that in the past few years I have been conducting studies on the origin of that most intricate and complex systems of organs, the nervous system, and in fact it is to this institution that I have come for a time to continue such investigations. It may not be inappropriate, therefore, if I attempt to tell you in as simple and direct a way as I can something of the problem on which I have been working and of the results that I believe I have attained.

Every one knows nowadays that there is an intimate and important relation between man's intelligence and his brain, that his eyes, ears and other sense organs deliver to him information concerning the exterior, and that by means of his muscles controlled through his nerves, he can mold his surroundings more or less to his liking. But perhaps few persons have realized how strictly nervous all these operations really are. Take, for instance, the apparently simple question of the seat of our sensations. To an untrained person the pain of a pin prick is located where the pin enters his skin. To him nothing seems more obvious and certain than that the punctured spot is the seat of the pain and any attempt to change his view on this point will usually be regarded by him with suspicion and mistrust, for it seems contrary to common sense. Such persons adopt more or less unconsciously the opinion held by many of the ancients that our sensations are spread completely through our bodies, an opinion which we have been obliged to give up. The reasons for this change of view are several. First, it has become well known that, if a nerve distributed to a given area of skin is cut at some distance from that area, the spot, though unaffected in any direct way by the operation, will give rise to no further sensations even when it is severely stimulated. Hence it is clear that the sensations do not reside simply in the skin.

But not only may pain thus be absent from a given area of skin; it may be present when the skin with which it is supposed to be associated is absent. Persons who by accident or otherwise have lost an arm or a leg often experience long after the loss vivid and intense sensations from definite parts of the missing member. So precise and sharp are these sensations and so certainly do they seem to be associated with the lost part that some of the less knowing of these unfortunates have attempted to exhume or otherwise get possession of the lost member in an endeavor to alleviate their unpleasant sensations. These misunderstandings, for such they are, can be swept away and the matter put in its true light when we recognize that our sensations are not located in the peripheral parts affected but in the central nervous system, and within that portion of it known as the cerebral cortex. As long as this organ is intact, sensations may arise, and, though these are usually due to nervous impulses from the sense organs, they may be called forth by an internal stimulus as well. Thus it is that a missing arm may be represented by sensations years after it has been severed from the body. With a loss of an appropriate part of the cerebral cortex, however, comes a loss of sensation that is absolute and final. From this there is no recovery. Our sensations then are not spread throughout our bodies, as was taught in ancient times but are limited strictly to the nervous system and in all probability to that part known as the cerebral cortex.

Not only are our sensations thus activities of the cortical part of the brain, but there is good reason for believing that our whole conscious life is similarly restricted. In the cerebral cortex lies memory with its wealth of stored experiences, in this organ love, hate and fear come into being; here

arise the cool deliberations of the man of science, the dreams and aspirations of the poet, the passion of the religious enthusiast, and, when abnormalities intervene, the ravings of the madman. Contrary to ancient belief, the spleen does not engender temper, nor do the affections flow from the heart. These and all other like attributes proceed from the brain. And yet the old traditions have so strong a hold upon us that I doubt whether any modern suitor would forward his cause by offering to the lady of his choice the real organ of his affection, his cerebral cortex, rather than his heart.

Accepting the modern view that the conscious life of man is not a function of his body as a whole but an activity limited strictly to his nervous system, it follows that the evolution of this system becomes a question of special interest. In man and the other higher animals this system consists of a most intricate collection of transmitting fibers, end-stations, centers and the like so disposed as to receive and record the influx of surrounding changes and to respond to these by appropriate movements. The light of a friendly countenance reaches us through the eye and a word of salutation through the ear and off comes the hat in response. When we scrutinize more closely the machinery of these operations, we find it simple in outline, though inconceivably intricate in detail. There are first of all the sense organs of the body, the eyes, ears, nose, mouth and so forth each attuned to a particular set of influences or stimuli and each delivering to the central organs evidences of the momentary states of these stimuli in the exterior. Next are the central organs, the brain, spinal cord and the like, parts that receive the flood of sensory information from the outer world and pass it on unnoticed or store some remnant of it as a part of life's experience. Last of all

are the voluntary muscles set in action by impulses from the central apparatus and capable of performing the thousand acts good or ill that make us the responsible beings that we are. These in gross outline are the three great categories of our nervous machinery, or better, of our neuromuscular machinery, for muscles are necessarily an integral part of this chain. When such a chain goes into action, sense organ, central nervous organ and muscle, we speak of this as a reflex, for it resembles light in that it passes from an external source inward to a central organ whence it is reflected, so to speak, outward to the muscle.

If we examine the nervous systems of animals lower than man, we find in them the same three categories of parts. All the vertebrates from the mammals to the fishes have sense organs, central nervous organs and muscles. The same is true of the snails, the clams, the insects, the crabs and many others. Even the worms possess these three classes of organs, though with less differentiation as a rule than in the higher animals.

