, that the ordinary idea of mechanical action 7nust be greatly expanded, let us enter upon the question at issue — the sufficiency of the hypothesis that the structure of each organ ism is determined by the polarities of the special molecules, or physiological units, peculiar to it as a species, which necessitate tendencies towards special arrangements. My proposition and the reviewer's criticism upon it, will be most conveniently pre sented if I quote in ful^ a passage of his from which I have already extracted some expressions. He says : — " It will bo noticed, however, that Mr. Spencer attributes the possession of these 'tendencies,' or 'proclivities,' to natural inheritance from ancestral organisms; and it may be argued that he thus saves the mechanist theory and his own consistency at the same time, inasmuch as he derives even the 'tendencies' themselves ultimately from the environ ment. To this we reply, that Mr. Spencer, who advocates the nebular hypothesis, cannot evade the admission of an absolute commencement of organic life on the globe, and that the 'formative tendencies,' without which he cannot explain the evolution of a single individual, could not have been inherited by the first organism. Besides, by his virtual denial of spontaneous generation, he denies that the first organism was evolved out of the inorganic world, and thus shuts himself off from the argument (otherwise plausible) that its ' tendencies ' were ultimately derived from the environment." This assertion is already in great measure disposed of by what has been said above. Holding that, though not " spontaneously generated," those minute portions of protoplasm which first dis played in the feeblest degree that changeability taken to imply life, were evolved, I am not debarred from the argument that the "ten dencies" of the physiological units ape derived from the inherited effects of environing actions. If the conception of a " first organ ism " were a necessary one, the reviewer's objection would be valid. If there were an " absolute commencement" of life, a definite line parting organic matter from the simplest living forms, I should be placed in the predicament he describes. But as the doctrine of Evolution itself tacitly negatives any such distinct separation ; and as the negation is the more confirmed by the facts the more we ALLEGED SPONTANEOUS GENERATION, ETC. 703 know of them ; I do not feel that I am entangled in the alleged difficulty. My reply might end here ; but as the hypothesis in question is one not easily conceived, arid very apt to be misun derstood, I will attempt a further elucidation of it. Much evidence now conspires to show that molecules of the sub stances we call elementary are in reality compound ; and that, by the combination of these with one another, and re-combinations of the products, there are formed systems of systems of molecules, un imaginable in their complexity. Step by step as the aggregate molecules so resulting, grow larger and increase in heterogeneity, they become more unstable, more readily transformable by small forces, more capable of assuming various characters. Those com posing organic matter transcend all others in size and intricacy of structure ; and in them these resulting traits reach their extreme. As implied by its name protein, the essential substance of which organisms are built, is remarkable alike for the variety of its meta morphoses and the facility with which it undergoes them : it changes from one to another of its thousand isomeric forms on the slightest change of conditions. Now there are facts warranting the belief that though these multitudinous isomeric forms of protein will not unite directly with one another, yet they admit of being linked to gether by other elements with which they combine. And it is very significant that there are habitually present two other elements, sulphur and phosphorus, which have quite special powers of holding together many equivalents — the one being pentatomic and the other hexatornic. So that it is a legitimate supposition (justified by analo gies) that an atom of sulphur may be a bond of union among half- a-dozen different isomeric forms of protein ; and similarly with phosphorus. A moment's thought will show that, setting out with the thousand isomeric forms of protein, this makes possible a number of these combinations almost passing the power of figures to express. Molecules so produced, perhaps exceeding in size and complexity those of protein as those of protein exceed those of in organic matter, may, I conceive, be the special units belonging to special kinds of organisms. By their constitution they must have a plasticity, or sensitiveness to modifying forces, far beyond that of protein ; and bearing in mind not only that their varieties are practically infinite in number, but that closely allied forms of them, chemically indifferent to one another as they must be, may coexist in the same aggregate, we shall see that they are fitted for entering into unlimited varieties of organic structures. The existence of such physiological units, peculiar