The Animal Mind: A Textbook of Comparative Psychology

The highest invertebrate animals belong to the phylum of the Arthropoda, like the annelid worms in their segmented structure, but more highly organized in many respects. The body of a typical arthropod consists of a series of segments, one behind another, each segment with a pair of appendages. The higher an arthropod stands in the scale, the more modification and differentiation of function there is in the segments and appendages; the former often become consolidated, and the latter become modified for swimming, walking, or sensory purposes. The lowest grand division of the Arthropoda is that of the Crustacea.

As the animals of this group are covered with a hard outside shell, sensitiveness to touch and chemical stimulation is ordinarily referred to certain hairs scattered over the body, and to the modified appendages of the anterior segments which we commonly know as “‘feelers,”’ the large and small antenne. That mechanical contact stimuli in certain Crustacea give rise to specialized reactions is evidenced by observations on the hermit crab. This animal, as is well known, has acquired the instinct of taking up its abode in empty shells, most commonly those of some gasteropod mollusk. When wandering about in search of a dwelling, the crab’s reactions to the objects it meets show adaptation to the character of the stimulus, for it will not investigate a glass tube or ball; the smooth surface seems not to be the adequate stimulus for beginning the movements involved in exploring and entering a shell (194).

The responses of Crustacea to food stimulation vary, as might be expected, with different genera and species. Nagel finds the réle of the food sense in aquatic Crustacea very insignificant; they occasionally show antennal movements in the presence of food, he says, but are not guided to it (522). That general restlessness is shown by various Crustacea in the neighborhood of food, but not in contact with it, has been observed by Bell in the crayfish (40), by Holmes in the amphipod Amphithoe longimana (329), by Bateson in shrimps and prawns (24), and by Bethe in the green crab (49). Bethe arranged a series of aquaria one above the other, with a connection between them, and found that when food was placed in the uppermost compartment the crabs in the lower ones were successively excited as the food juices diffused themselves from each compartment to the one below. In the amphipod Amphithoe longimana, the small antenne and the mouth parts appeared to be the regions especially sensitive to food stimulation; if the food touched one of the former, the animal instantly made a dart for it. Touching the antennule with a needle very rarely caused such a reaction (329). Bateson’s shrimps and prawns had their food sensibility located chiefly in the antennules, though if food was placed very near them they would show disturbance even when deprived of antennules (24). Balss (15) finds the sense of smell in the shrimp Palemon located in the antennz, and also in other parts; taste in the mouth parts and tips of the thoracic legs. This was the case also with Holmes’s amphipod. Bell, on the other hand, found the whole body of the crayfish sensitive to. chemical stimulation, and no evidence that the small antenne were especially concerned. The crayfish’s reactions to contact with food were such as to direct the stimulus toward the mouth; negative reactions of rubbing, scratching, and pulling at the affected part were obtained by stimulation with acids, salts, and other irritants (41).

Chidester (120) found that the crayfish would go to freshly cut meat more quickly than to meat whose surface had had time todry. Evidences of irritation by the neighborhood of asafoetida were observed also by Graber in Pagurus (268). In some Crustacea the sense of smell is possibly concerned in guiding the male to the female. Certain copepods which daily migrate from near the surface of the water to greater depths and back again have had this behavior explained as a result of the reactions of the females to light, plus the tendency of the males to follow the females. That the latter is an affair of chemical stimulation is indicated by the fact that the females were sought even when concealed in tubes (534). In the case of some other Crustacea, however, the sexes do not seem to be aware of each other’s neighborhood until they come into actual contact (331,

The two most important divisions of the phylum Arthropoda, besides the Crustacea, are those of the Arachnida and Insecta. Spiders, as is well known, have highly developed responses to mechanical stimulation; the web-making species in particular are sensitive to very slight web vibrations. The food reactions of spiders have never, so far as the writer knows, been tested, but various observers report sensitiveness to chemical stimulations, such as those produced by odorous oils, not in contact with the body. Spiders of the family Attide would react to glass rods dipped in such oils and brought close behind them, but would not react to clean glass rods when similarly placed (570). The reactions seem to be of a negative character (618), and, of course, in all such cases it remains uncertain whether the possible conscious accompaniment is a specifically olfactory unpleasantness or an unpleasant irritation of the body surface. Pritchett found that irritating and

non-irritating oils gave negative reactions (618); but an oil that belongs, for us, to the latter class might belong to the former in the case of a spider. If the sensibility were sharply localized, that fact would point in the direction of a specific olfactory sensation; but while some authorities think the spider’s feelers or palpi are smell organs (47), others believe that sensibility to chemical stimulation is distributed over the body (452, 618). Nagel finds no specific organ of smell and little smell sensibility in spiders (522).

