Excerpt from


A Stroll Through the Worlds

Of Animals and Men


A Picture of Invisible Worlds



Von Uexkull, J. (1934).  A Stroll through the Worlds of Animals and Men. In C. Schiller (ed.), Instinctive Behavior, New York, International Universities Press, 1957.







This little monograph does not claim to point the way to a new science.  Perhaps it should be called a stroll into unfamiliar worlds; worlds strange to us but known to other creatures, manifold and caries as the animals themselves.  The best time to set out on such an adventure is on a sunny day.  The place, a flower-strewn meadow, humming with insects, fluttering with butterflies.  Here we may glimpse the worlds of the lowly dwellers of the meadow.  To do so, we must first blow, in fancy, a soap bubble around each creature to represent its own world, filled with the perceptions, which it alone knows.  When we ourselves then step into one of these bubbles, the familiar meadow is transformed.  Many of its colorful features disappear, other no longer belong together but appear in new relationships. A new world comes into being.  Through the bubble we see the world of the burrowing worm, of the butterfly, or of the field mouse; the world as it appears to the animals themselves, not as it appears to us.  This we may call the phenomenal world or the self-world of the animal.


     To some, these worlds are invisible.  Many a zoologist and physiologist, clinging to the doctrine that all living being are mere machines, denies their existence and this boards up the gates to other worlds so that no single ray of light shines forth from all the radiance that is shed over them.  But les us who are not committed to the machine theory consider the nature of machines.  All out useful devices, out machines, only implement our acts.  There are tools that help our senses, spectacles, telescopes, microphones, which we may call perceptual tools.  There are also tools used to effect our purposes, the machines of out factories and of transportation, lathes and motor cars.  These we may call effector tools.


     Now we might assume that an animal is nothing but a collection of perceptual and effector tools, connected y an integrating apparatus which, though still a mechanism, is yet to carry on the life functions.  This is indeed the position of all mechanistic theorists, whether their analogies are in terms of rigid mechanics or more plastic dynamics.  They brand animals as mere objects.  The proponents of such theories forget that, from the first, they have overlooked the most important thing, the subject which uses the tolls, perceives and functions with their aid.


     The mechanists have pieced together the sensory and motor organs of animals, like so many parts of a machine, ignoring their real functions of perceiving and acting, and have even gone on to mechanize man himself.  According to the behaviorists, man’s own sensations and will are mere appearance, to be considered, if at all, only as disturbing static.  But we who still hold that our sense organs serve our perceptions, and our motor organs our actions, see in animals as well as not only the mechanical structure, but also the operator, who is built into their organs, as we are into our bodies.  We no longer regard animals as mere machines, but as subjects whose essential activity consists of perceiving and acting.  We thus unlock the gates that lead to other realms, for all that a subject perceives becomes his perceptual world and all that he does, his effector world.  Perceptual and effector worlds together form a closed unit, the Umwelt.  These different worlds, which are as manifold as the animals themselves, present to all nature lovers new lands of such wealth and beauty that a walk through them is well worth while, even though they unfold not to the physical but only to the spiritual eye.  So, reader, join us as we ramble through these worlds of wonder.


     Anyone who lives in the country and roams through woods and brush with his dog has surely made the acquaintance of a tiny insect which, hanging from the branches of bushes, lurks for its prey, be it man or animal, ready to hurl itself at its victim and gorge itself with his blood until it swells to the size of a pea.  The tick, though not dangerous, is still an unpleasant guest of mammals, including men.  Recent publications have clarified many details of its life story so that we are able to trace an almost complete picture of it.


     From the egg there issues forth a small animal, not yet fully developed, for it lacks a pair of legs and sex organs.  In this state it is already capable of attacking cold-blooded animals, such as lizards, whom it way-lays as it sits on the tip of a blade of grass.  After shedding its skin several times, it acquires the missing organs, mates, and starts its hunt for warm-blooded animals.


     After mating, the female climbs to the tip of a twig on some bush.  There she clings at such a height that she can drop upon small mammals that may run under her, or be brushed off by larger animals. 


     The eyeless tick is directed to this watchtower by a general photosensitivity of her skin.  The approaching prey is revealed to the blind and deaf highway woman by her sense of smell.  The odor of butyric acid, that emanates from the skin glands of all mammals, acts on the tick as a signal to leave her watchtower and hurl herself downwards.  If, in so doing, she lands on something warm-a fine sense of temperature betrays this to her-she has reached her prey, the warm-blooded creature.  It only remains for her to find a hairless spot.  There she burrows deep into the skin of her prey, and slowly pumps herself full of warm blood. 


