ae eae aia he ond a aot. os orn, OAs. Amare, eet Nm ~ oe Rte Pe apes res ow a ae ee er - we. : ~—* “ Ae hi ae owe aaonkt be = —— , oo AOR 9 pare ee 4 on ; ; ok ee - = : ‘ : “p wide Coe Z" 220-0 @e9-p FOR oe WN LIBRARY ONLY SEEN BY PRES ERVA TION SERVIC Cr 4 vitites Digitized by the Internet Archive in 2008 with funding from Microsoft Corporation http://www. archive.org/details/forcedmovementst00loebuoft ip ibis, pik oH We : i ANS a WAP Cala elt Rey , ab As Me matt! Win PNT Ti a) | } ANY MU tA AG Ae ye , iD ii. % me My) MONOGRAPHS ON EXPERIMENTAL BIOLOGY EDITED BY JACQUES LOEB, Rockefeller Institute T. H. MORGAN, Columbia University W. J. V. OSTERHOUT, Harvard University VOLUME I FORCED MOVEMENTS, TROPISMS, AND ANIMAL CONDUCT BY JACQUES LOEB, M.D., Pu.D., Sc.D. MONOGRAPHS ON EXPERIMENTAL BIOLOGY PUBLISHED VOLUME I FORCED MOVEMENTS, TROPISMS, AND ANIMAL CONDUCT By JACQUES LOEB, Rockefeller Institute IN PREPARATION THE CHROMOSOME THEORY OF HEREDITY By T. H. MORGAN, Columbia University INBREEDING AND OUTBREEDING: THEIR GENETIC AND SOCIOLOGICAL SIGNIFICANCE By E. M. EAST and D. F. JONES, Bussey Institution, Harvard University PURE LINE INHERITANCE By H.S. JENNINGS, Johns Hopkins University THE EXPERIMENTAL MODIFICATION OF THE PROCESS OF INHERITANCE By R. PEARL, Johns Hopkins University LOCALIZATION OF MORPHOGENETIC SUBSTANCES IN THE EGG By E. G. CONKLIN, Princeton University TISSUE CULTURE By R. G. HARRISON, Yale University PERMEABILITY AND ELECTRICAL CONDUCTIVITY OF LIVING TISSUE By W. J. V. OSTERHOUT, Harvard University THE EQUILIBRIUM BETWEEN ACIDS AND BASES IN ORGANISM AND ENVIRONMENT By L. J. HENDERSON, Harvard University CHEMICAL BASIS OF GROWTH By T. B. ROBERTSON, University of Toronto THE ELEMENTARY NERVOUS SYSTEM By G. H. PARKER, Harvard University COORDINATION IN LOCOMOTION By A. R. MOORE, Rutgers College OTHERS WILL FOLLOW ~ MONOGRAPHS ON EXPERIMENTAL BIOLOGY FORCED MOVEMENTS, TROPISMS, AND ANIMAL CONDUCT BY JACQUES. LOEB, M.D. Pu.D2 Sc.D. MEMBER OF THE ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH PHILADELPHIA AND LONDON J. Bowie PiNCOT &-€OMPANY. COPYRIGHT, I918, BY J. B. LIPPINCOTT COMPANY Electrotyped and Printed by J. B. Lippincott Company The Washington Square Press, Philadelphia, U.S.A. EDITORS’ ANNOUNCEMENT THE rapidly increasing specialization makes it im- possible for one author to cover satisfactorily the whole field of modern Biology. This situation, which exists in all the sciences, has induced English authors to issue series of monographs in Biochemistry, Physiology, and Physics.. A number of American biologists have decided to provide the same opportunity for the study of Experimental Biology. Biology, which not long ago was purely descriptive and speculative, has begun to adopt the methods of the exact sciences, recognizing that for permanent progress not only experiments are required but that the experi- ments should be of a quantitative character. It will be the purpose of this series of monographs to emphasize and further as much as possible this development of Biology. Experimental Biology and General Physiology are one and the same science, by method as well as by contents, since both aim at explaining life from the physico-chemical constitution of living matter. The series of monographs on Experimental Biology will therefore include the field of traditional General Physiology. Jacques Lozs, T. H. Morean, W. J. V. OstERHOUT. Ll Ta “a ars gat, | = = 0 aera V0. er a Mogens ae valk i ya | hy eto ~ 1) ei m4 } z ¥ a en iv % . fi 5 ale , ne \ : fa a ae Pm alte = Vo i : y er he el eae tee Oe ‘ Vi omer au, ae q waa P ‘ a , by, he ale cy a as —s 7 Ty 7 7 an) LA } ; = | " a il By a ‘ - a: aa or fl a aa win ‘it a iaiehoaia SE ae . iP - j 7 a 5 i wr, * She if ; iv a} th er Vv ‘ : ; \ i ; wed ‘ t 1 a ¢ ' AUTHOR’S PREFACE ANIMAL conduct is known to many through the roman- tic tales of popularizers, through the descriptive work of biological observers, or through the attempts of vital- ists to show the inadequacy of physical laws for the explanation of life. Since none of these contributions are based upon quantitative experiments, they have led only to speculations, which are generally of an anthropo- morphic or of a purely verbalistic character. It is the aim of this monograph to show that the subject of animal conduct can be treated by the quantitative methods of the physicist, and that these methods lead to the forced movement or tropism theory of animal conduct, which was proposed by the writer thirty years ago, but which has only recently been carried to some degree of com- pletion. Many of the statements, especially those con- tained in the first four chapters of the book, are familiar to those who have read the writer’s former publications, but so much progress has been made in the last few years that a new and full presentation of the subject seemed desirable. Chapters V to XIII and Chapter XVI are partly or entirely based on new experiments. Only that part of the literature has been considered which contributes to or prepares the way for quantitative experiments. “J 8 AUTHOR’S PREFACE The writer is under obligation for valuable criticism to his wife, to Professor T. H. Morgan, and to Lieutenant Leonard B. Loeb, who were kind enough to read the manuscript. dei, The Rockefeller Institute for Medical Research, New York. March, 1918. CONTENTS CHAPTER PAGE Ifn, od lisa) KOM AKOYA Aye ay, Moa eee CIAO ae: 5 GRACES ¢ Latte oReEniRiD any croc 13 Il. Toe SymmMerry RELATIONS OF THE ANIMAL Bopy AS THE START- ING PorInt FOR THE THEORY OF ANIMAL CONDUCT........... 19 [Mee HORCHD = MOVEMENTS). hs sn ccs cies iain a ccieehetanioe 24 TIVE ChATAVAINT OU ODESMin): 2c) ier nies eo erat eens ite ay ere ESAS I ons eens 32 V. Heuiorropism. THe INFLUENCE oF ONE Source or Liaut... 47 is Generale acts nserver eos EN eee aoe Aeslcnevevrensl ote 47 2. Direct Proof of the Muscle Tension Theory of Heliotrop- ismen Wo tie Animals Meant setters clevsishaee te aren cisiente Le 3. Heliotropism of Unicellular Organisms................. 62 A. Heliotropism of sessile Amimals iis aoe eiche 2. «oie aha toe 63 Vil ANT VARTIFIGIAD, EEDETORROPIC NVAGHIDNI seme ss es sciels ene oelee i. 68 WAU, JNeWavan ont a CoVo) WANE ONIUSIGIA an mig Rigi clo'd bodice oo oma de cedicicie 0 6.6 70 VIII. Two Sources or Licut or DirrERENT INTENSITY............ 75 IX. Tue Vauipiry or THE BuNSEN-Roscor Law For THE HELIO- TROPIC REACTIONS OF ANIMALS AND PLANTS.............-- 83 X. Tue Errect or Rarip CHANGES IN INTENSITY oF LIGHT...... 95 XI. Tue Revative Heviorroric Erricrency or Licut or Dirrer- TDN AN NON dhaal DIOISKE UU SISIG Ae MEET NoIS eure SG cin Mice oare GIB UEMCROTD Crcleesatc 100 MI. CHANGE IN THE SENSE OF HELIOTROPISM.:.................. 112 XG GH OTR ORISMe vache tei crs colo Patio oT er eI ORE IE Oe an eee 119 XIV. Forcep Movements Causep By Movina Retina IMaGgEs: RAHOTROPISM PANE MOTROPISMecs ie ciaeisicls cieretelere clcieycueieio cl elerens 127 PROVES DORE OTR OBREGN Ce ees taste ener rity) ene Shears Cpatan et snc UNH dei 134 NOVA © HIM OTROBIGNMM MEE Es helt aca Aner abi er hrs enn Oa eet dp rean 139 XG APT NTOTROPISM EN iter ae a elena eae ek sleet uadoelus 155 PXQVIMAMINSTINCTSM ey ee tract nm irne coer aM cua pa Agden Teli ice es, I 156 XEDXGa NV ieMmOn Ve UMAGES (AND) Ml UROPISMS) pierre a caalsiisis shots miane aisiers ah 164 LATTE NG OATS (Gh ah SIME cis teen eC eh IS CRE Rate EA Ne LEE A eat oe Stel 173 FIG. 1. 2. 4. Be dee S— 10. Le 12. 13. 14. 15. 16. fe 18. 19: 20. 21. 22. ILLUSTRATIONS Forced Position of Larva of the Dragon Fly whose Left Cerebral Ganglion! is Destroyed). s-.cs.ciorn slat ocshe dc MENG oss « disle eictaes Forced Position of Shrimp when Galvanic Current Goes from Head eh pe Date eV) i eae cc Merge Ln Sa eae MOUS Ceomeae ME tr! aMne aat ey Position of Legs of Shrimp when Current Goes Sideways through the NIMANEN EMIS carseat pene se ABS cea RA ca ae PCS LITT Fae TAREE RE ee ORES ah hes Ot 6. Show Same Effects of Current on the Common Crawfish as Those Gen SALUT My Bagg AAA sik. foee cece tee act ad abe Po eye ona Diagram Indicating the Orientation of the Neurons for Flexor and Extensor Muscles of the Right and Left Legs.................. 9. Diagram Indicating Orientation of Neurons for Flexor and Extensor Miusclesof thirdtand:Hitth: Pairs: of begs 35). ./420 02) Jos sei Forced Position of Amblystoma Larva Under Influence of Galvanic Current Going Through Animal from Head to Tail.............. Forced Position of Amblystoma Larva When Current Goes from Tail LORELOH Car pier ray Lara AcneNee ims. 2) sublet AAT eae MU LEN aga aM Tentacles and Manubrium of Jellyfish Under Influence of Galvanic (CURE S14 ses CARR NOC rREONS CS La se A A ee nc Strip of Jellyfish Under Influence of Galvanic Current.......... Froramecium inaer Normal Conditions; 52°. ),-...).2. 22 has ss oe lk CurrentGoing Through’ Paramecium... 60s Nace. oe eke Showing that Positively Heliotropie Animals Will Move from Sun- light into Shade if Illumination of Both Eyes Remains the Same... . Position of Water Scorpion When Right Eye is Towards the Light. . Positions of Ranatra When Light is in Front and Behind Animal... . Robber Ely Wnder NormalConditionsy 5 22 ::.0.'. 2.2 ae aes ene cle tle Robber Ely with-Right Eye Blackened)... 22)... 2.0).0 065.320 0n0 ss Position of Robber Fly when Lower Halves of Both Eyes are Blackened Position of Robber Fly when Upper Halves of Both Eyes are Blackened 11 PAGE 12 FIG. 23. 24. 25. 26. 27. 28. 29. 30. jl. 32. 33. 34. 35. 36. ov. 38. 39. 40. 41. 42. ILLUSTRATIONS PAGE Diagram Showing Position of the Flagellum as Seen in a Viscid WMeeditamiver nrc jit = ctete br tcl nie Cras Siceatel bate atcha pated ee te ee 62 ube Worms an Aiartumict,..cecose -cisica +2 on 2 oo tee aaa oe 63 Same Animals After Position of Aquarium was Reversed.......... 64 Polyps of Eudendrium all Growing Towards Source of Light........ 66 Fly with ‘Right ‘Bye ‘Blackened’: /Pa itis ts osteoid ee 72 Diagram of Apparatus Used to Produce Differential Bilateral Light SEI ELON Fos: ies, Snsla eater ae oe is ne bere: Sie eRe ce ce 76 Diagram to Show Method of Measuring Trails................... Gf Diagram for Constructing Direction of Motion of Larve........... 80 Method for Proving Validity of Bunson-Roscoe Law................ 90 A Glass Platte soo ols oe eee tee ato SNE Le re ep ee 91 Difference in Gathering Places of Animals....................... 96 Method of Determining the Relative Heliotropic Efficiency of Two Different ‘Parts of the Speetrum:: .)¢ 522. ies oa eee eee 107 Geotropic Curvature of Stems of Bryophyllum calycinum........... 120 All Stems were Originally Straight and Suspended Horizontally... .. 121 When the Size of the Leaf is Reduced by Cutting Out Pieces from the 1. 606 bo Ne ae CIENCIAS MS SAAS te 120 Effect of Cutting off Lateral Parts of the Leaves.................. 121 Influence of Motion of the Hand on a Swarm of Sticklebacks in an SA QUIATINIIIY 556000 0:5 S215 discos eRe en Cee tee oe eee 132 The Regenerating Polyp of Tubularia in Contact with Glass Wall of ViN(6 [UE Ha 1b U0 ely oe ee MPa Mee MOAR it. nies twba tale og oc - 137 Reactions of Chilomonas to a Drop of s'5 per cent. HCl............ 145 Method of Proving the Paramecia are not Positive to Acid of Low Concentration 9.5.4 Soo 6 is oe Jado eis be eee 146 FORCED MOVEMENTS, TROPISMS, AND ANIMAL CONDUCT CHAPTER I INTRODUCTION THe analysis of the mechanism of voluntary and instinctive actions of animals which we propose to under- take in this volume is based on the assumption that all these motions are determined by internal or external forces. Our task is facilitated by the fact that the over- whelming majority of organisms have a bilaterally sym- metrical structure, 7.e., their body is like our own, divided into a right and left half. The significance of this symmetrical structure lies in the fact that the morphological plane of symmetry of an animal is also its plane of symmetry in physiological or dynamical respect, inasmuch as under normal con- ditions the tension in symmetrical muscles is the same, and inasmuch as the chemical constitution and the velocity of chemical reactions are the same for symmetrical ele- ments of the surface of the body, e.g., the sense organs. Normally the processes inducing locomotion are equal in both halves of the central nervous system, and the ten- sion of the symmetrical muscles being equal, the animal moves in as straight a line as the imperfections of its 13 14 TROPISMS / locomotor apparatus permit. If, however, the velocity of chemical reactions in one side of the body, e.g., in one eye of an insect, is increased, the physiological symmetry of both sides of the brain and as a consequence the equality of tension of the symmetrical muscles no longer exist. The muscles connected with the more strongly illuminated eye are thrown into a stronger tension,® and if now impulses for locomotion originate in the central nervous system, they will no longer produce an equal response in the symmetrical muscles, but a stronger one in the muscles turning the head and body of the animal to the source of light. The animal will thus be compelled to change the direction of its motion and to turn to the source of light. As soon as the plane of symmetry goes through the source of light, both eyes receive again equal illumination, the tension (or tonus) of symmetrical muscles becomes equal again, and the impulses for locomotion will now produce equal activity in the symmetrical muscles. As a conse- quence, the animal will move in a straight line to the source of light until some other asymmetrical disturbance once more changes the direction of motion. What has been stated for light holds true also if light is replaced by any other form of energy. Motions caused by hight or other agencies appear to the layman as expres- sions of will and purpose on the part of the animal, whereas in reality the animal is forced to go where carried by its legs. For the conduct of animals consists of forced movements. The term forced movements is borrowed from brain physiology, where it designates the fact that certain ani- mals are no longer able to move in a straight line when a We are speaking of positively heliotropic animals exposed to only one source of light. INTRODUCTION 15 certain parts of the brain are injured, but are compelled to deviate constantly toward one side, which is (accord- ing to the species and the location of the injury in the brain) either the side of the injury or the opposite side. The explanation of these forced movements is that on account of the one-sided injury of the brain the tension of the symmetrical muscles is no longer the same. As a consequence, the impulses for locomotion which are equal for symmetrical muscles will cause greater contraction in certain muscles of one side of the body than in the symmetrical muscles of the other side, and the animal will no longer move in a straight line. The only difference between the forced movements induced by unequal illu- mination of the two eyes and by injury to the brain is that in the latter case the foreed movements may last for days or throughout the whole life, while in the former case they last only as long as the illumination on the two sides of the body is unequal. If we bring about a per- manent difference in illumination in the eyes, e.g., by blackening one eye in certain insects, we can also bring about permanent circus motions. This shows that animal conduct may be justly designated as consisting of forced movements. The idea that the morphological and physiological symmetry conditions in an animal are the key to the understanding of animal conduct demanded that the same principle should explain the conduct of plants, since plants also possess a symmetrical structure. The writer was able to show that sessile animals behave toward light exactly as do sessile plants ; and motile animals like motile plants. The forced orientations of plants by outside sources of energy had been called tropisms; and the theory of animal conduct based on the symmetrical struc- 16 TROPISMS ture of their body was, therefore, designated as the tropism theory of animal conduct. We started with symmetrical animals since in their ease the analysis of conduct is comparatively simple; the results obtained in the study of these symmetrical organisms allow us also to understand the conduct of asymmetrical animals. We shall see that the principles underlying their conduct are the same as in the case of symmetrical animals, the asymmetry of the body altering only the geometrical character of the path in which the animal is compelled to move, not, however, the mechanism of conduct. While a perfectly symmetrical organism, possessed of positive heliotropism, moves in a straight line to the source of light, the path deviates from the straight line in the case of an asymmetrical organism and may in some eases, as, e.g., in Euglena, be a spiral around the straight line as an axis. Some authors have tried to use asymmetrical organisms as a starting point for the analysis of conduct, but since it is impossible to understand the conduct of the asymmetrical organisms unless it is based upon that of the symmetrical animals, these authors have been led to anthropomorphie specula- tions, such as ‘‘selection of random movements’’ which, as far as the writer can see, cannot even be expressed in the language of the physicist. Although the tropism theory of animal conduct was offered thirty years ago 785, 286,287 its acceptance was delayed by various circumstances. In the first place, the majority of the older generation of biologists did not realize that not only the methods of the physicist are needed but also the physicist’s general viewpoint con- cerning the nature of scientific explanation. In many cases the problem of animal conduct is treated in a way INTRODUCTION 17 which corresponds more to the viewpoint of the intro- spective psychologist than to that of the physicist. The attempts to explain animal conduct in terms of ‘‘trial and error’’ or of vague ‘‘physiological states’? may serve as examples. None of these attempts have led or can lead to any exact quantitative experiments in the sense of the physicist. Other biologists have still more openly adopted an anthropomorphic method of explana- tion. If pleasure and pain or curiosity play a role in human conduct, why should it be otherwise in animal conduct? The answer to this objection is that typical forced movements when produced in human beings, as, e.g., 1m Ménieére’s disease or when a galvanic current goes through the brain, are not accompanied by sensations of pleasure or pain, and there is no reason to attribute the circus movements of an animal, after lesion of the brain or when one eye is blackened, to curiosity or thrills of delight. An equally forcible answer lies in the fact that plants show the same tropisms as animals, and it seems somewhat arbitrary to assume that the bending of a plant to the window or the motion of swarmspores of alge to the window side of a vessel are accompanied or deter- mined by curiosity or by sensations of joy or satisfaction. And finally, since we know nothing of the sentiments and sensations of lower animals, and are still less able to meas- ure them, there is at present no place for them in science. The second difficulty was created by the fact that the Aristotelian viewpoint still prevails to some extent in biology, namely, that an animal moves only for a pur- pose, either to seek food or to seek its mate or to under- take something else connected with the preservation of 2 18 TROPISMS the individual or the race.» The Aristotelians had ex- plained the processes in the inanimate world in the same teleological way. Science began when Galileo overthrew this Aristotelian mode of thought and introduced the method of quantitative experiments which leads to mathe- matical laws free from the metaphysical conception of purpose. The analysis of animal conduct only becomes scientific in so far as it drops the question of purpose and reduces the reactions of animals to quantitative laws. This has been attempted by the tropism theory of ani- mal conduct. b This view is still held, especially among authors, who lean more or less openly to vitalism, e.g., v. Uexkiill, Jordan, Franz, Bauer, Budden- brock, and others. CHAPTER II THE SYMMETRY RELATIONS OF THE ANIMAL BODY AS THE STARTING POINT FOR THE THEORY OF ANIMAL CONDUCT Tue starting point for a scientific and quantitative analysis of animal conduct is the symmetry relations of the animal body. The existence of these symmetry rela- tions reduces the analysis to a comparatively simple problem. Organisms show two forms of symmetry, radial sym- metry, for which jellyfish and the stems and roots of most plants offer a well-known example, and lateral sym- metry, such as exists in man and most animals. In radial symmetry the peripheral elements are distributed equally about an axis of symmetry, in the case of lateral sym- metry the peripheral elements are distributed equally to the right and left of the plane of symmetry (or the median plane) by which the body is divided into a right and left half. The importance of this symmetrical struc- ture lies in the fact that the morphological plane of sym- metry is also the dynamical plane of symmetry of the organism. Symmetrical spots of the surface of an animal are chemically identical, having the same chemical con- stitution and also the same quantity of reacting masses. Thus the two eyes are symmetrical organs, each contain- ing the same photochemical substances in equal quantity. In the eye itself each element is to be considered as chemically identical with the symmetrical point in the other eye. Hence, if the two eyes are illuminated equally, 19 20 TROPISMS the photochemical reaction products produced in the same time will be equal in both eyes. What is true for the eyes is true for all symmetrical elements of the surface of an animal. The median plane is also the plane of symmetry for the muscles and the muscular activity of the body. Sym- metrical muscles possess under equal conditions equal tension and symmetrical muscles are antagonistic to each other in regard to moving the body to the right or left. We say that impulses go from the central nervous system to the muscles; and from the surface of the body to the central nervous system. According to our present knowledge that which is called a nervous impulse seems to consist of a wave of chemical reaction traveling along a nerve fiber. The central nervous system is also sym- metrical and, moreover, we may conceive a projection of the elements of the surface of the body upon the ganglion cells and from here to the muscular system of the body. The complications in this system of projections consti- tute the difficulties in our understanding of the structure of the brain. This idea of a projection of the sense organs or the surface of the body upon the brain will explain why the morphological plane of symmetry of an organism is also its plane of symmetry in a dynamical sense. When symmetrical elements of the eyes are struck by light of the same wave length and intensity, the velocity of photo- chemical reactions will be the same in both eyes. Sym- metrical spots of the retina are connected with symmetri- eal elements in the brain and these in turn are connected with symmetrical muscles. As a consequence of the equal photochemical reactions in the symmetrical spots of the retina equal changes are produced in the symmetrical brain cells with which they are connected, and equal - SYMMETRY RELATIONS 21 changes in tension will be produced in the symmetrical muscles on both sides of the body with which the active brain elements are connected. On account of the sym- metrical character of all the changes no deviation from the original direction of motion will occur. If, however, one eye is illuminated more than the other eye, the influ- ence upon the tension of symmetrical muscles will no longer be the same and the animal will be forced to deviate from the original direction of motion. We have thus far considered only the relation between right and left. Aside from this symmetry relation we have polarity relations, between apex or head and base or tail end. Just as we found that the morphological plane of symmetry is also a dynamical plane of symmetry, we find that with the morphological polarity head-tail is connected a dynamic polarity of motion, namely, forward and backward. This will become clear in the next chapter on forced movements. Physiologists have long been in the habit of studying not the reactions of the whole organism but the reactions of isolated segments (the so-called reflexes). While it may seem justifiable to construct the reactions of the a Physiologists assume that stimulations are constantly sent from the brain to the muscles and that this maintains their tension. v. Uexkiill uses the term that “tonus” is sent out to the muscle and that the brain is a reservoir of “ tonus ” as if the latter were a liquid. The writer wonders whether it might not be wiser to substitute for such metaphors hypotheses in terms of chemical mass action. Constant illumination causes a sta- tionary process in photosensitive elements of our eye, in which the mass of the reaction product is determined by the Bunsen-Roscoe law. We assume, moreover, that in proportion to this photochemical mass action correspond- ing chemical reactions take place in the brain elements with which the eyes are connected; and that as a consequence corresponding chemical reactions take place in the muscles by which the tension of the latter is determined. These processes in the muscles may possibly consist in the establishment of a definite hydrogen ion concentration. Such hypotheses have the advantage over the “stimulation” hypothesis that they can be tested by physico- chemical measurements. 22 TROPISMS organism as a whole from the individual reflexes, such an attempt is in reality doomed to failure, since reactions produced in an isolated element cannot be counted upon to occur when the same element is part of the whole, on account of the mutual inhibitions which the different parts of the organism produce upon each other when in organic connection»; and it is, therefore, impossible to express the conduct of a whole animal as the algebraic sum of the reflexes of its isolated segments. KK. P. Lyon?” has shown that if the tail in a normal shark be bent to one side (without changing the position of the head) the eyes of the animal move as promptly as compass needles in association with the bent tail around the same axis in which the bending occurs, but in an opposite sense. On the convex side of the animal, the white of the eye is more visible in front, on the concave side it is more visible behind; hence the former has moved backward, the latter forward. This was observed not only in the normal fish but also when the optic and audi- tory nerves were cut. The central nervous system acts as one unit. R. Magnus **? and his fellow-workers have shown that an alteration in the position of the head of a dog inevitably alters the tone of the muscles of the legs.