Comparative Physiology of the Brain and Comparative Psychology

Hence the " instinct" that drives animals into the light is nothing more than the chemical — and indirect- ly the mechanical — effect of light, an effect similar to that which forces the stem of the plant at the window to bend toward the source of light, or which forces Palsemonetes to collect at the anode. The moth does not fly into the flame out of " curiosity," neither is it " attracted " by the light ; it is only oriented by it and in such a manner that its median-plane is brought into the direction of the rays and its head directed toward the source of light. In consequence of this orientation its progressive movements must lead it to the source of light.

We now come to the most important question in this chapter, namely, the relation of the central nervous system to the instincts. As long as such apparently complex things as the instincts are not analysed but treated as entities, it is easy to believe that they are based upon very mysterious nervous structures. It would harmonise with the centre- theory to assume for the moth a " flying-into-the- tlame centre," * and to seek for its localisation in the central nervous system. The fact that the flying of the moth into the flame is nothing but positive helio- tropism, and the fact that the positive heliotropism of animals is identical with the positive heliotropism of plants, proves that this reaction must depend upon conditions which are common to animals and plants. Plants, however, possess no central nervous system, therefore I believe that it is impossible for the helio- tropic reactions of animals to depend upon specific structures of the central nervous system. It is much

'Steiner tries indeed to "explain" the righting motions of the starfish by the assumption of a "righting centre " in the central nervous system. He does not consider the possibility that contact stimuli and the irritable structures at the periphery may be sufficient for this reaction, and that the nerves act only as protoplasmic conductors between the skin and the muscles. more probable that they are determined by properties which are common to animals and plants. From what has been said above it is easy to infer what these properties are : First, heliotropic animals as well as heliotropic plants must contain a substance on their surfaces which undergoes a chemical change when subjected to the influence of the light, and this change must be able to produce changes of tension in the contractile tissue. Second, heliotropic animals as well as heliotropic plants possess symmetry of form and a corresponding distribution of the irritabilities. These two groups of conditions determine the helio- tropic reaction unequivocally. But what has the central nervous system to do with this " instinct " of the moth to fly into the flame, or, as we may now say, with its heliotropism ? I believe nothing more than that the nervous system contains a series of segmental ganglia which establish the protoplasmic connection between the skin and muscles. If we destroy the central nervous system, the heliotropic reactions in many animals cease, but mainly for the reason that the connection between the skin, or the eyes, which are affected by the light, and the muscles, is interrupted. Hence it would be just as wrong to assume a specific centre for the flight of the moth into the flame as it would to assume a specific centre for the going of Palaemonetes to the anode.

3. We will select another instinct, namely, the habit many animals have of crawling into cracks and crevices. This " instinct " is very prevalent in the animal kingdom, especially among insects, worms, etc. This is called an instinct of self-preservation, and it is assumed that the animal thus escapes from its pursuers. The centre theory would assume a special centre for this instinct. This is, however, only an- other instance of a simple tropism. Many plants and animals are forced to orient their bodies in a cer- tain way toward solid bodies with which they come in contact. I have given this kind of irritability the name stereotropism. Like the positive and negative heliotropism and geotropism, there is also a positive and negative stereotropism, and there are also stereo- tropic curvations. I have found, for instance, that when a Tubularia is brought in contact with a solid body, the polyp and the growing tip bend away. from the body while the stolon sticks to it. The polyp is negatively stereotropic and the stolon positively stereotropic. Stereotropism plays a very important part in the processes of pairing and the formation of organs. The tendency of many animals to creep into cracks and crevices has nothing to do with self- concealment, but only with the necessity of bringing the body on every side in contact with solid bodies. I have proved this, for instance, in a peculiar species of butterfly, Amphipyra, that is a fast runner. As soon as free, it runs about until it finds a corner or a crack into which it can creep. I placed some of these animals in a box, one half of which was covered with a non-transparent body, the other half with glass. I covered the bottom of the box with small glass

plates which rested on small blocks, and were raised just enough from the bottom to allow an Amphipyra to get under them. Then the Amphipyra collected under the little glass plates, where their bodies were in contact with solid bodies on every side, not in the dark corner where they would have been concealed from their enemies. They even did this when in so doing they were exposed to direct sunlight. This re- action also occurred when the whole box was dark. It was then impossible for anything but the stereotropic stimuli to produce the reaction. The same phenom- enon may be observed in worms, for instance, in Nereis. If an equal number of Nereis and glass tubes be placed in a dish of sea-water, we may be sure that after a time we shall find a worm in each tube. This even occurs when the tubes are exposed to the direct rays of the sun, which kill the worms. This is also a reaction which is common to plants, hydroids, and animals possessing a central nervous system, which must therefore depend upon circumstances which have nothing directly to do with the central nervous system. These circumstances are apparently chemical effects in the skin, which are produced in these forms by the contact with solid bodies. This is another instance where the central nervous system only plays the part of a protoplasmic conductor. It would be entirely wrong to attempt to look for a " centre of self-concealment " in these animals. This is confirmed by experiments on worms that have been cut into pieces.

