D69r Dolley Reactions to Light in Vanessa Antiopa AY CREE. Lea Se - age Dan x ; "7 ed = 7s ene ; = 2 Se a See 36> = - * Gs reer ts “ UT ER PUTCO Return this book on or before the Latest Date stamped below. University of Illinois Library APR 12 1955 L161—H41 UNIVERSITY OF ILLINOTS LIBRARY HAL ysis JAN @ 2 1917 Reactions to Light in Vanessa Antiopa, with Special Reference to Circus Movements “BY WILLIAM LEE DOLLEY, Jr. A Dissertation SUBMITTED TO THE BOARD OF UNIVERSITY STUDIES OF THE JOHNS HOPKINS UNIVERSITY IN CONFORMITY WITH THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 1914 BALTIMORE : 1916 Rte ey: sy Was () all SV OIT_CL. j-i ah ar aca a UNIVERSITY OF ILI INOIS LIBRARY JAN 31 1917 Reprinted from Tue JOURNAL OF EXPERFMENTAL ZOOLOGY, Vol. 20, No. 3, : April, 1916 REACTIONS TO LIGHT IN VANESSA ANTIOPA, WITH SPECIAL REFERENCE TO CIRCUS MOVEMENTS WILLIAM L. DOLLEY, Jr. Professor of Biology, Randolph-Macon College From the Zoélogical Laboratory of The Johns Hopkins University TWENTY-ONE FIGURES CONTENTS ELEMIS Mey Pet eee a aH co s'E6 SE Fe aS ENS on CSN d io wiw Be ODT RECEP E SEde nro RAIA 2 UR Act cia chy te < dale see sicvid aia dette R eam dald slccles 367 SE ES EE IOSEL OSB TES foe ae. weeseis Gin op less. 9 oss wine es Abn Wie. os wis bsp Bask tho 370 Behavior of specimens with but one functional eye....................... 371 A. Behavior in normal conditions of illumination........................ 371 me Genaviorin a beam ‘of-lighti.8 (0. co2.c.. cdi eee OF rd] PRE ae 371 1. Description of reactions—deflection, circus movements and orien- SOONG Ss ig So RE Ae Oe ae eae ys a 371 2. Relation between the degree of curvature in circus movements and Lee ULENELGY fac sadayhe Gt he Peek: c's (eae eRe e ee 382 3. Relation between the angle of deflection and the luminous inten- SU loeione Jon lc Ggot ae erun ke Geee Cec ee nn ene en Coe 5 era 383 a. Effect of beginning the trials in different intensities........ 383 b. Effect of sudden changes of intensity on the angle of deflec- SIU Pane OR eis a ae 4) cE Ae ths Pas PU bb de dated dies « 386 4. Reorientation after changing the direction of the beam of light.. 389 >. Effect of the covering of the eye owing to contact................... 394 SRIRESOHANION I NOR-CureCtL VG: MENG... shen eee Teens ces ccna eneeeeees ts 399 E. Relation between the degree of curvature in circus movements and the luminous intensity of non-directive light.......................... 404 an titect OF INNMINAtING ONLY ONG CVO... 45.65 caus wend se veh aren Wyma 410 1. Effect of illuminating the entire surface of one eye.............. 410 2. Effect of illuminating different areas of one eye................. 413 See OIDINATY ANG CONCLUSIONIAS sac 5 in vata sid sata daWinn dandy dite tint tn =’ 415 NEON MLC el oer cc Sister, id Tete PHY ah oa Risley 06 W's, 5 MGR wha, Magda taialads des 419 INTRODUCTION One of the most thorough pieces of work, which have been done on the reactions to light itt butterflies, is that reported by Parker (’03) on the mourning-cloak butterfly, Vanessa antiopa. 357 308 WILLIAM L. DOLLEY, JR. This investigator found that these butterflies are highly positive in their reactions to light, but that when they come to rest in bright sunlight they ordinarily orient with the head directed away from the source of light. He found, however, that when one eye is painted black they do not orient, but continuously creep or fly in curves with the functional eye toward the center. Such reactions are usually called circus movements. This be- havior, the author asserts (p. 463), is in accord with the view ‘“‘that the orientation of an organism in light is dependent upon the equal stimulation of symmetrical points on its body.” A number of other investigators have, also, recorded experi- ments with other organisms in which circus movements have been observed. Reactions of this nature have been reported in experiments of three sorts: those in which one eye has been pre- vented from functioning, either by being blackened, or by being injured; those in which one antenna has been removed; and those in which certain parts of the brain or of the inner ear have been destroyed. . In these experiments it has been found that photo-positive animals, usually turn continuously toward the functional eye, while photo-negative animals usually turn in the opposite direc- tion. This is especially true in those cases in which one eye has been covered. Holmes (’01 and ’05) and his students, McGraw (13) and Brundin (’13), maintain that they have observed this behavior in the following organisms: Hyalella den- tata, Talorchestia longicornis, Orchestia agilis, two species of bees, the robber fly, Asilus, Tabinus, a Syrphid, Ranatra, Noto- necta, several beetles, Stenopelmatus, three species of flies, a number of species of butterflies, and the amphipod, Orchestia pugettensis. In all these cases, positive animals turned toward the functional eye, while negative animals turned toward the covered eye. ‘This, however, was not found to be true in all of the species investigated. Holmes and McGraw (11, p. 370) state that several species of butterflies, among them Vanessa antiopa, frequently went in circles toward the covered eye, while Brundin (13 p. 346) maintains that in positive specimens of the amphipod, Orchestia traskiana, ‘“‘cireus movements will occur REACTIONS TO LIGHT IN VANESSA ANTIOPA 359 as often toward the blackened eye as toward the normal eye.”’ Similar results have also been obtained with animals in which one eye was injured. Réadl (01, p. 458) extirpated one eye of the water scavenger beetle, Hydrophilus, and found that it de- flected toward the side of the injured eye. Hadley (’08, pp. 180-199) seared with a hot needle the surface of one eye of larval lobsters in all stages of development, and maintains (p. 198): “The immediate results following this destruction of photo- reception in one eye are: (1) The production of rapid rotations, often at the rate of 150 per minute on the longitudinal axis of the body, which are invariably in a determined direction. (2) A type of progression in which the larva continually performs ‘circus movements’ or turns toward the side of the injured eye.” Since these animals vary in the sign of their reaction to light at different stages of development, it is interesting to note that Hadley maintains that the circus movements made by animals of all ages were all in the direction of the blinded eye. Mast (10, p. 132) found that ‘‘Planaria with one eye removed, either by gouging it out or by cutting off one side of the anterior end obliquely, turn continuously from the wounded side for some time, evidently owing to the stimulation of the wound, since, after this is healed, they tend to turn in the opposite direction.”’ The destruction of the function of one eye is however not always followed by circus movements. Rddl (’03, pp. 58-64) states that Calliphora vomitoria is’ apparently not affected in its behavior by having one eye covered, while Musca domestica, although performing circus movements at times, can also ‘“‘run ‘rather long distances in one direction.’’ Carpenter (’08, pp. 483-491) blackened one eye of Drosophila ampelophila, and reported that now and then one performed circus movements, but he says (p. 486), ‘‘This conduct was exceptional, and was never persisted in except in the case of a single insect which had long been active and showed signs of fatigue.’’. They usually, however, deflected somewhat toward the functional eye as they proceeded toward the light. To quote further (p. 486), “‘They crept in a fairly direct path toward the light, although a ten- dency to deviate toward the side of the normal eye regularly 360 WILLIAM L. DOLLEY, JR. occurred. The insects generally moved in a peculiar, jerky manner. The tendency to diverge from the direct path toward - the side of the uncovered eye was overcome by a series of short, quick turns in the opposite direction, which kept them headed toward the light.”” Mast (11, p. 222) found that the toad, Bufo americanus, with the lens removed from one eye, hops or walks toward a source of light, usually deflecting slightly toward the injured eye. Some individuals, however orient nearly, if not quite, as accurately after the operation as before. Thus, it is evident that there are numerous exceptions to the idea that the destruction of one eye is followed by circus movements. Moreover, it has been found that some animals which make circus movements modify their behavior after having had a cer- tain amount of experience, and move directly toward the light. Holmes (’05), in a detailed description of the behavior of one specimen of Ranatra with the right eye blackened, says that in the first ten trials before an electric light, it made many circus movements, and showed a ‘‘marked tendency to turn to the left.”’