QH 311 H9 LIBRARY UNlV£R^TY OF CAUF ;Ntg: F. A. BROCKHAUS $efo gorfc: G. P. PUTNAM'S SONS Bombag anH Calcutta: MACMILLAN AND CO., LTD. All rights reserved Volvox globator Ehrenberg. An adult asexual colony, highly magni- fied. The hexagonal areas represent the gelatinous coats of the individual cells in surface view. The thin common envelope of the whole colony is seen round the circumference. In the hinder half of the colony are seen two of the large asexual reproductive cells, and various stages of their development into daughter- colonies. The two most advanced daughter-colonies have already secreted a common envelope of their own. (After A. Lang.) THE INDIVIDUAL IN THE ANIMAL KINGDOM JULIAN S. HUXLEY, B.A. Research Associate of the Rice Institute, Houston, Texas Late Lecturer of Balliol College, Oxford Cambridge : the University Press 1912 Cambridge : PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS With the exception of the coat of arms at the foot, the design on the title page is a reproduction of one used by the earliest known Cambridge printer, John Siberch, 1521 PREFACE I MUST confess that when I made choice of Animal Individuality as my subject, I had no idea of its real importance, its vastness and many ramifications : the teaching of philosophical biology is in England to-day somewhat of a Cinderella. The working out of the concept, full of interest as it was, brought also regret ; a book of the size could have been — should have been — made from every twig and a stout octavo from the central trunk. This might not be ; and the unavoidable compression must be pardoned. The general reader must imitate the Organic Individual (p. 26) and take unto himself wings of thought and conscious effort to skip across the unbridged gaps that perforce remain ; with them to aid, I think he will find the stepping-stones not too far apart. The professed biologist must not cavil when he finds some merely general truth set dogmatically down as universal; in biology (still so empirical and ten- tative) there are always exceptions to the poor partial "Laws" we can formulate to-day. To have qualified every statement that needed qualification would have added much to the book's bulk without aiding the argument or being really more " scientific." My indebtednesses are great. It will easily be seen how much I owe to M. Bergson, who, whether one agrees or no with his views, has given a stimulus (most valuable gift of all) to Biology and Philosophy viii PREFACE alike. The various Oxford philosopher-friends who have helped to comb out the tangles of a zoologist's mind know how grateful I am to them: I will not name them here for fear my heresies be laid to their charge. Certain criticisms have convinced me that some explanation of the scope of this book will here not be out of place. The task I have attempted in the following pages is a two-fold one. First, I have tried to frame a general definition of the Individual, sufficiently objective to permit of its application by the man of science, while at the same time admitted as accurate (though perhaps regarded as incomplete ) by the philosopher. Secondly, I have tried to show in what ways Individuality, as thus defined //// ///<•. manifests itself in the Animal Kingdom. I wish here to point out in general, that the failure of one of these aims does not preclude the success of the other ; and, in particular, this : — it is possible that the philosophically-minded will quarrel with my definition of the Individual (p. 28) as a "continuing whole with inter-dependent parts" (to put it at its baldest). But even if he denies that the definition applies to the Individual, he must. I think, admit that it does apply to something, and to something which plays a very important part in the organic world. He will, I believe, after reading the subsequent chapters, be brought to see that every living thing is in some way related to one of these PREFACE ix systems, these continuing wholes ; and that such wholes, though they may not in his eyes deserve the name of Individual, are yet sufficiently widespread and important to merit some title of their own. Put in other words, the major portion of this book is devoted to showing that living matter always tends to group itself into these " closed, independent >vl<»iiv <>f similar members: both are on the wav j to acquiring an individuality for themselves, both exhibit features which are the necessary foundations of that individuality, but neither can with justice be said tn jn»sess it. 102 ANIMAL INDIVIDUALITY [OH. Illustrating these theoretical points, there exist for us, among various other examples, the members of the family Volvocidae, — an old but well-tried object-lesson. These organisms, claimed by botanist and zoologist alike, are members of the Flagellata, unicellular organisms marked off by possessing long whip-lashes or flagella with which they swim. The Volvocidae seem to be a perfectly natural family. They are all free-swimming; they are all colonial, with a framework of transparent jelly common to the colony ; they all possess chlorophyll, nourishing them- selves after the fashion of plants ; and they all have two flagella, a single " eye-spot " and other morpho- logical characters. There can thus be little doubt that they are all descended from a single ancestor who combined these common characters in his person. The different forms vary very much, however, in the shape and size of the colonies, in the specializa- tion of the sexual elements, and in the degree of individuation of the colonies. At the base of the series stands Gonium — sixteen precisely similar flagellate cells embedded in firm transparent jelly, joined in definite arrangement to form a flat disc (Fig. 7). The colony thus constituted lives and prospers, nourishes itself, and grows till comes the time for reproduction. Then each cell of the sixteen divides — once, twice, thrice, and four times— into sixteen little ones. Each of the sixteen groups IV] THE SECOND GRADE 103 Fig. 7. Gonium. A, a species containing 16 cells embedded in a flat ' plate of gelatinous substance. B— F, another species, containing 4 cells. J3, C, adult colonies, seen from the top and side re- spectively. In D one, in E two, and in F all four cells have divided into four. The four groups of four cells in F will shortly separate and become independent daughter-colonies. (Highly magnified.) (From West.) 104 ANIMAL INDIVIDUALITY [OH. of sixteen breaks away from the rest, arranges its parts in the familiar way, and constitutes itself a minute but perfect new colony1. Among all the other members of the family except Vol vox, the asexual reproduction (with which alone we need here be concerned) is accomplished in a similar way — each cell takes upon itself to reproduce a whole new colony. They are colonies and nothing more — their members have united together because of certain benefits resulting from mere aggregation, but are not in any way interdependent, so that the wholes are scarcely more than the sum of their parts. Though, as we have said, Volvox is obviously related to Gonium and the others, it is separated from them by somewhat of a gap. In the first place, it contains, instead of sixteen or even sixty-four cells, a vast number, mounting up in some species to twenty thousand (see frontispiece). All these cells are inter-connected by fine strands of protoplasm passing through their party- walls2 and they are arranged in a single layer on the outside of a sphere whose inner parts are filled with a very fluid jelly, so that the Vol vox-colony has what we may call an internal medium of its own. Finally, and this is 1 Some species of Gonium, such as that represented in Fig. 7, are even simpler, being formed of but four cells. 2 Though these connections have not been described for other members of the family, it is possible that they have been overlooked. iv] THE SECOND GRADE 105 where Volvox has made the great advance, the cells are not all alike. Most are of the type already seen in Gonium and characteristic of the family ; these row the colony through the water, steer it, and feed it. Amongst them, in the hinder half of the sphere, are larger cells, lacking flagella and eye-spot, and connected by very numerous strands with their neigh- bours, "Their oarsmen-brothers, by whose toil, safe fed And guarded safe, they live a charmed life Within their latticed crystal, peaceably." And what do they do in return ? Now is discovered the skeleton in the flagellated cells' cupboard— they cannot reproduce the colony. They are sterile, and must leave reproduction to the big lazy-seeming cells who are only lazy, however, because they must store up food-materials to start the new colony fairly on its way. They grow and grow, bulge inwards, and finally come to float free in the centre space, where they still grow, meanwhile dividing up into a number of cells. In the end, they become perfect miniature colonies, burst out of their parent and swim happily away. Volvox is thus a real individual ; of the two kinds of cells each has given up something the better to fulfil its own special duty. There is division of labour, and, from the point of view of the species, each kind is meaningless apart from the other. The division of labour in Volvox is that usually 106 ANIMAL INDIVIDUALITY [CH. first seen in compound individuals — between the re- productive functions on the one side and all the rest on the other. In other words, one sort of cell is concerned entirely with the species, the other entirely with the separate individuals of which the species consists ; to use the current phraseology, the one sort is germinal, the other somatic. The word somatic opens up another view : Volvox is the first organism which, in the ordinary sense of the word, has a mortal body. Its substance is not passed on unimpaired from individual to individual, but with each act of generation the major part must die, sacrificed for the greater efficiency of the race. In Volvox, this body consists of but one sort of cell : in all the organisms usually known as Metazoa there are at least two sorts, if not more. Besides the division of labour between germ and soma, there is developed another in the soma itself, at the first between protective and nutritive cells, the one form- ing an outer covering round the other, which in its turn surrounds an internal cavity. But even if Volvox only possesses species-individuality, the individuality is none the less real ; and the fact that in the family Volvocidae we can positively affirm that the step from an aggregate to a higher individual has actually taken place, is one of the most important in biology. This, however, is not the only way in which the second grade can or has been reached. It is quite iv] THE SECOND GRADE 107 possible that division of labour should set in at the very beginning, and that no such thing as a colony, using the word in its usual sense as a number of equivalent individuals all derived from a single parent and still connected together, should ever have existed. The best examples of animals with such a history are the Catenata, a small group, all parasites of certain marine worms, discovered by Dogiel (6) only four years ago, and containing but* one known genus, Haplozoon. The structure of the most primitive member of the group is simplicity