to each spe cies of organism, is not unaccounted for. They are evolved simul taneously with the evolution of the organisms they compose — they differentiate as fast as these organisms differentiate ; and are made multitudinous in kind by the same actions which make the organism they compose multitudinous in kind. This conception is clearly 704 APPENDIX D. representable in terms of the mechanical hypothesis. Every physicist will endorse the proposition that in each aggregate there tends to establish itself an equilibrium between the forces exercised by all the units upon each and by each upon all. Even in masses of substance so rigid as iron and glass, there goes on a molecular re-arrangement, slow or rapid according as circumstances facilitate, which ends only when there is a complete balance between the actions of the parts on the whole and the actions of the whole on the parts : the implications being that every change in the form or size of the whole, necessitates sonic redistribution of the parts. And though in cases like these, there occurs only a polar re-arrangement of the molecules, without changes in the molecules themselves ; yet where, as often happens, there is a passage from the colloid to the crystal loid state, a change of constitution occurs in the molecules them selves. These truths are not limited to inorganic matter : they unquestionably hold of organic matter. As certainly as molecules of alum have a form of equilibrium, the octahedron, into which they fall when the temperature of their solvent allows them to ag gregate, so certainly must organic molecules of each kind, no mat ter how complex, have a form of equilibrium in which, when they aggregate, their complex forces are balanced — a form far less rigid and definite, for the reason that they have far less definite polarities, are far more unstable, and have their tendencies more easily modi fied by environing conditions. Equally certain is it that the special molecules having a special organic structure as their form of equilibrium, must be reacted upon by the total forces of this or ganic structure ; and that, if environing actions lead to any change in this organic structure, these special molecules, or physiological units, subject to a changed distribution of the total forces acting upon them will undergo modification — modification which their extreme plasticity will render easy. By this action and reaction I conceive the physiological units peculiar to each kind of organ ism, to have been moulded along with the organism itself. Set ting out with the stage in which protein in minute aggregates, took on those simplest differentiations which fitted it for differ ently-conditioned parts of its medium, there must have unceas ingly gone on perpetual re-adjustments of balance between aggre gates and their units — actions and reactions of the two, in which the units tended ever to establish the typical form produced by actions and reactions in all antecedent generations, while the aggregate, if changed in form by change of surrounding condi tions, tended ever to impress on the units a corresponding change of polarity, causing them in the next generation to reproduce the changed form — their new form of equilibrium. This is the conception which I have sought to convey, though it seems unsuccessfully, in the Principles of Biology ; and which I have there used to interpret the many involved and mysterious ALLEGED SPONTANEOUS GENERATION, ETC. 705 phenomena of Genesis, Heredity, and Variation. In one respect only am I conscious of having so inadequately explained myself, as to give occasion for a misinterpretation — the one made by the Westminster reviewer above referred to. By him, as by your own critic, it is alleged that in the idea of " inherent tendencies " I have introduced, under a disguise, the conception of " the archaeus, vital principle, nisus formatlvus, and so on." This allegation is in part answered by the foregoing explanation. That which I have here to add, and did not adequately explain in the Principles of Biology, is that the proclivity of units of each order towards the specific arrangement seen in the organism they form, is not to be under stood as resulting from their own structures and actions only ; but as the product of these and the environing forces to which they are exposed. Organic evolution takes place only on condi tion that the masses of protoplasm formed of the physiological units, and of the assimilable materials out of which others like themselves are to be multiplied, are subject to heat of a given degree — are subject, that is, to the unceasing impacts of undula tions of a certain strength and period ; and, within limits, the rapidity with which the physiological units pass from their indefi nite arrangement to the definite arrangement they presently assume, is proportionate to the strengths of the ethereal undulations fall ing upon them. In its complete form, then, the conception is that these specific molecules, having the immense complexity above described, and having correspondently complex polarities which cannot be