. In the next four trials it turned directly toward the source of light and in the succeeding ten trials it reached the light by a nearly straight path. After an interval of fifty min- utes, eleven more trials were made, ‘‘and it had not forgotten in the meantime how to reach the light by the most direct means,” for it went to the light in every case in a nearly straight course. The author also states that other specimens of Ranatra and Notonecta showed this same modification. Brundin (713, pp. 334-352) observed similar reactions in the amphipods, Orchestia traskiana and Orchestia pugettensis, except that being negative’ the animals turned toward the blackened eye. Mast tested on two successive days a toad with one eye destroyed. He says (11, p. 222): ‘The following day this toad was again exposed: it now went toward the source of light even more nearly directly than on the preceding day.”’ Thus, it is clear that the reactions of at least some of these mutilated organisms may become modi- fied as the result of repeated trials. This is apparently not true of some animals. Rdadl cut out one eye of Hydrophilus, and states that, though it lived for REACTIONS TO LIGHT IN VANESSA ANTIOPA 361 several weeks in an aquarium, it never moved in a straight line, but always in a course curved toward the side of the injured eye. He says (’01, p. 458): ‘‘Es hat darnach noch mehrere Wochen in meinem Aquarium gelebt, bewegte sich aber niemals gerade sondern immer nur in einem Bogen concav nach der Seite des extirpirten Auges.”’ This investigator (’03, p. 62) also observed a fly, Dexia carinifrons, on the second day after its eye was blackened and found its behavior was similar to that exhibited immediately after the eye was covered, that is, it moved con- tinually toward the functional eye. The second group of experiments, as previously stated, refer to insects with one antenna removed. V. L. Kellogg (’07, pp. 152-154) removed the left antenna from a male silk worm moth, and found that when such an animal was placed three or four inches from a female it ‘‘moved energetically around in repeated circles to the right, or, rather, in a flat spiral, thus getting (usually) gradually nearer and nearer to the female.’’ Males with the right antenna removed turned continually to the left. In the same year, Barrows (’07, pp. 515-537) removed the terminal segment from one antenna of some fruit flies, Drosophila ampelo- phila, and then, after twenty-four hours without food exposed ‘them to the odor of fermenting banana. He maintains that they moved in circles toward the uninjured antenna in all but a few cases in which they deflected in the opposite direction. The third group of experiments mentioned comprises those in which parts of the brain and inner ear have been injured or removed. In these cases it is also maintained that the animals make circus: movements. It ean thus be seen that great diversity exists among the results obtained by the various investigators in their experiments on animals with the sense organs on one side destroyed. Among these, those which refer to the eyes are of greatest immediate interest to us. In these experiments it was found that while photo-positive animals usually turn toward the functional eye and photo-negative animals toward the non-functional eye, some turn in the opposite direction and others orient fairly accurately, THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3 362 WILLIAM L. DOLLEY, JR. while still others make circus movements for a period and then orient fairly accurately. This marked lack of harmony between the results obtained may in some measure, at least, be due to the fact that the num- ber of sources of light was not the same in all of the experiments: Parker does not state the conditions under which the specimen of Vanessa antiopa used by him made circus movements. Radl presumably performed his experiments before a window, i.e., under conditions in which the animals received some light from many different directions. The same probably held also for the work of Holmes on amphipods and .several insects. In some experiments, however, as in those performed with Ranatra and Notonecta, he worked in a ‘darkened room,’ and used for a source of light a sixteen candle-power incandescent lamp. Brundin and Carpenter also used a similar source of light. It is significant indeed that in every case where a single source of light on the same horizontal plane with the organism was used, at least some trials are described in which no circus movements were made, the animals moving in a fairly straight course toward the light. This was true of Ranatra, Notonecta, Drosophila, Bufo ameri- canus, Orchestia traskiana, and Orchestia pugettensis. On the contrary, in none of the experiments but one, where the light’ conditions were not sharply defined, have the investigators re- corded any other behavior than movements in circles. This single exception is that described by Radl, in which Calliphora vomitoria and Musca domestica with one eye blackened ran for some distance directly toward a window. The experiments described in the present paper show that in the case of Vanessa antiopa, at least, a knowledge of the number of sources of stimulation is of great importance in a discussion of circus movements; for the same animals, which, in a hori- zontal beam, moved toward the source of light in a fairly straight course, performed circus movements continuously when placed before a window, or when the single source of light was placed above the animal so that the light was non-directive.t The 1 The term ‘non-directive light,’ as used in this paper, denotes diffuse illu- mination. REACTIONS TO LIGHT IN VANESSA ANTIOPA 363 reactions under the former conditions seem to indicate that both eyes are necessary for orientation; those under the latter, that only one eye is necessary. Consequently, if the butterflies had been studied only in front of a window, the conclusions would necessarily have been erroneous. Circus movements have been held by many to have a very important bearing on the question as to the nature of the process of orientation. Holmes discusses this question rather fully. He takes the position that the performance of circus movements indicates a direct or indirect connection between the impulses set up by light in the two retinas and the tension of the muscles of the legs or appendages on the two sides of the body, and that this is a ‘“‘sort of mechanical reflex process.’’ To him the pleasure- pain theory explains those cases in which orientation occurs in these asymmetrical animals. He says (11, p. 54): ‘In most crustacea, as in most insects, orientation is effected through the unequal action of the appendages on the two sides of the body. In a form which is positively phototactic, ight entermg one eye sets up impulses, which, passing through the brain and nerve cord, cause, directly or indirectly, movements predominantly of flexion of the legs of the same side and of extension of the append- ages of the opposite side of the body. If this is a sort of mechani- cal process, we should expect that, in a positively phototactic form, if one eye were destroyed or blackened over, the animal would move continuously toward the normal side.’”