itself (Fig. 9, e). It is a single row of cells, one end fixed to the wall of the worm's gut, the other sticking out into the gut- cavity. The cells, however, are by no means similar among themselves. The first one takes over all the business of attachment, and most of the nutrition. Actively movable, it possesses at its anterior end a piercing spine and a bundle of delicate protoplasmic -threads or pseudopodia, which insinuate themselves far up between the cells lining the host's digestive tube, and serve the double purpose of holding the parasite firm and of sucking up the juices of the neighbouring tissue. From its posterior end this head-cell is con- tinually dividing off new cells, which remain attached to each other in series, up to some seven or eight. The hinder cells of the series gradually become filled with particles of reserve food, analogous to the yolk granules in an egg, and finally lose their connection 108 ANIMAL INDIVIDUALITY [CH. with the rest, dropping off into the digestive cavity and passing thence to the outer world. Attempts to Fig. 8. Haplozoon macrostylum, x 300, showing the greatest com- -plexity reached by the Catenata. Only the cell-outlines are drawn, /i, head-cell with stylet and pseudopodia. A body-cell is being divided off from it posteriorly. (After Dogiel, slightly modified.) rear them further have not succeeded, but there can iv] THE SECOND GRADE 109 be no doubt that their function is reproductive, designed to spread the race to other hosts. That is the simplest form: thence to the most complex an interesting series may be traced, through species where a few of the hinder cells divide in such a way that the animal's posterior end is a plate, not a mere row, of cells, then up to others where this state of things begins much earlier, so that the plate is broadly wedge-shaped, and finally to forms where the hinder cells divide in all three directions of space, and the posterior end is large and club-shaped, several layers in thickness (Fig. 8). In the front half of the body, little openings exist between cell and cell, which serve to pass food-substances down from the " head " into the other cells. When these are full-fed, they close themselves off from their neighbours and pre- pare themselves for their reproductive destiny. The ancestry of these curious creatures is almost certainly to be sought in another group of plant-like unicellular flagellates, the Peridineae. These are two forms which serve to bridge the gap— a large one— between the active free Peridineae and the parasitic multicellular Haplozoon. The first, Gymnodinium pulvisculus (Fig. 9, a), is also a parasite but an external one: it is found at- tached to the skin of various pelagic creatures by a stalk or bundle of sucking pseudopodia like those of Haplozoon. So it thrives till it is full grown : then, 110 ANIMAL INDIVIDUALITY [OH. breaking off from its stalk, it divides up into a large number of little cells each of which develops two flagella, takes on the form characteristic of the free-swimming Peridineae, and is oft* to infest new hosts. Here, it will be seen, the same cell devotes itself at one period to nutrition and at another to dispersal. In Blastodinium mycetoides (Fig. 9, 6), these two functions are carried on by different structural units : the full-fed cell does not break off from the stalk that nourishes it, but divides transversely into two halves which become separated by a membrane. The one that is no longer attached to the stalk at once begins dividing up to form little flagellates, while the other goes on feeding, grows to full size again, and cuts off a second reproductive cell. Now imagine the reproductive cells to remain organically connected with the stalk-cell and to be nourished by it for some time after they have been divided off, and you have in essentials a simple species of Haplozoon (Fig. 9, c — e). The Catenata and Volvox are thus similar in being multicellular organisms with unified function and with division of labour among their parts ; but their origin is very different. In the making of Volvox, community-life — mere aggregation — came first, division of labour last. In Haplozoon's history, division of labour existed before IV] THE SECOND GRADE 111 any trace of communal existence, and only later was one cell built up upon another into an individual of a higher order. (a) (b) (c) (d) (e) Fig. 9. Diagram to show the probable evolution of the Catenata. (a) Gymnodinium pulvisculus, during its nutritive phase. (b) Blastodinium mycetoides. A nutritive cell remains per- manently attached to the host, and repeatedly divides off reproductive cells from itself, (c) — (e) Haplozoon lineare. h, head-cell. (c) One-cell stage, resembling (a). (d) Two-cell stage, resembling (b) except that the two cells adhere to each other. (e) Adult, with reproductive cells about to be de- tached posteriorly. [Somatic nuclei black ; germinal nuclei white ; mixed nuclei stippled.] (Modified from Dogiel.) To take parallel cases in a different grade of individuality, the simpler Volvocidae closely resemble 112 ANIMAL INDIVIDUALITY [OH. many low human races among which every family exercises all the ordinary arts and crafts, and where society, in spite often of strong communal life, can therefore not rise above the dead level conditioned by the impossibility of doing all things at once and doing them well. Curious and interesting it is that these same peoples if taught, can generally learn, and learn quickly and well, many arts and industries before undreamt of among them. The capability was there, but they had not learnt how to use it : only by sacrificing some of their multifarious functions is it humanly possible to advance in the rest, and so to raise society. As with men, so with cells — a jack-of-all-trades cannot advance in any, and the same lesson of sacrifice has to be learnt before the colony can become an individual organism. A human illustration for the methods of Haplozoon may also be found, or at least imagined. Imagine then a man inflamed with the desire to spread among a benighted race some gospel of good tidings. Poor, he prints the books himself ; then comes the question of sending them forth. It is obviously impossible for a single man to do one and the other simul- taneously. If he goes out to distribute them himself, the printing will be at a standstill while he is away. If, however, he can obtain volunteers to distribute the books, he himself can stay behind and pull off impressions all the time while a new man goes off iv] THE SECOND GRADE 113 with each consignment. Suppose further that while printing he can instruct the distributors in such a way that they will later be able to do their work more soundly, then there will be collected a crowd of embryo distributors at headquarters, from which the fully-trained ones will from time to time depart. In the first stage the business is like Gymnodinium pulvisculus: then like Blastodinium, and at the last like Haplozoon : the division of labour has come as the first forerunner of the higher development, and this it has done because in both cases there are two special functions to perform which cannot be per- formed simultaneously by a single individual. The existence of two mutually exclusive necessities is thus the origin of this type of higher individual : at first the single cell performs them both, but at the expense of not feeding while it is reproducing, not reproducing while it is feeding. Again the sacrifice by a part leads to improvement for the whole ; the great fact once discovered that of two cells one can feed for both, the other reproduce for both, and the later steps follow almost as a matter of course. It is to be remarked that for the two functions of nutrition and reproduction thus to clash with one another, it must needs be that the organism can only thrive in a very special and a very limited environ- ment. An individuality like that of the Catenata is therefore found chiefly among parasites, which exist H. 8 114 ANIMAL INDIVIDUALITY [OH. in just such an environment; but in the outer world the conditions are rarely narrow and rigorous enough to call forth such adaptations1. It was the other method, aggregation of similar units and subsequent division of labour among them, that opened to life the full resources of the second grade of individuality. In some colony like Volvox there once lay hidden the secret of the body and mind of man. CHAPTER V THE LATER PROGRESS OF INDIVIDUALITY " It is provided in the essence of things that from any fruition of success, no matter what, shall come forth something to make a greater struggle necessary." WALT WHITMAN. EVERY human being who has passed through the moral struggle will testify to the truth of these, Walt Whitman's words, in their own experience : the biologist will witness that they symbolize as real a truth in the history of life. Life can never be in equilibrium. Given the two well-established facts, that living substance can vary, and that living 1 To mention two examples, there is the strobila with its ephyrae, and the Syllids producing their special (epitokous) male and female forms hy division. v] LATER PROGRESS 115 things if left to themselves would multiply in rapid geometrical ratio, then change in the status quo is inevitable. A state of equilibrium may for a time exist, but every balanced organism is as it were pressing against every other, and a change in one means a rearrangement of them all. The correlated evolution of weapons of offence and defence in naval warfare is closely similar, though simpler far. The leaden plum-puddings were not un- fairly matched against the wooden walls of Nelson's day. Halfway through the century, when guns had doubled and trebled their projectile capacity, up sprang the "Merrimac" and the "Monitor," secure in their iron breast-plates ; and so the duel has gone on, till now, though our guns can hurl a third of a ton of sharp-nosed steel with dynamite entrails for a dozen miles, yet they are confronted with twelve- inch armour of backed and hardened steel, water- tight compartments, and targets moving thirty miles an hour. Each advance in attack has brought forth, as if by magic, a corresponding advance in defence. With life it has been the same : if one species happens to vary in the direction of greater in- dependence, the inter-related equilibrium is upset, and cannot be restored until a number of competing species have either given way to the increased pressure and become extinct, or else have answered 8—2 116 ANIMAL INDIVIDUALITY [CH. v pressure with pressure, and kept the first species in its place by themselves too discovering means of adding to their independence. While the balance of power lasts, variation no doubt takes place, but there is no strong necessity to guide it. Once let a large, favourable variation take place in a species, however, so giving it a handicap, and then for its competitors natural selection is at once made more active — they must perish or else adjust themselves by a variation, generally in a similar direction. So it comes to pass that the continuous change which is passing through the organic world appears as a succession of phases of equilibrium, each one on a higher average plane of independence than the one before, and each inevitably calling up and giving place to one still higher. This digression was necessary to give some ex- planation of the succession of ever more perfect individualities, and the continual repetition of the same methods in their attainment. Space forbids more than the merest outline of the developments of individuality after it has attained its second grade. We have seen (p. 64) that the method of aggregate differentiation is now for a time the less important : it still, however, exhibits some interesting points. To start with, division of labour in colonies of second-grade individuals, as in colonies of cells, Fig. 10. Part of a colony of Hydractinia. dz, dactylozooid (defensive person) ; gz, gastrozooid (nutritive person) ; &, blastostyle (asexual reproductive person); gon, gonophores (sexual repro- ductive persons) ; rh, hydrorhiza (creeping stolon). (Magnified.) (After Allman.) 