FIVE SOULS WITH BUT A SINGLE THOUGHT.
THE PSYCHOLOGICAL LIFE OF THE STAR-FISH.
The investigation of the psychical faculties of animals is comparable to a journey into fairy-land. We do not know, and according to Du Bois-Reymond, we shall never know, how our own mental activity has originated, yet in spite of this we deliberately form theories and opinions concerning the psychical powers and faculties of other beings that in point of nervous organisation are perhaps altogether different from us! The ancients wisely limited themselves to expressing the intelligence of animals in the form of instructive fables, and in the famous park of Versailles the charming idea was actually carried out of representing the fables of Æsop in a so-called labyrinth, every turn of the intricate lanes of which led to a different group of animals whose speech was symbolised by streams of water spouting from their mouths, and the purport of their imagined utterances was to be read in golden letters upon marble tablets placed at the side. How often have I wandered over the scene of those long since ruined mazes and have thought of the deep meaning that frequently lies in childish pastime of this kind.
But labyrinth aside—when we see an animal perform before our eyes purposive acts; and we recognise that our own thought operates in accordance with definite, rigorous laws; we shall still have to say to ourselves that a comparative animal psychology is after all not necessarily so hopeless a thing as one might be led to believe from the bold, and yet faint-hearted, "Ignorabimus" of the distinguished Berlin physiologist. And as a matter of fact the range of insight obtained in very recent times into this very field is highly encouraging. On this occasion I should like to select for discussion one of the most remarkable of questions, that, namely, which concerns the psychical activity of many-souled animals.
Quite a stir was made some years ago in the scientific world when Haeckel began to philosophise about the souls of cells, or so-called plastidule-souls; for it was patent that the course of life in the individual single cell of an animal or vegetable body flowed on in such strict conformity with reason that it was logically necessary to posit the presence of psychical guidance in the instance in question as much as in the case of composite cellular colonies in higher organic beings,—especially since every single one of these composite organisms begins its life as a simple cell, from which the others afterward spring. The wide-spread opposition that Haeckel's view met with, must be regarded as the result of current and common ignorance of the history of philosophy; since otherwise it must have been known that the idea of a cell-soul or a germ-soul which controls the development of the young, has been propounded by innumerable philosophers, and that it was proclaimed by Daniel Sennert, of Wittenberg, who died in 1637, with perfect consistency as the foundation of all psychological knowledge. Many beings, such as Algæ, Fungi, and Infusoria, never in their lives get beyond the state of a single cell, and yet under the microscope we may observe them seeking light, capturing prey, and in the majority of cases founding families. And when the Genevan Trembley discovered, in 1740, the fact of the divisibility of fresh-water Polyps and showed that after cutting them up every piece grew and developed into a new individual endowed with sensation, will, and other psychical capacities, philosophers began to debate whether there were initially present in every divisible polyp a number of souls in the germinal state, or, if such were not the case, whether the simple soul of a polyp possessed the property of divisibility. The Leipsic theologian Crusius, who died in 1775, declared in favor of the presence in every polyp of a plurality of germinal souls; the Dutch insect anatomist, Peter Lyonnet (died 1796) declared in favor of the divisibility of the single polyp soul.
[Illustration: Fig. 1.—STAR-FISH. (After Haeckel.)]
But let us pass by these subtle speculations to turn to a class of animals in the case of which we may speak with more propriety than in the case of polyps and other zoöphytes of a plural soul, since physically and psychically they act in every respect as if they had grown together out of five or more individuals,—I mean the Echinoderms in general and the Star-fish (Asteroidea) in particular. In the following paragraphs, for the sake of brevity, I shall speak of only five-rayed star-fishes, because the sacred number five is the one that lies at the basis of the physical structure of the great majority of star-fishes developed from the egg, and of all other echinoderms, although there really do occur star-fishes which are supplied, some with more and some with less than five rays,—single rays often being cast off and a larger number growing out in their places,—and although many species are regularly and normally supplied with more than five rays. From visits to the sea-shore or to aquariums, at any rate from pictures, my readers all know how a star-fish in general looks. In the first cut which accompanies this article a number of echinoderms are presented. The star-fish is in the centre to the left. It resembles the decorative star of an Order, and has short or long, broad or slender rays, as the case may be, and a disc-shaped central body.