? Mindful of the fact that the Ranatras and Notonectas in time straightened their courses, and followed the light nearly as precisely as if they had the use of both eyes, he also concludes that ‘‘ Phototaxis may fall, to a certain extent, under the pleasure-pain type of behavior. . . . . Light, in some animals, is followed much as an object of interest is pursued by a higher’ animal” (’11, p- 55). To these conclusions Brundin (’13) assents. According to Carpenter, the local action theory of tropisms would explain circus movements, were it not that some animals with one eye blackened can orient, as accurately as if both eyes were functional. The pleasure-pain theory, he holds, explains 364 WILLIAM L. DOLLEY, JR. this behavior. He says (’08, p. 486): ‘‘It is clear that the tropism theory, with its assumption of local action of stimulus on the side exposed to its effect, does not furnish a complete explanation of these reactions. . . . . A ‘pleasure-pain’ reaction appears to inhibit and dominate a ‘tropic’ reaction.” To Radl, cireus movements are an evidence of inequality in the tension of the muscles on opposite sides of the body, pro- duced by the blackening of one eye. He says (’038, p. 63): ‘Bei einem Tier, dem ein Auge geschwiarzt wurde, erschlaffen etwas die Muskeln an der Ko6rperseite, wo das Auge nicht sieht; da sich nun die Muskeln der anderen Seite kraftiger bewegen, so erfolgt eine Bewegung in einer nach der Seite dieser stirker arbeitenden Muskeln gekriimmten Bahn.” Parker (’03, p. 463), as has been previously stated, maintains that the circus movements he observed in Vanessa antiopa are in accordance with the view ‘‘that the orientation of an organism in light is dependent upon the equal stimulation of symmetrical points on its body.” He says further: ‘‘Should the eyes be the parts stimulated, any interference with one of these ought to result in a disturbance of the direction of the butterfly’s loco- motion. Thus, if the cornea of one eye were blackened, the insect in locomotion, being positively phototropic, ought to move as though that eye were in shade, namely in a circle, with the unaffected eye toward the center.” To Barrows, who worked on the reactions of Drosophila to odors, circus movements can only be explained by the ‘tropism theory.’ He says (’07, p. 535): “It seems impossible to explain the movements under these conditions in any other way than on the basis of the tropism theory. This theory has been stated in several ways. As applied to chemical stimulation, Verworn (99, p. 429) declares: ‘The word chemotaxis is applied to that property of organisms that are endowed with the capacity of active movement by which, when under the influence of chemi- cal stimuli acting unilaterally, they move toward or away from the source of the stimulus.’ ” V. L. Kellogg (07) and Bohn (11) agree with Loeb, whose views are given in the next paragraph, and Bohn even cites circus movements as one of his criteria for tropisms. REACTIONS TO LIGHT IN’ VANESSA ANTIOPA 365 Loeb (706, p. 140) attempts to refute any notion of a pleasure- pain type of behavior in lower organisms, and accepts the phe- nomenon of circus movements as a fact in support of his theory in explanation of the orientation of animals. This is discussed fully in the Mechanistic Conception of Life. (12, p. 35-62.) He holds that the orientation of animals is controlled unequivo- cally by external agents, and that in orientation to light, there are two essential factors, the continuous action of light and the symmetrical structure of the organisms. According to his view, which may be called the ‘continuous action theory,’ the tension of the muscles of the appendages on the two sides of the body is controlled through direct reflex arcs by the photochemical changes produced by light in the two retinas. He says (’12, p. 39): “When two retinae (or other points of symmetry) are iJluminated with unequal intensity, chemical processes, also of unequal in- tensity, take place in the two optic nerves (or in the sensory nerves of the two illuminated points). This inequality of chemical processes passes from the sensory to the motor nerves and even- tually to the muscles connected with them. We conclude from this that with equal illumination of both retinae the symmetrical groups of muscles on both halves of the body will receive equal chemical stimuli and thus reach equal states of contraction, while when the rate of reaction is unequal, the symmetrical muscles on one side of the body come into stronger action than those on the other side. The result of such an inequality of the action of symmetrical muscles of the two sides of the body is a change in the direction of movement on the part of the animal.” It is clear that in this theory it is assumed that light is effective in orientation through its continuous action, that after orienta- tion has occurred, light continues to stimulate the photosensitive areas, and through direct reflex arcs, continues to affect the muscles of the appendages on the two sides of the body. These assumptions, as stated above, are, according to Loeb, supported by the behavior of animals with the sense organs functional only on one side. He quotes Parker as follows (’06, p. 140): ‘‘ Loeb has pointed out that the orientation of an organism in light is dependent upon the equal stimulation of symmetrical points on 366 WILLIAM L. DOLLEY, JR. its body. Should the eyes be the parts stimulated, any inter- ference with one of these ought to result in a disturbance of the direction of the butterfly’s locomotion. Thus, if the cornea of one eye were blackened, the insect in locomotion, being positively phototropic, ought to move as though that eye were in shade; namely, in a circle, with the unaffected eye toward the center.” Mast holds that the precision with which some organisms with but one functional eye perform circus movements appears to add support to the ‘continuous action theory,’ but he also says (11, p. 222), as a result of his work on the toad, ‘‘ These results show that, in this form and in all other forms which orient after one eye is destroyed, difference of effective intensity on opposite sides does not regulate orientation.” A glance at these various views shows that the movement of ‘animals in circles when one eye is blackened, or when one antenna is removed, has been held by most of the investigators to support the view that the orientation of animals is in accord with the ‘continuous action theory’ described above. This theory is op-. posed by one that may be called the ‘change of intensity theory,’ the adherents of which hold that in some organisms, at least, light does not produce orientation through its continuous action, but by stimuli dependent upon the time rate of change of intensity. According to this theory, an organism going toward a source of light, may turn to one side; but when this occurs, then, imme- diately the photosensitive surfaces are exposed to a change of intensity, and this causes a reaction which results in reorienta- tion, after which the orienting stimulus ceases. The chief points at issue between the two theories concern the following questions: (1) Does light function in orientation through its continuous action, or through a change of intensity? (2) Does an animal, when oriented, continue to be affected by the same stimulus that is effective in producing orientation? and (3) Is bilateral symmetry essential in the process? In view of the bearing that circus movements have on the theories as to the mechanism of normal orientation in animals, and in view of the conflicting results recorded by previous workers it seemed desirable to make a more thorough and a more extended REACTIONS TO LIGHT IN VANESSA ANTIOPA 367 study of this phenomenon than has been done previously. More- over, such a study should throw light on the question as to whether or not the path of nerve impulses resulting in a given reaction can be altered, as well as on the very important prob- lem of modifiability in behavior in general. The mourning cloak butterfly, Vanessa antiopa, was chosen to begin with because the results secured with this animal by Parker are widely known and frequently quoted. This work is to be followed by a more general study of the phenomenon in question. Before entering upon a discussion of these experiments I wish to express my very sincere appreciation of the kindness of Pro- fessor S. O. Mast in suggesting this problem to me and in so unselfishly aiding me throughout the course of the work. METHODS The butterflies used were all reared in the laboratory from larvae secured from both the June and the August broods in Massachusetts, New York, and Pennsylvania. No difficulty was experienced in keeping them in excellent condition for long periods. They were kept in the laboratory in a large glass case, and fed on honey and a weak solution of maple syrup in water. At frequent intervals the insects were picked up and dropped on filter paper soaked in the latter sweet mixture. If the proboscis was not extended at once, it was uncoiled with a pin, and when once the tip touched the liquid, the animal continued to feed until its abdomen was swollen to an extent which seemed dan- gerous. Since these butterflies pass the winter in the imago state, it is not surprising that six specimens lived from August until the latter part of February. These were the survivors of a lot of about thirty which were received at the same time. Had proper care been taken, it is likely that nearly all would have. lived through the winter in the laboratory. The wings of the butterflies were-usually clipped to prevent their escape. This was in no wise injurious, for animals with clipped wings lived and thrived at well as those whose wings were intact, and they behaved in the same manner. 