Orn ES l,lUU Pi ¥ 4 esectiss Ree Lap eee ; Seat sits ihe Li + + , ta es TS : : : rae ; see: : . . 3 gt oe ae ee we {9 (ey rs } Tike ot ne ee ee — * aie * n Dr tr oe =e Bee So: ecb ees _ + *- ot ee ee Fahy ge ‘ 4 Ted + . ‘ ey : ~ SC Ore vie 8 ee yee wer! eles Role ron t ies Bh The Journal of Comparative Neurology and Psychology Founded by C. L. Herrick EDITORS C. JUDSON HERRICK, Manager, ROBERT M. YERKES, Denison University . Harvard University ASSOCIATED WITH OLIVER 5S. STRONG, HERBERT S. JENNINGS, Columbia University University of Pennsylvania COLLABORATORS J. MARK BALDWIN, Johns Hopkins University B. F. KINGSBURY, Cornell University FRANK W. BANCROFT, University of California FREDERIC S. LEE, Columbia University LEWELLYS F, BARKER, University of Chicago JACQUES LOEB, University of California H. HEATH BAWDEN, Vassar College E. P. LYON, St. Louis University ALBRECHT BETHE, University of Strassburg ADOLF MEYER, N. Y. State Pathological Inst. G,. E. COGHILL. Pacific University THOS. H. MONTGOMERY, Jr., Univ. of Texas FRANK J. COLE, University of Liverpool WESLEY MILLS, McGill University H. E. CRAMPTON, Columbia University C. LLOYD MORGAN, University College, Bristol Cc. B. DAVENPORT, University of Chicago T. H. MORGAN, Columbia University WM. HARPER DAVIS, Lehigh University A. D, MORRILL, Hamilton College HENRY H. DONALDSON, University of Chicago HUGO MUENSTERBERG, Harvard University LUDWIG EDINGER, Frankfurt a-M. W. A. NAGEL, University of Berlin 3. I. FRANZ, McLean Hospita’, Waverley, Mass. G H PARKER, Harvard University THOMAS H. HAINES, Ohio State University STEWART PATON, Johns Hopkins University A. VAN GEHUCHTEN, University of Louvain RAYMOND PEARL, University of Michigan R. G. HARRISON, Johns Hopkins University C. W. PRENTISS, Western Reserve University C. F. HODGE, Clark University C.S. SHERRINGTON, University of Liverpool S. J. HOLMES, University of Michigan G. ELLIOT SMITH, Gov't. Medical School, Cairo EDWIN B. HOLT, Harvard University EDWARD L. THORNDIKE, Columbia University G. CARL HUBER, University of Michigan JOHN B. WATSON, University of Chicago JOSEPH JASTROW, University of Wisconsin W. M. WHEELER, Am. Museum of Nat. History J. B. JOHNSTON, West Virgi» ia University C. O. WHITMAN, University of Chicago VOLUME XV DENISON UNIVERSITY, GRANVILLE, OHIO 1905 The Journal of Comparative Neurology and Psychology CONTENTS OF VOLUME XV, 1905 Number 1, January 1905. On the Areas of the Axis Cylinder and Medullary Sheath as seen in Cross Sections of the Spinal Nerves of Vertebrates. By HENRY H. DonaLtpson and G. W. Hoke. (from the Neurological Laboratory of the University of Chicago.) With one figure. On the Number and Relations of the Ganglion Cells and mccallated Nerve Fibers in the Spinal Nerves of Frogs of Different Ages. By IRvING HarRpDEsty. (from the Hearst Anatomical Laboratory of the University of California.) Editorial : Psychology and Neurology. The International Commission on Brain Rescorcit Literary Notices. Number 2, March, 1905. Observations on the Spinal Cord of the Emu and its Segmentation. By IrRvING HARDESTY. (from the Hearst Anatomical Laboratory of the University of California.) With four figures. . 5 The Selection of Random Movements as a Factor in Phototaxis. Byion le HouMEs. (from the Zoological Laboratory of the University le Mich- zgan.) : é Notes on the Development of ‘the Sympathetic Newous aystem in the Common Toad. By WALTER C. JoNEs, M.D. With twelve figures. Editorial Concerning the Genetic Relations of Types of Action. The Basis for Taxis and Certain Other Terms in the Behavior a; Infusoria. The Problem of jnstinct, A Review of Some Recent Literature on the Ghernistry of the Cental Nervous System. By Isapor H. CoriatT. Worcester Insane Hos- pital. Literary Notices. 81 98 113 132 138 144 148 160 Number 3, May, 1905. The Morphology of the Vertebrate Head from the Viewpoint of the Func- tional Divisions of the Nervous System. By J. B. JOHNSTON. (From the Zoological Laboratory of West Virginia University.) With Plates I to IV. : : : : - Literary Notices. Number 4, July, 1905. The Sense of Hearing in Frogs. By ROBERT M. YERKES. (From the Harvard Psychological Laboratory.) With seven figures in the text. The Reactions of Ranatra to Light. By. S. J. Ho_mes. (From the Zoological Laboratory of the University of Michigan.) Withsix fig— ures in the text. . : - : : - Literary Notices. No. 5, September, 1905. A Study of the Functions of Different Parts of the Frog’s Brain. By WI1- HELM LOESER, M.D. (From the Physiological Laboratory of the Uni- versity of Kansas.) : , The Central Gustatory Paths in the Brains, of Bong Fishes: By C. jooean HERRICK. (Studies from the Neurological Laboratory of Denison University. No. XVIII) : Literary Notices. Number 6, November, 1905. Some Cellular Changes in the Primary Optic Vesicles of Necturus. By CLARENCE LogEs, A.M., M.D. St. Louis. (From the Anatomical Lab- oratory, St. Louts Umea) With Plate V. Some Results of a Study of Variation and Correlation in Brain- Weight By RAYMOND PEARL. The Relation Between the coderenee of White ee bes wd dee Spin: al Accessory Nerve. By A. H. Rotu, A.B., M.D., Justructor of Anatomy in the University of Michigan. (With an Addendum by J. PLAYFAIR McMurrIcuH.) With one figure. , ‘ Respiration and Emotion in Pigeons. By JoHN E. hee “ire the Harvard Psychological Laboratory.) The ni of the Bearing of Young upon the Rady: wEinht and the Weight of the Central Nervous System of the Female White Rat. By JoHn B. Watson. (From the Neurological Laboratory of the University of Chicago.) With Plate VI. : ; Editorial The Work of Carl Wernicke. : . Papers on Reactions to Electricity in Ueieelinlar ean oae, = Heso: JENNINGS. Literary Notices. 175 276 279 395 35° 355 375 457 459 467 482 494 528 535 SUBECT AND AUTHOR INDEX. VOLUME Xv. Author’s names are in small caps. References to subjects and authors of originai articles are marked with an asterisk. ote, functions of nervous sys- tem, 164. Amoeba, reactions of, 170. *Action, instinctive, 144. *genetic relations of, 132. AGABABOW, A. Nerves of the sclera, 70. Amphibia, eyes of, 163. Amphioxus, nervous system of, 350. Anatomy, of head and neck, 67. ANDERSON, H. K. (and LANGLEY). Regeneration in nerves, 75. Union of nerve fibers, 74. ANDREWS, E. A. Breeding habits of crayfish, 79. * Animal behavior, 98, 132, 174. Anodonta, visceral ganglia of, 352. Audition in fishes, 166. *in frog, 279. * Axis cylinder, area of in spinal nerves, I. ALLOWITZ, E. Olfactory Petromyzon, 164. cells of BancuHt, A. Abnormal brain and mind, 352+ ; _ Bacriont, S. Physiology of reflex move- ment, 53)). BARCLAY-SMITH, FE. (and ELLIoTT). Muscular activities of colon, 75. *BARKER, L. F. Work of Carl Wer- nicke, 525. *BAWDEN, H. H. Psychology and neur- ology, 57. Behavior, determining factors in, 170. *forms of, 132. of Collembola, 78. of crayfish, 79. *of leech, 102.. of lower organisms, 166. *of Ranatra, 305. of spider, 75. *terminology, 138. BIGELow, H. B. Hearing in goldfish, 78. Birds, inheritance of song in, 174. origin of migration of, 80. : BIRUKOFF, B. ‘Theory of galvanotaxis, 73° BoINET, E. Evolution of medical doc- trines, 458. Bon, G. LE. Psychology of education, 458. Brain, anatomy of, 160. of Egyptians, 160. *morphology of, 175. *international commission, 62. *weight, variation and correlation, 407. BRESSLER, J. Mental diseases, 541. BURKHOLDER, J. F. Anatomy of brain, 160. (Os. J. and PAGNIEz, PH. Neur- asthenia and hysteria, 76. Cardio-accelerator nerves, of mol- luscs, 72. CARLSON, A. J. 72, 278. Heart-rhythm of molluscs, 72. Nerve cord of Myriapoda, 353. Cats, thinking, 539. Catfish, habits of, 278. Cerebellum, localization of functions of, 539: tumors of, 352. Cervical sympathetic, union with chorda Heart-beat of Limulus, tympani, 71. CuiLtp, C. M. Regeneration of nervous system, 354. Chorda tympani, and cervical sympa- thetic, 71. Ciliary movement, in metazoans, 540. Cocc1, A. Ampullae of Lorenzini, 352. Coun, P. Feeling and insanity, 173. Cote, R. L. Thinking cats, 539. Collembola, reactions of, 78. *Color preference, in pigeons, 494. Comparative psychology, 164. Co-ordination, nervous nature of,in Lim- ulus heart, 72. *CoriaT, I. H. Chemistry of nervous system, 148. *Correlation, in brain-weight, 467. Cranial nerves, development of, 353. distribution of fifth, 161. Crayfish, breeding habits of, 79. CusHInG, H. Fifth cranial nerve, 161. AVENPORT, C. B. Collembola, 78. Statistical methods, 67. DEAVER, J. B. Surgical head and neck, 67. DEITER’S nucleus, 7o. Delphinin, action on nerve endings, 72. Disease, frontiers of, 458. Dog, spinal reflex in, 75. *DoNALDsoN, H. H. and HOKE, G. W. Spinal nerves, I. anatomy of ducation, psychology of, 458. Egyptians, brain of, 160. *Electrotaxis, in unicellular organisms, 528. ELLioTT, T. R. and BARCLAY-SMITH, E. Muscular activities of colon, 75. *Emotion in pigeons, 494. *Emu, spinal cord of, 81. Equilibrium, and ‘‘forced movements,” 73- Ewinc, H. Z. Functions of nervous system in Acrididae, 164. Eye, in Amphibia, 163. physiology of, 73. 5 hae gustatory paths in brain of, 375: hearing in, 166. sense of taste in 277. Fieury, M. De. Manual of diseases of nervous system, 76. FREIDENFELT, T. Visceral ganglia of Anodonta, 352. *Frog, functions of brain, 355. *hearing of, 279. nervous system and musculature, 68. *number of ganglion cells etc., 17. FURBRINGER, M. Fourth nerve, 69. (aa theory of, 73. *Ganglion cells, number of in spinal nerves of frogs, 17. GARDELLA, E. Influence of phenic acid on taste, 7I. GEHUCHTEN, A. VAN. Structure of nerve cells and connections, 69. Vestibulo-spinal tract, 70. Genital organs, nerve terminations in, 68 il Goldfish, sense of hearing in, 78. GOLDsTEIN, K.~ Development of brain, 162. Influence of nervous system on de- velopment, 65. Gross, H. Criminal psychology, 353. H abit, migration; 80.” Habits, of catfish, 278. of Collembola, 78. of crayfish, 79. *of Ranatra, 305 *Haines, T. H. Instinct, 144. Hair, sense, organs of, 164. HALBEN, R. Pigment and light percep- tion, 174. HALL, G. S. Adolescence, 77. HarvDesty, I. Developmentand nature of neuroglia, 68. *Ganglion cells and nerves of frogs, 17. *Spinal cord of Emu, 81. Harris, W. Binocular and stereoscop- ic vision, 457. Harrison, R. G. Nervous system and musculature of frog, 68. *Head, morphology of vertebrate, 175. HeaTH, H. Nervous system of Solen- ogastres, 163. HELLPACH, W. Psychology of hysteria, 541. HERICONOT, J. Frontiers of disease, 458. *HERRICK, C. J. Gustatory paths in fishes, 375. Sense of taste in fishes, 277. Hearing in fishes, 166. *in frogs, 279. in goldfish, 78. HOCHSTETTER. Fissures in brain, 351. *HoLMEs, S.J. Phototaxisand random movements, 98. *Reactions of Ranatra, 305. Hornapbay, W. T. Natural history, 173. Horse, Berlin ‘‘thinking,” 539. Hyper, I. H. Respiratory centre in skate, 70. Hypophysis, structure and function of, 163, 542. Hypochondria, 540. Hysteria, psychology of, 541, Se terminology of behavior of, 138. Inheritance, of song in birds, 174. Instinct, and will, 276. *Instinct, problem of, 144. IorEYKO, J. Reaction of degenerated muscle, 72. Irritability, and degeneration of muscle, 72. | Seapeai L. (and MENDEL.) Neur- ology and Psychiatry, 67. Jennincs, H. S. Behavior of lower organisms, 166. *Reactions to Electricity lar organisms, 528. *Taxis and other terms, 13S. *JoHNsTON, J. B. Morphology of ver— tebrate head, 175. *JonEs, W. C. Nervous system of toad, in unicellu- 113. JosePH, H. Nervous system of Amphi- oxus, 350. AMON, K. ‘‘Geruchsknospen,’’ 163. KENDALL, W.C. Habits of catfish, 278. Kerr, J. B. Motor trunks in Lepidosir- en, 352. KLEIN, F. Physiology of the eye, 73. KOELLIKER, A. Nerve fibers, 350. yp Ane, J. N. Commissural fibers, between nerve cells, 74. Union of cervical sympathetic with chorda tympani, 71. LANGLEY, J. N. and ANDERSON, H. K. Autogenetic regeneration in nerve fibers, 75. Union of nerve fibers, 74. *Learning in lower organisms, 98. Leptoplana, regeneration of nervous sys- tem, 354 Levi, G. Histogenesis of ammonshorn, 163. Lewis, W. H. Development of amphi- bian eye, 163. Limulus, heart-beat of, 278. co-ordination of heart-beat, 72. *LOEB, C. Optic vesicles of Necturus, 359- Loes, J. General physiology, 276. *LOESER, W. Functions of frog’s brain, 355: Lusoscu, W. Olfactory Petromyzon, 351. LuxKas, F. Comparative psychology, 164, organs of ay, W. P. Innervation of muscu- lature of stomach, 75. *Medullary sheath of spinal nerve, I. *Medullated nerve fibres, in spinal nerves of frogs, 17. MEEHAN, J. The ‘“‘thinking”’ horse, 539. MENDEL, E. and JAcoBsoHN, L. Neur- ology and psychiatry, 67. Mental traits, inheritance of, So. Methods, statistical, 67. METTLER, L. H. Diseases of nervous system, 354. Migration of birds, origin of, So. Molluscs, heart-rhythm and nerves, 72. *Movement, random and phototaxis, 98. MuskEns, L. J. J. Maintenance of equil- ibrium etc., 73. Myriapoda, physiology of nerve cord, 353- AGEL, W. MHand-book of human physiology, 535- Natural history, 173. of salmon, 351. *Necturus, optic vesicles of 359. Nerve cells, structure and connections, 69. Nerve fibres, commissural, 74. development of, 350. union of 74. Nerves, of limbs, 75. of sclera, 70. *Nerve, spinal accessory, 482. trochlear, 69. *Nervous system, effects of bearing of young on, 514. *chemistry of, 148. *sympathetic in toad, 113. diseases of, 76, 354. *functional divisions of, 175. functions of in Acrididae, 164. influence of on development, 65. of Amphioxus, 350. *of fishes and gustatory paths, 375, *of frog, 355- of Myriapoda, 353- peripheral, 350. regeneration of, 354. and musculature in frog, 68. Neurasthenia, and hysteria, 76. Neuroglia, 163. development and nature of, 68. Neurology and psychiatry, 67. *Neurology and psychology, 57. physiological principles in, 173. Neurones, connections of, 69. ‘Ole vesicles, of Necturus, 359. Ostrich, spinal cord of, 69. | ene PH. (and Camus). Neur- esthenia and hysteria, 76. Pain, a pseudeffective reflex, 74. PARKER, G. H. Ciliary movement in metazoans, 540. Hearing in fishes, 166. *PEARL, R. Brain-weight, 467. Petromyzon, chemical sense cells, 164. olfactory organs of, 351. Phototaxis, 167. *and random movement, 98. *of Ranatra, 305. iil Physiology, hand-book of, 535. of adolescence, 77. of nervous system, 276. Pick. Zones of the head, 540. *Pigeons, respiration and emotion in, 494. Pinkus, F. MHair and sense organs, 1625, 164; PRINCE, M. Sensory fibres in spinal eord, 161. Protozoa, light perception of, 174. Psychiatry, and neurology, 67. and zones of the head, 540. Psychology, abnormal brain, mind, 352. Psychology, and neurology, 57. criminal, 353. of adolescence, 77. of hysteria, 541. of lowest animals, 164. PuTMAM, J. J. Principles in neurology, normal 173. AMSTROM. Innervation of periton- eum, 351. Ranatra, reactions of, 305. *Rat, effects of bearing young on, 514. Rawitz, B. Inheritance of mental char- acteristics, 80. *Reaction, method of in lower animals, 98. *types of, 132. of amoeba, 170. *of frog, 279, 355. of lower organisms, 166. ¥*of pigeons to light, 494. *of Ranatra to light, 30s. *to electricity in unicellular organ- isms, 528. Reflex, a pseudaffective and its spinal path, 74. Reflex movement, physiology of, 539. the ‘‘sham death,” in spiders, 75. Reflexes, nervous paths for, 73. spinal in dog, 75. *Respiration, and emotion in pigeons, 494. Respiratory centre in skate, 70. ROBERTSON, T. B. Sham death reflex in spiders, 75. *RotH, A. H. White rami and spinal accessory nerves, 482. ROTHMANN, M. Nervous mechanism of contact reflexes, 73. *RouseE, J. E. Respiration and emo- tion in pigeons, 494. RUBRASCHKIN, W. Neuroglia, 163. RuTrer, C. Natural History of Salmon, 351. RYNBERK, G. VAN. Localization of = functions of cerebellum, 539. almon, natural history of, 351. ScaAFFIDI, V. Efferent fibres in the posterior root, 540. Hypophysis of man, 163. SCHAPER, A. Fissures in brain, 351. SCHILLER, V. Action of delphinin, 72. SCHULTZE, O. Peripheral nervous sys- tem, 350. Sclera, nerves of, 70. Scotr, W. E. D. Inheritance of song in birds, 174. *Segmentation, of spinal cord of Emu, 8:. *Sense organs, morphology of, 175. of hair, 164. physiology of, 173. Sensory fibers in spinal cord, 161. SFAMENI, P. Nerve terminations of fe- male genital organs, 68. Sheep, brain of, 160. SHERRINGTON, C.S. Spinal reflexes in dog, 75. : Skate, respiratory centre in, 70. Smell, in Petromyzon, 351. SMITH, G. E. Brain of Egyptians, 160. *international brain research com- mission, 62. Solenogastres, nervous system of, 163 SOUKHANOFF. Structure of spinal gang- lion cells, 70. Spiders, sham death reflex of, 75. *Spinal accessory nerve, 482. Spinal cord, blood supply of, 161. *Spinal cord, of Emu, 81. sensory fibers in, 161. structure of in ostrich, 69. Spinal ganglia, structure of cells, 70. Spinal nerves, development of, 353. *Spinal nerves of frogs, 17. * of vertebrates, 1. Spinal path, pseudaffective, 74. Statistical methods, 67. STERZI, G. Blood supply of cord, 161. Structure of hypophysis, 542. Hypophysis of Petromyzon, 542. STEWART, T. P. A. A contrast experi- ment, 75. Stimuli and sense organs, 73. STREETER, G. L. Cranial and spinal nerves, 353- Spinal cord of ostrich, 69. > ‘Te in fishes, 277. influence of phenic acid on, 71. *paths in brain of fish, 375. TAVERNER, P. A. Origin of migration of birds, 80. *Taxis, basis for term, 138. Thought, in horse and cat, 539. *Toad, sympathetic nervous system, 113. binocular and stereoscopic, 457. *Trial and error method of learning, 98. method of reacting, 172. *\V/ arson, J. B. Effect of bearing *Tropism, terminology, 138. young on rat, 514. *and random movement, 98. WERNDLY, L. Turning fork-sound etc., theory of, 169. ee As ; : : WERNICKE, C. Work of, 525. o{ Jaicellaler organisms, reactions of to Wryssr, A. W. Animal behavior, 174, electricity, 528. WOoLLENBERG, R. Hypochondria, 540. WoopwortTH, R. S. and SHERRINGTON, V agus nerve, action of delphinin on,72. C. S. A pseudaffective reflex, 74. Variation, in brain-weight, 467. *Vertebrate, morphology of head of, 175. * ERKES, R. M. Genetic relations of binocular vision in, 457. types of action, 132. *spinal nerves in, I. *Hearing in frog, 279. Vision, and pigment, 174. sa itis Reap o bie ni ; ont 1, te TTA co] avis be The Journal of Comparative Neurology and Psychology Volume XV 1905 Number 1 ON ViibaecewAS OF THE AXIS CYLINDER ‘AND MEBWELARY SHEATH AS. SEEN IN. CROSS SECTIONS OF THE SPINAL NERVES OF VER- TEBRATES. By Henry H. Donartpson and G. W. Hoke. (from the Neurological Laboratory of the University of Chicago.) With one figure. Introduction.—The results presented in this paper are, in each case, based on averages of the measurements of twenty Or more spinal nerve fibers. The nerves were taken from vari- ous animals representing the five great classes of vertebrates. The measurements show that the areas of the medullary sheath and enclosed axis are nearly equal, and by consequence that the volume of the substance forming the axis cylinders is equal to that forming the medullary sheaths. The relation con- stitutes a point of similarity remarkable for its wide extension through the vertebrate series.’ It enables us, moreover, to estimate in any nerve the volume of the substance specialized for the conductioa of the nerve impulse. Since this quantitative relation between axis cylinder and sheath is so close, it strongly suggests that in some way the axis controls the formation of the surrounding medullary substance. In the spinal nerves of some animals this relation, as ex- pressed by the equal areas of the axis and sheath when the fibers are seen in the cross section, was pointed out several years ago 1 The Acrania and Cyclostomi do not develop medullary sheaths on their nerve fibers, and are therefore not included. 2 Journal of Comparative Neurology and Psychology. (DonaLpson, 1895, p. 154). The fact that it was maintained in the growing fiber was also noted (DoNALDsON, IgOl, p. 180; Igo01, A, p. 326); and later DuNN (’00, ’02) verified the relation by the study of the medullated fibers in the sciatic nerve of the frog. It seemed desirable, however, to extend the observations on this point, and in 1901, Mr. Hoke took up the question and determined the relative area of the axis and sheath in cross sec- tions of fibers from the nerves of 27 species of vertebrates rep- resenting the five great classes." Technique.—TYhe animals were killed with chloroform. The nerve, usually from the brachial plexus, laid bare and par- tially fixed z# sctu with osmic acid (1% sol.). After half an hour the nerve was removed on a piece of cardboard to prevent shrinking, and replaced in a 1% solution of osmic acid for 24 hours. Then imbedded in paraffin by the usual method. The sections were cut 3.5 » thick and mounted in colophonium. The measurements of the large fibers were made under the magnification of 340 diameters, or, in some cases, 265 diame- ters. The very small fibers were measured with the 1-12 oil immersion. The Effect of Osmic Actd Treatment upon the Size of Medullated Peripheral Nerves.—This reaction was studied be- cause of its obvious bearing upon the observations here pre- sented. Bott (’76) states that 1% osmic acid causes a swelling of the sheath to almost double its normal size. This, however, was the result of putting a fiber which had been ¢eased out while fresh, in a drop of the acid and examining it after a short time. Prolonged immersion in osmic, he says, in the same place, is followed by a shrinkage of the fiber. These statements lose value by reason of the fact that teasing out the fresh fibers stretches them and thus alters their reaction to the reagent. Bovert (85) concludes that the normal form and structure of the medullary sheath is very little modified by the osmic acid 1 Mr. HoKe’s account of his work was accepted as a thesis for the degree of Master of Science in the department of Neurology of the University of Chicago in 1902. The data in that thesis form the basis of the present paper. DonaLpson and Hoke, Medullary Sheath. 3 treatment, and this view is shared by a number of other ob- servers who have studied this question. The method employed in this investigation was practically the same as that used by Boveri. Speaking generally, it may be said that mistreatment tends to cause a swelling of the medullated fiber (in 1% osmic acid) in which the sheath becomes somewhat more swollen than the axis. The most reliable measurements, therefore, are those made on nerves which have suffered the least mechanical dam- age. To determine whether our method of treatment produced permanent alteration in the size of the nerves used, a series of observations was made upon the eighth, ninth and tenth spinal nerves running free along the dorsal wall of the body cavity of the frog, and also on the sciatic nerves of the white rat. The nerves were laid bare and a bristle bent in the iomim of tite letter U; exerting a tension’of .25:to .40 grams, according to the size of the nerve, was rapidly tied to either end of the nerve. In this way about one centimeter of nerve was included between the ends of the bristle. The nerve thus prepared was then removed and before putting it in any fluid its diameter was carefully measured under the microscope. It was then placed for twenty-four hours in a shallow cell containing osmic acid. The subsequent treatment was exactly similar to that given under the paragraph on technique. Bristie and attached nerve were finally mounted in colophonium and the diameter again carefully measured. The results of these observations are presented in Table I tor tae Prog and lable II for the Rat, The column on the left gives the diameter in yw of the fresh nerves with the bristle attached. On the right is given the di- ameters in while the nerves are in colophonium, after com- plete treatment by the osmic acid method as described above. In Table I, the middle column introduces the diameter of the nerves after having been in osmic acid twenty-four hours. The final number at the foot of each column gives the square of the average radius. This number, when multiplied by z would 4 Journal of Comparative Neurology and Psychology. give in sq. uw the total area of the nerves measured. As indi- cated, the nerves of the frog have increased in area 2.4%, those Gi the tat, 57%: : The measurements upon the rat were the last made, after some skill had been acquired in this manipulation, and are prob- ably the more reliable. TABER, TL: To show the effect of the technique upon the eighth, ninth and tenth spinal nerves of the Frog. Seven specimens. Diameter in “. Diameter in yu. Diameter in #4. Fresh Fiber, After Being in In Bristle Attached. Osmic Acid 1% Colophonium. 24 hrs. 456.00 498.75 456.00 513.00 541.50 527-25 541.50 570.00 541.25 627.00 701.25 641.25 470.25 470.00 484.50 427.50 441.75 427.50 498.75 527-25 498.75 Av. Diam. 504.85 538-80 510.95 Av. Radii Squared 63716.85 sq. 65264.92 sq. Percentage difference + 2.4%. TABLE, Il. To show the effect of the technique upon the sciatic nerve of the White Rat. Nine specimens. Diameter in 4. Diameter in “z. Fresh Fiber, In Bristle Attached. Colophonium. 1026.0 1062.0 926.0 969.0 1282.5 1282.5 912.0 926.0 912.0 883.5 1154.0 1168.0 997-5 969.0 1140.0 1140.0 997-5 983-0 Av. Diam. 1039.5 1042.5 Avy. Radii Squared 1080560.2 sq. 1086806.2 sq. u Percentage difference + .57%. Donatpson and Hoke, Medullary Sheath. 5 The results of these observations ‘seem to justify the con- clusion that the osmic acid treatment, followed by the prepara- tion for examination, produces but little change from the nor- mal diameter (or area) of peripheral nerve fibers. Conditions Determining the Choice of the Fibers to be Meas- uved.—There were used for measurement only those fibers which had been cut at right angles to their long axis and which stood vertically. It is easy to see that any departure of a fiber from the vertical would make the measurements for the thick- ness of the sheath too large, and those for the axis correspond- ingly too small. From measurement were excluded those fibers in which the medullary sheath appeared double, as occa- sionally occurs when the fiber has been cut through an enlarged cleft of LANTERMANN. The rare instances in which the section passes through an internodal nucleus, or just above or below a node—where the relative area of the medullary sheath is very greatly increased— were easily avoided. A fiber in which the sheath was wrinkled, or which departed much from the circular form, was not meas- ured. Where the section of the nerve fiber was suitable in other respects—and at the same time was slightly oval—two diameters were taken and the mean taken as the value to be used. Among the small fibers those that were stained gray and not black were classed as immature, and were not meas- ured. It is among the small fibers that the greatest normal range in the relative development of the medullary sheath ap- pears, and it is here too, that the greatest difficulties in making exact measurements are met, any departure from the vertical being especially disturbing. The very small medullated fibers which appear in the rami communicantes were not studied in this investigation. Method of Measurement.—On sections of fibers thus pre- pared and thus selected, the diameter of the entire fiber was first measured and then the diameter of the axis. In order to give an idea of this procedure we may take as an example the first group of ten measurements, the final results of which ap- pear in Table VI after Specimen I. Inthe first column of Table 6 Journal of Comparative Neurology and Psychology. IiI (see below) is given under A + 5S, (axis + sheath), the tota] diameter of each fiber, while under A (axis) is given the diame- ter of the axis. The two columns to the right give the corre - sponding radii. The measurements were first put down in terms of the divisions of the ocular micrometer—the subdivis- ions being estimated to tenths of these units. TABLE IIl. Diameters and Radii of entire fibers and axes, in divisions of the ocular micrometer. Diameter Kadit A+ S A A+ S58 A 4.0 2.9 2.00 1.45 4.0 2.9 2.00 1.45 4-7 3:1 2.3 1.55 4.2 ed 2.10 1.55 5.0 3.6 2.50 1.50 5.0 3.8 2.50 1.90 5.0 3:3 2.50 1.605 4.5 3.2 2.2 1.60 4.9 2a) 2.45 1.60 4.8 3.2 2.40 1.60 To transform these measurements into “ we multiply in each instance by the value of one division of the ocular micro- meter which in this case was 3.06 4. As the radii alone will be used, they only are reduced to uw. (See Table IV.) TABLE IV. A+S5 \ 6.12 4-43 Gane 4.43 7:19 4-74 6.43 4:74 795 5-50 7.018 5.51 7.65 5.04 6.85 4.89 7-49 4.59 7-2 4.59 It is on the basis of these radii that we calculate the areas of the fibers and of their axes, and for this we employ the formula z?* giving ~ the value of 3.14. As the square of the average radius for the group is not equivalent to the average of the squares of the radii, and as the Donatpson and HoKeE, Medullary Sheath. 7 latter is the number desired, it is necessary first to find the square of the radius in the case of each of these ten fibers ; then to take the average of these squares and multiply by z in order to obtain the average area of the fibers. TABLE V. The squares of the foregoing radii are as fo llows: (Radius A + 5S)? (Radius A)? 37.21 19.62 Ben 19.62 51.84 22.46 40.96 22.46 57-76 30.25 57-76 33-75 57-76 25-40 46.24 23.91 54-76 23.91 51.84 23-91 Total 493-34 Sq. 245.29 sq. A verage 49.33 sq. 24.53 sq. u The average for the squares of the radii in the case of the axis and sheath and of the axis alone, must be multiplied by 7 (= 3.14) to give in square yu the areas of the entire fiber and of the axis respectively. In this instance the areas are as follows: Areas. Entire Fiber Axis 154-9 sq. 76.99 sq. u The object of this investigation is to determine whether in the cross section of the fiber the area occupied by the ring-like sheath is equal to that of the enclosed axis. By hypothesis they should be equal in area, hence in the case of the average entire fiber containing 154.9 sq. s inits sec- tion we should expect to find one-half of this area 213 77°5 sq. in the axis and the other half in the sheath. With this ideal area, the area of the axis as observed is compared. Thus: Estimated area of sheath = 77.5 sq. p. Observed seals) =" 7ONOOStia (. According to the hypothesis, the area of the axis should equal that of the sheath. The observed area of the axis is seen to be less by 0.51 sq. yp, or using the ideal area of the sheath 8 Journal of Comparative Neurology and Psychology. as the standard, it is less by 0.6%. In this particular group, therefore, the actual area of the sheath is 0.6% greater than it would be if the assumed one to one relation of the axis and sheath were maintained. In working out the results, it is this ideal of one-half the area of the total fiber which is always taken as the standard, and the observed area of the axis is compared with it. If the area of the axis is less than one-half the area of the total fiber, then it follows that the sheath must have been move than one- half and the percentage value of the difference is written in plus, to show that the sheath is too large by this amount, or, under the reverse conditions, as minus, to show that it is too small. This difference is designated the average percentage deviation. In the case of each of the 1540 fibers here presented (Ta- ble V1) calculations similar to those just given, have been made. It is thus possible to say in each instance by what percentage the area of the sheath departs from that of the ideal, although in the table only the percentages for the extreme cases and for the average deviation are given. Description of the. Matertal Employed.—The following list of the specimens gives the common name; scientific name (en- tered only once where several specimens of the same species were examined); length of body; weight; sex; age; season when killed; nerves taken; locality; and by whom prepared. Where no statement is made; the sex is male; the season winter; the nerves are taken from the brachial plexus, and the material killed and prepared by Mr. Hoke in this laboratory. The omis- sion of any of the other data means that they are not available. Fish Amphibia Reptiles ——— -- =§ — | eh nas sn OOO ee kL Birds Mammals Dona.Lpson and Hoke, Medullary Sheath. 9 TABLES Vil; s ; Boag oe ° 7S ae SS Ox | oie a Animal Specimen Sn) omea| eo! eA hi ae tes eet ae Fis OP bp & 0 gan Fee sSug eS .o'5 Se gee aie is aes Zak tae Hoo 10.4 257 3.4 2.4 a 25.3 217 3.1 2.0 7 33-7 235 2.4 a7/ a 47-4 279 2.8 1.8 rs 61.8 338 3.7 2.1 fa 63.4 293 3.5 Ca Average ae. BN (x) VEO) 193 2.8 2.0 = 10.4 235 3.3 rash a 2533 239 2.9 2.2 Z, 33.7 273 2.7 1.6 e 47.4 341 225) 1.5 S 61.8 311 3.5 2.5 > 63.4 357 3.3 2.0 Average 3-0 Bolt 7.0 1491 2.6 2.4 cal 10.4 1231 3.7 3.4 ie 25-3 1211 2.6 2.4 fz] Bel 1808 2a 2:5 VA 47.4 1313 2.6 2.3% | 61.8 1645 3.0 2.7 wy] 63.4 1491 1 2.6 2.6 Average V@ ‘o F 9) | ee ic ~ 3 aS sl] Syne Balers 280 71 55 100 8 94 35 127 434 193 611 13 468 135 168 113 290 143 06 108 72 133 Boy, 278 436 196 575 2a: 1612 931 1361 719 1316 741 1982 1156 1528 1176 1828 1182 1713 936 en Aq — Percentage of dis- Sum of fibers in dor- sal and ventral roots Ratio of fibers in the ventral root to fibers in dorsal root No. of fibers in the tal excess. Sum of fibers in the dorsal branches. trunk and dorsal branches. “ © W distal excess to sums of Z = = ® a © ® © dorsal branches. aA ea g relations of sums of a w in = = 9 Ae a A 5 12) i PR distal excess to sums of 4 = =e As trunks & dor. branches. N he 2 7 aA a = g, relations of sums of b = an C © ne : dorsal branches tosums O a NX > © of trunks & dor.branches + w es 6 % nN ee Sums of ganglion cells e cS on ae = Es N less sums of dorsal root ty > ioe) ies) mn = NI fibers. Ratios of sums of distal =x excess to sums of gang- > —_ —_ } o © o oo rs} a y lion cells less sums of dorsal root fibers. TOE CUI ZIE 38 Journal of Comparative Neurology and Psychology. next in series is only about 13%. The first two and last two specimens differ less in weight than the others. The 47 gram frog was a male and the next in series, weighing 61 grams, was female. The distal excess in the two is about the same and the 63 gram frog, also female, shows an increase above the 47 gram male of only about 4%. Inthe older specimens the males are always of less weight than the females and the frog of 47 grams was no. doubt correspondingly as fully developed as the females weighing 13 and 16 grams more. This practical cessation of progressive changes in the relations of the distal excess at 47 grams is further indicated in some of the succeed- ing columns of the table. 5. The percentages of the distal excess in the individual nerves (col. H) are higher in the Vth and VIth nerves than in the IXth, as was noted in Table I, and they also show a de- cided though irregular increase in value with the increase in body weight. When again the percentage of the sums of the distal excess based upon the sums of the fibers in the two roots of each set of nerves is considered (col. I) it is seen that the value increases gradually, and much more regularly, with the in- crease in weight. From this it is evident that not only does the general distal excess of fibers increase with the growth of the animal, but that it increases at a more rapid rate than the number of fibers in dorsal and ventral roots. This suggests the question as to which of the two roots undergoes growth changes more nearly corresponding to those manifested by the distal excess. In column J the relation of the sums of the distal excess to the sums of the dorsal root fibers in each set of nerves is expressed in the form of percentages and in column K the same is done for the ventral root fibers. As shown in Table I, the number of dorsal root fibers is always greater than the ventral root fibers and so the sum of the distal excess in the smallest specimen is 14.4% of the sum of the dorsal root fibers and 24.4% of the ventral root fibers. The percentages of the ventral root vary in a more regular and con- stant progression than those of the dorsal root. From this it may be assumed that the changes in the number of the ventral Harpvesty, Spznal Ganglion Cells. 39 root fibers more nearly keep pace with the changes in the dis- tal excess. It is shown in Table IV that the ventral root gains fibers somewhat more rapidly than the dorsal root. The per- centage variations in the ventral roots of the individual nerves cannot be shown so well in a single column as the sum relations, for, in 6 out of the 14 smaller nerves (the nerves which possess relatively the largest distal excess), the distal excess exceeds the number of fibers in the ventral root. 6. The variations in the distal excess do not closely coin- cide with the variations in the number of fibers in the trunks and dorsal branches (col’s. F, A and B and col’s. Gand C). Yet when the percentage relations of the sums are considered (col. N) there is again evident a fairly regular and progressive increase. This indicates further that the fibers forming the distal excess increase at a proportionately more rapid rate than the sums of the trunks and dorsal branches in which the excess is contained. The excessive increase is similar to that relating to the two roots though less rapid and somewhat more irregular. In Table IV it is better shown that as the animal grows it gains fibers more rapidly in the trunks and dorsal branches than in the nerve roots. It is indicated here that some of this more rapid gain must take part in forming the distal excess. 