A member of the Arachnida which presents but slight superficial resemblance to the spiders is Limulus, the horseshoe crab. Limulus shows taste reactions, but no response to smell stimuli. If the mandibles at the base of the legs be rubbed with inedible objects, there is no reaction. Similar negative results are obtained by holding strong-smelling food close to the mouth or jaws. But if an edible substance be rubbed on the mandibles, strong chewing movements take place. Ammonia or acid vapor will produce these same chewing reflexes, but the claws make snapping movements “as though to pick away some disagreeable object.” If a wad of blotting paper wet with ammonia or acid be laid on the mandibles, the chewing movements are reversed and the object is sometimes picked up by the claws and removed. Patten found organs which he believed to be gustatory on both the mandibles and the claws (557). Pearl observed no gustatory reactions in the free-swimming embryo of Limulus

ria Throughout all the branches of the animal kingdom thus / far mentioned, the chemical sense has functioned chiefly as a food sense. There has been but little evidence of the development of qualitative discrimination within the sense itself. That is, while in many cases an animal can apparently distinguish the edible from the inedible, and gives negative reactions to irritating chemicals, one would hardly be justified in saying that it possesses more than one food~ sensation quality; while in our own case, of course, though we make comparatively little use of the sense of smell, the qualitative discriminations possible by its means are many. But we come now to a group of animals where there appears a remarkable development of qualitative variety in the sensations resulting from chemical stimulation; namely, the Insecta. As the reactions of animals to mechanical stimulation, on the other hand, offer evidence of little qualitative difference in the accompanying sensations, we shall give but slight attention to them in what follows.

To begin with, there is evidence that taste and smell are distinct in many insects: The water beetle Dytiscus marginalis, found apparently unresponsive to food at a distance, will bite with especial eagerness at filter paper soaked in what Nagel calls ‘“‘a pleasant solution” (522). Ants fed honey mixed with strychnin will taste it and then stop, and will do this even when the antenne and mouth palpi are removed, indicating that the taste organs are in the mouth itself (231). Similar results have been obtained from similar tests on wasps, and it has been observed that wasps so treated will hesitate when offered pure honey afterward (786).

Essenberg (208) found that the water strider, when offered flies which had been soaked, some in quinin and alcohol, some in coal oil, some in ammonia, approached them “ carefully,” left them, and then returned and devoured them, a proceeding which proved fatal in certain instances. The insects would stop and retreat just before reaching a drop of coal oil. Vitus Graber tested the reactions of various insects to odors by the method which we called on page 55 the Method of Preference. This was Graber’s favorite mode of studying the effect of stimuli upon animals. Applied to olfactory stimuli it consisted in offering a choice between different compartments, containing each a different odor. The animal’s power of discrimination was argued from the tendency to choose certain odors rather than others. Such preferences were shown by the insects (268). The method, however, as was noted above, is unsatisfactory, because discrimination might exist where preference did © not. Another criticism urged against Graber’s experiments is that the odors used were too strong and irritating. There is always the possibility that such substances affect other nerves than those of smell. The insects observed by Graber displayed choice between odors even when their antenne were removed. There is much evidence to show that the antenne are the true organs of smell in insects. Various flies and beetles which are in the habit of laying their eggs in putrefying flesh will not react to it when their antenne are removed, and it has been shown that insects which seem to find their mates by response to olfactory stimulation fail to do so when deprived of antenne (231). Interesting “compensatory movements” have been seen in silkworm moths with one antenna removed; they turned, that is, in the direction of the remaining antenna (397). We shall note movements of this class later in insects with one eye blackened, and in fish with one auditory nerve cut. The exploring movements of the antenne which certain insects make in seeking a proper place to

lay their eggs have been taken as evidence of the smell function of these organs (574). McIndoo (455, 456, 457, 458), however, has recently presented evidence against the olfactory function of the antenne. His experiments were performed on beetles, ants, honey bees, and hornets. His line of argument is as follows. While it is true that insects whose antenne have been removed fail to respond normally to odors, this is because such insects are abnormal in all their behavior. There exist in various regions of the body of insects, as for instance the bases of the wings and legs, small pores containing sense cells; these McIndoo calls olfactory pores. He finds by measuring the time required for insects to respond to odors, that this reaction time is lengthened more decidedly when the olfactory pores are varnished over than when the antenne are removed.

