Comparative Physiology of the Brain and Comparative Psychology

Bethe concludes from these pendulum-movements that the brain is an organ of inhibition. As regards this, the remarks hold good that have already been made in this connection on annelids (see p. 94). The weakening of the muscles in the crayfish whose brain has been extirpated shows itself also in the fact that the forceps no longer pinch as hard as those of normal animals. After what has been said concerning the segmental character of the central nervous system, it is to be expected in the crayfish that, since the segmental ganglia of the organs of mastication are located in the subcesophageal ganglion, extirpation of the supra-

cesophageal ganglion will not interfere with the nor- mal character of its eating movements. I give the description in Bethe's words : " The animal devoid of the supracesophageal ganglion is able to eat and selects its food. It is true that pebbles, small pieces of wood, etc., are seized by the forceps of the front pairs of legs, but when brought near the mouth they are rejected. A piece of meat, however, is always taken into the mouth and masticated. The swallowing is difficult, just as in the case of Carcinus. The piece often remains for a long time between the maxillipedes without being swallowed, and at last falls to the ground. Pieces of paper that have been satu- rated with meat-juice are treated in the same way. Stones that have been covered with meat-juice are also brought to the mouth, but no attempt is made to masticate them. They are usually dropped as soon as they come in contact with the maxillipedes." Thus we see that the nature of the stimulus determines the results just as in the case of Actinians. The brain of the crayfish has nothing to do with these reactions. The central nervous system is in this case to be con- sidered only as an organ for the conduction of stimuli, a function that could just as well be performed by plant protoplasm or muscle-tissue as by nerve-protoplasm. In the crayfish, the original segmental arrangement of the nervous elements is so well preserved that re- moval of the brain does not interrupt the proto- plasmic nervous connection between the surface of the mouth and the muscles of the thoracic appendages.

When these animals from which the brain has been removed are laid on their backs they return to the ventral position. The observations made by Bethe in crayfish in which he had severed the cesophageal commissures on only one side are interesting. The division was made on the right side. If he touched the left side of the head of such an animal, first the forceps of the stimulated side reached toward the stimulated spot and then those of the other side followed with accur- acy. At the same time, the animal attempted to escape backwards. If the same stimulus was applied to the right side of the head, the forceps did not react. Even with a strong stimulus no reaction followed. Hence the stimulus that produces the localising reflex can only be transmitted through the longitudinal commissure of the same side to the appendages. This seems to hold good generally for the Arthropods, since Bethe was able to prove it in Carcinus, Squilla, and Hydrophylus. It seems to hold good not only for the conduction through the cesophageal commissures but through all longitu- dinal commissures. After division of an cesophageal commissure, circus-motions often but not always occur toward the normal side. The animal is also able to move straight ahead, but this requires some effort.

If the right cesophageal commissure be severed, the tonus of the muscles on the right side (the injured side) of the abdomen is diminished, and as a result the abdomen is curved toward the left and becomes concave on that side. Division of the brain in the middle line — that is, separation of the two halves of the brain — destroys the geotropic reactions of the eyestalks. It is still more remarkable that such animals no longer prefer to re- main in the dark like normal animals.

If the longitudinal commissures be divided between the mouth-ganglia (subcesophageal ganglion) and the ganglion of the chelae, all locomotor movements be- come impossible, although the legs are not paralysed. This is strange, because the subcesophageal ganglion contains the segmental nerve-elements of the oral ap- pendages but not those of the locomotor appendages. In other Crustaceans,extirpation of the subcesophageal ganglion has no such paralysing effect on the loco- motor movements. It is impossible to tell at present what causes the exceptional behaviour of Astacus in this regard. I do not believe we are obliged to as- sume that this is an instance of a deviation from the laws of the segmental arrangement of the nerve-ele- ments (centres) of the limbs. This is shown by the fact that the legs of such an animal are not paralysed, but are unceasingly occupied in cleaning the abdo- men, the pedes spurii, or each other. Indeed, more than that, " if we give one of the forceps of a loco- motor appendage a piece of meat or paper, other legs approach immediately, seize the meat, and carry it to the mouth," in spite of the fact that all nervous connection between the nerves of the mouth-organs and the legs has been severed. It is true that the ap- pendages around the mouth often refuse to accept