118 ANIMAL INDIVIDUALITY [CH. almost universally sets in first between the nutritive and the reproductive functions — the somatic and the germinal. The Hydroids and their relations give us a series closely parallel at first, though in a different grade of individuality, with that of the Volvocidae, but exceeding it considerably in length. Hydra, one of the simplest hydroids known (Fig. 3, p. 39), has, like all others, the power of budding ; but its buds eventually become detached, so that it never forms more than a very small and temporary colony. Besides this, there is no division of labour among different polyps ; all are alike, and whether they shall reproduce sexually or asexually is dictated to them by the external conditions. Then come the colonial forms : and all of these show some division of labour. All, for instance, when ripe, bud off special sexually-reproductive individuals in the shape of little jelly-fish or medusae. Some- times any polyp of the colony may be able to give birth to one of these, but very often the ordinary polyps reserve themselves for feeding, and special mouthless polyps exist for the one purpose of budding off the jelly-fish ; they are the producers of the reproducers of the colony. It seems to be only later that the somatic functions, the functions pertaining to the single colony as opposed to the race, get differentiated, as in Hydractinia (Fig. 10), where there v] LATER PROGRESS 119 are special polyps that defend the colony as well as those that nourish it1. All these species are sedentary for most of their lives ; history again repeats itself, for once more it is in the free-swimming forms that the members of the colony have been most modified, most subordinated to a higher individuality. The Siphonophora, close relations of the hydroids, are a group of beautiful pelagic creatures, which slowly drive their trailing length through" the water by an array of pulsating bells. Besides these loco- motor organs, there are in the colony organs for feeding, for reproduction, for defence, for offence, and for flotation (see Fig. 11). Most of these apparent organs are really modified individuals, either of the polyp or medusa type. The reproductive "organs" are sometimes detached as perfect jelly- fish ; the swimming-bells and the protective bracts often show unmistakeable vestiges of medusoid structures. The nutritive "organs" are very like an ordinary polyp, but without tentacles, and the 1 It is interesting to note that in the Polyzoa, another group of colonial animals, there has been a different kind of division of labour. The ordinary animals both feed and reproduce the colony, and defence is undertaken by much modified persons called Avicularia (from their resemblance to birds' heads with snapping beaks). Here the differentiation is between most of the somatic and all the germinal functions on one side, and a single somatic function on the other. In some forms there are no Avicularia, the colonies then consisting of only one kind of person. 120 ANIMAL INDIVIDUALITY [OH. v defensive organs usually have a structure like that of the defensive polyps in a hydroid like Hydractinia. There can be no doubt therefore that the various " organs " do really represent modified hydroids ; and as these are themselves individuals of the second grade, a Siphonophoran is therefore an individual of the third grade. The same process — the subordina- tion of the lower individualities to a higher — which we traced from a simple flagellate up to Volvox is traceable again from Hydra to the Siphonophora : but the interesting point is that nowhere else in the animal kingdom is there an unbroken series — a series in which we can affirm positively that beginning and end are close relations — of such length. In the majority of Siphonophora, the persons of the colony have mostly only a historical individuality : some of them are sometimes so much modified and reduced that it has baffled all the zoologists to decide whether they are homologous with individuals or with mere appendages of individuals : and in function each is devoted so little to itself, so wholly to serving some particular need of the whole, that if one were separated from the rest, it would appear a perfectly useless and meaningless body to an investigator who did not know the whole to which it belonged. There are zoologists who say it is incredible that the cells of the Metazoa can be homologous with independent beings like the Protozoa, impossible that a colony Fig. 11. A, Diphyes campanulata (natural size). B, a group of appendages (cormidium) of the same Diphyes (magnified). (After C. Gegenbaur.) a, axis of the colony; wi, nectocalyx (swimming 'organ'); c, sub-umbral cavity of nectocalyx; v, radial canals of nectocalyx; o, orifice of nectocalyx; t, bract (protective 'organ'); n, siphon (nutritive 'organ'); d, gonophore (re- productive 'organ'); i, tentacle (defensive 'organ'). 122 ANIMAL INDIVIDUALITY [OH. should ever give rise to a single individual of a higher order than its members (see 5, p. 304). To them we commend the example of the Siphonophora, and pass on to consider some other individualities, formed through aggregate differentiation, but after an en- tirely new fashion. To start with, we have the old but ever interesting fact of symbiosis, where two organisms as it were inter-penetrate, entering into a very close relationship from which both parties derive profit. The classical examples of symbiosis are the Lichens, which, long supposed to constitute a distinct group of plants, were in the middle of last century discovered to be actually a mixture of two organisms, one a colour- less fungus, and the other a green plant — a simple alga. For the details of their organization any text- book of botany can be consulted : here it must suffice to say that there is a perfectly definite arrange- ment of the algal and fungal constituents. The in- teresting thing about them is that they will grow, as anyone can see for himself, in situations which no other plant would tolerate, so that both plants must obviously derive advantage from the combination. Put very briefly, the facts are these : fungi can only get the carbon of their food from organic matter, while green plants have the power of using the energy of light to appropriate carbon from the carbon dioxide of the atmosphere. In respect of v] LATER PROGRESS 123 the absorption of water and mineral salts, however, the fungus seems to be the better equipped. Thus (division of labour once more) the alga supplies Fig. 12. Physcia parietina ; building up of the Lichen out of the Alga and the Fungus. A, a germinating fungus-spore (sp) which has seized upon two cells («, a) of the alga Cystococcus humicola. 5, more advanced stage. The spores of the fungus have formed a network in which are embedded numerous algal cells ( x 400). . (From Scott, after Bonnier.) carbon compounds for both, the fungus looks after most of the rest of the nutrition, and also shelters the alga from frost and drought. Algae identical with the green cells of the lichen 124 ANIMAL INDIVIDUALITY [CH. are found free-living in spots less exposed than those where lichens grow: the alga, that is to say, can exist separately, but in the partnership grows more luxuriantly and has a wider range. The fungus, on the other hand, though it has been grown separately in an artificial medium, cannot develop in nature unless it meets with some algal cells. Fig. 12 shows a young fungus which has just germinated among a group of algae and is now sending forth little tentacles to seize and enwrap them. The fungus gains more than the alga, but this does not prevent the combination of both, the lichen, from being a very definite individual. A lichen on a barren rock is a something whose continuance as such and in such a situation is dependent upon the co-operation of its two constituents. Here the division of labour is given beforehand in the two kinds of plants, and the new individuality simply arises from the fitting together of these two separate beings into a very close and special relation. This relation is, however, only a special case of the general relation existing in nature between green plants and all other organisms. Put very crudely, the relation is this : — green plants can build up protoplasm from water, carbon dioxide, and mineral salts : the protoplasm thus formed is the ultimate source of all nourishment to the rest of life. Animals either eat green plants or else eat other animals v] LATER PROGRESS 125 that eat green plants ; many bacteria feed on the dead tissues of animals and plants, bringing about as a result of their activity the phenomenon known as decay ; and fungi live to a great extent on the substances produced during decay. Meanwhile, how- ever, the waste products of the current of metabolism and the final products of decay, which come eventu- ally to be degraded to simple stable substances such as water, carbon dioxide, ammonia, and nitrates, get diffused in the soil, and form the basis once more of the green plant's activity. In a sense, therefore, the whole organic world constitutes a single great individual, vague and badly co-ordinated it is true, but none the less a continuing whole with inter-dependent parts : if some accident were to remove all the green plants, or all the bacteria, the rest of life would be unable to exist. This in- dividuality, however, is an extremely imperfect one — the internal harmony and the subordination of the parts to the whole is almost infinitely less than in the body of a metazoan, and is thus very wasteful ; instead of one part distributing its surplus among the other parts and living peaceably itself on what is left, the transference of food from one unit to another is usually attended with the total or partial destruction of one of the units. Within this biggest system, nature has been per- sistent in her efforts to create other "naturally-isolated 126 ANIMAL INDIVIDUALITY [OH. systems," other individualities. Out of every little accidental company she tends to make an inter-related whole whose parts are largely dependent on each other, and only slightly on other wholes or their parts. It will be necessary to give a few more examples of the inter-relation of two distinct species before developing this idea. A very instructive example is that of Convoluta roscoffensis, a marine flatworm. Its story has been so clearly told by Prof. Keeble (10) that here an outline will be enough. In nature, the