The observation which is most important for our present discussion, and which strikes us on first seeing a star-fish, or its relatives the sea-urchin and the sea-anemone, consists of the fact that these animals possess no head, which even the most insignificant worm or insect does not lack, and that consequently its organs are in want of a guiding, regulative member, possessing externally organs of sense and having within a brain with the power to communicate the requisite commands for the movement and the conduct of the same. On the contrary, each single branch or ray possesses its own individual nervous system; and in the case of the voluntary separation of the rays, which frequently occurs, is able to continue life of its own independent accord, developing itself by the growth of new rays into a new and complete star-fish. (See Fig. 2.) But these five or more nervous systems do not radiate from a common central nerve-ganglion which might be termed a central brain, but are merely joined to a nerve-ring which lies in a common central portion, encircling the esophagus; this nerve-ring in the majority of cases forms a regular polygonic figure, and into each angle of the polygon the nerve-cord of a ray enters. It will be seen from this structural arrangement of things, that the psychical and mental guidance of these animals is entrusted to a board of five members who possess, it is true, sentient communication with each other, but act without the intermediation of a presiding officer.
[Illustration: Fig. 2.—COMET-FORM OF ARM OF A STAR-FISH.
A cast-off arm re-forming by the sprouting of four new rays.]
We may well look forward with intense interest to the outcome of a psychical administration of this kind, and to tell the truth, until recently its importance has been greatly underestimated. Every inference made with respect to the psychical excitability of an animal must be derived from its movements and actions in various natural and artificially produced positions, by observing what its conduct under these conditions is. To start with, star-fishes, like sea-urchins (which psychically are similarly governed), admit with respect to the position of their bodies a distinction of top and bottom; that is to say, the side on which the mouth lies situated in the centre of the five rays belongs properly face downwards, while the opposite surface is to be regarded as the dorsal side. But the conceptions of a forepart and a hindpart, of a right and a left are not applicable. The rays of the star-fish, like the central disc, also plainly exhibit a distinction of lower and upper parts. Among the real star-fishes (Asteroidea) the inferior or ventral surface of the arms is supplied either with two or with four rows of sucker-feet or pedicels, consisting of long, extensile, hollow sacs, which when filled and extended by the water let into their widely ramified ambulacral systems, protrude into the grooves of the arm through openings in the hardened calcareous integument. To level surfaces they easily cling fast by simply drawing back the terminal discs of their tubular feet and thus creating a rarefied atmosphere in the space between the object to which they adhere and the puffed out walls of the extremities of the pedicels. Star-fishes may be seen climbing in this way, with their hundreds and hundreds of tube-feet, up slippery cliffs and even the perpendicular glass walls of aquariums, and they are even able to hang suspended from a horizontal glass ceiling for a considerable length of time after they have been taken out of the water. When they wish to change their position they do it by alternately loosening and fastening their extensile feet in such a way that those loosened reach forward in one and the same direction uniform in all the arms, and fasten themselves to the surface anew, whereupon the others also let loose and go through the same movement in the same direction. The sucker-feet also help to convey to the mouth the food seized at the end of the arms.
[Illustration: Fig. 3.—MODE OF LOCOMOTION OF SAND-STARS. (After
Preyer.)
In the cut to the left 1 first advances, then (5) and (2); 3 and 4 remaining at rest. Whereupon (5) and (2) simultaneously come back to the positions 5 and 2, c is lifted and pushed forwards with 1, while the two rays 3 and 4 are pulled along behind. In the figure to the right the same animal first shoves forward the pairs (1) (2) and (5) (3), 4 remaining at rest, and then bends both pairs backwards, dragging only 4 behind; c is lifted and thrown forward in the direction of the arrow.]
While in this instance, accordingly, the arms, although they are not immovable and bend and approach each other, officiate rather as the bearers of organs than as prehensile and locomotory apparatuses themselves,—the sucker-feet performing the principal tasks and requiring for their work a very finely ramified nervous system; in the case of a certain other division of the star-fishes, the so-called sand-stars (Ophiuridae), the arms are thinner and more supple, and act as organs of prehension and locomotion, dispensing more or less entirely with their suctorial pedicels. By alternately thrusting three feet forward (Fig. 3) and then drawing back the two side feet of these three, the five-footed sea-stars move more swiftly than the others, sometimes proceeding by jumps even; but they cannot climb up smooth surfaces, or cliffs, unless irregularities are present which may be grasped by their pliant arms, whereas on the other hand the common star-fishes, which are furnished with sucker-feet, climb best of all on smooth and slippery surfaces, each one of their countless pedicels being able to suspend a considerable weight, in some species as much as twenty-five grammes. In other respects, especially with regard to the ring-shaped connection of the five nerve-cords, their organisation is essentially the same; only in the sand-stars the central portion forms a disc more distinctly separate from the arms, in which former the common organs of feeling and digestion have more fully retracted.