° These and other associations and mutual inhibitions make possible that simplification which allows us to treat the / b When the stem of a plant (e.g., Bryophyllum) is cut into as many pieces as there are nodes, each node will under the proper conditions give rise to one or two shoots. If we leave them in connection, only the buds at the apical end will grow out, the rest of the buds remaining dormant. The whole stem acts as though it consisted of only the bud situated at the apex. e The problem of codrdination will form the subject of another volume in this series by Professor A. R. Moore, and for this reason a fuller discussion of work on codrdination, such as that by Sherrington and by v. Uexkiill, may be reserved for Professor Moore’s volume. SYMMETRY RELATIONS 23 organism as a whole as a mere symmetry machine, a simplification which forms the foundation of the tropism theory of animal conduct. It would, therefore, be a misconception to speak of tropisms as of reflexes, since tropisms are reactions of the organism as a whole, while reflexes are reactions of isolated segments. Reflexes and tropisms agree, how- ever, in one respect, inasmuch as both are obviously of a purely physico-chemical character. CHAPTER III FORCED MOVEMENTS WHEN we destroy or injure the brain on one side we paralyze or weaken the muscles connected with this side. As a consequence the morphological plane of symmetry ceases to be the dynamical plane of symmetry and the animal has a tendency to move in circles instead of in a straight line. Suppose a fish swimming forward by motions of its tail fin. Normally the stroke occurs with equal energy to the right and to the left, and the rudder action of the tail is equal in both directions, but after the lesion of one side of the brain the stroke and the rudder action cease to be the same in both directions, it is weakened in one direction. Hence the animal instead of swimming in a straight line is forced to deviate contin- ually toward one side from the straight line of locomo- tion. We speak in such a ease of a forced motion. When we destroy the ventral portion of the left optic lobe in a shark (Scyllium canicula), the fish no longer swims in straight lines but in circles to the right (when the right optic lobe is destroyed it swims in circles to the left). After the destruction of the left optie lobe, the muscles on the left side of the tail are weakened or semi- paralyzed, and they no longer produce the same rudder action as the muscles on the right side. Hence the im- pulses (or nerve processes) which flow in equal intensity to the muscles on both sides will no longer produce equally energetic rudder action of the tail to the right and to the left, but the muscles turning the tail to the right wil] 24 FORCED MOVEMENTS 25 contract more powerfully than those turning it in the opposite direction. The outcome of this greater rudder action of the tail when moving to the right is that the fish instead of swimming in a straight line moves in a circle to the right.?*° It is often the case that the body of such a fish even when quiet is no longer straight but bent in a cirele, the left side forming the convex side; and when such a fish dies and rigor mortis sets in it may become stiff in this position. These latter observations prove that the circus movements to the right are due to the lowering of the tension of the lateral muscles of the body on the left side of the fish. This is the fundamental fact for the theory of forced movements—namely, that a lesion in one side of the brain lessens the tension of the muscles on one side of the body; as a consequence the motions of the animal become difficult or impossible in one direction and become easy in the opposite direction. In many cases the motions of an animal depend upon a cooperative activity of two sets of appendages, e.g., the pectoral fins of a fish or the legs of an animal. Such cooperative or associated action is determined by the fact that the same nerve center supplies antagonistic muscles of the two organs (e.g., the lateral fins). Thus_ the same nerve impulse causes both our eyes to move simultaneously to the right or to the left. When we look to the right, the same impulse which causes the contrac- tion of the rectus externus muscle in the right eye causes a contraction of the rectus internus muscle in the left eye. These two muscles then are associated. In a fish like the shark the position and innervation of the eyes differ from that of the human being. In the shark the eyes are not in front but on the side, and the 26 TROPISMS muscles which lift the eye on one side are associated with those which lower it on the other side of the head. A similar association exists in regard to the pectoral fins, the muscles which lift the right pectoral fin are associated with those which lower the left one, and vice versa. When a normal shark swims the two pectoral fins work equally and the fish swims without rolling over to the right or to the left. If we destroy in a shark the left side of the medulla oblongata forced changes in the position of the two eyes and the two pectoral fins will follow.*°° (There are in addition correlated changes in the other fins and the rest of the body which we will omit in order to simplify the presentation of the subject.) When a shark, whose left medulla is cut, is kept in a horizontal position, its left eye looks down and the right eye looks up. This change of position of both eyes indicates that the relative tension between the muscles of the eyes has changed. In the left eye the tension of the lowering muscles predominates over that of their antagonists, in the right eye the reverse is the case. The pectoral fins likewise show associated . changes of position. The left fin is raised up dorsally, the right is bent down ventrally. Since we know that the destruction of the central nervous system causes a paralysis of muscles and not the reverse we must con- elude that the destruction of the left side of the medulla in a shark causes a weakening or partial paralysis of the muscles which lower the left fin and of those which raise the right fin. Hence the muscles which press down on the water will press harder in the right than in the left fin. When such an animal swims rapidly, it will come under the influence of a couple of forees which must produce a rolling movement around the longitudinal axis of its FORCED MOVEMENTS 27 body toward the left. These rolling motions are another well-known type of forced movements. When such an animal swims slowly, it will roll more than a normal fish, but it will not roll completely around its longitudinal axis. These are the same motions which were observed in dogs by Magendie and Flourens'*® after an operation in the medulla or pons. We ean state, therefore, that the rolling motions are caused by the weakening of one group of (associated) muscles while their antagonists are not weakened. It is of interest to consider the nature of forced move- ments after injury of the cerebral hemispheres in a dog. When in a dog one of the cerebral hemispheres is injured the animal immediately after the operation no longer moves in a perfectly straight line, but deviates from the straight line toward that side where the brain is in- jured.178 When the left hemisphere is injured circus motions toward the left ensue. If one offers a dog which was operated in the left cerebral hemisphere a piece of meat, removing it as fast as the dog approaches, the dog will move at first a certain distance in a straight line; it will then suddenly turn to the left and describe a com- plete circle, moving afterward for a little while in a straight line toward the meat and turning again through an angle of 360° to the left, and so on.*** The explanation is the same as for the foregoing cases. The lesion of the left cerebral hemisphere caused a weakening or partial paralysis of the muscles which turn the body to the right. Hence the animal will, when following the meat, deviate to the left, and this causes a displacement of the retina image in the same direction and an apparent motion of the object to the right. We shall see in a later chapter on 28 TROPISMS the orienting effect of moving retina images that this deviation of the retina image to the left causes a forced motion of the animal to the right which compensates its tendency to deviate to the lett due to the effect of the brain lesion. Hence the animal approaches the meat in an approximately straight line. But it does so with diffi- culty and sooner or later tiring of this effort it moves in the usual automatic way, whereby equal impulses reach the muscles on both sides. This results in a complete circus movement to the left on account of the weakening (caused by the operation) of muscles which turn the body to the right. The retina image of the meat again induces a straight motion and the whole process described is repeated. When the injury to the brain was less severe the animal may follow the meat for long distances without turning in a circle. When such a dog is offered simultaneously two pieces of meat, one in front of the left, the other in front of the right eye, it invariably moves toward the one on the left side. The equal flow of impulses caused by the sym- metrically located pieces of meat results in a stronger contraction in the muscles on the left than on the right side of the body, since as a consequence of the lesion the | tension of the former muscles is greater than that of the latter. When two pieces of meat are simultaneously offered to the dog, but both pieces are in front of the left eye, the dog tries to get the piece nearest to its mouth, but its effort carries it a little too far to the left and then it takes the other piece of meat which is situated farther to the left.?** Some time after the operation these disturbances may become less and may ultimately disappear. If now the FORCED MOVEMENTS 29 dog is operated on the other, e.g., the right hemisphere, circus motions to the right appear. We do not wish to exhaust the chapter on forced move- ments but may perhaps for the sake of completeness point out the following facts. We have seen that if one cerebral hemisphere is injured the dog shows a tendency to circus movements to the operated side. When both hemispheres are injured, e.g., both occipital lobes are removed, the dog can hardly be induced to move forward and it is impos- sible to cause it to go downstairs, while it is willing to go upstairs. Its front legs are extended and its head is raised high, giving the impression as if such a dog had a tendency to move backward rather than forward or that the forward movement was difficult. If the two anterior halves of the cerebral hemispheres are removed the re- verse happens. The animal runs incessantly as if driven by a mad impulse; its head is bent down and it is in every respect the converse of the animal operated in the occipi- tal lobes. These two types of forced movements corre- spond to the morphological polarity tail-head. This corresponds to the idea of a projection of the surface elements upon the brain either directly or by crossing. These three types of forced movements: the cireus motions, the tendency to go backward, and the irresistible tendency to move forward will appear in the form of the tropistic reactions to be described in this volume. Since we shall deal in this volume chiefly with inverte- brates, it may be of importance to show that forced move- ments can also be produced in this group of animals by lesion of one side of the cerebral ganglion, and that these forced movements depend also upon the fact that as a consequence of the operation the tension of sym- metrical muscles (which is equal under normal condi- 30 TROPISMS tions) becomes unequal. Fig. 1, 6, gives the change in posi- tion of the body and of the legs in the larva of a dragon fly (A’schna) after the left half of the cerebral ganglion has been destroyed (Matula °4!). Such an animal moves in a circle to the right. The longitudinal muscles con- necting the segments of the body are under higher tension on the right side of the body than on the left and the body B Fic. 1.—B, forced position of larva of the dragon fly (4ischna) whose left cerebral ganglion is destroyed. The body is convex on the left side, due to a relaxation of the muscles connecting the segments on the left side. The position of the legs is such that the animal can only move in circles to the right. This asymmetry disappears again when both ganglia are destroyed, C. A, normalanimal. (After Matula.) is bent with its convex side to the left. The normally symmetrical position of the legs (Fig. 1, A) is now changed in such a way (Fig. 1, B) that the animal is no longer able to move in a straight line, but is forced to move in circles to its right. We shall see later that similar changes in the position of the legs are produced in a posi- tively heliotropic insect when the left eye is blackened and in a negatively heliotropie insect when the right eye FORCED MOVEMENTS bl is blackened. Circus motions after destruction of one cephalic ganglion in an insect are a general occurrence and have been known for a long time. The importance of these forced movements caused by lesion of the brain for the explanation of the conduct of normal animals lies in the fact that the latter is essen- tially a series of forced movements, The main difference between the forced movements after brain lesion and the conduct of a normal animal lies in the fact that the former are more or less permanent; while in the normal animal conduct ,the changes in the relative tone of sym- metrical muscles leading to a temporary forced movement are caused by a difference in the velocity of chemical reactions in symmetrical sense organs or other elements of the surface. CHAPTER IV GALVANOTROPISM WHEN we send a galvanic current lengthwise through a nerve, at the region near the anode the irritability of the nerve is diminished, while it is increased near the cathode. The condition of decreased irritability near the anode is called anelectrotonus and the increased irrita- bility near the cathode is called catelectrotonus. When a current is sent through an animal, those nerve elements which lie in the direction of the current will have an ane- lectrotonic and a catelectrotonic region; while the nerves through which the current goes at or nearly at right angles are not affected. Ganglia or nerve tracts in the anelectro- tonic condition will, therefore, act as if they were tem- porarily injured, and hence we need not be surprised to find that the galvanic current causes forced movements which last as long as the current lasts, and which cease with the current. Hermann reported in 1885 7°* that when a eurrent is sent through a trough containing tadpoles of a frog, the tadpoles orient themselves in the direction of the current curves putting their heads to the anode.® Blasius and Sehweizer °** found soon afterwards that a large number of animals when put into a trough with water through which a galvanic current passes have a tendeney to go to the anode. The explanation given by Hermann and by Blasius and Schweizer is not correct. They a The writer has never been able to repeat this observation. 32 GALVANOTROPISM 33 assumed that the current, acting upon the central nervous system, causes sensations of pain when it goes in the direction from tail to head in the animal; while it has a soothing or hypnotizing effect when it goes in the opposite direction, namely from head to the tail. In the latter case the head is directed toward the anode. The authors assume that the animals choose the position with least pain, z.e., with their heads to the anode. This assumption is wrong, since we know that when a galvanic current is sent through the head of a human being automatic motions comparable to those observed in animals occur which are not voluntary and which are unaccompanied by any pain sensation. Thus when a galvanic current is sent laterally through the head, the person falls toward the anode side but has no feeling of pain. Mach noticed the same effect of falling to the side of the anode when a galvanic current was sent sidewise through fishes.**° These galvanotropic motions are in reality forced move- ments, and this has been proved by direct observations. It was shown by Loeb and Maxwell *’ in experiments on crustaceans and by Loeb and Garrey *°* on salaman- ders that when we send a galvanic current through ani- mals which go to the anode, changes in the position of the legs occur comparable to the changes in the position of fins and eyes mentioned in the previous chapter, and that these changes are of such a character as to make it easy for the animal to move in the direction of the anode and difficult if not impossible to move in the opposite direction. Tn all these experiments it is of importance to choose the proper density of the current. For the experiments on the shrimp (Palemonetes)**" the animals were put into a 3 ‘ 34 TROPISMS square trough, two opposite sides of which were formed of platinum electrodes. ‘The cross section of the fresh water in the trough was 1,400 mm.? and the intensity of the current about 1 milliampere or a little less. We found it advisable to increase the intensity very gradually by increasing slowly the resistance of a rheostat in a short circuit until the phenomenon of galvanotropism appeared most strikingly. When the current is too strong or too weak the phenomena are no longer clear. The com- mon shrimp (Palemonetes) is a marine crustacean which Fig. 2.—Forced position of shrimp (Palemonetes) when galvanic current goes from head to tail. Tension of extensor muscles of tail fin prevails over that of flexors. Animal can swim forward (to anode), but not backward. (After Loeb and Maxwell.) lives also in brackish water and which can stand fresh water long enough for the purpose of these experiments. The animal can swim forward as well as backward; in forward swimming the extensor muscles of its tail fin work more strongly than the flexors (Fig. 2); in swim- ming backward the flexors work energetically (Fig. 3) and thus produce a powerful stroke forward, while the ex- tensors contract with less energy. When we put a Pale- monetes in a trough through which a current goes and if we put the animal with its head toward the anode the tail is stretched out (Fig. 2). This means that the tension of the extensor muscles prevails over that of the flexors and since the forward swimming is due to the stroke of GALVANOTROPISM 30 the extensors, and since it is antagonized by the tension of the flexors, the animal can swim forward but not backward, or only with difficulty; if we put the animal with its head toward the cathode the tail is bent ventrally (Fig. 3), which means that the tension of the flexors is stronger than that of the extensors. As a consequence the animal can swim backward but not forward, or only Fig. 3.—Forced position of shrimp when positive current goes from tail to head. Tension of flexors of tail fin prevails over that of extensors. Animal can swim backward (to anode), but not forward. (After Loeb and Maxwell.) with difficulty. In both cases the result will be a swim- ming of the animal to the anode, in the former case by swimming forward in the latter by swimming backward. We can further show that the tension of the muscles of the legs of Palemonetes is always altered in such a sense by the galvanic current that motion toward the anode is facilitated, while that toward the cathode is rendered difficult or impossible. The animal uses the third, fourth, and fifth pair of legs for its locomotion (Fig. 2). The third pair pulls in the forward movement 36 TROPISMS and the fifth pair pushes. The fourth pair acts like the fifth and requires no special discussion. If a current be sent through the animal longitudinally from head to tail and the intensity be increased gradually, a change soon takes place in the position of the legs. In the third pair the tension of the flexors predominates (Fig. 2), in the fifth the tension of the extensors. The animal can thus move easily by pulling of the third and by pushing of the fifth pair of legs, that is to say, the current changes the tension of the muscles in such a way that the forward motion is facilitated, while the backward motion is ren- dered difficult. Hence it can easily go toward the anode but only with difficulty toward the cathode. If a current be sent through the animal in the opposite direction, namely from tail to head, the third pair of legs is extended, the fifth pair bent (Fig. 3) ; 2.e., the third pair. can push, the fifth pair can pull backward. The animal can thus go backward with ease but forward only with difficulty. This again will lead to a gathering of such animals at the anode, this time, however, by walking backward. The phenomena thus far described recall the forced movements mentioned in the third chapter, where certain injuries of the brain accelerate forward motion while other lesions in the opposite parts of the brain make forward motion difficult if not impossible. Palemonetes can also walk sidewise. This movement is produced by the pulling of the legs on the side toward which the animal is moving (contraction of the flexors), while the legs of the other side push (contraction of ex- tensors). Ifa current be sent transversely, say from left to right, through the animal, the legs of the left side assume the flexor position, those of the right side the GALVANOTROPISM ay extensor position (Fig. 4). The transverse current thus makes it easy for the animal to move toward the left— the anode—and prevents it from moving toward the right —the cathode. If a galvanic current flows transversely Fig. 4.—Position of legs of shrimp when current goes sidewise through the animal, from left to right. In the legs on the left side the tension of the flexors, in those of the right side the tension of the extensors predominates. The animal can easily go to the left (anode), but not to the right. (After Loeb and Maxwell.) through the animal, it creates the analogue of the circus motions produced by injury of one side of the brain. Figs. 5 and 6 show that the current produces similar effects in the crayfish as those produced in the shrimp (Figs. 2 and 3). 38 TROPISMS It is not difficult to suggest by aid of a diagram the arrangement of the elements in the central nervous system required to bring about the phenomena of galvanotropism just described for Palemonetes. We take it for granted that the regular phenomena of anelectrotonus and cate- lectrotonus of motor nerve elements suffice for the ex- planation of these phenomena. We assume that if the cell body of a neuron is in the state of catelectrotonus Fia. 5. Fia. 6. Fics. 5 and 6.—Show the same effects of current on the common crayfish as those on alemonetes in Figs. 2 and 3. its activity is increased, when it is in anelectrotonic con- dition activity is diminished. Neurons having the same orientation will always be affected in the same sense by the current. Fig. 7 is a diagram of the arrangement of neurons giving rise to the bending of the legs on the side of the anode and to the extension of the legs on the side of the cathode when the current goes sidewise through the ani- mal. This diagram assumes that the nerves innervating the extensors come from the opposite side of the central GALVANOTROPISM 39 nervous system, while those innervating the flexors are on the same side. This diagram corresponds to reality, ac- cording to the histological work of Allen. When the ecur- rent goes from right to left through the crustacean the cell bodies of the neurons on the right side are in catelectro- tonus, those on the left side in anelectrotonus. The for- mer are, therefore, in a state of increased ‘‘irritability,”’ the latter in a state of diminished ‘‘irritability.’’ Hence the flexors of the right leg are contracted and the exten- sors relaxed, while the flexors of the left leg are relaxed and the extensors contracted. J ?° Ordinarily, when a starfish which is moving in an aquarium is touched, it stops immediately and clings tenaciously to the surface of the vessel with its tube feet, so that it is impossible to remove the animal without injury to the tube feet. This normal response to sudden contact can be completely reversed by the administration of strychnine, so that when touched the animal loosens its hold on the bottom completely. 112 HELIOTROPIC TRANSFORMATION 113 The starfish poisoned with strychnine upon sudden touch withdraws all the tube feet, so that it can be moved about like an inert object. lor this purpose 1 or 2 ce. of a V0.0 per cent. solution of strychnine sulfate were injected into a starfish of medium size. Jf the stretching out of the tube feet is due to an in- crease in the tone of the ring muscles (and a decrease in the tension of the longitudinal muscles) the drawing in is due to an increase in the tone of the longitudinal muscles of the tube feet. We therefore see that the same ‘‘stimulus,’’? namely, a sudden touch, which causes one set of muscles to contract in a normal animal causes the antagonists of these muscles to contract in an animal poisoned with strychnine. We shall see that a number of eases of reversal of heliotropism may well find their explanation on this basis. On the other hand, the phe- nomena of solarization known in photography indicate that the sign of heliotropic response may also be changed by an excessive action of light on the photochemical sub- stance. This effect, of course, may in the last analysis also result in an influence upon the central nervous system, such as that brought about by strychnine in Moore’s ex- periment. We will now consider some cases more in detail. The writer found ?°* that certain fresh water crusta- ceans, namely Californian species of Daphnia, copepods, and Gammarus when indifferent to light can be made intensely positively heliotropic by adding some acid to the fresh water, especially the weak acid CO,. When ear- bonated water (or beer) to the extent of about 5 or 10 ce. is slowly and carefully added to 50 cc. of fresh water containing these Daphnia, the animals will become in- tensely positive and will collect in a dense cluster on the 8 114 TROPISMS window side of the dish. Stronger acids act in the same way but the animals are lable to die quickly. LHsters, e.g., ethylacetate, act also like acids and the addition of lec. of a grammolecular solution of ethylacetate to 50 ¢.e. fresh water also makes all the organisms positively helio- tropic. Alcohols act in the same way. In the case of Gammarus the positive heliotropism lasts only a few seconds, while in Daphma it lasts from 10 to 50 minutes and can be renewed by the further careful addition of some CO,. The following table gives the minimal con- centration of various acids and alcohols for the production of positive heliotropism in certain California species of fresh water copepods, and Daphnia: For Copepods For Daphnia Honmicacrd. oe .yieri5 sake 0.006 N INCRUICLENG CL Goo cb aooesodoe 0.006 N NG plONIC! ACiG peeuer ore rtnatte 0.005, N IBUGyrich acid! s)tert sire ee 0.004 N Walleriante acid Wiener) 0.004 N Capronicwacidie\c ce atay-ieres 0.002 N 0.6 N 1D end ENGol Noes Soocooe 0.19 N 0.2N Propylralcohols tye.) yetscie-)-= 0.054 N 0.05 to 0.1 N Normal butyl alcohol ..... 0.019 N Tsobutyd ‘alcohol hy.2):0-t-ae 0.04 N Amy ialcohols iys:sclerettnieits 0.011 N As far as alcohols are concerned each higher alcohol is about three times as efficient as the previous one, with the exception of amyl alcohol. This order of relative efficiency is also characteristic for the surface tension effects of these alcohols.?