     Experiments with artificial membranes and fluids other than blood have proved that the tick lacks all sense of taste.  Once the membrane is perforated, she will drink any fluid of the right temperature.


     If after the stimulus of butyric acid has functioned, the tick falls upon something cold, she has missed her prey and must again climb to her watchtower.


     The tick’s abundant blood repast is also her last meal.  Now there is nothing left for her to do but drop to earth, lay her eggs and die.


     The tick’s life history provides support for the validity of the biological versus the heretofore customary physiological approach.  To the physiologist, every living creature is an object that exists in his human world.  He investigates the organs of living things and the way they work together, as a technician would examine a strange machine.  The biologist, on the other hand, takes into account each individual as a subject, living in a world of its own, of which it is the center.  It cannot, therefore, be compared to a machine, but only to the engineer who operates the machine.  If we ask whether the tick is a machine or operator, a mere object or a subject, the physiologist will reply that he finds receptors, that is, sense organs, and effectors, that is, organs of action, connected by an integrating device in the central nervous system.  He finds no trace of an operator.


     To this the biologist will reply, “You mistake the character of the organism completely.  No single part of the tick’s body has the nature of a machine; everywhere operators are at work.”  The physiologist will continue, undeterred, “We can show that all the actions of the tick are reflex in character and the reflex arc is the foundation of all animal machines.  It begins with a receptor, which admits only certain influences such as butyric acid and warmth, and screens out all others.  It ends with a muscle which moves an effector, a leg or proboscis.  The sensory cells that initiate the nervous excitation and the motor cells that elicit motor impulse serve only as connecting links to transmit the entirely physical waves of excitation (produced in the nerves by the receptor upon external stimulation) to the muscles of the effectors.  The entire reflex arc works by transfer of motion, as does any machine.  No subjective factor, no engineer or engineers appear anywhere in this process.”


     “On the contrary,” the biologist will counter, “we meet the operator everywhere, not merely machine parts.  For all the cells of the reflex arc are concerned, not with the transfer of motion, but with the transfer of the stimulus.  And the stimulus must be ‘perceived’ by a subject; it does not occur in objects.’  Any machine part, such as the clapper of a bell, produces its effects only if it is swung back and forth in a certain manner.  To all other agents, such as cold, heat, acids, alkalies, electric currents, it responds as would any other piece of metal.  The action of living organs is fundamentally different from this.  Since the time of Johannes Muller we know that a muscles responds to all external agents in one and the same way-by contraction.  It transforms all external interference into the same effective stimulus, and responds to it with the same impulse, resulting in contraction.  Johannes Muller showed also that all external influences affecting the optic nerve, whether ether waves, pressure, or electric currents, elicit a sensation of light.  Our visual sensory cells produce the same perception whatever the source of stimulation.  From this we may conclude that each living cell is an engineer who perceives and acts, and has perceptual or receptor signs (Merkzeichen) and impulses or effector signs (Wirkzeichen) which are specific to it.  The manifold perceiving and acting of the whole animal may thus be reduced to the cooperation of all the tiny cells, each of which commands only one receptor sign and one effector sign.


     In order to achieve an orderly collaboration, the organism uses the brain cells (these, too, are elementary mechanics) and groups half of them as “receptor cells” in the stimulus-receiving part of the brain, or “perceptive organ,” the smaller or larger clusters.  These clusters correspond to groups of external stimuli, which approach the animal in the form of questions.  The other half of the brain cells is used by the organism as “effector cells” or impulse cells, and is grouped into clusters with which it controls the movements of the effectors.  These impart the subject’s answers to the outer world.  The clusters of receptor cells fill the “receptor organs” (Merkorgan) of the brain, and the clusters of effector cells make up the contents of its “effector organs” (Wirkorgan).


     The individual cells of the perceptor organ, whatever their activity, remain as spatially separate units.  The units of information which they separately convey would also remain isolated, if it were not possible for them to be fused into new units which are independent of the spatial characters of the receptor organ.  The possibility does, in fact, exist.  The receptor signs of a group of receptor cells are combined outside the receptor organ, indeed outside the animal, into units that become the properties of external objects.  This projection of sensory impressions is a self-evident fact.  All our human sensations, which represent our specific receptor signs, unite into perceptual cues (Merkmal) which constitute the attributes of external objects and serve as the real basis of our actions.  The sensation “blue” becomes the “blueness” of the sky; the sensation “green,” the “greenness” of the lawn.  These are the cues by which we recognize the objects: blue, the sky; green, the lawn.