Recognising thus, that the star-fishes and all their relatives act physically like a federal animal-union, composed of five independent animal-states, I called attention in the first edition of my work "Werden und Vergehen" (1876) to the psychological enigma that we were here confronted with a five-fold Siamese monster, as it were, in which five separate persons were brought mentally under the same guidance, or where five minds had to pull, simultaneously, one rope. On account of the absence of a head and a brain in these animals, certain well-known modern animal psychologists have taken the position that their powers of psychical performance are very scanty, and that, in a much fuller sense than was predicated of all animals by the Cartesians, these especially were irrational automatons, or, to use a technical expression, were mere "reflex-organisms," animals in which only direct external excitations evoke with unalterable regularity responsive movements, so that, for example, if any unpleasant excitation were brought to bear on them from any direction they would move in the opposite direction, but world approach if anything became perceptible that excited their desire for food. On this ground the distinguished English animal psychologists Romanes and Ewart claim to have established that these animals actually do respond like machines to external excitations; if they were excited at any part of their body by a wound, by the application of acids, an electric current, or any other irritant, they would run without exception in a straight line in the opposite direction, but if the excitation were applied to any two parts of their body at some distance from each other they would move in the line of the diagonal of the two directions, in accordance with the principle of the parallelogram of forces. Similarly their movements after prey and food (the presence of which at a distance was made known by the emission of odors), their movements toward more brightly illuminated parts of the containing vessel, their flight from the air into the water, their recovery of their normal position when placed on their backs, and finally their so-called autotomy or self-amputation, that is the casting off of their members under the irritation of powerful stimuli—were all held to represent mere automatic responses to prearranged conditions without a trace of intelligence being exhibited.
In view of this condition of things it was a very welcome announcement, that one of the most brilliant representatives of modern experimental physiology and psychology, Professor W. Preyer, at present of Berlin, had determined to undertake a comprehensive series of experiments with these very animals, and was able to carry out his intention at the zoölogical station in Naples, so admirably adapted to the purpose. To obtain clear ideas generally with regard to animal reflex-mechanisms, fitter specimens for experiment could scarcely be presented than the star-fishes, which unite a rare degree of decentralisation, power of independent action, and absence of a cerebral centre, with a nervous system of the minutest ramifications. Here, if anywhere, were simple, clear and transparent results to be expected, and finally information relating to the co-operative activity of different nervous systems. Preyer published the results of his observations in the "Mittheilungen der Zoologischen Station in Neapel" for the years 1886 and 1887, and although he does not regard his labors as completed, the scientific reading public may nevertheless take sufficient interest in the present state of his researches to justify a presentment of the principal and most general results obtained.
In confirmation of the view that previously obtained it was found that these animals actually did respond in a rare degree to given stimuli in a manner determined once for all; it could be foretold with a degree of sureness verging on astronomical certainty, how, for example, the sucker-feet of a star-fish would act if the animal in its normal and sound condition was irritated at this or that place, powerfully or weakly, one time or many times successively, by mechanical or chemical applications, by electric currents, or heated instruments. With all the means of irritation employed the result was always identical, and consisted in the fact that the distensible feet were drawn in at the point of application when the irritation did not extend beyond its region, no matter whether it was applied at the inferior or superior surface of the animal, but that protrusion of the feet never resulted from local irritations of this character so long as they did not exceed a certain intensity. A more powerful irritation, on the other hand, radiating over a greater portion, or over the whole animal, produces a general protrusion of the distensible pedicels, so far as the irritation extends, with the single exception of the point of application itself when the same lies on the inferior surface.
Inasmuch as this swarming protrusion of pedicels may spread over the entire inferior surface when only a single arm is irritated in the neighborhood of its extremity, it follows from this that the nervous excitation must first be conveyed to the ring at the centre in order to radiate thence to the pedicels of the other arms; and from the manner in which the irritation is propagated, the course of the radiation can be accurately followed. Thus, if the irritation of an arm proceeded from the dorsal region, the distensible pedicels of this arm were the first to protrude, then those of the two adjacent arms, and finally those of the two remaining arms, but in the latter not quite out to the extremities unless the irritation exceeded a certain intensity. That is to say, the effect of the irritation was propagated through the inner nerve-ring according to the same laws by which a fluid under pressure or an electric current in a similar conductory system would proceed. But if the connection of the ring was severed at both sides of the irritated arm, the effect would remain confined to that arm. If the connection was broken only on one side the irritation advanced round the other side and reached the severed neighbor last. On the other hand, a powerful irritation of the central disc immediately provoked the extension of all the pedicels. The phenomena recorded occurred moreover in accordance with simple mechanical laws as was expected from the outset, and when the irritations were unusually powerful the effect was manifested by a continuous alternate extension and contraction of the pedicels.