% It was of importance to find means of making these organisms negatively heliotropic. Moore **8 found that eaffein makes the heliotropieally indifferent fresh water crustacean Diaptomus intensely negatively heliotropie. It required the addition of 1.2 ¢.c. of a 1 per cent. solution of caffein to 50 «ec. of water to bring about this intense HELIOTROPIC TRANSFORMATION 115 negativation. In two minutes all the animals are col- lected in a dense cluster on the negative side which lasts for about 35 minutes. A weak negative collection could also be obtained by adding 0.1 ¢.c. of a 0.5 per cent. solu- tion of strychnine nitrate. Moore found that if the Diap- tomus were first made positively phototropic by the addi- tion of aleohol or acids, it was impossible to alter their response by the action of caffein, strychnine, or atropine. On the other hand, animals which had formed a negative collection under the influence of caffein if treated with ear- bonated water at once changed their response and swim- ming to the light side of the dish formed a positive gathering. What causes these effects? The fact that alcohols | make the organisms positively helotropic suggested the | possibility of a ‘‘narcotic”’ effect; the writer found, how- | ever, that narcosis requires a concentration of alcohols | three times as high as the one required to produce positive heliotropism. He tried the effect of temperature on the reversal of the sign of heliotropism in Daphna and found that lowering of the temperature enhanced the effect of acids in making the animals positive.?°® The writer had found previously that in marine crus- taceans and in larve of a marine annelid, Polygordius, the sense of heliotropism can be reversed by changes of tem- perature as well as by changes in the osmotic pressure of the sea water.2°! Increase in the osmotie pressure of sea water (by adding about 1 gm. of NaCl or its osmotic equivalent of other substances to 100 ¢.c. of sea water) made the negative animals positively heliotropic, and lowering of the concentration by adding 30 to 60 e.e. dis- tilled water to 100 c.c. sea water made positive organisms negative. Negative larve of Polygordius or negative 116 TROPISMS marine copepods could be made positive by lowering the temperature, and positive larve could be made negative by slowly raising the temperature. Since in the latter case the animals suffered from the high temperature the results were not so striking as in the case of the positivat- ing effect of lowering the temperature. The same effect of the concentration of sea water and of temperatures was observed by Ewald for the larve of Balanus perfor- atus. He found, moreover, the interesting fact that a change of the ratio Me in the sea water affected the sign of heliotropism of barnacle larve. An increase of Na made them more positive, an increase in Mg more negative.1*4 The larve of Porthesia are strongly positively helio- tropic before they have eaten, while they lose their helio- tropism almost completely after they have eaten.?*7 The writer observed that male and female winged ants are strongly positively heliotropic but as soon as they lose their wings their heliotropism ceases.787 McEwen *!® has found that when Drosophila is deprived of its wings its heliotropism ceases. Holmes found that terrestrial amphipods are posi- tively, while the aquatic amphipods are negatively helio- tropic. By putting a terrestrial amphipod into water it became negatively heliotropic.?”° That a reversal in the sense of heliotropism may be due to a nervous effect is suggested by an observation by Miss Towle 4% that a certain ostracod, Cypridopsis, can be made positively heliotropie by mechanical shock, and the writer noticed that indifferent fresh water Gam- marus can be made negatively heliotropic by shaking them. In both eases the heliotropism lasts only a short time. HELIOTROPIC TRANSFORMATION 117 The attempt to explain all these reversals on the assumption of a change in the central nervous system meets with the difficulty that such reversals occur also in unicellular organisms which have no central nervous system. Thus the writer observed that Volvox, which occurred in the same ponds in California from where Daphnia came, could also be made positive by CQO,.?°° In swarmspores of alg reversals of heliotropism are a common phenomenon. While these unicellular organisms have no central nervous system they may have synapses such as exist between different neura of metazoa. The writer is not sufficiently familiar with the behavior of synapses in higher animals to suggest that this condition is responsible for the changes in the sense of heliotropism. We may finally discuss briefly a possible solarization effect. The writer found that it is possible to make ani- mals generally negatively heliotropic with the aid of ultraviolet light.2°* If once rendered negative such ani- mals will be negative not only to ultraviolet rays but also to the light of an incandescent lamp. A. R. Moore *° found that the ultraviolet rays having such an effect have a wave length shorter than 3341 A.U. Oltmanns had ob- served that Phycomyces is positively heliotropic in weak light, indifferent in somewhat stronger light, and nega- tively heliotropic in still stronger light. Blaauw found that when the illumination was strong the seedlings of Avena became negatively heliotropic.*7 He suggests the analogy with solarization effects in photography. The discovery of photodynamic effects by v. Tappeiner *% adds to the possibilities which should be considered in this connection. While Drosophila is usually positively heliotropic, McEwen has recently described a mutant of this species 118 TROPISMS which is not heliotropic. This lack of heliotropic response is linked with a peculiar color—‘‘tan’’—by which the mutant is characterized. The character ‘‘tan’’ is sex linked. The daughters inherit the factor for the character from their fathers but do not show the character, while the sons inherit the factor from their mothers and do show the character. The lack of heliotropic reaction in this mutant is apparently not due to any structural defect in the eye (McEwen **?). Keeping successive generations of flies in the dark does not influence their heliotropism. F. Payne °°: °°! raised sixty-nine successive generations of Drosophila in the dark, but the reaction of the insects to light (as well as their eyes) remained entirely normal. ee Se OL CHAPTER XIII GEOTROPISM 1. When the stem of certain plants is placed in a horizontal position, the apex grows vertically upward and the root downward. The downward growth of the root is called positive, the upward growth of the apex nega- tive geotropism. The writer has observed a similar phe- nomenon in a_ hydroid, Antennularia antennina ?°* °° and his observations were confirmed by Miss Stevens.°?? Animals as well as plants, therefore, show the phenomenon of geotropism. These phenomena have given rise to a strange dis- cussion, namely: What constitutes the ‘‘stimulus’’ in the ease of geotropism? When a galvanic current is sent through a motor nerve the muscle answers with a con- traction only when the current is made or broken, but not while a constant current is flowing through the nerve. The older physiologists were not able to form a mental picture of what happened in this case, and they cut the knot by invoking a verbalism, namely by calling the mak- ing or breaking of a current a ‘‘stimulus.’’ This perhaps innocent verbalism then led to the less harmless dogma that only a rapid change could act as a ‘‘stimulus.’?’ Thus Jennings ?°? and Mast *4° took it for granted that phe- nomena of orientation by light could only be produced by rapid changes in the intensity of light and not by constant illumination, since they had the @ prior convic- tion that only a rapid change in the intensity of a gal- vanie current or of light is a ‘‘stimulus.’’ The same diffi- 119 120 TROPISMS culty arose in regard to the action of gravity upon orien- tation, since it was contrary to the definition of a ‘‘stimu- lus’’ that the mere permanent lying in a horizontal posi- tion should cause the apex of a stem to bend upward. All these difficulties disappear if we take the law of chemical mass action into consideration. Light acts not as a ‘‘stimulus’’ but acts by mereasing the mass of certain chemical compounds, and it is the mass of these products which is responsible for the effect of light. Now, mass action is not proportional to the rapidity of the change of acting masses but to the acting mass itself. When two sides of an organism are struck by light of different intensity the quantity of photochemical products on both sides becomes unequal. In galvano- tropism the galvanic current alters the distribution of the mass of certain ions along the nerve elements. It can be shown that gravitation acts by influencing the distribution of chemical substances in an organism. When the stem of a plant is put into a horizontal position certain chemical substances gather in greater concen- tration on the lower side of the stem; and this causes a difference in the velocity of chemical reactions between the lower and the upper side. As a result of this we notice the bending. In the normal upright position of the plant the same substances were distributed equally about the axis of symmetry. The following facts may be offered as a proof for this statement.°2° When we put a piece of the stem of Bryo- phyllum calycinum in a horizontal position it soon bends and gradually assumes the form of a U with the concave side above (Fig. 35). This bending is due to the fact that the cortex on the under side of the stem grows in length while the cortex on the upper side remains unaltered Fie. 35.—Geotropic curvature of stems of Bryophyllum calyc’num. These stems were originally straight and suspended in a horizontal position. In 9! +t ten days they bent, becoming concave on the upper side. The black rings, made with india ink, which were originally parallel, remain unaltered on the upper side of the stems, while their distance increases on the lower side, indicating that the curvature is due to an incicase in growth on the lower side (of the cortex) of the stem. a — ——————_——S—“‘( eT | mn — ‘opis soddn ayy UO UBY4 X94109 944 Jo APIS JOMO] OY} UO SOSSBUT JoyROIT UT SJOOT[OO [RIIO}RVUI SIyT, “Spusdep Zurpueq oy} YoryM uo w194s ayy JO x94100 9Y4 04 MOF 1Oj [Bl1ayBuI BurAddns soavo, oy} :Seavo] [BoIdw OM} YIIM “YjoT 94} OF SUIOJS OY} ULY4 oUNT] OUTeS OY UT Ssey YONUT pueq ‘SOABO] JNOYJIM ‘4yFIt O49 OF Suloys OY, ‘A]]BJUOZIIOY pepuedsNs puB 4YSIBIYS A][VUIDIIO a19M SUIO4S [|] Y—'9E “PIA TEE NE Or pee, ce lia. 37.—When the size of the leaf is reduced by cutting out pieces from the middle (stems to the right), the rate of geotropic bending ot the stem is diminished, since the material sent by the leaf into the stem diminishes with the mass of the leaf. *L9WIIOJ 94} Ul ULYZ JOBUOIS YON St 1944B] 9Y} ULdInzeAINS o1do1j}099 dy} YeY 9OIO\Y ‘saAval JORIUT ssossod yy St a4} OF SUIAIS ‘“SAABAT 9Yy JO syed [RsaqR] VY} YO B1yWyno Aq poonpal st saaval 94} JO 9ZIs dy} 4a, JY} OF SUIOJS U]—'ge ‘oly GHOTROPISM 121 (Loeb *#2). This ean be demonstrated if we mark the cortex in definite intervals with india ink at the begin- ning of the experiment (Fig. 35). After some time the distance between these marks will increase in a certain region of the under side, while it remains constant on the upper side, and this difference causes the bending. This positive increase in length of the under side can only happen through growth, and this growth of the cortex on the lower side of the stem takes place at the expense of material furnished constantly by the leaves which send it in the direction toward the basal end of the stem. When we compare the rate of geotropic bending of horizontal stems without leaves and with one or two leaves at the apex, we find that the bending in the latter is much more rapid (Fig. 36), owing to the greater mass of material supplied for the growth of the cortex, and the same is true, if we compare the rate of curvature of stems having a whole apical leaf attached with that of stems having an apical leaf whose mass has been reduced by cutting off parts of the leaf (Figs. 37 and 38). The writer has shown in other experiments that under equal conditions leaves produce material fit for growth in proportion to their mass. It is, therefore, a safe inference that the influence of the mass of an apical leaf upon the rate of geotropic bending is due to the mass of material it sends into the stem. This material has obviously a tendency to behave like a liquid—which it probably is—and to sink to the lower level. It is, therefore, useless to look for a ‘‘gravi- iatronal stimmilis2? %2%:544 What has been demonstrated in this case explains probably also why the apex of many plants when put into a horizontal position grows upward, and why certain roots under similar conditions grow downward. It disposes 122 TROPISMS also in all probability of the suggestion that the apex of a positively geotropic root has ‘‘brain functions.’’ It is chemical mass action and not ‘‘brain functions’’ which are needed to produce the changes in growth underlying geotropic curvature. 2. As long as animals are in such a position that their plane of symmetry goes through the center of the earth, the position of their eyes and limbs is symmetrical in regard to their plane of symmetry. If, however, we incline the animal, we can bring about forced movements and forced changes of position of the same nature as those caused by injury of one side of certain parts of the brain. Thus we have seen that if we cut the left side of the medulla oblongata in a shark, its two eyes are no longer in a symmetrical position but the left eye looks down and the right eye up, when the shark is kept in a normal posi- tion. The same change can be brought about in a normal shark by the influence of gravitation. When the shark is kept in a position with its right side inclined downward, the right eye is turned upward, the left eye downward. This has nothing to do with light or vision, since it occurs in the dark just as well as in an illuminated room. The abnormal position of the eyes lasts as long as the animal is kept in this abnormal position. The experiment shows that if the plane of symmetry is no longer vertical, forced positions of the eyes can be produced of the same nature as those produced by one-sided injury of certain parts of the brain. Just as in the case of one-sided injury to the medulla oblongata the changes in the position of the eyes are accompanied by changes in the position of the pectoral fins, so also when we put a normal shark with one side downward or half downward.2*° If the rrght side of such GEOTROPISM 123 a fish is down the right pectoral fin is turned more ven- trally, the left fin is turned more dorsally. This means, the tension of the muscles causing the right fin to press down and the left fin to press up is increased. This is the mechanism by which the normal ‘‘equilibrium’’ or more correctly the normal geotropic orientation of the animal is maintained. If the animal should accidentally roll to one side in its normal movements, the tension of the muscles of the pectoral fins would automatically change in such a way as to restore the normal orientation of the animal, whereby the plane of symmetry becomes vertical again. This ‘‘maintenance of equilibrium’’ is therefore a case of automatic orientation by gravitation comparable to the automatic orientation by light. Geotropic changes in the position of the eyes are not confined to fishes,**° they can be demonstrated in a rabbit and in crustaceans as well. In vertebrates the reactions leading to the maintenance of equilibrium are apparently produced in the ear, since they disappear if the acoustic nerves are cut. Moreover, those parts of the brain whose injury brings about such changes in the position of the eye and the fins are parts of the receiving fibers from the acoustic nerve.?°° It seems that some change in the pressure upon the endings of the auditory nerve is responsible for the effects. There are fine grains of CaCO.—the otoliths—in the ear of many species pressing on the underlying nerve end- ings. If we put the median plane of a fish at an angle of 45° with the vertical, the otoliths will no longer press down equally in both ears. The idea first suggested by Delage that it is the pressure of the otoliths upon the nerve endings which is responsible for these reactions receives some support by a well-known experiment by 124 TROPISMS Kreidl?'® ee RHEOTROPISM 133 sticklebacks.17® When a swarm of such fish was kept in an aquarium it was noticed that all the fish were oriented with the long axes parallel and that the whole school swam in a course parallel, but in a direction opposite, to that of the moving observer. If the observer remains station- ary opposite the aquarium and moves an object, prefer- ably white, which is held in the hand, the little fish at once respond by moving slowly and oppositely to that of the moving object. They can be thus made to move up or down or to the right. or left (Hig. 39). By experiments which space forbids us to report in detail Garrey has reached the conclusion that the motion of a near object causes an apparent motion of the whole horizon in the opposite direction and this apparent motion the fish tries to compensate by the motions of its body. This brings the observations on the stickleback into har- mony with the general influence of moving retina images, consisting in a compensatory motion of the fish. We have already referred to the fact that the influence of a moving retina image is capable of compensating the forced movement of a dog after a one-sided lesion of the cerebral hemispheres. CHAPTER XV STEREOTROPISM Our orientation in space is determined by three groups of tropistic influences, two of which we have already dis- cussed, light and gravitation. The third one is pressure on certain nerve endings of the skin. When the tactile influences on the skin of the soles of the feet are weakened (as is the case in locomotor ataxia), the patient finds it difficult to stand and walk in the dark. When he can use his eyes the difficulty is diminished, since the orienting effect of the retina image can compensate the tactile de- ficiency ; just as we have seen that the effect of the loss of the ears in crustaceans can be compensated by the orienting influence of the eyes. The role of tactile influences on the orientation of ani- mals is most clearly demonstrable in starfish, flatworms, and many other animals, when put on their backs. The animals ‘‘right’’ themselves, 7.e., they turn around until the ventral surfaces or their feet are pressed against solid objects again. As the writer pointed out long ago,?*? eravitation has nothing to do with the phenomenon, since starfish will stick to solid surfaces with their tube feet even if by so doing their backs are permanently turned to the center of the earth. Unless the nerve endings on the sole of their tube feet are pressed against a solid surface the animals are restless and the arms move about until the feet are again in contact with solid bodies. This phe- nomenon of orientation the writer called stereotropism. Quantitative investigations of this form of tropism are 134 STEREOTROPISM 135 still lacking and we must be satisfied with a few descriptive remarks. Certain animals show a tendency to bring their body completely into contact with solid bodies, e.g., by creeping into crevices. Without further experimental test this might appear as an expression of negative heliotropism, but it can be shown that this assumption would be wrong. Amphipyra is a positively heliotropice butterfly which, in spite of its positive heliotropism, shows the peculiarity that it creeps into crevices when given an opportunity. Such animals were kept in a box at the bottom of which was a square glass plate resting with its four corners on supports just high enough to allow the animals to creep under the glass plate. After some time every Amphipyra was found under the glass plate. This happened also when the glass plate was exposed to full sunshine, while the rest of the box was in the shade.?87 The same stereotropism is found in female ants at the time of sexual maturity. When such animals are put into a box containing folded pieces of paper or of cloth, after some time every individual is found inside the folds. This happens also when the boxes are kept in the dark.?8? The same form of stereotropism is found in many species of worms. When earthworms are kept in jars with vertical walls they are found creeping in the corners where their body is as much as possible in contact with solid bodies. It is this tropism which compels the animals to burrow into the ground. Maxwell #49 kept Nereis, a form of marine worms, which burrows in sand, in a porcelain dish free from sand. Into the dish glass tubes were put, whose diameter was of the order of that of the worms. After 24 hours every tube was inhabited by a worm who made it its permanent 136 TROPISMS abode. They even remained in the tube when exposed to sunlight which rapidly killed them. We find the opposite, negative stereotropism, in many pelagic animals, e.g., larve of the barnacle or of other crustaceans, which avoid contact with solids. The phenomenon is lable to interfere with heliotropic experiments. | The importance of stereotropism in animals was first pointed out by the experiments of Dewitz on the sperma- tozoa of the cockroach.'”°; 171. He noticed that when a drop of salt solution containing the spermatozoa was put under a cover glass resting on low supports on a slide, the spermatozoa collect at the solid surfaces of the slide and cover glass, while the liquid between remains free from spermatozoa. When a small glass bead is put into the liquid the spermatozoa will also swim on the surface of the bead, never leaving it again. Dewitz is of the opin- ion that this stereotropism is of assistance in securing the entrance of a spermatozoon into the egg. The egg of the cockroach is rather large and the spermatozoon can enter it only through a micropyle. When the egg is laid it passes by the duct of the seminal pouch in which the female keeps the sperm after copulation. On passing the duct some spermatozoa reach the egg. Dewitz points out that these cannot leave the surface of the egg any more but are compelled to move incessantly on the surface of the egg until one of the spermatozoa by chance gets into the micropyle. It is an important fact that different organs of the same organism react differently. We have already men- tioned the tendency of starfish or flatworms to right them- selves, 7.e., their ventral surface is positively their dorsal negatively stereotropic. The stolons of hydroids stick - * STEREOTROPISM 137 to solid bodies, while the polyps bend and continue to grow away at right angles from solid bodies with which they come in contact. Thus the stem of T’ubularia mesem- bryanthemum, a marine hydroid, grows in a straight line. When such stems, after their polyp is cut off, are put with one end in sand, the free end forms a new polyp and the stem continues to grow in a vertical direction upward. When, however, the stem is put near the glass wall as soon as the polyp grows out it bends away from Fic. 40.—The regenerating polyp of Tubularia when in contact with the glass wall of an aquarium bends at right angles to the glass wall. the solid wall, and the stem will now continue to grow at right angles to the vertical wall (Fig. 40). This phenomenon raises the question whether or not the law of chemical mass action underlies phenomena of stereotropism. We have seen that this law dominates the phenomena of heliotropism, inasmuch as the Bunsen- Roscoe law is the expression of the influence of light on the mass of the photochemical reaction product. We have also been able to show that in the ease of the geo- tropic curvature of Bryophyllum the mass of the apical 158 TROPISMS leaf determines the rate of geotropical curvature of a horizontally placed stem. The only way in which the mass of the leaf could have such an influence is through the mass of substances it sends into the stem, so that this case of geotropism is a function of mass action. There are indications that the way contact with a solid in- fluences the behavior of living matter is also through the influence on the rate of certain chemical reactions. The writer observed that the stolons of a hydroid, Aglao- phenia, have a tendency to adhere to solid surfaces and not to leave them any more if they once reach them, and that as soon as such a stolon reaches a solid surface, e.g., a piece of a glass slide, its growth is accelerated con- siderably. It was very astonishing to notice how much more rapid the growth of roots of A glaophenia was when they were in contact with a solid body than when they grew in sea water. The rate of growth is the function of a chemical mass action (Loeb *4*). CHAPTER XVI CHEMOTROPISM 1. When we create a center of diffusion in water or in air we may theoretically expect orienting effects. Thus when a fine capillary tube containing a solution of a salt, e.g., sodium malate, is put into a drop of water containing motile organisms, and the right side of an organism is turned to the source of diffusion, the diffusing molecules will collect in increasing concentration on that side. On the left side of the organism, no such increase in the con- centration of molecules will occur. If now the molecules collecting on the right of the organism in increasing den- sity are able to produce some chemical or some concen- tration chain effect, the two sides of the organism will be acted upon unequally and the tension of the symmetrical motile organs will no longer be the same. As a conse- quence the organism will turn until the mass of molecules or ions striking the organism in the unit of time will be the same for both sides. These effects only take place when the organism is close to the opening of the capillary tube, since the diffusion from the tube is slow. It is obvious, however, that it is difficult to provide experimental conditions which give exact chemotropic reactions. First of all, if the diffusion is rapid the differ- ences in concentration of the effective chemotropic sub- stance on two sides of an organism are too slight to result inaturning movement. A second condition which is liable to vitiate the result are the unavoidable convection cur- rents due to changes or differences of temperature. In 139 140 TROPISMS order to get clear results a method must be used which prevents a rapid diffusion of the substance; and, more- over, the current of diffusion must be confined to an almost straight line. It is possible that Pfeffer’s method satisfies this condition.