Read CHAPTER I - THE SENSES IN THE LOWER ANIMALS of The Dawn of Reason / Mental Traits in the Lower Animals, free online book, by James Weir, on

I am inclined to believe that the primal, fundamental sense, the sense of touch, from which all the other senses have been evolved or developed, has been in existence almost as long as life.

It is quite probable that it is to be found in the very lowest animal organisms; and, if our own senses were acute enough, it is more than probable that we would be able to demonstrate its presence, beyond peradventure, in such organisms.

The senses of taste and smell, according to Graber, Lubbock, Farre, and many other investigators, seem to be almost as old as the sense of touch. My own observations teach me that certain actinophryans, minute, microscopic animalcules, can differentiate between the starch spores of algae and grains of sand, thus showing that they possess taste, or an analogous sense.

On one occasion I was examining an actinophrys (Actinophrys Eichornii), which was engaged in feeding. It would seize a rotifer (there were numerous Brachioni in the water) with one of its pseudopodia, which it would then retract, until the captured Brachionus was safely within its abdominal cavity. On the slide there were several grains of sand, but these the actinophrys passed by without notice.

I thought, at first, that this creature’s attention was directed to its prey by the movements of the latter, but further investigation showed me that this was not the case.

After carefully rinsing the slide, I placed some alga spores (some of which were ruptured, thus allowing the starch grains to escape) and some minute crystals of uric acid upon it. Whenever the actinophrys touched a starch grain with a pseudopod, the latter was at once retracted, carrying the starch grain with it into the abdominal cavity of the actinophryan; the uric acid crystals were always ignored.

I conclude from this experiment, that the actinophrys, which is exceedingly low in the scale of animal life, recognizes food by taste, or by some sense analogous to taste.

Many species of these little animals, however, are not as intelligent as the Eichorn actinophrys; they very frequently take in inert and useless substances, which, after a time, they get rid of by a process the reverse of that which they use in “swallowing.” By the latter process they put themselves on the outside of an object in fact, they surround it; by the former, they put the object outside by allowing it to escape through their bodies.

The sense of sight makes its appearance in animals quite low in the scale, therefore the reader will pardon me if, while discussing this sense, I prove to be a bit discursive. The subject is, withal, so very interesting that it calls for a close and minute investigation.

One of the immutable laws of nature declares that animals which are placed in new surroundings, not fatal to life, undergo certain changes and modifications in their anatomical and physiological structures to meet the exigencies demanded by such a modification of surroundings. Thus, the flounder and his congeners, the turbot, the plaice, the sole, etc., were, centuries and centuries ago, two-sided fishes, swimming upright, after the manner of the perch, the bass, and the salmon, with eyes arranged one on each side of the head. From upright fishes, swimming, probably, close to the surface of the sea, they became dwellers on its bottom, and, in order to hide themselves more effectually from their enemies or their prey, they acquired the habit of swimming with one side next to the ground, and of partially or wholly burying themselves in the mud, always, however, with one side down. They thus became flat fishes, losing the coloring of their under surfaces, and their eyes migrating across their foreheads and taking up positions on the upper surfaces of their heads. Again, when animals are placed among surroundings in which there is no need for some special organ, this organ degenerates, and passes wholly or partially into a rudimentary condition, or, entirely out of existence. These latter effects of changed conditions on animals are especially noticeable in the effect of continual darkness on the organs of sight of those creatures which, owing to said mutations, have been compelled to dwell in darkness for untold ages.

The mole, far back in the past, had eyes, and gained its livelihood above ground in the broad light of day; but, owing to some change in its surroundings, it was forced to burrow beneath the surface of the earth; consequently its organs of sight have degenerated, and are now practically worthless as far as vision is concerned. All moles, however, can tell darkness from light, consequently, are not wholly blind a certain amount of sight remains. This is due to the fact that, although the optic nerve, on examination, is invariably found to be atrophied or wasted, there yet remain in the shrivelled nerve-cord true nerve-cells; these nerve-cells transmit light impressions to the brain.

Even if the optic nerves, and, in fact, all of the structures of the eye, were absent, I yet believe that the mole could differentiate between daylight and darkness. The sensitive tufts and filaments of nerve in the skin, undoubtedly, in many instances, respond to the stimulation of light, so that totally blind animals, animals with no rudimentary organs of vision whatever, and the inception of whose ancestors, themselves wholly blind, probably took place thousands of years ago, show by their actions that light is exceedingly unpleasant to them. Thus, I have seen actinophryans taken from the River Styx in Mammoth Cave (which is their natural habitat), seeking to hide themselves beneath a grain of sand which happened to be drawn up in the pipette and dropped upon the glass slide beneath the object-glass of my microscope.