Amputated arms of the common sucker-footed star-fish act like arms isolated at both sides by severance of the nerve-ring, as just explained. Upon local irritation they draw in their pedicels, and protrude them upon being powerfully irritated; they creep forward in a definite direction, and when placed upon their backs are able even to turn themselves over like the uninjured animal. The severed arms of sand-stars are less independent. They twist about aimlessly hither and thither, but if any considerable portion of the central disc and nerve-ring adheres to them they are able to perform adaptive movements. Similarly the disc, with one or two arms attached, is not helpless; and is able to get along quite alone without any arms. We could explain all these movements by so-called reflex actions and might grant also that the mechanism that effects these results operates in this case upon a greater scale and with more independence than in other classes of animals, for the reason that here a real guiding organ is not present.
But whatever might be inferred from the experiments just described in favor of a senseless and unintelligent life of star-fishes, Professor Preyer was nevertheless able by extending his experiments to win the conviction that the old conception of star-fishes being real reflex animals was wholly untenable, since a great number of capacities and capabilities could be verified and provoked, which are intelligible only on the basis of adaptive co-operation and mutual concerted action in the five rays. We shall not discuss here whether this is also proved by the wonderful fact that a star-fish, which fastens its arms to everything possible, never seizes its own arm and thus, like Molière's miser, in its visits to its oyster beds never catches itself for a thief. We might say, indeed, that the arm seeking a hold does not seize its companion because it feels it and has learned by experience that it takes a Münchausen to pull one's self out of a swamp by the tops of one's boots. But we find exactly the same phenomenon among creeping plants, which clasp every kind of support in their way, but never, as Darwin observed, take hold of their own stalks; whence we might assume that there probably exists in these beings some sort of power of reflex inhibition dependent upon a property of the body and developed in consequence of the fact that clasping and grasping parts of itself would involve a useless waste of energy. We shall see, however, that under certain circumstances this instinctive "dread" of contact with self is inoperative.
But to our main task. In the simplest changes of place and position, intelligent co-operation of the arms is manifest. For if in moving from one place to another, or in turning around each arm tended to perform on its own account the necessary movements of extension or rotation, without giving any heed to the others, the animal would endure the torments of Tantalus before it could reach, if ever at all, the choice bit of food that it had scented from afar, or the ray of light towards which an obscure impulsion drove it. On the contrary, when a star-fish is spying after food, we observe it lift the ends of its pedicel-covered arms so that the downward deflected eye there situated may obtain a good view of things in the neighborhood, and if in any direction an object worth going after is discovered we see the many hundreds of sucker-feet on the five arms push out in one and the same direction,—a phenomenon that requires the presence of a very widely ramified nervous system, since every tactile pedicel needs its separate telegraph wire in order to be properly moved and not always in the same direction, as for example when the animal wishes to perform a rotation about its own axis. For these comical animals sometimes do rotate about their axis, although our simple mind wonders why a Janus-head should want to turn around, these animals being able to look simultaneously in the four directions of the compass, and having still another eye for looking downward. Similarly in the sand-stars, to which the Medusa-heads with branched arms belong, an adaptive co-operation of the arms in creeping and swimming occurs; which can be explained only as the result of a common understanding issuing from the central ring.
It would seem to follow from Preyer's extensive observations, that as a rule no one individual arm of a star-fish enjoys to the exclusion of its fellows the prerogative of universal or even general precedence; the lead of any one arm is rather solely determined by the object sought, so that the one next to the object generally starts first and assumes the lead of the little army of arms. Of course in the case of new-growing star-fishes which have sprung from a single arm by sprouting, this is different; for in this instance the old arm will undoubtedly retain control of the others for some length of time until the young ones have reached a certain size. Preyer does not seem to have instituted observations to ascertain this, but it would be interesting to determine whether an arm of this kind always takes the lead, or in the proper cases acts as driver from behind and pushes the baby-carriage with the children before it.