**+,42° He introduced the sub- stance to be tested for its chemotropic effect into a capil- lary tube, the end of which was then sealed. The other end was pushed into a drop of water containing the sus- pension of the organisms whose chemotropism was under investigation. From this capillary the diffusion was ex- tremely slow. Moreover, the current of diffusion was approximately linear at the orifice. Hence the test for the existence of positive chemotropism was perhaps pos- sible. When an organism, struck sidewise by the line of diffusion near the opening of the capillary tube, turns toward the tube going into it, some probability of positive chemotropism exists; and when all the organisms coming near the orifice of the tube are thus compelled to go into it, the probability may become certainty, provided that the substance used does not paralyze the organism and therefore act as a trap, allowing the organisms to come in but not to go out. The capillary tubes used were of 10 to 15 mm. length and of a width of about 0.1 mm. Pfeffer and his pupils found that the spermatozoa of ferns go in large numbers into a capillary tube containing sodium malate in a concentration of 0.01 per cent. (a solu- tion ten times as diluted is still slightly active). This effect of the malate is specific in this case and this indi- cates that either a definite chemical action of the malate ion or a specific permeability of the organism for it is the source of the chemotropism. Such specific chemotropic effects are not rare, since Pfeffer found that Bacterium termo and Spiridlum undula are positively chemotropic CHEMOTROPISM 141 to a liquid containing 0.001 per cent. of peptone or of meat extract. It is stated that cholera bacilli are strongly attracted by potato sap. Pfeffer found also that the sper- matozoa of certain mosses are positively chemotropie to cane sugar solution in dilutions of 0.1 per cent. Pfeffer’s work preceded the discovery of electrolytic dissociation, and his pupils Buller*® and Shibata *% made some of the additions required by the theory, namely, that it is the malate anion which acts in the case of the spermatozoa of the ferns, and that when the anion is offered in the form of malic acid the H ion counteracts the effect of the malate anion. Shibata made extensive experiments on the chemotrop- ism of the spermatozoa of Isoétes *°° which he found posi- tively chemotropic for the malate anion, and also for the succinate, tartrate, and fumarate anion, when offered in the form of their neutral salts. The anion of the stereo- isomere of fumarie acid, namely of maléic acid, was with- out effect. This indicates a high degree of specificity of these reactions. Neutral sodium malate acted best in dilutions from m/100 to m/1000, but some action could still be discovered in m/20,000 solutions. When malic acid was used no positive chemotropism could be discovered in solutions of m/100 or above on account of the contrary effect of the hydrogen ion, and the spermatozoa of Isoétes did not even go into capillary tubes containing m/1000 malic acid. When any acid other than malic was added to sodium malate the motion of the spermatozoa into the tube was prevented, even a m/6000 HCl solution still had such an effect. Shibata studied especially the mode by which the spermatozoa are oriented chemotropically by malates and found that the reaction consists always in a turning of 142 TROPISMS the axis of the body of the spermatozoa toward the capil- lary tube containing malates or succinates, as the tropism theory demands. When the capillary tube and the surrounding medium contain the same solute for which the organisms are posi- tively chemotropic, they will not go into the tube unless the concentration in the tube is a definite multiple of the concentration of the outside solution. Thus Pfeffer found that the concentration of sodium malate in the capillary must be at least thirty times as great as in the outside solu- tion to induce the spermatozoa of fern to move into it, and in the case of Bacterium termo the solution of meat ex- tract in the tube had to be at least four times as great as the outside solution. In the case of Isoétes spermatozoa Shibata found the ratio of about 400 to 1. This constancy of the ratio is known as Weber’s law, which therefore holds for chemotropic phenomena. Lidforss 78! found with the aid of Pfeffer’s method that the spermatozoa of Marchantia are positively chemo- tropic to certain proteins, especially egg albumin, vitellin from the egg yolk, hemoglobin, and mucin of the sub- maxillary gland; blood albumin, casein, and legumin were less effective. The lowest concentration for hemoglobin solutions and for egg albumin was 0.001 per cent. ! It may also be stated that Lidforss found a chemo- tropic effect of proteins upon the direction of growth of pollen tubes.?*° Bruchmann *! found that the spermatozoa of Lyco- podium were positively chemotropic to the watery extract in which pieces of the prothallium had been boiled. Pfef- fer’s capillary method was used. They showed also posi- tive chemotropism to the citrate anion. Thus, sodium citrate was efficient in a 0.1 to 0.5 per cent. solution. The CHEMOTROPISM 143 lower limit was a little above a U.001 per cent. solution. The effect of the free citric acid was a mixed one since the spermatozoa were negative to H ions and positive to the citrate anion. Instead of being able to use a 0.1 per cent. solution, as in the case of the sodium salt, a 0.01 per cent. solution was the highest concentration to which they were positively chemotropic. This means that the hydrogen ion of citric acid solutions above m/1000 repel the spermatozoa, while when solutions of m/2000 or below are used the hydrogen ion effect no longer in- hibits the positive effect of the citrate anion. In addition the validity of Weber’s law could be demonstrated. The spermatozoa were indifferent to malates, oxalates, and many other salts, as well as to sugar and proteins. 2. While all the botanical observers, from Buller on, had found that the hydrogen ion has only a preventive effect upon the positive chemotropism of lower organisms, Jennings tried to show that acids have a positive effect, especially when in low concentrations.?°° But his con- centrations are not quite as low as he seems to assume, since a 1/50 per cent. (m/180) HCl solution, toward which he believes to have proven positive chemotropism of Para- mecia, is a deadly concentration.2 Jennings’s interest in the problem was aroused by a phenomenon of aggregation, not infrequently found in the suspensions of infusorians. It is well known that when certain infusoria are left undisturbed they do not remain scattered, but gather in more or less dense groups. Thus, if they are mounted on a slide in a thin layer of water, soon dense aggregations will be formed in certain areas, while the remainder of the a The cells of the stomach resist a much higher concentration of HCl but this is an exception. Infusorians, fish, and organisms in general are killed in a short time in m/180 HCl or in a much lower concentration of acid. Thus Fundulus does not live more than one hour in m/3000 HCl or HNO,. (Loeb, J., and Wasteneys, H., Biochem Z., 1911, xxxiii, 489; 1912, xxxix, 167.) 144 TROPISMS slide will be nearly deserted. One of the first investigators to describe this phenomenon was Pfeffer. He observed its occurrence in Glaucoma scintillans, and less markedly in Colpidium colpoda, Stylonychia mytilus, and Paramecium. Pfeffer was inclined to believe that these aggregations were due, partly at least, to a contact stimulus, resulting from a striking of the organisms against small solid bodies, and especially against each other.25° This conclusion of Pfeffer may after all be correct, since it has been shown that sea water containing jelly from the egg of a sea urchin causes spermatozoa to stick together for some time when they impinge upon each other. This agglutination no longer occurs when the spermatozoa are immobilized. Jennings came to the con- clusion that these aggregations of infusorians are due to the fact that they can go into a weak concentration of acid, while they cannot escape from such a weak concen- tration; and since Paramecia themselves produce CO, he assumed that the CO, produced by themselves acts as a center of attraction for other Paramecia. In order to prove this he used the following method: The organisms were studied in a thin layer of water, by mounting them on a slide covered with a large cover glass supported near its ends by slender glass rods. Their reactions were tested by introducing with a capillary pipette a drop of the substance in question beneath the cover glass, or in some cases by allowing it to diffuse inward from the side of the cover glass.25° Thus Jennings introduced a drop of 1/50 per cent. (m/180) HCl on a slide containing Chilomonas. Very soon a somewhat denser ring of these individuals was formed around the drop (Fig. 41). A 1/50 per cent. HCl solution paralyzes (and soon kills) Chilomonas or Para- mecia and hence the surface of the drop must act like a trap into which the organisms will steadily swim, with- out being able to swim back. This will naturally increase CHEMOTROPISM 145 the density of organisms around the drop and may give rise to a ring formation around a high concentration of HCl although the organisms are not positive to the acid. Jennings found, however, that when such organisms are in a drop of weak acids which do not paralyze the organ- isms quickly, e.g., 1/50 per cent. acetic or in CO, solutions, they become negative to the surrounding neutral medium (H,O or hay infusion) and stay in the acid. He, therefore, assumes that the organisms are positive to weak acid, and a b Fie. 41.—Reaction of Chilomonas to a drop of 1/50 per cent. HCl. a, preparation AEG RR Genes SSeS es NEE emery negative to strong acid as well as to their natural neutral or faintly alkaline medium. This negativity to their natural surroundings when in weak acid as well as to strong acid when in weak acid Jennings does not interpret in terms of the tropism theory, and in this he is probably correct. He interprets both phenomena as a trap action due to the asymmetry of certain infusorians; a sudden change in the concentration of a solution causes a reverse of the stroke of their cilia by which the organism is driven back. When the old nor- mal stroke of the cilia is resumed the direction of the locomotion is changed on account of the asymmetrical arrangement of the cilia. This happens when the organ- isms go from weak into strong acid or from weak acid into 10 146 TROPISMS a neutral medium. In this way a collection of the organ- isms at the surface of a drop of acid may be brought about. This phenomenon is not tropistic in the strict sense of the word, and as a matter of fact Paramecium is not positively chemotropic to acid of any strength. Barratt + investigated the chemotropism of Para- mecia for varying concentrations of different acids with Distilled Water HG: NaOH 0,0001n 0,00in Hay Infusion Fia. 42.—Method of proving that Paramecia are not positive to acids of low concentration. (After Barratt.) Pfeffer’s method of capillary tubes, counting the number of individuals going into the tube containing acid and comparing it with the number going simultaneously into a control tube containing only distilled water free from CO, (Fig. 42). The acids used varied from 0.001 N to 0.0001 N. The results were unequivocal. Toward solu- tions of 0.001 N the Paramecia are negative and possibly b In addition two other controls accompanied the test, namely, one tube containing hay infusion (the natural medium of the organisms) and one alkali. CHEMOTROPISM 147 also slightly negative to acids as weak as 0.0001 N. In no case, not even with the weakest acid, was it possible to prove the existence of positive chemotropism for acid (or base). The number of Paramecia which went into a tube containing, e.g., 0.00002 N acid, was on the average not greater than that which went into the control tubes. The tubes were sufficiently wide so that the Paramecia could and did move into the tubes. Barratt, therefore, concludes that acids have only a repelling action upon Paramecia which, however, diminishes or disappears when the hydrogen ion concentration approaches that of distilled water. The observations of Barratt contradict the statement that Paramecia are positive to weak acid. We have seen that when spermatozoa or swarmspores are positive to malates this ean be elegantly shown by Barratt’s method. The same method has shown that when even a trace of acid is added to the neutral malates this positivity disappears. By testing systematically all concentrations of different acids within the range to be considered, Barratt found no trace of any positivity to or any trap action by weak acid for Paramecia. It may be true, however, that when the organisms are in very dilute acid neutral or faintly alka- line water repels them in the way described by Jennings. Barratt states also that there is nothing to support Jen- nings’s assertion that the CO, given off by the Paramecia causes the aggregation in their natural medium, since they are not positive to low concentrations of hydrogen ions. The natural aggregations of infusorians may be due, as Pfeffer suggested, to transitory agglutinations when Paramecia impinge upon each other, and the sticki- ness or tendency to agglutinate may possibly be increased 148 TROPISMS by certain substances produced and excreted by the organ- isms themselves, e.g., CO.. 3. The results obtained with the spermatozoa of ferns and mosses by Pfeffer and other botanists led some authors to the tacit assumption that the spermatozoa of animals were positively chemotropic toward substances contained in or secreted by the eggs of the same species. Some accepted this assumption without test, others made tests which they considered adequate but which seem doubtful, and it may be of some interest to discuss the subject, since far-reaching conclusions might be based on these experiments. Pfeffer’s method of testing for chemotropism with the aid of the capillary tube has proved satisfactory and the application of this method has shown that the spermatozoa of certain animals, e.g., of sea urchins, are not chemotropic toward substances contained in or given off by the egg. Thus Buller, who had worked in Pfeffer’s laboratory on the chemotropism of the sper- matozoa of ferns, investigated carefully and extensively the question whether or not the spermatozoa of echino- derms are positively chemotropie for egg substances.°° His results were entirely negative. Thoroughly washed, ripe unfertilized eggs of Arbacia (Naples) were put into a small volume of sea water for from 2 to 12 hours. Capillary glass tubes, about 12 mm. long and 0.1 to 0.3 mm. internal diameter, and closed at one end, were then half filled with the (super- natant) sea water (which had contained the eggs) by means of an air pump. The tubes were then introduced into a large open drop of sea water, in which fresh, highly motile spermatozoa were swimming. If the eggs excrete an attracting substance it was argued that it should be present in the tubes, and the spermatozoa should collect there. No attraction into the tube could be observed. Except for a surface- contact phenomenon to be further discussed, they went in and out with indifference. Apparently, therefore, the water which had contained the eges exercised no directive stimulus on the spermatozoa whatever. CHEMOTROPISM 149 I then attempted to find some substance which could give a chemo- tactic stimulus to spermatozoa. The substances tested were such as are known to give a directive chemical stimulus to many protozoa, the sper- matozoa of ferns, pollen-tubes, ete. The following solutions were tried by the capillary tube method: distilled water; meat extract 1 per cent.; KNO: 10 per cent., 2 per cent.; NaCl 5.8, 2.9, 0.58 per cent.; K2 Taal 1, 0.1 per eankss ; asparagin 1 per cent. ; eycene Oo per cent.; grape sugar 18, 9, 4.5, 2.25 per cent.; peptone 1 per cent.; alcohol 50, 25, 10 per cent. ; shane 1 per cent.; oxalic acid 0.9, 0.09, 0.009 per conte nitric a 1, 0.1, 0.01 per cent. No definite chemotactic reaction—neither attraction nor repulsion— was observed in any case. Into tubes containing the weaker solutions the spermatozoa went in and out with apparent indifference. On coming into contact with strong acid solutions (oxalic acid 0.9, 0. 09 per cent.; nitric acid 1, 0.1 per cent.) the spermatozoa were killed, and thus formed slight collections. They were thus not able to avoid acids by means of a negative chemotactic reaction.9° Other authors, e.g., Dewitz and the writer, have also reached the conclusion that the egg of the sea urchin con- tains no substance for which the spermatozoon of the same species is positively chemotropic, and that Buller’s conclusions that positive chemotropism plays no role in the entrance of the spermatozoon of sea urchins into the egg is correct. F. Lilie has recently expressed the opposite view, namely that the egg of the sea urchin contains a substance to which the spermatozoa are positively chemotropic and to which he gave the name ‘‘fertilizin.’’*5* He first tried Pfeffer’s correct method with capillary tubes with negative result, just as Buller and the rest of the obser- vers. Instead of concluding that the spermatozoa are not chemotropic he discarded the method and used Jen- nings’s method, stating that it gives ‘‘incomparably more delicate results than Pfeffer’s method of using capillary tubes’’ (p. 533). Lillie found with this method that the spermatozoa of Arbacia are positively chemotropic to 150 TROPISMS H,SO, of a concentration as high as N/10 and that they are never negatively chemotropic, not even to the highest concentrations of the strongest acid. It seems to the writer that Lillie’s observations are more naturally ex- plained on the assumption that when an acid is sufficiently strong and concentrated, e.g., N/10 HNO, or H,SO,, it will paralyze and kill the spermatozoa, and that when a drop of such acid is introduced in sea water containing spermatozoa, a somewhat denser ring of the organisms will be formed around the surface of the drop on account of this action of the acid. With the same method Lillie tried to prove that the spermatozoa of Nereis and Arbacia are positively chemo- tropic to extracts of their own eggs.?8* He proceeded as follows: A suspension of Arbacia sperm, freshly made, was put under a raised cover slip and a drop of the super- natant sea water which had been standing over eggs (as in Buller’s experiments) was introduced under the cover shp. Observation with the naked eye showed that around this drop of egg-sea water immediately a dense ring of spermatozoa formed and behind this a clear external zone was formed about 1.2 to 2mm. wide. The dense ring then broke up into small agglutinated masses. In Lillie’s opinion the formation of this dense ring of spermatozoa at the periphery of the egg-sea water is the expression of a positive chemotropism of the spermatozoa for a sub- stance contained in the egg-sea water, the ‘‘fertilizin.’’ He assumes that the spermatozoa near the drop of egg- sea water all swim to the egg-sea water, leaving a clear space behind them. While this ai lie don of the ring formation might be true—if supported by a direct chemo- tropic method like Pfeffer’s—it can be shown that the ring formation is in all probability due to an entirely different CHEMOTROPISM 151 phenomenon which has no relation to chemotropism or any other tropism. Buller had already observed that the supernatant sea water of sea urchins contains a substance which causes the agglutination of spermatozoa.®° A drop of sea water in which eges had been deposited was placed upon a slide and a drop containing spermatozoa near it. On joining the drops a large number of small balls were formed in a very few seconds. When very numerous spermatozoa were present the balls became 0.1 mm. in diameter, containing many thousands of spermatozoa packed together in a dense mass. Buller explains the phenomenon as being due to small bits of egg jelly floating in the sea water so small that they will (like spermatozoa) pass through ordinary filter paper and, so transparent that one cannot directly see them. A few spermatozoa become attached to each piece of jelly, the presence of which may be inferred from the manner in which the small groups of sperma- tozoa move about. Owing to the length of the spermatozoon, although its head may be imbedded in a jelly particle, the tail may remain partly free. The little collections of spermatozoa thus move about hither and thither in no particular direction. When two such groups come by accident into contact they fuse. Certain of the spermatozoa adhere to both little masses of jelly and lock them together. The fused mass combines with other simple and fused masses, and so on.¢ The writer was able to show that when the jelly of the ege of Strongylocentrotus purpuratus is dissolved by an acid treatment the eggs when washed and transferred to sea water no longer give off agglutinating substances, while the acid sea water containing the dissolved jelly, when rendered neutral through the addition of alkali, will cause the agglutination of sperm.*°? While all the jelly ean be washed off with an acid treatment in the egg of purpuratus, the same is not true for the egg of Arbacia ec This explanation of the fusion of two clusters to a larger one is per- haps not correct. The writer is inclined to ascribe it to the adhesion or agglutination of the spermatozoa of two neighboring clusters with each other, due to a sticky surface on the sperm head. 152 TROPISMS of Woods Hole. Here the acid treatment does not as a rule dissolve all the jelly, or possibly some new jelly may be given off by the egg. While Buller may be correct in assuming that micro- scopic pieces of the egg jelly form the center of these sperm clusters, the writer reached the conclusion that the dissolved mass of the jelly makes the surface of the spermatozoa transitorily sticky, so that if they impinge against each other they will stick together for some time, until the sticky compound formed by the jelly on the sperm head is dissolved by the sea water, which occurs after a short time. This agglutinating effect of the egg-sea water upon the sperm of Arbacia gives rise to that ring formation which Lille considers a proof of positive chemotropism. When a drop of egg-sea water is put into a sufficiently dense suspension of spermatozoa, the spermatozoa at the surface of the drop will agglutinate into practically one dense ring around it, and through the diffusion of some of the dissolved jelly through this ring numerous little clusters will form at the external periphery of the ring, and these clusters will fuse with the ring. In this way the clear region behind the ring originates. The process of fusion continues inside the ring with the result that the latter breaks up into numerous bead-like spherical clusters as Lillie described. In a former paper the writer has pointed out the analogy between the phenomena of transitory sperm agglutination (under the influence of egg-sea water) and surface tension phenomena, inasmuch as two small clusters upon coming in contact fuse into one larger one and inasmuch as elongated clusters break up into two or more spherical clusters. The ring formation described by Lillie has, therefore, VY CHEMOTROPISM 153 in the opinion of the writer no connection with positive chemotropism.? 4. The method of Pfeffer cannot well be used for larger organisms. Barrows ”° has devised an apparatus which allowed him to test quantitatively the chemotropic reactions of Drosophila. The flies which are positively heliotropic were allowed to go to the light inside of a narrow hollow groove. At a certain spot of the groove two glass bottles were inserted with their openings oppo- site each other, one of which contained the substance to be tested for chemotropic efficiency, while the other served as a control. The number of flies which on their path were deviated by the bottle containing the substance to be tested were counted and their number compared with that going into the control bottle. The collection of odor- ous matter in the groove was removed by suction. In this way it was possible to ascertain that the flies are posi- tively chemotropiec to ethyl and amyl alcohol, acetic and lactic acid, and to ether. The chemotropie effect of alcohol was increased through the admixture of traces of an ester, e.g., methyl acetate. In deseribing the manner of reaction of these flies, Barrows makes the statement that when the odor is weak the fruit fly ‘‘attempts first to find the food by the method of trial and error, but as the fly passes into an area of greater stimulation, these movements give way to a direct orientation. This orientation is a well defined tropism response.’’ A similar statement had been made by d Lillie also assumes that it is the intensity gradient which determines the direction of motion in tropistic reactions. This is not correct, since posi- tively heliotropic animals go to the light even if by so doing they have to go from strong into weak light (see page 50). The direction of motion in tropistic reactions is determined by differences in the mass of chemical substances on both sides of a symmetrical animal. 154 TROPISMS Harper for the heliotropism of certain worms, namely that in strong light the animals move by heliotropism, in weak light by ‘‘trial and error.’’ These statements are as erroneous as the assertion that while a stone falls under the influence of gravity a feather finds its way down by the method of ‘‘trial and error.”’ Barrows and Harper overlook the réle of mass action and reaction velocity. When an animal is struck on one side only by hght or by a chemically active substance emanating from a center of diffusion, the mass of this substance or of the photochemical reaction product in- creases on this side. These substances react with some substance of the nerve endings and as soon as the mass of the reaction product reaches a certain quantity the automatic turning, the tropistic reaction, occurs. When the ight is strong or when the animal is near the center of diffusion, this happens in a short time and the tropistic character of the reaction is striking, since the animal is quickly put back into its proper orientation if it deviates from it. When the light is weak or when the animal is at some distance from the center of diffusion it will take a longer time before this critical value of the reaction prod- uct is reached, and in this case the animal can deviate considerably out of the correct orientation before it is brought back into the right orientation. a ——— rc CSO rh CHAPTER XVII THERMOTROPISM Unpber the name of thermotropism M. Mendels- sohn *°?