and forward the pieces of meat that are thus offered them by the legs. As regards the further isolation of the ganglia that are located posterior to the subcesophageal ganglion, the facts which have been described in Limulus are in general true. As long as the ganglion of a seg- ment remains connected with the segmental organs, the functions of that segment remain unimpaired. Bethe has found single exceptions to this rule, but it is conceivable that these exceptions are shock-effects resulting from the operation.

We will now report more briefly concerning Bethe's experiments on some other Arthropods. 5. Sqtiilla no longer swims spontaneously after the supracesophageal ganglion has been isolated (that is, after division of the commissure between the suprace- sophageal ganglion and the mouth-ganglion). The spontaneous progressive movements usually seem to be destroyed. When stimulated, however, the ani- mal moves normally. The nervous mechanism for the locomotor reflexes is localised in the three ganglia of the locomotor appendages, that is, these append- ages still move normally, even though the connection with the ganglia lying in front has been interrupted.

In grasshoppers {Pachytylus cinerascens} isolation of the supracesophageal ganglion causes the spontan- eous progressive movements to cease. These animals, after the operation, clean their antennae with their fore-legs like a normal animal. According to Bethe these localised reflexes of the legs are produced by the stimulus of the operation. Abnormal positions of the legs, resulting from the operation, occur just as in Astacus and Squilla. If the supra- and subcesophageal ganglia be re- moved by decapitating the animals, they are still able to perform some walking movements, and especially hopping movements, when stimulated. This agrees with the idea of the preservation of the purely seg- mental arrangement of the nerve-connections. Yer- sin's experiments on crickets are very significant in this regard. I take them from Bethe's paper. They deal with crickets from which both longitudinal com- missures had been removed between the subcesophag- eal ganglion and the first thoracic ganglion. Yersin kept these animals alive for weeks. " When laid on their backs they were able to turn over. When stim- ulated they moved forward a few steps, or to the side, according to the point of stimulation. In doing so they occasionally tumbled over. When stimulated, they still made attempts at flying without being able to lift themselves from the ground." Yersin observed that a male and a female, both of which had been op- erated upon in this way, were able to pair. Of course it was necessary to place the male on the female in this case. The male on which he made this observ- ation had already given off a spermatophore.

Bees lived only a short time after the extirpation of the supracesophageal ganglion. The bee shows the same restlessness that was noticed in Astacus. symmetrical halves showed a perceptible functional disorder only in their behaviour toward the hive. ' If carried back to it they crawl about on the board be- fore the entrance but make no attempt to enter, and they pay no attention to their companions." If bees be decapitated, the supra- and subcesopha- geal ganglion being thus removed, they are still able to walk, although awkwardly. When laid on their backs they turn over with the help of their legs. " When stimulated on the ventral side they grasp the object (pencil) with their legs, pull it toward them, bend the abdomen, and attempt to sting it." But not all animals give such favourable results. In brain- physiology only those animals operated upon which show the slightest disorders can be considered, be- cause the exhaustion may render the rest of the cen- tral nervous system pathological.

As was to be expected a priori on the basis of the segmental theory, the stinging-reflex is possible as long as the abdominal ganglion is preserved. Bethe showed that the abdomen, when severed from the body, still bends if stimulated on the ventral side and reaches the stimulated spot with the outstretched sting. At the same time poison is ejected. The reflex also continues when all the abdominal segments with the exception of the last one have been amputated.