I have repeatedly seen the blind fish of Mammoth Cave seeking out the darkest spots in aquaria. In point of fact, I think it can be demonstrated that light is directly fatal to these fishes; they soon die when taken from the river and placed in aquaria where there is an abundance of light.

These fish, although they have rudimentary eyes, never have the slightest remaining trace of nerve-cells in the wasted optic nerve (that is, I have never been able to discover any), thus showing that their appreciation of light is not derived through the agency of their eyes. An eyeless spider (Anthrobia) taken from the same cavern showed a like distaste for light, and yet, in this insect, there is absolutely no vestige of an eye or its nerves.

Finally, a friend of mine, a youth of eighteen, totally blind since birth, can differentiate between daylight and darkness. On one occasion I carefully blindfolded him and led him into the well-lighted office of a brewery (he had never been in a brewery before), and asked him if it were light or dark. He answered that it was almost as light as day. I then conducted him into the dark beer vaults, and as soon as he passed the door he exclaimed, “How cold and dark it is here!” Thinking that he might possibly associate darkness with coldness, I asked him if this were the case. “No,” he replied, “I see the darkness and I feel the cold; they are not the same.”

In these animals and I include man continuous darkness has modified sensibility (sense of touch) to such an extent that it has partially taken on the functions of the useless organs the eyes; these creatures see with their skins.

I do not believe that there is a creature in existence to-day, whether it has eyes or not, which cannot tell the difference between night and day. Professor Semper says that in the Pelew Islands he found a small fresh-water creature, whose generic name is Cymothoe, in pools where daylight penetrated, that was absolutely blind. We have fresh-water Cymothoe living in our own waters that are close kin to the Pelew islander mentioned by Semper, and which are not blind. Along the middle of their backs, over the edge of each segment, there is an oblong dark spot. This little collection of coloring-matter is covered by a transparent membrane, the cornea, and has a special nerve leading to the brain, if I may use the word. These spots are primitive eyes, the analogues of which are preserved by many of the true worms. I am inclined to believe that Semper would find primitive eyes of some form or other in the Cymothoe he mentions, if he were again to examine it. The insects, etc., which dwell in caves, and which have eyes, are new arrivals; they have not dwelt long enough in total darkness to have experienced the full effects of changed surroundings. They show, however, that they are beginning to feel such effects, for there is more or less diminution in the color-cells of the eyes and body coverings. My experiments on fish and frogs show, conclusively, that the color-producing function is directly due to light stimulation. The longer fish and frogs are kept in total darkness, the lower is the number of color-cells and the smaller is the amount of coloring-matter. This accounts for the fact that all animals which have dwelt in darkness for untold ages are absolutely colorless. Pigmented or colored fishes, nevertheless, having well-developed organs of vision, have been taken from such depths (over a mile) as to preclude the possibility of a single ray of daylight. These fishes, however, are phosphorescent, and thus furnish their own light. Moreover, I am inclined to believe that the vast depths of the ocean, in certain localities, lie bathed in a continuous phosphorescent glow, so that creatures living there neither lose their color nor their eyes, sufficient light being present to prevent degeneration. Where eyeless and colorless fishes are brought up from great depths, there the ocean is not phosphorescent, but is in absolute darkness.

The preceding observations indicate that the sense of sight is a very old sense, and that it is to be found in a primitive form (ocelli) in animals of exceedingly low organization. That this is true, I will now attempt to demonstrate.