368 WILLIAM L. DOLLEY, JR. As already stated, three methods have heretofore been used to preyent the functioning of one eye; extirpation, searing with a hot needle, and covering with asphalt varnish. The latter method was used exclusively in the present work, because it was believed that fewer disturbing factors would be introduced thereby. In the early part of the work, one eye was covered with one or two coats of the asphalt varnish. After having made some experiments with animals treated thus, it was found, to my sur- prise, that insects with both eyes covered in this way still oriented fairly precisely, and went toward the source of light. Thus it is evident that the varnish as used did not exclude all of the light. The eyes were then painted repeatedly until the coats were so thick as to be distinctly evident when the observer was several feet from the butterflies. Under these conditions the animals were indifferent to light. Warned by this experience, the blinded insects used in all future experiments were so treated that it seemed certain that the eye was in every case effectively covered. Moreover frequent examinations were made to make sure that the varnish had not cracked or fallen off; and new coats were from time to time applied to make assurance doubly sure. In work of this sort it is important that the varnish be of such nature that it does not injure the eye in any way. The effect of the covering was consequently repeatedly tested by removing it from the eyes after it had been on for some time. Insects thus tested behaved as did those whose eyes had not been blackened, showing no effect from the varnish. The supply stock of butterflies was ordinarily kept in a large cage which was four feet high, four feet long and two feet wide. This was fastened against a south window in such a way that the window formed one side of the enclosure. The opposite side was also of glass and faced a small laboratory room. The other two sides, the top, and the bottom, were of wood. Careful observations were made on the insects in this enclosure, from time to time, throughout the whole period over which the experi- ments extended. But a much more thorough investigation of REACTIONS TO LIGHT IN VANESSA ANTIOPA 369 the behavior in light was made in a dark room under accurately controlled environmental conditions. In these experiments the animals ‘were exposed in a horizontal beam produced by means of a 110 volt Nernst glower. The glower was mounted in front of a small opening in a light-proof box that was painted dead black inside, so as to form a non-reflecting background. It was placed 10 cm. from and at the same level with the top of a table on which the animals were tested. By means of screens the light from the glower was so cut down as to produce a sharply defined beam of the size desired. The edges of this beam could be clearly seen on the black top of the table. This beam was the only light in the room, and this was in large part absorbed by means of dull black paper hung over the exposed walls. There was consequently very little ight in the room aside from that in the beam. Under these conditions therefore, the animals were exposed in a beam of light from a single, small and con- centrated source. The limits of this beam were very apparent in the dark room in which the experiments were made. ‘The nature of the source of light and the sharply defined character of the beam are im- portant, for experiments described later demonstrate that the behavior of animals with one eye blackened depends to a marked * extent upon whether there are one or more’ sources of light present. Not only was the behavior of the animals described by the observer, but the butterflies, themselves, were forced to make permanent records of their own behavior. This was done by allowing them to walk on sheets of paper which had been covered with soot from an oil lamp. These sheets measured 20 x 25 cm., but in some experiments, a number of them were placed side by side until the area was as large as desired. The tracings made by the insects were made permanent by means of a coat of shellac. The butterflies were frequently allowed to walk over the sheets of paper covered with soot, and then the same experi- ment was repeated without ‘the use of the blackened paper. The same results were secured in both cases. This shows that the behavior was not affected by the soot. This method of hav- 370 WILLIAM L. DOLLEY, JR. ing the animals make permanent records of their own behavior is most valuable, for the records can be kept indefinitely and studied, thus giving opportunity to recognize many significant features which otherwise might have been overlooked at the time the experiments were performed. It would be of value, no doubt, to the keenest observer. BEHAVIOR OF NORMAL SPECIMENS In the study of normal animals in the cage referred to above, Parker’s observations were confirmed. It was found that the insects were highly positive in their reactions to light. During the day, in the absence of direct sunlight, they were usually in active movement, flying against the window. Occasionally an animal would fly around the cage, but this was exceptional. When at rest the butterflies were usually grouped on the window side of the cage, where they assumed various positions on the bottom of the window sash, some facing the light, others in a horizontal position at right angles with the rays, some hanging ° on the sash in a vertical position with their heads up, and others hanging with their heads down. When the sun was so situated that the butterflies were exposed directly to its rays, and they were undisturbed, they usually ceased their active movements and oriented very definitely. ~ They turned so as to face directly away from the sun and spread their wings to their fullest extent, exhibiting behavior similar to that described by Parker. This position was retained indefi- nitely unless the insects were disturbed. In a beam of light in the dark room the responses were quite different. In making observations under these conditions the animals were placed in the beam at various distances from the glower so that they faced the-source of light. As soon as they were released they usually darted directly toward the glower and continued until they reached the edge of the table. The insects were always found to be highly positive in all intensities in which they were tested. They never exhibited the slightest indication of negative reactions. ‘They never came to rest with the head directed from the light and the wings spread, as they usually did in direct sunlight. REACTIONS TO LIGHT IN VANESSA ANTIOPA 371 BEHAVIOR OF SPECIMENS WITH BUT ONE FUNCTIONAL EYE A. BEHAVIOR IN NORMAL CONDITIONS OF ILLUMINATION In normal conditions of illumination the behavior of butter- flies with but one functional eye was very different from that described above. Such specimens were tested on the floor of the cage referred to previously, on a table before a window, and in a beam of light in the dark room. Before a window and on the floor of the cage it was found that whenever they moved they turned continuously toward the functional eye, exhibiting _ behavior similar to that described by Parker. The periods of activity, which in some cases lasted for several minutes, alter- nated with periods of rest in which the animals remained practi- cally motionless, as if recovering from fatigue. But the point that is of especial interest is that they continued to make circus movements from day to day, and that they did not learn to orient. Two insects with one eye blackened were kept for twenty-three days, and although they were observed many times each day no modification in their behavior was detected. In this respect, however, the reactions in a beam of light differed greatly. B. BEHAVIOR IN A BEAM OF LIGHT 1. Description of reactions—deflection, circus