4. We will now turn our attention to the consider- ation of some more complicated instincts. It always seemed to me one of the most wonderful arrange- ments in nature that, in many species, the female lays her eggs in places where the newly born larvse find just the kind of food they require. The fly lays its eggs on decaying meat, cheese, or similar material, and it is on these substances that the young larvse feed. I have often placed pieces of lean meat and pieces of fat from the same animal side by side on the window-sill, but the fly never failed to lay its eggs on the meat and not on the fat. I further tried to raise the larva? on fat. As was to be expected, they did not grow, but soon died. It was possible to dis- cover the mechanics of the peculiar instincts of the mothers through experiments on the young larvse. The larvse are oriented by certain substances which radiate from a centre, and this orientation takes place in the same way as in the orientation of heliotropic ani- mals by the light. The centre of diffusion takes the place of the source of light, and the lines of diffusion (that is the straight lines along which the molecules move from the centre of diffusion into the surrounding medium — /. e., the air) the place of the rays of light. The chemical effects of the diffusing molecules on certain elements of the skin influence the tension of the muscles, as the rays of light influence the tension of the muscles in heliotropic animals. The orienta- tion of an organism by diffusing molecules is termed chemotropism, and we speak of positive chemotropism

when the animal is forced to bring its axis of symme- try into the direction of the lines of diffusion and to turn its head toward the centre of diffusion. In such an orientation every pair of symmetrical points on the surface of the animal is met by the lines of diffusion at the same angle. It can easily be shown that larvae of the fly are positively chemotropic toward certain chemical substances which are formed, for instance, in decaying meat and cheese, but which are not contained in fat. The substances in question are probably volatile nitrogenous compounds. The young larvae are probably led by those substances to the centre of diffusion in the same way as the moth into the flame. The female fly possesses the same positive chemotropism for these substances as the larvae, and is accordingly led to the meat. As soon as the fly is seated on the meat, chemical stimuli seem to throw into activity the muscles of the sexual or- gans, and the eggs are deposited on the meat. It may also be possible that at the time when the fly is ready to deposit its eggs the positive chemotropism is especially strongly developed. It is only certain that neither experience nor volition plays any part in these processes. If the question be raised as to what is necessary in order to produce these reactions, the answer is, first, the presence of a substance in the skin or certain parts of the skin (sense-organs) of the ani- mal which is altered by the above-mentioned volatile substances contained in the decaying meat, and second, the bilateral symmetry of the body. The

central nervous system plays no other role in this than that it forms the protoplasmic bridge for the conduc- tion from the skin to the muscles. In organisms in which this conduction is possible without a central nervous system, in plants, for instance, we also find the same reactions. 5. We find another instance of a preservative in- stinct in the young caterpillars of many butterflies. The larvae of Portkesia chrysorrhcea creep out of the eggs in the autumn and winter in colonies in a nest on trees or shrubs. The warm spring sun drives them out of the nest and they crawl up on the branches of the tree or shrub to the tip, where they find their first food. After having eaten the tips, they crawl about until they find new buds or leaves, which in the mean- time have come out in great numbers. It is evident that the instinct of the caterpillars to crawl upwards, as soon as they awake from the winter sleep, saves their lives. Were they not guided by such an in- stinct, those that crawled downwards would die of starvation. What role does the central nervous sys- tem play in these instincts ?