7. As pointed out in the previous papers, the value of the distal excess is dependent upon or somehow correlated with the relative amount of the dorsal branches. Those nerves which have a proportionately large number of fibers in their dorsal branches as compared with the number in the nerve trunk al- ways have a high percentage of distal excess. Most of the smaller nerves of the frog are of this type. Of the 14 smaller (Vth and VIth) nerves employed here, 6 have dorsal branches containing even more fibers than the trunks themselves (com- pare col’s. A, Band H). All of them have higher percentages of distal excess than the IXth nerve. While in the individual nerves (col. B) as well as in the sums (col. L) it is seen that dorsal branches increase with the body weight, the variations do not appear so regular or to closely coincide with the varia- tions in the amount of the distal excess (col’s. F and G). A 40 Journal of Comparative Neurology and Psychology. comparison of their numbers alone shows that the dorsal branches contain many fibers which have nothing to do with forming the distal excess for in every case here the dorsal branches themselves contain at least a few more fibers than comprise the distal excess. However, in the nerves formerly dealt with it was found possible in some of the larger nerves, for the distal excess to exceed the amount of the dorsal branches thus making it necessary, in those cases at least, that some of. the distal excess be contained in the trunk. The percentage relations of the amount of the distal excess to the amount of the dorsal branches are shown in column M. In this it is seen again that the distal excess increases at a more rapid rate than the number of fibers in the dorsal branches, though the pro- gression is not so constant as in some of the other cases. If the fibers of the dorsal branches alone are concerned to any great extent in forming the distal excess, the relation of their number to the number composing both the trunk and dorsal branches should be: somewhat similar to the same relation main- tained by the amount of the distal excess. In column O such relations of the dorsal branches are expressed in percentages and when they are compared with the same values for the dis- tal excess (col. N) the variations of the two are not very simi- lar. Rather, a more fixed proportion is manifest, the dorsal branches comprising approximately 19% of the fibers on the dis- tal side of the ganglion up to 47 grams at which specimen the proportion suddenly changes to 24%. 8. Certain of the excess of cells in the spinal ganglion above the number of fibers in the dorsal root may take part in contributing to the distal excess. In column P are given the numbers of cells in the spinal ganglia in excess of the fibers in the respective dorsal roots and in the last column of the table the relations of the fibers of the distal excess to these extra cells are expressed in the form of ratios. Though it appears that the cells themselves increase with the increase in weight, the increase of the fibers in the distal excess is such that while in the youngest specimens there are twelve times as many cells as fibers, in the 47 gram frog there are only six times as many. Harpesty, Spzxal Ganglion Cells. 4! This shows it possible that some of these extra ganglion cells may send processes toward the periphery alone and thus con- tribute to the distal excess. It is further seen in the columns that if the cells of the ganglion increase in number, their increase does not keep pace with that of the distal excess, nor does the number of cells in excess of those giving origin to dorsal root fibers bear a constant relation to the fibers forming the distal EXCESS: As to the origin of the distal excess, it is indicated in the number relations noted above that it can hardly be due to any one cause. To explain its existence little can be added in this paper to that which was advanced in the previous papers. There are very few publications which even consider its presence, but certain of the findings of several investigators upon the struc- ture of the spinal ganglia may be interpreted toward its ex- planation. . One of the first explanations which suggests itself is that the excess may be due to the splitting of fibers on the distal side of the spinal ganglion. This was one of the first evidences sought for by the author. Both methylen blue zutra vitam, and gold chloride were employed in the preparations and serial sections as well as teasing were resorted to. The Vth and VIth nerves were chiefly used for this because they are the smaller of the nerves used in this paper and because the smaller nerves have the higher percentage of distal excess. A bifurcation of the fibers on the peripheral side of the ganglion was observed quite often but by no means was it ob- served in sufficient frequency to at all explain the entire origin of the distal excess. To give a distal excess of even 10%, every tenth root fiber must bifurcate at the peripheral border of the spinal ganglion and, while with the methods employed it was impossible to determine the exact proportion of dividing fibers, the author is convinced that it cannot occur even as fre- quently as this. It is seen in the tables that the smaller nerves always have a distal excess above 10% and that it may even exceed 50%. Most of the splitting observed occurred within the level of the peripheral border of the ganglion, and in order 42 Journal of Comparative Neurology and Psychology. to correctly interpret each case, the ends of the fiber had to be followed sufficiently to preclude the possibility of the T-fibers of Ranvier or those of Docret cells being mistaken for the type of bifurcation sought. As the fibers from the two roots join to form the trunk and dorsal branches, they cross and in- tertwine to an extent which renders teasing or following a fiber in sections quite difficult. Owing to tearing and breaking and the difficulty in following a fiber in question through the maze, certain of the bifurcations observed had to be discarded as un- certain. But including the uncertain cases would not have made enough to account for the average distal excess. The great majority of the fibers on the distal side of the ganglion show no branching at all. For the same reasons I was especially unable to determine the proportion of the dividing fibers belonging to each root separately. Bifurcations of ventral root fibers are somewhat more easily distinguished than those of fibers arising in the spinal ganglion. Of them it can only be said that they are certainly not frequent enough to give percentage values similar to those in column K, Table III. In most of the cases a ventral root fiber was seen to bifurcate, sending one product of the division to the dorsal branches while the other remained in the nerve trunk. This is of interest physiologically for the muscle sup- plied by the dorsal branches and by the trunk are usually consid- ered independent. It is not an unheard-of complication how- ever. CajaL (’99) pictures such an occurrence in the chick and discusses it physiologically, and Dunn (02) finds frequent di- visions of fibers in the sciatic of the frog, one product going to a branch supplying one muscle or set of muscles and the other going on in the trunk to be distributed to other muscles entirely distinct. Most of the fibers going from the ventral root to the dorsal branches do not bifurcate. Occasionally a fiber divides after entering the dorsal branches, its parts going to different divisions of the branches. If such a splitting occurs near enough to the spinal ganglion to be included in the section used in the counting, it of course would contribute to the dis- tal excess. Harpvesty, Spenal Ganglion Cells. 43 Some years ago STANNIUS (’49) and FrReEup (’78) observed splitting of the peripheral process of the spinal ganglion cell, the former in fishes and the latter in Petromyzon. DoaIEt (’96) describes the same for mammals and BUHLER (’98) suggests it as an explanation of the distal excess found by nim in the frog. It cannot be of very frequent occurrence in the frog. From my own observation I am led to believe that a splitting of the peripheral process of the dorsal root neurone is less frequent than in the ventral root fibers. Of the different frog’s nerves examined here only three cases of the bifurcation of this pro- cess was observed. In these one product went to the dorsal branches and the other continued in the nerve trunk. DoGIEL (p. 148) pictures this arrangement occurring in mammals. Do- GIEL (97) also finds division of axones in the dorsal root or on the central side of the spinal ganglion. It may be further added in explaining the distal excess that if it were mostly due to the splitting of fibers representing the two roots, then for it to obtain the rate of increase mani- fested, these fibers would have to either divide with increasing frequency asage advances or they would have to give off branches (divide) after they have grown into the nerve and become me- dullated. The latter at least is hardly probable, though it might be urged in support of it that the bifurcation always occurs at a node in the sheath. I know of no observations directly sup- porting either idea. The greater source of the distal excess lies perhaps in the presence of fibers connected with the spinal ganglion but not represented in the nerve roots at all. Such fibets are of sym- pathetic origin and have been repeatedly described (Cajal, 93, Huser, ’94, DocIeEL, ’96a, Cajal, ’99 and others) as entering the spinal ganglion and breaking up into numerous twigs which terminate in telodendria about the cells there, mostly the DocieL cells of Type II. Many of these sympathetic fibers are described as medullated. In my preparations of the frog, by comparing sections of the ramus communicans with sections of the trunk and dorsal branches, there may be seen in the lat- ter numerous medullated fibers similar to those considered of 44 Journal of Comparative Neurology and Psychology. sympathetic character in the ramus. They belong to the smaller type of fibers. The larger of them have a medullary sheath which is relatively thinner than that of fibers of undoubted spinal origin and which stains less black with osmic acid and shows a tendency to collapse in the sections. The smallest of the medul- lated fibers in the rami, however, cannot be distingushed from the smallest of the fibers known to arise in the spinal cord and spinal ganglia. Otherwise differential counts could be made to determine their exact “proportion in the trunk. As is well known, the rami contain fibers from both the ventral roots and spinal ganglia. The larger of these may be distinguished by the character of their sheaths. Fibers considered of sympathetic character were always observed in the dorsal branches. When the dorsal branches are much divided, often a small twig may be seen with the ma- jority of the fibers in itof thistype. This suggested that fibers from the sympathetic ganglia may enter the nerve trunk by way of the ramus, traverse it to the peripheral border of the spinal ganglion and there pass into the dorsal branches without con- necting with the spinal ganglion. Such fibers would of course be counted twice, once in the trunk and once in the dorsal branches and thus contribute to the distal excess. A special search was made for such fibers and none were found which could be so construed with certainty. Ifany exist they must be very few and it was assumed that the distal excess cannot be very materially affected by them. I think it necessary to explain at least most of the sympathetic fibers in the dorsal branches in some other way, and suggest that certain of the so-called mul- tipolar cells in the spina] ganglia have to do with them. There are numerous observations (cited above) noting the presence of these cells and many ascribed to them a sympathetic char- acter—cells left over in the spinal ganglia during the period of the offshoot of the anlage of the sympathetic. Telodendria of the centripetal sympathetic fibers are described as terminating about these cells and the role presumed for them here is that they are merely interposed in a sympathetic chain of neurones and that the fibers given off by them pass by way of the dorsal Harvesty, Spznal Ganglhon Cells. 45 branches to the blood vessels, etc., proximal to the vertebral column’ Such an arrangement would give two extra fibers on the peripheral side of the spinal ganglion. It should be men- tioned, however, that DoaGreLt (97) who has made a study of these cells, was unable to trace any of their processes beyond the confines of the spinal ganglion. He considers them either sympathetic or modifications of his spinal ganglion cell of Type I. Finally let it be added that early in this investigation counts were begun of the medullated fibers in the rami communicantes with the hope of gaining some clue as to the proportional part they play in forming the distal excess. It was soon found that the number of fibers in the distal excess of a nerve is often greater than the number of medullated fibers in its ramus and since many of the fibers of the ramus are of undoubted spinal origin and many of the smallest of uncertain origin, the research was discarded as unprofitable in that the ramus cannot account for all of the excess and in that it was impossible to determine the exact proportion it does contribute. So far the conclu- sions must be general, namely, that the distal excess is due to several causes, though probably the greater amount of it is due to medullated sympathetic fibers connected with the spinal ganglion but which are not continued into the nerve roots. VI. The gain of cells and fibers with the gain of weight. BirGe (82) determined that the frog while increasing from 1.5 grams to 111 grams gained in the ventral roots of its entire spinal nerve 51 fibers for each gram of weight gained. This estimation was based upon counts of all the ventral roots of one side of 6 specimens. He also counted the dorsal root fibers of one side of two frogs, one weighing 23 and the other 63 grams. Computations based upon the numbers he obtained give for all the nerves of both sides a gain of 77 dorsal root fibers per gram of weight gained. His data are not sufficient upon which to base estimations of the gain of fibers on the distal side of the spinal ganglion. The author (00) dealing with the VIth spinal nerve alone of frogs varying from 5 to 79 grams, ob- 46 Journal of Comparative Neurology and Psychology. tained numbers indicating a rate of gain in this one pair of nerves of about 3 ventral root fibers, 5 dorsal root fibers, and TABLE IV. (Frog) y A B C D E F G eles |#s | #3 [seg [ i2 |&. [Es “= > (e) el ye! xe) c a nn Tce) eee eee ss | “52 eeaioee z ogs ols See qc | See la aeeieneies eS ee a en rea yiess 2 Oe ee) ees ee ea taree Ses & 5 a Pa SI Ko fo) Pee: & i) ° a | ASE | AGS | APES |HESS| SSE |A2SBeee 28 E7i 6189 2316 1416 4205 S08 Dejan || shel 47-4 5201 1933 1647 4166 1022 27) TreeZ 61.8 7328 2294 1509 4384 1049 252 5 63.4 6771 2141 1283 4039 974 22 Tay Totals: 206.3 25489 $684 5855 16794 3853 2.9 Averages: 51.6 | 6372.2) 2171.0) 1463.7) 4198.5) 963.2) 2.9 1.5 7.0 5105 1888 I1I5 3275 620 207 Tay 10.4 6244 1723 962 2968 570 3.6 1.8 25.3 4462 1667 943 2903 534 2.7 1.8 Totals : 42.7 15811 5278 3020 9146 1724 3.0 Averages : 14.2 | 5270.3} 1759.3; 1006.6) 3048.6) 574.6; 3.0 1.7 Differences ri of averages: 37.4 1101.9 411.7 457.1) 1149.9) 388.6 Gained per gram of wt. gained : 1 205 11.0 12.2 30.7 10.4 | g, of gain: 20.9% 23.3% 45.4%! 37.7%' 58.9% TasLtE IV. The base numbers are taken from Tables Il and III. The specimens are entered in two groups, one of the four larger frogs, the other of the three smaller. Opposite the individual body weights are the sums of the gang- lion cells and of the nerve tibers in the localities indicated ot the three nerves. - The table allows a comparison of the number of cells the average specimen of each group would possess in the spinal ganglia of the three nerves (col. A), and of the number of fibers in the dorsal roots (col. B), ventral roots (col. €), the trunks and dorsal branches combined (col. D), the number of fibers in the dorsal branches alone (col. E), and finally the ratios of the ganglion cells to the dorsal root fibers (col. F) and the ratios of the fibers in the ventral roots to the fibers in the dorsal root (col. G). In the last two lines across the table are given. (1) the estimated number of cells and of fibers in the given parts of the nerve gained per gram of weight gained and (2) the gains in proportion to the numbers contained in each is expressed in percentages. Harpvesty, Sfzzal Ganglion Cells. 47 10 fibers in the trunk and dorsal branches for each gram gained in weight. This estimation was based on upon counts from 12 specimens. AL IMIRIEIE, Whe (White Rat) Z A B (E D E ize | 22 (ae \'es | ag eee yas les oo one = = a in tan ela oe ae e. (e) fs Toe Owes Oe) emcee aa ates bee Oph tons EO. ae Be v Gg oO Gy Se Ce oO as es) = oa & (Cyn ts! OB & Ga 4 2 oi. 2 = n Wy as wo ne wy ov oO Kel ahc=) ss) Bales B22 eae ist = ons a mes odes | mee || eae | age 59.0 28897 6420 2567 4-5 | 1:2.5 167.0 29048 7393 3115 3-9 2.4 Totals: 236.0 57945 13813 5682 Asae 3 Averages: 118.0 28972.5| 6906.5) 2841.0 4.2 2.4 10.3 26453 3328 1177 7-9 2.8 24.5 25001 4343 2139 5-8 2.0 Totals: 34:8 51514 7671 3316 GS7an| Averages: 17.4 |25757.0 $835.5) 1658.0 6.7 2.3 Difference of i averages: 100.6 3215.5) 3071.0) 1183.0 Gained per gram of wt. gained : 1 31.9 30-5 atlerd % of gain 12.5% 80.1% 71.4% TABLE V. Compiled from figures given by HATAI (’02) Table VII and (’03) Table III for the VIth cervical, [Vth thoracic and IInd lumbar nerves of four white rats of different ages. Constructed in the same way and showing the same relations as Table IV. (Note: In‘the two papers of HATAr there are some slight discrepancies in the body weights. For example, in one paper the results from a 68.5 gram rat are given in the other paper as obtained from one of 69 grams, and a specimen of 24.5 grams in one paper is given 25.4 in the other. These are considered oversights or misprints and of little importance anyway. The only specimen mentioned in the second paper as additional had a weight of 264.3 grams and it is not included here since its ganglion cells were not counted.) These indications of the rate of gain of the nerve fibers with growth suggest similar estimations for both the nerve fibers and the ganglion cells of the nerves dealt with in this paper. The re- sults of such estimations and the method by which they are made are shown in Table IV. And in order to compare the conditions 48 Journal of Comparative Neurology and Psychology. in the nerves of the frog with those ina mammal, the figures ob- tained by Harai (02 and ’03) for the white rat are compiled and arranged in the same way in the accompanying Table V. Harar also used but three nerves. So far as I know his results are the only available for such a comparison. In both tables the num- bers apply to the nerves of one side of the body only and therefore must be doubled for the approximate numbers for both sides. In the first place, it is further shown in Table IV that the average younger frog possesses a good many more cells than fi- bers in proportion to its weight than the older. It was shown in the previous papers that the younger gain fibers at a more rapid rate than the older. This is not so evident in the three nerves used here from the fact that the I[Xth nerves of the younger contain considerably above the usual relative proportion of fibers and thus produce larger sums for the three nerves. In the rat Hatar finds that the gain in the younger is considerably more rapid than in the older. It is also shown in Table IV (col’s. B, C, D and E) that as the frog increases in weight, for each gram of weight gained, there is an apparent gain of 11 dorsal root fibers, 12.2 ventral root fibers, 30.7 fibers in the trunks and dorsal branches and 10.4 fibers in the dorsal branches alone. Compared with results ob- tained in a similar way from BirGe’s figures, such gains in only three of the nerves of one side appear rather high. However, as was previously seen ('00), Rana virescens seems to possess an appreciably greater nuraber of fibers in its spinal nerves in proportion to body weight than does the European Rana escu- lenta employed by Brrce and therefore to maintain this, its ab- solute gain of fibers per gram of weight gained must be greater. It is also evident that apparently the ventral root gains fibers at a somewhat more rapid rate than the dorsal root, the relations being 12.2 to 11 per gram gained. In the previous paper, in the VIth nerve alone, the advantage seemed to be with the dorsal root, the ventral root gaining but 1.4 fibers to 2.4 gained by the dorsal root. Computations from the figures available Harpesty, Spzval Ganglion Cells. 49 for the purpose in BirGe’s records give for all of the spinal nerves also a higher gain in the dorsal root. And Harat’s counts (’03) for the rat, when tabulated in a similar way (Table V), show a considerably greater absolute gain of fibers in the dorsal root per gram of weight gained. The dorsal roots of all the spinal nerves here used of the frog and all of those used by Harat of the rat contain many more fibers than the ventral roots (col. L, Table I and col’s. G and E, Tables IV and V). One would therefore expect the absolute gain to be greater in the dor- sal root. But the gains in proportion to the number of fibers con- tained in each may show differently. It is seen in column C that the three ventral roots of the average frog of 14.2 grams gain about 45% in fibers with the increase to the average weight of 51.6 grams while the dorsal roots (col. B) gained but 23%. By comparing percentages of gain in this way it will be found that the figures for the VIth nerve alone in the paper above referred to also give a somewhat greater gain in the ventral root. By grouping Haral's figures in the same way (Table V) the dorsal roots appear to gain 30.5 fibers per gram of weight gained, while the ventral roots gain only 11.7 fibers and, in proportion to the fibers contained in them, the dorsal roots gain 80% and the ventral roots 71 %—a group result still in favor of the dor- sal root. However, Harat makes it one of his conclusions that the increase of medullated fibers in the ventral root is more rapid than in the dorsal root. He reaches this not by group- ing as above, but by simply comparing the relations of the nerve roots of the youngest rat with those of the adult individ- ual. In column E of Table V it is seen that in the 10.3 gram rat, for each fiber in the ventral root there are 2.8 fibers in the dorsal root, while in the 167 gram rat the ratio is 1:2.4, thus showing that, as far as these two individuals are concerned, the increase of ventral root fibers must gain on that of the dorsal root fibers during the growth of the animal. When, on the other hand, the ratios of the groups are considered it is evident that in the younger the average ratio of ventral root to dorsal root fibers is 1:2.3 while in the older it is 1:2.4, thus indicating a slightly more rapid increase in the dorsal roots. The same ratios 50 Journal of Comparative Neurology and Psychology. in the frog (col. G, Table IV) do not vary as much as they do in the rat. In fact, the extremes, the specimen of 7 grams and that of 63 grams, show similar ratios between their ventral and dorsal root fibers. The group or average ratios, however, indi- cate the more rapid increase of ventral root fibers mentioned above. Table IV further corroborates a relation indicated in the foregoing tables. Column D indicates that in the sums of the trunks and dorsal branches combined there is a gain of 30.7 fibers for each gram gained in weight. This is a greater gain than in either root or in both roots combined. In proportion to the number of fibers contained in them, the gain in the trunks and dorsal branches is only 37.7%, or less than the per- centage gain in the ventral roots. But the percentage rate is made up in the dorsal branches considered separately (col. E). Here the gain is about 59%. This again suggests that some correlation exists between the dorsal branches and the distal ex- cess, for as shown, the distal excess increases at a more rapid rate than the fibers in either the dorsal root, the ventral, or in the trunk and dorsal branches. The question of the ganglion cells is rather puzzling. The tenet more usually held is that in the vertebrates the number of nerve cells is fixed at quite an early stage in the development. This belief applied to the frog precludes an increase in the num- ber of spinal ganglion cells even at the youngest stages employed here. Yet, when the numbers of ganglion cells found in the different specimens are considered in the same way as the fibers in the nerves which admittedly increase with growth, the cells appear to undergo, in their sum relations at least, variations somewhat similar to those of the fibers. As arranged in Table IV (col. A) it is indicated that for each gram the frog increases in weight, there is a gain of 27.8 cells in the spinal ganglia, or, as the average specimen increases from 14 2 grams to 51.6 grams, the cells undergo an increase of 20.9%. This percent- age increase is less than that of the fibers as must be the case, but it is surprising that it appears so nearly equal to it. It is seen (col. F) that in the younger specimens the num- Harvesty, Spznal Ganglion Cells. 51 ber of cells per fiber in the dorsal root is greater than in the older specimens, but the difference is not so great as one would be led to expect nor do the ratios of the individual sums show a variation decreasing with the increase in weight. Rather, the relations between the number of cells and the number of dor- sal root fibers seem to be maintained approximately constant in the nerves here employed. All this can hardly be due to chance variations in the fixed number of cells in the individual ganglia of the different frogs. With Harai's enumerations for a mammal, the results are different. Using a similar tabulation of his numbers for the three nerves of the rat (Table V) it appears that, with the in- crease from the average weight of 17.4 grams to that of 118 grams, the ganglion cells undergo an increase of only 12% while the dorsal root fibers increase 80% and the ratio between the two is considerably higher in the younger than in the adult. Haral (02) notes that in some of the nerves of the rat of 10.3 grams, the ratio of fibers to cells is as muchas 1:11, while in the older it may be as low as 1:3. Based on this great decrease of the ratio with the progress of growth and the relatively small actual increase in the cells of the individual nerves of the different specimens, he concludes that the number of ganglion cells in the white rat remains approximately constant between the weight of 10.3 grams and the adult. He interprets the differences as probably due to individual variations in the ganglia of the dif- ferent specimens employed and cites the fact that the 24.5 gram rat gives a sum of cells in the three nerves chosen which is less than that of the rat of 10.3 grams. DonaLpson (02) supports the views of Harai and in discussing the investigation, lends observations which strengthen it. Harai states that the only argument in favor of an increase in the number of cells with age is the fact that of the four speci- mens employed the two older gave combined a greater number of cells than the two younger. Table V here given groups the older against the younger in order to compare the results with those from the frog in Table IV. The difference between the averages of the two groups of rats amounts to about 3200 cells. 52 Journal of Comparative Neurology and Psychology. In the frog at least, that in a limited number of nerves an older animal may show fewer cel!s than one somewhat younger, can be equally well explained as due to the fact that the pro- portional number of neurones apportioned to a given spinal nerve is by no means constant. The progress of growth in the frog is evidently different from that in the mammal. The 7 gram frog is no doubt rela- tively more developed than the 10 gram rat and in the rat of? 10 grams and younger the processes of growth must go on much more rapidly. This I think is indicated in the two tables. While the number of ganglion cells may not increase with age in the rat, the evidence though slight is, I think, a little stronger for the frog. It is needless, perhaps, to go into the literature for the support of this view for so far as I am aware, there are no observations which directly maintain it. BOUOHLER (98) in discussing the cells of the spinal ganglia suggests that the large cells are continually degenerating while the small cells enlarge and replace them. If this were true, the cells would have to multiply or else the number would, on the contrary, decrease with age. Of the 18 papers that I know of, which, dealing with tissues more or less mature, describe appearances in nerve cells (vertebrate and invertebrate) thought to be con- cerned in the processes of cell division, none of them describe cases of undoubted nerve cells which can be confidently consid- ered the actual process of division. Of the list LENHOsSEK (’95), DEHLER (95) and BUuLer ('98) describe such appearances in the spinal ganglion cells of the frog. Summary. 1. Due to variations in the relative number of neurones apportioned toa given spinal nerve, the number in a given nerve may not increase regularly with the increase in body weight but the sum obtained by adding the numbers in a given nerve of the larger specimens, as well as the sum of the several nerves of the larger specimens, is always greater than that of the smaller specimens. Harpvesty, Spznal Ganglhon Cells. 53 2. In the average there are nearly twice as many nerve fibers in the dorsal root as there are in the ventral root of the Vth, VIth and IXth nerves. The average is the highest for the Vth and in both the Vth and VIth is higher than in the IXth nerve. This agrees with the nature of the innervation supplied by the smaller nerves. 3. As compared with the corresponding trunk, the num- ber of nerve fibers contained in the dorsal branches 1s relatively much greater in the Vth and VIth than in the [Xth nerve, while in actual amount, the average number of fibers in the dorsal branches of each of the three nerves is similar. 4. The distal excess, or the excess in the sum of tie fibers of the nerve trunk and dorsal branches above the sum of the dorsal and ventral roots, occurs to an appreciable extent in every case. While it is less in the nerves of the smaller specimens, its average amount in each of the three nerves of the several specimens 1s similar. 5. The percentage of the distal excess ranges higher in the Vth nerve than in the VIth and it is much higher in both than in the [Xth nerve. 3 6. There is a general average of three times as many cells in the spinal ganglia as there are fibers in the dorsal roots. And there are more than twice as many ganglion cells as there are fibers in the trunk and dorsal branches less the number of fibers in the ventral root. The average ratios for each of the three nerves are similar, being somewhat higher in the Vth and VIth than in the IXth nerves. On neither side of the spinal gang- lion do the ratios of cells to fibers show a regular or marked decrease with the increase in body weight. 7. The distal excess in the three nerves of each specimen increases decidedly and with considerable regularity with the increase in body weight. *The distal excess increases at a more rapid rate than the fibers in both or in either of the nerve roots, and also at a more rapid rate than the fibers in the trunks and dorsal branches combined or in either separately. With increasing weight, the variations in the ventral roots coin- 54 Journal of Comparative Neurology and Psychology. cide more nearly with the variations in the distal excess than do the variations in the dorsal roots. 8. With the increase in weight, the fibers on the distal side of the spinal ganglion increase in number more rapidly than do the sums of the dorsal and ventral roots. In proportion to the fibers contained in them, the dorsal branches gain fibers at a more sapid rate than any other part of the nerve. This more rapid increase of the distal fibers is in some measure an expression of the more rapid rate of increase of the distal excess. g. Supported by direct observations, the distal excess is explained as due to three causes: (a) Centripetal medullated fibers from the sympathetic system which enter the spinal gang- lion to branch and terminate about the cells there; (b) The bi- furcation of ventral root fibers on the distal side of the spinal ganglion; (c) The bifurcation of the peripheral axone of the spinal ganglion neurone. In most of the bifurcations observed, one product of the division joins the dorsal branches while the other remains in the nerve trunk. The observed divisions of the fibers of the dorsal branches themselves may take part in producing the distal excess. There are some indications support- ing the assumption that certain of the excess of cells in the spi- nal ganglion may also contribute to the distal excess by sending processes into the periphery but not toward the central system. 10. With the increase in body weight the ventral roots of the Vth, VIth and IXth nerves gain fibers at a more rapid rate than do the dorsal roots, and at a more rapid rate than the nerve trunks considered separately. 11. With the increase in body weight there is an apparent gain in the number of spinal ganglion cells in the three nerves. Between the average weight of 14.2 grams and that of 51.6 grams the ganglion cells increase about 21%, or gain at the rate of 27.8 cells per gram of weight. Harpesty, Spznal Ganghe Cells. 55 BIBLIOGRAPHY Birge, ’82. Die Zahl der Nervenfasern und der Motorischen Ganglienzellen im Riickenmark des Frosches. Archiv fiir inat. und Physiol., Physiol. Abthl. H. V und VII. Buhler, ’98. Untersuchungen tiber den "au der Nervenzellen. Verhandlungen der phystk. med. Gesellschaft zu V" irzburg, N. F., 31. Cajal, 99. Textura del Sistem _rvioso del Hombre y de los Vertebrados. Tomo I, p. 364. Cajal, 93. Neue Darstell: vom histologischen Bau des Centralnervensys- tems. Arch fiir. inat. und Physiol., Anat. Adbthl, Cajal and Olori- 43. Los ganglios sensitivos craneales de los Mamiferos. vtsta trimestral micrographica, 2. Dale, ’00. On Some Numerical Comparisons of the Centripetal and Centrifugal Medullated Nerve-fibers in the Spinal Ganglia of the Mammal. /ournal of Phystology (Foster), 25, No. 3. Dehler, 795. Beitrage ziir Kentniss von feineren Bau der sympathischen Gang- lienzellen des Frosches. Archiv fiir Mikr. Anat., 16. Disse, 93. Ueber die Spinalganglien der Amphibien. Verhandlungen d. Anat. Gesellschaft auf d. Versamml. zu Gittingen. Dogiel, °95. Zur Frage iiber den feineren Bau des sympathischen Nervensys- tems bei den Saéugethieren. Archiv fiir mikros. Anat., 46. Dogiel, ’96. Der Bau der Spinalganglien bei Saiugethieren. Amat. Anz., 12 No. 6. Dogiel, 96a. Zwei Arten Sympathischen Nervenzellen. Amat. Anz., 11, No. 22. , Dogiel, 97. Zur Frage iiber den feineren Bau der Spinalganglien und deren Zellen bei Saéugethieren. Jnternat. Monatschr. fiir Anat. und Physiol., 14, H. 4 und 5. Donaldson, ’02. On the Number and Size of the Spinal Ganglion Cells and the Dorsal Root Fibers in White Rats of Different Ages. Amer. Journ. Anat., 1, No. 4. Dunn, ’oo. The Number and Size of the Nerve Fibers Innervating the Skin and Muscles of the Thigh in the Frog (Rana virescens brachycephala, Cope). four. Comp. Neurol., 10, No. 2. Dunn, ’02. On the Number and on the Relation Between Diameter and Dis- tribution of the Nerve Fibers Innervating the Leg of the Frog, Rana virescens brachycephala, Cope. /our. Comp. Neurol., 12, No. 4. Freud, ’78. Ueber Spinalganglien und Riickenmark der Petromyzon. Svtzungsd. d. K. Akad. d. Wien, 78, Abthl. 3, Juli Heft. Gaule and Lewin, ’96. Ueber die Zahlen der Nervenfaseren und Ganglien- zellen des Kaninchens. Centralblatt fiir Physiologie, Heft 15 und 16. Hardesty, 99. The Number and Arrangement of the Fibers Forming the Spinal Nerves of the Frog (Rana virescens). Jour. Comp. Neurol., 9, Nol 2: Hardesty, 700. Further Observations on the Conditions Determining the Number and Arrangement of the Fibers Forming the Spinal Nerves of the Frog (Rana virescens). Jour. Comp. Neurol., 10, No. 3. 56 Journal of Con arative Neurology and Psychology. Hatai, 02. Number and S. e of Spinal Ganglion Cells and Dorsal Root Fibers in White Rats of Diffei-nt Ages. Jour. Comp. Neurol., 12, No. 2. Hatai, ’03. On the Increase ir the Number of Medullated Nerve Fibers in the. Ventral Roots of the Spine! Nerves of the Growing White Rat. Jour. Comp. Neurol., 13, No. 3. - Hodge, ’88. Some Effects of Electi’cally Stimulating Ganglion Cells. Amer. Jour. of Psychology, 2. Huber, 97. Four Lectures on the Symp. “tic Nervous System. /our. Comp. Neural, Weg NOw2- Ingbert, 03. An Enumeration of the Medux... ° Nerve Fibers in the Dorsal Roots of the Spinal Nerves of Man. Jour. Cor. Neurol., 13, No. 2. Ingbert, ’04. An Enumeration of the Medullated Nerve “ers in the Ventral Roots of the Spinal Nerves of Man. Jour. Comp. Neurol. anew 'rh., 14, No. 3. : Kélliker, 93. Handbuch der Gwebelehre. Bd. 2. Kélliker, ’94. Der feinere Bau und die Functionen des sympathischen Nerven- systems. Sttzunysbr. d. Wiirzburger Phystk-med. Gesellschaft. Lenhossék, 794. Zur Kenntniss der Spinalganglien. Beitrage zur Histol. der Nervensystems und der Sinnesorgane, Wiesbaden, p. 129. Lenhossék, ’95. Centrosome und Sphire in den Spinal Ganglienzellen des Frosches. Archiv fiir Mikr. Anat., 46. Spirlas, ’96. Zur Kenntniss der Spinalganglien der Sdugethieren. Anat. Anz., 11, p. 629. Stannlus, ’49. Das periphere Nervensystem der Fische. Lostock. Stienon, ’80. Recherches sur la Structure des Ganglions Spineaux chez les vertébrés Supérieurs. Annales de 1 Université libre de Bruxelles. EDITORIAL. PSYCHOLOGY AND NEUROLOGY. In an earlier number of this /owvnal the need has been urged of some category common to the neurologist and psy- chologist in terms of which the problems of neural structure and mental function may be discussed without immediately arousing metaphysical prejudices. Such a category is action or behavior. The former is perhaps the more abstract concept and hence will lend itself more readily to the discussion of the phil- osophical questions which sooner or later are bound to arise. The latter has the advantage of being aterm of popular as well as of scientific usage and is more commonly employed to de- scribe the action of organisms. Mr. Moraan’s latest book is entitled ‘‘Animal Behavior’ and under this term he is success- ful, for the most part, in discussing the actions of organisms without prejudging the nature of the question of the psychical and its relation to the material processes. Likewise Mr. JEn- NINGS in the valuable article which appeared in the last issue of the Journal discusses the behavior of Paramecium in terms of ‘‘action-systems”’ in a way which does not preempt the field for either the mechanical or teleological interpretation of the phe- nomena. Researches carried on in this spirit are greatly needed at the present time. Only thus is it possible to construct a platform whose planks shall consist of facts interpreted in terms of a common technique. It is too early in the history of the movement to predict in detail the lines along which the two sciences will get to- gether, but it is safe to say that there will have to be consid- erable revision of working concepts on the part of both neu- rology and psychology. By this is meant that the newer in- sight into the energic nature of matter will in time inevitably 58 Journal of Comparative Neurology and Psychology. affect the biologist’s conception of the nature of what he calls an organism. Biology, in so far as it pretends to be an exact science, regards the organism as a complicated mechanism whose elements are to be understood in terms of the physical laws which hold for these elements outside the organism. Hence, if, for example, the study of the electrical properties of matter results in transforming our chemical and physical notions, and some form of an energic is substituted for the atomic theory, this dynamic view ultimately must reach into biology with trans- forming effect. In a similar way, the conception of the nature of conscious- ness is undergoing reconstruction in psychological science, in part due to this same energistic theory which is transforming physical science. The traditional formula which is satisfied to postulate a soul back of consciousness, just as it postulates ma- terial atoms back of motion or force, appears likely to be eclipsed by the results of inquiries which seek to discover the nature of the intimate relation which certainly seems to exist between mind and matter. There is no blinking the facts of brain structure nor of mental functioning; the problem is to understand what we mean by each in terms of the other. This it has been almost impossible to do in the past be- cause of the diverse historical conditions and techniques associ- ated with the two scjences. Biology had its roots in the natu- ral and positive sciences; psychology arose as a branch of phil- osophy and was long known as ‘‘mental philosophy.”’ But now that the basis has been laid for a scientific psychology, there is hope of its being possible for the psychologist and neurologist to get together in their work on this common problem. As has been intimated, this will involve a revision of psy- chological conceptions on many fundamental points. That this is already taking place is evident from recent tendencies in psy- chological thought. Consciousness is coming to be stated more and more in terms of action, in terms of the motor aspect of the organic circuit, instead of being stated exclusively in terms of the sensory aspect, which was the tendency with the older intellectualistic psychology. Great emphasis is now being placed Lditorzal. 59 on the motor character of attention, on the dynamogenic nature of ideas, on ideomotor impulses, on tactile-kinaesthetic imag- ery, on the emotions as vestiges of motor attitudes, on the growth of voluntary movement, on the constructive and recon- structive character of thought. Says Mr. MarsHati: ‘‘We are compelled to assume a unity of process in conscious life. From this point of view, the distinctions between reflex and instinctive activities and between habit and instinct are not fun- damental. The sharp distinction between instinct and intelli- gence implies denial of the unity of consciousness” (A/znd, Vol. XI, No. 44). Professor Ltoyp says: ‘‘Nothing in philosophy is so much needed at the present time as the adjustment of the science of abstract thought to the science of organic action, and every little hint as to how this adjustment can be brought about cannot but be at least a little help. The evolution of conscious- ness must be almost meaningless until the simplest case of ac- commodation as seen by the biologist is identified with the most perfect case of abstract thought that the logician knows” (Psy. Rev., Vol. Ill, p. 426). And arecent writer has gone so far as to define perception as ‘‘an attitude toward the object per- ceived.”” He says: ‘‘Perception is an attitude toward an ob- ject as well as a complex of sensations.” ‘‘All that objects mean to us is largely due to the sensations that flow backward from the bodily reverberations they excite directly in us. Per- ception is an attitude toward the objects perceived”’ (BoLTon, Biological View of Perception, Psy. Rev., Vol. LX, No. 6). How far these particular suggestions may prove fruitful in bringing about the desired synthesis is a matter of relatively little moment here. The important consideration 1s to note the fact of this tendency in recent literature and to keep in touch with the almost kaleidoscopic changes which are marking the progress of the comparative method as employed in this field. The further investigations of animal reactions are carried, the more difficult appears the problem of the distribution of consciousness. But, as if to counterbalance this, the further research in comparative psychology is carried, the more is the conviction forced upon the investigator that the reactions of 60 Journal of Comparative Neurology and Psychology. human beings (including their psychical processes, their con- scious acts) will never adequately be understood until we have formulated the laws of the behavior of these simpler types of organisms. The value of a study of the animal mind for human psy- chology has been emphasized by various writers. But its full significance, methodologically, has not always been realized. This deeper significance lies in the dynamic conception of con- sciousness, as itself a phase of the ultimate energic system, a bal- ance or tension of forces, admitting, like all other energic phe- nomena, of examination, description and explanation. The conditions of consciousness as represented in the complicated structures of the brain in the higher forms are too intricate to admit of exact statement as yet in scientific terms. Hence the promising character of researches upon the lower forms where the conditions are simpler, and where, if anywhere, the precise function of the brain as an organ for the transformation of en- ergy can be determined. Here first may we expect the laws of equilibration or tension of energies which we call conscious to be elucidated. The solution of the deepest problems of psy- chology, there is good reason to believe, lies in the hands of the comparative psychologist. SCHULTZ, ina recent article entitled ‘‘Gehirn und Seele” (Zettschr. f. Psy. u. Physiol. d. Sinnesorg., XXXII, Heft 3 u. 4, pp. 246-7) calls attention to the apparent dilemma in which the comparative psychologist finds himself. It is certainly a safe assumption that the higher, more complicated mental life of man and the higher animals can best be explained by a knowl- edge of the simpler conditions of mental life in the lower forms. On the other hand, it is a general principle that in explanation we should proceed from the known to the unknown. Now my own human individual consciousness is best known to me and most immediately given. We here seem to be under the com- pulsion equally of following what Professor BaLpwin has called the ‘‘leveling up’ and the ‘‘leveling down”’ methods, the mechan- ical and the teleological (or what some would call the anthropo- morphizing) tendencies. Editorial. 61 The limitations of the one method lie in the incredible chasm in degree (if not in kind) which must lie between my complicated conscious life and that of the simplest organisms (if they have any at all). This would seem to check any an- thropomorphizing tendency at the start. BuiNer’s mistake, for example, lies not chiefly in his assumption that the lower organ- isms have consciousness (this may or may not be true), but in his uncritical use of the categories of adult human psychology in describing the reactions of micro-organisms. It is, of course, an inference that any organism besides my own has conscious- ness, but it is an inference, in certain cases, of extreme proba- bility. But that perception, association, preference, choice, mean the same in these lower forms is a point to be demon- strated, not to be assumed. The great need of comparative psychology at the present time is the reduction of human con- scious reactions to the lowest terms, especially as they are rep- resented in the human infant, in the savage. and in primitive man, in order to make the comparison between human and ani- mal behavior more direct. On the other side, the difficulty lies in the fact that the terminology of tropisms and animal reactions has grown up al- most exclusively under the domination non-psychological sci- ence, with the result that the answer to the question as to the presence of mental life in these lower forms is prejudged from the outstart. Evidently there is need of some common basis of method in biology and psychology. This is supplied, in a general way, in the conception of conscious states as themselves acts, as truly asthe more obvious activities of the motor organs, but more subtle because remotely conditioned in the brain pro- cesses. One of the common problems thus, of comparative neurology and comparative psychology becomes, as has been said before, the problem of the evolution of action, and par- ticularly the problem of the determination of the conditions of conscious action. H. HEATH BAWDEN. dl 62 Journal of Comparative Neurology and Psychology. THE INTERNATIONAL COMMISSION ON BRAIN RESEARCH. The idea of appointing a special commission to advise the International Association of Academies as to the means best calculated to advance and coordinate research work on the brain originated, so far as Iam aware, with the late Professor His. He formulated a somewhat ambitious scheme, the main idea of which was the foundation in each country of a central institute to, in a sense, control the research work being done in that particular country and to serve as a means of communication with similar institutes in other countries. The function of these institutes was to receive material for research, sent by people who did not particularly want it, and to distribute it to workers to whom it would prove of special value; to receive and store specimens, photographs and other records of research, so that any worker might have the opportunity of examining the actual material upon which published memoirs were based. The au- thor of the scheme hoped that by means of such institutes more uniformity might be introduced in the methods of research, and in the presentment of results; that the data upon which inves- tigations were founded might be rendered more accessible than heretofore and so a common source of disagreement among workers might be removed; and especially that valuable ma- terial might be directed into those channels where the best use might be made of it. To discuss this proposed scheme a special commission of thirty-five members representing fourteen nationalities was ap- pointed. It was subdivided into seven sub-sections of five members each to consider the scheme from the standpoints of (1) Human Anatomy and Anthropology, (2) Comparative Anat- omy, (3) Histology, (4) Embryology, (5) Physiology, (6) Path- ology and (7) Clinical Medicine. The Commission met in London in the last week of May without its leader and prime mover, without the one man whose quiet persistency could have brought any measure of success in the realization of his scheme: Professor His died in Leipzig three weeks before the meeting. Editorial. 63 Under these depressing circumstances only about twenty of the remaining thirty-four members of the Commission were able to attend the meeting, over which Professor WaALDEYER presided. The subdivision into special subsections was aban- doned and a general discussion took plaee as to the feasibility of establishing such institutes as the late Professor His had suggested. In the public discussion the chief difficulty brought forward against the realization of the scheme was financial— the need for funds to establish and maintain the institutes ; but in private conversation with the members there seemed to be a general concensus of opinion that the scheme was too uto- pian; that it was hardly likely that any considerable body of men would be so self-denying as to present their material to an institute for distribution and that the possibility of accomplish- ing the other objects aimed at in the general scheme seemed to be very slight. However, the members present agreed to strive to make the existing institutions in which each of them was working serve as far as possible the function of such a central in- stitute as had been outlined in the general scheme. This pla- tonic resolution was the only result of the general meeting of the Commission. At the general meeting Professor EDINGER remarked that this exceptional meeting of neurologists afforded an excellent op- portunity to discuss certain problems of general interest, and he proposed that a special meeting be held to discuss the pri- mary subdivision of the vertebrate cerebral hemisphere. At the special meeting, which was presided over by Professor J. N. Lanctey, Professor EDINGER explained that his chief reason for calling the meeting was to discuss the possibility of devising some primary subdivision of the lowlier vertebrate types of cerebral hemisphere such as I had proposed for the Mammalia. I was requested to explain to the meeting the nature of my subdivision of the mammalian hemisphere and especially the significance of the neopallium. In the discussion, which was carried on chiefly by the chairman, Professors ReEtzius, EpIn- GER and the writer, it was agreed that it was not possible at present to suggest any satisfactory mode of subdivision which 64 Journal of Comparative Neurology and Psychology. could be applied to all vertebrates, because the differentiation of structure in the higher groups rendered useless the subdivis- ion which would apply to the lowlier groups. It was therefore decided to submit the question to further investigation and Pro- fessor EDINGER invited me to prepare a report proposing a sub- division, which might be submitted to all those interested in the problem, whether members of the Commission or not, for criticism and suggestions. The other question brought forward for discussion was the possibility of describing cerebral sulci from their relationship to areas of known physiological significance. I explained the definite relationship which the calcarine sulcus, the sulcus lunatus (‘‘Affenspalte’’) and the superior and inferior occipital sulci present to the visual cortex. The essential part of the suprasylvian sulcus is a superior limiting furrow of the auditory cortex. The central sulcus in the Primates is a posterior limit- ing sulcus of the excitable or motor area, whereas the crucial sulcus of the Carnivora is an anterior sulcus of the motor cor- tex. In time it will probably be possible to describe all the important furrows of the hemisphere in terms of their relation- ship to certain definite cortical areas and so to correlate the data of morphology and physiology. The excellent researches of Dr. A. W. CampBeE.Lt of Liverpool and the well-known work of Professor FLECHSIG are rapidly preparing the way for such an advance. In the discussion of this matter, in which Professors HEn- SCHEN, ReETzius, VON Monakow, EDINGER and LANGLEY took part, it was agreed that it was too early to adopt the proposed method of describing sulci. At other informal meetings various members of the Com- mission gave demonstrations. Professor RAMON y CajaL showed extraordinary specimens of neurofibrillae in ganglion cells stained by his new method and Professor HrENscHEN showed many sections of the calcarine region exhibiting various forms of degeneration in the visual area. The Commission is to meet again three years hence. G. ELLIOT SMITH. Pith RAR YS NOTICES: Goldstein, Kurt. Kritische und experimentelle Beitrage zur Frage nach dem Einfluss des Nervensystems auf die embryonale Entwicklung und die Re- generation. Three plates and two text-figures. Arch. f. Entwkmech., 1904, 18, 57-110. ScHAPER’S experiment which showed motility in a frog larva in which he had destroyed the brain and found the spinal cord in a state of disorganization, left a certain desire for more evidence. WOLFF failed to obtain the same decisive result, and Moskowski1 actually con- sidered the claim refuted. GoLDSTEIN, a pupil of SCHAPER, now supplements the first description by a drawing which is more conyinc- ing than SCHAPER’s original one, and he adds new experimental ma- terial, which shows Wo.rFr’s error and firmly establishes very import- ant data in harmony with ScHAPER’s observations. Wotrr divided frog larvae of less than 5 mm. so that the dorsal part contained the entire neural tube, and failed to corroborate ScHa- PER. GOLDSTEIN succeeded in keeping both parts alive for five days, through the use of LocKe’s solution, and he showed that they recover motility in two days. Hence, spontaneous and reflex motility in an early embryonic period does not depend on the existence of nerve conduction of a central organ. Moreover, the ventral piece showed further development; notwithstanding the elimination of the neural tube it reached the size corresponding to a larva of about 6.5 to7.omm. Against these facts any arguments based on laws of regenerative pro- cesses have absolutely no weight, since we deal here merely with a pri- mary condition of development. GOLDSTEIN next turns against certain views of NEUMANN. ‘The latter had concluded that at least for a start in the development of mus- cles, nervous centers were necessary; that, once started, they would develop independently from the central organ, and, in post-embryonic life the trophic center of cord and brain would again put them into a dependent position. The first point is contradicted by various facts. BARDEEN found that muscle differentiation began before the nerves grew forth from the tube. Also Harrison demonstrated an inde 66 Journal of Comparative Neurology and Psychology. pendent development of muscle with fibrils, striation and sarcolemma after excision of the spinal cord and ganglia in larvae of 2.9 and 3.7 mm. NussBAuM, too, admits an independent development of embry- onic muscles up toa certain degree—all agree with GOLDSTEIN’s result that NEUMANN’s first claim is incorrect. His second claim, made in order to explain the persistence of muscles in the amyelic monsters, would not be conclusive on his own assumptions. The muscles need not have degenerated within the short time between the lesion (3d or 4th month) and birth (usually in the 6th or 7th month). In WeBEr- ALESSANDRINI monsters the lesion must have occurred at 2-3 months and the animal reached full term; the muscles were, therefore, degen- erated and mere fat layersand tendons. LEoNnowa also found the mus- cles of her case of amyelia extraordinarily fatty. (It seems, more- over, that the condition of the motor nerves in these monsters is not satisfactorially ascertained, but should be of great importance in view of BeruHe’s claims). HERsst’s attempt to attribute a trophic control over muscles to the spinal ganglia is refuted. Taking all the facts to- gether, GOLDSTEIN comes to the conclusion that the central nervous system during a certain early period of development has no demon- strable morphogenetic influence on the developing organism. The second part of GOLDSTEIN’s article furnishes evidence show- ing that this same rule holds for regeneration. Regeneration need not follow the rules of development. It also depends largely on the age of the animal or embryo. The results in invertebrates are con- tradictory; those on vertebrates (BARFURTH), probably favorable to the theory of independence from the central neryous system. In adult Tritons Wourr thought he had proved the necessity of a nervous influence. He obtained regeneration of a leg after removal of the cord, but with intactness of the ganglia; when the operation was done while regeneration had begun it was arrested zz all but six cases. In an experiment of SCHAPER on a Triton larva of 30 mm., an ex- tremity was regenerated after destruction of the cord, and although there was complete absence of sensibility and motility. What nerves there were, came ‘‘largely” from the spinal ganglia ; the muscles were normal; even a piece of 1 mm. of spinal cord had reformed at the posterior end of the cut of the cord. The conclusion is: In the stage of organ formation (Roux) the normal development and regeneration take place quite independent of the nervous central system. In the stage of functional development there is, however, a decided influence from the central organ. Ae M; Literary Notices. 67 Davenport, C. B. Statistical Methods with special reference to biological variation. Mew York, John Wiley and Sons, viii + 223, second, revised edition, 1904. In this edition DavenporT has revised and enlarged his hand- book of statistical methods in a manner which greatly increases its value to the student of biological variation. An important new chap- ter deals with the results of statistical work, several new methods are described, and the bibliography is much enlarged. The present scope and nature of the book is well indicated by the titles of the several chapters: I. On methods of measuring organisms, II. On the seriation and plotting of data and the frequency poly- gon, III. The ‘classes of frequency polygons, IV. Correlated varia- bility, V. Some results of statistical biological study. The work of the publisher is no less admirable than that of the author of this guide to statistical methods. Every student of exact science will find the book serviceable, and no student or investigator of biological variation can afford to be without it. Dr. DAVENPORT deserves much credit for the impetus which his energy and enthusiasm have imparted to biometric research in America. R. M. Y. Deaver, John B. Surgical Anatomy of the Headand Neck. Philadelphia, P. Blakiston’s Son & Co., 1904, pp. 770. This book is printed from the same plates as the author’s three volume work on Surgical Anatomy, those sections being assem- bled which will be of greatest interest to specialists in diseases of the eye, ear, nose, mouth, throat and nervous system. The book will prove useful to these and also to physiologists, psychologists and general readers who require a manual for ready and rapid consultation. The text is brief and clear and the illustrations areadmirable. There are 177 full page plates drawn from original dissections, which by themselves constitute a useful atlas of topographical anatomy. All parts are designated on the plates in full, thus permitting the reader to glean much of his information by simple inspection without con- sultation of the text. The external and gross features of the brain are fully and clearly figured, without, however, any attention to histo- logical detail. The printing and binding are exceptionally good. cos Mendel, E. and Jacobsohn, L. Jahresbericht iiber die Leistungen und Fort- schritte auf dem Gebiete der Neurologie und Psychiatrie. VII Jahrgang: Bericht iiber das Jaht 1903. Berlin, S. Karger, 1904. Price, M. 35. The Jahresbericht is issued this year in two volumes and, like its predecessors, is indispensable to all who wish to keep abreast of the vol- uminous literature of neurology and psychiatry. The bibliographies are 68 Journal of Comparative Neurology and Psychology. grouped by topics and accompanied by critical annotations on the con- tents of nearly all of the papers cited. Compendious indexes make the whole mass of material instantly available. Gr J.) Sfameni, Pasquale. Sulle terminazioni nervose nei genitali femminili esterni e sul loro significato morfologico e funzionale. Archivio at Frsiologia, 1904, 1, 345-384. In this careful and thorough investigation the author has confined his attention to the nerve terminations in the clitoris and the vulva. Topographically these are of three classes: (a) Intrapapillar nerve terminations; (b) nerve terminations in the reticular layer of the derma; (c) terminations in the subdermal connective tissue. The first and second of these are by far the most important. All of these terminations reduce to the single type of ‘‘a nervous organ, with or without an envelop of connective tissue, composed of one or more nerve fibers which, after divesting themselves of their myelin sheaths, if they have any, ramify in and arounda granular, nucleated sub- stance.” The nerve corpuscles are not the terminations of the sensory nerves but are peripheral ganglia, corresponding to spinal ganglia, and their function is to bring about a more subtle division and modifi- cation of the stimuli. The real terminations are always differentiated ectoderm cells scattered through the epithelium and the superficial layers of the derma, and connected with sensory nerve fibers. There is a bibliography of 46 citations. Jo sC. BEER; Harrison, Ross Granville. An Experimental Study of the Relation of the Nervous System to the Developing Musculature in the Embryo of the Frog. Zhe American Journal of Anatomy, 1904, 3, 197-220. Observations upon embryos the spinal cord of which had been completely isolated before the appearance of either nerve fibers or contractile substance in the musculature, and upon larvae which were reared in a state of constant narcosis by means of a dilute solution of acetone chloroform. Conclusion: ‘‘all of the constructive processes involved in the production of the specific structure and arrangement of the muscle fibers take place independently of stimuli from the nervous system and of the functional activity of the muscles them- ' selves. GARG. Hardesty, Irving. On The Development and Nature of the Neuroglia. Zhe American Journal of Anatomy, 1904, 3, 229-268. A study of pig embryos to demonstrate the syncytial nature of the neuroglia as proposed in the author’s earlier paper on the spinal cord of the elephant. Attention is called to cells resembling the nerve- corpuscles of the peripheral nerve which encircle the medullating ax- ones of the cord. G. E. C. Literary Notices. 69 Streeter, George L. The Structure of the Spinal Cord of the Ostrich. The American Journal of Anatomy, 1904, 3, 1-27. A description of the meninges and the macroscopic and micro- scopic features of the cord; including noteworthy contributions on the arachnoidea, the relation of the peripheral glia sheath to the sinus rhomboideus, REISSNER’s fiber, and the nuclei marginales. Tabulated measurements and a diagram of the cross-section area, in each seg- ment of the cord, of the funiculi ventro-laterales, substantia grisea, and funiculi dorsales. G. BE, 6: Fiirbringer, Max. Morphologische Streitfragen. 1. Nervus trochlearis. 2. Rabl’s Methode und Behandlung der Extremitatenfrage. Morph. Jahro., 1902, 30, 85-274. Part I (pp. 86-143) is an important contribution to the morphol- ogy of the fourth nerve. It is, in the main, a reply to the criticisms made by Rast and Douwrn upon the author’s theory to account for the dorsal origin and the crossing of the nerve in question: viz. that the superior oblique muscles were originally muscles of the parietal eye, and that with the disappearance of that organ the originally right oblique muscle became associated with the left eye, and zvce versa. A bibliography of 296 titles. Ges Ge Van Gehuchten, A. Considérations sur la structure interne des cellules nerv- euses et sur les connexions anatomiques des neurones. Le Névraxe, 1904, 6, 83-116. The author places great emphasis upon the fact that the anatom- ical independence of neurones, as they are demonstrated by the methods of Gore and EHRLICH, is the substance of the neurone theory. He considers that, so interpreted, the neurone theory is not contradicted by a single anatomical fact. Intracellular continuity by means of nets and ‘‘nerv6se Grau” as proposed by Berue, Nissi and others is purely hypothetical. Even the auto-regeneration of the ax- one as demonstrated by BeTHE, and vAN GEHUCHTEN repeats this ex- periment successfully, affects only our idea of the origin of the neu- rone and does not bear upon the neurone theory proper. While in some nerve cells the fibrillae seem to be independent, in many they clearly anastomose in the dendrite and especially in the perikaryon. This condition refutes BeTHeE’s and NIss_’s opposition to the idea of polarity of the nerve cell, and supports the neurone theory. Gah C: Van Gehuchten, A. Connexions centrales du noyau de Deiters et des masses grises voisines (Faisceau vestibulo-spinal, Faisceau longitudinal postérieur, Stries médullaires). Le Névraxe, 1904, 5, 19-74. A critical review of recent literature on the subject, and a report 70 Journal of Comparative Neurology and Psychology. on several of the author’s degenerative experiments on rabbits. The Marchi method was supplemented with the methods of indirect Walle- rian degeneration and of Nissi. The vestibulo-spinal tract arises ex- clusively after DEITER’s nucleus and descends in the anterior column as far as the lumbo-sacral region. The spinal portion of the posterior longi- tudinal fasciculus is exclusively descending. Ascending fibers are found in this tract only within the bulb and mesencephalon. Both ascending and descending heterolateral fibers probably come as inferior arcuate fibers either from the terminal vestibular nucleus or from the tuberculum acusticum. The ascending homolateral fibers arise higher up, probably from the nucleus of BECHTEREW. The striae medullares arise exclusively in the tuberculum acusticum. Giese Soukhanoff. Contribution 4 l’étude du réseau endocellulaire dans les éléments nerveux des ganglions spinaux. Le Névraxe, 1904, 6, 75-80. The endocellular net as observed by the Kopscu osmic acid method is identical with the Gouai endocellular net, and is not the same structure as the canaliculi of HOLMGREN and others. G. Ee. Agababow, A. Ueber die Nerven der Sclera. Archiv f. muk. Anat., Bd. 63, H. 4, pp- 701-709, 1904. Hyde, Ida H. Localization of the Respiratory Center in the Skate. dmer. Jour. Phystol., 1904, 10, 236-258. By the employment of careful and precise methods of experi- mentation on living skates, Miss Hype has demonstrated the segmen- tal arrangement of the respiratory center. The animal under observa- tion was placed on a board, and sea-water was passed in a continuous stream through a tube into the mouth. Artificial respiration could in this way be maintained for days. In a skate thus situated the medulla may be separated from the spinal cord and from those portions of the brain lying anterior to it without destroying its function as a respiratory center. Medisection of the medulla is followed, after the inhibitory effects of shock have passed off, by a resumption of codrdinated respiratory movements on both sides of the body. The gill arches of one side may move in a rhythm quite different from that of the opposite side. The spiracles may keep time with the gill arches of their re- spective sides, or both spiracles may be in rhythm with the arches of one side. From the results of median section of the medulla it be. came evident that ‘‘the centers for the nervous respiratory mechanism in the skate were bilateral, each half controlling the movements of its respective side.” Evidence of the segmental character of these bilateral respiratory Literary Notices. 71 centers was obtained by following medisection with hemisection. One lateral half of the medulla was separated into anterior and posterior divisions by a transverse cut. The arches and spiracle of the unin- jured side continued their normal movements. The spiracle and first gill arch, controlled by the anterior division of the opposite side, some- times exhibited a rhythm which differed both from the rhythm of the uninjured side and also from that of the remaining gill arches of the same side, which were under the control of the posterior division of the lateral half of the medulla. At times the respiratory mechanisms connected with all three divisions of the medulla moved in unison. Lesions of the different lobes of the medulla indicated that the ganglion cells of sensory respiratory neurones, those of the seventh, ninth and tenth cranial nerves, are situated in the lobus vagi. Motor ganglion cells and neuraxones were found ventrad of the lobus vagi and in the fasciculus longitudinalis posterior. FW. Gardella, Eloisa. Azione dell’ acido fenico sulla sensibilita gustativa. 246. Camera lucida. Reichert, Qs Ay (Ooo 7/ Be ment of the sympathetic as a whole has proceeded father than elsewhere. These places are in the region of the brachial and the lumbar plexuses. Also, the sympathetic is usually better developed in the immediate region of the nerves than it is be- tween them (Fig. 9). Eighteen Millimeter Stage.—Between the vagus ganglion and the second nerve, the sympathetic is easily traced as a large, distinct, and continuous cord (Fig. 10, Sy.). Posterior to the second spinal nerve, the ridge (Fig’s. 5 and 6, Az.) now is well 124 Journal of Comparative Neurology and Psychology. marked, especially in the region of the lumbar plexus, where it has reached the height of its development (Fig. 10, Az.). The angle which it makes with the horizontal plane varies in differ- ent regions. Anteriorly, it extends upward and inward (Fig. 5, Az.), approaching even a horizontal position in some places. Following it backward, in the region where the median aorta begins (Fig’s. 1oand 11, *), itassumes rather abruptly a vertical position, and then immediately begins to lean outward, till, in the region of the kidney, it points upward and outward (Fig. 6, Rz.), making an angle with the horizontal plane varying from 30° to 60°. Fig. 6.—Transverse section of 18.5 mm. toad, between the sixth and sev- enth spinal nerves (see Fig. 10), showing the sympathetic ridge, Az., and the sym- pathetic cord, Sy., well differentiated at the top of the ridge. Abbreviations, same as in preceding figures. 246. Camera lucida. Reichert, oc. 2, obj. 7 a. The sympathetic cord (Fig. 6, Sy.) is larger and more defi- nite, and is found surrounded by a membrane more frequently than it isseen without one. The cord lies at the top of the ridge, including in a few places the greater part of the latter. The rami communicantes, at this stage, have increased in size and distinctness. Besides those in connection with the fourth, Jones, Development of the Sympathetic. 125 fifth, sixth, seventh, and eighth nerves, there is also an incipient one on the ninth. Twenty-one Millimeter Stage.—In a toad 21 mm. long, the sympathetic cord is continuous from the vagus ganglion back to the region between the ninth and tenth nerves. But it is to be borne in mind that the development back of the second nerve is different from that in front of this point. The ridge has mostly disappeared. A considerable portion of it remains, how- ever, between the fourth and fifth nerves and smaller parts, pos- teriorly. Compare Fig. 10, Az., where the ridge is well devel- oped, with Fig. 11, Az., in the region of the eighth and ninth nerves, where the ridge has almost completely disappeared. Between the vagus ganglion and the second spinal nerve, the sympathetic cord is removed a considerable distance dor- sally from the aorta. (Cf. Fig. 2, Sy., where it lies almost up- on the aorta, do. 2.) The mass of cells anterior to the kidney, with which the ridge was connected in earlier stages (Fig’s. I and 7, Ma.), is still present, but is flattened posteriorly, where it occurs as a horizontal plate-like mass of cells extending later- ally from the aorta. As the ridge disappears, the sympathetic cord is left alone, large and distinct, lying most of the way upon this mass of cells but not continuous with it and removed later- ally a considerable distance from the aorta. In the region of the kidney, the cords lies on the dorsal side of this organ. The sympathetic cords of the two sides can be traced back as far as a point midway between the ninth and tenth nerves, where they unite underneath the aorta. Beginnings of rami are found in connection with the first and third nerves ; a small one is seen on the second, while rath- er distinct ones appear on the fourth, fifth. sixth, seventh, eighth, and ninth nerves (Fig. 11, &.). The sympathetic cord is sur- rounded by a well-developed membrane, throughout most of its extent. The cord is composed now not of cells alone, for most of the way it shows fibrous structure also. Furthermore, it is better developed in the immediate region of the nerves than it is between them (Fig. 11, Sy.), a condition only slightly no- ticeable in earlier stages. Between the nerves, the cord is rela- 126 Journal of Comparative Neurology and Psychology. Fic. 7 Fie. 8 fig. 7.—Diagrammatic reconstruction of the sympathetic nervous system of agmm. toad, dorsal view. The kidney and the sympathetic with its related structures are represented as having been shifted from a position inferiorly along side the aorta (see Fig. 1) to a position on a level with the spinal cord, but re- moved laterally a distance equal to that between the sympathetic and the spinal cord before the change of position. The more closely dotted portion represents sympathetic tissue; posterior to the second spinal nerve, the w2dth of this closely dotted portion represents the Aezght of the sympathetic ridge. The lightly dot- ted area represents the structures with which the sympathetic is connected dur- ing its development. X marks the anterior end of the adult kidney. The con- nection between the sympathetic and the spinal nerves is not shown. * marks the anterior end of the median dorsal aorta. H. X., head kidney. V’. 7V., fourth ventricle. X., vagus ganglion. 7., 2., etc., ganglia of first, second, etc. spinal nerves. For other abbreviations, see Fig’s. 1-6. 21. fig §.