The function of the chemical sense in the mating processes of insects is one of the most remarkable phenomena connected with the sensory reactions of animals. Forel says he had a female Saturnia moth shut up in his city room, and that within a short time a number of males came and beat against the window (231). Riley hatched in Chicago some moths from the Ailanthus silkworm, which were carefully confined. No other specimens were known to exist within hundreds of miles. A virgin female was put in a wicker cage on an ailanthus tree, and a male, with a silk thread tied around the abdomen for identification, was liberated a mile and a half away. The next morning _ the two were together (637).

The most interesting observations on the sense of smell as used in the mating of insects, however, are those of Fabre. A cocoon of the “Bombyx du chéne,” a species of which Fabre had not seen a specimen in the locality for twenty years, was brought to him, and from it a female hatched. Sixty males sought her within a few hours after she reached maturity. Fabre noticed in this and other cases that shutting the female in an air-tight box prevented the males from being guided to her, but that the smallest opening was enough to allow the odor to escape; that the males were not in the least confused or led astray by placing dishes of odorous substances about, and that they would seek anything on which the female had. rested for a time, a-fact which suggests that the stimulus is a secretion of the body, as it is known to be in silkworm moths. Fabre offers the suggestion that smell stimuli as they are operative in the animal kingdom generally may be of two classes: (1) substances which give off particles in vapor \ or gas, and (2) substances which give off a form of vibration. Our own olfactory sense is limited to the first class of stimuli, but some animals, notably insects, may be sensitive to both (216). Certainly the marvellous sensitiveness involved in these mating reactions suggests a kind of response to stimulation unknown in human experience.

In many ways the Hymenoptera are the most interesting of insects, particularly those members of the order which have developed community life. Their reactions to chemical stimulation have been the subject of a large mass of literature, some of the more important results of which we may now undertake to survey, considering ants, bees, and wasps successively. Sir John Lubbock was among the earliest observers to indicate the great importance of chemical stimuli in the life of ants. In the first place, he demonstrated that it is by chemical stimulation that

ants are able to follow each other to supplies of food; or to larve, for an ant’s behavior to an ant larva found in the course of its wandering is like its behavior to food; the larva is picked up and carried to the nest. Lubbock put some larvee on a glass plate at a little distance from one of his artificial ant nests, and set a similar empty plate beside it; he then made a bridge of a strip of paper leading from the nest toward the plates, and connected each of them with this bridge by a separate short paper strip. He placed a marked ant at the larve; she picked up one and returned to the nest. She soon appeared followed by several others ; when she had reached the larve, and before the others had arrived at the dividing of the ways, Lubbock exchanged the short strips, so that the one over which the marked ant had passed now led to the empty plate. The following ants all took this path, indicating that they were guided by some trace which her footsteps had left. Lubbock was inclined to think, however, that some kind of communication must have passed between the marked ant and her fellows in the nest to induce them to follow her, and also that this communication might on occasion convey some notion of the quantity of food or larve to be had. He placed three glass plates near an ant nest, connecting each of them with the nest by means of a paper strip. On one plate he put a heap of several hundred larve, on the second two or three only; the third was empty. He put a marked ant on each of the plates, and captured all the ants which they led back with them. Many more ants came to the plate with the larger heap of larve than to the others. Lubbock explained this by supposing that the ant from that dish had in some way communicated to the nest the greater numbers at her disposal (441, pp. 172 ff.). Obviously it would be enough to suppose that the smell of food or

larve about an ant returning laden to the nest is a stimulus to her nest mates to follow her; that this smell is stronger, the larger the stock she has found, and hence acts as a more powerful stimulus. The question arises, however, as to how an ant can distinguish between the smell of food or larve on an ant that has just found a store of either, and the smell of the food and larve in the nest, which must adhere to all her nest mates. Some peculiarity of behavior on the part of the foraging ant would seem to be needed if she is to induce her fellows to accompany her to food. Wheeler, whose knowledge of ants is unsurpassed, but who is perhaps a little too much inclined to humanize them, says (783, page 535), ‘‘I believe that no one who has watched ants continuously and under a variety of conditions will doubt that they actually communicate with one another. This is clearly indicated by the rapidity with which they congregate on a spot where one of their number has found food, or retire from any spot in which a few of their number have been killed or injured.” Such communication, whatever its nature, concerns us here only so far as smell may be involved in responding to it.