worm is always associated with a unicellular green plant which lives in great numbers beneath its skin. The plant on the other hand is found abundantly apart from the worm, but swarms round the egg- capsules in order to procure nitrogenous food, and gets ingested by the young animal. Unless this happens, the worm cannot develop further — the presence of the green cells is the only stimulus which will start its machinery on the next stage of its working. At first both members gain from the association, much as in the lichen, but finally, after the worm (which at last takes no food, but depends entirely on the surplusage of the alga) has produced its eggs, it finds itself short of nitrogenous material, and begins attacking and digesting the green cells ; they cannot last for ever, and when they are all gone last of all the worm dies also, trusting to chance that its young will find new algae. This shows a transition v] LATER PROGRESS 127 from symbiosis to parasitism, though the host here enters the relation of its own free will. Convoluta somewhat resembles an employer of slave-labour in a country where slaves are very kindly treated : the green slaves are well provided for during their in- dividual lives, but they have sacrificed the power of further perpetuating their species. A growing Con- voluta plus its contained green cells is therefore that anomaly, a temporary individual. Take next a case of true parasitism. With most internal parasites, such as trypanosomes (the flagel- lates which cause sleeping-sickness and other diseases), or tapeworms, each species of parasite is confined normally to one host-species, and cannot come to perfection elsewhere. It is often extraordinarily closely adapted to its environment both in structure and life-history, as a study of any tapeworm will show ; but that environment is an extremely limited one. After this consider an apparently very remote subject — the relation between insects and flowers. I need here merely point out that many insects, such as bees and butterflies, procure all their food from the honey or pollen of flowers, and that most plants with conspicuous flowers rely exclusively or chiefly on in- sects for their fertilization, and so for their continuance as species. Both insect and flower have been radically modified in structure and appearance through this 128 ANIMAL INDIVIDUALITY [CH. mutual relation. Most flowers are fairly catholic in their tastes, and are adapted for fertilization by a number of different insects, and the same is true, mutatis mutandis, of the insects. But sometimes the relation is a much narrower one, till finally an insect may be able to get food only from one particular flower, the flower to be fertilized only by this parti- cular insect. A relation of this degree of intimacy (though with not quite the same purposes) is found between the Yucca-plant and a moth of the genus Pronuba (Fig. 13). Here (for the details I must again refer the reader to other books ; e.g. (17), Vol. i, p. 201) the Yucca can in nature only be fertilized by the one agency of the moth : she, when the time comes for egg-laying, flies to the Yucca, rakes up a large ball of pollen by means of a unique structure on her head, and then flies with the ball to another flower ; there she sticks her long and curiously-shaped ovipositor into the ovary of the flower, and lays her egg among the unfertilized seeds inside. Last she lifts the pollen- ball on to a special hollow on the top of the stigma, and pokes it firmly down. The pollen fertilizes the ovules, of which there are about two hundred, and they start developing into seeds ; meanwhile the cater- pillar hatches, and feeds at the expense of the seeds. However, it only needs some twenty or so before undergoing its transformations into pupa and moth, and leaves the rest to grow into new Yucca-plants. v] LATER PROGRESS 129 The whole proceeding is of great interest, showing as it does the blind and instinctive nature of the Fig. 13. The Yucca and its Moth (Pronuba yuccasella). A, ovipositor of the moth, op, its sheath; sp, its apex; op', the protruded oviduct. B, two ovaries of the Yucca, showing the holes by which the young moths escape, and (r) a caterpillar in the interior. C, head of the female moth, with the sickled-shaped process (si) on the maxillary palps for sweeping off the pollen and rolling it into a ball, mx', the proboscis ; au, eye ; p't base of first leg. D, longi- tudinal section through an ovary of the Yucca, soon after the laying of two eggs (ei). stk, the canal made by the ovipositor. organisms' actions, and giving us an example of two species absolutely dependent on each other for their H. 9 130 ANIMAL INDIVIDUALITY [OH. continued existence. If the moth had not the struc- ture to form the pollen-ball and the instinct to put it on the stigma, the ovules would not be fertilized and her offspring would have no food; and if the plant was not prepared to sacrifice some 10 per cent, of its brood, the rest would never develop at all. Here it is of course the two species that are affected, while the single moth and the single plant do not depend on each other in any way ; but the essential point of the relation — the mutual helpfulness of two unrelated kinds of protoplasm — remains the same. Now return and consider these various relation- ships from the point of view of individuality. The different species of living things and their members are all bound up, though but loosely, into a general whole. Any single species relies on others for some of the necessities of its existence. In many green plants this dependence on other species is very slight and very indirect, while animals, owing to their mode of nutrition, are always directly dependent on the one or many organisms on which they feed. None the less, in nett total of true independence most animals are far ahead of plants. They have had to make more effort to get their food, and throughout life, effort always seems to bring in its train advantages, unfore- seen and unconnected with the effort's immediate object. To give an extreme example, the eyes and ears and other sense-organs of animals were developed v] LATER PROGRESS 131 chiefly for the capture of prey and the avoidance of enemies; but once formed, they were the starting- point for the life of consciousness that has culminated in ourselves. A blind deaf-mute child can be fed and live a healthy physical life ; its mind, however, scarcely exists : "for the book of knowledge fair Presented with a Universal blank." But wisdom at one entrance still can find a way — through the gateway of touch ; and the story of Helen Keller, the American girl who became blind and deaf and dumb in infancy, will show how absolutely de- pendent on external stimulus, even in its dealings with the abstract and the non-spatial, is the mind of man. The necessity for effort — the "struggle for exist- ence" in the most general sense — has from age to age raised the average level of independence, the measure of individuality s perfection in living beings. In spite of this general rise of level, there has been in every age a falling away, a decline in perfection of in- dividuality in certain species. This decreased in- dependence reveals itself not only as structural degeneration, but also in degeneration's opposite, structural specialization. There is, however, a common cause beneath these opposed effects, and that is over-close adaptation, adaptation to very narrow conditions. 9—2 132 ANIMAL INDIVIDUALITY [OH. It is self-evident that all organisms must be more or less adapted to their surroundings ; in other words they must be more or less dependent upon their environment. Failure to exist in any but a very limited environment is obviously a weakness, a lack of independence, and it seems to be a fact that adaptation to any such limited environment makes it impossible or very difficult for an animal to exist in any other environment. The very success of the adaptation decreases the creature's adaptability. The adaptation may be concerned only with in- organic nature, as when plants are adapted to conditions of temperature, light and moisture, or only with other animals or plants, or with both. Let us take the second as being most germane to our present purpose. The nutrition of animals falls within this province, since they are always dependent on the protoplasm of other living species for their food. This is a limitation, but its boundary is a wide one. The animal may either make an effort1 to secure its food, or it may prey parasitically on the labours of another animal. Both ways, if too special adaptation is allowed, may lead to a back-sliding in individuality. We can take a series of examples . l A metaphorical effort, as when a carnivorous species acquires new powers of speed to run down its prey, or an actual effort, as when the members of that species make use of those powers. v] LATER PROGRESS 133 from birds. The Rook and the Sparrow are almost omnivorous, and therefore very independent as regards food-supply. A bird like the Swallow is a little more dependent. In its large gape and strong flight it shows a general adaptation for catching small insects on the wing, but as long as they are insects and small and flying, it is content ; it has taken advantage of a common property of many insects, and is de- pendent in no narrow way. Dependent it is, however, and when the insects fail it must migrate. Finally, such a bird as the Skimmer (Rhynchops nigra) exhibits a very special adaptation indeed. Darwin (3, p. 137) gives a graphic account of them. " The beak is flattened laterally.. . .It is flat and elastic as an ivory paper-cutter, and the lower mandible, differently from every other bird, is an inch and a half longer than the upper/' When feeding, "they kept their bills wide open, and the lower mandible half buried in the water. Thus skimming the surface . . .they dexterously manage with their projecting lower mandible to plough up small fish, which are secured by the upper and shorter half of their scissor-like bills." This strange bill is without doubt an ex- tremely efficient instrument for catching fish near the surface of the water, but the length of the lower mandible, the very particularity which makes it so efficient for this one purpose, renders it unavailable for any other. The narrow domain where air and 134 ANIMAL INDIVIDUALITY [OH; water meet it has made its own, but to that one domain it is rigidly confined. The path to parasitism, in spite of apparent differences, is very similar. Here too what the animal seeks is adaptation to an environment which by very reason of its peculiarity and narrowness is not already occupied by other competitors. Eventu- ally the fate of the parasite becomes bound up with that of the host. The final result is thus the same ; the form which has made the too-special adaptation loses independence. Such happenings the phrase-monger will find place for under some vague, comprehensive title such as " Filling a vacant place in the Economy of Nature," and be content. But, though it is undoubted that the pressure of the struggle is always forcing life into these vacuums of vacant spaces, we have to look further before we find what the effect on life will be. Then we see that the process is not always so wholly satisfactory as phrase would make