—Diagrammatic reconstruction of the sympathetic nervous system ofa 12.5 mm. toad. The representation of the rami communicantes here and in succeeding figures is exceedingly diagrammatic. For abbreviations and other explanations, see Fig. 7. 28. Jones, Development of the Sympathetic. 127 Fig. g.—Diagrammatic reconstruction of the sympathetic nervous system of a Ig mm. toad. A#., ramus communi- cans ; dotted line lettered #., ramus only partially developed. Other abbreviations, same asin Fig’s. 7and 8. X 28. fig. 1o.—Diagrammatic reconstruc- tion of the sympathetic nervous sys- tem of an18.5mm.toad. The ridge, Rz., which is figured as extending inward horizontally throughout its entire extent has, in the actual speci- men, an upward and zzward direction anteriorly (see Fig. 5, Az.) and an upward and outward direction poste- riorly (see Fig. 6, z.). Reference marks, same as in Fig’s. 7, 8, and 9. x 24. 128 Journal of Comparative Neurology and Psychology. tively slender, this condition being especially marked in the re- gion of the kidney. The cellular enlargements of the sympa- thetic cord in connection with the nerves now may be called ganglia, and the constricted portions between the nerves, which are becoming distinctly fibrous in structure, may be called com- missures. Fig. 11.—Diagrammatic reconstruction of the sympathetic nervous system of a 21mm. toad. Reference marks, same as in previous figures. X 24. Jones, Development of the Sympathetic. 129 Condition after the Metamorphosis.—By the time the tail has almost disappeared, the sympathetic cord not only is completely separated from its antecedent structures, but is removed dorsal- ly and somewhat laterally from the aorta. In the mid-trunk region, it lies as high as the upper border of the notochord (Fig. 12, Sy. G. 2.), while in the preceding stage it was on a level with the lower border of it. Fig. 12.—Transverse section through the second spinal nerve, from a toad in which the tail has almost completely disappeared. Co/. Sy., collateral sympa- thetic. #&., ramus. Sf. G. 2., ganglion second spinal nerve. Sf. NV. 2., second spinal nerve. Other abbreviations, same as in preceding figures. For develop- ment of ramus, cf. Fig. 4. XX 246. Camera lucida. Reichert, oc. 4, obj. 3. The ridge and the structure with which it was connected, have now atrophied almost completely. Nearly all of the rami communicantes have become much longer, and the collateral sympathetic also is well developed (Fig. 12, Col. Sy.), while the differentiation of ganglia and commissures is now almost complete. 130 Journal of Comparative Neurology and Psychology. Summary. (1) In the region between the vagus ganglion and the sec- ond spinal nerve, the sympathetic arises ina comparatively sim- ple and direct manner: cells, probably of epiblastic origin, scat- tered in the mesoblast gradually become aggregated (Fig. 2, Sy.) to form a cellular cord. This is similar to the process in mam- mals described by PATERSON, except that he finds the cord is at first entirely independent of any other structure, while in the toad the cells of the sympathetic cord lie in contact with the fi- bers of the first and second spinal nerves, from the earliest stages. (2) In the region posterior to the second spinal nerve,the origin of the sympathetic system is more complex. It appears first as a small ridge of cells (Fig. 1, Az.) lying close along side the aorta. The cells at the top of this ridge, as it becomes higher, are differentiated to form the sympathetic cord (Fig’s. 5 and 6, Az. and Sy.). Later, the ridge disappears entirely, leaving the cord free, save its connections with the collateral sympathetic and with the spinal nerves (Fig. 12, Col. Sy. and &.). (3) The sympathetic ganglia and commissures arise di- rectly from the sympathetic cord. The latter becomes enlarged in the region of the nerves, forming the ganglia, while the por- tions between the nerves become reduced, forming commissures, which, immediately after metamorphosis, are composed largely of nerve fibers. (Fig. 11 shows the enlargements and the constricted portions.) These findings contrast somewhat with the observations of BaLFour on elasmobranchs, where he finds that the ganglia arise entirely independent of each other, the commissures appearing later as outgrowths from the ganglia. (4) The rami communicantes arise in the toad in the same manner as in elasmobranchs (BaLFour). The cord (the gang- lion in elasmobranchs) lies in contact with the nerve from the very first (Fig. 4, Sy.). Later it gradually is removed from the nerve, retaining, however, fibrous connections, which constitute the ramus. The rami appear earliest in the mid-trunk region, my preparations showing the first one in connection with the Jones, Development of the Sympathetic. 131 sixth nerve .(12 mm. stage). The first and the ninth are the last nerves to develop rami. LITERATURE. For publications prior to 1878, seeONODI, Arch. f. Anat. u. Entwickelungsch. 85, and PATERSON, Philosophical Transactions, ’91. Balfour, F. M. 78. Monograph on the Development of Elasmobranch Fishes. Pp. 172- 173 and 239-244. 81. Comparative Embryology. Vol. 2, pp. 358-386 and 548. Hertwig, Oscar. *92. Text-book of Embryology. P. 462. His, W., Jr. 97. Ueber die Entwickelung Bauchsympatheticus beim Hiihnchen und Menschen. c. Segment 2. Neuromere ii, lateral eyes, hypophysis. The interpretation of the eyes as the representative of the cutaneous division has been given above. In the central nerv- ous system important centers are developed. Neuromere ii in- cludes the striatum area and also that of the pallium. The writer has previously referred to the striatum as probably repre- senting the tract cells of the cord and oblongata. The nature Jounston, Worphology of the Head. 251 of the specialized nucleus known as the epistriatum is a difficult question. It serves in fishes as the end nucleus of two very different classes of fibers. The one comes from the inferior lobes and corpora mammillaria by way of the anterior commis- sure; the other comes from the cells of the olfactory bulb through a somewhat isolated portion of the anterior commissure. It is probable that this is the more primitive tract and that it is gradually supplanted by tracts from the hypothalamus and per- haps other regions. In any case the epistriatum seems to be- long chiefly to the visceral sensory apparatus. The origin and relationships of the cerebral pallium have been discussed by the writer elsewhere (70). The massive pallium which is related to the olfactory apparatus is regarded as a neomorph in gnathostomes and as such it is not of especial importance for our present subject. It has been suggested above, however, that this olfactory pallium may have been preceded by a structure which was the general cutaneous nucleus of the first segment. The pallium, then, is to be re- garded as a new structure developed in the space from which the lateral eyes were derived. If Hicv’s interpretation of the neuromeric relations is cor_ rect, we are brought to the interesting result that the dienceph- alon is formed from two neuromeres, the hypothalamus belong- ing to the same neuromere with the striatum and pallium and lying morphologically ventral to them. The writer has shown that in fishes (Acipenser, 67) throughout the whole length of the ventral wall of this second neuromere the structures adjacent to the middle line (nucleus thaeniae, inferior lobes in part, and corpus mammillare) are histologically identical. In Petromyzon (68) the inferior lobes and corpus mammillare are fundamentally alike, there being but slight differentation. It seems, then, that a single nucleus has been interrupted by the optic chiasma and accompanying decussations. The posterior portion of this nucleus was associated with the saccus vasculosus and also came to receive tertiary tracts from both the olfactory and the somatic sensory centers. It has consequently developed into a large coordinating center. The anterior portion of the nucleus (nuc. 252 Journal of Comparative Neurology and Psychology. thaeniae) received secondary olfactory tracts and remained at a lower stage of development. The absence of epibranchial placodes in segments 2 and 3 is noteworthy. If the hypophysis is in segment 2 no placode is to be expected. The absence of one in segment 3 may argue against the supposition that a gill was ever present in that seg- ment. The lense placode and the N. thalamicus would then appear to be the vestiges of the nervous structures connected with the most anterior ancestral gill slit. Whether the hypophysis is to be assigned to this segment or to segment I involves the question whether we are to recog- nize a prostomium in vertebrates. The hypophysis invagin- ates about opposite the groove between neuromeres i and ii and extends back beneath neuromere ii. This canal is perhaps equivalent to the buccal cavity of invertebrates. The treatment of the olfactory organ in this paper and the interpretation of the hypophysis as the invertebrate mouth are both consistent with the recognition of the first segmeut as a prostomium. d. Segment 1. Prostomium. Neuromere i, nerve of Locy, olfactory epithelum and nerve. The writer is unable to accept KUPFFER’s idea of a median olfactory organ. It does not appear from his descriptions that the median thickening between the olfactory placodes is ever sensory. Its connection with the brain for some time is to be explained as a mere persistence of the continuity of the neural tube with the ectoderm at the lower edge of the neuropore. The olfactory sense cells exist from the first in bilateral groups and are innervated by paired nerves. As may be inferred from references to Amphioxus made above, the writer thinks that the interpretation of the olfactory pit as a true olfactory organ requires further evidence. The olfactory bulbs are formed by great growth of the lateral walls of the first neuromere. In lower fishes (67, 16) and cyclostomes (68) these bulbs still show a structure compar- able to that of the primitive brain wall. The highly specialized mitral cells are not primitive features of the olfactory apparatus, Jounston, Morphology of the Head. 253 but are neomorphs in craniates which are just beginning their specialization in cyclostomes. The general cutaneous nerve of Locy and the olfactory nerve are to be taken together as roughly the equivalent of the nerve of the prostomium in segmented worms. 17. The dorsal commuissures of the brain. In Figs. 1-7 are shown the longitudinal zones of the brain belonging to the four functional divisions of the nervous system. A further review of these zones does not fall within the scope of the present paper. Some remarks upon the dorsal commis- sures and their relations to the zones, however, will perhaps be of value. It should be said at the outset that the fiber crossings in the brain of lower vertebrates, both dorsal and ventral, are in the greatest part if not wholly mere decussations. True com- missures are almost unknown. When the word ‘‘commissure”’ is used in the following paragraphs it is used because it has come to be part of the accepted name of a given fiber-crossing. The dorsal decussation of the spinal cord in higher verte- brates contain splanchnic sensory (sympathetic) fibers, collaterals from cutaneous fibers, and perhaps secondary elements. At the junction of the spinal cord and brain in all vertebrates this decussation is greatly enlarged just behind the choroid plexus of the IV ventricle. This enlarged portion, known as the com- missura infima HALLERI, is composed chiefly of splanchnic sen- sory fibers from the roots of the VII, IX and X nerves. These fibers for the most part end in the median nucleus of the com- missure of Caja (46, 67, 68). A part of them without cross- ing (and a part of the crossed fibers also?) pass on back into the spinal cord (68). Other fibers in the commissura infima come from the cells of the nucleus funiculi (90, 46). From these facts it is evident that both splanchnic sensory and somatic sensory elements cross in the dorsal decussation of the cord. The somatic sensory elements are chiefly or wholly secondary fibers, or only collaterals. These two components must be rigidly distinguished if we are to understand the dorsal decussations of the brain. The 254 Journal of Comparative Neurology and Psychology. dorsal decussation of the medulla oblongata is not obliterated on account of the non-nervous roof, but its elements are crowded forward or backward. Behind the choroid plexus the commis- sura infima contains the splanchnic sensory elements proper to the segments of the VII, IX and X nerves. It is probable that the course of the root fibers of these nerves within the brain has been influenced by the crowding backward of their decussation and median nucleus by the choroid plexus. It is further prob- able that those fibers which take this caudal course are the more primitive components of these nerves, namely the general vis- ceral fibers as distinguished from end bud fibers. It is known that the end bud fibers in teleosts (48) end chiefly in the lobus facialis. The point of especial interest in the present connec- tion is that the concentration of the visceral decussation for the VII, [X and X nerves behind the choroid plexus precludes the expectation that the visceral elements of the first order will be found in the dorsal decussations farther forward. There are no visceral nerves anterior to N. VII. The somatic sensory elements have behaved differently with reference to the IV ventricle. Instead of concentrating behind it they have concentrated in front of it. In those verte- brates in which the cerebellum is most primitive (Petromyzon, Protopterus, Urodeles) a commissure constitutes a prominent part of it. This decussation consists of axones of granule cells situated in the cerebellum destined to the somatic sensory nuclei of the medulla oblongata. This is therefore to be con- sidered as the homologue of the somatic sensory portion of the dorsal decussation of the spinal cord. It is an important de- cussation in all lower vertebrates. A second prominent cerebellar decussation is found in fishes (67). This is situated farther ventrally and cephalad and in- stead of connecting the dorsal portions or lateral lobes of the cerebellum, connects two nuclei which in fishes lie in the lateral walls distinctly ventral to the somatic sensory centers, the sec- ondary vagus nuclei. The fibers of the secondary vagus tract coming from the vagus lobe end in part in the secondary vagus nucleus of the same side and in part cross Jounston, Morphology of the Head. 255 to the opposite side. The remainder of the decussation is formed by axones of cells of these nuclei. The destination of these axones is unknown, so that we are uncertain whether true commissural elements are present. It is evident, however, that the decussation belongs to the splanchnic sensory division of the nervous system. In mammals the tract which corresponds to the secondary vagus tract is the direct cerebellar tract arising from the cells of Crarke’s column in the cord. This tract ends in a nucleus which lies in the roof of the IV ventricle in the vermis. It is, however, probably homologous with the secondary vagus nucleus of lower vertebrates. The dorsal decussation of the optic lobes requires but brief mention. In accordance with the interpretation of the lobes given in this and previous papers it must be regarded asa somatic sensory decussation comparable with the somatic por- tion of the decussation in the spinal cord. The posterior commissure is a decussation of fibers arising from a nucleus in the dorsal part of the diencephalon and mesencephalon (75, 68). After crossing the fibers run toward the base of the medulla oblongata. The destination of the fibers is unknown, and nothing is known of the fiber tracts which may come to end in the nucleus of origin. The fact that the decussation is somewhat intermingled with the dorsal de- cussation of the optic lobes suggests that the two may be related. Some of the cells of origin of the posterior commissure in Petromyzon are so situated as to be indistinguishable by their position from those of the optic lobes. Without knowing the connections and functions of the posterior commissure, nothing further can be said. In the roof of the diencephalon two decussations are pres- ent, the well known superior or habenular commissure and a decussation closely related to the base of the epiphysis known only in a few forms (67, 62). The superior commissure con- tains decussating fibers from the olfactory nuclei of the fore-brain (tractus olfacto-habenularis) and also, according to CaTots (16) and CAMERON (15) true commissural fibers. A certain similarity 256 Journal of Comparative Neurology and Psychology. is to be noticed between this and the decussation between the secondary vagus nuclei inthe cerebellum. Decussating fibers of the second and third order are present in each case. A further point of comparison is found in the fact that the ganglia habenulae appear to be a part of the central grey some distance removed from the dorsal wall of the brain, which here is a choroid plexus. If we accept the supposition that the somatic sensory nucleus of the diencephalon has degenerated, the morphological position of the ganglia habenulae corresponds rather closely to that of the secondary vagus nucleus beneath the somatic sensory centers of the cerebellum. The choroid plexus of the diencephalon is regarded as morphologically equivalent to the optic lobes or dorsal part of the cerebellum and the ganglia habenulae are morphologically lateral. These hypotheses have a significance in connection with the question of the relation of the olfactory and gustatory organs and centers discussed above. Not enough is known about the epiphysial decussation to admit of any discussion. The anterior commissure consists of two distinct parts: a smaller, anterior portion, sometimes isolated, composed of fibers from cells of the olfactory bulb destined to the epistriatum ; and a larger portion composed of fibers from the inferior lobes also destined to the epistriatum. A third element, consisting of fibers from the lateral cortex to the opposite epistriatum, need not be considered since it is not primitive in vertebrates. The tract from the inferior lobes is a tertiary tract which may be either olfactory or somatic sensory in character. We have seen reasons for thinking that the hypothalamus has been modified by the entrance into it of the somatic sensory tracts. We must therefore regard the secondary (and tertiary?) olfactory tracts as constituting the primitive portion of the anterior commissure. The writer is unable to see any resemblance between this and the somatic sensory decussation, while there is a certain simi- larity between the anterior commissure and the splanchnic sen- sory decussations of the ganglia habenulae and the secondary vagus nuclei. If the anterior commissure is to be compared Jounston, Morphology of the Head. 257 with the other brain commissures it is doubtless to be considered as a part of the dorsal splanchnic decussations. We may summarize the dorsal commissures by saying that the dorsal decussation of the cord has been differentiated in the brain into separate somatic and splanchnic sensory decussations. The commissura infima HALLERI, the decussation between the secondary vagus nuclei, the superior commissure, and the an- terior commissure represent the splanchnic portion. The dorsal commissure of the cerebellum, the dorsal decussation and _ pos- terior commissure of the mesencephalon constitute the somatic portion. Whether the pallial commissure will be brought into the latter category on account of the relations of Locy’s nerve remains to be seen. Some reference was made to the ventral commissures in discussing the morphology of the eye. The writer has nothing further to add. 1S. The sympathetic system. The relation of the sympathetic to the four functional divisions of the nervous system is important in connection with the subjects dealt with in the present paper. Although the sympathetic in lower vertebrates, where we must look for its genetic relations, is very imperfectly understood, yet sufficient is known to indicate that the sympathetic is morphologically related to the visceral divisions. This is what the function of the sympathetic and the central relations of its fibers in higher forms has led us to expect. In the trunk regions in selachians (60) the sympathetic ganglia are budded off from the distal portion of the spinal ganglia after the union of the ventral with the dorsal root. It does not appear that anything is contributed to the sympathetic by the ventral root in fishes. In the adult (64, 98) sen- sory fibers coming from the viscera pass through the sym- pathetic and spinal ganglia to end in the region of CLARKE’S column in the cord, and motor fibers arising in the lateral motor nucleus enter the sympathetic by way of the dorsal root (and in higher forms by way of the ventral root also). If we interpret 258 Journal of Comparative Neurology and Psychology. the formation of the sympathetic ganglia in the light of the adult structure, we must suppose that the spinal ganglion cells which migrate to the sympathetic ganglia are those of the gen- eral visceral component. It is a striking fact which has not passed unnoticed that the composition of the sympathetic closely resembles that of a branchial nerve minus the cutaneous components of the latter. In cyclostomes and selachians no sympathetic ganglia have been found in the head, except the ganglion ciliare. If this be the true condition then in these forms the cranial ganglia must be considered to contain the equivalent of the sympathetic. That they can not as a whole be considered homologous with the sympathetic ganglia of the trunk is obvious from the presence of taste fibers and general cutaneous fibers. In teleosts (46) sympathetic ganglia are present in connection with the typical ganglia of the profundus, V, VII, IX and X nerves, in addition to the ciliary ganglion which is the sympathetic ganglion of the segment anterior to the profundus. The ganglia are connected by a longitudinal fiber strand as in the trunk. The high develop- ment of the sympathetic in the head of teleosts suggests that it may yet be found in selachians. 19. Relation of dorsal and ventral nerve roots to the myotomes. In Amphioxus the ventral root emerges from the spinal cord opposite a myotome and enters the muscle directly. The dorsal root emerges from the cord between two myotomes, passes along the myoseptum to the surface and is distributed to the ectoderm overlying the myotome next anterior to its root. I can add from my own observation that although the ventral ramus (the visceral fibers of which do not concern us here) usually passes vertically ventrad and so crosses the surface of three myotomes, it not infrequently happens, especially in the caudal half of the body, that the ventral ramus runs caudo- ventrally at the same angle as the myotomes and a single nerve is confined to the area overlying a single myotome. In Ammocoetes by putting together the work of HaTscHEK (44) and Ko.rzorF we can account for every one of the dorsal Jounston, Morphology of the Head. 259 and ventral roots of the cranial and first spinal nerves and can state their origin, relation to the myotomes and distribution. Reference to Fig. 10, with which HartscuHex’s Fig. 11 and Ko.rzorr’s diagrams may be compared, will make the relations clear. The profundus passes over the caudal and ectal surface of somite 1, which is innervated by N. III, and is distributed to the ectoderm outside and in front of that somite. The trigem- inus passes over the caudal and ectal surface of somite 2, in- nervated by N. IV, and is distributed to the ectoderm overlying that somite and its mandibular arch. N. VII passes caudal to somite 3, innervated by N. VI, and supplies the hyoid arch. It has no cutaneous component. N. IX lies between somites 4 and 5 and has a dorsal ramus passing out along this septum (HatscHEK’s Occ. 1). The vagus ganglion appears between somites 5 and 6 and its dorsal ramus passes out along this sep- tum. Thereisno ventral root to either somite 4 or § on account of the early reduction of the mesial part of each of these somites. Behind somite 6 (KoLTzorFr) both dorsal and ventral roots are present. The ventral root of somite 6 probably innervates myotomes 4, 5 and 6 in the larva. The dorsal root sends a ramus to the skin of the occipital region (Occ. 3, HaTSCHEK). We should expect the dorsal rami of N. IX, X and Sp. 1 to be distributed to the ectoderm overlying somites 4, 5 and 6 re- spectively. It is probable that this is their actual position in the embryo but owing to the migration forward of myotomes 4, 5, 6and 7 during development myotome 5 is brought beneath the ectoderm belonging to somite 4, myotome 6 beneath the ectoderm of somite 5, etc. This accounts for the apparent distribution of HatTscHEK’s Occ. z, 2 and 3 to the area over myotomes 5, 6 and 7. These dorsal nerves all persist in the adult but the ventral nerve of somite 6 disappears and myo- tomes 4, 5, 6 and 7 are all innervated by the ventral nerve of myotome 7. From the work of these two authors, then, it would appear that the relations in cyclostomes are the same as in Amphioxus, the dorsal nerves innervating the ectoderm overlying the myotomes next anterior to the dorsal roots. Two further remarks are to be made. NEAL’s suggestion that 260 Journal of Comparative Neurology and Psychology. N. VI includes the ventral nerve of somite 4 (and that of somite 5 ?) does not affect the the present question. It is an important question, however, whether HarscHExK’s Occ. 1, 2 and 3 are all general cutaneous nerves. If they are lateral line nerves without general cutaneous fibers they are worthless for the present purpose. The writer has described a branch from the N. lateralis to this part of the skin. The cranial nerves of Petromyzon require to be reinvestigated, but so far as our pres- ent knowledge goes the above account of the relation of the dorsal roots to the myotomes appears to the writer to be per- fectly sound. The same relation of the nerves to the somites is found in Spinax (12) where N. IX lies behind somite 4, N. X behind somite 5, and a rudimentary ganglion is formed behind each of the following somites. Six of these rudimentary dorsal nerves eventually disappear owing to the reduction and shifting of myotomes and consequent reduction of cutaneous area. HaTscuHEK in 1892 came to the same conclusion as I have stated with regard to the relation of dorsal roots to myotomes in Amphioxus and cyclostomes. In 1893 he published a brief correction (45) in which he said that in all higher vertebrates the dorsal root unites with the next following ventral root. This can be made out most readily, he says, in amphibian larvae. I have examined such sections of amphibian embryos as I have by me and although I have none old enough to show the distri- bution of the nerve rami, I find two facts opposed to HATSCHEK’S statement. The dorsal roots are always a short distance caudal to the ventral roots, and the ventral roots run across the cephalic face of the ganglia. I do not see how this could result if each dorsal root joined the next following ventral root. I hope soon to investigate the matter farther in Amblystoma. The second statement of HaTscHEK seems to have been generally accepted by later workers. I am inclined to think that his first statement was correct for the fishes at least. 20. Comparison of head and trunk. Aside from the development of special organs in the head, the chief differences between the head and trunk lie in the skele- Jounston, Morphology of the Head. 261 ton and somatic muscles and in the relation of the dorsal and ventral nerve roots to one another and to the myotomes. The formation of a rigid cranium has had very important consequnces in the disappearance of postauditory myotomes and the develop- ment of complicated conditions in the occipital region. To this also is due the fact that certain myotomes have been released from their attachment to a segmented skeleton and have come to move the eyeball. It may be said that the same cause has indirectly determined the relation of the nerve roots to the myotomes. In cyclostomes, where the buccal apparatus has demanded the preservation of the dorso-lateral portion of the postauditory myotomes, the nerve roots are covered by these very much as in the trunk. In gnathostomes, however, when postauditory myotomes completely disappear the nervesare given free access to the ectoderm. When trunk myotomes shift for- ward it is their ventro-mesial portions which become attached to the cranium and so the nerves retain their superficial position. The union of the dorsal and ventral roots in the trunk is a late development and the head has retained the more primitive con- dition. In the constitution of the dorsal and ventral roots also the head has retained the primitive condition, while the trunk nerves have been somewhat modified at least in higher vertebrates. The dorsal roots originally contained the somatic sensory, splanchnic sensory and _ splanchnic motor components, as in Amphioxus. In the trunk a part of the splanchnic motor component has come to run in the ventral root and perhaps other modifications have taken place. SUMMARY OF THE CHIEF CONTENTS. 1. The primitive vertebrate was a segmented animal with probably very slight cephalization. 2. Each segment consisted of derivatives of the ectoderm, dorsal mesoderm, lateral mesoderm and entoderm, and of somatic sensory, somatic motor, splanchnic motor, and splanch- nic sensory divisions of the nervous system primarily related to the skin, the myotomes, the visceral muscles, and the visceral surfaces respectively. The definite relations existing between the 262 Journal of Comparative Neurology and Psychology. functional divisions of the nervous system and the organs sever- ally innervated by them make the nervous system the best guide to the segmentation of the head. 3. The anterior end of the head is indicated in existing vertebrates by the point at which the neural plate meets the general ectoderm and the entoderm, in those forms in which the rostral entoderm is most completely preserved. Lateral to this the olfactory epithelium is formed. Ventral to it the hypophysis represents the vertebrate paleostoma or invertebrate mouth. That part of the head and brain which extends over the hypophysial opening may be compared to the inverte- brate prostomium and as such contains only cutaneous and olfactory nerves. 4. It is probable that one or two pairs of gills formerly existed between the paleostoma and the present mouth. This is indicated by the presence of epibranchial placodes and palatine and trabecular arches in Petromyzon, by the mode of formation of the ciliary ganglion, and by the labial cartilages of selachians. Similarly one or two formerly functional myotomes have been lost from the anterior end of the head. The anterior head cav- ity of selachians is the rudiment of one of these. Another more anterior, is possibly indicated by the somatic motor nucleus far forward in the thalamus. The loss of these several organs has been followed by the loss of the typical nerves or their modification into special sense organs. The nerve of Locy and the ciliary ganglion are the only nerves in the first four seg- ments which retain their primitive relations. 5. Following this region of greatest modification, it is believed that the segments can be reduced to common terms and the segmental position of all the organs determined. See Table B and Figure Io. | a. The gill slits were originally intersegmental. b. Each typical dorsal root contained a general cutaneous component distributed to the skin; a communis component dis- tributed by way of the posttrematic, pretrematic, and pharyngeal rami to the mucosa; and a visceral motor component to the visceral musculature by way of the posttrematic ramus. The TABLE B. HEAD SEGMENTS 1 2 3 4 5 6 if 8 9 10 11 12 13 14 15 16 17 NEUROMERES i ii iii iv Vv vi vii viii ix x xi xii xiii xiv xv xvi xvii SOMITES een]! ly Mees 1 2 3 4 5 6 7 8 9 10 II 12 13 i mandib hyoid a larger number of branchial arches in lower BRANCHIOMERES ---- ---- | arch arch br. ore br..3 Dent BEG Dae cyclostomes and primitive vertebrates. comp’t 5 sp. Pet. SOMATIC SENS. DIVISION comp’t comp’t | in N. X.| 1 sp. Pet. rudiment in 6 sp. Pet. | 7 sp. Pet. general cutaneous inN. V ==== in N.IX | shifts to | joins 2 sp. Pet.| 3 sp. Pet.| 4 sp. Pet.) Gnath.; permanent | permanent | 8 sp. Pet. N. of N. ophth.} shifts [joins shifts to | x in N. X, rudiment | rudiment) rudiment} permanent root | root in root in 2 sp. ? peripheral Locy prof. to vii N.V?]! Ix Gnath. !Gnath. ! in Gnath.! in Gnath.! in Gnath.| in Acanthias? | Acanthias | Gnath. Gnath, central pallium (tectum), cerebellum, acusticum, gen. cutaneous nucleus, sp. V tract, nuc. funiculi. special cutaneous a ee th peripheral acustico-lateral system of organs and nerves. central cerebellum, acusticum, spinal VIII tract to the nucleus acustici spinalis. cial F later. | Ist. 2nd. Special sense eyes |epiph.| epiph SOMATIC MOTOR DIVISION Ta : . peripheral eee Ne ON TV eM vce | eicbee) S el u v w x y s tsp. Fiirb. | 2 sp. central nuc. | Sm. f. | nuc. III | nuc. IV | nuc. VI |s. m. f. Sade dt. |g. muff. | s.am, f | sats 1s s. m. f. sem. f ventral ventral s. m. f, mot. col. mot. col, SPLANCHNIC SENS. DIV. Sarees ,, | comp’t E % | compit | comptt comp’t | inN.X;/ comp comp I pa , , ‘ general visceral N. thal in N.VII] in N. IX] shifts col’ct’d | col’ct’d | col’ct’d ee d ere rg t ur t comp’t v. ci hift ‘ : int int into . : * in r. peripheral N. cil Ti ee ean N.X N.X N. X Lae, G br.-int. X br.-int. X br.-int. X | py,-int.X central ? lob. fac. | lob. vagi | lob. vagi| lob. vagi| lob. vagi lobus vagi and nucleus commissuralis of Cajal. seid wisceral The gustatory components and their centers have not been fully distinguished SEMeEAESUICEre from the general visceral in any vertebrate. special sense N. olf. | | | eS mot. N.V| mot. N. | mot. N | mot. N. | mot.N. | mot. N. set fm a ak | SPLANCHNIC MO" v. shift VII shifts} IX shifts | X shifts | col’ct’d | col’ct’d | col’ct’ col’ct’ _ oo ~_ to-vil to viii to ix tox Gn. | into N.X| into N.X| into N.X] into N.X| N. access. N. access. N. access. |N. access. peripheral lat. mot. | lat. mot. | lat. mot. | lat. mot. - central nuc. V nuc. V nuc. VII | nuc. IX and X; continued as the lateral motor column of spinal cord. Journal of Comparative Neurology and Psychology. Vol. XV. To face p..262. “i Jounston, Morphology of the Head. 263 nerve root passed behind (caudal to) the myotome of the seg- ment to which it belongs. c. Various shiftings of organs have taken place, due to (1) the expansion of the branchial apparatus and (2) the form- ation of a rigid cranium with the consequent loss of dorsal mus- culature. The shifting which may be observed during the ontogeny is a valuable source of information which should be further studied. d. Largely on account of the peculiar relations with the ear, the nerve roots connected with the medulla oblongata have shifted backward during the phylogeny, and have left two neuromeres without nerve roots. e. Asa result of the expansion of the branchial apparatus the visceral sensory and motor components of the nerves caudal to the glossopharyngeus have been collected into a common root, the vagus. The somatic sensory and motor components of more or fewer of these nerves are present as rudimentary or complete dorsal and ventral roots which occupy the posi- tion of the original nerves. The number of these nerves retained depends upon the reduction of myotomes and cutaneous area in the postauditory region. In _ cyclo- stomes all the general cutaneous roots are present and independent; two of the somatic motor roots have disap- peared. In gnathostomes, owing to the shifting backward of the vagus root at its attachment to the brain, the general cu- taneous root following it has been absorbed and appears in the adult as the second r. auricularis vagi. f. There has been no shifting forward of spinal nerves into the oblongata. 6. The typical sense organs of vertebrates fall into two categories: the neuromast organs constituting the acustico-lateral system, and the end buds or taste buds. These two sets of or- gans are absolutely distinct in structure, function, innervation, and central nerve relations. 7. It has previously been shown that the acustico-lateral system was derived from the general cutaneous. It is thought that the neuromast organs appeared first in a marginal portion 264 Journal of Comparative Neurology and Psychology. of the primitive neural plate. The material used in the form- ation of these organs was a portion of that part of the neural crest which gave rise to the general cutaneous component. The neuromast area was largest in the region of the VII nerve and neuromere vii, but extended forward probably one or two segments. It can not be exactly compared with the dorsal rami. It is thought that this area, together with the cutaneous ganglion cells, remained outside the neural tube and that later the ganglion cells migrated into the space between the ectoderm and neural tube. This is repeated in the ontogeny in the phe- nomena of the dorso-lateral placodes and the formation of gan- glia from them. | 8. The visual organs are thought to have been derived from the neural crest area also, in segments 2, 3 and 4. The retina of the lateral eye is supposed to contain the equivalent of a general cutaneous ganglion and its primary brain center. The optic tract is homologous with the internal arcuate fibers which arise from the cutaneous centers, decussate in the base of the brain and run to the tectum opticum. The epiphyses are thought of as modified general cutaneous ganglia whose centers have remained in the brain. g. The olfactory organ is regarded as a special collection of sense cells of the invertebrate type, sensitive to chemical stimuli, which are gathered above the hypophysial opening as the organs of the same type in the invertebrate are gathered in the roof of the mouth and on the prostomium. 