I have found that the young caterpillars of Por- thesia are oriented by the light. Until they have taken food they are positively heliotropic. This positive heliotropism leads them to the tips of the branches where they find their food. During the win- ter they are stiff and do not move. The higher tem- perature of the spring brings about chemical changes in their bodies, and these chemical processes cause them to move. But the direction of their movements is determined by the light. Out-of-doors, where the diffused light strikes the animal on all sides, every ray of light can be resolved into a horizontal and a verti- cal component. The horizontal components destroy each other, and only the effect of the vertical compo- nents remains. Hence the animals are forced, as a re- sult of their positive heliotropism, to crawl upwards until they reach the tip of a branch. They are held there by the light. The chemical stimuli which are transmitted to the animal by the young buds produce the eatino- movements. In this instinct, which is

necessary for the preservation of life, we have an- other instance of simple positive heliotropism, and the central nervous system plays only the role of a proto- plasmic connection between the skin and contractile tissue, which in plants is performed just as success- fully by undifferentiated protoplasm. We have seen, however, that these same caterpil- lars leave the tips of the branches as soon as they have eaten and crawl downward. Why does the light not hold them on the highest point permanently ? My experiments showed that these caterpillars are only positively heliotropic as long as they remain un- fed ; after having eaten they lose their positive helio- tropism. This is not the only instance of this kind, for I have found a series of facts which show that chemical changes influence the irritability of the ani- mal toward light. We can imagine that the taking up of food leads to the destruction of the substances

in the skin of the animal which are sensitive to light, upon which substances the heliotropism depends, or that through the consumption of food the action of these substances is indirectly prevented. 6. The analysis of other instincts, for instance, the migratory instinct of animals, leads to the same result as the analysis of the protective instincts. These in- stincts are not functions of certain localised " centres," but of irritabilities of certain peripheral structures and of the connection of the same with the muscles, whereby the central nervous system only serves as a protoplas- mic connection. It would naturally be more inter- esting to select for our discussion the migrations of birds, but it is difficult to make laboratory experi- ments on this subject, and without laboratory experi- ments we cannot easily obtain reliable results. For this reason I have made use of another class of periodic migrations, namely, the periodic depth-migra- tions of pelagic animals. A great number of these animals begin a vertical upward migration toward the surface of the ocean in the evening, while in the morning they migrate downwards. It is a remarkable fact that these forms never go below a depth of four hundred metres in their downward migrations. This fact suggests that the light is the controlling power in these depth-migrations. Water absorbs the light, and the thicker the layer of water the more the light is absorbed. It has been found that at a depth of four hundred metres a photographic plate is no longer affected. My investigations show that the movable

animals living at the surface of the ocean are all per- manently or transitorily positively heliotropic (and also often negatively geotropic). Those among them that carry out the daily depth-migrations described above have some other peculiarities which we can only understand if we go somewhat deeper into the theory of animal heliotropism. We have already mentioned that there is a negative as well as a posi- tive heliotropism : negatively heliotropic animals bring their median-plane into the direction of the rays of light, but turn their aboral pole toward the source of light. The difference in the behaviour of negatively and positively heliotropic animals is as follows : If light strikes one side of a positively heliotropic animal, an increase takes place in the tension of those mus- cles which turn the head to the source of light, while in the negatively heliotropic animal under the influ- ence of one-sided illumination a decrease takes place in the tension of the same muscles. The result is that the negatively heliotropic animal is forced to move away from the source of light. Perhaps still another possibility should be considered here, namely, that the light aids the progressive movement when it strikes the oral end of a positively heliotropic animal, while it inhibits the progressive movement when it strikes the aboral end. The opposite may be true of negatively heliotropic animals. This would suggest a further analogy between heliotropism and galvano- tropism.

of Balanus perforates which were known to make periodic depth-migrations (2). As one of our results, we found that these animals are sometimes negatively, sometimes positively heliotropic, and that we were able to make them positively or negatively heliotropic at desire. By weak light, especially gaslight, which contains comparatively few of the heliotropically effect- ive blue rays, they became and remained positively heliotropic, while in strong light they soon became negatively heliotropic. This circumstance determines the periodic depth-migration of these animals. When they are near the surface of the ocean in the morning, the strong light makes them negatively heliotropic and forces them to go downwards vertically, because in the open sea only the vertical components of the re- flected skylight have any effect. As soon as they approach a depth where the light is sufficiently weak, they become positively heliotropic. They must then begin to migrate upward again, but cannot reach the surface, because they soon come to a region where the light is so strong that they again become negatively heliotropic. Hence during the day they are held at a certain depth, which is, however, less than four hun- dred metres. But as soon as it becomes dark and the intensity of the light decreases more and more, they are forced to rise to higher regions on account of their positive heliotropism, until during the night, while the intensity of the light is weak, they are held at the sur- face of the water. Toward morning, when it begins to dawn, they again become negatively heliotropic and

pelagic animals also show another depth-movement of a greater period, which corresponds more nearly with the migration of birds of passage. Chun has found that in the Bay of Naples during summer cer- tain forms also remain at a greater depth during the night, never coming to the surface. This is probably due to the higher temperature which the surface of the water has in summer. I have found that certain animals, for instance, the larvae of Polygordius, are positively heliotropic in a low temperature, while in a higher temperature they become negatively heliotropic (4).