it. In our par- ticular cases the result of " filling a vacant space " is that one species gets preyed upon, and the other, the claim-staker, though gaining the gold in the vacant claim, thereby ties himself down to that little plot of ground, and sinks in the scale of individuality. Now suppose that the one organism does not merely rush into a ready-made vacuum provided by the other, but that the two should conspire together v] LATER PROGRESS 135 to create a vacuum of their own, into which, as fast as it is created, they jointly creep. This is in effect what happens when two species become mutually depen- dent. Here again the relation is at first a general one, as between insects and flowers, but at the last may get very special, as between the Yucca and its moth. Both species here have lost independence. The Yucca, for instance, has to be propagated artificially in Europe, for when it was brought over the moth was left behind, and so no seed can be set. At first sight, then, such a system appears like a double parasitism, and twice the evil that parasitism brings should be its portion. This is not really so, for while the true parasite takes what he can get and gives nothing in return, here each pays the other willingly, for services rendered. In extremes of parasitism there is maximum waste; mutual aid (though it implies mutual dependence) establishes minimum waste. Moth and Yucca together constitute a system which is harmonious and economical because division of labour is at work : each does what it can do best and gives of its superfluity to its partner. If the two parts have sunk in the scale, yet by that very sinking the beginnings of a new whole have sprung up. They have lost in independence, but something else — the system formed by their combination- has gained in harmony. Put in other words, their own individuality has become impaired, but this is 136 ANIMAL INDIVIDUALITY [CH. compensated for by the formation of a totally new individuality, rudimentary though it be. If the parts of the system, instead of being related by but one tie and for a short space only, were to be brought into relation for the whole of their lives, the resulting system would have the chance of becoming not only more harmonious, but even a more independent individuality than was either of its parts before their mutual adaptation — a consummation actually realized in the Lichens. This necessity for the parts of a compound in- dividual to lose their own independence for the ultimate greater independence of the whole — this increasing mutual parasitism of the units within an individual — is in fact a brief statement of the main facts observable concerning internal differentiation. Internal differentiation, indeed, to be strictly accurate, is the only way in which individuals are formed, for aggregate differentiation is only a convenient label for the combination of two processes — first the forming of an aggregate, be it of molecules, cells, or persons, and then the welding of this mere aggregate into a true individual by means of internal differentiation. The progress of the individual of the second grade is in essence a progress towards greater complexity, more harmonious co-ordination, higher independence ; this is revealed to the eye in the multiplication and specialization of its various kinds of cells. When it v] LATER PROGRESS 137 is reflected that these lesser individuals were originally all alike and all self-supporting, the modifications which they have undergone are nothing short of amazing, as a glance at any text-book of histology will show. We can but mention a few of the most re- markable. For shape, the ordinary nerve-cell (Fig. 14) is striking enough ; the cell-body is an ordinary, some- what polyhedral mass of protoplasm, but from it are given off branching processes which divide and sub-divide and with their finest sub-divisions come into contact with the branches of other nerve-cells ; and at one point runs out a single thread, the nerve- fibre, which, though its thickness is to be measured in hundredths of an inch, may yet reach a length of several feet before it finds the muscle it is to move or the sense-organ whose message it is to carry. Remarkable in another way are the epithelial cells of our skin, which, continually produced in the deeper layers, undergo a gradual metamorphosis into the thin plates of horny matter called scurf, or scarf-skin ; by their perpetual wearing off and replacement from below, they give us an outer covering which shall be at once pliant and sensitive, of considerable strength, and quick-healing. When an individual's only duty is to commit suicide for the good of the society to which he belongs, the process of subordination has gone a very long way. In what are known as syncytial 138 ANIMAL INDIVIDUALITY [CH. tissues it has gone perhaps still further : here the cells, surrendering all separateness of existence, have fused to form mere sheets of continuous protoplasm studded with nuclei. These syncytia are only the final outcome of a process whose beginnings we saw in Volvox and Haplozoon — the connection of the separate cells by means of strands of protoplasm passing from one to another. These connections seem to exist in all multicellular green plants, and have now been demonstrated in a great number of animals1. Many zoologists indeed believe that the fine endings of the nerve-fibrils are always in direct protoplasmic continuity with the organ they supply. It is worth remembering that the actual history of every individual runs roughly parallel with what we know of the history of the race. Those who cannot bring themselves to believe that the ancestor of a nerve-cell, for instance, was once independent and capable of all the functions of separate existence, often do not consider that every nerve-cell started its life simple, rounded, and undifferentiated, only later throwing out its complex branching processes, and later yet coming into protoplasmic continuity with other cells, originally far distant in the body (Fig. 14). In many animals indeed every individual epi- tomizes in its own the history of the race. Starting as a fertilized ovum, an individual of the first grade, 1 See Dobell (5) for facts and references. v] LATER PROGRESS 139 it next becomes a " colony " of nearly similar cells, and then an obvious second-grade individual, with (e) (c) (b) (a) Fig. 14. Five stages in the early development of a nerve-cell from the brain. In (a) the rudiment of the nerve-fibre is seen. In (c) the dendrite with its branching processes has become obvious. (e) does not represent the final stage ; in the adult nerve-cell size and complication are many times greater. (Highly magnified.) (After Kamon Cajal.) outer protective and inner nutritive layer. Then 140 ANIMAL INDIVIDUALITY [OH. comes the internal differentiation of this individual : blood-cells and blood-vessels, nerve-cells and sense- organs, muscles, sinews, bone, kidney, liver — kind after kind of cell is created. And let it never be forgotten that in the embryonic development of any and every individual all these and many others are descendants of a single and a simple cell. It is noteworthy that the course of internal differentiation has over and over again — in worms, in insects, in Crustacea, in spiders, in molluscs, and in vertebrates — tended in the same direction — towards the formation of a Brain. Brain-development has usually gone hand in hand with the specialization of other organ-systems — the brain seems a mere bit of machinery necessitated by the complexity of the other parts. In the higher insects and the higher mammals, however, the brain seems to have tran- scended all the other parts of the body, to have gone farther than they in specialization, and to be now in truth the master by whom the rest are to be employed. This development of sense-organs and brain has had great influence on the progress of individuality. We do not usually stop to consider in what dense darkness the majority of living things must live and move and have their being. Without brain or sense- organs, theirs must be a dim and windowless existence. The world lies waiting round about ; but it cannot v] LATER PROGRESS 141 make its way into their beings. Or say, the world is locked, and living things must make their own keys to it. So it is with men : educating their minds, they forge key after key, each opening a new chamber, letting in a new flood of light from every material ob- ject. Show a flower to an aboriginal savage : what he sees is something very different from what Wordsworth or Sir Joseph Hooker would have seen. What he sees, however, contains more of reality than what a beetle or a snail, with their imperfect eyes, could see. The effect produced on an organism when some object is presented to its senses thus depends partly on the perfection of its sense-organs, partly on that of its brain. As we go down the scale, both dwindle : veil upon veil is let down : till at the last there is an almost utter darkness, and not of sight alone. It is this darkness at the base of the animal king- dom which has there made it almost imperative that the parts of an individual should cohere physically ; separate them and they would be lost, and could never enter again into their mutual relationship. Once produce a sense-organ, however, which with the brain behind it is capable of clearly perceiving and accurately localizing distant objects, and it at once becomes possible to construct an individual, such as an ant-community, whose parts, though not contiguous in space, are yet bound together as fast as the cells of a sponge or the persons of a Siphonophoran ; here 142 ANIMAL INDIVIDUALITY [OH. as elsewhere the real bond is an impalpable one — mutual dependence. The communities of ants and bees are undoubted individuals. Wheeler in a recent paper (18) has abundantly justified this view from a somewhat different standpoint. Here I can only say that if the ideas and definitions put forward in Chap. I are accepted, their individuality is beyond dispute. In spite of space, I cannot refrain from giving one example of the lengths to which internal differ- entiation of parts can go in such apparently loose- connected wholes. In several species of ants there are special workers whose duty it is to imbibe honey till their fair round bellies are drum-tight, then to suspend themselves, a row of living jars, from the roof, and there to wait until their store is needed by the colony and they are taken down arid tapped for general consumption. One interesting property gained by brains and sense-organs :— organisms possessing them can easily enter into more than one individuality. The Yucca and its moth, for instance, constitute a definite individual that works for its own perpetuation. But their time of contact is a short one ; and there is nothing to prevent the moth from entering into re- lations with some other flower for the sake of food (in return of course fertilizing the flower) and so forming together with it another " whole with inter-dependent v] LATER PROGRESS 143 parts working for its own continuance" — another individual. When we come to man, this power possessed by one unit of entering into more than one individual "at once" (see note, p. 13) becomes very marked. A man can very well be at one time a member of a