10. Qn account of the similarity of their function it is ex- pected that some morphological relation will be found between the olfactory and gustatory organs. The source of the end buds, the origin and history of the nerve components which in- nervate them, and the course of the gustatory paths in the brain constitute one of the most important problems in vertebrate morphology. 11. It is important that the origin of each of the sensory components in the cranial nerves should be fully worked out in at least a few forms. The cells which enter the ganglia from the neural crest and from the placodes should be traced con- Jounston, Morphology of the Head. 265 tinuously until their fate is determined. The cells derived from the neural crest should be distinguished into general cutaneous, general visceral, or others as the result might be. Naples, October 25, 1904. LIST OF PAPERS CITED. For numerous other papers see the literature lists in Nos. 35 and 70. Ahlborn. 1. Untersuchungen iiber das Gehirn der Petromyzonten. Ze?t. f. wiss. Zool., Bd. 39, 191-294. 1883. 2. Ueber den Ursprung und Austritt der Hirnnerven von Petromyzon. Zewt. f. wiss. Zool., Bd. 40, 286-308. 1884. Allis. 3. The Cranial Muscles and Cranial and First Spinal Nerves of Amia calva. Jour. Morph., Vol. 12, 487-808. 1897. 4. The Lateral Sensory Canals, the Eye-Muscles, and the Peripheral Distribution of certain of the Cranial Nerves of Mustelus laevis. Quart, Jour. Mier. Sct., Vol. 45 N. S., 87-236. 1901. 5. On Certain Features of the Lateral Canals and Cranial Bones of Polyodon folium. Zool. Jahrb., Abth. f. Anat. u. Ontog., Bd. 17, No. 4. 1903. Beckwith. 6. The Early History of the Lateral Line and Auditory Anlages of Amia. Abstract. Sccence, N.S., Vol. 15, 575. 1902. Bigelow. 7. The Sense of Hearing in the Goldfish, Carassius auratus L. Amer. Nat. Vol. 38, 275-284. 1904. Bochenek. 8. Nowe szcze godly do budowy przysadki méozgowej plazow. (Neue Beitrage zum Bau der Hypophysis cerebri bei Amphibien). Az//. Internat. Akad. Krakéw, 1902, 397-403. Boeke. 9. Die Bedeutung des Infundibulums in der Entwickelung der Knochen- fische. Anat. Anz., Bd. 20, 17-20. 1901. Boveri. 10. Ueber die phylogenetische Bedeutung der Sehorgan des Amphioxus. Zool. Jahrb., Suppl. 7 (Festsch. Weismann), 409-428. 1904. Brauer. 11. Beitrage zur Kenntniss der Entwickelung und Anatomie der Gym- nophionen, Zool. Jahré., Suppl. 7, 381-408. 1904. 266 Journal of Comparative Neurology and Psychology. Braus. 12. Beitrige zur Entwickelung der Musculatur und des peripherischen Nervensystems der Selachier. Morph. Jahrd., Bd. 27, 415-496; 501-629. 1899. Burckhardt. 13. Die Einheit Sinnesorgansystems bei den Wirbeltheren. Ser. i. d. Verh. da. 5. Internat. Zool.-Cong. Berlin, 1901. 621-628. Cameron. 14. On the origin of the Pineal Body as an Amesial Structure, deduced from the Study of its Development in Amphibia. | oe S ; = Ca. s. c. lat. we Si. post. utr. Rec. utr. Amp. post. Amp. ant R. ant. N. Vill R. post. N. VIII. Mac. sacc. Lag Sacc. fig. 1. Membranous labyrinth of Rana esculenta, After GAUPP’s modifi- cation of RETz1Us’ drawing ; A, seen from the outside; 3, seen from the inside. the lagena, in which together there are five sense organs. Figure 1, Aand B are reproduced from Gaupr’s ‘‘Anatomie des 284 Journal of Comparative Neurology and Psychology. Frosches.”’ Fig. 1 A isa lateral view of the labyrinth organs; Fig. 1 B a median view. These figures together represent clearly the important sensory portions of the ear of the frog. Since there is no organ of Corti, whatever ability to hear the animals may possess must be due to the functioning of some portion of the membranous labyrinth. Figure 3 is presented for the purpose of showing the strik- ing difference in the size of the tympanum of male and female green frogs. The individual on the right is a male, that on the left a female. Although these two frogs were of the same length and weight the maximum diameter of the tympanum in weernb.Lab Fig. 2. Transverse section of the head of the frog to show the relations of the various parts of the ear (diagrammatic). ¢ymp. meméb., tympanic membrane ; col., columella; s¢/., stapes ; mzemé. /ab., membranous labyrinth ; Vv. VZ//., au- ditory nerve; ed. 0b/., medulla oblongata ; ch. f2x., choroid plexus ; ¢ymp. cav., tympanic cavity ; fez. ov., fenestra ovalis ; duc. cav., buccal cavity ; ews.t., Eusta- . chian tube ; an. ¢ymp., annulus tympanicus; 4. hy., body of hyoid; o. st., epi- sternum ; mnd., mandible; stg., pterygoid ; gu. 7u., quadrato—jugal. From PAR- KER and HASWELL. the male is one-third greater than that in the female. Measure- ments of several other individuals yielded the following results. For ten males whose average length was 7.31 cm. the average maximum diameter of the tympanum was 8.15 mm. ; for ten females 6.52 cm. in length it was 5.99 mm. Or if we compare individuals of like size: for a male 6.2 cm. the diameter was 6.3 mm. in contrast with 5.0 mm. for a female of the same YERKES, The Sense of Hearing in Frogs. 285 size; in case of two individuals 6.5 cm. the measurement of the male was 7.5 mm., that of the female 6.0 mm.; the tympanum of a male 8.8 cm. long measured 11.5 mm., that of a female g.o cm. long, g mm. In almost all cases the difference in the size is so marked as to be noticeable to a casual observer. fig. 3. Photograph of green frogs (Rana clamitans), male on the right, female on the left. To show the difference in size of tympana. 3. Problems. The purpose of the investigation of which this paper gives an account was the study of the influence of sounds on the reactions of the frog. The definite questions for which answers were sought are four: 1. Do frogs react to sound? 2. Dothey hear? 3. If so, what sounds are heard ? 4. Under what conditions do reactions to sounds occur? No attempt was made to localize the function of audition within the labyrinth organs, for the problems of research concern be- havior rather than the functions of special organs. In studies of this sort it is to be remembered that normal behavior can not be studied by vivisectional methods. Oper- 286 Journal of Comparative Neurology and Psychology. ations on sense-organs, nerve cutting and like methods may aid us in determining what organ or portion of an organ is neces- sary for a particular function, but they can give us no trust- worthy information concerning the relation existing between the senses and the normal behavior of the animal. Therefore, in the experiments now to be described, with the exception of those which were made to ascertain whether the ear is necessary for reaction to sounds, normal frogs were studied either in their native haunts or in the laboratory. All the detailed work was done with the green frog, Rana clamitans, but tests were made also with the leopard frog, R. pzpiens, and the bull frog, A. cateshiana. II. Reactions oF Frocs In NATURE TO SOUNDS. My attention was first drawn to the subject of frog audition by failure to obtain motor reactions to sounds in an investiga- tion of the time relations of the neural process of the green frog. Although a large number of sounds of different qualities, pitches and intensities were employed, no visible motor reactions were observed. This led me to seek the significance of what ap- peared to be either a surprising lack of sensitiveness to changes in the environment which would naturally be expected to stimulate the animal, or an interesting and important case of the inhibition of reaction to auditory stimuli. The question to be answered is, Are frogs deaf, or do they under certain con- ditions completely inhibit their usual reactions to sound ? Since they bear upon the question of deafness I quote the following observations on the influence of sounds in Nature from the auditory-reaction section of my earlier reaction-time paper.’ In order to learn how far fear and artificial conditions were causes of the in- hibition of responses to sounds in the laboratory, and how far the phenomenon was indicative of the animal’s inability to perceive sounds, I observed frogs in their native haunts. By approaching a pond quietly, it is easy to get within a few yards of frogs sitting on the banks. In most cases they will not jump until they have evidence 1The Instincts, Habits and Reactions of the Frog. Harvard Psychological Studies, 1, 629-630 (Psychological Review Monograph, 4), 1903. YERKES, The Sense of Hearing in Frogs. 287 of being noticed. Repeatedly I have noted that it is never possible to get near to any frogs in the same region after one has jumped in. In this we have addi- tional proof that they hear the splash-sound. To make sure that sight was not responsible for this on-guard condition in which one finds the frogs after one of their number has jumped into the water, I made observations on animals that were hidden from one another. The results were the same. I therefore con- clude that the splash of a frog jumping into the water is not only perceived by other frogs in the vicinity, but that it is a peculiarly significant sound for them, since it is indicative of danger, and serves to put them ‘on watch.’ A great variety of sounds, ranging in pitch from a low tone in imitation of the bull frog’s croak to a shrill whistle, and in loudness from the fall of a pebble to the report of a pistol, were tried for the purpose of testing their effects upon the animals in their natural environment. To no sound have I ever seen a motor response given. One can approach to within a few feet of a green frog or bull frog and make all sorts of noises without causing it to give any signs of uneasi- ness. Just as soon, however, as a quick movement is made by the observer the animal jumps. I have repeatedly crept up very close to frogs, keeping myself screened from them by bushes or trees, and made various sounds, but have never succeeded in scaring an animal into a motor response so long as I was invisible. Apparently they depend almost entirely upon vision for the avoidance of dangers. Sounds like the splash of a plunging frog or the croak or pain-scream of another member of the species serve as warnings, but the animals do not jump into the water until they see some sign of an unusual or dangerous object. On one occasion I was able to walk to a spot where a large bull frog was sitting by the edge of the water, after the frogs about it had plunged in. This individual, although it seemed on the alert, let me approach close to it. I then saw that the eye turned toward me was injured. The animal sat still, despite the noise I made, simply because it was unable to see me; as soon as I brought myself within the field of vision of the functional eye the frog was off like a flash. Many observers have told me that frogs could hear the human voice and that slight sounds made by a passer-by would cause them to stop croaking. In no case, however, have such observers been able to assert that the animals were unaffected by visual stimuli at the same time. I have myself many times noticed the croaking stop as I approached a pond, but could never be certain that none of the frogs had seen me. It is a noteworthy fact that when one frog in a pond begins to croak the others soon join it. Likewise, when one member of such a chorus is frightened and stops the others become silent. This indicates that the cessation of croaking is a sign of danger and is imitated just as is the croaking. There is in this fact conclusive evidence that the animals hear one another, and the probability is very great that they hear a wide range of sounds to which they give no motor reactions, since they do not depend upon sound for escaping their enemies. The phenomenon of inhibition of movement in response to sounds which we have good reason to think the frogs hear, and to which such an animal as a turtle or bird would react by trying to escape, is thus shown to be common for frogs in nature as well as in the laboratory. This inhibition is in itself not sur- prising, since many animals habitually escape certain of their enemies by remain- ing motionless, but it is an interesting phenomenon for the physiologist. We 288 Journal of Comparative Neurology and Psychology. have to inquire, for instance, what effects sounds which stimulate the auditory organs and cause the animal to become alert, watchful, yet make it remain rigidly motionless, have on the primary organic rhythms of the organism, such as the heart-beat, respiration, and peristalsis. It is also directly in the line of our investigation to inquire how they affect reflex movements, or the reaction time for any other stimulus—what happens to the reaction time for an electrical stimulus, for example, if a loud noise precede or accompany the electrical stimulus. Ill. THE INFLUENCE OF SouUNDS ON REACTIONS TO OTHER STIMULI. Z. Influence of sound on respiration and visual reactions.— Observations described in my earlier paper prove that respira- tion is modified by sounds, and it was also noted that the attempts of a frog to seize a moving pier are reinforced by the sound of a tuning fork.’ 2. Influence of sounds on tactual reactions. —A more detail- ed study has been made of the influence of sounds on tactual reactions and of the significance of the temporal relations of the stimull. A reflex movement of the leg was chosen as an indication of the action of the stimuli and the influence of sounds was observed under the following conditions. A frog was placed on a saddle-like holder and kept in position by linen bands over the back and a wire screen cap over the head, as shown in Fig. 4. Under these conditions the hind legs usually hang free and limp and any movement which may be made by them in response to a stimulus can be read in millimeters from a scale, attached to the holder. This method of measuring the value of stimuli in terms of leg reflex has been used by several other investigators, most recently by MeErzBacHER. In this connec- tion it isof interest to note that neither MERZBACHER nor EWALD were able to detect movements of the leg of the frog in response to sounds. Even the croaking of another frog near by had no apparent effect.” 1. c. p. 634. ne IMERZBACHER, L. Ueber die Beziehungen der Sinnesorgane zur den Reflex- bewegungen des Frosches. Pflger’s Arch., 81, 254, 1900. YERKES, The Sense of Hearing in Frogs. 289 I found it desirable, as did MERZBACHER, to observe the movements of a shadow of the leg on the scale and thus read the amount of movement, rather than to watch the leg itself and attempt to project it upon the scale. As is indicated in the figure the auditory and tactual stim- uli were given automatically by means of a swinging pendulum (P) which was held in position by the magnet a until released by the experimenter. Early in its swing the pendulum turned the key m thus completing a circuit which caused the auditory stimulus to be given; later in the swing the key z was turned, and the tactual stimulus thus given through the magnetic release of the lever 7. The interval between the auditory and the tact- ual stimuli could be varied from .1” to .9” by change in the position of the key ~. For giving the two stimuli simultan- eously a double hand key was employed.’ The auditory stimulus was either the sound of a quick hammer blow or the ringing of an electric bell for a certain interval. Figure 4 shows the bell. It was placed 80 cm. from the frog, and in order that the influence of vibrations might be avoided was suspended from the pendulum frame. When the hammer was used it was placed 60 cm. from the frog, on the pendulum table. The frog and the apparatus for tactual stim- ulation occupied a separate table which was not disturbed by the jars of the pendulum table. The tactual stimulus was giv- en by a rubber cone, 7, Fig. 4, 2 mm. in diameter at its apex. This rubber point, after the electric release of the lever to which it was attached, struck the frog at the middle point of a line drawn between the posterior margins of the tympana. The intensity of the stimulus could be varied by weighting the lev- er (see zw in the figure). Under the conditions of experimentation described above, a tactual stimulus regularly causes a reflex movement of the 1A full account of this method and the results of a study of the phenom- ena of auditory-tactual reinforcement and inhibition may be found in Pfliger’s Archiv, Bd. 107, S. 207, 1905, under the title ‘‘Bahnung und Hemmung der Reac- tionen auf tactile Reize durch akustiche Reize beim Frosche.’”’ In this connec- tion I mention only such aspects of the investigation as bear on the subject of audition. 290 Journal of Comparative Neurology and Psychology. YerKEs, The Sense of Hearing in Frogs. 291 suspended leg, which varies in amount with the state of the animal and the strength of the stimulus. A sound, on the contrary, never causes the slightest movement, and that no matter how loud or high it be. This makes it possible to study the influence of sounds on tactual reactions, under different temporal relations of the stimuli, for even when the sound pre- cedes the touch there is no reaction until after tactual stimula- tion. The results now to be presented were given by the green frog, but test experiments indicate that both the leopard and the bullfrog are influenced in similar manner by sounds. The experimental procedure was as follows. After an ani- mal had been placed in the proper position and had ceased to struggle to escape, reactions to stimuli were taken in pairs regu- larly at half minute intervals, first a reaction to the tactual stim- ulus alone, then a reaction to the same intensity of touch when accompanied or preceded by an auditory stimulus. The series consisted of 50 pairs of reactions taken without pause. So far as the frog is concerned there seems to be noth- ing undesirable in long series, for there is no indication of fatigue, and so long as the animal is kept moist and in a com- fortable position it does not often struggle to escape. The advantage, for the purposes of this investigation, of taking the reactions in pairs isobvious. It permits us to compare directly the reactions of each pair, and to note at once whether the auditory stimulus has reinforced or inhibited the tactual reaction. During a series the intensity of the tactual stimulus was changed as conditions demanded, but for any one pair of reac- tions it was always the same. It not unfrequently happened that an intensity which at first caused only slight movement of the leg, later in the series uniformly brought about a maximum contraction, or the reverse might be true, and since the maxi- fig. 4. Auditory-tactual apparatus. (Drawn by Dr. Wm. E. HockING.) f, pendulum; Z, contact point of P; 4, attachment for electro-magnet, a; m, key for electric bell circuit; &, electric bell; x, key for magnet circuit of touch apparatus; A, hand-key for release of pendulum and temporary closing of electric bell circuit; 2', £7, 4, keys in circuits; e, f, g, magnetic release for touch apparatus ; /, pivoted lever bearing rubber cone, 7, and weights, w. 292 Journal of Comparative Neurology and Psychology. mum amount of movement left no opportunity for judging of the influence of the auditory stimulus it was always necessary in such cases so to alter the intensity of the tactual stimulus that a medium reaction would result. The animals seldom struggled during experiments, but if too firmly bound they became irresponsive to the stimuli.’ It was therefore necessary to place them carefully in posi- tion, and then, after they had ceased to struggle, to draw the linen bands over them just tightly enough to prevent change in position. For the purpose of excluding the influence of vis- ual stimuli a wire screen cap covered with black cloth was put over the head. This served to help keep the frog in the prop- er position as well as to exclude visual stimulation. TABLE I. THE INFLUENCE OF SOUND ON THE TACTUAL REACTIONS OF THE GREEN FROG. Green frog A | Tactual Stimulus Alone | Auditory and Tactual Stimuli Position of shadow] Amount Position of shadow Amount on scale of on scale of No. of ‘ = She p: OF Exp before after |movement before after movement the stimulus the stimulus Pair 1 fe) 52 42mm 10 go M* Somm. Se: 15 28 13 20 90 M 70 sae 15 29 14 15 go M 75 Be ck 15 19 4 15 g0 M 75 Soe) 10 20 10 Co) 20 10 fc 6, 20 27 7 20 g0 M 70 vey 25 40 15 25 50 25 eon 30 32 2 30 49 19 Lee) 30 33 3 Struggle — — LO 25 31 6 2 46 21 Green frog B Pair 1 20 23 3 20 go M 70 Sea 2 20 25 5 20 90 M 70 ae eS 20 24 4 20 90 M 70 ee 20 23 3 20 90 M 70 fred at 20 23 3 20 90 M 70 pee) 20 35 15 20 60 40 aad ad Zo 21 I 20 90 M 70 eae 20 21 I 20 go M 70 ee) 20 22 2 20 90 M 70 Bek) 20 21 I 20 90 M 70 *M indicates maximum movement of leg. 1A case of inhibition. YERKES, The Sense of Hearing in Frogs. 293 The two series of reactions of Table I, chosen at random from several hundred, will serve to indicate the method of recording the results as well as the nature of the results themselves. The first ten pairs of reactions fairly represent the variableness of the reactions; the second show still more clearly the influence of the auditory stimulus. The results obtained with four frogs, two males (Nos. 1 and 3) and two females (Nos. 2 and 4) will suffice to indicate the influence of sounds on tactual reactions. For each of the four frogs fifty pairs of reactions were taken in series, and that for each of seven different temporal relations of the two stimuli. The individual averages therefore are based upon fifty reactions, and the total number of reactions for each individual is seven hundred. Asis clear from column one of Table II, the tem- poral relations of the stimuli ranged from simultaneity to .9” (i. e., the auditory preceded the tactual by .9”). The influence of the sound, which for these experiments was a sudden hammer blow, is discovered by direct comparison of the tactual reaction of each pair with its corresponding audi- tory-tactual reaction. When the tactual reaction is the greater, we infer that the sound has partially inhibited reaction; when it is the smaller, that it has reinforced reaction ; when the two are equal, that it has been without influence. The influ- ence of sound may be expressed either in terms of the number of reactions reinforced, inhibited and equal, or in terms of the amount of reinforcement or inhibition. Both methods have been employed. Table II presents the percentage value of the auditory-tactual reactions in comparison with the tactual, and also the number of reactions over half which were reinforced or inhibited, while Figures 5 and 6 graphically represent the amount of influence in terms of the tactual reaction. The audi- tory-tactual reaction is always expressed as so many per cent greater (1+ i. e., reinforcement) or less (—i. e., inhibition) than the tactual. Inthe table + always indicates reinforcement, — in- hibition, and in the curves the portions above the zero line indi- cate reinforcement, those below it inhibition. The number of reactions over half, that is over twenty five, since there were 294 Journal of Comparative Neurology and Psychology. fifty pairs of reaction for each interval and each animal, which were reinforced or inhibited furnishes an excellent quantity for comparison with the averages. As such comparison reveals close agreement between amount of influence of the auditory stimulus and the number of reactions either reinforced or inhib- ited it is clear that the averages are trustworthy, even though the variability of the reactions is enormous. TABLE II. INFLUENCE OF SOUND ON THE TACTUAL REACTIONS OF THE GREEN FROG FOR DIFFERENT TEMPORAL RELATIONS OF THE STIMULI. Length of/piff. in per cent.|Number of re-} Diff. in per cent. |Number of re- interval |between tactual andjactions rein-| between the tac- jactions rein- auditory-tactual re-|forced or in-| tual and auditory |forced or in- actions hibited tactual reactions |hibited Male No. t. | Male No. 3. Om + 62.0 % | + 17.0 103.1 % + 18.0 ens 4 30.3 + 17.0 85.9 + 17.0 25/7 + 33-3 + 13.0 + 12.5 a ee + 1.7 + 0.5 + 2.0 wage — 22.3 — 10.0 — 4.5 265% | — 10.0 — 6.0 — 6.5 -90”” “te 10:7 pes ie tee 0” + 60.9 % + 14.5 + 40.7 % + I1.0 Does + 19.8 + 6.5 + 31.1 + 10.5 25 + 30.4 + 12.0 + 49.2 + 13.5 Bbw — 6.3 = 36 — 13.2 — 3.5 ASA — 8.1 — 3.5 — 19.8 — 11.0 1657 — 15.8 — 9.5 — 7.8 — 5.5 .90’” — 09 + 3.0 — 45.1 — 4.0 The results tabulated in Table II show that the sound when occurring simultaneously with the tactual stimulus greatly in- creases the amount of the reflex, while on the contrary it decreases the amount of reaction if it precedes the tactual stim- ulus by .5 to 1.0’. Number 1, forexample,exhibited reinforce- ment equal to 62 % of the amount of the tactual reaction when the stimuli were given simultaneously, but when the sound occurred .65”’ before the touch the resulting reaction was 10 % less than the tactual. In Figures 5 and 6 are curves, representing the amount of reinforcement and inhibition for the four frogs, constructed YERKES, The Sense of Hearing in Frogs. 295 according to the following method. Let the zero point on the ordinates represent the value of the tactual reactions; then the value of the auditory-tactual may be indicated on the same ordinate as so many per cent. greater (above the zero point) or less (below the zero point) than the tactual. In Fig. 5, for instance, the sound when simultaneous with the touch caused a Hite HE a fH +H + cH Hae speccgsegececscs Hatth Hit rH Fig. 5 Fig. 6 fig. 5. Reinforcement-inhibition curve for momentary auditory stimula- tion, contructed on the basis of amount of reaction. Ig) 5 oe eS Curve for Male No. 3. —-Curve for male No. fig. 6. Reinforcement-inhibition curve for momentary auditory stimulation, constructed on the basis of amount of reaction. Curve for Female No. Re Curve for Female No. 4.} 1The curve for No. 4, Fig. 6, as originally published in Pfliiger’s Archiv, Bd. 107, S. 219, is incorrect in that it starts with 50.7 % instead of with 40.7 %- 296 Journal of Comparative Neurology and Psychology. reaction 62 % greater than the tactual, in the case of one frog, and 103.1 % greater in the case of the other. On the other hand, when the sound preceded the touch by .45” the resulting audi- tory-tactual reaction was 22.3 % and 4.8 %, less, respectively, than the tactual. The figures on the left margin of the curves above the zero point indicate reinforcement in per cent. of the tactual reaction, those below the zero point, inhibition. Below the base line the time intervals are given in tenths of a second. Each curve is plotted, from the data of Table II, on the basis of seven hun- dred reactions. It is to be noted that the curves of Figure 5, for the two males, show considerably more reinforcement than those for the females in Figure 6. Furthermore, the curves for the females cross the transition line between reinforcement and inhibition sooner and return to it more slowly than do those for the males. In other words, inhibition begins with a shorter interval between the stimuli and continues longer. These experiments prove conclusively that sounds, although they do not call forth the reflex movement under consideration, modify in important ways the action of other stimuli. It is therefore certain that lack of auditory reaction is due to some form of inhibition and not to insensitiveness. IV. HEARING OF FROGS IN AIR AND IN WATER. It has: been held by many investigators of the sense of hearing that sounds in the aircannot be heard by animals under water for the simple reason that the air waves cause only very slight disturbances in the water. In view of this statement it is of interest to test the ability of the frog to hear when the tym- panum is exposed to air and when it is under water. Experiments were made with the apparatus represented in Fig. 7. The reflex reaction method of testing the influence of sounds was again employed, and pairs of reactions were record- ed for frogs whose ears were either exposed to air waves or sub- merged in the water of the aquarium. The level of the water, with reference to the ear, was controlled by changing the vol- ume in the aquarium, and the leg of the frog was kept from YERKES, The Sense of Hearing in Frogs. 297 floating upward by the attachment of a one gram weight. The two stimuli were given by means of the hand key, K. In all cases the auditory stimulus was the sound of an electric bell, B, suspended above the water in such a way that its vibrations could not be transmitted either to the aquarium or the frog holder. Precautions were taken to exclude also the influence of visual stimuli. During the month of December, 1904, ten green frogs were tested with this apparatus and it was found, contrary to the expectations aroused by previous results, that the females fig. 7. Auditory apparatus for testing hearing in air and in water. 4, aquarium ; 4, electric bell; 7, tactual stimulus apparatus ; A, hand-key for giv- ing stimuli; w, weight to hold leg. reacted far more uniformly and vigorously to sounds than the males. Indeed the irregularity of response and irresponsive- ness of the males were so marked that it was seldom possible to get more than two or three pairs of reactions in series. For this reason it has been impossible to present averages for the males. The females reacted with a fair degree of regularity, but with notning like the vigor and uniformity which character- ized the reactions of animals tested in April and May. Evi- 298 Journal of Comparative Neurology and Psychology. dently the seasonal condition of the animal is an important mat- ter to consider in studies of audition. The experiments included tests under three conditions: 1. When the tympanum was exposed fully to air, although the body was submerged up to the level of the ear drum ; 2. When the tympanum was half under water, the head and nares being in air; 3. When the frog was submerged to a depth of 4 cm. The results prove beyond doubt that sounds made in the air stimulate frogs when their tympana are under water. Furth- ermore, there is evidence that sounds stimulate the green frog even when it is totally submerged to a depth of four centime- ters. I cannot better describe these results than by giving the sample series of Table III. Although the amount of reaction under the conditions of these experiments is small, the difference between the tactual and the auditory-tactual is sufficiently great to establish the frog’s ability to hear under water. The averages for ten reactions of another female under four sets of external conditions follow: Condition Amount of reaction to Amount of reaction to the tactual stemulus alone. audrtory-tactual alone. Spay aNNAY Sh EVE 2.) IAT ane ree eee eee 16.4 mm. = halfvunderwaterss2- 6O). 59 ia a ee Wiois, OC sUsiccm. under waters 221.2) 0 a eee eee SS 325) hs ‘cc4.cm. under water2_2_ 5, 69 = eeeeeee Se an ae Rea. 4 With several other individuals reactions were obtained which just as clearly indicated audition under water. We may therefore conclude that the green frog can hear both in air and under water. There is some evidence that the reaction to sound is great est when the tympanum is half submerged. V. Tue RANGE oF HEARING. By one or another of the methods of experimentation already described the value of the following sounds as auditory stimuli for the frog has been demonstrated during the course of this investigation. The croaking of green, leopard and bull- frogs ; splashing of water ; pistol explosions; tuning forks rang- YERKES, The Sense of Hearing in Frogs. 299 TABLE III. HEARING OF GREEN FROG IN AIR AND UNDER WATER. Female. Dec. 5, 1904. Weight for tactual stimulus 5 grams. No. of Tactual stimulus alone Auditory and tactual stimuli pa (Con-|— =a tinuous |Position of shadow] Amount |/|/Position on shadow) ‘Amount series) on scale of on scale of nl | LO OC Ch hn | S| ovement before | after etore after the stimulus : : the stimuli Series I. Tympanum exposed to air. F 28 30 2mm. az | se 23 mm. 2 27 30 3 26 30 4 3 26 29 3 26 29 3 4 25 27 | 2 25 28 3 Series II. Tympanum entirely under water. 5 25 25 o 25 a2, || 7 6 25 2 2 25 28 3 7 25 28 3 25 28 a 8 19 | 19 Oo ] 19 | 21 2 Series III. Tympanum half under water. 9 19 20 I 19 22 3 we 19 19 fo) 19 22 3 ~- 19 20 I 19 25 6 re 19 | 21 2 19 aI 2 13 19 20 I Ig 22 3 14 19 20 I 19 21 2 15 18 18 Oo 18 20 2 16 18 19 I 18 20 2 Series V. Tympanum exposed to air as in Series I 17 18 20 2 18 21 3 81 18 19 I 18 21 3 19 18 20 2 18 22 4 20 18 20 2 18 25 7 ing from 100 to 1000 vibrations per second; electric bell with metal gong and also with wooden gong ; sudden hammer blow; Galton whistle; Appunn whistle, and a variety of sounds pro- duced by the human vocal organs. The sound of the electric bell produces the most marked modification of reaction, probably because it consists, like the induced electric shock, of a rapid succession of stimulating 300 Journal of Comparative Neurology and Psychology. changes. The green frog is stimulated by sounds as low as 50 vibrations per second. No experimental tests were made with lowersounds. For the purpose of determining the upper limit of audibleness tests were made with Galton and Appunn whis- tles. The tactual reflex was again employed as a means of testing the influence of sound. The tests, like those of the previous section of the paper, were made during the winter and responses to both tactual and auditory stimuli were obtained much more regularly with females than with males. A suffi- cient number of reactions have been recorded for males, howev- er, to prove that they are influenced by sounds as high as 10,000 vibrations per second, asare the females also. The fol- lowing series of averages for a female is indicative of the nature of the results of these tests : Green frog Galton whistle Amount of tactual reaction Amount of audttory-tac- female vibration rate Average of twenty reactions tual reaction in each case. SeresHi aes eae FLOOO Se ee aaa 27S Opti mene eette sn 2 2 St ae 4.65 mm, ie eee ee Sos 3000 ses eee 25COW wie me pee eee ee pets 0 Pi FG) (eee es LOSOOO 20 ae ee 21 Ome oe eee 8 eed 4.2088! GG" (WiLL leibnee GE eine Flory ZAG aot ee eee NE Le Se 2°30 Series IV serves as a control on the influence of the sound of escaping air which accompanies the tone of the whistle. Its result indicates that the tone is the effective stimulus in the pre- ceding series. Similar results obtained by the use of the Appunn whistles prove that up to 10,000 vibrations per second the frog is stimu- lated by sound. With neither the Galton nor the Appunn whistles was evidence of reaction to sounds of higher vibration rate ob- tained. We may therefore conclude, until further investigation by more satisfactory methods is available, that the green frog is influenced by sounds ranging in rate of vibration from 50 to 10,000 per second. It should be noted, however, that neither the upper nor the lower limit of audition has been accurately determined by these experiments. YERKES, The Sense of Hearing in Frogs. 301 VI. Tue RELATION OF THE EAR To REACTION TO SOUND. Abundant evidence has now been presented in support of the statement that the frog is stimulated by sound, but the use of the term audition in connection with these reactions has not been justified. Ifthe investigation were dropped at this point the criticism would doubtless be made that the modifications of tactual reactions produced by sounds may be due to stimulation of certain cutaneous sense organs instead of the organs of the ear, and that therefore nothing has been proved concerning hearing in the frog. In anticipation of this objection to the conclusions which have been drawn from the results of experi- mentation check observations were made on frogs whose ears had been operated upon in various ways.’ The operations whose effects serve as evidence of the rela- tion of the ear to the responses to sounds which we are now considering were three: (1) Cutting the tympana; (2) Cutting the columellae as well as the tympana ; (3) Cutting the eighth nerves from the dorsal side.” Briefly stated, the results of the three operations mention- ed are as follows. 1. After cutting of the tympana there is no apparent change in the nature of the influence of sounds. The frogs are at times less responsive to stimuli, and asa rule they do not show as marked reactions to either touch or sound as do the normal animals. 2. Sounds continue to modify tactual reactions after both columellae and tympana are cut. In one case it was noticed that the influence of the sound of a wooden gong was much increased by this operation, whereas there was no marked change in the influence of the sound of the metal gong. There 1Through the kindness of Mr. J. H. Mason, graduate student in the depart- ment of zodlogy of Harvard University, I was enabled to make the following tests on frogs which he had operated upon for the purpose of studying the static functions of the labyrinth organs. *Postmortem examination in case of attempted cutting of the nerves showed in most cases that the ear or brain had been injured. In only two instances was the operation sufficiently clean to fulfill the requirements of the experiments. 302 Journal of Comparative Neurology and Psychology. is an observation which suggests the importance of the relation of vibration rate to the nature and condition of the transmitting structures. Many individuals failed to react to any moderate- ly intense stimuli within a period of several hours after this operation. The sample series of reactions recorded in Table IV is sufficient comment upon the conclusiveness of the exper- iments so far as the value of these transmitting organs for so- called auditory reaction is in question. SANE; IAW THE INFLUENCE OF SOUNDS ON FROGS WITHOUT COLUMELLAE OR TYMPANA. Green Frog. Operated April 17, 1904. Reaetions taken immediately after operation . Tactual stimulus alone Auditory and tactual stimuli. Position of shadow Position of shadow Amount Amount on scale on scale f No. of B pair before after | Movement before after movement the stimulus the stimuli I 4! 