mutually balanced by any simple form of aggregation, have, for the form of aggregation in which all their forces are equilibrated, the structure of the adult organism to which they belong ; and that they are compelled to fall into this structure by the co-operation of the environing forces acting on them, and the forces they exercise on one another — the environing forces being the source of the power which effects the re-arrangement, and the polarities of the molecules determining the direction in which that power is turned. Into this conception there enters no trace of the hypothesis of an " archaeus or vital principle ; " and the principles of molecular physics fully justify it. It is, however, objected that " the living body in its develop ment presents a long succession of differing forms ; a continued series of changes for the whole length of which, according to Mr. Spencer's hypothesis, the physiological units must have an 'in herent tendency.' Could we more truly say of anything, ' it is unrepresentable in thought ? ' " I reply that if there is taken into account an element here overlooked, the process will not be found " unrepresentable in thought." This is the element of size or mass. To satisfy or balance the polarities of each order of physiological units, not only a certain structure of organism, but a certain size of organism is needed ; for the complexities of that adult struc- YOG APPENDIX D. ture in which the physiological units are equilibrated, cannot be represented within the small bulk of the embryo. In many minute organisms, where the whole mass of physiological units required for the structure is present, the very thing does take place which it is above implied ought to take place. The mass builds itself directly into the complete form. This is so with Acari, and among the nematoid Entozoa. But among higher animals such direct transformations cannot happen. The mass of physio logical units required to produce the size as well as the structure that approximately equilibrates them, is not all present, but has to be formed by successive additions — additions which in vivipa rous animals are made by absorbing, and transforming into these special molecules, the organizable materials directly supplied by the parent, and which in oviparous animals are made by doing the like with the organizable materials in the " food-yelk," de posited by the parent in the same envelope with the germ. Hence it results that, under such conditions, the physiological units which first aggregate int? the rudiment of the future organism, do not form a structure like that of the adult organism, which, when of such small dimensions, does not equilibrate them. They dis tribute themselves so as partly to satisfy the chief among their complex polarities. The vaguely -differentiated mass thus pro duced cannot, however, be in equilibrium. Each increment of physiological units formed and integrated by it, changes the dis tribution of forces ; and this has a double effect. It tends to modify the differentiations already made, bringing them a step nearer to the equilibrating structure ; and the physiological units next integrated, being brought under the aggregate of polar forces exercised by the whole mass, which now approaches a step nearer to that ultimate distribution of polar forces which exists in the adult organism, are coerced more directly into the typical struc ture. Thus there is necessitated a series of compromises. Each successive form assumed is unstable and transitional : approach to the typical structure going on hand in hand with approach to the typical bulk. Possibly I have not succeeded by this explanation, any more than by the original explanation, in making this process u reprc- sentable in thought." It is manifestly untrue, however, that I have, as alleged, re-introduced under a disguise the conception of a " vital principle." That I interpret embryonic development in terms of Matter and Motion, cannot, I think, be questioned. Whether the interpretation is adequate, must be a matter of opinion ; but it is clearly a maHer of fact, that I have not fallen into the inconsistency asserted by your reviewer. At the same time I willingly admit that, in the absence of certain statements which 1 have now supplied, he was not unwarranted in represent ing my conception in the way that he has done. NEW EDITION OF PROFESSOR HUXLEVS ESSAYS. Collected Essays. By THOMAS H. HUXLEY. New complete edition, with revisions, the Essays being grouped according to general subject. In nine volumes, a new Introduction accom panying each volume. I2mo. Cloth, $1.25 per volume. Vol. I. Methods and Results. II. Darwiniana. III. Science and Education. IV. Science and Hebrew Tradition. V. Science and Christian Tradition. VI. Hume. VII. Man's Place in Nature. VIII. Discourses, Biological and Geological. IX. Evolution and Ethics, and Other Essays. " Mr. Huxley has covered a vast variety of topics during the last quarter of a century. It gives one an agreeable surprise to look over the tables of contents and note the immense territory which he has explored. To read these books carefully and studiously is to become thoroughly acquainted with the most advanced thought on a large number of topics." — New Tork Herald. D. A PPL ETON AND COMPANY, NKW YORK. BOOKS BY CHARLES DARWIN, LL.D., F.R.S. Origin of Species by Means of Natural Selection ; or, The Preservation of Favored Races in the Struggle for Life. From sixth and last London edition. 