family, a race, a club, a nation, a literary society, a church, and an empire. "Yes, but surely these are not individuals," — I seem to hear my readers' universal murmur. That is a question which neither the size nor the scope of this book permits. Here we can but express a pious opinion : — that they are individuals, that here once more the tendency towards the formation of closed systems has manifested itself, though again in very varying degrees, so that some of the systems show but a glimmer of individuality, others begin to let it shine more strongly through. That their individuality is no mere phantasm I think we must own when we find men like Dicey and Maitland (12, p. 304) admitting that the cold eye of the law, for centuries resolutely turned away, is at last being forced to see and to recognize the real existence, as single beings that are neither aggregates nor trusts, of Corporate Personalities. This being so, it yet remains true that the state or society at large is still a very low type of individual : the wastage and friction of its working are only too prominently before our eyes. With the examples of 144 ANIMAL INDIVIDUALITY [OH. what life has accomplished in producing our own bodies, we can never despair. But we must not be too far tempted by biological analogies : the main problem is the same, but the details all are new. The individuals to be fused into a higher whole are separate organisms with conscious, reasoning minds — personalities ; and the solution will never be found in the almost total subordination of the parts to the whole, as of the cells in our own bodies or the sweated labourer in our present societies, but in a harmony and a prevention of waste, which will both heighten the individuality of the whole and give the fullest scope to the personalities of all its members. CHAPTER VI THE RELATION OF INDIVIDUALITY TO MATTER; CONCLUSION "Shall man into the mystery of breath, From his quick-beating pulse a pathway spy? Or learn the secret of the shrouded death, By lifting up the lid of a white eye ? " MEREDITH. A VERY striking experiment can be made on many of those free-living flatworms, the Planaria. If they are cut in two longitudinally, the halves will regenerate into perfect wholes, and this whether they are fed or VI] RELATION TO MATTER 145 not. If not fed they present us with a strange spectacle (Fig. 15). Without food, they cannot of Fig. 15. Planaria lugubris. Four stages in the regeneration of a whole from a longitudinal half. The dotted line in (a) marks the line of the cut. The stippled areas represent regenerated tissue. The figures are all drawn to scale. (After Morgan.) (Slightly magnified.) course rebuild their missing block of buildings as we should, with new bricks : indeed, as energy has to be H. 10 146 ANIMAL INDIVIDUALITY [OH. expended in the construction, some of the existing materials must be sacrificed as energy-producers, so that by the time the bit of worm-protoplasm has turned itself into a worm, it has actually decreased in bulk (Fig. 15). The half- worm has never ceased to exist as a half, but has somehow managed to become an ever smaller half while remodelling itself continually and at the same time handing over material for the building of what is missing. Finally the other half is completed — a whole worm has been made ; up till now the old half had been decreasing rapidly in size, the new increasing almost as fast. From the time that a whole is formed, both halves behave alike, decreasing slowly together as a result of starvation. This and many other similar facts tend to show that the relation of form, and so (since specific form or structure is only the visible machinery of a specific working) of individuality in living things to its physical basis of matter, is primitively a simple one, though one that is at variance with all our precon- ceived ideas. It seems to be this : any separate mass of one kind of protoplasm will be able to, or rather must, make itself into an individual with the form characteristic of the species. The only provisions are that it is neither too large nor too small within certain defined limits and, of course, that the external con- ditions are favourable. Facts suggesting this we have seen in Clavellina, vi] RELATION TO MATTER 147 in Stentor, and in Sycon1 : indeed, as I have said, it really seems to be an original attribute of life, only more wonderful and startling than ordinary embryonic development because it is no regular part of the cycle of the species. Through its help the animal can extri- cate itself from positions in which it has never before been. But, like most other primitive attributes of life, it has undergone considerable restrictions in the course of evolution. Animals, like men, cannot have their cakes and eat them. Three main factors have led to a restriction of this power of regeneration. The first is the formation of different substances for the performances of different functions, and their subse- quent segregation into different regions of the body. These substances may get so specialized, so different from each other and from their common ancestor, that one cannot produce the other, and the presence of both is necessary in a mass of substance which is to give rise to a whole individual. In Stentor, for instance, although both nucleus and cytoplasm alike are living Stentor-protoplasm, yet a bit of one with- out the other will not regenerate. Here the two substances have been segregated by internal differ- entiation within the cell. Something similar occurs in Sycon, where the collar-cells by themselves cannot regenerate the other forms of tissue necessary to make 1 pp. 46, 47 and 94 respectively. 10—2 148 ANIMAL INDIVIDUALITY [CH. a complete sponge ; here aggregate differentiation has been at work, and whole cells and tissues are affected instead of parts of cells. The second narrowing factor is harder to precise ; but though we do not know its exact nature, we can often see it at work. There are many animals, such as man himself, where regeneration is almost non- existent although in any given case all the necessary substances and kinds of tissue would appear to be present. Here the failure to regenerate seems to stand in some general relation with the degree of specialization of the tissues; most animals can regenerate more completely when young or embryonic than when they are grown up. The third factor is more obvious : certain bits of organic machinery are of such a nature that it is physically impossible for the animal to live at all if they are seriously tampered with. It is just because our blood-circulation is so swift and efficient and our nervous system so splendidly centralized that damage to heart or brain means almost instant death to us, while a brainless frog will live for long, and a heart- less part of a worm not only live but regenerate. Thus here again sacrifice is at the root of progress, and only by surrendering its powers of regeneration and reconstitution has life been able to achieve high individualities with the materials allotted her. But this original property of living matter is vi] RELATION TO MATTER 149 important to us in one way. We begin to realize what an influence the correlation of parts can exert —how one part can affect others by its mere presence or absence. In Stentor, each bit that if separated from the rest would grow into a perfect little whole, remains as a part as long as it is connected with the other parts. If it forms a part, it is because of its relation with other parts ; if it forms a whole, it is because it is freed from that relation. Whatever it does, in fact, is due to the tendency of any separate mass of Stentor-protoplasm to form a whole Stentor. Exactly similar is the behaviour of the blastomeres or separate cells of the segmenting egg (p. 69) only here the subordination is in one way more startling, for each of them is a single cell and represents historically a whole individual. Similarly in all animals where small fragments can reconstitute miniature wholes, the fate of any particular cell in a fragment is determined very largely by its position in the fragment, and would be different if the fragment were of a different size or shape. This " tendency towards wholeness " thus manifests itself across cell-boundaries as easily as through the more continuous substance of a single cell. More than this, it often seems to disregard them altogether. Many facts of embryology, as when form appears first and cells only later, lead us inevitably to a standpoint resembling that of Whitman (19), when he says of 150 ANIMAL INDIVIDUALITY [OH. normal development: — "the plastic forces heed no cell-boundaries, but mould the germ-mass regardless of the way it is cut up into cells/ ' Such considera- tions have led him and several others to throw up the cell-theory altogether, saying that the cells of a metazoan are not homologous with free-living protozoan individuals, but are merely convenient bricks, so to speak, or centres of local government, produced by the forces of life after the form of the creature had been established. But such a conclusion cannot be justified. We must carefully distinguish between what exists to-day, whether in adult body or developing embryo of a metazoan, and what we believe to have happened in the past. Volvox and Haplozoon, whose cells we can with no shadow of doubt affirm to be homologous with free-living Protozoa, show that it is possible for a higher individual to be evolved from a collection of lower ones. If we refuse to the Metazoa an ancestor formed thus by aggregate differentiation, we are landed in far more and far worse difficulties than any we escape from. Whitman is right in drawing attention to the remarkable fact that the so-called Kupffer's vesicle of embryonic Teleost fish is non- cellular, a mere thin sheet of protoplasm which is not even nucleated, whereas it is certainly homologous with a structure of other vertebrates which is composed of very definite cells, but to reject the vi] RELATION TO MATTER 151 cell-theory altogether on this account is not warranted. Rather should we in such facts see examples of the extreme lengths to which the degradation of the individuality of the parts can go — a degradation which we found to be everywhere (except in man's societies) a necessary accompaniment of the formation of a higher individual from an aggregate. Here the cells have become degraded to the level of mere bricks, with even less share in determining the form of the whole than real bricks have in determining the form of a house. But how different is the structure of our Sponge or of Volvox — and they deserve equal consideration with the fish. It is better to believe in the historical individuality of the cells and to wonder at the idea of the whole's form that can thus penetrate the substance and absorb the individualities of its parts, robbing them of all their ancestral freedom, as the universal mind (some would believe) absorbs and loses in itself our souls at death. But here we have come down to the bed-rock questions of biology — the old problems of ordered growth and purposeful working, which are still shrouded in their dense cloud of ancient mystery. Yet though, like enquirers who try to push far after knowledge in any direction, we are at length brought face to face with