If the supraoesophageal ganglion in a water-beetle (Hydrophilus) be extirpated, the progressive loco- motor movements are not only not interrupted, but tJic animal goes about almost unceasingly, showing only modifications which suggest that the relation in the ten- sion of the antagonistic muscles of its legs is changed. The animal turns out for obstacles that come in its way. If a beetle that has lost the supraoesophageal ganglion is thrown into water it swims off, drawing in the first pair of legs. The normal water-beetle rests quietly under dark objects. The water-beetle whose supraoesophageal ganglion has been divided by a longitudinal incision no longer shows these reactions, although the light is still able to produce other effects in the animal. If suddenly exposed to strong light or a dark shadow — when in motion, namely — it ceases to move.

An animal whose right cesophageal commissure has been severed does not brace itself against obstacles as strongly with the legs of the right side as with those of the left side. It seems to me this shows that the extensors of the right side are weakened, as it is they that have to perform the task of bracing. Further- more, the right legs are moved constantly. It may be possible that these two facts are in some way con- nected. The decreased opposition of the extensors renders the pendulum-movements of the legs easier. The same explanation may hold for Astacus, bees, etc. If the supra- and subcesophageal ganglia be extirpated, the animal only makes progressive movements when stimulated. But the ability to perform coordinated progressive movements is not destroyed. When laid on its back the animal still tries to regain the ventral position, but the efforts made by the legs are vain.

If put under water it still makes swimming move- ments, but these do not help it forward. The experiments on the other ganglia of this ani- mal performed by Bethe do not concern us in this book. We will only quote that result of Bethe's which is of most importance for our purpose : " Nei- ther the subcesophageal nor the prothoracic ganglion is the seat of the reflex for righting the animal when turned on its back, nor of the coordination of the mus- cles of locomotion, walking, or swimming, as Faivre maintains. It would seem as though these reflexes were located rather in each thoracic ganglion for the cor- responding segment" This last sentence expresses the principal truth for all complicated central nervous sys- tems. Each segment of a segmented animal may be regarded as a simple reflex animal, comparable to the- Ascidian, and the analysis of the reflexes depends upon the same principles and leads to the same re- sults in both cases. The complication that appears in segmented animals consists in the fact that when a process of stimulation takes place in one segment it is communicated to the neighbouring ganglia, and these ganglia produce processes of the same kind. It is possible that the nature of the stimulation also helps to determine the nature of the movement. The assumption of special centres of coordination is superfluous. One other fact is of importance in exper- iments in extirpating and severing nervous connec- tions, namely, that the division may bring about in those parts which are protoplasmically connected with

the place of operation a change which is sometimes transitory, sometimes permanent — the so-called shock- effects. The highest degree of these shock-effects is attained in case of degeneration. It is a remarkable fact that, in an operation on the central nervous sys- tem, the effect of the shock is much greater in the part posterior to the place of operation than in the anterior part, toward the head. This may indicate that there is a constant current of impulses or influ- ences in the direction from the brain to the posterior parts of the central nervous system. The interrup- tion of these influences may be responsible for the condition which we call shock-effects and which may be transitory. These shock-effects are incomparably less stronor in cold-blooded than in warm-blooded ani-

mals. We do not possess enough facts to enable us to give an explanation of the shock-effects. 1. HYDE, IDA H. The Nervous Mechanism of the Respiratory Movements of Limulus Polyphemus. Journal of Morphology, vol. ix., 1894. 2. LANGENDORFF, O. Studien iiber die Innervation der Athembe- wegungen. I. Mittheilung. Archiv f. Physiologie, 1880. 3. PORTER, W. T. The Path of the Respiratory Impulse from the Bulb to the Phrenic Nuclei. Journal of Physiology, vol. xvii.,

4. VULPIAN. Lemons sur la Physiologie generate et compare'e du Systeme Nerveux. Paris, 1866. 5. BETHE, A. Vergleichende Untersuchungen iiber die Functionen des Centralnervemy stems der Arthropoden. Pfliiger s Archiv, Bd. Ixviii., 1897. 6. BETHE, A. Das Cenfralnervensystem von Carcinus mcenas. Archiv f. microskop. Anatomic und Entwicklungsgeschichte, Bd. 1., 1897 ; Bd. li., 1898. 7. STEINER, J. Die Functionen des Centralnervensy stems und ihre Phylogenese. III. Abtheilung. Die wirbellosen Thiere. Braunschweig, 1898.