I have also mentioned that geotropism also plays a part in these depth-migrations. The same circum- stances which make the animals negatively helio- tropic also make them positively geotropic, and vice versa. Thus I was able to show that in a low tem- perature the larvae of Polygordius are also negatively geotropic, \vhile in a high temperature they are posi- tively geotropic (4). By means of this geotropism they are also forced in the dark to go to the surface when the temperature of the water is low. It is also probable that in many forms internal conditions simi- lar to the nyctitropic phenomena in plants are in- fluential in causing periodic depth-migrations.1 We thus find that the migratory instinct, as far as it is

1 This may account for the periodic migrations of certain animals (Medusa?) in polar regions. In such animals, changes in the specific gravity may take the place of heliotropic reactions. expressed in the depth-migration of pelagic animals, is frequently determined by the presence of substances in the surfaces of the animal which are sensitive to light. These substances, however, produce different effects according to the intensity of the light or of the temperature (or perhaps according to internal conditions). They are further determined by the re- lations of symmetry of the animals. The central nervous system has nothing further to do with these phenomena than that it furnishes the protoplasmic connection between the skin and muscles. This dis- agrees with the centre theory of these instincts, but agrees with the segmental theory.

7. One might think that these ideas held good only for Invertebrates. Goltz has, however, made a re- markable discovery which seems to confirm the opin- ion that in Vertebrates the conditions are practically the same. A female dog that has given birth to a young one bites off the navel cord, licks the young, is very affectionate towards it, and allows no stranger to touch it. These motherly instincts are inherited, and there is no doubt that with the act of giving birth and the resulting processes in the sexual organs changes take place in the animal which make these instincts possible. One might think, especially in this case, of centres in the central nervous system which are stim- ulated directly through the nerves of the uterus. Now Goltz found that these instincts are also fully devel- oped in dogs whose spinal cord is severed so far up that the stimuli from the uterus cannot reach the

brain (6). It is probable that certain substances which are developed during the pregnancy, birth, and lactation influence the character of the animal, just as certain poisons, for instance, alcohol, tobacco, or morphine, influence the reactions of a human being. It is of course possible that the sympathetic plays a part here, although this has been rendered improbable through the more recent experiments of Goltz and Ewald and of Ribbert1 8. We have confined our attention to the simplest instincts, for these are best adapted for a complete an- alysis. Should we attempt a complete enumeration and discussion of instincts, we should have to devote several volumes to that subject alone. We should like to call attention to the conditions which are re- sponsible for the fact that many instincts are difficult to analyse. One source of complication lies in the fact already mentioned, that changes in the condition of the blood, for example, those produced by metabol- ism, may change the forms of irritability and reaction. The young caterpillar of Porthesia is only heliotropic so long as it is starving, while it becomes indifferent to light as soon as it is fed. In plant-lice, the helio- tropic irritability is connected with the growth of wings. The wingless forms may or may not show positive heliotropism ; if we produce wings (by lowering the temperature or by letting the plant on which it lives dry out), the animal becomes energetic- ally positively heliotropic. In ants heliotropism is more

intimately connected with the sexual development. I have never found true heliotropism in the workers, while the sexually mature males and females are de- cidedly positively heliotropic. Wherever these tran- sitory changes of irritability are present, it requires experimental work to succeed in the analysis of the instinct. A second series of difficulties arises from the influ- ence of associative memory in many cases of instincts. The periodic depth-migration of marine animals is a simple case of instinctive migrations, while the migra- tions of birds or the accomplishments of the carrier- pigeon seem to be complicated by memory. It seems to be certain that the carrier-pigeon finds its way back by its visual memory of the locality from which it started. In the same way the migration of birds may be determined, if it is true that migrating birds return to their old nest. In the case of the birds, there is present in addition a purely inherited, instinctive element which causes restlessness at the time of migration. This restlessness and, perhaps to a cer- tain extent, the direction of its flight are susceptible of a purely physiological analysis. The element of memory complicates many instinctive actions of wasps. I have had a chance to observe solitary wasps and am convinced that they find the way to their nest by means of the visual memory of the locality where it is situ- ated. The same is apparently true of bees and pos- sibly of ants. (See Chapter XV.)