Sight is the result of the conversion of one form of motion into another a conservation, as it were, of energy. Thus, waves of light coming from a luminous body are arrested by the pigment-cells of the retina in our eyes and are transmuted into another form of motion, which is called nerve energy (in this instance, sight). It would seem that as far as sight (vision is not included) is concerned, eyes of very simple construction would amply satisfy the needs of thousands of creatures whose existence does not depend upon vision. This supposition is undoubtedly correct; there are many creatures in existence to-day with eyes so exceedingly simple that they can form no visual picture of objects they are only able to discriminate between light and darkness. Primitive eyes appear in animals very low in the scale of life; probably the most remarkable of these early organs of sight are to be found in the medusa, or jelly-fish. This creature, with its bell-shaped body and pendent stem, bears a striking resemblance to an umbrella; noting this resemblance, naturalists have given the name manubrium, “handle,” to the stem. Around the edge of the umbrella, and situated at regular intervals, are certain round, cell-like organs, which vary considerably in number. Some species have only eight, while others have sixty, eighty, and even (in OEquorea) as high as six hundred. These so-called “marginal bodies” are the eyes of the jelly-fish. By many biologists these organs are considered to be ears; they contain within their capsules transparent bodies, which some scientists deem otoliths, or “hearing-stones.” Experimentation and microscopical examinations, however, have taught me very recently to believe otherwise. In these marginal bodies there is always a deposit of pigment; this is, unquestionably, a primitive retina, while the transparent disk is, indubitably, a primitive lens. That these creatures can tell the difference between light and darkness is a fact easily demonstrated. Time and again have I made them follow a bright light around the wall of the aquarium in which they were confined. On one occasion I made some medusae tipsy, and their drunken gravity as they rolled and staggered through the water in pursuit of the light was as sorrowful as it was instructive; their actions in this respect were those of intoxicated men. After I had siphoned off the alcoholized water and replaced it with pure, they rapidly regained their normal status; whether or not any of them felt any evil effects from their involuntary debauch, I am not prepared to state.

The eyes of sea-urchins are rather highly developed, having corneae, retinae, and lenses. The lens generally lies in a mass of pigment, and, as Lubbock remarks, looks like a brilliant egg in a scarlet nest. The eyes are scattered over the dorsal surface of the creature’s body, and are commonly situated just beneath the skin; they are, however, sometimes elevated on pear-shaped bulbs. The eyes of starfish are generally quite primitive in character, as far as I have been able to determine, being simply pigmented spots which are supplied with nerves; in several species, however, I have been able to make out lenses. The eyes are arranged along the rays or arms, and vary in number.

Even the stay-at-home and humble oyster has eyes (not the round, fleshy muscle called the “eye” by gourmands and epicures, but bright spots around the edge of the mantle) primitive eyes, it is true, yet amply sufficient for the needs of a domestic, non-travelling, home body like the oyster.

In most of the worms the eyes are simple ocelli spots of pigment supplied with nerves. These eyes can discriminate between light and darkness, which is all that is required of them; but in the Alciope, a small sea-worm, these organs are brought to a high degree of perfection. This worm is exceedingly transparent, so that when observing it, it is difficult to make out more than its large orange eyes and the violet segmental organs of each ring. It looks like an animated string of violet disks surmounted by a pair of orange-colored eyeglasses. The eye of this creature is strikingly like that of a human being; it has a cornea, an “eye-skin,” a lens, vitreous humor (posterior chamber), and retina.

Another aquatic worm, Myrianida, is still more remarkable, not only on account of its eyes, but also on account of the wonderful way in which it reproduces its young. When seen swimming in the water it presents the appearance of a long, many-ringed worm, which impels itself through and by the aid of its hundreds of flat, oar-like legs. Closer inspection reveals the startling fact that this seemingly single worm is really a multiple worm six or more individuals being joined together, thus forming a living chain. This creature reproduces itself by fissigemation; that is, when the young worms arrive at a certain age they separate from the parent worm and begin life as individuals. These in turn eventually become multiple worms and divide into individuals, and so on ad infinitum. The tail worm, or that section farthest from the head, is the oldest and is always the first to leave its comrades and take up a separate existence. The adverb always in the above sentence is, strictly speaking, not exactly accurate, for on one occasion I saw the separation occur at the second head from the tail, thus producing twins. The two sections came apart, however, in a very few seconds after their departure from the colony. I am inclined to believe that this deviation from the normal was due to accident; probably to manipulation. This annelid is really “many in one” until the very moment of division; the alimentary canal, nerves, blood-vessels, etc., extend in unbroken continuity from the head of the parent worm to the tail of the last section. In every fourth (sometimes fifth) ring two round, dark-colored spots will be observed; these spots are ocelli, and some of them eventually become the eyes of young worms. These organs even in their embryonic state possess sight, for they have special nerves and pigment-cells; they can differentiate between light and darkness.