The literature on the functions of the central nervous system of Mollusks is extremely meagre. It is nevertheless valuable, as it furnishes us with further proofs of the theory that the simple and rhythmical spontaneity, as well as reflex processes, do not depend upon the brain or specific peculiarities of the ganglia. A Gastropod whose brain (g, Fig. 33) has been removed continues to move spontaneously. Stei- ner has observed this in a transparent pelagic species of snail, Pterotrachea,

swimming organ. Neither one- nor two-sided de- struction of the supracesophageal ganglion has the slightest influence upon the character and the quantity of the spontaneous progressive movements. Destruction of the pedal ganglion, on the other hand, puts an end to all locomotion. Steiner concludes, therefore, that " the pedal ganglion alone has control of the entire locomotion of the ani- nial." This anthropo- morphic conclusion goes too far. The only conclusion we are justi- fied in drawing from this observation is, that the protoplasmic con- necting fibres between the skin and the foot- muscle of the animal pass through the gan- glion. Steiner further attempted to see if he could produce circus-motions by means of a one-sided divi- sion of the oesophageal commissure in other Mollusks, Pleurobranchia and Aplysia. He succeeded no better than in Pterotrachea. One-sidecl destruction of the pedal ganglion in Cymbulia, however, caused paralysis of one-half of the locomotor or^an. The animal

naturally moved in a circle, for only one wing served as an oar. The Cephalopods have an extremely complicated brain (Fig. 34). It consists of a dorsal and a ventral mass, each of which is composed of several ganglia. Cg; cerebral ganglion ; S/>g, supraoesophageal ganglion ; Bg; buccal ganglion ; Tg; ganglia of the tentacles. (After Claus.) The dorsal and ventral ganglia are connected by commissures. In addition, they possess a series of peripheral ganglia, the tentacle-ganglia (Tg, Fig. 34), for instance. It is of significance for the segmental theory that the tentacle-ganglia suffice to produce ten- tacle-reflexes, as v. Uexkull has shown in Eledone (2). It has been inferred from experiments on Vertebrates that peripheral ganglia cannot transmit reflexes.

Now, as regards experiments on the brain of Ceph- alopods, Steiner reports as follows concerning Oc- topus vulgaris : "If the dorsal ganglion on one side be removed, or both commissures of one side be severed, not the slightest change is visible in the life- processes of the animal, for it moves spontaneously as before, attacks its prey (Carcinus mcenas} cleverly, and devours it. But the picture changes if the dorsal ganglion be entirely removed. To be sure the two forms of locomotion are preserved, for the animal creeps with the aid of its arms, or shoots like an arrow through the waves, when water is forced out of the mantle-cavity rhythmically. These movements are, however, no longer spontaneous, for they occur only when the animal is stimulated, neither does it take its food spontaneously. The normal octopus, which is endowed with marked intelligence [?], is wont to observe its surroundings most attentively, but now it sits indifferent to its surroundings, as though idiotic, and only its regular breathing gives evidence that it still lives. Vision is unimpaired, for it draws back when a stick is brought toward its eye." V. Uexkull's

article on Eledone is more exhaustive than Steiner's. One of his observations, describing the extraordinarily excited condition of an animal whose cerebral gan- glion had been removed, is worthy of mention. " All the reflexes seemed increased. When anyone ap- proached the basin the Eledone that had undergone this operation swam off, while the normal animals remained quiet. There was an incessant play of colors. During the second night, in spite of the pro- tecting net, it escaped and died on the floor of the laboratory." V. Uexkull concludes from this that there are inhibitory centres in the cerebral ganglion. We have seen that Bethe arrived at a similar conclusion in regard to the supracesophageal ganglion of the Arthropods. We have discussed this possibility in connection with Maxwell's experiments on Nereis.