°5 has described the observation that Paramecia gather at a definite end of a trough when these ends have a different temperature. The organisms were put into a flat trough resting on tubes through which water was flowing. When the water in the tube had a temperature of 38° at one end of the trough, while the tube at the opposite end was perfused by water of 26° the organisms all gathered at the latter end. If then the temperature of the water in the two tubes was reversed the organisms went to the other end of the trough. If one end had the temperature of 10° the other of 25°, all went to the latter end. In this case we are in all probability not dealing with a tropistic reaction but with a collection of organisms due to the mechanism of motion described for Paramecium by Jennings. When these organisms come suddenly from a region of a moderate temperature to one of lower tem- perature the activity of their cilia is transitorily reversed, but owing to the asymmetrical arrangement of their cilia they do not go back in the old direction but deviate to one side. This can lead to a collection of Paramecia such as Mendelssohn described. CHAPTER XVIII INSTINCTS Tue teleological way of analyzing animal conduct has predominated to such an extent that there has been a tendency to connect all animal reactions with the preser- vation of the individual and the species. Instinets are considered to be such reactions of the organism as a whole which lead to the nutrition of the individual, the mating of the two sexes, and the care of the offspring. If the tropism theory of animal conduct is justified it must be possible to show that instincts are tropistic reactions. We have insisted in previous chapters that animals indifferent to light can be made strongly positively or negatively heliotropic by certain chemicals or vice versa (e.g., the experiments on certain fresh water crustaceans with acids or alcohol and caffein). We know that the body itself produces at various periods of its existence definite hormones and such hormones can act similarly as the acids or the caffein in the experiments on crustaceans, since it makes no difference whether such substances as acid are introduced into the blood from the outside or from certain tissues of the animal’s own body. We know through F. Lillie’s observations that in the blood of the male cattle embryo substances circulate which inhibit the develop- ment of secondary sexual characters of the female embryo, and we know through Steinach’s experiments that the in- termediate tissue from the sexual gland of one sex when introduced into the castrated organism of the opposite sex may impart to the latter the sexual instincts of the 156 Atlas es —— oor INSTINCTS 157 former. Hormones produced by definite tissues, there- fore, influence the instincts. We want to show that this influence is due to a modification of tropistic reactions by the hormones. Mating in certain fish, like Pundulus, consists in the male pressing that part of its body which contains the opening of the sperm duct against the corresponding part of the female body. The latter responds by pressing back, and the pressure of the body is maintained by both sexes through motions of the tail. During this mutual pressure or friction both sexes shed their sexual cells, sperm and eggs, into the water, and since the openings of the cloaca of the male and female, through which the sex cells are shed, are brought almost in contact with each other, sperm and eggs mix at the moment they are shed. This act of mating is due to a stereotropism which exists only during the spawning season and which is supposedly due to cer- tain hormones existing at this time in the animal. The existence of such hormones is also indicated by certain colorations which develop and exist in the male during this period. This stereotropism is to some extent specific since it is exhibited by the contact between the two sexes. The specificity of this stereotropism is of importance and needs further experimental analysis, but that it is in reality a type of common stereotropism is evidenced by the fact that if during the spawning season we keep females isolated from males in an aquarium the females will go through the motions of mating and shed the eggs every time they come in contact with the glass walls of the aquarium. When they are kept permanently isolated from the male they repeat this non-specific purely stereotropic mating throughout the season. The eggs which they shed they quite frequently devour. 158 TROPISMS These manifestations of a highly developed stereo- tropism in the segments of the reproductive organs are probably widespread in the animal kingdom. The late Professor Whitman told the writer that male pigeons when kept in isolation will try to go through the motions of mating with any solid object in their field of vision, e.g., glass bottles, and even with objects which give only the optical impression of a solid, namely, their own shadow on the ground. In ants, the winged males and females become intensely positively heliotropic at the time of mating. Copulation occurs in the air, in the so-called nuptial flight. At a cer- tain time—in the writer’s observation toward sunset, when the sky is illuminated at the horizon only—the whole swarm of males and females leave the nest and fly in the direction of the glow. The wedding flight is a heliotropie phenomenon *87 presumably due to substances produced in the body during this period. After copulation the female loses its wings and also its positive heliotropism.? It becomes now intensely stereotropic. When kept in a dark box with pieces of cloth in folds the wingless female will now be found in the folds where its body is as closely as possible in contact with the solids. This positive stereotropism leads the queen to begin a subterranean existence which marks the founding of a new nest. Helio- tropism and stereotropism are, therefore, the controlling factors in mating and the starting of a new nest in these ants.7*7 V. L. Kellogg **> has made observations which show that the nuptial flight in bees is also due to an outburst of positive heliotropism as in the ant. aIt has already been mentioned that artificial removal of the wings of the fruit fly will also abolish its heliotropism. a INSTINCTS 159 In the course of some experiments on the sense-reactions of honey- bees, I have kept a small community of Italian bees in a glass-sided, narrow, high observation hive, so made that any particular bee, marked, which it is desired to observe constantly, can not escape this obser- vation. The hive contains but two frames, one above the other, and is made wholly of glass, except for the wooden frame. It is kept covered, except during observation periods, by a black cloth jacket. The bees live contentedly and normally in this small hive, needing only occasional feeding at times when so many cells are given up for brood that there are not enough left for sufficient stored food supplies. Last spring at the normal swarming time, while standing near the jacketed hive, I heard the excited hum of a beginning swarm and noted the first issuers rushing pellmell from the entrance. Interested to see the behavior of the community in the hive during such an ecstatic condition as that of swarming, I lifted the cloth jacket, when the excited mass of bees which was pushing frantically down to the small exit in the lower corner of the hive turned with one accord about face and rushed directly upward away from the opening toward and to the top of the hive. Here the bees jammed, struggling violently. I slipped the jacket partly on; the ones covered turned down; the ones below stood undecided; 1 dropped the jacket completely; the mass began issuing from the exit again; I pulled off the jacket, and again the whole community of excited bees flowed—that is the word for it, so perfectly aligned and so evenly moving were all the individuals of the bee current—up to the closed top of the hive. Leaving the jacket off permanently, I prevented the issuing of the swarm until the ecstasy was passed and the usual quietly busy life of the hive was resumed. About three hours later there was a similar performance and failure to issue from the quickly unjacketed hive. On the next day another attempt to swarm was made, and after nearly an hour of struggling and moving up and down, depending on my manipulation of the black jacket, most of the bees got out of the hive’s opening and the swarming came off on a weed bunch near the laboratory. That the issuance from the hive at swarming time depends upon a sudden extra-development of positive heliotropism seems obvious, The ecstasy comes and the bees crowd for the one spot of light in the normal hive, namely, the entrance opening. But when the covering jacket is lifted and the light comes strongly in from above—my hive was under a skylight—they rush toward the top, that is, toward the light. Jacket on and light shut off from above, down they rush; jacket off and light stronger from above than below and they respond like iron filings in front of an electromagnet which has its current suddenly turned on, 160 TROPISMS Iinally there are indications of the role of chemo- tropism in mating. It has been observed for a long time that if a female butterfly is kept hidden from sight in a not too tightly closed box, male butterflies of the same species will be attracted by the box and settle on it. The female apparently gives off a substance to which the male is positively chemotropic. All these observations should be worked out more systematically. The data suffice, however, to indicate that what the biologist and psycholo- gist call instinct are manifestations of tropisms. The fact that eggs are laid by many insects on material which serves as a nutritive medium for the offspring is a typical instinct. An experimental analysis shows again that the underlying mechanism of the instinct is a positive chemotropism of the mother insect for the type of sub- stance serving her as food; and when the intensity of these volatile substances is very high, 7.e., when the insect is on the material, the egg-laying mechanism of the fly is auto- matically set into motion. Thus the common housefly will deposit its eggs on decaying meat but not on fat; but it will also deposit it on objects smeared over with asafcetida, on which the larve cannot live. Aseptic banana flies will lay their eggs on sterile banana, although the banana is only an adequate food for the larvee when yeast grows on it. It seems that the female insect lays her eggs on material for which she is positively chemotropic, and this is generally material which she also eats. The fact that such material serves as food for the coming genera- tion is an accident. Considered in this way, the mystic aspect of the instinctive care of insects for the future generation is replaced by the simple mechanistic concep- tion of a tropistic reaction. In this case natural selection plays a role since species whose females would too fre- INSTINCTS 161 quently lay their eggs on material on which the larve cannot thrive would be liable to die out. As an illustration of the role of tropisms in the instinc- tive self-preservation the writer wishes to apologize for selecting an example which he has used so often in pre- vious discussions, namely the role of heliotropism in the preservation of the life of the caterpillars of Porthesia chrysorrhea.*** ‘This butterfly lays its eggs upon a shrub, on which the larve hatch in the fall and on which they hibernate, as a rule, not far from the ground. As soon as the temperature reaches a certain height, they leave the nest; under natural conditions this happens in the spring when the first leaves have begun to form on the shrub. (The larve can, however, be induced to leave the nest at any time in the winter, provided the temperature is raised sufficiently). After leaving the nest, they crawl directly upward on the shrub where they find the leaves on which they feed. If the caterpillars should move down the shrub they would starve, but this they never do, always crawl- ing upward to where they find their food. What gives the caterpillar this never-failing certainty which saves its life and for which the human being might envy the little larva? Is it a dim recollection of experiences of former generations, as Samuel Butler would have us believe? It can be shown that this instinct is merely posi- tive heliotropism and that the light reflected from the sky guides the animals upward. The caterpillars upon waking from their winter sleep are violently positively heliotropie, and it is this heliotropism which makes the animals move upward. At the top of the branch they come in contact with a growing bud and chemical and tactile influences set the mandibles of the young caterpillar into activity. If we put these caterpillars into closed test tubes which lie 11 162 TROPISMS with their longitudinal axes at right angles to the window they will all migrate to the window end where they will stay and starve, even if we put their favorite leaves into the test tube close behind them. These larve are in this condition slaves of the light. The few young leaves on top of a twig are quickly eaten by the caterpillar. The ight which saved its life by mak- ing it creep upward where it finds its food would cause it to starve could the animal not free itself from the bondage of positive heliotropism. After having eaten it is no longer a slave of hght but can and does creep down- ward. It can be shown that a caterpillar after having been fed loses its positive heliotropism almost completely and permanently. If we submit unfed and fed caterpillars of the same nest to the same artificial or natural source of light in two different test tubes the unfed will creep to the light and stay there until they die, while those that have eaten will pay little or no attention to the lght. Their positive heliotropism has disappeared and the ani- mal after having eaten can creep in any direction. The restlessness which accompanies the condition of starva- tion makes the animal leave the top of the branches and ereep downward—which is the only direction open to it— where it finds new young leaves on which it can feed. The wonderful hereditary instinct upon which the life of the animal depends is its positive heliotropism in the unfed condition and the loss of this heliotropism after having eaten. The chemical changes following the taking up of the food abolish the heliotropism just as CO, arouses positive heliotropism in certain Daphnia. Mayer and Soule have shown that negative geotropism and positive heliotropism keep the caterpillars of Danais plexippus on its plant (the milk-weed). The chemical — INSTINCTS 163 nature of the leaf starts the eating reactions, but ‘‘once the eating reaction be set into play, it tends to continue, so that the larva may then be induced to eat substances which it would never have commenced to eat in the first instance. ’’ 3> These few examples may suffice to show that the theory of tropisms is at the same time the theory of instincts if due consideration is given to the role of hormones in producing certain tropisms and suppressing others. A systematic analysis of instinctive reactions from the view- point of the theory of tropisms and hormones will prob- ably yield rich returns. As an example we may quote the fact that diurnal depth migrations of aquatic animals, consisting in an upward motion during the night and a downward motion during the day, are in all probability determined by a periodic change in the sense of heliotropism.18%; 3°° CHAPTER XIX MEMORY IMAGES AND TROPISMS WHEN a muscle is stimulated several times in succes- sion, the effect of the second or third or later stimulation may be greater than that of the first. A consistently anthropomorphic author should draw the inference that the muscle is gradually learning to react properly. What seems to happen is that the hydrogen ion concentration is raised by the first stimulations to a point where the effect of the stimulation becomes greater. When the stimula- tions’ continue and the hydrogen ion concentration be- comes still greater, the response of the muscle declines and finally becomes zero; the hydrogen ion concentration has now become too high. The writer observed that when winged plant lice of a Cineraria were taken directly from the plant, they did not react as promptly as after they had gone through several heliotropic experiments. There is nothing to indicate that this is a case of ‘‘learning,’’ since it may also be the result of a change in the hydrogen ion concentration or of some other reaction product. It may also be the result of some purely mechanical obstacle to rapid locomotion being removed. We can speak of learning only in such organisms in which the existence of associative memory can be proved. By associative memory we mean that mechanism, by which a stimulus produces not only the direct effects determined by its nature, but also the effects of entirely different stimuli which at some former period by chance attacked the organism at the same time with the given 164 MEMORY IMAGES 165 stimulus. Thus the image or the odor of a rose may call up the memory of persons or surroundings which were present on a former occasion when the image or odor of the flower impressed us. Brain physiology shows that this type of associative memory is the specific function of definite parts of tie brain, e.g., the cerebral hemispheres which exist only in definite types of animals. We see also that certain species among vertebrates, insects, crus- tacea, and cephalopods possess associative memory, while to the knowledge of the writer no adequate proof for its existence has ever been given for worms, starfish, sea urchins, actinians, meduse, hydroids, or infusorians.?%* Claims for the existence of such memory in these latter groups of animals have frequently been made, but such claims are either plain romance or due to a confusion of reversible physiological processes with the irreversible phenomena of associative memory. The less a scientist is accustomed to rigid quantitative experiments, the more ready he is to confound the reversible after effects of a stimulus—e.g., the after effects due to an increase in hydrogen ion concentration—with indications of associa- tive memory. Learning is only possible where there exists a specific organ of associative memory, the physical mechanism of which is still unknown. The manifestations of associative memory are gener- ally discussed by the introspective psychologists, who as a rule are not familiar with or do not appreciate the methods of the physicist. There have been made repeated attempts to develop methods for the analysis of associa- tive memory, among which thus far only one satisfies the demands of quantitative science, namely Pawlow’s method. As is well known even to the layman, eating causes a flow of saliva. The quantity of saliva excreted 166 TROPISMS by the parotid (one of the salivary glands) in the dog ean be collected and measured. The earlier physiological workers had observed that in a dog which had often been used for the study of the influence of eating upon the flow of saliva, the saliva began to flow whenever the prepara- tions for feeding were made before the eyes of the dog, even when no food was given. Pawlow made use of this fact to study quantitatively the ‘‘strength’’ of such asso- ciative phenomena, which he terms ‘‘conditioned re- flexes’? (to escape the terminology and interpretations of the introspective psychologist).°** A fistula® of the duct of the parotic gland allows the saliva to flow outside the cavity of the mouth. This fistula is connected with a long manometer which by a special air chamber arrange- ment gives a considerable change in the height of the meniscus for the secretion of as little as one drop of saliva. The variations of the height of the column of liquid in the manometer are observed outside of the room where the dog is. For each dog which is to serve for such experiments the meal is preceded by a certain signal, the sounds of a metronome of definite rhythm, or a definite musical sound, or a definite optical signal, and so forth, which is to form the special conditioned reflex for this dog. After a certain number of repetitions the association is established and from now on the flow of saliva commences from the dog’s parotid when the typical signal is given. It was found that the quantity of saliva excreted by the signal changes in a definite sense and quantity when the signal varies or when other conditions accompanying the signal vary. a The writer is indebted for the details of Pawlow’s method to a short review by Dr. Morgulis.5387, 538 MEMORY IMAGES 167 Thus in one dog ‘‘by persistent training a conditioned reflex has been established to the stimulation with 100 oscillations per minute of the metronome. The stimu. lation of intermittent sounds of such frequency called forth 6 to 10 drops of saliva every time. The interval between successive oscillations was then modified, the moment of the disappearance of the conditioned salivary reflex indicating the lowest limit of differentiation. With- out going into any details of this most interesting investi- gation or quoting actual data, I will say that the dog could sharply distinguish the shortening of the interval by less than 1/40 to 1/438 of a second. Indeed with the well-developed reflex to the stimulation of 100 beats per minute a change of the rate to either 96 or 104 beats was immediately reacted upon by a marked diminution or even complete cessation of the flow of saliva.’’ This example will give an indication how sensitive is this method of measuring the effect of a memory association. It is not our purpose to give the details of Pawlow’s | results—they have only been published in Russian and are therefore not accessible to the writer—but to show | that the influence of an associative memory image is as | exactly measurable as, e.g., the direct illumination of the | eye; and moreover that what we call a memory image | is not a ‘‘spiritual’’ but a physical agency. We there- fore need not be surprised to find that such memory images or ‘‘conditioned reflexes’’ can vary and multiply the number of possible tropistie reactions. We have mentioned in the previous chapter that the stereotropism in the mating instinct includes apparently an element of species specificity inasmuch as naturally only males and females of the same species mate. The _ 168 TROPISMS late Professor Whitman has shown by experiment that this specificity is, in pigeons at least, not inherited but the effect of memory images (a ‘‘conditioned reflex’’ in the sense of Pawlow). Whitman took the eggs or young of wild species, giving them to the domestic ring-dove to foster, with the result, that the young reared by the ring- doves ever after associated with ring-doves and tried to mate with them. Passenger pigeons when reared by ring- doves refuse to mate with their own species but mate with the species of the foster parents.**® This shows inciden- tally that racial antagonism is not inherited but acquired. We have mentioned the fact that the mating instinct is determined by tropisms aroused by specific internal secretions, and that in isolated male pigeons any solid body can arouse the mating reaction. Craig 4° raised male pigeons in isolation so that they never came in con- tact with other pigeons until they were adult. One pigeon was hatched in July and isolated in August. Throughout the autumn and early winter this bird cooed very little. But about the first of February there began a remarkable development of voice and social behavior. The dove was kept in a room where several men were at work, and he directed his display behavior toward these men just as if they belonged to his own species. Each time I put food in his cage he became greatly excited, charging up and down the eage, bowing-and-cooing to me, and pecking my hand whenever it came within his eage. From that day until the day of his death, Jack continued to react in this social manner to human beings. He would bow-and-coo to me at a distance, or to my face when near the cage; but he paid greatest attention to the hand—naturally so, because it was the only part with which he daily came into direct contact. He treated the hand much as if it were a living bird. Not only were his own activities directed toward the hand as if it were a bird, but he received treatment by the hand in the same spirit. The hand could stroke him, preen his neck, even pull the feathers sharply, Jack had absolutely no fear, but ran to the hand to be stroked or teased, showing the joy that all doves show in the attentions of their companions. —— ee MEMORY IMAGES 169 When this pigeon was almost a year old it was put into a cage with a female pigeon, but although the female aroused the sexual instinet of the formerly isolated male the latter did not mate with her, but mated with the hand of his attendant when the hand was put into the cage, and this continued throughout the season. Thus the memory images acquired by the bird at an impressionable age and period perverted its sexual tropisms. It is perhaps of more importance to show that memory images may have a direct orienting influence. The chemo- tropic phenomenon of an insect laying its egg on a sub- stance which serves as food (for both mother and off- spring) and for which the mother is positively chemo- tropic, may be modified by an act of associative memory, e.g., When a solitary wasp drags the caterpillar on which it lays its eggs to a previously prepared hole in the ground. The essential part of the instinct, the laying of the eggs on the caterpillar, does, perhaps, not differ very much from the fly laying its eggs on decaying meat; and the solitary wasp may be strongly positively chemotropic for the caterpillar on which it lays the eggs, although this has not yet been investigated. But the phenomenon is complicated by a second tropism, which we will eall the orienting effect of the memory image. As is well known, the wasp before ‘‘going for’’ the caterpillar digs a hole in the ground to which it afterwards drags the caterpil- lar, often from a distance. The finding of this previously prepared hole by the returning wasp, the writer would designate as the tropistic or orienting effect of the memory image of the location of this hole; meaning thereby that the memory image of the location of this hole makes the animal return to this location. The conduct of these wasps 170 TROPISMS is familiar to many readers and the writer may be par- doned for quoting from a formerly published observation. Ammophila, a solitary wasp, makes a small hole in the ground and then goes out to hunt for a caterpillar, which, when found, it paralyses by one or several stings. The wasp carries the caterpillar back to the nest, puts it into the hole, and covers the latter with sand. Before this is done, it deposits its eggs on the caterpillar which serves the young larva as food, An Ammophila had made a hole in a flower bed and left the flower bed flying. A little later I saw an Ammophila running on the sidewalk of the street in front of the garden, dragging a caterpillar which it held in its mouth. The weight of the caterpillar prevented the wasp from flying. The garden was higher than the sidewalk and separated from it by a stone wall. The wasp repeatedly made an attempt to climb upon the stone wall, but kept fallmg down. Suspecting that it might have a hole prepared in the garden, I was curious to see whether and how it would find the hole. It followed the wall until it reached the neigh- boring yard, which had no wall. It now left the street and crawled into this yard, dragging the caterpillar along. Then crawling through the fence which separated the two yards, it dropped the caterpillar near the foot of a tree, and flew away. After a short zigzag flight it alighted on a flower bed in which I noticed two small holes. It soon left the bed and flew back to the tree, not in a straight line but in three stages, stopping twice on its way. At the third stop it landed at the place where the caterpillar lay. The caterpillar was then dragged to the hole, pulled into it, and the hole was covered with tiny stones in the usual way.293 It is not enough to say that the animal possesses associative memory and returns to the hole; we must add that the brain image of the region of the hole becomes the source of a forced orientation of the animal—of an added special tropism—compelling the animal to return to the region corresponding to the image. And the same may be said in regard to the return of the wasp to the caterpillar which had been temporarily deposited at the foot of the tree. This example, which might be easily multiplied, will MEMORY IMAGES 171 show the addition necessary to the tropism theory to make it include the endless number of reactions in which associa- tive memory is involved. The psychiatrist would find it easy to supply numerous examples of this type of forced movements toward certain objects which have left a memory image. Since the writer has not investigated this subject sufficiently he is not in a position to give more | than a suggestion for the direction of further work. He is inclined to believe that with this enlargement the trop- ism theory might include human conduct also if we realize that certain memory images may exercise as definite an orienting influence as, e.g., moving retina images or sex hormones. This tentative extension of the forced movement or tropism theory of animal conduct may explain why higher animals and human beings seem to possess freedom of will, although all movements are of the nature of forced movements. The tropistice effects of memory images and the modification and inhibition of tropisms by memory images make the number of possible reactions so great that prediction becomes almost impossible and it is this impossibility chiefly which gives rise to the doctrine of free will. The theory of free will originated and is held not among physicists but among verbalists. We have shown that an organism goes where its legs carry it and that the direction of the motion is forced upon the organ- ism. When the orienting force is obvious to us, the motion appears as being willed or instinctive; the latter generally when all individuals act alike, machine fashion, the former when different individuals act differently. When aswarm of Daphnia is sensitized with CO, they all rush to the source of light. This is a machine-like action, and many 172 TROPISMS will be willing to admit that it is a foreed movement or an instinctive reaction. After the CO, has evaporated the animals become indifferent to light, and while formerly they had only one degree of freedom of motion they now can move in any direction. In this case the motions appear to be spontaneous or free, since we are not in a position to state why Daphnia a moves to the right and Daphnia b to the left, ete. As a matter of fact, the motion of each individual is again determined by something but we do not know what itis. The persistent courtship of a human male for a definite individual female may appear as an example of persistent will, yet it is a complicated tropism in which sex hormones and definite memory images are the determining factors. Removal of the sex glands abol- ishes the courtship and replacing the sex glands of an individual by those of the opposite sex may lead to a complete reversal of the sex instincts. What appears as persistent will action is, therefore, essentially a tropistic reaction. The production of heliotropism by CO, in Daphnia and the production of the definite courtship of the male A for the female B are similar phenomena differ- ing only by the nature of the hormones and the additional tropistic effects of certain memory images in the case of courtship. Our conception of the existence of ‘‘free will’’ in human beings rests on the fact that our knowledge is often not sufficiently complete to account for the orienting forces, especially when we carry out a ‘‘premeditated’”’ act, or when we carry out an act which gives us pain or may lead to our destruction, and our incomplete knowl- edge is due to the sheer endless number of possible com- binations and mutual inhibitions of the orienting effect of individual memory images. LITERATURE 173 LITERATURE 4 1 Apport, J. F., and Lire, A. C.: Galvanotropism in Bacteria. Am. J. Physiol., 1908, xxii, 202-206. 