The homing of ants is a puzzling problem. Bethe (51) thinks that ants, as reflex machines, are drawn along the path back to the nest by the chemical stimulus deposited on the path by their own bodies. Piéron (579) has maintained that in some species we have to do with a kind of muscular memory, the ants simply reversing, on the homeward path, all the turnings they took on the way out, like a top unwinding itself. Cornetz (143, 144, 145) claims for ants the mysterious power of registering in their bodies

the general direction of their outward course and reversing it when they have found a load to be carried home. We may consider very briefly the facts that have been brought to the support of these various hypotheses. There are really two problems involved in the homing of ants. There is, first, the problem of the homing of a solitary forager, who, having found food at the end often of a very long and rambling course, is able to get back to the nest. Secondly, there is the problem of the nature of a frequented ant road, along which many ants constantly travel to and from the nest. The evidence that smell functions in the homing process is strongest in the case of such a frequented trail. Lubbock’s experiments showed that on these trails the recognition of visual landmarks plays no important part. For instance, he placed larve in a dish on a table connected by a bridge with an ant nest. He accustomed the ants to go back and forth between the dish and the nest by a path which he diversified with artificial scenery, such as rows of bricks along either side, and a paper tunnel. When the path was thoroughly learned, he moved the bricks and the tunnel so that they led in a different direction: the ants, however, were not at all disconcerted by this cataclysm of nature, but followed the same track as before, evidently guided by their own footprints (441, p. 259). Forel (233) showed that when a piece of wood is laid across a wellfrequented path of certain species of ants, they are much disturbed and at a loss to follow the trail, and Bethe (51) reports that drawing a finger across the trail will apparently _ break its effectiveness as a guide. That the chemical deposited by the ants is volatile he concludes from the following observation.

If a strip of paper be placed across an ant path, the ants on coming to it stop, quest about, and are delayed until one accidentally runs across the strip and others follow. The piece of paper is thus gradually adopted into the ant road; if it is subsequently removed, the ants stop and are bewildered at the place where it was, showing that the earlier traces of their footsteps, under the paper, have evaporated. Again, Bethe thinks he has evidence that the chemical stimulus left by the feet of ants going from the nest is different from that deposited by those going to the nest, and that ants on the way home will not follow a track made by the feet of other ants on the outward journey, and vice versa (51). Bethe found that when the usual road to an ant nest had been interrupted by the removal of a heap of sand, and the road across the breach had been established solely by incoming ants, the outgoing ants refused to follow it, and made a new road for themselves (51). Wasmann thinks this may have been done merely on account of the faintness of the recently established path as compared with the old one (762). Bethe observed also that if a strip of paper had been adopted into an ant road, and was then, while an ant was on it, rotated through 180 degrees, the ant stopped and was disturbed on coming to the end of it (51). Experiments on rotating ants were made also by Lubbock (441), and seem to give puzzling and conflicting results; it is not clear why, even on the assumption that'there is a difference in odor between the road to the nest and that from the nest, an ant on a road which led both ways should have found her course interrupted by rotation. One fact, Bethe thinks, shows that even assuming two road smells is not enough. Ants of certain families (Lasius) which habitually make regular and frequented roads can, if they come upon one of these roads in wandering, at once take the proper direction, either to or from the nest. Evidently the mere presence of two smells would not enable them to do this.

Bethe suggests that the particles of the two chemical substances are also differently polarized, so that one of them can be followed only in one direction, the other in the opposite direction (51). Wasmann objects to this that an ant returning on its own traces would destroy them, as the opposite polarizations would cancel; and that similar confusion would occur on a narrow and much frequented road (762). He and Forel (233) both think that, granting the discrimination between the outward and inward paths, which is made by only a few families of ants, the direction is most probably given by a perception obtained through the antenne, of the “smell form” of the footsteps. Since the antenne are movable organs, like the hands, they may well, Forel suggests, mediate spatial perceptions of the form and size of odorous patches. This hypothesis would fall to the ground if McIndoo’s contention that the antenne are not smell organs were sustained.