movements, and orrentation Under the conditions of illumination described in the preced- ing paragraph, the animal receives light from all sides, and all the large areas of the functional eye are approximately equally illuminated in every position assumed by the insect. When exposed to the light in a beam the animal receives light from only one direction, and consequently every movement that is not directed toward the glower produces a change in the illumi- nation of different large areas of the uncovered eye. This may account for the difference in behavior observed under the two conditions of illumination. The behavior in a beam of light of Vanessa with one eye blackened was studied in 46 different individuals and many of ake WILLIAM L. DOLLEY, JR. these were tested on several successive days. In nearly all cases the animals were forced to record their reactions on carbon paper, as previously described. In all tests the butterflies were placed in the beam so that they faced the light directly. The results obtained varied considerably in different individuals and also in the same individual under different conditions. In some respects, however, there was but little variation. Nearly all of the butterflies tested turned toward the functional eye immediately after they were exposed, regardless of the luminous intensity or the axial position with reference to the Fig. 1 Reproduction of various trails made by different specimens of Vanessa with the left eye blackened when exposed in a beam froma Nernst glower. The diverging straight lines represent the limits of the horizontal beam. The arrows indicate the direction of motion. Their trails show that there is great variation in the reactions of different individuals under the same conditions. direction of the rays of light. Some of them continued to turn in this direction making repeated circus movements? (fig. 1, a and b) until they became fatigued and stopped, or until they reached the edge of the beam, where many turned sharply toward the glower and traveled along the edge of the beam toward the source of light, as is shown in figure 1, c. A few, however, did not turn toward the light when they reached the edge of the beam, but passed into the shaded region, continuing to make circus movements (fig. 1, e€). Others did not make circus move- ments, but turned until the longitudinal axis made a certain 2 In the present paper the term ‘circus movements’ with no further explanation means continuous movement toward the functional eye. REACTIONS TO LIGHT IN VANESSA ANTIOPA 373 angle with the rays of light, and then continued until they reached the edge of the beam. Here they usually turned sharply toward the glower and moved along the edge of the beam toward the source of light (fig. 1, f) but occasionally they continued to turn here and made circus movements (fig. 1, 7), and sometimes they did not respond at all when they reached the edge of the beam, but continued until they had passed into the shaded region from 2 to 5 em. when they usually turned and proceeded directly toward the glower, remaining in this region (fig. 1, g). Ona few occasions, however, they did not turn when they reached the edge of the beam, but proceeded on in the shaded region indefi- nitely (fig. 1, h). A few animals did not turn toward the func- tional eye, but oriented fairly accurately and walked toward the glower in a nearly straight course (fig. 1, k). Several specimens in some trials turned toward the blackened eye, crossed the beam, and on reaching the edge turned and walked along it toward the source of light (fig. 1, 7). Many insects, as the trials proceeded, showed an increase in accuracy of orientation. This was evident in three respects: (1) in the number of circus movements made, (2) in the angle of deflection, and (3) in the promptness with which they oriented at the edge of the beam. The above general description may perhaps be made clearer if the reactions of one organism are described in detail. This animal designated as butterfly 10/25-a (left eye blackened) was tested on three successive days. On the first day this butterfly was given twenty trials (fig. 2). In every one it turned toward the unblackened eye immediately upon being placed in the beam. In the first trial it crossed the beam at an angle of approximately 95 degrees with the rays of light, and passed into the shaded region. After it had gone 6 em. in this region it turned to the left (the blinded eye) and walked toward the glower in a slightly zig-zag course, remaining, however, in the comparative darkness to the right of the beam. In the second trial, after crossing the beam at an angle of nearly 80 degrees, it again went to a point 6 cm. beyond the edge of the beam, but then it turned sharply to the right (toward the func- 374 ; WILLIAM L. DOLLEY, JR. tional eye) and performed a circus movement. ‘This was fol- lowed by a fairly straight course for 7.5 em. At this point the organism turned again to the right as if to make a circus move- ment but did not complete it, turning instead to the left toward the source of light. In the third trial the insect made a circus movement as soon as it was placed in the beam and then crossed the beam at an angle of about 95 degrees with the rays of light, and went 3 em. into the shaded region where it turned toward the blackened eye and moved in a course nearly parallel with the edge of the beam. In the fourth the behavior was like that in the preceding trial except that after the organism passed the Fig. 2 Reproduction of 20 successive trails made by butterfly 10/25-a (left eye blackened) on the first day of the tests. aand b, limits of horizontal beam of light; 1-20, trailsmade in successive trials; small arrows, direction of movement of animal; large arrows, direction of rays of light; illumination at x, 624 mc.;3 at y, 250 mc. edge of the beam it did not turn toward the glower, but con- tinued on in a fairly direct course until it reached the edge of the table. In the fifth trial the butterfly continued across the beam at about the same angle as in the previous trials until it had gone 2.5 cm. beyond the edge. At this point it turned toward the blackened eye and moved fairly directly toward the glower. In the sixth the organism again made a circus movement imme- diately upon being placed in the beam. It then crossed the beam at right angles with the rays, and on reaching the right 3 Throughout this paper the abbreviation ‘me.’ will be used to indicate meter- candles. , REACTIONS TO LIGHT IN VANESSA ANTIOPA 315 edge, immediately turned toward the blackened eye and moved along the edge of the beam toward the glower. In the seventh, eighth, and in the twelfth to the nineteenth trials the behavior of the butterfly was essentially the-same as in the fifth, but it usually went further in the shaded region before turning toward the glower, this distance varying from 2.5 to 14cm. After orien- tation, however, it continued to move in all cases fairly directly toward the glower. In the tenth and third trials, the behavior was essentially similar. In the ninth, eleventh, and twentieth the reactions were also very much alike, the organism in each trial curving gradually toward the functional eye, in this way passing beyond the edge of the beam into the shaded region outside, and then coming back to the edge. again. On reaching the edge of the beam the second time the butterfly turned much more sharply toward the functional eye, thus completing a circus movement and at the same time arriving at the edge of the beam a third time. When this occurred, the insect turned toward the glower and moved along the edge of the beam toward the source of light. : These reactions in the trials on the first day of the tests show: (1) that Vanessa with but one functional eye tends to turn toward this eye when placed in a beam of light; (2) that it can orient; (3) that orientation does not usually occur in the beam, but does occur either at the edge of the beam or several centimeters beyond it; (4) that after circus movements have been performed in a given trial the animal often orients and moves directly toward the source of light; and (5) that a change in illumination seems to favor the performance of circus movements, since, out of 8 circus movements, 4 were made almost immediately after the insect was placed in the beam and before it had reached the edge of the beam, 3 were made at the edge of the beam, and only 1 was