2 Apams, G. P.: On the Negative and Positive Phototropism of the Earthworm Allolobophora fetida (Sav.) as Determined by Light of Different Intensities. Am. J. Physiol., 1903, ix, 26-34. 3 Auten, W. C.: An Experimental Analysis of the Relation Between Physiological States and Rheotaxis in Isopoda. J. Hxp. Zool., 1912, xill, 269-344. 4 AuutEE, W. C.: The Effect of Molting on Rheotaxis in Isopods. Science, 1913, xxxvii, 882-883. 5 Auten, W. C.: Further Studies on Physiological States and Rheotaxis in Isopoda. J. Exp. Zool., 1913, xv, 257-295. 6 Auten, W. C.: Certain Relations Between Rheotaxis and Resistance to Potassium Cyanide in Isopoda. J. Exp. Zool., 1914, xvi, 397- 412. 7 ALLER, W. C.: The Ecological Importance of the Rheotactie Reaction of Stream Isopods. Biol. Bull., 1914, xxvu, 52-66. 8 ALLEE, W. C.: Chemical Control of Rheotaxis in Asellus. J. Exp. Zool., 1916, xxi, 163-198. 9 ALLEE, W. C., and TasHiro, 8.: Some Relations Between Rheotaxis and the Rate of Carbon Dioxide Production of Isopods. J. Animal Behav., 1914, iv, 202-214. 10 AnLEN, G. D.: Reversibility of the Reactions of Planaria doroto- cephala to a Current of Water. Biol. Bull., 1915, xxix, 111-128. 11 Arty, L. B.: The Orientation of Amphioxus During Locomotion. J. Hap. Zool., 1915, xix, 37-44. 12 Artsz, W. H.: On the Connection Between Stimulus and Effect in Phototropie Curvatures of Seedlings of Avena sativa. Proc. Roy. Acad. Amsterdam, 1911, xiu, 1022-1031. 18 AXENFELD, D.: Quelques observations sur la vuefdes arthropodes. Arch. Ital. Biol., 1899, xxxi. 14 Bacu, H.: Ueber die Abhingigkeit der geotropischen Priisentations- und Reaktionszeit von verschiedenen dusseren Faktoren. Jahrb. wiss. Bot., 1907, xliv, 57-123. 15 Bauss, H.: Uber die Chemorezeption bei Garneelen. Biol. Centr., 1913, xxxii, 508-512. a The list of literature does not claim to be complete. Aside from un- intentional omissions, some of the controversial and amateurish publica- tions have not been included. 174 TROPISMS 16 Bancrort, F. W.: Note on the Galvanotropie Reactions of the Me- _ dusa Polyorchis penicillata, A. Agassiz. J. Exp. Zool., 1904, i, 289-299. 17 Bancrort, F. W.: Ueber die Giiltigkeit des Pfliiger’schen Gesetzes fiir die galvanotropischen Reaktionen von Paramecium. Arch. ges. Physiol., 1905, evil, 535-556. 18 Banorort, F. W.: On the Influence of the Relative Concentration of Calcium Ions on the Reversal of the Polar Effects of the Galvanic Current in Paramecium. J. Physiol., 1906, xxxiv, 444463. 19 Bancrort, F. W.: The Control of Galvanotropism in Paramecium by Chemical Substances, Univ. Cal. Pub. Physiol., 1906, iii, 21-31. 20 BancrortT, F. W.: The Mechanism of Galvanotropie Orientation in Volvox. J. Exp. Zool., 1907, iv, 157-163. 21 Bancrort, F. W.: Heliotropism, Differential Sensibility, and Gal- vanotropism in Euglena. J. Exp. Zool., 1913, xv, 383-428. 22 Banta, A. M.: Experiments on the Light.and Tactile Reactions of a Cave Variety and an Open Water Variety of an Amphipod Species. Proc. Soc. Exp. Biol. and Med., 1913, x, 192. 23 BARANETZKI, J.: Influence de la lumiére sur les plasmodia des myxo- mycétes. Mém. Soc. Sc. Nat. Cherbourg, 1876, xix, 321-360. 24 Barratt, J. O. W.: Der Einfluss der Konzentration auf die Chemo- taxis. Z. allg. Physiol., 1905, v, 73-94. 25 Barrows, W. M.: The Reactions of the Pomace Fly, Drosophila ampelophila Loew, to Odorous Substances. J. Exp. Zool., 1907, iv, 515-537. 26 Bauer, V.: Ueber die reflektorische Regulierung der Schwimmbe- wegungen bei den Mysiden, mit besonderer Beriicksichtigung der doppelsinnigen Reizbarkeit der Augen. Z. allg. Physiol., 1908, vill, 343-370. 27 Baugr, V.: Ueber sukzessiven Helligkeitskontrast bei Fischen. Centr. Physiol., 1909, xxiii, 593-599. 28 Bauer, V.: Ueber das Farbenunterscheidungsvermogen der Fische. Arch. ges. Physiol., 1910, exxxiii, 7-26. 29 Baurr, V.: Zur Kenntnis der Lebensweise von Pecten jacobeus L. Im besonderen iiber die Funktion der Augen. Zool. Jahrb. Abt. allg. Zool., 1912, xxxiii, 127-150. 30 BAUNACKE, W.: Statische Sinnesorgane bei den Nepiden. Zool. Jahrb. Abt. Anat., 1912-13, xxxiv, 179-346. 31 BauNACKE, W.: Studien zur Frage nach der Statocystenfunktion. I. Statische Reflexe bei Mollusken. Biol. Centr., 1913, xxxiii, 427— 452. — LITERATURE 175 32 BaunAcKE, W.: II. Noch einmal die Geotaxis unserer Mollusken. Biol. Centr., 1914, xxxiv, 371-385; 497-523. 83 Beer, TH.: Vergleichend-physiologische Studien zur Statocysten- funktion. I. Ueber den angeblichen Gehérsinn und das angebliche Gehororgan der Crustaceen. Arch. ges. Physiol., 1898, xxiii, 1-41. 34 Beer, Tu.: Il. Versuche an Crustaceen (Peneus membranaceus). Arch. ges. Physiol., 1899, Ixxiv, 364-382. 35 Benet, J.: Der richtende Einfluss stromenden Wassers auf wach- sende Pflanzen und Pflanzenteile (Rheotropismus). Ber. bot. Ges., 1883, i, 512-521. 36 BERNSTEIN, J.: Chemotropische Bewegung eines Quecksilbertropfens. Zur Theorie der amodboiden Bewegung. Arch. ges. Physiol., 1900, Ixxx, 628-637. 37 Bert, P.: Les animaux voient-ils les mémes rayons lumineux que nous? Mém. Soc. Sc. Phys. et Nat. Bordeaux, 1868, vi, 375-383. 38 Bert, P.: Sur la question de savoir si tous les animaux voient les mémes rayons lumineux que nous. Arch. de Physiol., 1869, ii, 547-554. 39 Betue, A.: Ueber die Erhaltung des Gleichgewichts. Biol. Centr., 1894, xiv, 95-114; 563-582. 40 Berne, A.:Die Otocyste von Mysis. Zool. Jahrb. Abt. Anat., 1895, vill, 544-564. 41 Berne, A.: Die Locomotion des Haifisches (Scylliwm) und ihre Beziehungen zu den einzelnen Gehirnteilen und zum Labyrinth. Arch. ges. Physiol., 1899, lxxvi, 470-493. 42 Biren, KE. A.: The Vertical Distribution of the Limnetie Crustacea of Lake Mendota. Biol. Centr., 1897, xvi, 371-374. 43 Brrukorr, B.: Untersuchungen iiber Galvanotaxis. Arch. ges. Physiol., 1899, Ixxvii, 555-585. 44 Brrukorr, B.: Zur Theorie der Galvanotaxis. Arch. Anat. u. Physiol., Physiol. Abt., 1904, 271-296. 45 Brrukor?®, B.: Zur Theorie der Galvanotaxis. II. Arch. ges. Physiol., 1906, exi, 95-143. 46 Buaauw, A. H.: The Intensity of Light and the Length of Illumina- tion in the Phototropic Curvature in Seedlings of Avena sativa (Oats). Proc. Roy. Aikad. Amsterdam, 1908. 47 Buaauw, A. H.: Die Perzeption des Lichtes. Rec. trav. bot. Neér- landais, 1909, v, 209-377, 48 Buaauw, A. H.: Licht und Wachstum. Z. Bot., 1914, vi, 641-703; 1915, vii, 465-532. 48a Buasius, E., and ScHweizer, F.: Elektrotropismus und verwandte Erscheinungen. Arch. ges. Physiol., 1893, lin, 493-543. 176 TROPISMS 49 Bonn, G.: Les Convoluta roscoffensis et la théorie des causes aetu- elles. Bull. Mus. Paris, 1903, 352-364. 50 Boun, G.: Théorie nouvelle du phototropisme. Compt. rend. Acad. Sc., 1904, exxxix, 890-891. 51 Boun, G.: Attractions et oscillations des animaux marins sous l’in- fluence de la lumiére. Recherches nouvelles relatives au phototae- tisme et au phototropisme. Mém. Inst. génér. Psychol., 1905, 1, 1-111. 52 BOHN, G.: Impulsions motrices d’origine oculaire chez les crustacés. (Deuxieme mémoire relatif au phototactisme et au phototropisme.) Bull. Inst. génér. Psychol., 1905, v, 412-454. 53 Boun, G.: Intervention des réactions oscillatoires dans les tropismes. Compt. rend. Assoc. Francaise avancement des Sc., Congres de Reims, 1907, 700-706. 54 Boun, G.: Observations biologiques sur le branchellion de la torpille. Bull. Station biol. Arcachon, 1907, x, 283-296. 55 Boun, G.: Les tropismes, la sensibilité différentielle et les associations chez le branchellion de la torpille. Compt. rend. Soc. Biol., 1907, Ixiii, 545-548. 56 Boun, G.: A propos des lois de l’excitabilité par la lumiére. I. Le retour progressif 4 l’état d’immobilité, aprés une stimulation mécan- ique. Compt. rend. Soc. Biol., 1907, xiii, 655-658. 57 Boun, G.: II. Du changement de signe du phototropisme en tant que manifestation de la sensibilité différentielle. Compt. rend. Soc. Biol., 1907, lxiu, 756-759. 58 BoHn, G.: Introduction 4 la psychologie des animaux a symétrie rayonnée. I. Les états physiologiques des actinies. Bull. Inst. génér, Psychol., 1907, vii, 81-129; 135-182. 59 Boun, G.: II. Les essais et erreurs chez les étoiles de mer et les ophi- ures. Bull. Inst. génér. Psychol., 1908, viii, 21-102. : 60 Bown, G.: Les rythmes vitaux chez les actinies. Compt. rend. Assoc. Frangaise avancement des Sc., 1908, 613. 61 Boun, G.: De l’orientation chez les patelles. Compt. rend. Acad. Sc., 1909, exlviui, 863-870. 62 Boun, G.: Les variations de la sensibilité périphérique chez les ani- maux. Bull. Sc. France et Belgique, 1909, xlii, 481-519. 63 Boon, G.: Quelques problémes généraux relatifs 4 l’activité des ani- maux inférieurs. Bull. Inst. génér.-Psychol., 1909, ix, 439-466. 64 Bonn, G.: Quelques observations sur les chenilles des dunes. Bull. Inst. génér. Psychol., 1909, ix, 543-549. 65 Boun, G.: La naissance de l’intelligence. Paris, 1909. LITERATURE aly OG 66 Boun, G.: Les tropismes. Rapport VIme Congr. Internat. Psychol. Genéve, 1909, pp. 15. 67 Boun, G.: A propos les lois de l’excitabilité par la lumiére. IIT. De Vinfluence de l’éclairement du fond sur le signe des réactions vis-d- vis la lumiére. Compt. rend. Soc. Biol., 1909, Ixvi, 18-20. 68 Boun, G.: IV. Sur les changements périodiques du signe des réac- tions. Compt. rend. Soc. Biol., 1909, lxvii, 4-6. 69 Boun, G.: V. Intervention de la vitesse des réactions chimiques dans la désensibilisation par la lumiére. Compt. rend. Soc. Biol., 1910, Ixvii, 1114-1117. 70 Boon, G.: La sensibilisation et la désensibilisation des animaux. Compt. rend. Assoc. Frangaise avancement des Sc., Congres de Toulouse, 1910, 214-222. 71 Boun, G.: Quelques expériences de modification des réactions chez les animaux, sulvies de considérations sur les mécanismes chimiques de V’évolution. Bull. Sc. France et Belgique, 1911, xlv, 217-238. 72 Boun, G.: La nouvelle psychologie animale. Paris, 1911, pp. 200. 73 Boun, G.: La sensibilité des animaux aux variations de pression. Compt. rend. Acad. Sc., 1912, cliv, 240-242. 74 Boun, G.: Les variations de la sensibilité en relation avec les varia- tions de l’état chimique interne. Compt. rend. Acad. Sc., 1912, cliv, 388-391. 75 Boun, G.: L’étude des phénoménes mnémiques chez les organismes inférieurs. J. Psychol. u. Neurol., 1913, xx, 199-209. 76 Borina, E. G.: Note on the Negative Reaction Under Light Adapta- tion in the Planarian. J. Animal Behav., 1912, 11, 229-248. 77 Born, G.: Biologische Untersuchungen. Ueber den Einfluss der Schwere auf das Froschei. Arch. mikr. Anat., 1885, xxiv, 475. 78 BREUER, J.: Ueber die Funktion der Bogengiinge des Ohrlabyrinths. Med. Jahrb., 1874. 79 Breuer, J.: Beitrige zur Lehre vom statischen Sinne. Med. Jahrb., 1875. 80 BrevER, J.: Ueber die Funktion der Otolithenapparate. Arch. ges. Physiol., 1891, xlviii, 195-306. 80a BreugrR, J.: ‘Ueber den Galvanotropismus (Galvanotaxis) bei Fischen. Sitzngsb. Akad, Wiss. Wien. mathem.-naturw. K1., 1905, exiv, 27-56. 800 Breurr, J., and Kreipu, A.: Ueber die scheinbare Drehung des Gesichtsfeldes, wihrend der Einwirkung einer Centrifugalkraft. Arch. ges. Physiol., 1898, lxx, 494-510. 81 BRuCHMANN, H.: Chemotaxis der Lycopodium-Spermatozoiden. Flora, 1908-09, xcix, 193-202. 12 178 TROPISMS 82 Brun, R.: Die Raumorientierung der Ameisen und das Orientierungs- problem im allgemeinen. Jena, 1914, pp. 242. 83 BruNDIN, T. M.: Light Reactions of Terrestrial Amphipods. J. Ani- mal Behav., 1913, 111, 334-352, 84 y, BUDDENBROCK, W.: Untersuchungen iiber die Schwimmbewegungen und die Statocysten der Gattung Pecten. Sitzngsb. Heidelberger Akad. Wiss., mathem.-naturw. K1., 1911, pp. 24. 8° vy. BUDDENBROCK, W.: Ueber die Funktion der Statocysten im Sande grabender Meerestiere (Arenicola und Synapta). Biol. Centr., 1912, xxxii, 564-585, 86 vy, BUDDENBROCK, W.: Ueber die Funktion der Statocysten von Branchiomma vesiculosum. Verhandl. naturhist.-med. Vereines, Heidelberg, 1913, N.F. xii, 256-261. 87 vy, BUDDENBROCK, W.: Ueber die Orientierung der Krebse im Raum. Zool. Jahrb. Abt. Zool., 1914, xxxiv, 479-514. 88 vy. BUDDENBROCK, W.: A Criticism of the Tropism Theory of Jacques Loeb. J. Animal Behav., 1916, vi, 341-366. 89 Buuuer, A. H. R.: Contributions to Our Knowledge of the Physiology of the Spermatozoa of Ferns. Annals Bot., 1900, xiv, 543-582. 90 Burr, A. H. R.: Is Chemotaxis a Factor in the Fertilization of the Eggs of Animals? Quart. J. Micr. Sc., 1902-03, xlvi, 145-176. 91 BoYSEN-JENSEN, P.: Ueber die Leitung des phototropischen Reizes in der Avenakoleoptile. Ber. bot. Ges., 1913, xxxi, 559-566. 92 Buntina, M.: Ueber die Bedeutung der Otolithenorgane fiir die geo- tropischen Funktionen von Astacus fluviatilis. Arch. ges. Physiol., 1893, liv, 531-537. 93 CARLGREN, O.: Der Galvanotropismus und die innere Kataphorese. Z. allg. Physiol., 1905, v, 123-130. 94 CARLGREN, O.: Ueber die Einwirkung des konstanten galvanischen Stromes auf niedere Organismen. Arch. Anat. u. Physiol., Physiol. Abt., 1900, 49-76. 95 CARPENTER, F. W.: The Reactions of the Pomace Fly (Drosophila ampelophila, Loew) to Light, Gravity, and Mechanical Stimulation. Am. Nat., 1905, xxxix, 157-171. 95@ CLAPAR®DE, E.: Les tropismes devant la psychologie. J. Psychol. u. Neurol., 1908, xii, 150-160. 96 CLaRK, G. P.: On the Relation of the Otocysts to Equilibrium Phe- nomena in Gelasimus pugilator and Platyonichus ocellatus. J. Physiol., 1896, xix, 527-343. 97 CLARK, O. L.: Ueber negativen Phototropismus bei Avena sativa. Z. Bot., 1913, v, 737-770. es LITERATURE 179 98 CorHN, A., and Barratt, W.: Ueber Galvanotaxis vom Standpunkte der physikalischen Chemie. Z. allg. Physiol., 1905, v, 1-9. 99 Conn, F.: Ueber die Gesetze der Bewegung mikroskopischer Tiere und Pflanzen unter Einfluss des Lichtes. Jahr.-ber. Schles. Ges. vaterl. Kultur, 1864, xli, 35-36. 100 Coun, L. J.: The Influence of Direction vs. Intensity of Light in De- termining the Phototropie Responses of Organisms. Science, 1907, xxv, 784. 101 Conapon, E. D.: Recent Studies Upon the Locomotor Responses of Animals to White Light. J. Comp. Neurol. and Psychol., 1908, xvlil, 309-328. 102 CorneTz, V.: Ueber den Gebrauch des Ausdruckes “ tropisch ” und iiber den Charakter der Richtungskraft bei Ameisen. Arch. ges. Physiol., 1912, exlvii, 215-233. 103 Cow.ss, R. P.: Stimuli Produced by Light and by Contact with Solid Walls as Factors in the Behavior of Ophiuroids. J. Exp. Zool., 1910, ix, 387-416. 104 Cowes, R. P.: Reaction to Light and Other Points in the Behavior of the Starfish. Papers from Tortugas Lab. Carnegie Inst. Wash- ington, 1911, ii, 95-110. 105 Cowes, R. P.: The Influence of White and Black Walls on the Direction of Locomotion of the Starfish. J. Animal Behav., 1914, iv, 380-382. 105¢ Craig, W.: The Voices of Pigeons Regarded as a Means of Social Control. Am. J. Sociology, 1908, xiv, 86-100. 1050 Crarc, W.: Male Doves Reared in Isolation. J. Animal Behav., 1914, iv, 121-133. 105¢ Cratc, W.: Appetites and Aversions as Constituents of Instinets. Biol. Bull., 1918, xxxiv, 97-107. 106 Crozier, W. J.: The Orientation of a Holothurian by Light. Am. J. Physiol., 1914, xxxvi, 8-20. 107 Crozier, W. J.: The Behavior of Holothurians in Balanced I]lumina- tion. Am. J. Physiol., 1917, xliu, 510-513. 108 Crozier, W. J.: The Photoreceptors of Amphioxus. Anat. Rec., 1917, xi, 520. 108a CrozieR, W. J.: The Photie Sensitivity of Balanoglossus. J. Exp. Zool., 1917, xxiv, 211-217. 109 CzAPEK, F.: Ueber Zusammenwirken von Heliotropismus und Geo- tropismus. Sitzngsb. Akad. Wiss. Wien. mathem.-naturw. K1., 1895, civ. 110 CzapeK, F.: Untersuchungen tiber Geotropismus. Jahrb. wiss. Bot., 1895, xxvii, 243-339. 180 TROPISMS 111 CzaPEK, F.: Weitere Beitriige zur Kenntnis der geotropischen Reiz- bewegungen. Jahrb. wiss. Bot., 1898, xxxii, 175-308. 112 Date, H. H.: Galvanotaxis and Chemotaxis of Ciliate Infusoria. J. Physiol., 1901, xxvi, 291-361. 113 DAvENPORT, C. B.: Experimental Morphology. Part I. Effects of Chemical and Physical Agents Upon Protoplasm. New York, 1897. 114 Davenport, C. B., and Cannon, W. B.: On the Determination of the Direction and Rate of Movement of Organisms by Light. J. Phys- tol., 1897, xxi, 22-32. 115 Davenport, C. B., and Lewis, F. T.: Phototaxis of Daphnia. Science, 1899, ix, 368. 116 Davenport, C. B., and Perxins, H.: A Contribution to the Study of Geotaxis in the Higher Animals. J. Physiol., 1897, xxii, 99-110. 117 Day, E. C.: The Effect of Colored Light on Pigment Migration in the Eye of the Crayfish. Bull. Mus. Comp. Zool., 1911, liii, 303- 343. 118 Deuce, Y.: Etude expérimentale sur les illusions statiques et dyna- miques de direction pour servir 4 determiner les fonctions des canaux semicirculaires de J’oreille interne. Arch. Zool. expér. et génér., 1886, (2) iv. 119 DeLace, Y.: Sur une fonction nouvelle des otocystes comme organes d’orientation locomotrice. Arch. Zool. expér. et génér., 1887, (2) v, 1-26. 120 DewiTz, J.: Ueber die Vereinigung der Spermatozoen mit dem Ei. Arch. ges. Physiol., 1885, xxxvii, 219-223. 121 Dewirz, J.: Ueber Gesetzmiissigkeit in der Ortsverinderung der Spermatozoen und in der Vereinigung derselben mit dem Ei. Arch. ges. Physiol., 1886, xxxvili, 358-385. 122 Dewitz, J.: Ueber den Rheotropismus bei Tieren. Arch. Physiol., 1899 (Suppl.), 231-244. 123 Dotitey, W. L., JRr.: Reactions to Light in Vanessa antiopa, with Special Reference to Circus Movements. J. Exp. Zool., 1916, xx, 397-420. 124 DriescH, H.: Heliotropismus bei Hydroidpolypen. Zool. Jahrb., 1890, v, 147-156. 125 DriescH, H.: Die taktische Reizbarkeit der Mesenchymzellen von Echinus microtuberculatus. Arch. Entwcklngsmech., 1896, iii, 362- 380. 126 Driescu, H.: Die organischen Regulationen. Leipzig, 1901, pp. 228. 127 Pugors, R.: Sur le mécanisme des fonctions photodermatique et photogénique dans le siphon du Pholas dactylus. Compt. rend. Acad. Sc., 1889, cix, 233-235, ee LITERATURE 181 128 Dupois, R.: Sur l’action des agents modificateurs de la contraction photodermatique chez le Pholas dactylus. Compt. rend. Acad. Sc., 1898, cix, 320-322. 129 Dusors, R.: Sur la perception des radiations lumineuses par la peau, chez les Protées aveugles des grottes de la Carniole. Compt. rend. Acad. Sc., 1890, ex, 358-361. 130 Dusois, R.: Note sur l’action de la lumiére sur les echinodermes (oursin). Commun. Ime. Cong. internat. Zool., Monaco, 1913, (1), 8-9. 131 Dustin, A. P.: Le role des tropismes et de ’odogenése dans la ré- génération du systéme nerveux. Arch. Biol., 1910, xxv, 269-388. 132 ENGELMANN, T. W.: Ueber Reizung kontraktilen Protoplasmas durch plotzliche Beleuchtung. Arch. ges. Physiol., 1879, xix, 1-7. 133 HNGELMANN, T. W.: Ueber Licht- und Farbenperzeption niederster Organismen. Arch. ges. Physiol., 1882, xxix, 387-400. 134 ENGELMANN, T. W.: Bacterium photometricum. Ein Beitrag zur ver- eleichenden Physiologie des Licht- und Farbensinnes. Arch. ges. Physiol., 1882, xxx, 95-124. 135 ENGELMANN, T. W.: Ueber die Funktion der Otolithen. Zool. Anz., 1887, x, 591, 664. 136 |}NGELMANN, T. W.: Die Purpurbakterien und ihre Beziehungen zum Licht. Bot. Ztg., 1888, xlvi, 661-669, 677-689, 693-701, 709-720. 137 EneuiscH, E.: Ueber die Wirkung intermittierender Belichtungen auf Bromsilbergelatine. Arch. wiss. Phot., 1899, 1, 117-131. 138 ENGLISCH, E.: Ueber den zeitlichen Verlauf der durch das Licht verursachten Verinderungen der Bromsilbergelatine. Arch, wiss. Phot., 1900, 11, 131-134. 139 ErHarD, H.: Beitrag zur Kenntnis des Lichtsinnes der Daphniden. Biol. Centr., 1913, xxxiii, 494-496. 140 Estrerty, C. O.: The Reactions of Cyclops to Light and Gravity. Am. J. Physiol., 1907, xviii, 47-57. 141 KwaLp, J. R.: Physiologische Untersuchungen tiber das Endorgan des Nervus octavus. Wiesbaden, 1892. 142 Hwap, J. R.: Ueber die Wirkung des galvanischen Stroms bei der Lingsdurchstromung ganzer Wirbeltiere. Arch. ges. Physiol., 1894, lv, 606-621 (Berightigung, 1894, lvi, 354). 143 Hwatp, W. E.: Ueber Orientierung, Lokomotion und Lichtreaktionen einiger Cladoceren und deren Bedeutung fiir die Theorie der Trop- ismen. Biol. Centr., 1910, xxx, 1-16, 49-63, 379-399. 144 Hwap, W. E.: On Artificial Modification of Light Reactions and the Influence of Electrolytes on Phototaxis. J. Exp. Zool., 1912, xii, 591-612. 182 TROPISMS 145 Ewatp, W. E.: The Applicability of the Photochemical Energy Law to Light Reactions in Animals. Science, 1913, xxxviii, 236-237. 146 Hwap, W. E.: Ist die Lehre vom tierischen Phototropismus wider- legt? Arch. Entweklngsmech., 1913, xxxvii, 581-598. 147 Hwaup, W. E.: Versuche zur Analyse der Licht- und Farbenreak- tionen eines Wirbellosen (Daphnia pulex). Z. Sinnesphysiol., 1914, xlvili, 285-324. 148 HycLeESHYMER, A. C.: The Reactions to Light of the Decapitated Young Necturus. J. Comp. Neurol. and Psychol., 1908, xviii, 303— 308. 149 FAUVEL, P., and Boun, G.: Le rythme des marées chez les diatomées littorales. Compt. rend. Soc. Biol., 1907, Ixii, 121-123. 150 Wiapor, W.: Ueber Helio- und Geotropismus der Gramineenblitter. Ber. bot. Ges., 1905, xxiii, 182-191. 151 Wiapor, W.: Experimentelle Studien iiber die heliotropische Empfind- lichkeit der Pflanzen. Wiesner Festschrift, Wien, 1908. 152 Figpor, W.: Heliotropische Reizleitung bei Begonia-Blattern. Ann. Jardin bot. Buitenzorg., 1910 (Suppl.), i, 453-460. 153 Wiapor, W.: Ueber thigmotropische Empfindlichkeit der Asparagus- Sprosse. Sitzngsb. Akad. Wiss. Wien. mathem.-naturw. Kl. Abt. I, 19115, exxiv,: 353. 154 Witting, H.: Untersuchungen tiber den geotropischen Reizvorgang. Jahrb. wiss. Bot., 1905, xli, 221-398. 155 WLOURENS, P.: Recherches expérimentales sur les propriétés et les fonctions du systéme nerveux dans les animaux vertébrés. Paris, 1842, pp. xxvii + 516. 156 ForsSMAN, J.: Ueber die Ursachen, welche die Wachstumsrichtung der peripheren Nervenfasern bei der Regeneration bestimmen. Beitr. path. Anat., 1898, xxiv, 56-100. 157 WorssMAN, J.: Zur Kenntnis des Neurotropismus. Beitr. path. Anat., 1900, xxvii, 407-430. 158 FRANDSEN, P.: Studies on the Reactions of Limax maximus to Diree- tive Stimuli. Proc. Am. Acad. Arts and Sc., 1901, xxxvu, 185-227. 159 Franz, V.: Phototaxis und Wanderung. Nach Versuchen mit Jung- fischen und Fischlarven. Int. Rev. ges. Hydrobiol. u. Hydrographie, 1910, iii, 306-334. 160 Franz, V.: Beitriige zur Kenntnis der Phototaxis. Nach Versuchen an Siisswassertieren. Int. Rev. ges. Hydrobiol. u. Hydrographie, Biol. Suppl. (2), 1911, 1-11. 161 Franz, V.: Weitere Phototaxisstudien. I. Zur Phototaxis bei Fischen. II. Phototaxis bei marinen Crustaceen. III. Phototak- tische Lokomotionsperioden bei Hemimysis. Int. Rev. ges. Hydro- biol. u. Hydrograpiie, Biol. Suppl. (3), 1911, 1-23. LITERATURE © 183 162 Franz, V.: Zur Frage der vertikalen Wanderungen der Planktontiere. Arch. Hydrobiol. u. Planktonkunde, 1912, vii, 493-499. 163 Franz, V.: Die phototaktischen Erscheinungen im Tierreiche und ihre Rolle im Freileben der Tiere. Zool, Jahrb., 1913, xxxiii, 259- 286. 164 y, Friscu, K.: Ueber farbige Anpassung bei Fischen. Zool. Jahrb., 1912, xxxu, 171-230. 165 y, Frisco, K.: Sind die Fische farbenblind? Zool. Jahrb., 1912, xxxlil, 107-126. 166 y, Friscu, K.: Ueber die Farbenanpassung des Crenilabrus. Zool. Jahrb., 1912, xxxiil, 151-164. 167 vy, Frisco, K.: Weitere Untersuchungen iiber den Farbensinn der Fische. Zool. Jahrb., 1913, xxxiv, 43-68. 168 y, FriscuH, K.: Der Farbensinn und Formensinn der Biene. Zool. Jahrb., 1914, xxxv, 1-182. 169 y, Friscu, K., and Kupetwieser. H.: Ueber den Einfiuss der Licht- farbe auf die phototaktischen Reaktionen niederer Krebse. Biol. Centr., 1913, xxxiii, 517-552. 170 FROHLICH, F. W.: Vergleichende Untersuchungen iiber den Licht- und Farbensinn. Deutsch. med. Wehnschr., 1913, xxxix, 1453-1456. 171 FrROScHEL, P.: Untersuchung iiber die heliotropische Prisentations- zeit. I. Sitzngsb. Akad. Wiss. Wien. mathem.-naturw. Kl, 1908, exvil, 235-256. 172 FROSCHEL, P.: Untersuchung iiber die heliotropische Priisentations- zeit. II. Sitzngsb. Akad. Wiss. Wien. mathem.-naturw. Kl., 1909, exvill, 1247-1294. 173 Fucus, R. F.: Der Farbenwechsel und die chromatische Hautfunk- tion der Tiere. Winterstein’s Handb. vergl. Physiol., 1914, iu, I. Halfte 2, 1189-1656. 174 GaLIANO, E. F.: Beitrag zur Untersuchung der Chemotaxis der Para- mecien. Z, allg. Physiol., 1914, xvi, 359-372. 