4! omm. 4I 45 | 4 mm. 2 20 ay | i 20 90 M 70 3 15 28 13 15 go M 75 4 20 20 fo) 18 25 7 5 25 30 5 15 go M 75 6 20 90M 70 20 40 20 ik 20 35 15 20 go M 70 8 30 50 20 35 70 35 9 25 33 8 25 35 10 10 25 27 2 25 27] 2 | Average for series 14.0 mm. | 36.8 mm. 3. After the cutting of the eighth nerves reactions to sounds were not obtained. Tests were made with green frogs and bull frogs, but only with the latter could reactions to tact- ual stimuli sufficiently great for the purposes of the investiga- tion be obtained after the operation. Of fifteen frogs used only four reacted regularly to tactual stimuli after being operated, and these gave no sign of reaction to sounds. Typical of the results for those individuals which continued to be responsive to tactual stimuli after the operation is the following series, Table V. The eighth nerves of the bull frog used in the exper- iments of this series were cut May 17; two days later a series of twenty five pairs ‘of reactions was obtained. Experiments were continued at intervals until June 14. The animal was apparently in good condition, the skin wound had healed by the latter date, but auditory reactions were wholly lacking. YeRKES, The Sense of Hearing in Frogs. 303 TABLE V. THE INFLUENCE OF SOUNDS ON FROG WITH EIGHTH NERVES CUT. Bull Frog Operated May 17, 1904. Amount of reaction;Amount of reaction to au- |Number of reactions Date of | to tactual stimulus | ditory and tactual stimuli greater (+) S@RGS | | less (—) Each result is the average for 25 reactions equal (=) May 19 4.16 mm, 4.04 mm. g+, 11—,5=. May 20 19.24 18.20 g+, 14—, 2=. May 21 15.04 14.28 Io-+, 10—, 5 = May 24 13.08 13.28 Ilo+, 6—, 9=. June 14 8.60 8.76 7+, 12—, 6=. Averages 12.02 | Bl 70 | 9 +, 10.6 —, 5.4=. Cutting of the eighth nerves renders the frog iresponsive to sounds which markedly influence the tactual reactions of the nor- mal animal. We may therefore conclude that the reactions with which we have dealt in this investigation are due to stimulation of certain sense organs of the ear, and that the use of the word hear- ing in connection with them ts appropriate. VII. SumMMARY AND CONCLUSIONS. 1. Observation of frogs in their natural habitat shows that they are stimulated by sounds. The sense of hearing apparently serves rather as a warning sense which modifies reac- tions to other simultaneous or succeeding stimuli than as a con- trol for definite auditory motor reactions. 2. Experimental tests prove that sounds modify the frog’s reactions to visual and tactual stimuli. When the sound accom- panies the visual or tactual stimulus it serves to reinforce the visual or tactual reaction, but when given alone it never causes a motor reaction. 3. The sound of an electric bell occurring simultaneous- ly with a tactual stimulus markedly increases (reinforces) the leg reflex of green-, leopard- and bull-frogs. If the sound pre- cedes the touch by 1” it is without effect on the reaction ; if the interval is not longer than .35” it usually causes reinforce- ment, whereas for an interval of from .4” to .g” there is partial inhibition of reaction. According to its temporal relation to 304 Journal of Comparative Neurology and Psychology. another stimulus, an auditory stimulus may either reinforce or inhibit the reaction appropriate to that stimulus. What may be called reinforcement-inhibition curves for auditory stimuli are presented in this paper. 4. The green frog responds to sounds made in the air whether the tympana be in the air or in water. There is some evidence that the influence of auditory stimuli is most marked when the drum is half submerged in water. The influ- ence of sounds upon tactual reactions is evident when the frog is submerged in water to a depth of 4 cm. 5. Sounds varying in pitch from those of 50 to 10,000 vibrations per second effect the frog. The most striking results were obtained by the use of an electric bell with a metal gong. With this sound in connection with a weak tactual stimulus a maximum reaction of the leg may often be obtained even when either stimulus alone causes no perceivable reaction. 6. Sounds modify the reactions of the frog after tympana and columellae are removed. Cutting of the eighth cranial nerves causes disappearance of the influence of sound. It is clear then that the reactions to sounds are really auditory reac- tions and that the sense of hearing in the frog is fairly well developed, although there is little evidence of such a sense in the motor reactions of the animal. 7. Those portions of this investigation which were carried out in the spring months show marked influence of sounds for both males and females, whereas experiments made during the winter indicate a much diminished sensitiveness to auditory stimuli in both sexes, but especially in the male. THE REACHONS OF RANATRA TO LIGHT. By S.J: “HOLMES. Contributions from the Zoological Laboratory of the University of Michigan, No. roo. With Six Figures in the Text. CONTENTS. I. INTRODUCTION. II. GENERAL Hasits. III. REAcTIoNs To LicurT. 1—General features of the phototactic response. 2—The negative reaction. 3—Head and swaying movements in negative phototaxis. 4—The effect of contact on phototaxis. 5—The effect of temperature on phototaxis. 6—Phototaxis leading to fatal results. 7—Inhibition of phototaxis by other activities. 8—The effect of hemisecting the brain. g—The effect of covering the anterior half of the eyes. 1o—The effect of covering the posterior half of the eyes. 11—The effect of destroying or covering one eye. 12—Reactions of specimens with only a small part of the lateral sur- face of one eye exposed. 13—Phototaxis as modified by experience and habit. 14—Formation of habits of turning. IV. GENERAL CONSIDERATIONS ON THE PHOTOTACTIC RESPONSE. I. INTRODTCTION. In endeavoring to ascertain the way in which animals of various kinds orient themselves to the rays of light I have ex- perimented with quite a large number of speciesin the hope of finding forms in which the exact mode of response would reveal itself. Animals vary greatly as regards both the definiteness. of their reactions to light and the ease with which their move- ments can be followed. Among creatures of small size such as. the Copepoda, Cladocera and Ostracoda, it is almost impossible 306 Journal of Comparative Neurology and Psychology. to observe the precise movements concerned in orientation, and in many larger forms the rapidity, irregularity, or indefiniteness of their light reactions renders the same difficulty almost equal- ly great. In studying the reactions of animals to light we are naturally confronted with the question as to how far the move- ments involved are the result of choice, or something analogous thereto, and how far they may be explained as the result of reflex responses to photic stimuli. If they mainly fall into the latter category we are led to inquire just what these reflexes are and how they produce the particular kind of behavior observed. It is a quite commonly accepted hypothesis that the pho- totactic reactions of organisms are effected by the action of light directly or indirectly upon the tension of muscles concerned in locomotion. In nearly all insects and ina large proportion of other arthropods this tension, if it exists, must be brought about through the central nervous system, since the opacity of the integument prevents any appreciable direct effect of light upon the musculature. In most arthropods phototactic impulses are set up by means of light entering the eyes, and not as in many lower forms through the stimulation of the integumental nerves; this is shown by the fact that when the eyes are black- ened over or destroyed responses to light no longer occur. In most animals it is not possible to observe any effect of light upon muscular tension, although there is considerable indirect evidence that such aneffect is produced. As Rapt' has remark- ed, it is difficult to explain the fact that an insect with one eye blackened over moves about ina circle except on the assump- tion that light affects unequally the tension of the muscles on the two sides of the body. Such circus movements are com- parable to those which take place in a vertebrate animal upon the destruction of the semicircular canals in one side of the head. After this operation there is produced a marked differ- ence in the muscular tonus of the two sides of the body and, as a consequence, the animal, instead of going in a normal manner i Untersuchungen iiber den Phototropismus der Tiere, 1903. Hoimes, Zhe Reactions of Ranutra to Light. 307 veers continually toward the weaker side. A small difference in the muscular tension of the two sides of an insect body which would be sufficient to cause the creature to orient itself to the rays of light might not be patent to direct observation, espe- cially if the movements are rapid or irregular, as they frequent- ly are. There are several forms, however, in which the effect of light upon the muscular tone is quite clearly manifested, but none more so than in the common water scorpion, Ranatra fus- ca. In many ways this species is admirably adapted for the study of phototaxis; it is of large size, its long slender legs move in a slow and deliberate manner so that one can observe just how each action is performed; it may be readily kept for a long time in the laboratory, shows no signs of fear when being experimented with, and reacts to light witha remarkable degree of precision. For an investigation of the modus operandi of the phototactic response Ranatra is probably not equalled by any other known form. It is especially advantageous to study phototaxis in some such organism if we wish to ascertain how far the reflex theory of orientation will carry us. If orientation is the result of com- paratively direct reflexes we are better able to determine their precise mode of action. If a more involved type of reaction occurs there is a better opportunity afforded for proving its ex- istence, and, perhaps, ascertaining something of its nature. It does not follow that because we can construct a theory to account for orientation by means of direct reflexes that the pro- cess necessarily takes place in so simple a manner. Between the stimulus and the reaction there may be processes of a com- plicated nature whose existence is not ordinarily betrayed by any outward and visible sign. No one would consider a dog’s following the scent of a rabbit a matter of simple chemotaxis. While it is not a process requiring conscious ratiocination, it is doubtless one involving psychic operation of considerable com- plexity. The possibility should be borne in mind that many of the tropisms of insects may be less simple and direct reac- tions than is commonly supposed. Ifa bee finds its way to its hive over miles of woods and fields guided by its memories of 308 Journal of Comparative Neurology and Psychology. the various objects that come into its field of vision, it is cer- tainly something more than a mere reflex machine. In organ- isms which are capable of a higher type of response we should at least be on our guard in attempting to explain their tropisms as due entirely to direct reflexes involuntarily performed in re- sponse to outer stimuli. The conduct of higher animals is guided in large measure by their likes and dislikes, however we may interpret this kind of behavior in physiological terms. Between such behavior and those tropisms which are the result of comparatively simple reflexes there are, no doubt, numerous intermediate kinds of conduct. It is not unreasonable to sup- pose that tropisms which in low forms are brought about by direct reflexes may in higher animals complicate into reactions of the pleasure-pain type while still preserving outwardly the appearance of a more mechanical mode of response. At the same time an element of direct reflex action may be retained, although closely associated with and capable of being modified by more complicated neural processes. A consideration of the experiments described in this paper will lead us, I think, to some such view. II. GENERAL HABIts. Ranatras are generally found in ponds or streams among masses of vegetation where they lie quiet the greater part of the time. Although capable under certain conditions of manifest- ing considerable activity, these insects are usually sluggish in their movements. Their choice of habitat is probably deter- mined, in great part at least, by their positive thigmotaxis, since they tend to insinuate themselves between objects which afford considerable contact stimuli. Their habit of coming together to form groups is a manifestation of the same tenden- cy. When several individuals are placed in an aquarium they mass together when at rest to form a cluster in which they are often so closely. aggregated and so tangled together that those which are near the center of the group experience much diffi- culty in disengaging themselves. In this way they may lie for n an almost motionless state. Homes, Zhe Reactions of Ranatra to Light. 309 The general form and dull coloration of Ranatra tend to make it inconspicuous in its natural habitat, especially as it does not reveal its presence by its movements. When lying in the water the long breathing tube through which air is admitted to the body rests at the surface. The two parts of which it is composed occasionally approach and recede from each other, moving the air between them to and fro, an operation which doubtless assists in respiration. Airis prevented from escaping when the valves are separated, by the rows of hairs which line the margins of the concave inner faces of these structures. Ranatra is carnivorous in habit, seizing its prey with its anterior raptorial limbs and holding it until it has sucked out its juices. It is quite destructive of fish eggs and frequently attacks and sucks the blood from young fishes. It is also reported to prey upon young tadpoles. Dr La TorrRE Bueno! describes the method Ranatra employs in capturing prey as follows: ‘‘When a fly attracts its attention Ranatra very slow- ly, almost imperceptibly, moves its fore legs, with the knife-like tarsus away from the tibia, towards its prey. When the tibiae are almost, or quite, touching the victim the movement is so sudden and quick that one is aware of it only by seeing the prey seized. Sometimes its hold is not satisfactory, and then it willlet go with one tarsus, get'a firmer grip with that, and then do the same with the other. Once it has the fly securely held, Ranatra slowly approaches it to its extended beak, with which it seems to touch and feel until it finds a suitable spot, and proceeds to a leisurely meal.’’ I have usually fed Rana- tras during the winter on JVofonectas, or back-swimmers, as these insects were easily obtained during this time of year. The Ranatras did not pursue the back-swimmers, but as soon as their attention was attracted to the prey they lay quietly in readiness for them with their anterior limbs prepared to quickly seize the small insects should they swim sufficiently near. If a Notonecta strikes against a Ranatra the latter makes a quick 1Notes on the Stridulation and Habits of Ramatra fusca Pal. B., Canadian Entomologist, Vol. 35, p- 235, 1903. 310 Journal of Comparative Neurology and Psychology. grab for it, and, if successful in seizing it, proceeds to suck out its blood in the manner described by DE LA Torro BUENO. In locomotion, either by swimming or walking, the anter- ior limbs do not usually play a part; they are held straight in front of the body and are employed only occasionally to aid in changing the direction of locomotion or to clamber over some obstruction. Out of the water Ranatra walks rather awkward- ly. Its long slender second and third pairs of legs are articu- lated close together near the center of the body and the insect is frequently tilted over so that one extremity or the other strikes against the surface over which it walks. While Rana- tra is capable of flight, it rarely if ever flies to lights at night as many other aquatic hemiptera do; I have never seen any specimen around electric lights where other insects are found in abundance. Ranatras pass the winter in the adult state. I have col- lected numerous specimens in a small stream north of Ann Arbor late in November, but on visiting the same locality dur- ing a thaw in January following, although a diligent search was made in their favorite habitat among aquatic plants and by dig- ging in the mud in the sides and bottom of the stream, I did not obtain a single specimen, although Zaithas and water boat- men were found to be quite common. Possibly the Ranatras burrowed more deeply than I could dig with the apparatus employed, although the general form of the animal renders this supposition improbable. Egg laying occurs in the spring. The eggs are long and narrow and furnished at one end with a pair of filamentous processes which, according to KoRSCHELT, have a respiratory function. In ovoposition the female inserts the eggs into the stems of aquatic plants, or even into wood, the filaments projecting from the exposed ends. Ranatras make a feeble sound by rubbing the bases of the anterior legs against the lateral processes of the prothorax. When a Ranatra is picked up in the fingers one can feel a slight tremor when the animal stridulates, although the sound is so faint that it cannot be heard farther than a few inches from the ear. What use, if any, is made of this sound is uncertain. Howimes, The Reactions of Ranatra to Light. 311 The method of sound production has been described by Torre Bueno. The statement of this writer that the stridulation of Ranatra was not previously described is not correct, for the subject was briefly treated of by Locy’ in 1884. The instinct Of feigning death, which is remarkably well developed in Ranatra, will be described in a subsequent paper. III. Reactions To LIGHT. General Features of the Phototactic Response. When Ran- atras are kept ina glass dish of water near a window they are usually to be found facing the light, often swimming towards it and repeatedly colliding with the side of the dish and clawing against the invisible barrier which blocks their course. These movements may be kept up, with intervals of rest, all day. When an artificial light is used the Ranatras may be caused to swim in any desired direction by placing the light in the proper position. In experiments with this species I have usually em- ployed an ordinary 16 candle-power incandescent lamp attached to a flexible cord of wire which permitted it to be readily mov- ed about at will. The work was carried onin a darkened room so that the specimens experimented with were exposed to light only from this source. When Ranatras are taken out of water and laid on a table they generally feign death, and, while in that condition, they at first give no reaction to light. One may move the light about near them or hold it almost against their eyes without eliciting the least sign of a response. This apparent insensi- bility, gradually wears away, and after some minutes the move- ments of the light are followed by scarcely perceptible motions of the head. By passing the light back and forth laterally over the body the head may be caused to rotate laterally each time the position of the light is changed. These are the first move- ments that can be made to appear, and they grow more decid- ed the longer the experiment is continued. A little later the animal may be made to respond by vertical head movements 1Anatomy and Physiology of the Family Nepidae, dm. Wat., 1884, p. 364. 312 Journal of Comparative Neurology and Psychology. when the light is passed back and fourth over the long axis of the body. When the light is in front the head is bowed down and when it is passed behind the body the head is tilted up- ward. Both the lateral and vertical movements are such that they tend to place the upper surface of the head at right angles to the direction of the rays. The vertical movements, like the lateral ones, are at first slight, and increase in vigor the longer they are caused to continue. The animal performs these move- ments with machine-like regularity and precision and without showing the least activity in any other part of the body. If the light is moved around the body ina circle the head will follow it with a corresponding rotary motion. If the light is in front and to the right of the animal the head will be tilted over to the right and at the same time pointed downward in front; or if the light is to the left and behind the animal the head will be tilted over to the left and raised up in front. For each position of the light there is a corresponding attitude of the head. The orientation of the head is remarkably precise. By carefully watching the tip of the beak with a lens as the light is moved it may be observed that a change of only two or three degrees in the direction of the rays produces a corresponding change in the direction in which the head is pointed. After some time the movements of the head are accom- panied by movements of the breathing tube. When the light is in front of the body the tube is lowered; when it is carried behind the body the tube is raised. These movements are at first slight but they become more decided and more regular the longer they are continued. Lateral movements of the breath- ing tube in response to light do not occur. The next movements to appear are those of the limbs. The animal, after a time, shows irregular twitchings of the leg muscles, and soon afterwards slowly and unsteadily raises itself upon its legs and stands as if undecided whether to walk away or subside again into a state of repose. If now the light is passed over the body from side to side the creature will perform swaying movements each time the position of the light is chang- ed. If the light is on the right, the back of the insect is tilted Hoimes, 7he Reactions of Ranatra to Light. 313 over towards it, the right legs are flexed and the left ones extended (See fig. 1). Pass the light over to the left side of fig. r. Attitude of Ranatra when the right side is toward the light. the body and the back tilts over to the left, the left legs become flexed and the right ones extended. For a short time after coming out of its feint Ranatra will usually sway back and forth as the light is moved over it without attempting to walk, but soon it begins to follow the light, at first with slow and unsteady steps, but later with more and more vigor, until finally its efforts to go towards the light become almost desperate, and it becomes oblivious to everything else. Besides the lateral swaying movements which Ranatra per- forms when light is passed over the body from side to side there are equally pronounced longitudinal swaying movements when the light is passed back and forth along the axis of the body. When the light is placed behind the animal the body is raised up in front and the head held high in the air. Now place the light in front, and immediately the body is lowered, and the head bowed down, the grovelling attitude contrasting almost 314 Journal of Comparative Neurology and Psychology. comically with that assumed when the light is in the rear. By moving the light around the animal in a circle all combinations of lateral and longitudinal swaying movements may be produc- ed, the body following the light by twisting about in a most curious fashion. With the light to the right and behind the animal the body is raised up in front, tilted over to the right, the legs on the right side flexed and those of the opposite side extended, the head turned to the right and the beak held high in the air. If the light is passed in front of the animal on the left side the head and body are both bowed down and tilted to the left, the left legs flexed and the right ones thrown in a state of extension. As with the head, so with the body, there isa certain attitude assumed for each particular position of the light. Fig. 2. The lower figure represents the position of Ranatra when the light is behind the body. The upper figure represents the position assumed when the light comes from in front. Ranatras may be made to follow the light in any direction in the most slavish manner. By keeping the light to one side and a little behind the middle of the body the animal may be kept wheeling about in one spot, often, however, falling over on one side in its eagerness to get around. One reason for its awkwardness in this case is that as the light comes from the Hormes, Che Reactions of Ranatra to Light. ars rear the anterior part of the body is carried high in the air and the creature consequently easily loses its balance. At any time after Ranatra has ceased to feign death it can be made to perform swaying movements in either direction, although these may be combined with efforts at locomotion. By carefully controlling the light, however, the tendency to loco- motion may be largely checked. By moving the light around the animal in a circle the tendency to turn back when the light is behind may be made to balance the tendency to go forwards when it is in front, and the animal simply sways around in its tracks. Light seems to dominate entirely this creature’s behavior when the phototactic reactions are once started. It does not manifest any fear or awareness of any object in its environment save the light which it so strenuously seeks. Its excitement increases the longer it is operated with, and after a time it may be picked up without feigning death, or with only a momentary feint. Not content with walking as rapidly as possible towards the light, the insect begins to fly towards it, always doubling up its fore legs ina curious manner before spreading its wings. The wings are never used, however, until the creature has sought for some time to reach the light by the ordinary meth- od of locomotion. Their employment marks the attainment of a high pitch of excitement in which the insect seems animated by an uncontrollable frenzy which lasts until it is checked by approaching exhaustion. If a Ranatra is placed on its back it often has considerable difficulty in righting itself, and if near a light it will often walk towards it without turning over. Locomotion under these cir- cumstances is effected mainly by the anterior legs which are flexed dorsally at the middle joint. These legs are not employ- ed in ordinary locomotion, but when the creature is in an in- verted position they are used with considerable dexterity. By bending the legs dorsally the anterior end of the body is elevat- ed, and by the alternate movement of these appendages the insect walks along in a tolerably efficient manner. It will fol- low the light around in this way in any direction. When out 316 Journal of Comparative Neurology and Psychology. of orientation it reaches over to one side with the anterior leg nearest the light and pulls the body over until it is parallel with the rays. 2. The Negative Reaction. While under ordinary circum- stances Ranatra is positively phototactic it may in certain con- ditions become strongly negative. If Ranatras which have been kept for several hours in the dark are brought back again into the light they usually show a marked negative reaction, but this negative phototaxis is never so violent as the positive sometimes becomes. Instead of appearing to be the result of reflexes which are comparatively direct and involuntary, the behavior of Ranatra gives the impression of being caused by the desire to escape from a situation which is unpleasant. It is perhaps remotely analogous to the action of a man when, after having been for some time in the dark, he instinctively turns away from the sudden glare of a strong light. The behavior of specimens after having been kept in the dark may be illus- trated by the following experiments : Twenty-five Ranatras which had been in a dark room for twelve hours were placed, one at a time, in a glass trough through which light was passed from an incandescent lamp situated a foot from one end. Each specimen was placed in the water in the center of the trough at rivht angles to the direction of the rays and let go in that position. If the specimen swam to the negative end, and within one minute returned to the other end when the light was changed it was classed as negative; and a similar criterion was employed for the positive reac- tion. If a specimen swam to one end of the trough and did not return to the other end within one minute after the light was changed it was classed as doubt- fully positive or negative according to which end it first reached. Seventeen of the specimens proved to be negative; one was positive; four were doubtfully negative and two doubtfully positive. Out of the twenty-five specimens employed only one was unmistakably positive in its reaction, and this one swam to the positive end of the trough upon change of the light several times in succession. One spectmen did not swim to either end for five minutes. The Ranatras were then left exposed to the light of an incandescent lamp placed three inches from the end of the trough for one hour and forty minutes. At the end of this time all of the specimens were positive, The light was then held eight feet from the trough and the positive reaction still continued. One of the specimens which showed a very marked negative phototaxis was singled out. During the time the others were being experimented with it was exposed to the light, and when again studied (after about a half hour’s exposure) it showed a very evident negative phototaxis, but not so strong as before. After a time the negative reaction became so faint that it was scarcely distinguishable. Hoimes, The Reactions of Ranatra to Light. 397 The specimen was then exposed to the strong light from a projection lantern. It showed at first a weak positive phototaxis which grew stronger the longer it was exposed, until it finally became almost violent. When exposed to the much weaker illumination from a 16 candle power lamp it still showed a marked posi- tive phototaxis, but not so strong as when exposed to the light of a projection lantern. At another time a Ranatra was placed in the trough which was exposed to the light of an incandescent lamp placed two feet from one end. The specimen immediately swam to the negative end of the trough. When the lamp was placed two feet from the other end the specimen quickly returned. The light was then changed repeatedly several times and each time the Ranatra would swim to the negative end of the trough, usually within four or five seconds, After a time its responses became slower and less definite. The light was then held close to the end of the trough and the responses became as prompt as before. It was changed from one end of the trough to the other forty-two times, and each time the insect within four or five seconds went to the negative end. Then it was left several minutes,after which its negative responses became less marked. When it was exposed to the strong light of a projection lantern it was still nega- tive. It was then taken out of the water and laid on the table. In a few min- utes it came out of its feint and showed the usual swaying movements when an incandescent lamp was moved near it, but it was very reluctant to walk. After 15 minutes of hesitation it became more active and showed an unmistakable posi- tive reaction, and several times flew towards the light. When placed in the water again it still showed a strong positive phototaxis. The next morning (it was not in the meantime exposed to light, the room being darkened) it was markedly negative, and was driven from one end of the trough repeatedly by changing the position of the light. Then it was taken out of the water and placed on the table and an incandescent lamp was moved about near it to bring it out of its feint. It was a long time in awakening and for several minutes afterward it was disinclined to walk. When it did so it began to follow the light and soon became so excited that it would fly towards it repeatedly when four or five feet away, When put back into the water it was still positive and would follow the light in every direction. It was then exposed to the light from a pro- jection lantern and became more strongly positive than ever, moving wildly towards the light even in the intense glare of the focus. Brought back to an incandescent lamp again it showed only a comparatively feeble response. The negative reaction is associated with a condition of low- ered phototonus. It is rarely shown except when the animal is in a condition of comparative sluggishness. When in great excitement, when its movements take place with quickness and vigor, Ranatra always shows a positive response. It never flies away from the light. Whenever it is wrought up sufficiently to use its wings, its reaction is invariably positive. The nega- tive movements are slow and stealthy, often giving one the impression that the insect is attempting to sneak away unob- 318 Journal of Comparative Neurology and Psychology. served. The promptitude and decision of its negative move- ments may increase up to a certain point if the insect is kept close to the light, but when the movements begin to become vigorous there is a transition to the positive type of reaction. Often the advent of positive phototaxis is accompanied by a marked accession of energy as if a strong dormant propensity had suddenly been awakened. The causes that produce the negative reaction are, as a rule, those which lead to diminished activity and excitement. Cold, exposure to darkness, the quieting effect of contact stimuli lead to a condition of lessened excitability and, perhaps as a result of this, to a negative reaction to light. 3. Head and Swaying Movements in Negative Phototaxts. It would naturally be expected that the leg movements in nega- tive specimens are the reverse of those in positive ones, and to a certain extent this is true. It was thought not improbable that the movements of the head would be reversed as well; but it was found that in all cases in which Ranatras moved away from the light the head reflexes take place exactly as in individ- uals that are positive. Both in strong and in weak light, under a variety of different conditions the head reflexes are the same in kind regardless of the general sense of the response. The swaying movements in negative phototaxis are readily observed in Ranatras that have been resting quietly in the dark for some time in a glass dish of water. If an incandescent light be brought near them they are at first irresponsive. By moving the light slowly about them the head reflexes are first induced. Then there may be very slow and at first scarcely perceptible movements of the legs, the second and third pairs being very lazily extended on the side towards the light, and flexed on the opposite side, the back being rolled over so that it more nearly faces the light. On placing the light on the opposite side of the body there is a very gradual extension of the legs previously flexed and a flexion of those previously extended, the body rolling over at the same time so that its dorsal surface lies more nearly at right angles to the rays. The animal may be made to repeat this performance many times in succession. After a Hormes, The Reactions of Ranatra to Light. 319 time its movements become more vigorous and it turns to walk away from the light; it can then be driven about in any direc- tion at will. The difference in the swaying movements of positive and negative specimens is mainly brought about by the different movements of the legs at the femoro-tibial joint. In negative specimens the legs on the side toward the light are extended at this joint while those on the opposite side are flexed; in posi- tive specimens the reverse relation occurs. The rolling of the body is the same in both cases so that the muscles extending between the legs and the body are similarly affected in both kinds of reaction. The same relation probably obtains with the muscles between the joints of the upper parts of the leg. The vertical swaying movements of the body which involve the employment of these muscles are the same in both kinds of response. When light is behind a negative specimen the ante- rior part of the body is held high in the air as the insect walks away. When the light is held in front of the insect the ante- rior end of the body is lowered as it is turned from the light. Only a part of the organism is subject to a change in the sense of its phototactic response. The head reflexes and sway- ing movements of the body are always such as to bring their upper surfaces more nearly at right angles to the direction of the rays, whether the organism as a whole is going towards or away from the stimulus. No matter how strong or how weak the light, or whatever may be the condition of the aninfal, these responses, if made at all, always occur in the same way. 4. The Effect of Contact on Phototaxis. As shown by the following records of experiments, Ranatra may be made nega- tively phototactic by means of contact stimuli. In one experi-— ment seven specimens that were swimming against the side of the dish towards the window were picked up by their breathing tubes and dropped back into the water. At first they remained quiet but soon showed a negative reaction, swimming vigor- ously against the side of the dish away from the light. In about twenty minutes all but two had become positive again. They were all picked up by the breathing tube a second time 320 Journal of Comparative Neurology and Psychology. and dropped back into the water without touching any other part of the body. Soon all became negative without exception. After a few minutes they began to cross to the positive side of the dish one by one, and it was but a short time before every individual was positive. When I returned after an absence of an hour and a half all of the specimens were negative, although the light to which they were exposed had increased in intensity. Warm water was then added so as to bring the temperature of the medium up to 30° C._ Four of the specimens soon became strongly positive. These were picked up by the breathing tube and dropped back into the water; all became markedly negative. As specimens came over to the light side of the dish they were picked up and dropped as before, with the result, in almost every instance, of producing a marked temporary negative reac- tion. The next morning at 10 o'clock all of the specimens in this dish and in another that was beside it were swimming towards the light. They were all picked up and dropped back into the water when, without exception, they became negative. Soon they began to come over to the positive side of the dish and in about half an hour they were all positive again. They were all picked up and dropped a second time. All but two became negative. At 2:40 in the afternoon the specimens in each dish were aggregated into a dense bunch at the negative end. When stirred up some seemed positive and some nega- tive, but their reactions were not decided. The temperature of the water in one dish was increased to 32° C. when about half of the specimens became positive in an unmistakable de- gree. When picked up and dropped into the water they quickly became negative. When they became positive again they were handled under the water without taking them out; as soon as released they showed an unmistakable negative reaction. I have tried handling positive specimens under water re- peatedly. The effect is, in nearly all cases, to produce a change in the sense of the phototactic response. The effect of contact and disturbance is very marked also on specimens while out of the water. This as well as other Homes, The Reactions of Ranatra to Light. 