the unknown and perhaps unknowable, we have made some solid progress. Without discovering the origin or the inner being 152 ANIMAL INDIVIDUALITY [OH. of individuality, we have been able to see it made objective in the various streams and masses of proto- plasm which we call animals and plants, and to trace an upward progress in its course, at the same time getting light on many related problems of biology. We have seen the totality of living things as a continuous slowly-advancing sheet of protoplasm, out of which nature has been ceaselessly trying to carve systems complete and harmonious in themselves, isolable from all other things, and independent. But she has never been completely successful: the systems are never quite cut off, for each must take its origin in one or more pieces of a previous system ; they are never completely harmonious, as MetschnikofFs long list of the " disharmonies " in man will show ; and they are never completely independent. These very incompletenesses, due to the limitations of the material stuff with which life has to work, have proved the foundations of fresh advance. It is just because every system is bound to be in some degree dependent, that a number of systems can adjust their various ways of dependence to each other, till a condition of minimum waste and maximum inter- dependence is gradually set up, and a new system, better equipped than any and all of the earlier ones, is made. These systems are individuals, and it thus comes about that individuals exist in grade upon grade, vi] RELATION TO MATTER 153 any one in any grade being able to combine with others like itself or with others unlike itself to form the beginnings of a new system, a new individual. Moreover, within each grade there may exist indi- viduals of every degree of perfection. At the bottom, a Gonium-colony is but a possibility of an individual ; the individual formed by the inter-relation in food- matters of plants and animals is so vague as scarce to deserve the name. At the top, Man astounds by his harmonies, his purposeful completeness, and power over nature ; but none are perfect. Thus we must not expect any hard-and-fast rule; there are many grades, many degrees, and many kinds of individuality, and each individual must be judged on its merits, as something really new. Finally we have learnt to appreciate the historical point of view, and through it to be brought to admire the seemingly infinite changeableness of life. On the one hand we have seen many structures and many habits of animals that can only be made fully in- telligible through their history. Each new species must go through its period of storm and stress while striving to come into harmony with its environment ; " And 'mid this tumult Kubla heard from far Ancestral voices ! " —the forms and patterns of its forefathers rise up and will not be denied, forcing themselves into the 154 ANIMAL INDIVIDUALITY [OH. vi altered mould, and thereby often taking on new and unfamiliar shapes. The ancestral plan may persist in spite of present uselessness, like the elaborate arrangement of the lines of hair on the body and limbs of man ; or it may take on some new use, like our Eustachian tube, in fish-like ancestors a gill-slit. It is by this in- corporation of the old in the new that we can trace such adventurous histories as that of the cell- individual. But this persistence is not absolute : with necessity and long lapse of time life seems able to cast away every vestige of the old forms, as when gills are replaced by lungs in air-breathing vertebrates, or when a metazoan structure, once cellular, builds itself without cells. All roads lead to Rome: and even animal indi- viduality throws a ray on human problems. The ideals of active harmony and mutual aid as the best means to power and progress ; the hope that springs from life's power of transforming the old or of casting it from her in favour of new ; and the spur to effort in the knowledge that she does nothing lightly or without long struggle : these cannot but help to support and direct those men upon whom devolves the task of moulding and inspiring that unwieldiest individual- formless and blind to-day, but huge with possibility — the State. LITERATURE CITED 155 LITERATURE CITED (1) BERGSON, H. "Creative Evolution" (Translated). London. Macmillan. 1911. (2) CALKINS, G. N. " The Protozoan Life Cycle." Biol. Bulletin XL 1906, p. 229. (3) DARWIN, C. " Journal of Researches." London. J. Murray. 1888. (4) "The Variation of Animals and Plants under Domestication." London. J. Murray. 1875. (5) DOBELL, C. C. " The Principles of Protistology." Archiv f. Protistenkunde xxin. 1911, p. 269. (6) DOGIEL, V. (Catenata.) Zeitschr. f. Wiss. Zool. LXXXIX. 1908, p. 417 and xciv. 1910, p. 400. (7) ENRIQUES, P. (Conjugation, &c., in Infusoria.) Arch. f. Protistenkunde xn. 1908, p. 213. (8) HUXLEY, T. H. "Collected Scientific Memoirs." London. Macmillan. (a) " Upon Animal Individuality." Vol. I. p. 146. (b) " On the Agamic Reproduction and Morphology of Aphis." Vol. II. p. 26. (9) HUXLEY, J. S. (Regeneration in Sycon.) Phil. Trans. Roy. Soc. (B), vol. ecu. 1911, p. 165. (10) KEEBLE, F. " Plant-Animals." Camb. Univ. Press. 1911. (11) LEDANTEC, F. " Theorie nouvelle de la vie." Paris. F. Alcan. 1908. (12) MAITLAND. Collected Papers. Vol. 3, pp. 285 and 302. Camb. Univ. Press. 1911. (13) MORGAN, T. H. " Regeneration." New York. Macmillan. 1901. 156 ANIMAL INDIVIDUALITY (14) NEWMAN AND PATTERSON. (Armadillo Quadruplets.) Biol. Bulletin xvn. 1909, p. 181. (15) PERKIER , E. "Les Colonies Animales." Paris. 1881. (16) Roux, W. "Der Kampf der Theile im Organismus." Leipzig. 1881. (17) WEISMANN, A. "The Evolution Theory" (Translated). London. Arnold. 1904. (18) WHEELER, W. M. "The Ant-Colony as an Organism." Journ. Morphology, 1911, p. 307. (19) WHITMAN, C. 0. " The Inadequacy of the Cell-Theory." Biol. Lectures, Wood's Hole, vol. n. 1893, p. 105. (20) WOODRUFF, L. L. (Life-Cycle of Paramaecium.j Biol. Bulletin xvu. 1909, p. 287. APPENDIX A TABLE TO SHOW THE FIRST THREE GRADES INDIVIDUALITY; AND TO INDICATE THE DIFFERENCE BETWEEN ACTUAL AND HISTORICAL INDIVIDUALITY OF (Aj) Individuals of the First Grade. (A2) Compound wholes made up of first-grade indi- viduals ; without division of labour. (A8) = (B0) Ditto, but with division of la- bour (rudimentary second-grade indi- viduals). . (a) Functioning as wholes: Actual Individuals. One of the hypothetical non-nucleated ancestral cells (p. 56). A Protozoan. A fertilized ovum. Gonium (p. 102). Volvox (p. 104). Haplozoon (p. 107). Functioning as parts, but descended from an^ cestors that functioned as wholes ; thus, though in point of fact not actual individuals, they are morphologically and historically equivalent to them, and may be called Historical In- dividuals. A tissue-cell of or Man. Hydra A cell of Volvox or Haplozoon. A green cell in Convo- luta. 158 ANIMAL INDIVIDUALITY (Bj) Full individuals of the Second Grade. (B2) Compound wholes made up of second-grade indi- viduals ; without division of labour. (B3) = (C0) Ditto, but with division of la- bour (rudimentary third - grade indi- viduals). (Cj) Full individuals of the Third Grade. w Clathrina (p. 90). Hydra (p. 40). Man, regarded singly. Pronuba, in certain re- spects (p. 128). Many Sponges. Many Corals. Some Polyzoa (p. 119 n.). Hydroid colonies such as Bougainvillea (p. 38). Polyzoa with avicularia (p. 119 n.). Siphonophora (p. 119). An Ant Community (pp. 12, 142). Human Society (p. 143). Yucca-plant plus Pro- nuba (in certain re- spects) (p. 128). A Lichen (p. 122). Convoluta plus its green cells (p. 126). W A single polyp of Bou- gainvillea (p. 38), or of a Siphonophoran (p. 119). Man, regarded as a Unit of Society. Pronuba, in certain re- respects (p. 135). Convoluta, considered apart from its green cells (p. 126). A single Ant (p. 142). APPENDIX B ON THE DIFFERENCES BETWEEN THE CELLS OF THE HIGHER PLANTS AND THE HIGHER ANIMALS It is probable that in certain points the cells of the higher animals and the higher plants are not strictly homologous with each other. Botanists distinguish three main types of elementary structure among plants, their differences arising out of differences in the method of cell-division practised (Fig. 16). In the first type Fig. 16. Diagram to show the three main types of elementary structure found in plants, (a) coccoid, (b) filamentous, (c) coenocytic. In each case is shown the sum of the changes following upon binary division of the nucleus of a single cell. (Coccoid), the entire cell, with its cell-wall, divides into two similar and quite separate halves. This is practised, e.g., by unicellular Algae. In the second type (Filamentous), the cell- body (cytoplasm and nucleus) divides as before, but the cell-wall does not divide ; instead, an entirely new party-wall is laid down between the two cell-bodies, and in this partition small apertures 160 ANIMAL INDIVIDUALITY are left, through which the two cell-bodies enjoy protoplasmic communication. This type of organization is found in all the higher green plants. In the third type (Coenocytic) the nucleus alone divides, and the final result is a coenocyte — a single over- grown cell with a single cell-wall and many nuclei. This plan has been adopted by the Siphoneae (p. 89). It is obvious that the first method is the most primitive and will be most generally practised by unicellular organisms; but whereas it has been abandoned by the higher plants, it seems to have been retained by the higher animals. Almost the only difference between the division of a protozoan and a metazoan cell lies in the fact that the two daughter-cells separate in the one case, cohere in the other. The essential separateness of the cohering cells is well seen in the collar-cells of simple Calcareous Sponges like Clathrina ; here indeed there is even no continuity of coherence during normal life (p. 93). Similar if less strikingly separate cells can be seen in many other groups of multicellular animals, and there can be very little doubt that the first method of division was employed by the common ancestor of all M-etazoa1 ; true party- walls like those of filamentous plants do not exist in animals, and animal syncytia (tissues formed by the coenocytic method) are undoubtedly secondary. We must now try and see what these facts mean. In the filamentous type the units are still homologous, as units, with the original units we called cells (p. 56) ; but they have sacrificed a considerable amount of independence. The whole mode of division by which they arise is an obvious adaptation to a state of existence where each is to be part of a continuous whole. 1 It is more than probable that Sponges have an ancestry quite separate from the rest of the Metazoa : if so, then the common ancestor of Sponges employed, though quite independently, the same method as the ancestor of the Metazoa proper. APPENDIX B 161 In Metazoa the separation of the cells is as a rule total, and if protoplasmic continuity exists, it appears to be secondarily produced. As regards their mode of cell-division, therefore, the Metazoa are more primitive than the Metaphyta; yet in spite of — or perhaps because of— this very separateness of their units, there has been a much greater division of labour between different kinds of units in animals than in plants. To sum up : the cells of the higher plants and of the higher animals are both true cells— they are both broadly homologous with the original units of living matter. But the mode of cell- division in the two groups, in so far as it concerns the separation of the cells and the formation of the boundary between them, is not homologous. 