The snail carries its eyes in telescopic watch-towers. This animal is, for the most part, nocturnal in its habits, and, since prominent and commanding view points are assigned to its organs of sight, one would naturally expect to find a comparatively high degree of development in them; and this supposition is correct. The eyes of the creature are in the extreme tips of its “horns,” and consist of (1) a cornea, (2) a lens, and (3) a retina. Lubbock is rather disposed to decry the visual powers of the snail; my conclusions, drawn from personal observations, are, however, directly the opposite. The position of the eyes at the extreme tips of the horns naturally indicates that they subserve a very useful purpose; otherwise they would not have attained such prominence and such a high degree of development. Actual experimentation declares that the garden snail can see a moving white object, such as a ball of cotton or twine, at a distance of two feet. In my experiments I used a pole ten feet in length, from the tip of which a white or dark ball was suspended by a string. The ball was made to describe a pendulum-like movement to and fro in front of the snail on a level with the tips of its horns. Time and again I have seen a snail draw in its horns when it perceived the white ball, to it an unknown and terror-inspiring object. I have likewise seen it change its line of march, and proceed in another direction, in order to avoid the mysterious white stranger dancing athwart its pathway. Dark-colored objects are not so readily perceived; at least, snails do not give any evidence of having seen them until they are brought within a foot of the creatures under observation. A snail will generally see a black ball at twelve or fourteen inches; sometimes it will not perceive the ball, however, until it has been brought to within six or eight inches of its eyestalks. During the season of courtship snails easily perceive one another at the distance of eighteen or twenty inches. I have often watched them at such times, and have been highly entertained by their actions. The emotional natures of snails, as far as love and affection are concerned, seem to be highly developed, and they show plainly by their actions, when courting, the tenderness they feel for each other. This has been noticed by many observers of high authority, notably Darwin, Romanes, and Wolff. Mantagazza, a distinguished Italian scientist, in his Physiognomy and Expression, writes as follows: “As long as I live I shall never see anything equal to the loving tenderness of two snails, who, having in turn launched their little stone darts (as in prehistoric times), caress and embrace each other with a grace that might arouse the envy of the most refined epicurean."

Darwin tells us that two snails, one of them an invalid, the other in perfect health, lived in the garden of one of his friends. Becoming dissatisfied with their surroundings, the healthy one went in search of another home. When it had found it, it returned and assisted its sick comrade to go thither, evincing toward it, throughout the entire journey, the utmost tenderness and solicitude. The healthy snail must have used its sight, as well as its other senses, to some purpose, for, if my memory serves me correctly, we are told that the sick snail rapidly regained its health amid its new surroundings.

The crayfish also has its eyes at the tips of eyestalks, but the eyes of this creature are very different, indeed, from the eyes of the snail. They are what are known as compound eyes, a type common to the crayfish and lobster families. Viewed from above, the cornea of a crayfish is seen to be divided into a number of compartments or cells, and looks, in this respect, very much like a section of honeycomb. The microscope shows that in each one of these cell-like compartments there is a transparent cone-shaped body; this is called the crystalline cone. The apex of this cone is prolonged into an exceedingly small tube, that enters a striped spindle-like body called the striated spindle; the entire structure is called a visual rod. Nerve-fibrils emanating from the optic nerve enter the striated spindle at its lower extremity, and in this way nervously energize the visual rod. There is a deposit of pigment about the visual rod which arrests all rays of light save those which strike the cornea parallel to the long axis of the crystalline cone. We see from this that the visual picture formed by a crayfish’s eye must be made up of many parts; it is, in fact, a mosaic of hundreds of little pictured sections, which, when united, form the picture as a whole. Each visual rod receives its impression from the ray or rays of light reflected from the object viewed which strike it in the line of its long axis; the other rays are stopped by the layer of pigment-cells. When the impressions of all the visual rods are added together, the sum will be a mosaic of the object, but such a perfect one that the junction of its many portions will be absolutely imperceptible.

The crayfish can see quite well. It has been thought that this creature uses its sense of smell more than its sense of sight in the procurement of its food. This is undoubtedly true where the animal is surrounded by water that is muddy, or that is otherwise rendered opaque. The odoriferous particles coming from the food being carried to the creature by the water, it follows them until it arrives at this source.

It is different, however, in clear water and on land. I have seen crayfish rush down stream after bits of meat thrown to them, thus showing that here, at least, the sense of sight directed them. Again, I have enticed crayfish from clear streams by slowly dragging a baited hook in front of them. Moreover, when high and dry on land, I have seen them follow with their eyes and bodies the tempting morsel as it waved to and fro in the air above their heads.