The arm-nerves originate in the pedal ganglion. But the latter is connected with the supracesophageal ganglion directly by means of the anterior commis- sures and indirectly by means of the posterior commis- sures. Now it is of interest to know that the influence which the anterior part of the supracesophageal gan- glion exerts on the arm-movements when stimulated is exactly the opposite of that exerted by the posterior part ; if the entire supracesophageal mass between both pairs of commissures be separated by a frontal incision and both stumps be stimulated down deep, where the central ganglia are located, according to v. Uexkull, we obtain the following results : Stimulation of the anterior stump causes the cup-like suckers to

take hold strongly ; stimulation of the posterior stump causes the suckers to let go and the arms to be with- drawn. Thus the antagonistic activities of the arms depend upon two different parts of the central nervous system. " An animal whose supracesophageal mass has been divided in the vicinity of the first central ganglion behaves like an animal that is only able to take hold of objects. It grasps every object firmly and liberates itself again only with difficulty. It usually retains its hold and sits with extended arms, or crawls forward with the greatest difficulty. Such an animal placed on the back of a torpedo seizes it firmly with the arms, and no shocks of the electric organs are of avail to rid the fish of its burdensome rider. On the other hand, it is evident that the Ele- done only participates in the ride involuntarily from the fact that it becomes dark brown and throws ink. If a normal Octopus by mistake grasps after a tor- pedo, it never remains in so dangerous a neighbor- hood more than a few seconds [I have observed this in Octopus, never in Eledone]." It seems to me that the conclusion to be drawn from these facts is, that the anterior and posterior parts of the supra- cesophageal ganglion are connected with antagonistic muscle-groups. This relation is of interest in view of galvanotropic experiments, which we shall discuss later on. It is furthermore probable from v. Uex- kiill's experiments that the act of eating depends upon the integrity of the first central ganglion, while the second and third central ganglia are necessary for all

the remaining functions of the arms, for instance, loco- motion and steering. The fact discovered by v. Uexkiill that the basal ganglion, when no longer connected with the central nervous system, produces coordinated chewing move- ments when stimulated is of great importance for the segmental theory. The skin and muscles are in this case connected by nerve-fibres which do not pass through the central nervous system but through a peripheral ganglion that v. Uexkull terms the bucco- intestinal ganglion. This is another fact that speaks for the idea that the ganglia are only to be considered as organs of transmission, that is, as connecting pro- toplasmic threads for reflexes, and not as bearers of mysterious reflex mechanisms.

1. STEINER, J. Die Functionen des Centralnervensy stems der wirbellosen Thiere. Sitzungsberichte der Berliner Academic der Wisscnschaften, 1890, i., p. 32. 2. V. UEXKULL. Physiologische Untersuchungen an Eledone moschata. Zeitsch. f. Biologic, Bd. xxxi., 1895. 3. STEINER, J. Die Functionen des Centralnervensystems und ihre Phylogenese. III. Abtheilung. Die wirbellosen Thiere, Braun- schweig, 1898. i. The segmental arrangement of the central nerv- ous system of Vertebrates is suggested by the ar- rangement of the spinal nerves. The number of segmental ganglia present in the head exceeds the number of cranial nerves. The auditory nerve and the vagus, for instance, originate from more than one segment each. Dohrn, Locy, and others have shown this. Locy states that there are originally fourteen segments in the head of the embryo of the shark, while there are only twelve cranial nerves. Physi- ology is more interested in the decision of this quest- ion than morphology, because upon it depends the theory of coordinated movements. The question of segmentation may also be of importance indi- rectly in connection with the idea of localisation in the cerebral hemispheres, for the so-called centres of the cerebral cortex are merely the places where the fibres from single segments of the central nervous system enter.