On the whole, there is much evidence indicating that smell plays an important part in determining the response of ants to well-frequented roads. We may now consider the case of the solitary forager. Santschi (654) believes that he has seen a smell trail ‘‘intentionally” deposited by an ant, dragging her abdomen along the path. Bethe, whose general position that ants, and indeed all invertebrate animals, are reflex machines requires him to avoid any hypothesis that would involve learning or memory on the part of these animals, is of course anxious to explain the homing of the solitary foraging ant as a smell reflex. He placed near the entrance of a nest a large sheet of paper covered with lampblack, on which the footsteps of the ants could be traced. On this paper he put.a supply of food. When an ant had found the food, Bethe reports that in returning to the nest she always followed the path by which she had

come, except that when the original path had crossed itself in loops, the ant omitted the loops in her homeward way (51). Apparently, however, many species of ants do not thus retrace their own footsteps. The ‘‘muscular memory” theory of Piéron (579) is based on the observation that if a homing ant be carefully lifted and deposited at a little distance away, she will continue her course until she has traversed a distance equal to that which she would have had to go to reach her nest, if her course had not been interrupted. Cornetz’s theory (143, 144, 145), that an ant has some mysterious power of retaining an impression of the direction in which she set out, and of reversing this direction when she is ready to return home, is derived from a long series of very careful field studies. He reports that a foraging ant takes a certain general direction and makes excursions to right and left in search of food. When the food has been discovered, she reverses her original direction, but does not actually retrace any part of her outgoing path. Piéron (591) is impressed by these observations, and inclined to think that a mysterious factor is © actually involved. That the direction of the light may serve as a guide in the homing of ants is indicated by observations of Lubbock (441), Turner (722 a), and Santschi (654), but the ability of ants to find their way about in the dark is sufficient proof that it cannot be the sole factor.

Another problem of ant life to which smell appears to furnish the key is that of the recognition of nest mates. It has long been known that an ant entering a strange nest, though of the same species, is likely to meet with rough treatment, and even be put to death. Now Forel found in 1886 that ants of the genus Myrmica whose antennz were removed would attack their own nest mates (231). It seems probable that each nest of ants has a peculiar odor which is the basis of the distinction between friends and foes. Bethe tested the smell theory by dipping an ant first in weak alcohol, then in water, and then in the juices obtained by crushing the bodies of a number of ants of another species. He found that an ant thus treated would be attacked and killed by its own nest mates, but could be introduced, though not so easily, into the nest whose odor it now presumably bore, even though its appearance was quite different from that of the ants therein (51). Wasmann repeated these experiments with much less success than Béthe ; bathing Myrmica ants with essence of Tetramorium ant did not preserve them from final destruction at the jaws of the latter, though it delayed their fate; nor did much bathing with foreign nest odors induce the ants to attack beetles of the species Lomechusa strumosa, their accustomed ‘‘guests” in the nest, though they seemed disturbed at first. Wasmann apparently thinks other factors besides smell, vision perhaps, enter into the recognition process (762). Bethe, in a later paper, suggests that Wasmann’s negative results may have been due to the fact that the nest smell very quickly returns to the ants after it has been removed; he himself took account only of the first reaction of other ants toward the one subjected to treatment (52). Piéron (581 a) has repeated Bethe’s experiments and confirmed his results with eighteen different combinations of ant species. Many factors, however, modify the hostile reaction to foreigners. Piéron finds that certain species are inclined to be tolerant. At- tacks are more frequent near the nest than at a distance from it. A solitary ant tends to run away rather than to

attack. Males do not distinguish strangers from nest mates, and a female after the marriage flight will be received in a strange nest. Brun (104) has observed that ants carrying larvee will be tolerantly received, and that if ants from two nests are tumbled into a sack together and then tumbled out into a strange place, their hostility to each other is inhibited by their general disturbance and fright. Termites, which, although they belong to the order of neuropterous insects and not to the Hymenoptera, have developed an organized community life much like that of ants, show the same tendency as ants to attack strangers. The young are not attacked, nor does the fighting response occur when large numbers are hastily tumbled together. That the hostile response is made to a chemical stimulus, at least in part, appears from the fact that ‘“‘a well-washed termite is attacked by both aliens and fellows,’”’ but the observations do not give quite so definite results as those on ants (6).