made elsewhere. On the second day in all of the first eight trials, except the fifth, the butterfly assumed an angle of about 90 degrees with the rays, and then traveled across the beam and into the shaded region for a distance of from 1.5 to 9 cm. where orientation occurred (fig. 3). In the fifth it continued on to the right in 376 WILLIAM L. DOLLEY, JR. a moderately straight course until it fell off the table. The behavior in the next three trials was very much alike, the organ- ism performing a circus movement upon first being placed in the beam, and then, after having gone a few centimeters beyond the edge, it turned and went toward the glower. The eleventh trial is interesting in that, although the organism was started very much nearer to the glower, and consequently in much stronger Fig. 3 Reproduction of 34 successive trails made by butterfly 10/25-a (left eye blackened) on the second day of thetests. a and b, limits of horizontal beam of light; 1-34, trails made in successive trials; small arrows, direction of movement of animal; large arrows, direction of rays of light; illumination at x, 624 me.; at y, 250 me. light, it, after having performed a circus movement, deflected at an angle of only 40 degrees with the rays of light, while in several of the previous trials in which it had started further away from the source of light it deflected at a much greater angle. In the twelfth trial the butterfly made a circus move- ment when first started and then after having gone 1.5 em. beyond the edge of the beam it again performed a circus move- ws REACTIONS TO LIGHT IN VANESSA ANTIOPA old ment. This was followed by a zig-zag course nearly parallel with the edge of the beam. This circus movement is worthy of notice for it was made.in the shaded region outside the beam, when the animal was in very weak light. It should also be noted that the diameter of the curve made is very nearly the same as the diameter of the curve made in the beam in comparatively strong light, when the insect was first started in this trial. This peculiarity will be correlated later with the results of other experi- ments. In the thirteenth trial after performing a circus move- ment in the beam the organism continued to the right in a fairly straight course to the edge of the table. In the fourteenth a circus movement in the beam was made, and then the animal went 7 cm. beyond the edge and oriented, moving toward the glower. In the fifteenth it crossed the rays of light and made a circus movement to the right of the beam. It then went toward the glower in a fairly straight line, but before reaching the source of light it made another circus movement. In the sixteenth a circus movement was made to the right of the beam. This was followed by a zig-zag course toward the glower. The behavior in the succeeding eighteen trials was essentially similar to that described above. It should be noted, however, that in the twenty-fourth trial the butterfly after moving to the right until the edge of the beam was reached turned more sharply toward the functional eye at this point. It did not, however, perform a circus movement, but gradually turned to the left. This sharp turn toward the functional eye on reaching the edge of the beam seems to support the conclusion arrived at from the trials on the previous day, namely, that change in illumination tends to favor the performance of circus movements. These trials on the second day thus confirm strongly the con- clusions drawn from the reactions on the first day, and they show moreover that after a certain amount of experience the angle of deflection tends to decrease, for on the first day the average angle between the path of the butterflies and the rays of light was 100 degrees while on the second day it was only 89.5 degrees. The reactions on the third day (fig. 4) differed very markedly from those described for the first two days in several respects. THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3 ‘ 378 WILLIAM L. DOLLEY, JR. In all but the fourth and fifth trials the organism turned toward ° the functional eye, crossed the beam at a definite angle which was smaller than on the preceding days, and, on. reaching the — edge of the beam, turned at once to the left and walked along this edge toward the glower. In the fourth trial it responded very much like a normal specimen, walking down the center of the beam in a fairly straight line. In the fifth it deflected toward the blackened eye. No circus movements were made in any of the trials on this day. Fig. 4 Reproduction of 23 successive trails made by butterfly 10/25-a (left ~ eye blackened) on the third day of the tests. a and b, limits of horizontal beam of light; 1-23, trails made in successive trials; small arrows, direction of movement of animal; large arrows, direction of rays of light; illumination at x, 906 me.; at y, 266 mc. Compare figures 2, 3 and 4 and note that the insect on the third day made no circus movements, while on the two preceding days, it made numerous ones. Note also that the angle at which it deflected with the rays of light decreased. By comparing all of the reactions observed during the three days it will be seen that modification occurred in three different respects, as follows: (1) On the first two days there were numer- ous circus movements; on the third day there were none what- ever; (2) On the first two days the butterfly usually passed into the shaded region a considerable distance before it turned and went toward the glower; on the third day it turned toward the glower promptly on reaching the edge of the beam; (8) The angle of deflection was greatest on the first day and least on the third, the average angle at the edge of the beam for the three days being respectively 100, 89.5, and 41.5 degrees. The reac- REACTIONS TO LIGHT IN VANESSA ANTIOPA 379 tions of three other insects showing similar behavior are pre- sented in figures 5, 6 and 7. The results presented in these figures as well as in the preced- ing ones seem to show that butterflies with but one functional eye improve in the accuracy of orientation with experience. This conclusion and others are strongly supported by the results yh tl t t yO obi lalz Fig.5 Reproduction of 15 successive trails made by butterfly 7/29-c (right eye blackened). a and 6, limits of horizontal beam of light; 1-15, paths made in successive trials; small arrows, direction of movement of animal; large arrows, direction of rays of light; illumination at z, 4892 mc.; at y, 544 mc. Note that this insect made three circus movements in the first four trials, while in the next eleven trials it made none. obtained in all of the tests made. These are briefly summarized in table 1. This table will be clearer if a brief explanation of some of the data is given. In the columns headed ‘Direction turned’ is stated the direction toward which the butterflies turned 7mmedi- ately after they were placed in the beam. The average angle of deflection was ascertained in the following way. The angle 380 WILLIAM L. DOLLEY, JR. between the rays of light and the trail of the insect at the edge of the beam in each of the trials was measured. ‘This angle is termed the ‘angle of deflection.’ The average then was com- puted for a number of the first trials on each day, this number — being equal to the number of trials on that day on which fewest trials were given. The columns marked ‘Place where orientation Fig.6 Reproduction of 40 trails made by butterfly 10/1-b (left eye blackened). A, 1-20, trails made in successive trials on the first day of the tests; B, 1-20, trails made on the second day of the tests; a and b, limits of horizontal beam of light; small arrows, direction of movement of animal; large arrows, direction of rays of light; illumination at x, 925 mc.; at y, 266 mc. Note that this insect modified its reactions in that it made numerous circus movements in the trials on the first day, but made none in the trials on the second day. occurred’ also demand some explanation. By ‘Orientation’ is meant the assumption of an axial position with the head pointed directly toward the glower followed by movement in this direc- tion. If the animal turned and moved directly toward the source of light before it reached the edge of the beam it is said to have oriented ‘in the beam.’ If it, however, went more than one centi- meter beyond the edge before it turned toward the glower it is . ‘ee ree s,s 2 eR a ae + as aeO 7s . be Ma a. s na rR w y " =>or ens ¢ = as 7 is s . iad ~ s « — 4, Manecaes _ ~ ee ‘sgemracaaec ~, AS aa Sac 20e.