The female crayfish carries her eggs beneath her tail, and, when they have hatched out, the young find this sheltering member a safe and cosey dwelling-place until they have grown strong enough to enter life’s struggle. At such times, the mother crayfish is quite brave, and will do battle with any foe. With her eyestalks protruded to their utmost extent, she vigilantly watches her enemy. Her eyes follow his movements, and her sharp nipper is held in readiness for immediate use.

Actual experimentation has taught that these animals can descry a man at the distance of twenty or twenty-five feet. When approaching a crayfish “town” for the purpose of making observations, I use the utmost caution; otherwise, each inhabitant will retreat into its burrow before I can come close enough to observe them, even with my field-glasses.

The gyrinus, or “whirligig beetle,” whose dwelling-place during the greater portion of its life is, like that of the crayfish, in ponds and streams, has remarkably acute vision. This insect is a true cosmopolite, however, and is as much at home on dry land as it is in the water. All seasons seem to be alike to it, just so the sun shines; for, during the hottest days of summer and the coldest days of winter (that is, if there is sunlight and no ice on the water), it may be seen on the surface of ponds and streams, gyrating hither and thither in a seemingly mad and purposeless manner.

Several of these creatures will be seen at one moment floating on the water, still and motionless; the next moment they will be darting here and there over the surface of the water, their black and burnished backs shining in the sunlight like brilliant gems. Suddenly, it is “heels up and heads down,” and they disappear beneath the surface, each of them carrying a bubble of air caught beneath the wing-tips; or, as the late William Hamilton Gibson expresses it, “they carry a brilliant lantern that goes gleaming like a silver streak down into the depths, for a bubble of air is caught beneath their black wing-covers, and a diamond of pure sunlight accompanies their course down among the weeds until they once more ascend to the surface." This little beetle is well provided with eyes, for it has a large pair beneath its head, with which it sees all that is going on in the water below, and another pair on the sides of its head, with which it keeps a bright lookout above. That it has remarkably keen vision with the latter pair, any one who has tried to steal upon them unawares can testify.

The queerest of all queer-eyed animals is, probably, the Periophthalmus, a fish inhabiting the coasts of China, Japan, India, the Malayan Archipelago, and East Africa.

I use the word coasts advisedly, for this strange creature when in pursuit of its prey leaves the sea and comes out on the sands, thus existing, for the greater portion of its life, in an element which, according to the general nature of things, ought to be fatal to it. The laws of evolution have, however, eminently prepared it for its peculiar mode of life, for its gill-cavities have become so enlarged that when it abandons the sea it carries in them a great quantity of water which yields up the necessary supply of oxygen.

Its locomotion has been provided for likewise, for continued use along certain lines has so developed its pectoral fins that the creature uses them as legs, and jumps along at a surprising rate of speed.

Its eyes are very large and prominent, and possess, for a fish, the peculiar faculty of looking around on all sides, hence its name, “periophthalmus,” which is derived from the Greek words, [Greek: peri], around, and [Greek: ophthalmos], eye. These eyes are situated on top of the animal’s head, and present a very grotesque appearance.

The favorite food of this fish is Onchidium, a naked mollusk. And, in the matter of eyes, this last-mentioned creature is itself worthy of remark. Its cephalic, or head, eyes are like those of other mollusks of its genus, and are not worthy of special mention, but its dorsal eyes, sometimes several dozen in number, are truly remarkable. These eyes, although they are very simple in structure, in type are the same as those of vertebrates, having corneae, lenses, retinae, and “blind spots.” (In the vertebrate eye, the spot where the optic nerve pierces the external layer of the retina is not sensitive to light impressions; hence, it is called the “blind spot.”)

When this mollusk sees periophthalmus bounding over the sands (and that it does see is beyond all question), what does it do? It contracts a thousand or so of little bladder-like cells in the skin of its back, thereby discharging a hailstorm of minute concrétions in the face of its enemy. The fish, terrified and amazed by the volley, often turns aside, and the mollusk is saved. Thus we see that its dorsal eyes are of great service to onchidium.