Fielde, as the result of a study of the genus Stenamma, concludes that each ant is the bearer of three distinct odors: the individual odor, which enables her to follow her own trail in a labyrinth, and the reception of which depends upon the tenth segment of the antenne; the race odor, dependent on the eleventh segment; and the nest odor, dependent on the twelfth (219). No other investigator, however, finds evidence of any such specialization of the antennal segments, and McIndoo, as we have seen, wholly rejects the antenne asasmell organ. In a later article Fielde concludes that the nest odor of the worker ants is derived from their queen mother; that the odor of the queen is unchanging, and is imparted to her eggs. The worker, however, gradually changes its odor. Queens of diverse

odors may be produced by the influence of males that are the offspring of worker mothers and have the differentiated worker odor. A young ant isolated from the pupa stage until many days old will single out its queen mother from queens of other species, but will show decided suspicion of older sister worker ants. A mixed nest formed of newly hatched ants of different species was separated for seven months. On rejoining each other, the ants showed hostility; their odor, Fielde argues, had changed. But young ants of one species were received by those of the other species. Fielde does not hesitate to introduce the psychic factor and say that the latter remembered the odor of the young ones, having been associated with it in their own youth. The suggestion might be made that the young ants had not as yet developed any specific odor, but this is opposed by the observation that newly hatched Lasius ants from a strange colony were not received by a nest of Stenammas, while young Lasius ants from a colony with which the Stenammas had been acquainted in youth were accepted eleven months after the latter had been segregated. It is an affair of the memory, Fielde is assured ; and she says, “Tf an ant’s experience be narrow, it will quarrel with many, while acquaintance with a great number of ant odors will cause it to live peaceably with ants of diverse lineage, provided the odors characterizing such lineage and age environ it atits hatching” (224). Bethe held that an ant’s own nest odor offered no stimulus to it at all, but that fighting reflexes were occasioned by any foreign nest odor (51). Many facts, however, seem to tell against this view; among others, the early observation of Forel that a Myrmica ant deprived of its antenne attacks everything in sight (231). It should, according to Bethe’s theory, live peaceably with all.

Thus we see that in spite of some divergence of testimony, there is evidence that ants have a variety of qualitatively different smell experiences: the smell of food and of larvee, probably distinct, though there is no experimental proof of the fact; the individual smell of an ant’s own footsteps; a possible distinction, in some species, between the smell of the outgoing and that of the incoming paths; and the different odors which seem to be responsible for the discrimination between nest mates and foreigners. If it were true, as Fielde maintains, that loss of the eighth and ninth segments of the antenne renders an ant incapable of caring for the young, then the recognition of larve and pupz would depend upon a specific odor (219).

In bees the sense of smell is equally well developed. But no topic in comparative psychology has been more hotly disputed than the use which bees make of this sense, and the extent to which they depend, rather, upon sight. Darwin (170) and H. Miiller (512, 513) thought both color and fragrance influential in attracting insects toflowers. Plateau maintains that the chief influence guiding bees to flowers is smell, and that color has little effect. He made a number of experiments in which the brightly colored corollas of flowers were cut off without disturbing the nectaries, © and claims to have found that the visits of bees to the mutilated flowers were as frequent as before (600-603, 605). On the other hand, Giltay obtained opposite results; the flowers whose corollas were removed were neglected by bees, while those which were covered so as to be invisible but not so as to prevent the odor from escaping, were also unnoticed (259). Josephine Wéry found that the propor-

tion of bees visiting flowers with intact corollas to those visiting flowers with the corollas removed was 66:18 (778). Kienitz-Gerloff criticises Plateau’s figures and the accuracy of his experiments (400). Forel found that a bee with the antenne and all the mouth parts removed, hence probably incapable of smell, returned to flowers for honey, though of course without success (231). An- dree thinks that among diurnal insects those which live on the ground, and take but short flights, are more influenced by smell; while the freely flying insects are attracted by the sight of flowers (5). On the whole, inconspicuous flowers are more often fertilized by wind than by the visits of insects.

Most complicated of all is the problem as to how bees find their way back to the hive. It is obvious that the simple ant method of following a chemical trail is ruled out for insects that fly. Bethe abandons the puzzle as insoluble (51). Von Buttel-Reepen attempts at length, and with a vast amount of apic lore, to refute his position. It would be impossible to give more than the briefest statement of the arguments of both sides. ‘ Bethe maintains that the smell of the hive does not guide the bees back to it, because he found that if the hive were rotated slowly enough to allow the cloud of nest smell at the opening to move with the opening, the bees returning would not follow it for more than 45°, but would go to the place where the opening had been. He thinks they are not guided by sight, because when he completely changed the appearance of the hive, masking it with branches and other coverings, the bees were not disconcerted, but flew straight to the mouth of the hive. He brings other evidence against the vision