175 Garrey, W. E.: The Effect of Ions Upon the Aggregation of Flagel- lated Infusoria. Am. J. Physiol., 1900, 111, 291-315. 176 Garry, W. E.: A Sight Reflex Shown by Sticklebacks. Biol. Bull, 1905, vii, 79-84. 177 Garrey, W. E.: Proof of the Muscle Tension Theory of Heliotropism. Proc. Nat. Acad. Sc., 1917, iii, 602-609. 178 Gourz, F.: Ueber die Verrichtungen des Grosshirns. I-V. Arch. ges. Physiol., 1876, xiii, 144; 1877, xiv, 412-443; 1879, xx, 1-54; 1881, xxvi, 149; 1884, xxxiv, 450-505. 179 GRABER, V.: Fundamentalversuche iiber die Helligkeits- und Farben- empfindlichkeit augenloser und geblendeter Tiere. Sitzngsb. Akad. Wiss. Wien, 1883, lxxxvii, 201-236. 184 TROPISMS 180 Graper, V.: Grundlinien zur Erforschung des Helligkeits- und Far- bensinnes der Tiere. Leipzig, 1884, pp. vii +322. 181 Graper, V.: Ueber die Helligkeits- und Farbenempfindlichkeit einiger Meertiere. Sitzngsb. Akad. Wiss. Wien., 1885, xci. 182 GraBeR, V.: Thermische Experimente an der Kiichenschabe (Peri- planeia orientalis). Arch. ges. Physiol., 1887, xli, 240-256. 183 Groom, T. T., and Logs, J.: Der Heliotropismus der Nauplien von Balanus perforatus und die periodischen Tiefenwanderungen pelag- ischer Tiere. Biol. Centr., 1890, x, 160-177. 184 Gross, A. O.: The Reactions of Arthropods to Monochromatie Lights of Equal Intensities. J. Hap. Zool., 1913, xiv, 467-514. 185 TTABERLANDT, G.: Ueber die Perzeption des geotropischen Reizes. Ber. bot. Ges., 1900, xviii, 261-272. 186 HapiEy, P. B.: The Relation of Optical Stimuli to Rheotaxis in the American Lobster (Homarus americanus). Am. J. Physiol., 1906, xvii, 326-343. 187 Hapuey, P. B.: Galvanotaxis in Larve of the American Lobster (Homarus americanus). Am. J. Physiol., 1907, xix, 39-52. 188 Hap.ey, P. B.: The Reaction of Blinded Lobsters to Light. Am. J. Physiol., 1908, xxi, 180-199. 189 HapLey, P. B.: Reactions of Young Lobsters Determined by Food Stimuli. Science, 1912, xxxv, 1000-1002. 190 Harper, E. H.: Reactions to Light and Mechanical Stimuli in the Earthworm, Pericheta bermudensis (Beddard). Biol. Bull., 1905, x, 17-34. 161 }Tarper, EK. H.: Tropic and Shock Reactions in Pericheta and Lum- bricus. J. Comp. Neurol. and Psychol., 1909, xix, 569-587. 192 Harper, E. H.: The Geotropism of Paramecium. J. Morphol., 1911, xx1l, 993-1000. 193 Harper, E. H.: Magnetic Control of Geotropism in Paramecium. J. Animal Behav., 1912, ii, 181-189. 194 FARRINGTON, N. R., and LeaminG, E.: The Reaction of Ameba to Lights of Different Colors. Am. J. Physiol., 1899, iii, 9-18. 195 Haseman, J. D.: The Rhythmical Movements of Littorina littorea Synchronous with Ocean Tides. Biol. Bull., 1911, xxi, 113-121. 196 HAUSMANN, W.: Die photodynamische Wirkung des Chlorophylls und ihre Beziehung zur photosynthetischen Assimilation der Pflan- zen. Jahrb. wiss. Bot., 1909, xlvi, 599-623. 197 HreLtmMHouTzZ, H.: Handbuch der physiologischen Optik. Hamburg, 1909-11, 3. Kd. 198 Henri, Mme. V., and Henri, V.: Excitation des organismes par les rayons ultra-violets. Compt. rend. Soc. Biol., 1912, xxii, 992-996 ; Ixxil, 326-327. LITERATURE 185 199 Tenet, V., and LARGUIER DES BANCELS, J.: Photochimie de la rétine. J. Physiol. et Path. génér., 1911, xiii, 841-856. 200 Henri, V., and LARGUIER DES BANCELS, J.: Un nouveau type de temps de réaction. Compt. rend. Soc. Biol., 1912, xxiii, 55-56. 201 HENRI, V., and LARGUIER DES BANCELS, J.: L’excitation provoquée par les rayons ultra-violets comparée avec les excitations visuelle et nerveuse, d’une part, et les réactions photochimiques, d’autre. Lois des phénoménes. Compt. rend. Soc. Biol., 1912, 1xxiii, 328-329. 202 Henri, V., and LArRGUIER DES BANCELS, J.: Sur l’interprétation des lois de Weber et de Jost: recherches sur les réactions des Cyclops ex- posées & la lumiére ultra-violette. Arch. Psychol., 1912, xii, 329-342. 203 Hrerpst, C.: Ueber die Bedeutung der Reizphysiologie fiir die kausale Auffassung von Vorgiingen in der tierischen Ontogenese. I. Biol. Centr., 1894, xiv, 657-666, 689-697, 727-744, 753-771, 800-810. 204 TlerMANN, L.: Eine Wirkung galvanischer Strome auf Organismen. Arch. ges. Physiol., 1885, xxxvii, 457-460. 205 HERMANN, L.: Weitere Untersuchungen iiber das Verhalten der Froschlarven im galvanischen Strome. Arch. ges. Physiol., 1886, xxxix, 414419. 205¢ TIERMANN, L., and Marruias, F.: Der Galvanotropismus der Larven von Rana temporaria und der Fische. Arch. ges. Physiol., 1894, lvui, 391-405. 206 Herms, W. B.: The Photie Reactions of Sacrophagid Flies, Espe- cially Lucilia caesar Linn. and Calliphora vormitoria Linn. J. Exp. Zool., 1911, x, 167-226. 207 Herter, E.: Ueber die Beeinflussung des Organismus durch Licht, speciell durch die chemisch wirksamen Strahlen. Z. allg. Physiol., 1904, iv, 1-43. 208 HerteL, E.: Ueber physiologische Wirkung von Strahlen verschie- dener Wellenliinge. Z. allg. Physiol., 1905, v, 95-122. 209 Hess, C.: Untersuchungen iiber den Lichtsinn bei Fischen. Arch. Augenheilk., 1909, Ixiv, 1-38. 210 Huss, C.: Untersuchungen tiber den Lichtsinn bei wirbellosen Tieren. Arch. Augenheilk., 1909, lxiv, 39-61. 211 Huss, C.: Neue Untersuchungen itiber den Lichtsinn bei wirbellosen Tieren. Arch. ges. Physiol., 1910, exxxvi, 282-367. 212 Huss, C.: Experimentelle Untersuchungen zur vergleichenden Physi- ologie des Gesichtssinnes. Arch. ges. Physiol., 1911, exlii, 405-446. 213 Hess, C.: Der Gesichtssinn. Wéinterstein’s Handb. vergl. Physiol., 1912, iv, 555-840. 214 Hess, C.: Neue Untersuchungen zur vergleichenden Physiologie des Gesichtsinnes. Zool. Jahrb. Abt. Zool., 1913, xxxiii, 387-440. 186 TROPISMS 215 Hess, C.: Experimentelle Untersuchungen iiber den angeblichen Far- bensinn der Bienen. Zool. Jahrb. Abt. Zool., 1913, xxxiv, 81-106. 216 Hess, C.: Eine neue Methode zur Untersuchung des Lichtsinnes bei Krebsen. Arch. vergl. Ophthalmol., 1913-14, iv, 52-67. 217 Hess, C.: Untersuchungen iiber den Lichtsinn mariner Wiirmer und Krebse. Arch. ges. Physiol., 1914, elv, 421-435. 218 Huss, C.: Untersuchungen iiber den Lichtsinn bei Echinodermen. Arch. ges. Physiol., 1914, elx, 1-26. 219 Hess, C.: Messende Untersuchung des Lichtsinnes der Biene. Arch. ges. Physiol., 1916, elxiii, 289-320. 220 Hesse, R.: Untersuchungen iiber die Organe der Lichtempfindung bei niederen Tieren. I. Die Organe der Lichtempfindung bei den Lubri- eiden. Z. wiss. Zool., 1896, Ixi, 393-419. 221 Hesse, R.: IJ. Die Augen der Plathelminthen, insonderheit der trikladen Turbellarien. Z. wiss. Zool., 1897, 1xi1, 527-582. 222 Hess, R.: TV. Die Sehorgane des Amphiorus. Z. wiss. Zool., 1898, Ixi, 456-464. 223 Tlmsse, R.: Die Lichtempfindung des Amphiorus. Anat. Anz., 1898, xiv, 556. 224 Hoayes, A.: Der Nervenmechanismus der assoziierten Augenbewe- gungen. I-III. Mitt. mathem.-naturw. Kl. Ungar. Akad. Wiss. Budapest, 1881, x, 1-62; xi, 1-100. (Ref. Biol. Centr., 1881-82, 1, 216-220.) 225 Houtmes, 8. J.: Phototaxis in the Amphipoda. Am. J. Physiol., 1901, v, 211-234. 226 HoumEs, 8. J.: Phototaxis in Volvox. Biol. Bull., 1903, iv, 319-326. 227 Houtmes, 8. J.: The Selection of Random Movements as a Factor in Phototaxis. J. Comp. Neurol. and Psychol., 1905, xv, 98-112. 228 HouMEs, S. J.: The Reactions of Ranatra to Light. J. Comp. Neurol. and Psychol., 1905, xv, 305-349. 229 HoumeEs, 8. J.: Observations on the Young of Ranatra quadridentata Stal. Biol. Bull., 1907, xu, 158-164. 230 HoutmEs, S. J.: Phototaxis in Fiddler Crabs and Its Relation to Theories of Orientation. J. Comp. Neurol. and Psychol., 1908, xvill, 493-497. 231 HoumeEs, 8. J.: Description of a New Species of Hubranchipus from Wisconsin with Observations on Its Reaction to Light. Trans. Wis. Acad. Sc., Arts and Letters, 1910, xvi, pt. II, 1252-1255. . 232 FHiotmgs, S. J.: Pleasure, Pain and the Beginnings of Intelligence. J. Comp. Neurol. and Psychol., 1910, xx, 145-164. 233 HoumeEs, 8. J.: Evolution of Animal Intelligence. New York, 1911, pp. 296. LITERATURE 187 234 Houtmes, 8. J.: The Reactions of Mosquitoes to Light in Different Periods of Their History. J. Animal Behav., 1911, i, 29-32. 235 Houmes, 8. J.: The Beginnings of Intelligence. Science, 1911, xxxiii, 473-480. _#236 Hotmes, 8. J.: The Tropisms and Their Relation to More Complex Modes of Behavior. Bull. Wis. Nat. Hist. Soc., 1912, x, 13-23. 237 Houmes, S. J.: Phototaxis in the Sea Urchin, Arbacia punctulata. . J. Animal Behav., 1912, ii, 126-136. 238 Houimes, S. J.: Studies in Animal Behavior. Boston, 1916, pp. 266. 239 Hotes, S. J., and McGraw, K. W.: Some Experiments on the Method of Orientation to Light. J. Animal Behav., 1913, in, 367-373. 240 Hout, E. B., and Ler, F. §.: The Theory of Phototactic Response. Am. J. Physiol., 1901, iv, 460-481. 241 Howarp, L. O.: Butterflies Attracted to Light at Night. Proc. Ent. Soc., Washington, 1889, iv. 242 Tnyin, P.: Das Gehdrbliischen als Gleichgewichtsorgan bei den Ptero- tracheide. Centr. Physiol., 1900, xiii, 691-694. 243 Jackson, H. H. T.: The Control of Phototactie Reactions in Hyalella by Chemicals. J. Comp. Neurol. and Psychol., 1910, xx, 259-263. 244 Jennines, H. S.: Studies on Reactions to Stimuli in Unieellular Organisms. I. Reactions to Chemical, Osmotic and Mechanical Stimuli in the Ciliate Infusoria. J. Physiol., 1897, xxi, 258-322. 245 Jenninas, H. S.: II. The Mechanism of the Motor Reactions of Paramecium. Am. J. Physiol., 1899, 11, 311-341. 246 Jennines, H.S.: III. Reactions to Localized Stimuli in Spirostomum and Stentor. Am. Nat., 1899, xxxiii, 373-389. 247 Jenninas, H. S.: V. On the Movements and Motor Reflexes of the Flagellata and Ciliata. Am. J. Physiol., 1900, iii, 229-260. 248 Jmenninas, H. S.: VI. On the Reactions of Chilomonas to Organic Acids. Am. J. Physiol., 1900, ii, 397-403. 249 Jmnnines, H. S., and Crospy, J. H.: VII. The Manner in Which Bacteria React to Stimuli, Especially to Chemical Stimuli. Am. J. Physiol., 1901, vi, 31-37. 250 Jennines, H. S., and Moors, E. H.: VIII. On the Reactions of Infusoria to Carbonic and Other Acids, with Especial Reference to the Causes of the Gatherings Spontaneously Formed. Am. J. Physiol., 1902, vi, 233-250. 251 Jenninas, H. S.: Contributions to the Study of the Behavior of Lower Organisms. Carnegie Institution of Washington, Pub. No. 16, 1904, pp. 256, 81 figs. 188 TROPISMS 252 JENNINGS, H. S.: Modifiability in Behavior. II. Factors Determin- ing Direction and Character of Movement in the Earthworm. J. Exp. Zool., 1906, iii, 435-455. 253 JENNINGS, H. S.: Behavior of the Lower Organisms. New York, 1906, pp. xiv + 366. 254 JENNINGS, H. S.: The Interpretation of the Behavior of the Lower Organisms. Science, 1908, xxvii, 698-710. 255 JenninGs, H. 8.: Tropisms. Rapport VIme Congr. Internat. Psy- chol. Genéve, 1909, pp. 20. 255a JENSEN, P.: Ueber den Geotropismus niederer Organismen. Arch. ges. Physiol., 1893, lin, 428-480. 256 JorDAN, H.: Rheotropic Responses of Epinephelus striatus Bloch. Am. J, Physiol., 1917, xlii, 438-454. 257 JorpAN, H.: Integumentary Photosensitivity in a Marine Fish, EH pi- nephelus striatus Bloch. Am. J. Physiol., 1917, xliv, 259-274. 258 Jupay, C.: The Diurnal Movement of Plancton Crustacea. Trans. Wis. Acad. Sc., Arts and Letters, 1904, xiv, 534-568. 259 Karka, G.: Einfiihrung in die Tierpsychologie. I. Die Sinne der Wirbellosen. Leipzig, 1914, xiit594. 260 Kanpa, 8.: On the Geotropism of Paramecium and Spirostomum. Biol. Bull., 1914, xxvi, 1-24. 261 Kanpa, §.: The Reversibility of the Geotropism of Arenicola Larve by Salts. Am. J. Physiol., 1914, xxxv, 162-176. 262 Kanpa, 8.: Geotropism in Animals. Am. J. Psychol., 1915, xxvi, 417-427. 263 KanpA, §.: Studies on the Geotropism of the Marine Snail, Littorina littorea. Biol. Bull., 1916, xxx, 57-84. 264 Kanpa, S.: The Geotropism of Freshwater Snails. Biol. Bull., 1916, xxx, 85-97. 264¢ Kanpa, S.: Further Studies on the Geotropism of Paramecium caudatum. Biol. Bull., 1918, xxxiv, 108-119. 265 Kruioac, V. L.: Some Insect Reflexes. Science, 1903, xviii, 693-696. 266 KeLioac, V. L.: Some Silkworm Moth Reflexes. Biol. Bull., 1907, xii, 152-154. 267 Kniep, H.: Untersuchungen iiber die Chemotaxis von Bakterien. Jahrb. wiss. Bot., 1906, xl, 215-270. 268 KRANICHFELD, H.: Zum Farbensinn der Bienen. Biol. Centr., 1915, xxxv, 39-46. 269 KrECKER, F. H.: Phenomena of Orientation Exhibited by Ephe- meride. Biol. Bull., 1915, xxix, 381-388. 270 KreipL, A.: Weitere Beitriige zur Physiologie des Ohrlabyrinthes. Sitzengsb. Akad. Wiss. Wien, mathem.-naturw. Kl., 1892, ci, 469- 480; 1893, cii, 149-174. LITERATURE 189 271 Kriss, H. G.: The Reactions of Molosoma to Chemical Stimuli. J. Exp. Zool., 1910, viii, 43-74. 272 KUnne, W.: Untersuchungen iiber das Protoplasma und die Kon- tractilitit. Leipzig, 1864, pp. 158. 273 KijwNE, W.: Chemische Vorgiinge in der Netzhaut. Hermann’s Handb. Physiol., 1879, iii, pt. 1, 235-342. 274 Kusano, S.: Studies on the Chemotactie and Other Related Reactions of the Swarmspores of Myxomycetes. J, Coll. Agriculture, Imp. Univ. Tokyo, 1909, ii. 275 LASAREFF, P.: Ionentheorie der Nerven- und Muskelreizung. Arch. ges. Physiol., 1910, exxxv, 196-204. 276 LAURENS, H.: The Reactions of Amphibians to Monochromatic Lights of Equal Intensity. Bull. Mus. Comp. Zool., 1911, xlii, 253-302, 277 LAURENS, H.: The Reactions of Normal and Eyeless Amphibian Larve to Light. J. Exp. Zool., 1914, xvi, 195-210. 278 Ler, F. §.: A Study of the Sense of Equilibrium in Fishes. I. J. Physiol., 1893, xv, 311-348. 279 Len, F. S.: A Study of the Sense of Equilibrium in Fishes. II. J. Physiol., 1894-95, xvii, 192-210. 280 Tiprorss, B.: Ueber den Chemotropismus der Pollenschlauche. Ber. bot. Ges., 1899, xvii, 236-242. 281 Liprorss, B.: Ueber die Reizbewegungen der Marchantia-Spermato- zoiden. Jahrb. wiss. Bot., 1905, xl, 65-87. 282 L.prorss, B.: Ueber die Chemotaxis eines Thiospirillum. Ber. bot. Ges., 1912, xxx, 262-274. 283 Linuin, F. R.: Studies of Fertilization. V. The Behavior of the Spermatozoa of Nereis and Arbacia with Special Reference to Egeg-extractives. J. Hap. Zool., 1913, xiv, 515-574. 284 Lorp, J.: Beitrige zur Physiologie des Grosshirns. Arch. ges. Physiol., 1886, xxxix, 265-346. 285 Lonp, J.: Die Orientierung der Tiere gegen das Licht (tierischer Heliotropismus). Sitzngsb. Wiirzb. physik.-med. Ges., 1888. 286 Lors, J.: Die Orientierung der Tiere gegen die Schwerkraft der Erde (tierischer Geotropismus). Sitzngsb. Wiirzb. physik.-med. Ges., 1888. 287 Logg, J.: Der Heliotropismus der Tiere und seine Uebereinstimmung mit dem Heliotropismus der Pflanzen. Wiirzburg, 1889, pp. 118. 288 Lorp, J.: Weitere Untersuchungen iiber den Heliotropismus der Tiere und seine Uebereinstimmung mit dem Heliotropismus der Pflanzen. (Heliotropische Kriimmungen bei Tieren). Arch. ges. Physiol., 1890, xlvii, 391-416. 190 TROPISMS 289 Lorn, J.: Ueber Geotropismus bei Tieren. Arch. ges. Physiol., 1891, xlix, 175-189. 290 Logs, J.: Ueber den Anteil des Hérnerven an den nach Gehirnver- letzung auftretenden Zwangsbewegungen, Zwangslagen und assozi- ierten Stellungsinderungen der Bulbi und Extremititen. Arch. ges. Physiol., 1891, 1, 66-83. 290a Lors, J.: Untersuchungen zur physiologischen Morphologie der Tiere. I. Heteromorphose. II. Organbildung und Wachstum. Wiirzburg, 1891-1892. 291 Logs, J.: Ueber kiinstliche Umwandlung positiv heliotropischer Tiere in negativ heliotropische und umgekehrt. Arch. ges. Physiol., 1893, liv, 81-107. 292 Lors, J.: Zur Theorie der physiologischen Licht- und Schwerkraft- wirkungen. Arch. ges. Physiol., 1897, lxvi, 439-466. 293 Lors, J.: Comparative Physiology of the Brain and Comparative Psychology. New York, 1900, x+309. 294 Lors, J.: Studies in General Physiology. Chicago, 1905, 2 vols., x +782. 295 Lors, J.: The Dynamics of Living Matter. New York, 1906, xi+ 233. 296 Lors, J.: Ueber die Erregung von positivem Heliotropismus durch Sdure, insbesondere Kohlensiure und von negativem Helio- tropismus durch ultraviolette Strahlen. Arch. ges. Physiol., 1906, exv, 564-581. 297 Lorn, J.: Concerning the Theory of Tropisms. J. Exp. Zool., 1907, iv, 151-156. 298 Lors, J.: Ueber die Summation heliotropischer und geotropischer Wirkungen bei den auf der Drehscheibe ausgelosten kompensa- torischen Kopfbewegungen. Arch. ges. Physiol., 1907, exvi, 368- 374. 299 Logs, J.: Chemische Konstitution und physiologische Wirksamkeit von Alkoholen und Siéuren. II. Biochem. Z., 1909, xxii, 93-96. 300 Lorn, J.: Die Tropismen. Woéinterstein’s Handb. vergl. Physiol.,- 1911, iv, 451-519. 301 Lorp, J.: The Mechanistie Conception of Life. Chicago, 1912, pp. 232. 302 Lozs, J.: On the Nature of the Conditions Which Determine or Prevent the Entrance of the Spermatozoon into the Egg. Am. Nat., 1915, xlix, 257-285. 303 Logs, J.: The Organism as a Whole. From a Physico-chemical View- point. New York, 1916, pp. 379. LITERATURE on 303¢ Loup, J.: The Chemical Basis of Regeneration and Geotropism. Science, 1917, xlvi, 115-118. 3030 Lorns, J.: Influence of the Leaf upon Root Formation and Geo- tropic Curvature in the Stem of Bryophyllum calycinum and the Possibility of a Hormone Theory of These Processes. Bot. Gaz., 1917, lxii, 25-50. 303¢ Lors, J.: The Chemical Mechanism of Regeneration. Ann. Inst. Pasteur, 1918, xxxii, 1-16. 304 Lors, J., and Bupcerr, 8. P.: Zur Theorie des Galvanotropismus. IV. Ueber die Ausscheidung electropositiver Ionen an der iiusseren Anodenfliiche protoplasmatischer Gebilde als Ursache der Abwei- chungen vom Pfliiger’schen Erregungsgesetz. Arch. ges. Physiol., 1897, Ixv, 518-534. 305 Lors, J.. and Ewaup, W. F.: Ueber die Giiltigkeit des Bunsen- Roscoe’schen Gesetzes fiir die heliotropische Erscheinung bei Tieren. Centr. Physiol., 1914, xxvii, 1165-1168, 306 Logs, J., and GArrey, W. E.: Zur Theorie des Galvanotropismus. II. Versuche an Wirbeltieren. Arch. ges. Physiol., 1896, lxv, 41-47. 307 Logs, J., and Maxwe.t, 8. §.: Zur Theorie des Galvanotropismus. Arch. ges. Physiol., 1896, xiii, 121-144. 308 Logs, J.. and MAxweELL, 8. 8.: Further Proof of the Identity of Heliotropism in Animals and Plants. Univ. Cal. Pub. Physiol., 1910, iui, 195-197. 309 Lorn, J., and Norrurop, J. H.: Heliotropic Animals as Photometers on the Basis of the Validity of the Bunsen-Roscoe Law for Helio- tropic Reactions. Proc. Nat. Acad. Sc., 1917, iti, 539-544. 310 Lors, J.. and WASTENEYS, H.: On the Identity of Heliotropism in Animals and Plants. Proc, Nat. Acad. Sc., 1915, 1, 44-47; Science, 1915, xli, 328-330. 311 Lors, J.. and WASTENEYS, H.: The Relative Efficiency of Various Parts of the Spectrum for the Heliotropic Reactions of Animals and Plants. J. Exp. Zool., 1915, xix, 23-35; 1916, xx, 217-236. 312 Lors, J.,.and WASTENEYS, H.: A Re-examination of the Applicability of the Bunsen-Roscoe Law to the Phenomena of Animal Heliotrop- ism. J. Exp. Zool., 1917, xxu, 187-192. 313 Louner, L.: Untersuchungen tiber den sogenannten Totstellreflex der Arthropoden. Z. allg. Physiol., 1914, xvi, 373-418. 314 Luppock, J.: On the Sense of Color Among Some of the Lower Animals. I and II. J. Linn. Soe. (Zool.), 1881, xvi, 121-127; 1882, xvii, 205-214. 315 Luppock, J.: On the Senses, Instincts and Intelligence of Animals, with Special Reference to Insects. Internat. se. Series, London, 1899. 192 TROPISMS 316 Luppock, J.: Ants, Bees and Wasps. New York, 1904, xiiit435. 317 LupLorr, K.: Untersuchungen iiber den Galvanotropismus. Arch. ges. Physiol., 1895, lix, 525-554. 318 Lyon, E. P.: The Functions of the Otocyst. J. Comp. Neurol. and Psychol., 1898, vii, 238-245. 319 Lyon, E. P.: A Contribution to the Comparative Physiology of Com- pensatory Motions. Am. J. Physiol., 1899, ii, 86-114. 320 Lyon, E. P.: Compensatory Motions in Fishes. Am. J. Physiol., 1900, iv, 77-82. 321 Lyon, E. P.: On Rheotropism. I. Rheotropism in Fishes. Am. J. Physiol., 1904, xii, 149-161. 322 Lyon, E. P.: Rheotropism in Fishes. Biol. Bull., 1905, viii, 238-239. 323 Lyon, E. P.: On the Theory of Geotropism in Paramecium. Am. J. Physiol., 1905, xiv, 421-432. 324 Lyon, E. P.: Note on the Geotropism of Arbacia Larve. Biol. Bull., 1906, xii, 21-22. 325 Lyon, E. P.: Note on the Heliotropism of Palemonetes Larve. Biol. Bull., 1906, xii, 23-25. 326 Lyon, E. P.: On Rheotropism. II. Rheotropism of Fish Blind in One Eye. Am. J. Physiol., 1909, xxiv, 244-251, 326a Lyon, E. P.: Note on the Geotropism of Paramecium. Biol. Bull., 1918, xxxiv, 120. 3260 MCCLENDON, J. F.: Protozoan Studies. J. Exp. Zool., 1909, vi, 265— 283. 327 MacCurpy, H.: Some Effects of Sunlight in the Starfish. Science, 1913, xxxvi, 98-100. 3274 McEWwEN, R. S.: The Reactions to Light and to Gravity in Droso- phila and its Mutants. J. Exp. Zool., 1918, xxv, 49-106. 328 McGinnis, M. O.: Reactions of Branchipus serratus to Light, Heat and Gravity. J. Exp. Zool., 1911, x, 227-240. 329 Macu, E.: Physikalische Versuche iiber den Gleichgewichtssinn des Menschen. Sitzngsb. Akad. Wiss. Wien., 1873, xviii; 1874, Ixix. 330 Macu, E.: Grundlinien der Lehre von den Bewegungsempfindungen. Leipzig, 1875, pp. 127. 331 Macu, E.: Beitriige zur Analyse der Empfindungen. Jena, 1902. 332 Maanus, R.: Welche Teile des Zentralnervensystems miissen fiir das Zustandekommen der tonischen Hals- und Labyrinthreflexe auf die Korpermuskulatur vorhanden sein? Arch. ges. Physiol., 1914, clix, 224-250. 333 Macnus, R., and De Kuersn, A.: Die Abhingigkeit des Tonus der Extremitiitenmuskeln von der Kopfstellung. Arch. ges. Physiol., 1912, exlv, 455-548. LITERATURE 193 334 Maenus, R., and De Kuertsn, A.: Die Abhingigkeit des Tonus der Nackenmuskeln von der Kopfstellung. Arch. ges. Physiol., 1912, exlvun, 4035-416, 335 Maanus, R., and De Kirin, A.: Die Abhiingigkeit der Korperstel- lung vom Kopfstande beim normalen Kaninchen. Arch. ges. Physiol., 1913, eliv, 163-177. 336 Maanus, R., and De Kuen, A.: Analyse der Folgezustinde einsei- tiger Labyrinthexstirpation mit besonderer Beriicksichtigung der Rolle der tonischen Halsreflexe. Arch. ges. Physiol., 1913, cliv, 178-306. 337 MaGnus, R., and vAN LEEUWEN, W. S.: Die akuten und die dauernden Folgen des Ausfalles der tonischen Hals- und Labyrinthreflexe. Arch. ges. Physiol., 1914, elix, 157-217. 338 Maanus, R., and Wor, C. G. L.: Weitere Mitteilungen iiber den Einfluss der Kopfstellung auf den Gliedertonus. Arch. ges. Phys- tol., 1913, exlix, 447-461. 339 MarcHat, P.: Le retour au nid chez le Pompilus sericeus V. d. L. Compt. rend. Soc. Biol., 1900, lu, 1113-1115, 340 Massarv, J.: Recherches sur les organismes inférieurs. I. La loi du Weber vérifiée pour Vhéhotropisme du champignon. Bull. Acad. Roy. Belg., 1888, (3) xvi, 590. 341 Massarr, J.: Sur Virritabilité des spermatozoides dans l’oeuf de la grenouille. Bull. Acad. Roy. Belg., 1888, (3) xv; 1889, xviii. 342 Massart, J.: La sensibilité tactile chez les organismes inférieurs. J. Soc. Roy. Sc. med, et nat., Bruxelles, 1890. 343 Massarrt, J.: Recherches sur les organismes inférieurs. III. La sensi- bilité & la gravitation. Bull. Acad. Roy. Belg., 1891, (3) xxu, 158-167. 344 Massarv, J.: Essai de classification des réflexes non-nerveux. Ann. Inst. Pasteur, 1901, xv, 635-672. 345 Massart, J.: Versuch einer Einteilung der nichtnervésen Reflexe. Biol. Centr., 1902, xxii, 9-23. 346 Mast, S. O.: Light and the Behavior of Organisms. New York, 1911, pp. 410-++xi. “#7 Mast, S. O.: Behavior of Fire-flies (Photinus pyralis?) with Special Reference to the Problem of Orientation. J. Animal Behav., 1912, 11, 256-272. 348 Mast, S. O.: The Relation between Spectral Color and Stimulation in the Lower Organisms. J. Exp. Zool., 1917, xxi, 471-528. 348¢ Marunta, J.: Untersuchungen iiber die Funktionen des Zentral- nervensystems bei Insekten. Arch. ges. Physiol., 1911, exxxviii, 388-456. 13 194 TROPISMS 349 MaxwELL, 8. S.: Beitriige zur Gehirnphysiologie der Anneliden. Arch. ges. Physiol., 1897, |xvii, 263-297. 350 MAXWELL, 8. S.: Experiments on the Functions of the Internal Ear. Univ. Cal. Pub. Physiol., 1910, iv, 1-4. °91 Maygr, A. G., and Sour, C. G.: Some Reactions of Caterpillars and Moths. J. Exp. Zool., 1906, i, 415-433. 352 MENDELSSOHN, M.: Ueber den Thermotropismus einzelliger Organ- ismen. Arch, ges. Physiol., 1895, lx, 1-27. 353 MENDELSSOHN, M.: Recherches sur la thermotaxie des organismes unicellulaires. J. Physiol. et Path. génér., 1902, iv, 393-409. 354 MENDELSSOHN, M.: Recherches sur |’interférenece de la thermotaxie avee d’autres tactismes et sur le mécanisme du mouvement thermo- tactique. J. Physiol. et Path. génér., 1902, iv, 475-488. 355 MENDELSSOHN, M.: Quelques considérations sur la nature et le réle biologique de la thermotaxie. J. Physiol. et Path. génér., 1902, iv, 489-496. 356 MENKE, H.: Periodische Bewegungen und ihr Zusammenhang mit Licht und Stoffwechsel. Arch. ges. Physiol., 1911, exl, 37-91. 357 MeREJKOWSKY, C. pe: Les erustacés inférieurs distinguent-ils les couleurs? Compt. rend, Acad. Sc., 1881, xeii, 1160-1161. 358 MriuuER, F. R.: Galvanotropism in the Crayfish. J. Physiol., 1907, xxxv, 215-229. 359 MINKIEwIcz, R.: Sur le chromotropisme et son inversion artificielle. Compt. rend. Acad. Sc., 1906, exlii, 785-787. 360 MInKIEwicz, R.: Le réle des phénoménes chromotropiques dans Vétude des problémes biologiques et psycho-physiologiques. Compt. rend. Acad. Sc., 1906, exliii, 934-935. 361 Minktewicz, R.: Une expérience sur la nature du chromotropisme chez les némertes. Compt. rend. Acad. Sc., 1912, elv, 229-231. 362 Mirsuxuri, K.: Negative Phototaxis and Other Properties of Lit- torina as Factors in Determining Its Habitat. Amnnotationes Zoologica Japonenses, 1901, iv, 1-19. 363 Mouiscu, H.: Untersuchungen iiber den Hydrotropismus. Sitzngsb. Akad. Wiss. Wien. mathem.-naturw. Kl., 1883. 364 Moorr, ANNE: Some Facts Concerning Geotropic Gatherings of Paramacia. Am. J. Physiol., 1903, ix, 238-244. 365 Moorr, A. R.: On the Righting Movements of the Starfish. Bzrol. Bull., 1910, xix, 235-239. 366 Moore, A. R.: Concerning Negative Phototropism in Daphnia pulex. J. Exp. Zool., 1912, xiii, 573-575. 387 Moorg, A. R.: Negative Phototropism in Diaptomus by Means of Strychnine. Univ. Cal. Pub. Physiol., 1912, iv, 185-186. LITERATURE 195 368 Moorr, A. R.: The Negative Phototropism of Diaptomus Through the Ageney of Caffein, Strychnine, and Atropin. Science, 1913, xxxvili, 131-133. 369 Moore, A. R.: The Mechanism of Orientation in Gonium. J. Exp. Zool., 1916, xxi, 431-432. 3692 Moorg, A. R.: The Action of Strychnine on Certain Invertebrates. J. Pharm. and Exp. Therap., 1916, ix, 167-169. 370 Moore, A. R., and Ketioac, F. M.: Note on the Galvanotropic Response of the Earthworm. Biol. Bull., 1916, xxx, 131-134. 371 Moore, B.: Observations of Certain Marine Organisms of (a) Variations in Reaction to Light, and (b) a Diurnal Periodicity of Phosphorescence. Biochem. J., 1909, iv, 1-29. 371¢ MorGan, C. L.: Animal Behavior. London, 1900. 371 Morcuuis, S.: The Auditory Reactions of the Dog Studied by the Pawlow Method. J. Animal Behav., 1914, iv, 142-145. 871¢ Morcuuis, S.: Pawlow’s Theory of the Function of the Central Nervous System and a Digest of Some of the More Recent Con- tributions to This Subject from Pawlow’s Laboratory. J. Animal Behav., 1914, iv, 362-379. 372 Morse, M. W.: Alleged Rhythm in Phototaxis Synchronous with Ocean Tides. Proc. Soc. Exp. Biol. and Med., 1910, vii, 145-146. 373 MULier, H.: Ueber Heliotropismus. Flora, 1876, lix, 65-70, 88-95. 374 MULLeR-HeTrLinGEN, J.: Ueber galvanische Erscheinungen an kei- menden Samen. Arch. ges. Physiol., 1883, xxxi, 193-212. 375 Murpacu, L.: The Static Function in Gonionemus. Am. J. Physiol., 1903, x, 201-209. 376 MurpacuH, L.: Some Light Reactions of the Medusa Gonionemus. Biol. Bull., 1909, xvii, 354-368. 377 Musset, Cu.: Sélénotropisme. Compt. rend. Acad. Sc., 1890, ex, 201-202. 378 NaGEL, W. A.: Beobachtungen iiber den Lichtsinn augenloser Musch- eln. Biol. Centr., 1894, xiv, 385-390. 