% oo = - rt. a en fd Ol -- a 4 / eka hake thee - ‘ Sas +e ee Kae [on SEES GER ee a ont SF ee a een ep 2 elm _—— —} ° - rec ta i erat yertinsim — ; 3 é ¢ ee ibaa =r 2 e re =" : —— ee send — ad > - & S a < 2 wv hy fi mm 1G ” al tee . he 1 oh . . , % f ~ TABLE 1 Summary of reactions in a beam of light of 46 specimens of Vanessa antiopa with but one functional eye DISTANCD NUMBER OF PLACD WHERE rH GLOWER OREN ORG gornicans ORIENTATION OCCURRED DESIGNATION IN TOTAL AveRkGm | — pees oh a aa brittle Svs see Ie, oe N Som ete a PER DAY besa Toward] nig not] In |Outside| PEFEECTION | In aes te als a Ne TRIALS WERE tional |°°Vee4] “turn | beam | beam beam | of | a iiton ae BHGUN eye eye beam October 13 23-45 21 Left 21 0 0 31 1 99.0 0 9 10 2 10/13-a..... u 23-45 22 Left 22 0 0 1 0 65.0 0 19 2 1 15 23-45 21 Left 21 0 0 1 1 60.0 0 18 2 1 16 23-45 21 Left 19 0 2 0 0 35.0 0 19 0 2 October 13 23-45 22 Right 22 0 0 72 5 97.0 0 16 5 1 10/18-b..... 4 23-45 7 Right 7 0 0 1 0 100.0 0 4 3 0 15 23-45 20 Right 20 0 0 28 2 81.4 0 il 4 5 7 23-45 20 Right 20 0 0 1 0 69.2 1 4 13 2 October 10/l4-a..... 14 25-60 21 Left 21 0 0 8 0 78.2 0 19 1 1 15 18-45 21 Left 21 0 0 0 0 54,2 0 20 1 0 17 20-45 20 Left 20 0 0 0 0 43,2 0 20 0 0 October 10/25-a..... 25 28-45 20 Right 20 0 0 4 4 100.0 0 4 15 1 26 28-45 34 Right 34 0 0 4 4 89.5 0 4 24 6 27 15-43 23 Right 22 0 1 0 0 41.5 1 18 3 1 October Tbjacse 6 23-45 20 Left 20 0 0 18 0 101.2 ) 10 5 5 ae 7 25-80 20 Left 15 5 0 0 0 30.0 4 re) 4 0 8 28-80 20 Left 10 9 1 0 0 14.7 0 14 0 6 October 10/1-a...... } 1 28-45 41 Left 41 0 0 25 30 78.0 2 0 1 38 2 28-45 30 Left 28 1 1 0 5 50.0 1 ll 0 18 October 2 23-45 20 Left 20 0 0 2 0 81.8 0 4 11 5 pa ‘ 25-45 20 Left 19 0 1 0 0 37.5 3 12 4 1 4 23-45 21 Left 21 0 0 0 0 54.3 2 18 1 0 5 18-45 20 Left 0 20 0 0 0 46,2 0 19 0 1 6 20-47 21 Left 16 5 0 0 0 42.5 0 21 0 0 July 24 30 21 Left 18 2 1 0 2 62.0 3 8 4 6 7/24-4-a... 25 30 35 Left 29 4 2 0 0 49.0 3 14 4 14 26 30 10 Left 7 2 1 0 0 31.5 i 6 0 3 27 30 10 Left 7 0 3 0 0 23.5 3 7 0 0 July 7/11-3 ll 30 21 Left 19 2 0 0 1 44.2 0 it 0 20 he 12 “30 51 Left 45 6 0 0 0 35.0 2 4 6 39 13 30 40 Left 15 8 17 0 0 11.0 19 itt 2 8 October 10/8-c..... 7 8 18-78 22 Left 22 0 0 0 2 44,3 0 15 5 9 28-82 23 Left 19 at 3 0 0 14.5 3 19 0 1 October 10/24-a..... 4 24 25-82 20 Left 19 0 1 17 0 110.7 0 16 0 4 25 25-65 21 Left 21 0 0 98 3 88.5 0 9 5 7 October 10/14-b } 14 18-45 33 Right 31 2 0 22 3 86.3 0 19 10 4 ‘eee 15 18-45 20 Right 19 0 if 17 2 83.0 2 14 0 4 L 16 18-45 21 Right 21 0 0 2 i 0 ll 10 0 September 9/21-8 21 18-28 5 Right 5 0 0 1 0 107.0 0 2 3 0 3° ae 22 28-45 10 Right 10 0 0 0 0 53.0 0 10 0 0 23 23 Right 23 0 0 0 0 0 23 0 0 October 10/8-a...... 4 8 40 Left 38 1 1 0 1 71.5 8 28 3 1 9 20 Left 18 2 0 0 0 29.75 0 19 0 1 July 7/16-0..... 16 30 17 Left 17 0 0 0 3 62.3 2 14 1 0 July 7/29-c....+. 29 30 15 Left 7 0 8 0 3 20.6 8 6 1 0 September 22 30 25 Right 25 0 0 0 0 67.5 0 3 16 6 23 30 21 Right 20 1 0 0 0 62.5 0 il 9 1 24 45 20 Right 9 9 2 1 0 25.5 2 15 1 2 9/22-c..... 4 25 23-45 20 Right 20 0 0 0 0 62.0 0 20 0 0 26 23-45 21 Right 21 0 0 f 3 79.0 0 13 0 8 27 25-45 26 Right 26 0 0 0 0 51.5 0 26 0 0 29 23-45 32 Right 32 0 0 0 0 51.0 0 32 0 0 30 17-45 32 Right 32 0 0 0 0 57.2 1 29 2 0 September 22 28 45 Left 45 0 0 1 2 85.7 0 1 18 26 24 45 20 Left 20 0 0 1 5 39.2 0 12 1 vf 9/22-b 25 45 21 Left 14 2 5 0 0 34.7 5 10 4 2 aie a 26 23-45 33 Left 31 0 2 1 0 60.7 2 9 15 - 7 27 20-45 36 Left 32 0 4 0 0 40.5 4 32 0 0 29 23-45 20 Left 20 0 0 2 0 A 0 13 4 3 30 18-45 30 Left 28 1 1 0 0 56.0 1 19 9 1 October 1 23-43, 20 Right 20 0 0 9 2 67.7 0 9 9 2 2 23-45 20 Right 19 st 0 0 0 41.5 0 16 4 0 10/1-b 3 23-43 20 Right 20 0 0 0 0 55.2 0 12 7 1 ra Bk 4 23-45 20 Right 20 0 0 0 0 68.7 0 18 2 0 5 23-45 21 Right 21 0 0 0 0 63.2 0 19 2 0 6 23-80 24 Right 24 0 0 0 0 36.0 0 24 0 0 7 20-80 27 Right 26 1 0 0 0 33,7 0 26 0 a July 7/8-3 8 30 73 Left 58 10 5 3 10 36.5 11 17 16 29 A Sareea A) 9 30 58 Left 51 4 3 3 14 51.0 4 9 8 37 10 30 33 Left 18 8 7 0 3 16.3 if 20 0 6 September : 22 30 25 Left 24 1 0 0 3 69.2 0 0 17 8 9/22-0..... 4 23 30 20 Left 20 0 0 0 0 57.5 0 7 13 0 24 45 20 Left 20 0 0 0 1 68.0 0 u 9 0 25 25-45 20 Left 20 0 0 0 0 69.0 0 10 10 0 September : 22 30 25 Right 25 0 0 1 0 82.0 0 ll 14 0 23 30 20 Right 15 2 3 0 0 19.0 11 8 0 1 24 40-45 20 Right 20 0 0 0 0 43.0 0 20 0 0 9/22-d..... { 25 20-42 20 Right 20 0 0 1 0 68.0 0 20 0 0 26 28-45 20 Right 0 0 20 0 0 20 0 0 0 27 18-45 22 Right 21 1 0 1 0 44.0 0 21 0 1 29 18-45 2 Right 20 0 0 0 0 48.0 0 20 0 0 30 | 23-45 10 Right 5 5 0 0 0 0 10 0 0 October 2 23-45 22 Right 22 0 0 0 0 71.0 0 13 5 4 3 25-45 20 Right 20 0 0 1 6 73.0 0 4 7 9 1O/d-0, 25 -.,- 4 18-45 23 Right 22 1 0 0 0 68.0 0 13 7 3 5 15-45 21 Right 21 0 0 0 0 68.0 1 15 4 1 6 13-78 22 Right 14 6 2 0 0 27.0 5 13 1 3 7 20-80 24 Right 19 5 0 0 0 43.0 0 23 0 1 July ot 30 36 Left 32 1 3 0 0 26.5 4 23 5 4 22 20-28 35 Left 23 11 1 0 0 65.0 2 27 3 3 7/21-6..... | 23 28 31 Left 16 13 2 0 0 47.0 4 11 6 10 24 20-28 13 Left 13 0 0 0 0 56.5 0 8 2 3 | 25 28 14 Left 13 0 1 0 0 64.5 1 7 3 3 l 26 28 11 Left 10 0 1 0 0 58.0 0 0 4 7 July | 24 30 10 Left 10 0 0 0 0 28.0 0 10 0 0 7/24-4..... 25 30 11 Left ll 0 0 0 0 35.0 0 ll 0 0 26 30 nb Left il 0 0 0 0 33.0 0 ll 0 0 27 30 11 Left Il 0 0 0 0 0 10 0 1 September 24 30-60 50 Left 39 7 4 7 17 59.0 9 10 1 30 0/24-a..... 4 25 25-60 20 Left 19 if 0 0 0 79.0 0 14 5 1 26 25-45 31 Left 30 0 1 9 3 77.0 1 16 9 5 27 23-45 20 Left 20 0 0 5 6 64.0 0 10 4 6 July 23 30 11 Left 11 0 0 0 0 29.3 0 11 0 0 7/28-4...0. 24 30 rT Left 11 0 0 0 0 36.2 0 11 0 0 | 25 30 8 Left 8 0 0 0 0 26.2 0 8 0 0 26 30 ll Left 11 0 0 0 0 31.2 0 10 1 0 July 11 30 51 Right 48 2 1 0 0 31.0 12 ri 17 15 T/l1-4..... 12 30 75 Right 71 0 4 0 0 50.8 7 8 13 47 13 30 32 Right 30 0 2 0 0 37.6 4 14 Ny 13 14 30 30 Right 27 0 3 0 0 52.5 3 4 ll 12 July 5 | 23 30 18 Left 16 2 0 1 0 33.5 4 if 2 5 7/23-40.... 4 24 30 10 Left 10 0 0 0 0 24.5 2 6 0 2 25 30 10 Left 9 1 0 0 0 31.5 0 8 2 0 26 30 10 Left 10 0 0 0 0 37.0 0 8 1 1 July T/2G-Biasvas'e'ds 29 30 16 Left il 0 5 0 0 20.3 8 8 0 0 July G/B Deter 16 30 23 Left 23 0 0 0 2 45.6 7 3 0 13 July 7/16-ph...... 16 30 12 Left 11 1 0 0 1 50.8 0 4 2 6 July 7/20-d....0+« 29 30 10 Left 1 1 8 0 0 11.0 8 1 1 0 July C/20-D saeuln a 29 30 13 Left 7 2 4 0 0 18.0 5 4 2 2 July 7/16-b....% +. 16 30 20 Left 16 0 4 0 1 27.2 4 14 2 C) July 7/16-0.5 eee 16 30 18 Left 0 8 10 0 0 16 1 0 i July Fi ih > ee 21 30 11 Left 2 5 4 0 0 6.0 7 4 0 0 July TYAS 2, wis 22 30 4 Left 22 0 2 0 1 34.0 | 8 9 3 4 July T/Nadis occu 21 30 61 Left 56 1 4 5 18 12 17 2 30 July T/18-p... 2.0 16 30 17 Left 17 0 0 0 1 38.0 2 4 1 0 July 7/16-e....... 16 30 15 Left 15 0 0 0 0 38.2 0 9 0 6 July 1/15-2..... 15 30 21 Left 20 0 1 0 1 33.5 1 20 0 0 16 30 27 Left 7 8 2 0 0 20.9 16 2 6 Wee ted 30 56 Left at v o a 28 3 8 6 39 7/16-a aoe ve 30 3 Left AON a2 d ¥ 0 g8 | 2B 0 | 10 10/8-Big. aoe et: 20-78 25 Right 25 0 0 1 3 68.0 0 8 5 12 [An St... Total Lee 3077 2699 207 Wi | 477 204 287 | 1619 493 678 REACTIONS TO LIGHT IN VANESSA ANTIOPA 381 said to have oriented in the ‘shaded region.’ When orientation occurred either precisely at the edge of the beam or within one centimeter beyond the edge it is considered to have occurred ‘near the edge of the beam.’ In those trials in which the insect either continued to perform circus movements or passed on out- side the beam into the shaded region beyond, in a more or less straight course with no turn toward the source of light, ‘no orientation’ is said to have occurred. An examination of this table shows that out of a total of 3077 trials the butterflies turned toward the functional eye in 2699 trials, and away from it in 207 trials, while in 171 trials they Fig. 7 Reproduction of 33 successive trails made by butterfly 10/14-b (left eye blackened) on the first day of the tests. a and b, limits of horizontal beam of light; 1-33, paths made in successive trials; small arrows, direction of move- ment of animal; large arrows, direction of rays of light; illumination at z, 1510 mec.; at y, 250 mc. Note that this insect modified its behavior in that it per- formed circus movements in 13 out of the first 16 trials, but made circus move- ments in only 6 of the next 16 trials. moved toward the glower without first turning toward one side or the other. This indicates clearly that there is in Vanessa with one eye blinded a strong tendency to turn toward the func- tional eye. The table shows aiso that in 2399 of the 3077 trials individuals with but one functional eye oriented and moved fairly directly toward the light, and that in 287 trials orientation occurred in the beam of light, indicating strongly that both eyes are not necessary in this process. 