[Illustration: Fig. 4.—RECOVERY OF NORMAL POSITION BY ASTROPECTEN
AURANTIACUS. (After Preyer.)
Through the end of each ray of the animal a thread is drawn and affixed to a cork; the animal lying back downwards. At first the creature swung the corks alternately inwards and outwards, taking the positions represented in the above figure. After the lapse of an hour the ray with the smallest cork attached, upon which thus the least upward pressure was exerted, was pulled downwards and sidewise and brought beneath an adjacent ray; the two opposite rays were retracted centrally, the disc lifted, the centre of gravity of the animal thus displaced, and the turning effected.]
Examples of surprisingly dexterous co-operation and concerted adaptive action are observed in these animals in their climbing on difficult surfaces, and in their attempts, also, to regain their normal position when placed on their backs or made to swim in reversed positions by discs of cork fastened to the extremities of their arms. Scientists have observed members of the orders Asteroidea and Ophiuroidea, in difficult positions of this kind, display an astounding sense of equilibrium and a skilfulness in gaining firm holds, suggestive of the athletic feats of monkeys, and that even when placed in very unusual positions such as never occur in nature. Thus many star-fishes let themselves drop from steep rocks and cliffs, if that happens to be the best way of getting down; but in such cases before they let their whole weight go hold fast to the last moment with one or two arms, as if it were previously necessary to calculate the leap into the depths below. To furnish the counter-test of this, and to prove that the central nerve-ring is, as assumed, the indispensable and necessary condition of this united co-operation, Preyer severed the ring in individual specimens of the class between every two arms, sparing the other parts as much as possible. In this way the nervous systems of the five rays were disconnected. As was expected, it was found that the more connections there were severed, the more difficult the animal found it when placed on its back to regain its normal position. For since the recovery of the normal position must be introduced by the groping about and the fastening of the pedicels of one or of several adjacent and half-turned arms, two arms or pairs of arms might for want of a mutual understanding act directly in opposition to one another and thus make the turning impossible. On the other hand, the central disc was able, though deprived of all arms, to accomplish the turning, if only the nerve-ring were preserved intact; and the more there remained of the nerve-ring on a single arm the better the single arm was able to do it.
But in circumstances which were wholly new, the adaptive co-operation of the arms demonstrated itself in so striking a manner that we may say they are not to be easily put out of countenance or confounded. When Professor Preyer, for example, slipped narrow rubber bands or cylinders over their rough spiny arms, they rid themselves as a rule of these unwonted fetters in a very short time, and in the most various but always well calculated ways. Generally the two nearest ones seized their poor imprisoned fellow "under the arms," bracing themselves with their rough spiny surface against the rubber sleeve, and thus finally stripping it off. (See Fig. 5; next page.) Sometimes, when the band was loosely adjusted, twisting movements of the arm in the water sufficed gradually to loosen it, until it could be finally cast off. Often the peeling off was effected by pressing against a rough surface, whereby sometimes an adjacent arm held the sleeve fast; and when no other expedient was of avail the animal cast the arm, sleeve and all, away from itself; and the latter may possibly have not gotten rid of it at all. At times the casting off of the arm occurred subsequently, after the obstacle had been entirely removed, and often even a day later, as if the impeded arm was still sensible of some obstruction which caused it to afterwards separate from its companions.
[Illustration: Fig. 5.—REMOVAL BY OPHIOMYXA OF A RUBBER SLEEVE. (After
Preyer.)
The figure represents the moment at which the band is about to be removed. An adjacent arm is braced against the lower edge of the band, forcing it off in the direction of the extremity of the ray.]