379 NaceL, W. A.: Ein Beitrag zur Kenntnis des Lichtsinnes augenloser Tiere. Biol. Centr., 1894, xiv, 810-813. 379a NaGEeL, W. A.: Experimentelle sinnesphysiologische Untersuchungen an Ceelenteraten. Arch. ges. Physiol., 1894, lvii, 495-552. 380 Nacet, W. A.: Ueber Galvanotaxis. Arch. ges. Physiol., 1895, lx, 603-642. 381 NaceL, W. A.: Der Lichtsinn augenloser Tiere. Jena, 1896, pp. 120. 382 NaceL, W. A.: Phototaxis, Photokinesis und Pa tersclaedos pane, lichkeit. Bot. Ztg., 1901, lix, 298-299. 196 TROPISMS 883 NaGeL, W. A.: Methoden zur Erforsechung des Licht- und Farben- sinnes. Tigerstedt’s Handb. physiol. Methodik, 1909, iii, Abt. 2, Sinnesphysiologie, 11, 1-99. 384 NATHANSOHN, A., and PrinGsHEIM, E.: Ueber die Summation inter- mittierender Lichtreize. Jahrb. wiss. Bot., 1908, xlv, 137-190. 385 Nfémec, B.: Ueber die Wahrnehmung des Schwerkraftreizes bei den Pflanzen. Jahrb. wiss. Bot., 1901, xxxvi, 80-178. 385a Nernst, W., and Barratt, J. O. W.: Ueber die elektrische Nerven- reizung durch Wechselstrome. Z. Electrochem., 1904, x, 664-668. 386 NeuBEeRG, C.: Chemische Umwandlungen durch Strahlenarten. Bio- chem. Z., 1908, xiii, 305-320; 1909, xvii, 270-292. 387 NuEL, J. P.: La vision. Paris, 1904, pp. 376. 388 NyperGH, T.: Studien iiber die Einwirkung der Temperatur auf die tropistische Reisbarkeit etiolierter Avena-Keimlinge. Ber, bot. Ges., 1912, xxx, 542-553. 389 OLTMANNS, F.: Ueber die photometrischen Bewegungen der Pflanzen. Flora, 1892, Ixxv, 183-266. 390 OurMANNS, F.: Ueber positiven und negativen Heliotropismus. Flora, 1897, lxxxiii, 1. 391 OsrwaLD, Wo.: Ueber eine neue theoretische Betrachtungsweise in der Planktologie, insbesondere iiber die Bedeutung des Begriffs der “inneren Reibung des Wassers” fiir dieselbe. Forsch.-ber. biol. Station Plén, 1903, pt. 10, 1-49. 392 OstwaLD, Wo.: Zur Theorie der Richtungsbewegungen schwimmen- der niederer Organismen. Arch. ges. Physiol., 1903, xev, 23-65; 1906, exi, 452-472; 1907, exvii, 384408. 393 OsrwaLp, Wo.: Ueber die Lichtempfindlichkeit tierischer Oxydasen und iiber die Beziehungen dieser Eigenschaft zu den Erscheinungen des tierischen Phototropismus. Biochem. Z., 1908, x, 1-130. 394 Paat, A.: Ueber phototropische Reizleitungen. Ber. bot. Ges., 1914, xxx, 499-502. 395 Parker, G. H.: Photomechanical Changes in the Retinal Pigment Cells of Palemonetes, and Their Relation to the Central Nervous System. Bull. Mus. Comp. Zool., 1897, xxx, 273-300. 396 Parker, G. H.: The Photomechanical Changes in the Retinal Pig- ment of Gammarus. Bull. Mus. Comp. Zool., 1899, xxxv, 141-148. 397 Parker, G. H.: The Reactions of Copepods to Various Stimuli and the Bearing of This on Daily Depth-migrations. Bull. U. S. Fish Comm., 1901, 103-123. 398 Parker, G. H.: The Phototropism of the Mourning-cloak Butterfly, Vanessa antiopa Linn. Mark Anniversary Vol., 1903, 453-469. ES LITERATURE ds 399 Parker, G. H.: The Skin and the Eyes as Receptive Organs in the Reactions of Frogs to Light. Am. J. Physiol., 1903, x, 28-36. 400 Parker, G. H.: The Stimulation of the Integumentary Nerves of Fishes by Light. Am. J. Physiol., 1905, xiv, 413-420. 401 Parker, G. H.: The Reactions of Amphioxus to Light. Proc. Soc. Exp. Biol. and Med., 1906, 11, 61-62. 402 Parker, G. H.: The Influence of Light and Heat on the Movement of the Melanophore Pigment, Especially in Lizards. J. Exp. Zool., 1906, inl, 401-414. 403 Parker, G. H.: The Sensory Reactions of Amphioxus. Proc. Am. Acad. Arts and Sc., 1908, xlin, 415-455. 404 Parker, G. H.: The Integumentary Nerves of Fishes as Photore- ceptors and Their Significance for the Origin of the Vertebrate Eyes. Am. J. Physiol., 1909, xxv, 77-80. 405 Parker, G. H.: Mast’s “Light and the Behavior of Organisms.” J. Animal Behav., 1911, 1, 461-464. 406 Parker, G. H., and Arkin, L.: The Directive Influence of Light on the Earthworm Allolobophora fetida (Sav.). Am. J. Physiol., 1901, v, 151-157. 407 Parker, G. H., and Burnett, F. L.: The Reactions of Planarians, With and Without Eyes, to Light. Am. J. Physiol., 1900, iv, 373- 385. 408 Parker, G. H., and Mercatr, C. R.: The Reactions of Karthworms to Salts: a Study in Protoplasmie Stimulation as a Basis of In- terpreting the Sense of Taste. Am. J, Physiol., 1906, xvii, 55-74. 409 Parker, G. H., and Parsuuny, H. M.: The Reactions of Earthworms to Dry and to Moist Surfaces. J. Exp. Zool., 1911, xi, 361-363. 410 Parker, G. H., and Parren, B. M.: The Physiological Effect of In- termittent and of Continuous Lights of Equal Intensities. Am. J. Physiol., 1912, xxxi, 22-29. 411 ParmuEE, M.: The Science of Human Behavior. New York, 1913, xviit 443. 412 Parren, B. M.: A Quantitative Determination of the Orienting Reaction of the Blowfly Larva (Calliphora erythrocephala Meigen), J. Exp. Zool., 1914, xvii, 213-280. 413 Parren, B. M.: An Analysis of Certain Photie Reactions with Reference to the Weber-Fechner Law. I. The Reactions of the Blowfly Larva to Opposed Beams of Light. Am. J. Physiol., 1915, xxxvili, 313-338. 414 Papren, B. M.: The Changes of the Blowfly Larva’s Photosensitivity with Age. J. Exp. Zool., 1916, xx, 585-598. 198 TROPISMS 415 Parren, B. M.: Reactions of the Whip-tail Seorpion to Light. J. Exp. Zool., 1917, xxiii, 251-275. 416 Payne, F'.: The Reactions of the Blind Fish, Amblyopsis speleus, to Light. Biol. Bull., 1907, xiii, 317-323. 416¢ Payne, F.: Forty-nine Generations in the Dark. Biol. Bull., 1910, xvill, 188-190. 4160 Payne, F.: Drosophila ampelophila Loew Bred in the Dark for Sixty-nine Generations. Biol. Bull., 1911, xxi, 297-301. 417 PearL, R.: Studies on Electrotaxis. I. On the Reactions of Certain Infusoria to the Electric Current. Am. J. Physiol., 1900, iv, 96-123. 418 Peart, R.: Studies on the Effects of Electricity on Organisms. ILI. The Reactions of Hydra to the Constant Current. Am. J. Physiol., 1901, v, 301-320. 419 Peart, R.: The Movements and Reactions of Fresh-water Planarians : a Study in Animal Behavior. Quart. J. Micr. Sv., 1902-03, xlvi, 509-714. 420 PEARL, R., and Couz, L. J.: The Effect of Very Intense Light on Organisms. Third Rep. Mich. Acad. Sc., 1901, 77-78. 421 Pearse, A. S.: The Reactions of Amphibians to Light. Proc. Am. Acad. Arts and Sc., 1910, xlv, 161-208. 422 PeREZ, J.: Notes zoologiques. De l’attraction exercée par les odeurs et les couleurs sur les insects. Acta Soc. Linn., Bordeaux, 1894, vii, 245-253. 423 PrerrerR, W.: Locomotorische Richtungsbewegungen durch chemische Reize. Ber. bot. Ges., 1883, 1, 524-533. 424 Prerrer, W.: Locomotorische Richtungsbewegungen durch chemische Reize. Unters. Bot. Inst. Tiibingen, 1884, 1, 363-482. 425 Prerrer, W.: Ueber chemotaktische Bewegungen von Bakterien, Flagellaten und Volvocineen. Unters. Bot. Inst. Tiibingen, 1888, ii, 582-661. 426 Pyipps, C. F.: An Experimental Study of the Behavior of Amphipods with Respect to Light Intensity, Direction of Rays, and Metabolism. Biol. Bull., 1915, xxviu, 210-223. 427 Puareau, F.: Recherches sur la perception de la lumiére par les myriopodes aveugles. J. Anat. et Physiol., 1886, xxii. 428 Piareau, F'.: Nouvelles recherches sur les rapports entre les insectes et les fleurs. Mém. Soc. Zool. France, 1899, xii. 429 PuarEau, F.: La choix des couleurs par les insectes. Mém. Soc. Zool. France, 1899, xii, 336-370. 430 PLateau, F.: Expériences sur l’attraction des insectes par les étoffes colorées et les objets brillants. Ann. Soc. Ent. Belgique, 1900, xliv. LITERATURE 199 431 Puart, J. B.: On the Specific Gravity of Spirostomum, Paramecium, and the Tadpole in Relation to the Problem of Geotaxis, Am. Nat., 1899, xxxiil, 31-38. 432 PorrmaNtI, O.: Ueber eine beim Phototropismus des Lasius niger L. beobachtete Eigentiimlichkeit. Biol. Centr., 1911, xxxi, 222-224. 433 Potimantl, O.: Sul reotropismo nelle larve dei batraci (Bufo e Rana). Biol. Centr., 1915, xxxv, 36-39. 434 PoropKo, TH. M.: Vergleichende Untersuchungen iiber die Tropis- men. I. Das Wesen der chemotropen Erregung bei den Pflanzen- wurzeln. Ber. bot. Ges., 1912, xxx, 16-27. 435 PoropKo, Tu. M.: II. Thermotropismus der Pflanzenwurzeln. Ber. bot. Ges., 1912, xxx, 305-313. 436 PoropKko, Tu. M.: IV. Die Giiltigkeit des Energiemengengesetzes fiir den negativen Chemotropismus der Pflanzenwurzeln, Ber. bot. Ges., 1913, xxxi, 88-94. 437 PoropKo, Tu. M.: V. Das mikroskopische Aussehen der tropistisch gereizten Planzenwurzeln. Ber. bot. Ges., 1913, xxxi, 248-256. 438 Powers, E. B.: The Reactions of Crayfishes to Gradients of Dis- solved Carbon Dioxide and Acetic and Hydrochloric Acids. Biol. Bull., 1914, xxvu, 177-200. 439 Prentiss, C. W.: The Otoeyst of Decapod Crustacea: Its Structure, Development, and Functions. Bull. Mus. Comp. Zool., 1901, xxxvi, 165-251. 440 PringsHEIM, E. G.: Die Reizbewegungen der Pflanzen. Berlin, 1912, viii +326. 441 PrrngsHEIM, E. G.: Das Zustandekommen der taktischen Reaktionen. Biol. Centr., 1912, xxxii, 337-365. 442 PrzipramM, K.: Ueber die ungeordnete Bewegung niederer Tiere. Arch, ges. Physiol., 1913, cli, 401-405. 443 Pirrer, A.: Studien iiber Thigmotaxis bei Protisten. Arch. Anat. u. Physiol., Physiol. Abt., 1900, Suppl., 243-302. 444 Ravi, E.: Ueber den Phototropismus einiger Arthropoden. Biol. Centr., 1901, xxi, 75-86. 445 RApL, E.: Untersuchungen iiber die Lichtreaktion der Arthropoden. Arch. ges. Physiol., 1901, Ixxxvii, 418-466. 446 RApu, E.: Ueber die Lichtreaktionen der Arthropoden auf der Dreh- scheibe. Biol. Centr., 1902, xxii, 728-732. 447 RApu, E.: Untersuchungen iiber den Phototropismus der Tiere. Leip- zig, 1903, viiit+188. 448 RApL, E.: Ueber die Anziehung des Organismus durch das Licht. Flora, 1904, xeiui, 167-178. 449 RApu, E.: Einige Bemerkungen und Beobachtungen iiber den Photo- tropismus der Tiere. Biol. Centr., 1906, xxvi, 677-690. 200 TROPISMS 450 RéaumuR: Mémoires pour servir a l’histoire des insectes. Paris, 1740. 451 Reese, A. M.: Observations on the Reactions of Cryptobranchus and Necturus to Light and Heat. Biol. Bull., 1906, xi, 93-99. 452 Ringy, C. F. C.: Observations on the EKeology of Dragon-fly Nymphs: Reactions to Light and Contact. Ann. Ent. Soc. Am., 1912, v, 273- 292. 453 RomANES, G. J.: Animal Intelligence. New York, 1883, pp. 520. 454 RoMANES, G. J.: Jelly-fish, Star-fish and Sea-urchins. New York, 1893, x+323. 455 RorHert, W.: Ueber Heliotropismus. Beitr. Biol. Pflanzen, 1894, Wale de 456 Rornert, W.: Beobachtungen und Betrachtungen iiber taktische Reizerscheinungen. Flora, 1901, Ixxxviii, 371-421. 457 Roux, W.: Ueber die Selbstordnung (Cytotaxis) sich “ beriihrender ” Furchungszellen des Froscheies durch Zusammenfiigung, Zellen- trennung und Zellengleiten. Arch. Entweklngsmech., 1896, iii, 381468. 458 Royce, J.: Outlines of Psychology. New York, 1903, pp. 417. 459 RUCHLADEW, N.: Untersuchungen zur Kritik der Methodik chemotak- tischer Versuche und zur Biologie der Leukozyten. Z. Biol., 1910, liv, 533-559. 460 ScHirer, K. L.: Ueber den Drehschwindel bei den Tieren. 2. Psy- chol. u. Physiol. Sinnesorg., 1891. 461 ScHarrrer, A. A.: Reactions of Ameba to Light and the Effect of Light on Feeding. Biol. Bull., 1917, xxxii, 45-74. 462 Scumip, B.: Ueber den Heliotropismus von Cereactis aurantiaca. Biol. Bull., 1911, xxxi, 538-539. 4620 ScHNEIDER, G. H.: Der tierische Wille. Leipzig, 1880. 4620 ScHNEIDER, K. C.: Tierpsychologisches Praktikum in Dialogform. Leipzig, 1912, pp. 719. 462c ScHNEIDER, K. C.: Vorlesungen tiber Tierpsychologie. Leipzig, 1909. 463 SCHOENICHEN, W.: Die Empfindlichkeit der Nachtschmetterlinge gegen Lichtstrahlen. Prometheus, 1904, xvi, 29-30. 464 ScHouTEDEN, H.: Le phototropisme de Daphnia magna Straus (Crust.). Ann. Soc. Ent. Belgique, 1902, xlvi, 352-362. 465 Suipata, K.: Studien iiber die Chemotaxis der /soétes-Spermato- zoiden. Jahrb. wiss. Bot., 1905, xli, 561-610. : 466 SyouL, A. T.: Reactions of Earthworms to Hydroxy! Ions. Am. J. Physiol., 1914, xxxiv, 384404. | LITERATURE 201 467 Smirnu, A. C.: The Influence of Temperature, Odors, Light, and Contact on the Movements of the Earthworm. Am. J. Physiol., 1902, vi, 459-486. 468 Suiru, G.: The Effect of Pigment-migration on the Phototropism of Gammarus annulatus 8. I, Smith. Am. J. Physiol., 1905, xiii, 205-216. 469 SosnowskI, J.: Untersuchungen iiber die Veriinderungen des Geo- tropismus bei Paramecium aurelia. Bull. Internat. Acad. Se. Cracovie, 1899, 130-136. 470 STaTKEWITSCH, P.: Ueber die Wirkung der Induktionschlige auf einige Ciliata. Le Physiologiste Russe, 1903, 11, 41-45. 471 SrarKewitscH, P.: Galvanotropismus und Galvanotaxis der Ciliata. Z. allg. Physiol., 1904, iv, 296-332; 1905, v, 511-534; 1907, vi, 13-43. 472 SrrAspurGeER, E.: Wirkung des Lichtes und der Wirme auf Schwiirm- sporen. Jenaische Z. Naturwiss., 1878, (N.F.) xii, 551-625, Also separate, Jena, pp. 75. 473 SzyMANSKI, J. S.: Ein Versuch, das Verhiltnis zwischen modal ver- schiedenen Reizen in Zahlen auszudriicken. Arch. ges. Physiol., 1911, exxxvin, 457-486. 474 SzyMANSKI, J. S.: Aenderung des Phototropismus bei Kiichenschaben durch Erlernung. Arch. ges. Physiol., 1912, exliv, 132-134. 475 SzyMANSKI, J. S.: Ein Beitrag zur Frage tiber tropische Fortbewe- gung. Arch. ges. Physiol., 1913, cliv, 343-363. 476 SzyMANSKI, J. S.: Methodisches zum Erforschen der Instinkte. Biol. Centr., 1913, xxxiil, 260-264. 477 y, TappEINER, H.: Die photodynamische Erscheinung (Sensibilisier- ung durch fluoreszierende Stoffe). Ergeb. Physiol., 1909, viii, 698— 741. 478 Terry, O. P.: Galvanotropism of Volvox. Am. J. Physiol., 1906, xv, 235-243. 479 ToRELLE, E.: The Response of the Frog to Light. Am. J. Physiol., 1903, ix, 466-488. 480 Torrey, H. B.: On the Habits and Reactions of Sagartia davist. Biol. Bull., 1904, vi, 203-216. 481 Torrey, H. B.: The Method of Trial and the Tropism Hypothesis. Science, 1907, xxvi, 313-323. 482 Torrey, H. B.: Trials and Tropisms. Science, 1913, xxxvii, 873-876. 483 Torrey, H. B.: Tropisms and Instinctive Activities. Psychol. Bull., 1916, xiii, 297-308. 484 Torrey, H. B., and Hays, G. P.: The Role of Random Movements in the Orientation of Porcellio scaber to Light. J. Animal Behav., 1914, iv, 110-120. 202 TROPISMS 485 Tow Le, E. W.: A Study in the Heliotropism of Cypridopsis. Am. J. Physiol., 1900, iii, 345-365. 486 TurneR, C. H.: An Experimental Investigation of an Apparent Reversal of the Responses to Light of the Roach (Periplaneta orientalis L.). Biol. Bull., 1912, xxiii, 371-386. 487 vy, UrxKULL, J.: Vergleichend-sinnesphysiologische Untersuchungen. II. Der Schatten als Reiz fiir Centrostephanus longispinus. Z. Biol., 1897, xxxiv, 319-339. 488 vy. UEXKULL, J.: Die Wirkung von Licht und Schatten auf die Seeigel. Z. Biol., 1900, xl, 447-476. 489 vy. UrxKisLL, J.: Umwelt und Innenwelt der Tiere. Berlin, 1909, pp. 261. 490 ULEHLA, Vu.: Ultramikroskopische Studien iiber Geisselbewegung. Biol. Centr., 1911, xxxi, 645-654, 657-676, 689-705, 721-731. 491 Van HeRWERDEN, M. A.: Ueber die Perzeptionsfihigkeit des Daph- nienauges fiir ultra-violette Strahlen. Biol. Centr., 1914, xxxiv, 213-216. 492 Verworn, M.: Psycho-physiologische Protistenstudien. Experimen- telle Untersuchungen. Jena, 1889, viiit219. 493 VeRworN, M.: Die polare Erregung der Protisten durch den galvan- ischen Strom. Arch. ges. Physiol., 1889, xlv, 1-36; 1890, xlvi, 267-303. 494 Verworn, M.: Gleichgewicht und Otolithenorgan. Experimentelle Untersuchungen. Arch. ges. Physiol., 1891, 1, 423-472. 495 VeRworn, M.: Untersuchungen iiber die polare Erregung der leben- digen Substanz durch den konstanten Strom. Arch. ges. Physiol., 1896, Ixii, 415-450. 496 VeRwoRN, M.: Die polare Erregung der lebendigen Substanz durch den konstanten Strom. Arch. ges. Physiol., 1896, Ixv, 47-62. 497 VeRWoRN, M.: General Physiology. New York, 1899. 498 VinWEGER, TH.: Recherches sur la sensibilité des infusoires (alealio- oxytaxisme), les réflexes locomoteurs, l’action des sels. Arch. Biol., 1912, xxvu, 723-799. 499 pz Vries, H.: Ueber einige Ursachen der Richtung bilateralsym- metrischer Pflanzenteile. Arb. bot. Inst. Wiirzburg, 1872, 1, 223. *500 pg Vries, M. S.: Die phototropische Empfindlichkeit des Segerhafers bei extremen Temperaturen. Ber. bot. Ges., 1913, xxxi, 233-237. 501 Wacer, H.: On the Effect of Gravity upon the Movements and Ageregation of Huglena viridis Ehrb., and Other Microorganisms. Phil. Trans. Roy. Soc. London, 1911, eci, (B), 333-390. 502 WALLENGREN, H.: Zur Kenntnis der Galvanotaxis. I. Die anodische Galvanotaxis. Z. allg. Physiol., 1903, 1, 341-384. ~ 7 ¢ a Se LITERATURE 203 503 WALLENGREN, H.: IJ. Eine Analyse der Galvanotaxis bei Spiro- stomum. Z. allg. Physiol., 1903, 1, 516-555. 504 WALLENGREN, H.: III. Die Entwirkung des konstanten Stromes auf die inneren Protoplasmabewegungen bei den Protozoen. Z. allg. Physiol., 1904, iii, 22-32. 505 WaurerR, H. E.: The Reactions of Planarians to Light. J. Exp. Zool., 1907, v, 35-162. 506 WasuBurn, M. F.: The Animal Mind. New York, 1909, pp. 333. 507 Wericert, F': Die chemischen Wirkungen des Lichts. Stuttgart, 1911. 508 WHEELER, W. M.: Anemotropism and Other Tropisms in Inseets. Arch. Entweklngsmech., 1899, viii, 373-381. 509 WHITMAN, C. O.: Animal Behavior. Woods Hole Biol. Lectures, Boston, 1899, 285-338. 510 p—E WILDEMAN, E.: Sur le thermotaxisme des Fuglénes. Bull. Soc. Belg. Micros., 1894, xx, 245-258. 511 y, Wiesner, J.: Heliotropismus und Strahlengang. Ber. bot. Ges., 1912, xxx, 235-245. 512 WiiueM, V.: La vision chez les gastropodes pulmonés. Compt. rend. Acad. Sc., 1891, exii, 247-248. 513 WitLEM, V.: Sur les perceptions dermatoptiques. Bull. Sc. France et Belgique, 1891, xxiii, 329-346. 514 Winson, E. B.: The Heliotropism of Hydra. Am. Nat., 1891, xxv, 413-433. 515 WODSEDALEK, J. E.: Phototactic Reactions and Their Reversal in the May-fly Nymphs Heptagenia inter gumclata (Say.). Biol. Bull., 1911, xxi, 265-271. 516 Yerxus, R. M.: Reaction of Entomostraea to Sumaliion by Light. I. Am. J. Physiol., 1899, in, 157-182. 517 YeRKES, R. M.: II. Reactions of Daphnia and Cypris. Am. J. Physiol., 1900, iv, 405-422. 518 YERKES, R. M.: A Study of the Reactions and the Reaction Time of the Medusa Gonionemus murbachiti to Photie Stimuli. Am. J. Physiol., 1903, ix, 279-307. 519 YerKES, R. M.: Reactions of Daphnia pulex to Light and Heat. Mark Anniversary Vol., 1903, 361-377 520 YerKES, R. M.: The Reaction Time of Gonionemus murbachii to Electric and Photie Stimuli. Biol. Bull., 1904, vi, 84-95. 521 ZAGOROWSKI, P.: Die Thermotaxis der Paramecien. Z. Biol., 1914, lxv, 1-12. 522 ZeELIONY, G. P.: Observations sur des chiens auxquels on a enlevé les hémispheres cérébraux. Compt. rend. Soc. Biol., 1913, lxxiv, 707- 708. 204 TROPISMS 523 Buasius, E., and Scuweizer, F.: Elektrotropismus und verwandte Erscheinungen. Arch. ges. Physiol., 1893, liii, 493-543. 524 Nernst, W., and Barratt, J. O. W.: Ueber die elektrische Nervenrei- zung durch Wechselstrome. Z. Electrochem., 1904, x, 664-668. 525 Moorg, A. R.: The Action of Strychnine on Certain Invertebrates. J. Pharm. and Exp. Therap., 1916, ix, 167-169. 526 Logs, J.: The Chemical Basis of Regeneration and Geotropism. Science, 1917, xlvi, 115-118. 527 BreveR, J.: Ueber den Galvanotropismus (Galvanotaxis bei Fischen. Sitzngsb. Akad. Wiss. Wien, mathem.-naturw. Kl., 1905, exiv, 27-56. 528 Breuer, J., and Kremu, A.: Ueber die scheinbare Drehung des Gesiehtsfeldes, wihrend der Einwirkung einer Centrifugalkraft. Arch. ges. Physiol., 1898, Ixx, 494-510. 529 HerMANN, L., and Marrutas, F.: Der Galvanotropismus der Larven von Rana temporaria und der Fische. Arch. ges. Physiol., 1894, Ivii, 391-405. 530 JENSEN, P.: Ueber den Geotropismus niederer Organismen. Arch. ges. Physiol., 1893, liu, 428-480. 531 Crozier, W. J.: The Photie Sensitivity of Balanoglossus. J. Exp. Zool., 1917, xxiv, 211-217. 532 CLAPAREDE, E.: Les tropismes devant la psychologie. J. Psychol. u. Neurol., 1908, xii, 150-160. 533 NaceL, W. A.: Experimentelle sinnesphysiologiche Untersuchungen an Coelenteraten. Arch. ges. Physiol., 1894, lvu, 495-6552. 534 ScHNemER, G. H.: Der tierische Wille. Leipzig, 1880. 535 SCHNEIDER, K. C.: Tierpsychologisches Praktikum in Dialogform. Leipzig, 1912, pp. 719. 536 SCHNEIDER, K. C.: Vorlesungen iiber Tierpsychologie. Leipzig, 1909. 537 MorGcuLis, S.: The Auditory Reactions of the Dog Studied by the Pawlow Method. J. Animal Behav., 1914, iv, 142-145. 538 Moracuis, S.: Pawlow’s Theory of the Function of the Central Ner- vous System and a Digest of Some of the More Recent Contributions to This Subject from Pawlow’s Laboratory. J. Animal Behav., 1914, iv, 362-379. 539 Craic, W.: The Voices of Pigeons Regarded as a Means of Social Control. Am. J. Sociology, 1908, xiv, 86-100. 540 Craic, W.: Male Doves Reared in Isolation. J. Animal Behav., 1914, iv, 121-133. 541 Maruua, J.: Untersuchungen iiber die Funktionen des Zentralnerven- systems bei Insekten. Arch. ges. Physiol., 1911, exxxvili, 388-456. LITERATURE 205 542 Lorn, J.: Influence of the Leaf upon Root Formation and Geotropic Curvature in the Stem of Bryophyllum calcycinum and the Possi- bility of a Hormone Theory of These Processes. Bot. Gaz., 1917, Ixiii, 25-50. 543 Lor, J.: Untersuchungen zur physiologischen Morphologie der Tiere. I. Heteromorphose. II. Organbildung und Wachstum. Wiirzburg, 1891-1892. 544 Lors, J.: The Chemical Mechanism of Regeneration. Ann. Inst. Pasteur, 1918, xxxii, 1-16. 545 Craig, W.: Appetites and Aversions as Constituents of Instincts. Biol. Bull., 1918, xxxiv, 91-107. 546 Kanpa, S.: Further Studies on the Geotropism of Paramecium cau- datum. Biol. Bull., 1918, xxxiv, 108-119. 547 Lyon, E. P.: Note on the Geotropism of Paramecium. Biol. Bull., 1918, xxxiv, 120. 548 McCLENDON, J. F.: Protozoan Studies. J. Exp. Zool., 1909, vi, 265— 283. 549 McEwen, R. 8.: The Reactions to Light and to Gravity in Drosophila and its Mutants. J. Exp. Zool., 1918, xxv, 49-106. 550 Payng, F.: Forty-nine Generations in the Dark. Biol. Bull., 1910, xvui, 188-190. 551 Payng, F.: Drosophila ampelophila Loew Bred in the Dark for Sixty- nine Generations. Biol. Bull., 1911, xxi, 297-301. 552 Moraan, C. L.: Animal Behavior. London, 1900. 553 Srmvens, N. M.: Regeneration in Antennularia. Arch. Entwcklngs- mech., 1910, xxx, pt. 1, 1-7. 554 MAXwELL, S. S.: On the Exciting Cause of Compensatory Move- ments. Am. J. Physiol., 1911-12, xxix, 367-371. INDEX Aschna, 30 Aglaophenia, 138 Allen, 39 Amblystoma, 41, 53, 59 Ammophila, 170 Amphipyra, 135 Anelectrotonus, 32ff. Anemotropism, 132 Antennularia antennina, 119, 125 Arbacia, 148 ff. Arenicola, 106, 108, 109 Aristotelian viewpoint of animal conduct, 17, 18 Asymmetrical animals, 70 ff. Avena sativa, 84, 105, 106, 117 “Avoiding reactions,” 96 Axenfeld, D., 54 Bacterium termo, 140, 142 Balanus eburneus, 75, 108 perforatus, 116 Bancroft, F. W., 41 ff. 62, 72, 74, 98 Barratt, J. @. W., 146, 147 Barrows, W. M., 153, 154 Bauer, V., 18 Bees, heliotropic reactions of, 103 ff. 159 Bert, P., 101, 102 Blaauw, A. H., 84, 104, 106, 117 Blasius, E., 32 Blowfly, 51, 76, 109 Bohn, G., 75, 82 Brain lesions in fish, 24 ff. in dogs, 27 ff. in Aschna, 30 Bruchmann, H., 142 Bryophyllum calycinum, 22, IBS BI Buddenbrock, W., 18 Budgett, S. P., 46 Buller, A. H. R., 141, 143, 148 ff Bunsen-Roscoe law, 21, 83 ff., 99, 100, 137 Butler, S., 161 120, Catelectrotonus, 32 ff. Centrifugal force, 125, 126 Chemotropism, 139 ff., 160 Chilomonas, 144, 145. Chlamydomonas pisiformis, 106, 109 Cineraria, 48, 164 Circus movements, fish, 24 ff., dogs, 27 ff., Aschna, 30 housefly, 44, Ranatra, 54, Proctacanthus, 60, 61, 72, Euglena, 72 ff., Vanessa Antiopa, 54 Color sensations, 100 ff. Colpidium colpoda, 144 Compensatory motions, 126, 128 ff. “Conditioned reflexes,” 166 ff. Craig, W., 168 Crayfish, 38 Cucumaria cucumis, 125 Cypridopsis, 116 PDanais plexippus, 162 Daphnia, 88, 89, 92, 96, 101, 102, ye ieee, GY abl aly Delage, Y., 123, 124 Dewitz, J., 136, 149 Diaptomus, 114, 115 Dragon fly larva, 30 Drosophila, 111, 116, 117, 153 Budendrium, 66, 73, 83, 85, 106 Euglena, 16, 45, 62, 70, 72 ff., 97 ff., 106, 109 Ewald, W. F., 85, 88, 104, 116 ““Fertilizin,” 149, 150 Flourens, P., 27 Forced movements, 24 ff. Franz, V., 18 “Fright reactions,” 96 v. Frisch, K.., 103, 104 Fundulus, 143, 157 Galileo, 18 Galvanotropism, 32 ff. Tammarus, 113, 114, 116 Garrey,-W. E., 33, 40, 41, 51 ff., 71 (2s se ie Gelasimus, 39, 124 Geotropism, 119, ff. 207 208 Glaucoma scintillans, 144 Gonium, 109 Graber, V., 47, 100, 104 Groom, T. T., 112 Hammond, J. H. Jr., 68 Harper, E. H., 154 Heliotropic machine, 68 ff. Heliotropism, 47 ff. Hering, E., 127 Hermann, L., 32 Hess, C., 102 ff. Holmes, 8S. J., 51 ff., 73, 116 Instincts, 156 ff. “Trritability,” 39 Isoétes, 141, 142 Jellyfish, 41, 42 Jennings, H. S., 73, 96 ff., 119, 125, 143 ff., 155 Jordon, H., 18 Kellogg, V. L., 158 Knight, 125 Kreidl, A., 124 Kupelwieser, H., 104 Lidforss, B., 142 Lillie, F., 149 ff., 156 Littorina, 75 Lizard, nystagmus in, 126, 129, 130 Lubbock, J., 47 Ludloff, K., 43 Lumbricus, 109 Lummer-Brodhun photometer, 90 Lycopodium, 142 Lyon, E. P., 22, 125, 128, 131 McEwen, R. S., 111, 116 ff. Mach, E., 33 Magendie, 27 Magnus, R., 22 Marchantia, 142 Mast, S. O., 73, 99, 108, 109, 119 Matula, J., 30 Maxwell, S. S., 33 ff., 106, 108, 126, 135 Mayer, A. G., 162 Mazda lamp, 86 Memory images, 164 ff. Mendelssohn, M., 155 Méniére’s disease, 17, 110 Miessner, B. F., 68 INDEX Moore, A. R., 22, Morgulis 8., 166 Muscle tension, 20 ff.; after brain lesions in fish, 24 ff., dogs, 27 ff.; under influence of, galvanic cur- rent, 32 ff., one source of light, 47 ff., two sources of light, 75 ff., changes in intensity of light, 95 ff. 112, 115, 117 Nereis, 135, 150 Nernst, W., 46, 95 Nernst lamps, 76 Neurons, orientation of, 38 ff. Northrop, J. H., 75, 89, 90 Nystagmus, 126, 129, 130 Oltmanns, F., 117 Palemon, 124 Palemonetes, 33 ff., 52, 59 Pandorina, 106, 109 Paramecium, 43 ff., 97, 125, 148, 144, 164 ff., 155 Parker, G. H., 54, 75 Patten, B. M., 75 ff., 92 Pawlow, 165 ff. Payne, F., 118 Pfeffer, W., 140 ff. Phacus Triqueter, 109 Phrynosoma, 126, 129, 130 Phycomyces, 105, 117 Platyonichus, 124 Polygordius, 115 Polyorchis penicillata, 41, 42 Porthesia chrysorrhea, 48, 116, 161 Proctacanthus, 55 ff. Radl, E., 54, 88, 128 Ranatra, 52 ff. Vy Reflexes, 21 ff., 166 Retina images, 127 ff. Reversal of helitropism, 112 ff. Rheotropism, 131 ff. Robber fly, 55 ff., 72 Sachs, 101. Salamander larve, galvanotropism of, 41 Schweizer, F., 32 Scyllium canicula, 24 Serpula, 95, Shark, forced movements in, 22, 24 ff. Sherrington, 22 INDEX Shibata, K, 141, 142 Shock movements, 97, 98 Shrimp, galvanotropism in, 34 ff. Soule, C. G., 162 Spirillum undula, 140 Spirographis spallanzani, 63, 83 Spondylomorum, 109 Steinach, 156 Stereotropism, 134 ff., 157 Stevens, N. M., 119 Sticklebacks, 132 Strongylocentrotus purpuratus, 151 Stylonychia mytilus, 144 Symmetry relations of animal body, 19 ff. v. Tappeiner, H., 117 Terry, O. P., 44 209 Thermotropism, 155 Towle, E. W., 116 Trachelomonas euchlora, 109 “Trial and error,” 17, 73, 153, 154 Tubularia mesembryanthemum, 137 v. Uexkiill, J., 18, 21, 22 Vanessa antiopa, 54 Verworn, M., 42 Vitalism, 18 Volwog, 44, 45, 62, 83, 117 Wasteneys, H., 86, 99, 106, 108, 143 Wave lengths, heliotropic efficiency of, 100 ff. Weber’s law, 78, 142, 143 Wheeler, W. M., 132 Whitman, 158, 168 Loeb, Jacques Forced movements hides. | i 4 PLEASE DO NOT REMOVE CARDS OR SLIPS FROM THIS POCKET UNIVERSITY OF TORONTO LIBRARY » 2 bate a SE Ow es Pm te ~ - et ae aie - es as s Py saad Misses. mAs - =e hw weg Se ene Se © ren sate tem Le 2 on ~ 5 tee SPER oe uit rll yi tae a I LM a oe ln te eee : ; % : ; ‘ Oe hee aoetia tO hea x ay eae ° tee 74 Saacaaenee ae te Fg hy ap a Olay Y i“ OOD so. oa me cones Bi 43009 ei at AV aed an Mowat wossee tone oat Monae eee a te ey Seer