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.]