The Greeks were, unwittingly, very near an anatomical truth when they ascribed to certain monsters, called cyclopes, only one eye apiece, which was placed in the centre of their foreheads. The cyclopean eye exists to-day in the brains of men in a rudimentary form, for in the pineal gland we find the last vestiges of that which was once a third eye, and which looked out into the world, if not from the centre of the forehead, at least from very near that point. There is alive to-day a little creature which would put to shame the one-eyed arrogance and pride of Polyphemus, and Arges, and Brontes, and Steropes, and all the rest of the single-eyed gentry who, in the days of myths and myth-makers, inhabited the “fair Sicilian Isle.” The animal in question is a small lizard, called Calotis. Its well-developed third eye is situated in the top of its head, and can be easily seen through the modified and transparent scale which serves it as a cornea. Many other lacertilians have this third eye, though it is not so highly organized as it is in the species just mentioned. A tree lizard, which is to be found in the mountains of East Tennessee and Kentucky, has its third eye quite well developed. This little animal is called the “singing scorpion” by the mountaineers (by the way, all lizards are scorpions to these people), and is a most interesting creature. I heard its plaintive “peep, peep, peep,” on Chilhowee Mountain a number of times before I became aware of the fact that a lizard was the singer. On dissection, the third eye will be found lying immediately beneath the skin; it has a lens, retina, and optic nerve.

Thus we see that the sense of sight is to be found in animals very low in the scale of life. From a simple accumulation of pigment-cells which serves to arrest light rays (in simple organisms such as rotifers) to that complex and beautiful structure the human eye the organs of vision have been developed, step by step.

We will also see in the course of this discussion that, just as these simple and primal organisms have given place to more complex forms, just so have the operations of mind become higher and more involved. We see, in periopthalmus, a creature exceedingly well adapted by form, function, and intelligence to its manner of life. We must admit, in fact, the correlation and interdependence of morphology, physiology, and psychology in the evolution of this creature from its ancestral form to its present status.

The primitive organ of audition as it is to be observed in creatures of simple, comparatively speaking, organization is as simple as is the anatomy of the animals in which it is found. Commonly, it is a hollow hair, which is connected by a minute nerve-filament with the sensorium. Sound vibrations set the hair to vibrating, which in turn conveys the vibrations to the nerve-filament, and so on to the auditory centre. Sometimes the hair is not hollow; in this case, the root of the hair is intimately associated with nerve-filaments which take up vibrations.

It is highly probable that the majority of the lower animals, especially those which are sound-producers, can hear just as we hear. It is also highly probable that the so-called deaf animals can hear, just as we hear when we have either been born deaf, or through disease have lost the power of hearing by feeling the sound waves.

Owing to our own lack of acuteness, all of the problems involved in this question of audition in the lower animals will, probably, never be definitely settled; yet, reasoning by analogy, we can, approximately, solve some of them.

By far the larger number of entomologists locate the auditory organs of insects in their antennæ. I have only to mention the names of such men as Kirby, Spence, Burmeister, Hicks, Wolff, Newport, Oken, Strauss, Durkheim, and Carus, who advance this opinion, to show what a formidable array of talent maintains it. Yet my observations lead me to believe otherwise, though these authorities are in part correct. As far as Lepidoptera are concerned, and certain of Hemiptera, they are right the antennæ in these creatures are the seat of the organs of audition. But in Orthoptera, in most of Coleoptera, Hymenoptera, and Diptera, and in certain bugs (Hemiptera), they are located elsewhere. The habit that almost all insects have of retracting their antennæ when alarmed by noise, or otherwise, has done much to advance and strengthen the opinion that these appendages are the seat of insect ears; yet I am confident that in nine cases out of ten the antennæ are retracted through fear of injury to them, and not through any impression made on them by sound. The antennæ are the most exposed and least protected of any of the appendages or members of the insect body; hence their retraction by insects when alarmed is an instinctively protective action. They shelter them as much as possible in order to keep them from being injured. Again, although the antennæ of most insects are provided with numerous sensitive hairs, or setae, we have no right to assume that these hairs are auditory; no “auditory rods,” otoliths, etc., are to be found generally in antennæ, yet there are exceptional instances. Leydig found auditory rods in the antennæ of Dyticus marginalis (Furneaux), the giant water-beetle, and I myself have observed them in Corydalis cornuta and other neuropterous insects. I am inclined to believe that the entire order of Neuroptera has antennal ears, and should therefore in this respect be classed with Lepidoptera.