2 vols. 121110. Cloth, $4.00. Descent of Man, and Selection in Relation to Sex. Many Illustrations. A new edition. I2mo. Cloth, $3.00. A Naturalist's Voyage around the World. Journal of Researches into the Natural History and Geology of Countries visited during the Voyage of M. M. S. " Beagle." Maps and 100 Views, chiefly from sketches, by R. T. PRITCHETT. 8vo. Cloth, §5.00. Also popular edition. I2ino. Cloth, $2.00. The Structure and Distribution of Coral Reefs. Based on Observations made during the Voyage of the " Beagle." Charts and Illustrations. I2mo.' Cloth, $2.00. Geological Observations on the Volcanic Islands and Parts of South America visited during the Voyage of the " Beagle." Maps and Illustrations. I2mo. Cloth, $2.50. Emotional Expressions of Man and the Lower Animals. I2mo. Cloth, $3.50. The Variations of Animals and Plants under Domestication. Preface by Prof. ASA GRAY. 2 vols. Illustrations. Cloth, $5.00. Insectivorous Plants. i2mo. Cloth, $2.00. Movements and Habits of Climbing Plants. Illustrations. 121110. Cloth, $1.25. The Various Contrivances by which Orchids are Fertilized by Insects. Revised edition. Illustrations. I2mo. Cloth, $1.75. The Effects of Cross and Self Fertilization in the Vegetable Kingdom. 121110. Cloth, $2.00. Different Forms of Flowers on Plants of the same Species. Illustrations. I2mo. Cloth, $1.50. The Power of Movement in Plants. Assisted by FRANCIS DARWIN. Illustrations. I2mo. Clotn, $2.00. The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits. Illustrations. 121110. Cloth, $1.50. D. APPLETON AND COMPANY, NEW YORK. RECENT BOOKS BY DISTINGUISHED SPECIALISTS. The Comparative Physiology and Morphology of Animals. By Prof. JOSEPH LE CONTE. Illustrated. i2mo. Cloth, $2.00. Evolution by Atrophy. By JEAN DEMOOR, JEAN MASSART, and EMILE VANDERVELDE A new volume in the International Scientific Series. I2mo. Cloth, $1.50. Foot-Notes to Evolution. A Series of Popular Addresses on the Evolution of Life. By DAVID STARR JORDAN, Ph. D., President of Leland Stanford Junior University. I2mo. Cloth, $1.50. Outlines of the Earth's History. A Popular Study in Physiography. By Prof. N. S. SHALER, of Harvard University. Illustrated. i2mo. Cloth, $1.50. Studies of Good and Evil. By JosiAH RoYCE, Professor of the History of Philosophy in Harvard University. I2mo. Cloth, $1.50. Evolutional Ethics and Animal Psychology. By E. P. EVANS, author of "Animal Symbolism in Ecclesiastical Architecture," etc. I2mo. Cloth, $1.75. Wages and Capital. An Examination of the Wages Fund Doctrine. By F. W. TAUS- SIG, Professor of Political Economy in Harvard University, author of "Tariff History of the United States " and "The Silver Situa tion in the United States." I2mo. Cloth, $1.50. What is Electricity? By Prof. JOHN TROWBRIDGE, of Harvard University. i2mo. Cloth, $1.50. The Psychology of Suggestion. A Research into the Subconscious Nature of Man and Society. Bv BORIS SIDIS, M. A., Ph. D., Associate in Psychology at the Pathological Institute of the New York State Hospitals. With an Introduction by Prof. William James, of Harvard University. Illustrated. I2mo. Cloth, $1.75. U. APPLETON AND COMPANY, NEW YORK. BOOKS BY JOHN TYNDALL, LL. D., F. R S. Essays on the Floating Matter of the Air in Relation to Putrefaction and Infection. Illustrations. 121110. Cloth, $1.50. Forms of Water in Clouds and Rivers, Ice and Glaciers. (International Scientific Series.) I2mo. Cloth, $1.50. Heat as a Mode of Motion. New edition. i2mo. Cloth, $2.50. Sound. 12010. Cloth, $2.00. Fragments of Science for Unscientific People. A Series of Detached Essays, Lectures, and Reviews. Revised and enlarged edition. i2mo. Cloth, $2.00. Light and Electricity. Notes of Two Courses of Lectures before the Royal Institution of Great Britain. 121110. Cloth, $1.25. Lessons in Electricity, Royal Institution, i875-'76. I2mo. Cloth, $1.00. Hours of Exercise in the Alps. With Illustrations. 12010. Cloth, $2.00. Faraday as a Discoverer. A Memoir. 12010. Cloth, $1.00. Contributions to Molecular Physics in the Domain of Radiant Heat. Memoirs published in the "Philosophical Transactions " and " Philo sophical Magazine." With additions. 8vo. $5.00. Six Lectures on Light. Delivered in America in iS72-'73. i2mo. Cloth, $1.50. Address delivered before the British Association assembled at Belfast. Revised. 12010. Paper, 50 cents. Researches on Diamagnetism and Magne-Crys- tallic Action. Including the Question of Diamagnetic Polarity. 10 Plates. 12010. Cloth, $1.50. New Fragments. izmo. Clwth, $2.00. D . APPLE TON AND COMPANY, NEW YORK. QH 307 S7 1902 v.l Spencer, Herbert The principles of biology Rev. and enl. ed. PLEASE DO NOT REMOVE CARDS OR SLIPS FROM THIS POCKET UNIVERSITY OF TORONTO LIBRARY