11 INDEX /= figure. n = note. Adaptability, importance of, 6 Adaptation, 86 ; to special modes of life, 77-79, 131 ; not univer- sal in living things, 57 ; may be too perfect, 77, 79 Aggregate differentiation, 64, 116 Albatross and wren, 86 Algae, mode of feeding, 122 American water- weed introduced into England, 71 • Amoeba, pseudopods of, 1 ; repro- duction in, 17 Amphibia, regeneration, 46 Animals,food-relation with plants, 125, 130 Ants, 24, 36, 50 ?i, 65, 141, 142, 158 Aphis, asexual reproduction in summer, 67 Armadillo, produces quadruplets, 68,70 Bacteria, duration of life, 25 ; lack of sexual process, 71 ; food- relations, 128 ; lack of formed nucleus, 59 Bee, and hive, 9; communities of bees as single individuals, 36, 65, 142 Begonia, regeneration in, 19 Benjamin Franklin's kite, 66 Bergson, . definition of individu- ality, 1, 9 ; and continuance, 20 n ; indetermination and brain-machinery, 6 Blastodinium, 110 Blastomere, definition, 69 ; re- generation of, 149 Bones, brittleness when old, 18 Bougainvillea (Hydroid colony), 37/; 158 Brain, 63, 140; and choice, 6; and individuality, 29, 65, 83, 141; modifies method of indivi- duation, 65, 140 Budding, in animals, 38, 79, 80, 118 Bud-sports, 81 Butterfly, metamorphosis in, 75 ; and flowers, 127 Catenata, 107-114 Caterpillar, metamorphosis, 77 ; " skin and squash," 78 Caulerpa, a single enlarged cell, 89 Cells, 65, 68, 150; units of structure in higher animals, INDEX 163 36 ; form the whole bodies of protozoa, 38 ; origin of, decreed by nature of protoplasm, 56, 65; influence of, upon history of life, 65 ; size of, 86, 89 ; repro- duction of, 41 /, 42, 44; modi- fications of, 137 ; and indivi- duality, 65 ; independence of, in some animals, 97; of Sponges, 90-97; of Volvox, 104; of Catenata, 107 Chess, 14 n Chick, before hatching, 77 Choano-flagellates, 95 Chromatin, 59 Chromosomes at sexual fusion, 80 Church architecture, 61 Ciliata, sexual process in, 67, 71 Clathrina, 90, 158 Clavellina, regeneration of half the body, 46, 146 Closed Systems, 9 Coenocyte, definition, 89 n Colonies, 139 ; how formed, 38 ; individuality of, 99; of Volvoci- dae, 102 ; of Hydroids, 36-40, 67, 75, 76; of Siphonophora, 37, 119, 141, 158 ; of corals, 36 ; of Termites, 12 ; of ants, 24, 36, 65, 141, 142 ; of bees, 9, 36, 65; of man, 65, 112, 143 Communities, 24, 36, 65 Comparative anatomy, uncon- scious, 35 Complexity, importance of, 5 Conjugation, definition, 67 Consciousness, and indetermina- tion, 6; and continuance, 26; and personality, 30, 84 ; states of, 13 ; beginnings of, 29 Continuance, of individuals, 15, 24, 25, 33 ; only partial, 20 ; increase in, 25 Corporate personalities, 143 Crystals, difference from indivi- duals, 21, 51, 52 Cytoplasm, 59, 147 Darwin, 1, 6, 133 Death, includes two separate pro- cesses, 16 ; and growth, 18 Dermal cells, 91-97 De Vries, and mutations, 80 Dicey, on personality, 143 Distomum, 22 /, 23 Division, reproduction by, in animals, 41 /, 42 Division of labour, 107, 116, 123 ; in man, 112 Dogiel, 107 Double monsters, 68 Echinoderms, 79 Egg, 43, 67-70, 149; a cell, 43 Elephant, 86 Elodea, lack of sexual process in England, 71 Embryo, of man, 34 ; more than one formed from a single ovum, 67-70 England, 54 Enriques, and sexual process in protozoa, 71 Environment, adaptation to, 77-79, 127 Etymology, and individuality, 82, 83 Eustachian tube, 154 Evolution, its meaning, 27 ; altered point of view due to, 31 Fertilization, 45, 71 ; of ovum 164 ANIMAL INDIVIDUALITY supposed to mark beginning of a new individual, 67, 72 Field-mouse and elephant, 86 Fission, in animals, 41/, 42, 71 ; in protozoa, 67, 71 Flagellum, part of a cell, 90, 102 Flowers, and insects, 127 Fluke of liver-rot, 23 Franklin, B., experiment with kite, 66 Frog and tadpole, individuality in, 72, 75-78 Fungi, mode of feeding in, 122 Gamete, definition, 45 Germ-cells, of Sponges, 92 ; of Volvox, 105 Gonium, 102, 153, 157 Growth, difficulties involved in, 17 Grub, metamorphosis of, 72 Gymnodinium, 109, 113 Hand, relation with rest of body, 9, 10, 15 ; grasping function of, 12 Haplozoon, 107-114, 138, 150, 157 Helen Keller, 131 Heterogeneity, of individuals, 10, 14, 28 History, all-important in Biology, 32, 48 ; as a clue to individu- ality, 48 Hooker, Sir J., 141 Huxley, J. S., 94 Huxley, Prof. T. H., view of in- dividuality, 72, 75, 76 Hydra, 39/, 40, 67, 118, 157, 158 Hydractinia, 118, 120 Hydroid polyps, 36-40, 47, 67, 75, 118 Independence of the individual, 3 et seqq., 28, 130, 135 ; per- fection of, 8, 28; progress of, 87 ; of cells, 97 Individual, 125, 152, 154; certain organisms naturally regarded as individuals, 3 ; unconscious use of word by average man, 3, 35 ; etymology, 3, 82, 83 ; general definition of, 28 ; de- finitions by other writers, 67, 83; heterogeneous, 10, 11; in- dependent, 3 ; unified, 9, 11 ; continuing, 15, 16, 20, 24, 127 ; actual, 157; historical, 120, 157 ; degraded to an organ, 120; man the most perfect, 70 ; physical continuity of one in- dividual with its offspring, 46 ; the perfect, 7, 21 Individuality, 62, 98, 125, 135, 142 ; general definition, 28 ; tendencies and progress of, 28, 116; etymology of, 3, 82, 83; various definitions of, 31, 67, 83, 85 ; its attributes, 3, 9, 10, 15, 28 ; compound, 98, 99 ; of a species, 23-25, 82; spatial, 25; simultaneous, 25; tempor- ary, 127; historical, 120, 157; according to Bergson, 1 ; and man, 31-35, 48, 70, 143 ; and personality, 30, 34 ; in colonies, 36-40; and regeneration, 46- 47 ; and brain, 6, 29, 65, 83, 140; and sex, 67, 71, 72; and metamorphosis, 72-80 ; and re- production, 17, 18; and matter, 18, 29, 30, 146; and hetero- geneity, 57, 99, 101 Internal differentiation, 60, 136, 140 INDEX 165 Jelly-fish, reproductive in func- tion in Hydroids, 118, 119 ; lack of complexity, 6 ; artificial production of twins and quad- ruplets in, 69 Jerboa, thigh-muscles, 87 Kangaroo, size of, 87 Keeble, 126 Keller, Helen, 131 Kite, used to bring lightning to earth, 66 Kubla, 153 Kupffer's vesicle, 150 LeDantec, definition of indivi- dual, 83 Lichens, compound species, 122, 136, 158 Limbo, 34 Liriope, a jelly-fish, 69 Liver Fluke, 22/, 23, 82 Maitland, 143 Malaria, 5 Man, 148, 153, 157, 158 ; great independence of, 6 ; and in- dividuality, 31-35, 70; the tool-maker, 13 ; communities of, 65, 112, 143 Materialism, errors of, 85 Medusae, 118, 119 " Merrimac" and " Monitor," first armoured ships, 115 Metamorphosis, 20 n, 72-80; rea- son of, 77-80 Metazoa, and protozoa, 43, 44 ; compound individuals, 36, 44 Metschnikoff, and death, 20 M, and disharmony, 152 Microscope, 5 Milton, and life before birth, 34 Minoan dancers at bull-fights, 19 Monsters, double, 68 Mutations, and individuality, 80 Nectarine, produced as bud-sport from peach, 82 Nelson, 115 Nemertine worms, metamorphosis in, 72-75, 79 Nero, 56 Nerve-cell, 137 Nervous system, 63 ; supposed basis of individuality, 83 Newt, regeneration of lost organs by, 46 ; artificial production of twins in, 69, 70 Nietzsche, 1, 9 Nucleus, 57 n, 59, 89rc, 147; in sexual process, 71, 80 Organs, and individuals, 120 Ovum, 43, 157 ; erroneously sup- posed to contain the potentiality of only one individual, 67 ; division of, into independent parts, 67, 139 Paramaecium, reproduction in, 17 Parasites, special environment of, 113, 127, 134 Particular, in philosophical sense, 9 Peaches, and bud-sports, 82 Peridineae, 109 Personality, definition, 30 ; and matter, 30; and individuality, 34, 84 ; corporate, 143 Phagocytes, 78 Pilidium, strange metamorphosis of, 72-75, 79 Planaria, 144 Polyzoa, 119 n, 158 166 ANIMAL INDIVIDUALITY Pores, of Sponges, 91, 97 Potentiality, 8 Printing press, 16 Printing, and increase of indivi- duality, 26 Pronuba, 128, 135, 142, 158 Protoplasm, its properties in rela- tion to individuality, 8, 17, 49, 56 ; its advancing flow, 28 Protozoa, reproduction in, 17, 18, 19 ; free-living cells, 38, 157 ; and metazoa, 44, 67, 120, 150 ; views as to individuality of, 67 ; sexual reproduction in, 67, 71 ; size of, 88 ; relative lack of independence, 5 Psychical research, 30 Quadruplets, always given birth to by one species of Armadillo, 68, 70 Raindrops, influence of electricity on, 11 Regeneration, 10 n, 11, 19, 21, 46-47, 147 ; an original attri- bute of life, 46; in Vertebrates, 46 ; in Protozoa, 10 n, 47 ; in Flatworms,47,144; in Sponges, 94-97 Regulation, 11 Reorganization as opposed to true regeneration, 95, 145, 149 Reproduction, in Protozoa, 17, 41 /, 42 ; of molecules, 51 ; and individuality, 18, 19, 40, 42; by budding, 38, 40; by fission (division), 41-43; asexual, 38-43, 81 ; sexual, 43-45 ; not involved in metamorphosis, 77 ; by cuttings and slips, 80 Rhynchops, 133 Rome, 154 Rook, 133 Roux, extension of idea of natural selection, 6 ; idea of growth, 17 Salamander, replacement of lost organs, 46 Scurf, 137 Sea-urchins, artificial production of twins, quaduplets cfec., 69, 70 ; metamorphosis, 79 n ; will die if cut in half, 83 n Self-consciousness, implies exten- sive individuality, 30 Sense-organs, and individuality, 64, 140 Sexual fusion, 43, 45, 67, 70-72, 80, 81 ; in Bacteria, 71 ; in Protozoa, 67 ; in Metazoa, 80 Sexual reproduction, 43 ; not es- sential, 45, 70 Sheep, and Liver Fluke, 23 Siphoneae, single cells, 89 Siphonophora, 119-122, 141, 158 Size, 64 ; advantages of, 5, 7, 86 ; disadvantages of, 17 Skeleton, 17 Skimmer, 133 Sleeping sickness, 127 Snails, and Liver Fluke, 23, 24 Societies, of man, 65, 143, 158 Solar System, difference from an individual, 9, 21 Sparrow, 133 Species, 27 Species-individuality, 23-25, 82 Speech, increases individuality, 26, 29 Spermatozoa, 18 n Spicules, of Sponges, 92, 96 Sponges, 90, 141, 148, 151, 158 Sports, in plants, 80 INDEX 167 Stentor, regeneration in, 10 w, 47, 147, 149 Stomach, in young nemertines, 74, 75 Stylonychia, reproduction in, 41/, 42 Suez Canal, 5 Suicide, 137 Surface-tension, 59 ; effects of, 53, 86 ; alteration of, by living matter, 55, 86 Surface-volume ratio, 50, 55, 88 Swallow, 133 Sycon, 94 rc, 147 Symbiosis, definition, 122; exam- ples of, 122, 124 Syncytia, 137 Tadpole, change into frog, 72, 75- 78 Tapeworm, 127 Teeth, in old age, 18 Teleology, errors of, 85 Teleost fish, 150 Termites, 12 Tools, part of man's individuality, 14, 29 ; inorganic organs, 13 Trees, in old age, 18; duration of life, 26 Trypanosomes, 127 Twins (identical), 68, 70 ; normal production of, 68, 70; artificial production of, 69, 70 Volvocidae, evolution of , 102-107, 111 Volvox, 95, 104, 110, 114, 138, 150, 151, 157 Walt Whitman, 114 Warfare, evolution of, 115 Water, its ** metamorphosis," 76 Weismann, on sex, 45 Wheeler, 142 " White ants," 5 Whitman, 149 Woodruff, and lack of sexual process in Ciliates, 71 Wordsworth, 141 Worms, Nemertine, 72-75, 79 Wren, size of, 86 Yolk-sac of unhatched chick, 77 Yucca-plant, dependence on an insect, 128, 135, 142, 158 Zarathustra, his independence of accidents, 1, 3, 8 Zoothamnium, 100 Zygote, definition, 45 ; fertilized ovum, 67 CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS. 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