In grasshoppers and crickets the ears are situated in the anterior pairs of legs. If the tibia of a grasshopper’s anterior leg be examined, two (one before and one behind) shining, oval, membranous disks, surrounded by a marginal ridge, will be at once observed. These are the tympana or ear-drums of the ear of that leg. Where the trachea, or air-tube, enters the tibia it becomes enlarged and divides into two channels; these two channels unite again lower down in the shaft of the tibia. The tracheae of non-stridulating grylli are much smaller than those of sound-producing grasshoppers. The same may be said of the tibial air-tubes of the so-called dumb crickets. In grasshoppers and crickets the ear-drums lie bathed in air on both sides the open air on the external side and the air of the air-tube, or trachea, on the inside. Lubbock calls attention to the fact that “the trachea acts like the Eustachian tube in our own ear; it maintains an equilibrium of pressure on each side of the tympanum, and enables it freely to transmit atmospheric vibrations.”

In grasshoppers the auditory nerve, after entering the tibia, divides into two branches, one forming the supratympanal ganglion, the other descending to the tympanum and forming a ganglion known as Siebold’s organ. This last-mentioned ganglion is strikingly like the organ of Corti in our own ear, and undoubtedly serves a like purpose in the phenomenon of audition. The organ of Corti is composed of some four thousand delicate vesicles, graduated in size, each one of which vibrates in unison with some particular number of sound vibrations. The organ of Siebold in the grasshopper’s ear begins with vesicles, of which a few of the first are nearly equal in size; these vesicles then regularly diminish in size to the end of the series. Each of these vesicles contains an auditory rod, and is in communication with the auditory nerve through a delicate nerve-fibril. I have observed that each of these nerve-fibrils swells into a minute ganglion immediately after leaving its particular vesicle; the function of these ganglia is, I take it, to strengthen and reenforce nerve-energy. No other observer mentions these ganglia, as far as I have been able to determine; they may have been absent, however, in the specimens studied by others, yet in the specimens studied by myself the “red-legged locust” (Melanoplus femur-rubrum, Comstock) and the “meadow grasshopper” (Xiphidium), they were always present.

That grasshoppers, locusts, and crickets can hear, no one who has observed these creatures during the mating season will for one instant deny; they hear readily and well, for in most of them the sense of hearing is remarkably acute.

Immediately behind the wings of flies two curious knobbed organs are to be observed; these are considered to be rudimentary hinder wings by entomologists, and are called the haltères. Bolles Lee and others of the French scientists call them balanciers. This latter name I consider the correct one, for these organs unquestionably preside over alate equilibrium: they are true balancers. I do not propose to enter into any discussion as to whether these organs are rudimentary wings or not; suffice it to say that they appear to me to be organs fully developed and amply sufficient to serve the purposes for which they were created. Whether or not in the process of evolution there has occurred a change of function, is a point which will not be discussed in this paper. As they now exist, I deem them to be auditory organs of Diptera (flies, gnats, etc.).

The semicircular canals are, to a great extent if not entirely, the seat of equilibration in man. Any derangement or disease of these canals interferes with equilibration; this is well shown in Meniere’s disease, in which there is always marked disturbance of the equilibrating function.

If the balancers of a horsefly be removed, the insect at once loses its equilibrium; it cannot direct its flight, but plunges headlong to the ground. The same can be said of Chrysops niger in fact, of the entire family of Tabanidae, of the gall gnat (Diplosis resinicola, Comstock), and of the March flies (Bibionidae). These widely differing flies constitute the material from which I have derived my data; I will venture to assert, however, without fear of contradiction, that what has been said about the flies mentioned above is equally true of all flies.

When the knobbed end of the balancers of the horsefly (Tabanus atratus, Comstock) are examined with the microscope, the cuticle will be found to be set with minute hairs or setae; some of these hairs penetrate both cuticle and hypoderm, are hollow, and receive into their hollows delicate nerve-fibrils. These nerve-fibrils pass inward toward the centre, and enter ganglia, which in turn are in immediate connection with the great nerves of the balancers. There is but one nerve in the insect’s body that is larger than the balancer nerve, and that is the optic nerve; hence, it is natural to infer that the balancer nerve leads to some special sense centre. This centre in my opinion is, unquestionably, the seat of the auditory function.