321 features of interest is shown in the following experiments per- formed upon one individual : The specimen was taken out of water from a darkened room where it had been placed the day before and placed near a light ona table. Soon it awoke and began to turn away from the light. The light was moved around it in differ- ent directions and, although the insect seemed at first dazed and walked about with no very decided tendency to go either towards or away from the light, it soon began to show a more pronounced negative reaction. It was then picked up by the breathing tube and placed at right angles to the rays from an incandes- cent lamp four feet away. During eight successive trials in which the right and left sides were presented alternately to the light to eliminate any tendency to turn to a particular side that might be due to habit, it turned in each case away from the light. Its movements were at first slow and stealthy. At the ninth trial it turned slightly towards the light, but reached the edge of the table before it had turned very far. At the tenth and several subsequent trials it turned towards the light and went up to it rather quickly. Its movements now became much more rapid. It was then placed ten feet from the light and still showed a posi- tive response. It was then placed on the floor 22 feet away from the light, which was laid on the floor at the other end of the room. Although the light to which it was exposed was relatively very dim, the insect traveled to the light across the whole length of the room in nearly a straight line. When brought near the light the insect became more and more strongly phototactic and in about twenty min- utes its efforts to reach the light became almost frantic. After a time it became apparently exhausted and settled down to rest. It was then immersed in water and laid down on the table. Its movements were very sluggish and its responses to light slow. When placed at right angles to the rays it would slowly and stealthily creep away. It did this eight times in succession when the right and left sides were alternately placed towards the light. At the ninth and several subsequent trials it went towards the light. Then it was caused to follow the light about for a few minutes and soon it became quite excited. It was picked up and stroked but it could not be induced to feign death and as soon as released it made for the light, which was four feet away. It was then held in water for several seconds, but as soon as liberated it showed an unmistakable though not very strong positive reaction. It went up to the light, touched the bulb with its anterior legs, jerked back quickly as if burned, then stopped for a moment and walked away from the light. As the light was moved about, the insect would flee from it repeatedly as if it feared a repetition of its disagreeable experience. Soon, however, its responses became weak and indefinite ; its movements were sluggish. After a time it showed a positive reac- tion and began to follow the light all around the table. A little later it became much excited and flew towards the light repeatedly. The light was placed ina cylinder of water and the insect struggled to go towards it for ten minutes. It was then held in cool water for a short time and placed again on the table. After this experience it showed a marked negative response. The light was moved about the insect in various directions so as to keep it close to the body for about twenty minutes when positive phototaxis was again induced. When its reaction became very strong, the insect was picked up and stroked, but it feigned 322 Journal of Comparative Neurology and Psychology. death only momentarily and then resumed its efforts to go to the light. A repetition of the experiment was followed by essentially the same result. When dipped in water again it showed a faint negative reaction. It would go ‘towards the light when it was placed in front of the body or away from it when it was placed behind. Its general behavior was sluggish and it would perform only scarcely perceptible swaying movements when the light was moved over its body. Soon its negative reaction became more pronounced and it would turn away from the light every time it was placed to one side of the body. The insect was then placed under a bell jar near the light and upon my return after a two hours absence it was markedly positive. When dipped in water it showed a suggestion of a negative reaction, and for some time was apparently indifferent to the light. Repeated dippings failed to make the specimen more negative, and after a time a sluggish positive response began to appear. The light was then moved around it and finally the creature became very violent in the eager- ness of its response and flew towards the light several times. When it was dip- ped in water it became sluggish. When placed at right angles to the rays it turned away from the light and started to doso a second time, but turned to- wards the light and went up to it. The same experiment was repeated three times in succession, and each time the insect turned at first away from the light and then towards it before having proceeded more than a few inches. After thirty minutes of positive reactions it was dipped in the water again. It went slowly towards the light but passed by it, and in several subsequent trials went away from the light; soon, however, it became weakly positive and in a short time its positive response was strong. After three hours of exposure to strong light it was still positive. When dipped into the water it showed at first a faint negative response but soon turned and went up tothe light. Subsequent dippings failed to evoke a negative response. It is not the effect of water in itself that changes the response, but the experience of being dipped in water. If the Ranatras are allowed to remain in the water they soon show a positive reaction. If then they are lifted out and put on the table they almost at once become negative if they are not thrown first into the death feint. Curiously enough, dipping into water is more effective in changing the sense of the re- sponse than handling or stroking the specimens in the air. Specimens which have been handled so much that they no longer respond to that treatment either by feigning death or by showing a negative response to light may usually be rendered negative after dipping into water. As handling positively phototactic specimens usually causes their reaction to become negative, unless the experiment is repeated too often, it is probable that the change produced by dipping them in water is due to the influence of contact stimu- Hoimes, The Reactions of Ranatra to Light. 323 li. It takes place independently of differences of temperature, and it cannot be satisfactorily accounted for by attributing it to chemical or osmotic changes produced by the surrounding media. Anything which makes towards the peculiar nervous condition which accompanies the death feint tends to produce the negative response. Dipping Ranatras into water usually throws them into condition of quiet when other influences fail, and the negative reaction is doubtless a result of the nervous state thus brought about. Whena Ranatra is either placed in the water or removed from it, every portion of the surface of the insect is stimulated, and, although the stimulus upon no part is strong, the general effect may well be considerable. That the general integument is very sensitive is indicated by the fact that decapitated specimens often respond very strongly to the slightest breath of air. 5. The Effect of Temperature on Phototaxis. Raising the temperature tends to accentuate the positive phototaxis in Ran- atra and lowering it tends to produce the negative reaction. In several experiments two dishes containing Ranatras were set before a window so as to receive the same amount of light. As the specimens had been previously kept in the dark, they show- ed a negative reaction. Into one dish warm water was poured raising the temperature from about 20° C to nearly 30° C. In a few minutes the specimens in the warmer dish became posi- tive, the ones in the cool water still showing a negative photo- taxis. Ranatras transferred to the cooler dish soon became negative while those which were picked up in the same way and dropped back into the warm water from which they were taken soon resumed their positive reaction. Onthe other hand, transferring negative specimens from cool to warm water pro- duced in a short time a positive response. In cool water there is a marked tendency to forma dense cluster in the negative end of the dish. In warmer water the insects become more active and the groups are more apt to be broken up. Water at a temperature of 30° C usually stimulates them to very ener- getic movements. That negative phototaxis in Ranatra is in- duced by a reduction of temperature affords an illustration of 324 Journal of Comparative Neurology and Psychology. the general fact that circumstances which reduce the excitabili- ty of the insect tend to produce the negative reaction. 6. Phototaxis Leading to Fatal Results. Wishing to ascer- tain if Ranatra would continue to be positively phototactic if it were thereby led into a situation which exposes it to stimuli having injurious, if not fatal, effects I performed the following experiment. A strong arc lamp was placed on a table so that the focus or space between the carbons was about five inches from the top, this elevation being chosen so that the specimen could not walk directly into the luminous arc although it was free to move about beneath it. As the lamp gave out a large amount of heat the insect in approaching the focus would he brought into a region sufficiently heat- ed to produce a fatal effect if it remained there long. A Ranatra placed on the table, moved toward the light until it came under the focus, then starting off again, only quickly to return. It soon became wildly excited and made repeated dashes toward the light. Several times it flew towards it, but luckily escaped coming between the carbons. After a time it gave signs of being overcome with the heat, but whenever removed from the light it would quickly return. Its movements became weaker, although its efforts to go to the light were no less per- sistent. It became unable to raise its body off the top of the table as it walked, but used its legs to slide its body towards the light, and it would quickly re-orient itself when placed obliquely to the rays. Even its very last piteous efforts were devoted to pushing its body a little nearer the light. When no longer able to move it was placed in cool water, but it did not revive. When a moth flies into a flame it is probably because it does not have time to check or change the course of its flight after it has drawn near enough to experience the injurious effects of the heat. The suicidal conduct of Ranatra, however, cannot be accounted for in this way. The movements of the insect are slow and deliberate enough, especially when it becomes weakened, so that it need not be carried by its momentum into a region from which it would otherwise flee. It reacts positive- ly at every step, even when nearly overcome by the heat. Essentially the same phenomenon is seen in 7alorchesttas which when exposed to direct sunlight, keep jumping towards the light until the heat overcomes them and they die. 7. Inhibition of Phototactic Responses by other Activities. The phototactic responses of Ranatra which usually occur with such regularity and precision are sometimes checked when the insect is engaged in performing some other function. Speci- mens that have been following the light for some time often Hoimes, Zhe Reactions of Ranatra to Light. 325 stop to rub their eyes with their first pair of legs, using their claws in what seems to be an effort to scrape off some foreign object from the cornea. If a light is moved over an insect when it is engaged in this operation the swaying movements of the body will no longer be performed. The head reflexes are also sometimes inhibited, but usually the head can be kept moving about at the same time the insect is rather ineffectually attempting to rub its eyes The swaying movements are like- wise inhibited when Ranatra stops to rub its wings or any oth- er part of the body. These actions may be caused by daubing asphalt varnish upon the insect, when efforts are made to get rid of the offending substance. As soon as the cleaning move- ments are over the insect promptly reacts to light as before. It generally makes no attempt to do two things at once. The phototactic response may also be inhibited by efforts to obtain food. JRanatras which are swimming towards the light can often be caused to discontiuue their phototactic efforts if several small insects are placed near them. If the phototac- tic activities are very lively and vigorous it is more difficult to divert the attention of the insect to the capture of prey. When attention is once directed to seizing the smaller insects the light is disregarded. When the prey has once been captured and the Ranatra is engaged in sucking out its juices little attention is paid to the light. The repast being finished the insect may resume its positive response. - Efforts to go towards the light are frequently inhibited by contact stimuli. When several individuals are put into a dish of water near a window they commonly cease, after a time, to swim towards the light and form a dense cluster in which they lie at all possible angles to the direction of the rays. If now the individuals are placed in separate dishes they soon show a positive phototaxis. When placed together again they quickly form a group as before. Contact stimuli not only inhibit posi- tive phototaxis but they produce a negative reaction as we have already seen: the latter tendency however, is often held in check by the same cause by which it is brought about. Phototactic activities may also be checked by the sudden 326 Journal of Comparative Neurology and Psychology. appearance ofa large object in the field of vision. Ranatras that are swimming towards the light generally check their move- ments and lie perfectly quiet for some minutes as soon as they perceive one’s approach, but if no movement is made near them they soon resume their phototactic activities. This inhibition of movement recalls that which in higher forms is often brought about by fear, but of the usual manifestation of fear in the efforts to escape from enemies by flight Ranatra evinces no sign. Control in Ranatra probably amounts to nothing more than supplanting one instinctive tendency by another. The reac- tions of the insect to light seem to take place inevitably unless some circumstance calls into play some other equally stereo- typed form of instinctive response. 8. The Effect of Hemtsecting the Brain. Cutting the brain of Ranatra through the middle was accomplished by means of a fine needle ground down to a sharp edge. Only a small opening need be made, and there does not follow the pro- fuse bleeding which results from making larger incisions. After hemisection of the brain specimens are easily kept alive for sev- eral days. Their behavior may be illustrated by the following records of experiments : The brain was hemisected in three specimensjat 38:45 A. M. In one minute or less they came out of their death feint; in five minutes they were picked up and stroked and then laid on the table. None feigned death for more than two or three seconds. At 9:25 they were still very restless and none of them paid the least attention to the light that was held near them. They all performed circus movements to a greater or less extent, due, doubtless, to the fact that the brain was not cut exactly through the middle. At 11 A. M., one flew out of the dish. They were all picked up aud stroked again, but none feigned for more than a few seconds. When the light was moved about near them they would show no head reflexes or other decided response, although the light seemed to stimulate them in an indefinite way. During the next two or three days they continued the same restless movements and could be induced to feign death only for a few seconds. Definite responses to light failed to return. The brain in three other specimens was hemisected at 12 M. Theyall soon came out of the death feint that was induced by handling them during the oper- ation. At1:20 P. M., when they were again observed, they were very restless. When picked up, stroked, and laid on the table they feigned death for one min- ute, four minutes, and ten minutes respectively. The next day they could not be induced to feign for more than a minute and they showed no definite response to light. They were also tried on each of the three following days and their be- Hoimes, The Reactions of Ranatra to Light. 327 havior was essentially the same. Two specimens seemed to respond when the light was moved near them but when the rays were passed through water before reaching them no response could be evoked. It is probable, therefore, that their movements were the result of stimulation by heat. Ranatras with the brain cut through the middle, like those with the brain removed, are very sensitive to all sorts of stimuli, and they are set into action by causes which would produce no manifest effect in a normal individual. Bethe’ found that hemisecting the brain of Carcimus caused the phototaxis of the animal to disappear, although most of its other responses took place ina normal manner. I have found the same in several species of insects’. In theamphipod Ta/or- chestta longicornts, which has a remarkably strong positive pho- totaxis, hemisection of the brain is followed by a complete loss of the power of orientation. Sensitiveness to light, however, is not entirely destroyed. If when a specimen is resting quiet- ly ina shaded spot a beam of light filtered through an alum cell is thrown upon its eyes it usually responds by a few irregu- lar movements. Since a large part of the fibers of the optic nerves cross in the brain, hemisection of this organ cuts off the main path of the impulses concerned in orientation to light. 9. The Effect of Covering the Antertor Half of the Eyes. Ranatras with the anterior surface of both eyes blackened over walk with the head strongly upturned and the anterior end of the body high in the air. Sometimes they stand nearly vertic- ally, and several times I have seen them fall directly over back- wards. Even when going towards the light the anterior part of the body is elevated, but not so much so as when the light is held above or behind the insect. When the light is moved backward and forward above the insect the body sways to and fro, and the head responds with the usual vertical reflexes. When the light is behind the insect the head and front part of the body are much elevated; if now the light is carried to the front the creature bows down only for a short distance instead of assuming the grovelling attitude of a normal individual in the same situation. l Archiv f. mik. Anat. 1897, 50, 617. 2Am. Jour. Physiol. 1902, 5, 211. 328 Journal of Comparative Neurology and Psychology. When Ranatra is compelled to walk on a glass plate while the light is held beneath the body it still carries the head and anterior part of the body high in the air. The head and body are lowered somewhat if the light is placed below and in front ofthe insect, but not nearly so much so as ina normal specimen. If the light is passed to the rear ‘beneath the glass plate the head and front part of the body are raised up. Lateral head and body movements are performed in the usual way when the light is passed transversely over the posterior part of the body, but as the light is carried forwards these movements become less marked. Similar results are obtained if the light is moved beneath an insect which is placed on a glass plate ; the responses become less evident and precise as the light is carried in front of the body. Ranatras with the anterior surface of their eyes blackened over are still able to follow the light when it is in front of them, but their movements are hesitating and their orientation inac- curate. This is a very natural result since the insects must be guided by the light which enters the posterior sides of the eyes. ro. The Effect of Covering the Posterior Half of the Eyes. Blackening over the posterior surfaces of both eyes produces effects opposite to those observed when the anterior surfaces are blackened over. The insect walks with the anterior part of the body lowered and the head inclined slightly downward. If a light is held behind the insect the head and anterior part of the body are elevated, but not so much so as in a normal indi- vidual. When the light is in front the body is lowered anter- iorly and the head bowed down. The same effects are produc- ed when the Ranatra is placed on a glass plate and the light moved beneath the body. The light is followed very readily when it is kept in front of the body; if, however, the light is moved to the rear the insect experiences considerable difficulty in orienting itselfand frequently travels for some distance direct- ly away from the light before finally turning around. Lateral movements of the head and body are readily brought about when the light is moved from side to side in front of the insect, but they become less pronounced when it is carried further back. Homes, The Reactions of Ranatra to Light. 329 ri. The Effect of Destroying or Covering One Eye. If one eye of Ranatra is blackened over or destroyed the insect in most cases no longer walks in a straight line but performs more or less decided circus movements towards the normal side. Under the stimulus of light the insect assumes a peculiar atti- tude ; the body leans over towards the normal side and the head is tilted over in the same direction. When alight is held oppo- site the normal eye the insect leans over towards it, and holds the legs nearest the light in a flexed condition while those on the other side of the body are extended. When the light is passed over the body transversely swaying movements are per- formed as long as the light is opposite the normal eye, but when it is passed to the other side of the body the insect sways back only to the middle position or slightly farther. The lon- gitudinal swaying movements of the body and vertical move- ments of the head are performed when light is moved forward and backward above the insect. These movements become less decided, however, as the light is held over towards the blind side. Fig. 3. Head of Ranatra fusca showing the almost stalked condition of the eyes. If a light is held directly in front of ‘a Ranatra with one eye blackened over the insect frequently does not travel straight towards it, but veers over towards the normal side until it comes to go in a quite different direction from that in which it 330 Journal of Comparative Neurology and Psychology. started out. In one experiment a Ranatra with the the right eye blackened over was placed at a distance of four feet from a 16candle power lamp. In all of the twelve trials that were made it started on a nearly straight course towards the light as it was originally pointed. In all cases it veered to the left and naturally diverged from the straight path more and more the farther it proceded. When a little more than half the distance to the light had been covered it corrected its course and pro- ceeded towards the light again ina more direct path. This took place by two methods and usually occurred when the nor- mal eye was looking away from the light. In this situation the insect would frequently stand for some time as if undecided which way to turn. In four instances it turned towards the right and proceeded again in the direction of the light. In eight cases it continued turning to the left until it had gone completely around in a circle after which it went up to the light. Specimens with one eye blackened over present, however, marked individual differences of behavior. In some cases the insect walks toward the light in a nearly straight line. Rana- tras which were taken late in the fall or early in the winter in most cases went nearly straight to the light while those experi- mented with in the early fall usually performed circus move- ments. This difference may have been due to accidental indi- vidual differences in the specimens, or it may have been the result of differences in age, the older Ranatras being better able to correct their course than the younger ones. The tendency to turn away from the blind side is manifested to a greater or less extent in all cases, but in many specimens it does not go so far as to produce decided circus movements. If the whole of one eye and all but the posterior surface of the other is blackened over the insect in many cases is. still capable of following a nearly straight path towards the light. A tendency to perform circus movements is more or less mani- fest and many specimens will go around in a circle repeatedly, especially when the light is near them. When all but the pos- terior surface of one eye is blackened over the insect is able to guide itself to the light nearly as well as when one eye is entire- Homes, The Reactions of Ranatra to Light. 331 ly exposed. It may even follow the light by turning towards the blind side as the following experiment shows : The right eye and all but a small part of the posterior surface of the left was thickly blackened over.. When the specimen came out of its death feintit walked nearly straight to the light. The light was then moved over toward the right side of its path several times, and the course of the insect was changed so as to continue going towards it. The light was then held to the right and behind the body and the insect circled around to the right. By keeping the light in the proper position the insect could be caused to keep circling around to the right in the same spot. The head and body in these movements were tilted over slightly to the right, but not so strongly as they are inclined to the left when the light is held on that side. The insect would perform circus movements to the left more readily than in the opposite direction, but it would make sharp turns to the right whenever it was necessary to maintain a position of orientation. When the light was placed behind the body the insect would usually turn around to the left to reach it. If, however, it was placed behind the body and a little to the right the specimen would turn around towards the right side. 12. Reactions of Specimens with only Small a, Part of the Lateral Surface of One Eye Exposed. ‘The right eye of a speci- men was completely blackened over and all but a small part of the lateral surface of the left. The insect was at first sluggish. When the light was held on the left side the head and body were tilted over towards it, and the specimen turned slowly to the left. When the light was placed two feet ahead of the specimen it moved very slowly and with the greatest hesitation, turning this way and that as if seeking to get its bearings, but going, nevertheless, nearly straight tothe light. Although a decided tendency to make circus movements to the left was manifest, deviations in that direction were corrected by a direct turn towards the right side. When the light was held on the right side of the body the insect seemed confused and undecided which way to turn. When the light was held to the front and to the right so that the rays struck the body at an angle of about 45° the insect would not turn towards the light but moved about aimlessly until the left eye was presented to the light when it would turn to the left and go up to it. By keeping the light nearly in front of the body the insect would follow it all around the table. The experiment was then tried of holding the light farther over towards the right. The insect could then be caused to keep turning slightly towards the right in order to follow it. When the light was held still further to the right the insect still followed it. After a while it would follow it when held in a position to which it would not turn at the beginning of the experiment. After having got into the way of turning to the right side it would turn in that direction much more abruptly than at first. A second specimen was treated in the same way, but it showed at first a pro- nounced negative reaction. It would pay little attention to the light except when it was held opposite the left eye when the insect would move away from it sidewise, much like a crab, by extending the legs on the left side and flexing 332 Journal of Comparative Neurology and Psychology. those on the right. When the light was held on the blind side the insect showed no inclination to turn away from it. The movements of the insect were slow, but, after about twenty minutes, it suddenly began to turn vigorously to the light and became much more active, following the lamp around with eagerness and rapidity. In several trials in which it was placed three feet away from the lamp it went towards it in nearly a straight line, correcting its deviations from a straight course, whether to the right or the left, by the appropriate turn. It soon became quite excited and several times attempted to fly. It would follow the light when it was in front and to the right side by turning directly to the right. If, when the light was reached, it was changed to some other part of the table the insect would turn around and make for it in nearly a straight line. After moving about in this way for some time it settled down so as to rest its body against the top of the table. The light was then placed near the specimen, but it paid no attention to it until it was moved opposite the left eye, when it began to move slowly away from it by crawling sideways. The whole character of the insect’s behavior now became suddenly changed. It became sluggish and stealthy in its actions instead of vigorous and excited. It would respond to the light by moving sidewise instead of straight ahead, and only when the light was placed in a certain posi- tion. After moving the light around the specimen its negative reaction became more decided and then suddenly changed to positive. It would follow the light around either to the right or to the left, but if the light were held too far to the right side it would not turn directly towards it. The specimen had several other fits of reacting negatively when its conduct was essentially as described above. It was caused to become positive each time by keeping the light near the left eye. Its negative reaction would in each case grow more vigorous and then suddenly give way to the positive response. The appearance of the positive response seemed to indicate the attainment of a certain degree of excitement. The differences between the negative and positive responses of the specimens experimented with are very striking. The peculiarites of the negative reaction are probably due to the fact that only when the light shines directly into the left eye is the stimulus strong enough to produce action. When out of the direct glare of the light the insect is content, and it gets away by the most direct method. In the positive reaction the insect is attempting to get more of the stimulus; it is in a state of increased phototonus, and each movement that brings it nearer the light tends to increase its activity. 13. Phototaxis as Modtfed by Experience and Habit. That Ranatra is able to modify its reaction to light as the result of experience was shown by several experiments. The attempt was made to determine if Ranatras which perform circus move- ments when one eye is blackened over would in time come to Hoimes, The Reactions of Ranatra to Light. “333 travel to the light in a more direct course. A Ranatra with its right eye blackened over was placed on the top of a table three feet away from an incandescent lamp. Each time the specimen reached the lamp it was picked up by its breathing tube and placed in its original position facing the light. The course over which it traveled was in each case followed by a pencil. The paths taken in successive trials are represented in the accom- panying diagram (Fig. 4). e -->-2. ® e ° A fig. 4. Paths taken by a Ranatra in successive trips to the light. The position of the lamp is indicated by a dot at the upper side of each path. The cross lines indicate places where the insect took wing. When it flew directly to the light its course is represented by a dotted line. At A the experiment was discontinued for fifty minutes, after which the remaining tracings were taken. The specimen showed a strong tendency to fly as it drew near the light, and after the tenth trial its wing covers were stuck down by asphalt varnish. After a few ineffectual attempts to raise the wings the insect gave up trying to use them and walked to the light more quickly and with fewer pauses. The 334 Journal of Comparative Neurology and Psychology. points on the path where the specimen took flight are indicated by a short cross line, and the position of the lamp is represented by a dot. In the first trial the insect veered over constantly to the left, passed by the lamp and went off from the table before it turned around. In the following trials a marked tendency to turn to the left is also shown; frequently the insect makes one or more complete circus movements to the left before reaching the light. At the eleventh trial its course is corrected for the first time by a turn to the right side, but, instead of going straight up to the light, it performed a com- plete circus movement to the left before reaching it. The next time the course was corrected bya sharp turn to the right and the circus movement was dispensed with. At the next trial the course was corrected in the same way, and at the fourteenth attempt the insect deviated only slightly to the left side and then turned to the right to reach the lamp. In the following ten trials it reached the light by a nearly straightpath. Whenever it began to turn away from the light to the left it corrected its course by a direct turn in the opposite direction instead of going around in a complete circle as at first. During the latter half of the experi- ment the insect became more excited and walked to the light more rapidly and with less hesitation and wavering. The experiment was discontinued at 12: 10 P. M. and resumed at t P. M. The insect had not forgotten in the meantime how to reach the light by the most direct means. In eleven trials it went to the light in nearly a straight course, as is shown by the second series of tracings. The specimen was then placed with its left side towards the light. In each of its successive trials it turned sharply to the left and went up to the lamp. It was then placed with its right or blind side towards the light. In the first two trials it turned sharply towards the light and went up toit. In the third trial it first turned towards the light, but soon veered over to the left and went away from the light instead of towards it. When placed again with its left side to the light it nolonger went towards it as before. It manifested a decided negative phototaxis in fifteen successive trials. When placed facing the light, as in the first experiment, it turned sharply to the left and went away from it for three times in succession. Then a fit of positive phototaxis began to manifest itself again. In the fourth and fifth trials it reached the light by an irregular course. After this it went nearly straight to the light fourteen times. It was now allowed to rest for an hour anda half, when it was experimented with again. At the first trial it turned to the left, but corrected its course by a turnin the opposite direc- tion and reached the lamp. In the second trial it went to the lamp in nearly a straight line. At the third attempt, after it had gone nearly to the light, in an almost straight line it turned away from it and went off in another direction. A fit of negative phototaxis now began to assert itself and in the next thirty trials it turned to the left and went away from the light. It was now nearly exhausted and could scarcely raise its body from the table. When near the light it would move in an excited manner in an effort to get away from it, but when it reached a darker region its movements became much slower, and it would soon come to rest. The experiments were then discontinued until the following day, when the specimen proved to be still strongly negative. After fifteen trials were made, in which it turned away from the light, except during a short fit of Hormes, The Reactions of Ranatra to Light. 