But, when we study the jelly fishes, the sea anemones, or hydroids, the case is different. Here we meet with an obvious simplification and what is noteworthy is that all three parts are not equally reduced, but that one, namely, the central organ, has suffered almost complete obliteration. In these lowly creatures the sense organs, either in the definite form of eye spots and the like, or as broad receptive surfaces without great specialization, are superimposed almost directly upon the more deeply seated muscles. Such animals often have not even a trace of an intervening nervous organ that could be called a central organ. The sense organs may thus connect directly with the muscles. Obviously under these circumstances the sense organs lack entirely that function that they showed in so marked a degree in the higher animal,

namely, the supply to the central organs of information, so to speak, as to environmental changes. In these more simplified conditions they must be restricted to the simple process of exciting the muscles to activity in consequence of special forms of sensory stimulation. They act, in other words, as a series of local triggers to set off muscular activity in various parts of the body as needed. Here then we see a stage in the evolution of the nervous system in which the sense organ and the muscle are the essential parts, but the central organ is to all intents and purposes omitted. Obviously, this stage must precede that in which central organs are present and these organs, brain, spinal cord and the like, must be looked upon as of later racial origin than sense organs and muscles. It may at first sight seem strange that so significant and all-important an organ as the brain should have been evolved secondarily in relation to sense organs, but such seems to be the case and we are justified, I believe, in stating that animals possess a brain in consequence of their having previously had sense organs, not that they possess sense organs because they have a brain.

The absence of a central organ and the presence merely of sense organs and muscles in sea anemones and other like forms makes itself felt in the activities of these animals. As I have already pointed out, that feature above all others that makes one of the higher animals, and especially man, a unit, is the possession of mental traits. Our conscious life affords our strongest claim to individuality. When this is disturbed, as in cases of double personality or in the various forms of insanity, even so practical a matter as the law takes cognizance and we treat such individuals differently from the common run of men. This unifying influence of the nervous system, technically spoken of as its integrative ac

tion, is almost completely absent from such animals as the jelly fish and sea anemones. With them individuality is a very subordinate character, and it is questionable whether they possess any trace whatever of that trait which we denominate personality in ourselves. They possess no single organ to which the nervous experience of their various parts may be referred to the advantage of the whole. Hence such nervous organization as they have is appropriately styled diffuse, in contrast with the centralized condition of higher forms.

The significance of this state of affairs is well seen in the activities of sea anemones. Many years ago it was shown that, if a single tentacle is snipped from the mouth region of a sea anemone and held in seawater so that the observer can recall which side of the tentacle was originally turned toward the mouth of the animal, the tentacle will be found to entangle food and to twist itself in a direction that would be appropriate for the delivery of the food to the mouth were that aperture still in its original relation with the tentacle. This response, which has been repeatedly confirmed by others, including myself, shows that each tentacle contains within itself the necessary nerve and muscle to carry out its own movements, and that it is not dependent, as in the case of the arms, legs, jaws and so forth of the higher animals, upon a distantly located central nervous organ to initiate, control and subdue its movements. In a similar way I have recently shown that the pedal disc with which many sea anemones creep about will, in certain species, carry out perfectly normal locomotor movements even after the other half of the animal, including the mouth and tentacles, has been cut away. This instance also demonstrates the neuromuscular adequacy of the part of the animal concerned and its relative independence of the rest. Auton

omy of parts, then, is one of the most striking aspects of the neuromuscular organization of the sea anemones and is strong evidence in favor of the absence of a centralized nervous organ in these animals. The same conclusion can be drawn from certain aspects of the feeding habits of sea anemones. If one of these animals is persistently but slowly fed by the tentacles on one side of its mouth, it will sooner or later cease to take food by these tentacles, though the muscles of the tentacles are in no sense fatigued. If food is now applied to the tentacles on the opposite side of the mouth, feeding will recommence almost as though the animal had not been fed previously. Thus the change of response induced on one side of the mouth has had little or no effect on the other, a condition referable to the absence of a central nervous organ. It is thus evident how different the organization and the responses of an animal without a central nervous organ are as compared with those of forms possessing such an organ.

Sense organs and muscles may therefore be regarded as two elements more primitive than the central nervous organs in the evolution of the neuromuscular mechanism. What is the source of these two parts? Did they arise together, twins at a single birth, or is one the older, and, if so, which? Kleinenberg in his theory of the neuromuscular cell, and the Hertwigs in their account of the nervous system of sea anemones, were both led to declare in favor of the simultaneous and dependent origin of nerve and muscle. Claus believed that these two elements arose independently and came together secondarily, a view subsequently espoused by Chun. When, however, animals more primitive than sea anemones, such, for instance, as sponges, are studied, a different solution to the problem from those just suggested is obtained.

These lowly forms as mature animals possess no powers of locomotion whatever and the few movements that their bodies exhibit are carried out with the utmost deliberation and slowness. They can very slightly and always with great slowness bend and unbend their bodies as a whole, and they can close and open the numerous inlets and the few outlets by which the spaces within their substance are set into communication with the surrounding water. All these movements are carried out by a very simple form of muscular tissue and so far as concerns the study of their bodies, both anatomical and physiological, there is no evidence whatever of the presence of sense organs or other forms of nervous tissue. It therefore seems quite certain that in sponges we have primitive animals possessed of muscle but devoid of nerve even in the form of sense organs, and we may therefore conclude that, between muscle and sense organs, the muscle is of more ancient origin and marks the beginnings of that series of functionally related parts that culminates in the central nervous systems of the higher animals.

These views as to the steps in the evolution of the nervous system, as to the sources of our nervous structures and activities, have already found expression. They carry with them, however, certain implications concerning the manner in which we should frame our hypotheses as to the springs of nervous action, implications that have not been so generally appreciated. In the early part of this address I sketched the commonly accepted view of the organization of nerve and muscle in the higher animals. From the standpoint of human interests the sense organ is the avenue through which we gather in the course of our lives that enormous body of information concerning our surroundings. By smell, taste and touch we gain a knowledge of the more elemen