as has been said above, suggest externally its segmental character. Each has a ventral motor and a dorsal sensory root, and we desire to call attention to the fact that the dorsal root passes through a ganglion (the spinal ganglion). If the ventral root be severed, paralysis of the muscles of the corresponding segment occurs. If the dorsal root be severed, the correspond- ing segment becomes insensible, or, more properly speaking, the transmission of impulses which proceed from the periphery to the muscles of this segment and to the remaining segments becomes impossible. The operation itself, however, has still another influence on the tension of the muscles of the same segment (perhaps also of other segments). The amount of the muscle-tension under normal conditions varies (prob- ably with the chemical conditions of the muscles). If a muscle be stretched with a certain weight it attains a certain length. But if the posterior nerve-roots be severed while the muscle is still nervously connected with its segment the muscle lengthens (E. v. Cyon). The operation causes a shock, in other words, prob- ably a chemical change in the muscle. The nature of this change is as yet unknown. This influence of the posterior roots on the muscles shows itself also in the movements of an animal in which the posterior roots of the hind-legs have been severed : the movements of the legs are disturbed. It is known that the nerves of the brain are also of segmental origin, only in this case the inequalities of growth obliterate externally the segmental relations. From the fact that the chiefly

sensory trig-eminus, which may be considered as the posterior root of the facialis, possesses a peripheral ganglion (ganglion Gasseri), while the chiefly motor facialis has no peripheral ganglion, Bell concluded that the posterior roots of the spinal cord, which pos- sess peripheral ganglia, are sensory, while the anterior roots, which possess no ganglia, are motor. Bell found (by means of vivisection) that division of the trigeminus produces disturbances in eating in those animals that take their food with the lips : these disturbances are caused, naturally, by the weakness of the corresponding muscles.

We will add a word here concerning the import- ance of the ganglion-cells for the preservation of the axis cylinder. The axis cylinder may be regarded as a protoplasmic extension of a ganglion-cell, which lives only as long as it is connected with the cell. Now the ganglion-cells of the dorsal roots are located in the spinal ganglion, those of the ventral roots in the ventral horns of the spinal cord. If the posterior roots be severed, that part of the fibres which is con- nected with the spinal cord degenerates, while the part that is connected with the spinal ganglion is preserved, and grows or regenerates. If the ventral roots be severed the peripheral stump degenerates, while the stump that is still connected with the spinal cord is preserved and grows. We may mention here briefly that the nerve-fibres of the posterior roots, according to Golgi's school, are not fused with the ganglion-cells of the posterior horns in the spinal

cord, but are only in contact with them.1 For the transmission of the impulse this fact is of no import- ance ; it is not necessary in either case that the gan- glion-cells of the posterior horn and the sensory nerves be grown together, they need only to be in sufficiently close contact. Engelmann called atten- tion to these relations long ago in his excellent article on conduction in the ureter. 2. Sufficient data exist for proving the segmental localisation of reflexes in the spinal cord. In a dog whose spinal cord has been severed somewhere in the thoracic region the posterior part is entirely separated from the anterior part as far as the motor and sensory functions are concerned. Immediately after the oper- ation severe shock-effects appear, but these are only temporary, and we shall return to this subject later. The interruption of the continuity is permanent, for in the central nervous system of higher animals no re- generation has been observed, but only a healing together of the cut surfaces by means of connective tissue. In such an animal the part located behind the point of division shows all the reactions which are possible in the corresponding segments. Goltz has proved this for dogs. Rubbing of the skin produces scratching movements of the hind-legs ; erection of the penis and urination can be produced by stimulat- ing the foreskin. The reflexes of the rectum and

1 Apathy's publications arouse suspicion as regards the results obtained by Golgi's methods. have already called attention to the fact that the re- spiratory movements are segmental processes. Goltz has shown that those reflexes in which the muscles of the arms are active are also segmental (2). During the period of heat the male frog clasps the female with his fore-limbs. If the head and back part of the body of a male frog be amputated during this time, so that only a piece consisting of the arms and the segmental piece of the spinal cord belonging with the arms remains, rubbing the skin on the ventral side of this piece suffices to produce the clasping reflex.