logical point of view will ultimately furnish the data for a scientific ethics. Human happiness is based up- on the possibility of a natural and harmonious satis- faction of the instincts.1 One of the most important instincts is usually not even recognised as such, namely, the instinct of workmanship." Lawyers, criminologists, and philosophers frequently imagine that only want makes man work. This is an errone- ous view. We are instinctively forced to be active in the same way as ants or bees. The instinct of workmanship would be the greatest source of happi- ness if it were not for the fact that our present social and economic organisation allows only a few to sat- isfy this instinct. Robert Mayer has pointed out that any successful display or setting free of energy is a source of pleasure to us. This is the reason why the satisfaction of the instinct of workmanship is of such importance in the economy of life, for the play and learning of the child, as well as for the scientific or

10. We have finally to defend our physiological analysis of instincts against the reproach that it ignores the theory of evolution. In other words, it has been 1 It is rather remarkable that we should still be under the influence of an ethics which considers the human instincts in themselves low and their gratifi- cation vicious. That such an ethics must have had a comforting effect upon the Orientals, whose instincts were inhibited or warped through the combined effects of an enervating climate, despotism, and miserable economic conditions, is intelligible, and it is perhaps due to a continuation of the unsatisfactory eco- nomic conditions that this ethics still prevails to some extent.

2 I take this name from Veblen's book on The Theory of the Leisure Class, New York, 1899. urged against us that instincts should be explained historically and not physiologically or causally. It seems to me that living organisms are machines and that their reactions can only be explained according to the same principles which are used by the physicist. Our ultimate aim in the analysis of instincts is to find out by which physical and chemical properties of pro- toplasm they are determined. Of course the physicist finds it useful to illustrate the mechanism of compli- cated machines by the comparison with simpler or older machines of the same kind. We have made use of this same method and heuristic principle by utilis- ing in this book the reactions of simpler forms for the analysis of more complicated forms. Even if we were in possession of a scientific phylogeny instead of the fairy tales that go by that name at present, it would not relieve us of the task of explaining the instincts on the basis of the physical and chemical qualities of protoplasm.

ii. At first sight it may seem a hopeless task to find a connection between the instinctive actions of animals and the properties of their protoplasm. And yet the task is not so great if we choose the right method. This method, in my opinion, consists in varying the instincts of an animal at desire. If we succeed in this we are able to find out how the physi- cal qualities of protoplasm may affect the instincts. I have tried this in one case. A number of marine ani- mals (Copepods, larvae of Polygordius) which go away from the light can be forced to go to the light in two

ways, first by lowering the temperature, and second, by increasing the concentration of the sea-water (whereby the cells of the animals lose water). This instinct can again be reversed by raising the tempera- ture or by lowering the concentration of the sea- water. Hence these instincts must depend upon such reversible changes in the material of the proto- plasm as can be brought about by a loss of water or by a reduction of temperature. What these changes are can only be determined by further experiments. We find other instances where decrease in tempera- ture has the same physiological effects as a loss of water. Plant-lice exist in wingless and in winged forms. We can at any time cause the growth of wings in the wingless forms by lowering the tempera- ture or by letting the plant dry out (whereby the amount of water in the cells of plant-lice is reduced).1

1. LOEB, J. Der Heliotropismus der Thiere und seine Ueber- einstimmung mit dem Heliotropismus der Pflanzen. Wurzburg 2. GROOM and LOEB. Der Heliotropismus der Nauplien von Balanus perforatus iind die periodischen Tiefenwanderungen pelagis- cher Thiere. Biologisches Centralblatt, Bd. x., 1890. 1 1 have found repeatedly that by the same conditions by which phenomena of growth and organisation can be controlled the instincts are controlled also. This indicates that there is a common basis for both classes of life phenomena. This common basis is the physical and chemical character of the mixture of substances which we call protoplasm.