382 WILLIAM L. DOLLEY, JR. It shows, moreover, that in 16 of the 27 individuals tested on more than one day orientation occurred in more trials of the last day than in those of the first, and that in 18 of the 27 individuals orientation at the edge of the beam occurred more promptly during the trials on the last day than it did during those on the first. This is well illustrated by the reactions of butterfly 10/25-a, described in table 1 and in figures 2, 3, and 4. It shows, furthermore, that in 20 of the 27 individuals circus movements decreased in number, and that in 20 the average . angle of deflection was less in the trials of the last day than it, was in those of the first. Although not shown in table 1, 10 indi- viduals performed fewer circus movements in the last trials of the first day of the tests than in the first trials on this day. This seems to indicate clearly that with practice there is in Vanessa with but one functional eye improvement in the accuracy of orientation in three respects, as previously stated: (a) increase in promptness of orientation, (b) decrease in the number of circus movements performed, and (c) decrease in the angle of deflection. If this is true, then it is evident that orientation is not depend- ent upon the stimulation of both retinas by equal amounts of light energy. This conclusion is strongly supported by the fact that in 171 out of 3077 trials the organism with but one functional eye did not turn either to the right or the left, but moved fairly directly toward the source of light. It is moreover supported by the results obtained in observations on: the relation between the degree of curvature in circus movements and the luminous intensity, relation between the angle of deflection and the lumin- ous intensity, and reorientation after changing the direction of the beam of light. These are discussed in the following para- graphs. 2. Relation between the degree of curvature in circus movements and the luminous intensity According to the ‘continuous action theory’ smaller curves should be made in the strong light in the beam than are made in the weak light outside the beam, for the adherents of this theory, ~ as stated above, hold that the tension of the muscles of the legs REACTIONS TO LIGHT IN VANESSA ANTIOPA 383 on the two sides of the body varies with the relative amount of light energy received by the two retinas. No such relation, however, was at all evident in the observations on Vanessa. Curves of the same size were made in both positions, and very frequently those in the region of low illumination outside the beam were smaller than those in the region of comparatively high illumination in the beam. This is well seen in the ninth trial made by animal 10/14-b on the third day (fig. 8). In this case the butterfly, while in the beam, began to perform a circus movement of a diameter of 6.5 cm. By the time it was half Fig. 8 Reproduction of 21 successive trails made by butterfly 10/14-b (left eye blackened) on the third day of the tests. a and b, limits of horizontal beam of light; 1-21, paths made in successive trials; small arrows, direction of move- ment of animal; large arrows, direction of rays of light; illumination at x, 1510 mc.; at y,250mc. Note that in trial 9 this insect turned very much more sharply toward the functional eye while in the shaded region to the right of the beam than it did while in the comparatively strong light in the beam. completed the animal was 3 cm. beyond the edge, and in the weak light to the right of it. On reaching this point, the insect turned sharply to the right, and made another circus movement of a diameter of only 1.5 cm. ie., in weak light the organism turned more sharply toward the functional eye than in strong. Similar reactions were observed in many other cases. 3. Relation between the angle of deflection and the luminous intensity a. Effect of beginning the trials in different intensities. It has been shown that in those trials before the Nernst glower in which circus movements are not performed continually, Vanessa antiopa 384 WILLIAM L. DOLLEY, JR. usually turns until it assumes a certain angle with the rays of light, and that it then proceeds diagonally across the beam. If orientation is dependent upon the relative amount of light energy received by the two eyes, as demanded by the ‘continuous action theory,’ the degree of deflection ought to be greater in high illumination than in low, for if only one eye is functional, the greater the intensity, the greater the difference in the amount of energy received by the two eyes. This was tested by measur- ing the angles of deflection in different intensities of light in each one of the trials made by all of the insects. The results of some of these tests are recorded in figure 9 and in table 2. TABLE 2 Angles of deflection made in different intensities of light by four butterflies with one eye blackened 5 BUTTERFLY 9/22-a BUTTERFLY 10/1-3-b BUTTERFLY 10/8-a BUTTERFLY 10/1-4-b B | egee jal ees i |eere | 2 7 eeeeue e\ScF_| 3 |Se28_| = |Sect.| = |Sec8.| § sped OH od q Ok wo q OR ah Og a Be Bs aee| #3 | $2 EE EE oe EE gs S525 P| #3 1 380 50 257 80 234 85 234 50 2 380 85 383 80 445 110 275 30 3 624 50 758 50 445 90 624 55 4 2153 60 758 70 624 85 234 30 5 380 95 ‘791 40 275 80 234 30 6 448 65 936 50 791 70 634 50 7 624 50 234 40 383 70 634 50 8 1223 50 337 40 1044 70 936 95 9 2153 65 624 35 218 50 257 90 10 380 75 936 50 234 85 337 90 11 448 80 257 50 257 85 416 75 12 624 60 314 60 634 70 234 100 13 839 65 416 60 291 70 337 80 14 1497 55 624 50 1044 70 624 85 15 2883 80 936 45 416 60 936 _ 110 16 380 65 257 65 234 60 17 547 80 337 45 624 50 18 624 75 624 35 259 60 19 711 80 257 110 1044 50 REACTIONS TO LIGHT IN VANESSA ANTIOPA 385 By referring to this figure, which represents the course of a given individual in different intensities of light it will be seen that the angle of deflection is essentially the same in all, in spite of the fact that the illumination varied from 76 to 3397 me. This is a typical case. It seems to show that the degree of deflection is within wide limits independent of the intensity of the light. Fig. 9 Diagram showing the angles of deflection made by butterfly 10/8-b (left eye blackened) when exposed in light of different intensities. A A, limits of horizontal beam of light; 14-25, successive trials; 76 and 3397, intensity of light in meter candles at the corresponding points. Note that the insect deflects at about the same angle with the rays of light, no matter whether the trials are begun in an intensity of 76 me. or in an intensity of 3397 mc. The results presented in table 2 support this contention. They demonstrate that, while the degree of deflection varies greatly in different individuals and in the same individual under different conditions, there is no apparent correlation between it and the intensity of the light. Since the degree of deflection is a measure of the difference in tension of the muscles of the legs on the two sides of the body these results also show that there is no apparent correlation between this difference in tension and the intensity 386 WILLIAM L. DOLLEY, JR. of the ight. This conclusion receives still further support from the results obtained in non-directive light which are reserved for discussion later. Before entering upon further discussion based on table 2 we will describe experiments as to the effect upon behavior of changes of intensity. b. Effect of sudden changes of intensity on the ek of deflection. The previous experiment in which the position of the glower was | unchanged, but in which the intensity of the light varied in different trials was supplemented by others. In some of these the light was increased after the butterflies had oriented. In others it was suddenly decreased. The insects with only one eye functional were placed in a beam of light, and, as soon as TABLE 3 Effect upon the angle of deflection of suddenly increasing the illumination from 104 mc. to 1400 mc. NUMBER OF NUMBER OF NUMBER OF DESIGNATION OF TRIALS IN WHICH TRIALS IN WHICH TRIALS IN WHICH BUTTERFLIES ANGLES WERE ANGLES WERE NO EFFECT WAS INCREASED DECREASED EVIDENT 10/2021