Attempts at flight and liberation from unwonted compulsory positions or narrow confinement, also deserve special attention. Many a person who has put a star-fish into a cage and fancied that he was assured of its possession, has been disappointed on finding that the animal had effected its escape through the meshes. But star-fishes have, in consequence of their abhorrence of the air, been made to creep into the narrow necks of bottles filled with water. Professor Preyer, for example, thrust two of the arms of a common star-fish species (Asterias glacialis) into a tube filled with salt water leaving the three other arms exposed to the atmosphere outside; and although it would have been impossible to force the animal into the tube without crushing it, the three arms exposed to the air were also pulled in within the space of three minutes. If the tube was placed perpendicularly in water the animal quickly crept out again. The performance seemed utterly impossible, for each single arm of the star-fish was almost as thick at its base as the greatest width of the tube, and yet three of these arms had to pass in side by side. This was made possible by the animal emptying during the passage all the numerous water-vesicles in the interior of the arms which serve to fill and to empty the distensible pedicels therein; the star-fish, after the expulsion of the water, becomes very soft in all its parts and does not harden again until it has forced itself completely through and refilled itself with water. In order to accomplish these emptyings, bendings, turnings, and rollings, thousands of muscular fibres must work in harmony within the body of the animal. This experiment was also successfully carried out with other star-fishes, but I cannot agree with the observer when he says that in so doing he brought the animals into a completely new and hitherto unexperienced position. In their haunts on rocky coasts they must assuredly often have to force their way through narrow fissures and holes; and they must find occasion to make use of the advantages of being able to evacuate water in the case also of single arms, as when they search with them in narrow apertures and snail-houses.
But undoubtedly new for these animals was the position in which they were fastened to a board by five long pins with broad heads, which Preyer drove in close to the central disc between the rays, so that the star-fish, as it seemed, was fastened to its resting-place in a way that admitted of no escape. Nevertheless, the star-fish found a means of freeing itself with ease and elegance from this constrained imprisonment in a great variety of ways, even when the exterior parts of their bodies were girded in by a much greater number of pins. Ordinarily they began by shoving one of their rays, accompanied by a backward bending movement of its two companions, far out between the two encompassing pins, and then drew with the greatest care first the one and then the other adjacent ray through the same narrow avenue of escape, whereupon then the two remaining rays, the one slightly overlapping the other, were enabled to follow with perfect ease. (See Fig. 6.) A practised knot-untier who had studied the position could not have given them better advice. But if no agreement of plan and purpose existed in this case between the separate rays, if each ray sought to free itself of its own accord, a successful extrication from the difficulty could hardly have been foreseen; and we must infer from this great unanimity of action in times of danger.
[Illustration: Fig. 6.—EXTRICATION OF STAR-FISH IMPRISONED
INTERRADIALLY BY TACKS. (After Preyer.)
1. Original encompassment. 2. First stage of extrication. 3. Second stage. 4. Third and last stage. The smaller figures indicate the successive positions of the same rays.]
Preyer thinks that at times the concurrence of all the rays in matters of concerted action might have to be effected by first obtaining the concurrence and assent of any individual ray that might be hostilely disposed; he holds it as not improbable that profound dissensions may arise between the united brothers, and refers to the fact that perhaps the voluntary section of a star-fish into a three-rayed and a two-rayed portion,—which frequently takes place,—may have to be regarded as the violent dissolution of a community of fellow animals formerly living in harmony, but now lapsed into a state of conflict. We shall pass this view by, however, to point out in a few words Preyer's general inferences with regard to the mutual relation of the five communal souls. Progression and flight in a direction once taken and unimpeded by obstacles,—an observation often made and easily verified,—the acrobatic performances, and lastly the intelligent behavior, so to say, of imprisoned and fettered star-fishes, prove that generally, and especially in moments of peril, strength-giving unanimity prevails.
But Preyer is nevertheless of opinion that it is not therefore necessary to assume the existence of a permanent central government, a central soul, holding simultaneous sway over the five radial souls, and in which is lodged, especially in times of battle, full executive power. He employs the simile of five hunting-dogs yoked together in the form of a ring, of like age, like power, and the same training, who hunt a hare in concert, or stand simultaneously and mechanically before a partridge; when thrown into the water make for the shore all in the same direction, and when equally tired fall simultaneously asleep. "Like the Siamese twins," he says, "these yolked-together dogs will have upon the whole apparently but one will, although they often obey only necessity in this and not their own impulses." Preyer arrives in this at the same conclusion that I pronounced in 1876 in the work I have mentioned, where I compared the concerted actions and movements of star-fishes and sea-urchins to the walking and dancing of human twin-monsters, who in spite of a difference of mental individuality, often very far reaching, nevertheless bring about perfect harmony in their external movements. In this I had especially in mind the so-called "two-headed nightingale," two girls closely united in growth, who often violently quarreled but sang and danced so harmoniously with one another that for the time being the sorrowful fate of the indissoluble union of two so different natures was completely forgotten. In the majority of their relations the five or more associates united in the star-fish are much better off than unfortunate human beings like those just described, and especially in this one particular that they do not have to die with one another, but are able to break loose with impunity from a companion whom death threatens, when they observe that he has suffered a wound or loss, simply expelling him from the community.