4. LOEB, J. Ueber kiinstliche Umwandlung positiv heliotropis- cher Thiere in ncgativ heliotropische und umgeke/irt. Pfluger's Archiv, Bd. liv., 1893. 5. LOEB, J. On Egg Structure and the Heredity of Instincts. The Momst, July, 1897. 6. GOLTZ, F. Ueber den Einfluss des Nervensy stems anf die Vorgdnge wahrend der Schwangerschaft und des Geburtsaktes. Pfliigers Archiv, Bd. ix., 1874. I. The question as to how far the central nervous system comes into consideration for the processes of heredity is of great importance in educational prob- lems. If we could hope that, as a result of the activ- ity of a generation, its descendants would be born with a talent for this special activity, there would be a fertile field for the improvement of the human race. In order to decide this question, we must first turn our attention to those peculiarities which we know to be hereditary — namely, the form of the body and the in- stincts. The analysis of the instincts given in the previous chapter places us in a position to answer the question as to how they can be transmitted through the egg. All hereditary qualities of form, instincts, and reflexes must be transmitted through the sex- ual cells. The difficulty that appears is this : How can the sexual cells, which only represent a liquid mass enclosed in solid membranes, be the bearers of such apparently complicated structures as the forms that originate from them with their instincts and

reflexes ? Either the apparent simplicity of the struct- ure of the egg is only an illusion, and in reality the structure of the egg is no less complicated than the full-grown animal, or the sum of the elements which we call the form and instincts of the full-errown ani- mal is only the resultant of a few simpler elements which can readily be transmitted through the egg without its possessing a complicated structure. The discussion of the mechanics of instincts in the last chapter shows the latter to be the case. Let us con- sider those instincts that depend on heliotropic reac- tions— for instance, the flying of the moth into the flame. This instinct is unequivocally determined, first, by the presence of a substance in the surface of the animal which is sensitive to light, and second, by the symmetrical structure of the animal. For the trans- mission of a substance which is sensitive to light through the egg no complicated mysterious structure is necessary. Neither is a complicated structure necessary for the egg in order that it may transmit the symmetrical relations of the animal.

For the inheritance of form the conditions are not very different. The egg is not the bearer of the form of the full-grown animal, but of certain chemical sub- stances, especially of ferments. According to the stereochemical configuration of the latter, the products of assimilation, and with these the materials of the body, turn out differently. The process of develop- ment is not only a morphological but a chemical dif- ferentiation, and new combinations of substances are

continually formed from the original raw material. A further differentiation of the form may be and often is connected with every metabolic differentiation of the substance of the body. The results of experi- mental morphology harmonise entirely with this con- ception which was originated by Jaeger and Sachs, and which I have tried to develop in a series of articles. I will only mention the experiment in which the egg of the sea-urchin (Arbacia) was given the form of a double sphere, whereby each sphere de- veloped into a complete sea-urchin. In this case it makes no difference whether the transformation of the sea-urchin into a double sphere takes place in the freshly fertilised egg or after the egg has already reached the i6-or 32-cell stage. These facts can only be understood if we think of the egg as nothing more than the bearer of certain c/iemzcal substances and not of mysterious morphological structures of a nature as complicated as that of the full-grown animal ; and if we regard the morphological process of development only as a result or accompanying phenomenon of corresponding chemical transformations and physical changes. We may mention further in this connec- tion that the processes of heteromorphosis — that is, the transformation or substitution of one organ for a morphologically different one by means of certain external influences — force us to the same view.

2. Tornier has developed a theory of the inherit- ance of acquired characters on the assumption of a new role of the central nervous system. According to this theory, every change that takes place in the body is said to be accompanied by a corresponding change in the central nervous system. The changes in the central nervous system are then said to bring about a corresponding change in the egg. Thus, ac- cording to this theory, just as close a relation must exist between the central nervous system and the morphogenetic processes as between the central nerv- ous system and the motor and sensory functions. It can readily be shown, however, that this assumption of Tornier goes much too far. When the larva of Amblystoma transforms itself into a sexually mature animal, it loses the gills which are located on the head and the tail-fins that are on the tail. Both organs disappear simultaneously. In a series of Amblystoma larvae I severed the spinal cord in the vicinity of the shoulder-girdle. The parts of the animal before and behind the place of division are, as regards motor and sensory functions, like two separate animals. If the morphogenetic processes were as closely related to the central nervous system as the sensory and motor functions - - as Tornier's theory demands - - we should have expected that the gills and tail-fins would no longer be absorbed simultaneously, but at different times, just as in two different animals. Without ex- ception, in these animals with severed spinal cord the absorption of the head- and tail-organs occurred simul- taneously (i). In some of the animals operated upon, the change took place in a few days after the division, in others a longer interval elapsed. There can thus