It has been demonstrated beyond doubt that analogous hollow hairs, or setae, are prominent factors of audition in many animals, notably crustaceans, such as the lobster, the crab, and the crayfish, and many of the insect family; hence, it is logically correct to conclude that the hollow hairs on the balancers of flies are likewise auditory hairs. Moreover, there are grouped about the bases of these knobbed organs certain rows of vesicles, which contain auditory rods almost identical in appearance with the auditory rods of the grasshopper. Indeed, I have found those in the upper row of vesicles to be precisely similar in appearance to the rods found in Melanoplus.

I have determined that in the horsefly (Tabanus atratus) there are six rows of these vesicles, and that they are graduated in size. There are in the knobs of the balancers minute spiracles (I do not think that these have been pointed out before by any other observer) through which air passes into the large, vesicular cells which make up the greater portion of the knobs; spiracles are also to be found in the shafts of the balancers, thus providing an abundance of air to the internal structures of these organs and allowing for the free transmission of sound vibrations.

I am well aware of the fact that in considering these organs to be the ears of flies, I antagonize Lee and others who consider them olfactory in character. The position I take in regard to these organs is, however, a tenable one, and one that cannot easily be overthrown.

The ears of Lepidoptera (butterflies) are situated in their antennæ. This fact has been clearly demonstrated by Lubbock, Graber, Leydig, and Wolff. Newport has made an especially exhaustive study of the antennæ of insects; and he, too, places the organs of audition in these appendages. But in Coleoptera my experiments and microscopical researches compel me to assert that I differ somewhat from the conclusions of the above-mentioned authorities. These gentlemen locate the ears of beetles also in their antennæ. Lubbock bases his conclusions on an experiment of Will an experiment which, if it had been carried a little further, would have demonstrated the fact that the ears of beetles are not in their antennæ, but are, on the contrary, in their maxillary palpi.

Will put a female Cérambyx beetle into a box, which he placed on a table; he then put a male Cérambyx on the table, some four inches from the box. When he touched the female she began to chirrup, whereupon the male turned his antennæ toward the box, “as if to determine from which direction the sound came, and then marched straight toward the female.” Will concluded from this that the ears of the beetle were located in its antennæ.

Seeing that Will’s experiment as described by him was incomplete, I took a pair of beetles belonging to the same family (genus Prionus), and determined the true location of their ears by a system of rigid exclusion. These beetles, when irritated, make a squeaking chirrup by rubbing together the prothorax and mesothorax.

When I irritated the female she began to chirrup, and the male immediately turned toward the small paper box in which she was confined. I then removed the antennæ of the male, and again made the female stridulate; the male heard her, and at once crawled toward her, although his antennæ were entirely removed.

This showed conclusively that the organs of audition were not located in the antennæ, as Will supposed and as Lubbock advocates. I then removed the maxillary palpi of the male, after which the insect remained deaf to all sounds emanating from the female.

Again, I took an unmutilated male, which at once turned and crawled toward the chirruping female. I then removed its labial palpi, leaving maxillary palpi and antennæ intact; it heard the female and made toward her. The maxillary palpi were then removed (the antennæ being left in situ), and at once the creature became deaf.

If the maxillary palpi of long-horned beetles be examined, certain vesicular organs, each containing a microscopic hair, will be observed in the basal segments; these, I take it, are auditory vesicles. In some of the Coleoptera I have found auditory rods in the apical segments, though this is by no means a common occurrence. In Cicindelidae and Carabidae these auditory vesicles are exceedingly small, and require a very high-power objective in order to be clearly seen.

In justice to other observers I must say, however, that I am inclined to believe that in all beetles the antennæ in some way aid or assist audition, but they are adjuncts, as it were, and not absolutely necessary. It is a matter of easy demonstration to show that some of these insects hear less acutely where they are deprived of their antennæ. I presume they are about as necessary in audition as are the external appendages of the human ear; this, however, is mere supposition, and has no scientific warrant for its verity.

I have purposely said but very little about the senses of touch, taste, and smell in this discussion of the senses in the lower animals. These three senses have been so exhaustively treated by Lubbock in his Senses, Instincts, and Intelligences of Animals, that I could not hope to introduce any new data in regard to them. Graber, Frey, Leuckart, Farre, Hertwig, and a host of others have likewise investigated these senses most thoroughly.

As to the senses of sight and hearing, the matter presented a different aspect. I was confident that I could add somewhat to the knowledge already formulated, consequently I have treated these senses at some length. Technicalities and the details of microscopic investigation, especially microscopic anatomy, have been omitted; they have no place in a work like this.