335 positive phototaxis, when it turned twice towards it, the specimen was put back into the water. At one o’clock on the day following, it was taken out again. It still showed a decided negative reaction and turned to the left and went away from the light twenty-five times in succession. In nearly all cases after it had turned its back upon the light it went away from it in nearly a straight line. After a rest of an hour and a half the asphalt varnish was removed from its eye. When placed on the table, three feet from the light, the specimen went towards the light and passed by it, but it turned around before proceeding very far and went uptoit. After this it went to the light eleven times in nearly a straight line. The left eye was then blackened over. In the first two trials the insect veered slightly to the left, but reached the lamp by a turn to the right. In the third trial it turned sharply to the right and went off from the table. In the fourth trial it went straight to the lamp. After this another fit of negative phototaxis apparently seized it, for it turned from the light and walked away from it in numerous trials. It then became fatigued and the experiment was discontinued. It is worthy of note that while the insect, after one eye was first painted over, came to take a direct course to the light only after several trials, it went to the light, when the opposite eye was painted over in nearly a straight line at the first attempt. Unfortunately the fit of negative phototaxis which supervened prevented observation on this point from being carried out as fully as would be desirable. Owing probably to fatigue or frequent handling, the speci- men became more prone to react negatively the longer it was worked with, until it no longer served the purpose of the experiment. Other experiments showed a similar straightening of the course after a number of trials. As experiments on this subject were undertaken late in the season, most of the inviduals worked with went nearly straight to the light at the first trial. In one case a specimen went nearly straight to the light six times in succession; it was then taken up and its right eye given another coat of varnish to make sure that it was entirely cov- ered. When put down again it seemed confused and performed a number of circus movements to the left. After several attempts, however, it came to travel to the light in nearly a straight line. Similar experiments were tried on Notonecta with much the same results. These insects when placed on a table near a lamp travel towards the light with much eagerness. If one eye is blackened over they perform circus movements towards the normal side. _ After quite a number of trials, however, the Notonectas come to take a nearly straight course to the light. When they become deflected from their course they orient them- selves by a direct turn in the appropriate direction. If the 336 Journal of Comparative Neurology and Psychology. lamp is kept over towards the blind side they may be made to perform circus movements in a direction opposite to that in which they would otherwise tend to go. Fig. 5. Tracings of successive paths towards the light taken by a Notanecta, which had the left eye blackened over. After a number of other trials the speci- men came to travel towards the light in nearly a straight line. 74. Formation of Habits of Turning. In working with Ranatras I have several times noticed what appeared to be a tendency to fall into habits of action, and I was naturally led to test the matter further by experiment. A Ranatra with its right eye blackened over was placed so that its head pointed directly away from a lamp three feet behind L its body. As was to be expected, the Rana- tra turned around to the left and went to the B light. It was then picked up and placed in the same position ten successive times. In each trial it turned to the left and went up to ar the light as at first. In these and all subse- quent trials the insect, when picked up, was ee turned alternately to the right and to the left D before it was put down again. In this way the possibility that the results might be due A to compensatory motions was eliminated. fig. 6. After the first ten trials the insect was placed obliquely (at an angle of 45°) to the rays with its right side towards the light (position B in Fig. 6). In each of the ten trials that were made the insect turned towards the right or blind side, and went to the light. It was then placed Hormes, The Reactions of Ranatra to Light. 337 at right angles to the rays, the light falling on its right side as before (position C). In each of the ten trials made it turned towards the right as in the previous experiment. Then it was placed with its head pointing obliquely away from the light (position D), when it still turned to the right in each of ten suc- cessive trials. Finally, it was put back into its original position, A, with its head pointing directly away from the light. Instead of turning to the left, as it did at first, it turned to the right as in the experiment immediately preceding, and it repeated the performance in the same way ten times in succession. It was then placed in a slightly oblique position so that its left side was exposed to the light. Twice it turned to the right as before, but in the third and several subsequent trials it turned to the left. It would then continue to do so when placed back in its original position, or even with its right side slightly turned towards the light. The experiments afford unmistakable evidence that when Ranatra has turned in any direction once it tends, zpso facto, to turn in the same direction a second time. The habit thus formed may even overcome the tendency to turn towards a »ar- ticular side which is caused by blinding one eye. IV. GENERAL CONSIDERATIONS ON THE PHOTOTACTIC RESPONSE. The behavior of Ranatra in relation to light is, I believe, not without interest in relation to the general theory of the photo- tactic response. Many features of the phototaxis of this insect seem to afford strong support to the reflex theory. The per- fectly definite and regular movements of the head in response to changes in the position of the light and the fact that these move- ments take place under all conditions in exactly the same way indicate that they are as machine-like as the most devoted parti- san of the reflex theory of tropisms could wish. There is no evidence of choice, properly so called, in the performance of these actions. It is true that during the death feint they are no longer performed, but this affords no ground for regarding them as in any sense voluntary, since, as is well known, undoubted 338 Journal of Comparative Neurology and Psychology. reflexes are no longer performed in certain conditions of the nervous system. The swaying movements of the body in response to changes in the position of the light seem almost as mechanical as the head reflexes. They are more easily inhibited, however, since they are often checked by efforts to rub the eyes, to clean the body, or to raise the wings after they have been fastened down, but they are immediately resumed as soonas the energies of the insect are no longer diverted to other actions. The swaying movements of the body are the result of a strong and definitely directed tendency to action which, when the insect is in a cer- tain condition of tonus, it seems powerless to control. It is only when other instinctive responses are brought into play that the insect is able to overcome its phototactic activities. The swaying movements of the insect vary, however, according as it reacts to light in a positive or a negative manner, but there is little evidence of choice as regards which mode of response is followed. In one nervous condition the insect is always negative; in another condition it is always positive. A Ranatra that is lethargic and sluggish reacts to light in a nega- tive manner, while one that is highly wrought up and excited is always strongly positive. In intermediate states of excitement there is often a hesitation between the two modes of response, and the insect may exhibit alternate fits of positive and negative phototaxis of short duration. The power of one instinctive response to inhibit or overcome another may be considered as the first step towards the voluntary control. Choice as mani- fested by Ranatra is determined by which of two instinctive ten- dencies to action gains ascendency. The mechanical nature of the phototactic response is further evinced by the effect of blackening over different parts of the eyes. When the posterior sides receive light the legs are ex- tended and the anterior part of the head and body are held high in the air. When only the anterior sides receive light the head and body are bowed down. If light comes in only at the side of one eye the legs are flexed on the side towards the light and extended on the side away from it. It would almost seem as Hoximes, Zhe Reactions of Ranutra to Light. 339 if different areas of the compound eyes have special connection with particular sets of muscles such that when a given area is stimulated the muscles are set in action which bring about a particular attitude of the body. We should bear in mind the possibility of interpreting the phototaxis of Ranatra as due to the fact that the light is sought because the insect derives from it an agreeable stimulus. We might regard the creature as so constituted that it derives pleasure from light and reacts toward it so as to get as much of this stimulus as psssible. Its behavior would then come under the head of what BaLtpwin calls the ‘‘circular reaction.”’ The movements of the head and body would be interpreted, according to this conception, as efforts to place the body in such a posi- tion that it can receive more of the desired stimulus. What- ever the position of the light Ranatra reacts towards it so as to place the upper side of the head more nearly at right angles to the direction of the rays. Both the head movements and the swaying movements of the body conspire to this end. And in this position it is probable that more light is received by the eyes than in any other. Whatever may be the explanation of the process in physio- logical terms, it is evident that animals perform many actions simply because they derive pleasure from so doing. Such actions are, I am inclined to believe, not quite the same as simple reflex acts, even in such a creature as Ranatra. Simple reflex acts may, however, be accompanied either by pleasure or by pain, although neither of these states nor their nervous correlates determines the nature of the reaction. But in most cases of the pleasure-pain response the character of the nervous analogue of these states somehow determines whether move- ments producing them shall be continued or inhibited. Move- ments which bring agreeable stimulation are persisted in, while those which produce painful effects are checked. If any stimu- lus brings a pleasant sensation an animal is apt to make efforts to get more of that stimulus. If the creature possesses any power of association, movements bringing an increase of the stimulus are repeated and come to be performed with ever increasing 340 Journal of Comparative Neurology and Psychology. readiness. In view of the fact that insects are capable of form- ing quite complex associations and of guiding their action by their previous experiences there is no reason to balk at the admission of the possibility that an insect may seek the light because it thereby derives an agreeable feeling. Whether the phototaxis of Ranatra is to be interpreted as a form of pleasure seeking, or as a matter of direct reflexes, a sort of behavior forced upon the creature from without, is a question not to be decided without careful observation and experiment. That an organism travels towards the light in the direction of the rays, even though it goes from a brighter area into a darker one, is no decisive proof of the latter theory. We might interpret the orientation of an animal going towards the light as due, not to forced reflexes, but to a more or less voluntary effort to retain a maximum of stimulation. If a creature has reached that plane of psychic development at which it acquires a capacity of reacting with in- creasing readiness to stimuli which produce an agreeable effect, and of discontinuing those reactions which give rise to unpleas- ant results, it seems probable that it would not stupidly continue to orient its body and go towards the light if this were not asso- ciated with some sort of gratification. If the organism be capable of profiting by experience, we should expect such meaningless behavior sooner or later to be stamped out. The impulses which are concerned in the reactions of Ranatra to light pass through the principal centers of the nervous system. The responses of the creature to light, if we consider them as reflex acts, cannot, therefore, be reflexes of a very simple kind. The impulses involved must pass from the eye to the brain, thence through the sub-oesophageal ganglion and the ganglia of the ventral nerve cord to the nerves supply- ing the legs. There are several links in the chain of neurons between the reception and the discharge of the stimulus, and there is abundant opportunity afforded for modification of the reaction through impulses coming from associated parts of the nervous system. Asa matter of fact, we have found that the light reactions of Ranatra are modified in this way, as well as conditioned by the general nervous state of. the animal. And Hoimes, The Reactions of Ranatra to Light. 341 whatever changes in the nervous system may be due to the formation of associations or the effect of habit afford a further element in determining the nature of the phototactic response. Now, while the light reactions of Ranatra take place to a large degree ina stereotyped and mechanical way, there is much to indicate that the insect seeks stimulation by light much as a bit of food or other object of interest is sought by a higher animal. A dog seeing a piece of meat on the other side of a fence makes a variety of efforts to get the prize. He runs up and down looking for a hole where he can get through or per- haps a low place where he can jump over. Wecannot class his actions as direct reflexes in response to outer stimuli. His con- duct is determined by the effort to secure a gratifying experi- ence and various methods are employed to gain that end. A Ranatra seeking the light is much less resourceful than a dog trying to get on the other side of a fence, but, to a certain extent, the behavior of both animals is determined by interest in the object sought. As we have seen, Ranatra is able to go towards the light despite obstacles of various kinds. Even when one eye is totally blackened over and all but a small part of the posterior surface of the other is covered, many Ranatras are able to go towards the light in nearly astraight line. How is this done? A Ranatra in this condition is in much the same situation a man would be if one eye were blindfolded and he were attempting to reacha light by walking backwards. A man would accomplish this, if he had not previously seen where the light was situated, in a very indirect manner. By moving his head from side to side he could determine the darkest part of his visual field, and by facing in that direction he would finally be brought by walking backwards to the light. The darkest part of the visual field in this case is a rather indefinite thing as anyone may readily assure himself by trying the ex- experiment. A man’s course towards the light would proba- bly be very indirect, and it is not a little remarkable that so benighted a creature as Ranatra can reach the goal by so direct a course. The two sides of the compound eyes must function differ- 342 Journal of Comparative Neurology and Psychology. ently in one respect, since in going towards the light the anter- ior side is turned so as to face the brightest part of the field of vision while the posterior surface of the eye is kept facing the darkest part. The impulses from the two sides of the eyes do not antagonize each other. The experiments of blackening over the anterior sides of the eyes show that the sides looking away from the light, as well as those looking towards it, play a part in orientation, although they must respond, so far as seek- ing intensity of stimulus is concerned, in opposite ways. The method of trial and error plays, I think, only a sub- ordinate role in the phototaxis of Ranatra, although in some situations it undoubtedly comes into play. There is a certain amount of random movement in the behavior of this form, but deviations from the direct path to the light are usually corrected by an appropriate turn, and not by making a lot of trial move- ments and following up the successful ones. Ranatras often show periods of hesitation between two directions of turning. Specimens that perform circus movements when one eye is blackened over usually manifest a decided hesitancy when they have turned so that the normal eye looks approximately away from the light. They often stop in their course, turn this way and that, often many times, and occasionally settle down to rest, as if indespair over the situation. Sometimes they turn directly towards the blind side and go to the light; at other times they reach the light only after performing a complete circus move- ment to the left. When past the critical point their movements usually take place with little hesitation. Specimens with only the posterior half of one eye exposed often turn slightly this way and that during the first part of their course, as if attempting to get their bearing. If they deviate either to the one side or the other they frequently stop, as if they perceived something to be wrong, turn back and forth sev- eral times, and then proceed nearly straight towards the light. In nearly all specimens thus treated one can detect a tendency to veer over towards the normal side, but there are equally ob- vious efforts to check deviations that are made from the direct path. There is an uneasiness which appears much like impa- _Hormes, The Reactions of Ranatra to Light. 343 tience when a Ranatra that shows a strong positive reaction has _ deviated considerably from a straight path towards the light. When the normal eye looks away from the light the specimen may sway from side to side, back off, then go ahead again, growing continually more excited until finally it takes to flight. If the wings are fastened down to prevent their being used, the insect frequently spends several minutes before getting out of its dilemma. Sooner or later a fortunate movement is made which brings the creature into a situation such that the tendency to turn to a particular side meets with little opposition. Out of many trials made in this state of perplexity a successful one is finally made and followed up. Individuals vary greatly in their conduct in such a situation. Many correct their course before getting far out of orientation ; others, when they get out of line, turn back again with comparative readiness. We might explain the function of the posterior side of the eye in orientation on the supposition that a movement which brightens the visual field brings about a reflex that causes a turn in the opposite direction. In this way deviations from the po- sition that kept the darkest part of the field of vision in focus would be checked and the insect would, therefore, travel towards the light. It is more difficult, however, to explain the orienta- tion of an insect in which a small area of the lateral surface of one eye is the only part exposed. If the insect moved so that the eye would look toward the darkest part of the visual field it would place its body with the blind side towards the light. If, on the other hand, it moved so that the eye would receive the maximum amount of stimulus, the opposite side would be brought toward the light. It is obvious that the insect moves so that the eye receives neither the maximum nor the minimum amount of stimulus, but is kept exposed to light of an interme- diate degree of intensity, The degree of intensity varies, more- over, in every step of its course, so that there is no justification for explaining the orientation of the insect through the effort to keep a certain intensity of light constantly before the eye. It is remarkable that Ranatras so treated frequently go towards the light in nearly a straight line. Moreover, if the light is moved 344 Journal of Comparative Neurology and Psychology. during their progress they change their direction of locomotion so as to continue going towards it. Ifthe light is not carried too far to one side the insect may be made to follow it around in either direction. In the specimens employed care was taken that every other part of the eyes was thickly covered except a small portion of the surface of one side, so there is no doubt that the movements of the insect were directed only by light entering at this point. The side of the eye in this case doubt- less functions as it does in a normal individual, but it is difficult to explain satisfactorily the orientation of the specimen either through direct reflexes, or by the method of trial and error. Were the insect so constituted as to respond to an increase of light entering the left eye bya turn to the left and to a decrease of light by a turn to the right, we can understand how, when once pointed towards the light, a straight course might be pre- served. If the insect turned towards the right there would be an increase of light entering the left eye which we might sup- pose stimulates the insect to turn in the opposite direcrion. Deviations to the left would cause a diminution of light entering the left eye, which we might suppose acts as a stimulus to turn to the right side. The right eye may be supposed to act, m- tatis mutandis, in a similar manner. The numerous cases of re- action to shadows (Scattenempfindlichkert) which are found among several groups of animals show that diminution in the intensity of light may act as a stimulus as well as an increase in intensity. If it be the variations in the intensity of light which afford the stimuli for turning in the one or the other direction, we can attribute to all parts of the eye essentially the same function. If the posterior side of the left eye is all that is ex- posed and a Ranatra that is facing the light turns to the right side the exposed part of the eye receives an increased stimulus which we may suppose brings about a turn to the left. A turn to the left of the median position, up to a certain point, would probably (owing to the body intercepting a part of the rays) diminish the light entering the posterior side of the eye, thus causing a turn to the right, In this way the creature might be supposed to maintain a straight course towards the light. A Homes, The Reactions of Ranatra to Light. 345 similar explanation might be applied to the orientation of a Ranatra with only the anterior half, or in fact any other part of the eye exposed. The difficulty with this explanation is that an insect that started with an oblique orientation to the direc- tion of the rays would tend to continue in that position, since a departure from it towards either side would be followed by a compensatory movement. If, however, light produces a con- stant effect upon the muscular tonus of the body, irrespective of affording stimulation by variations in intensity arising from turning towards different sides, we can better explain the fact of orientation. Take the case of a Ranatra with only the lateral surface of one eye exposed. Light entering the eye tends to increase the action of the flexors on the same side, and that of the extensors on the opposite side of the body. Through this action alone the insect, so far as light directs its movements, would continue to go around in a circle indefinitely. But as a matter of fact, as its circus movements bring the eye away from the light, they become checked and are followed by a turn in the opposite direction. What is the stimulus to this turn? Ob- viously there is a diminution of light received by the eye as it turns away, and we may regard this diminution as a stimulus to a movement in the opposite direction. This stimulus may be conceived, then, to overcome the tendency to the perform- ance of circus movements, and thereby bring about an approxi- mate re-orientation of the creature to the direction of the rays. That there is a conflict of impulses as the insect turns away from the light towards the side with the functional eye is evinced by the hesitancy, the swaying this way and that which often occurs when the creature has reached a position such that the amount of light received by the eye is materially diminished. The effect of light upon the tonus of the muscles of which the behavior of Ranatra gives so much evidence, fails to account for the fact of compensation in the movements of the insect. The responses to variations in the intensity of light, on the other hand, do not adequately account for the preservation of efforts to attain a parallel orientation to the direction of the rays. Each of these factors may, however, supplement the other in such a way as to 346 Journal of Comparative Neurology and Psychology. cooperate in the maintenance of a direct course towards the light. But even if we invoke the aid of both the factors mentioned, we are not able completely to bring the phototaxis of Ranatra under the category of direct, mechanical reflexes. Consider the behavior of the Ranatra with its right eye blackened over, placed at right angles to the rays with the normal eye looking away from the light. The effect of light upon the muscular tonus of the creature would tend to make it turn towards the left side. But either at first, or after a few trials, the insect turns directly to the right and goes to the light. This is done with greater readiness after several trials are made ; soon the in- sect turns immediately after being set free. In these experi- ments the specimens were turned about, first one way and then the other, before being set down on the table, but this made no difference in the directness with which they turned towards the light. In many cases the insects would struggle to turn towards the blind side to get to the light before they were liberated from my hand. So far as could be observed, there was no prelimi- nary feeling about, no employment of the method of trial and error; the insect seemed to retain awareness of the position of the light, since it immediately made for it by the shortest route as soon as it was liberated. The non-mechanical character of the response is further evinced by the fact that habits of turn- ing towards a certain side may be persisted in in situations in which turning would otherwise take place in the opposite direc- tion. The fact that Ranatras and Notonectas which have one eye blackened over come, after several trials, to dispense with circus movements towards the normal side and correct devia- tions from their course by a direct turn in the right direction affords further evidence for the same conclusion. We have seen that Ranatras which at first will turn only a slight way towards the blinded side when the light is carried over in that direction will make sharper turns after they have become accustomed to following the light around towards that side. These features of the phototaxis of Ranatra indicate that seeking the light has an attractiveness or interest much like that which catching prey has Houmes, Zhe Reactions of Ranatra to Light. 347 for a higher animal. The phototactic movements of the crea- ture are not merely stereotyped reflexes which the insect is in- voluntarily forced to perform. To get to the light is an end which is arrived at if not by: one method, then by another. The phototaxis of Ranatra comes, toa considerable degree, I believe, under the pleasure-pain type of response. Why a creature should be so constituted as to derive satisfaction from so stupid a performance as wildly chasing after a strong light is a subject that need not concern us in our present quest. The behavior of Ranatra presents the essential features of the pleas- ure-pain reaction of higher forms, and we are justified, I believe, in classing it under this heading. The fact that Ranatra will continue to follow the light even when it is brought thereby into a situation that produces a fatal effect does not necessarily ex- clude its conduct from this category. While it is true that ani- mals tend to continue reacting towards stimuli that produce a beneficial effect and away from stimuli that bring about delete- rious results, the rule is by no means absolute. Ina state of nature Ranatras probably are rarely, if ever, exposed to condi- tions that produce as strong positive phototaxis as they show under artificial conditions in the laboratory ; and there seems to be no benefit that possibly can be derived from their strong propensity to seek the light. This propensity, like that of hu- man beings for certain stimulants and narcotics, has probably not been evolved by natural selection for any useful purpose, but is an incidental result of the way the creature is constituted. Whether there is any connection between pleasure-giving acts which tend to be repeated and acts which secure some benefit to the organism closer than that which would naturally be established through selection may well be doubted. Neither an animal’s direct reflexes nor its attempts to seek some source of gratification infallibly lead to securing some benefit; and the fact that a certain kind of behavior is persisted in until it brings about fatal effect does not zfso facto enable us to decide under which of these categories it falls. It is the apparent telecity in the efforts of Ranatra to reach the light which it is difficult to understand according to a purely 348 Journal of Comparative Neurology and Psychology. reflex theory of phototaxis. This is a feature of the creature’s behavior which, I am inclined to believe, we shall not be able to understand until we can explain the physiology of the pro- cess whereby certain stimuli when-they have been received one or more times are sought either directly, or indirectly, by a more or less round-about method, while other stimuli when they are experienced one or more times come to be avoided. Did light afford a stimulus of an unpleasant nature, it is probable that the positive phototaxis of Ranatra would soon be inhibited. If the phototaxis of Rantra falls to a certain extent under the category of reflex action, as much in its behavior indicates, the reflexes concerned are in line with a strong instinctive interest of the animal in seeking the light. This interest may lead to successful attempts to get to the light in situations in which purely reflex responses alone would fail. It acts as a sort of reg- ulatory agent in the conduct of the insect, bringing its actions to a successful issue, which could not be attained by a purely machine-like mode of response. It is through instinctive interests in certain things rather than by simple or even complex reflex acts that the conduct of higher animals is mainly guided. The play activities of higher animals, for instance, are performed, not because they are reflex responses to particular things in the environment, but because the animal is so constituted that it derives satisfaction from their performance. An animal interest may be chained, by virtue of its organization, to certain ends, such as the capture of a certain kind of prey, or the construction of a particular kind of habita- tion; but at the same time its conduct may show considerable plasticity as regards the methods by which these ends are at- tained. In instinctive behavior, as in the morphogenic pro- cesses which lead to the establishment and maintenance of the normal form of the body there is an apparent effort to reach a certain end result, despite obstacles and unusual conditions. The explanation of this peculiarity of animal behavior is a prob- lem of fundamental interest. If we attempt to resolve highly complex modes of behavior into simple direct reflexes, we soon find ourselves at the end of our tether. Even in so apparently Houimes, The Reactions of Ranatra to Light. 349 mechanical procedure as the phototaxis of Ranatra we encoun- ter peculiarities which indicate that we have not struck bottom in our analysis of the phenomenon. In many ways the phototaxis of the Ranatra seems to be intermediate between purely reflex conduct on the one hand and conduct of the pleasure-pain type on the other. These two kinds of behavior seem to be harmoniously combined in many instincts, if not in most of the more highly involved modes of instinctive action. Just what the steps are which lead from the one to the other we do not know. We are still in want of a satisfactory explanation of the pleasure-pain type of response. When we are able to supply one we shall be in a position to give a more adequate interpretation of the phototaxis of higher forms than can be supplied at the present time. LITERARY NOFCES: Verhandlungen der Anatomischen Gesellschaft auf der Achtzehnten Versammlung in Jena. Anat. Anz. LErganzungsheft zum 25 B. 19O4. Schultze, O. Ueber die Entwickelung des peripheren Nervensysteme. 2-7. The growing nerves in the embryo are syncytial in structure. The sheath nuclei are derived from the nuclei of this nervous syncytium. The plexus nervosus profundus of amphibian larvae (CZERMAK) is a sensory syncytium which is, and has arisen, 7” continuo with the de- veloping nerve, and is not derived by a fusion of independent units. SCHULTZE’s interpretation is in opposition to the neurone theory. Koelliker, A. Ueber die Entwickelung der Nervenfasern. 7-12. This paper is directly opposed to ScHULTze’s and in favor of the neurone theory. Each axone grows out as a process of a single nerve cell and the sheath nuclei are mesodermal in origin. This mode of development, the author asserts, is followed in Vertebrata, Arthropoda and Mollusca. The process may be simpler in lower forms. In the discussion which follows these two papers, FRORIEP argues for the ectodermal origin of the sheath nuclei by a migration from the central system along the nerve roots. Rerzius, Benpa, BALLowITz, Harrison and DIsse cite various instances and observations in favor of the neurone theory. The necessity of experimental work upon the regeneration of the peripheral end of the severed nerve fiber is empha- sized by Roux and BARFURTH. Joseph, H. Ueber eigentiimliche Zellstrukturen im Zentralnervensystem von Amphioxus. 16-26. The cells in question are the large cells in the anterior region of the nerve cord which v. KupFFER called ‘‘dorsale Ganglienplatte.” The author finds similar cells in the corresponding position in the caudal region of the cord. All of these dorsal cells, contrary to other authors who differ among themselves, are unipolar, and, in structure, correspond exactly with the ‘‘Sehzelle” of Hesse. They are not, how- ever, capped with the pigment cell which is characteristic of the typi- cal ‘‘Sehzelle.” Their axones pass towards the periphery of the cord and probably enter the posterior roots. In the caudal region of the cord ‘‘Sehzelle” occur without the pigment cap, in which case they are identical in structure with the dorsal plate cells of the same region. Literary Notices. ast Hochstetter. Ueber die Nichtexistenz der sogenannten Bogenfurchen an den Gehirnen lebensfrisch konservierter menschlicher Embryonen. 27-34. Schaper, A. Zur Frage der Existenzberechtigung der Bogenfurchen am Gehirne menschlicher Embryonen. 35-37. 30th of these papers on the embryonic fissures agree with the re- cent work of Rerzrus, Matt and Go.upsTEIN, who find no true fissures in the well preserved human brain during the period to which His assigned his ‘‘Bogenfurche.” Ramstroém. Ueber die Innervation des Peritonaeums der vorderen Bauchwand. This study was made upon zv/ra vifam methylene blue impregna- tions of the peritoneum and associated tissues. In the mouse, the perito- neum on one side the median line was mounted entire. No fibers from the phrenic were found entering this region. The innervation is wholly from the intercostal nerves, through a complicated system of plexuses. Lubosch, W. Uber den Bau und die Entwickelung des Geruchsorganes von Petromyzon. 67-75. This paper bears upon BLAue’s theory of the origin of the olfactory epithelium by a process of fusion of primitive cutaneous sense organs. ‘The author conceives the olfactory buds of Petromyzon as represent- ing a protracted ontogenetic process. The fundament of the olfactory organ is in the form of a bud-like differentiation of the integument. The organ develops by a repetition of this process. LuBoscH considers that BLAUE’s theory may be tenable upon the hypothesis that in the olfactory organ the nerve cell has maintained the primitive position, which it originally held in both olfactory and taste organs. Perfectly closed follicles are found in the nasal cavity of ten-centimeter larvae. ene Der Rutter, Cloudsiey. Natural History of the Quinnat Salmon. Auwl/. U. S. fish Commission for 1902, 65-142. 9 Pls., 13 Figs. 1904. The objects of this investigation were to determine when young salmon should be liberated from the hatcheries, to discover a method for removing and fertilizing the eggs left in the fish after artificial spawning, and to fix the site for a new hatchery. Other matters of interest discussed are the activity of spermatozoa after the milt is mixed with water, the fertilization of the ova, care in handling embryos, alevins and their enemies, the fry and their food, parasites, and migra- tions, the food of young salmon and their period of growth. ‘The adult salmon are treated in relation to migrations, changes after entering fresh water, sexual differentation, natural propogation, injuries and diseases, and death which ensues after once spawning. This contribution is of considerable scientific importance as well as being of practical value. I) Ad) FIELD: 352 Journal of Comparative Neurology and Psychology. Kerr, J. Graham, On Some Points in the Early Development of Motor Trunks and Myotomes in Lepidosiren paradoxa (FITz.). Zzvans. Roy Soc. Edinburgh, 41, Part sr (No. 7), pp. 119-128, 6 plates, 1904. The author’s observations support the conclusion that the motor spinal nerves of Lepidosiren first appear as strands of soft granular protoplasm, extending between the spinal cord and the myotome. These strands are not cellular. They later become fibrillated and in- vested by mesenchymatous sheaths. Ciale/Eis Coggi, Alessandro. Le ampolle di Lorenzini nei Gymnofioni. Jonztore Zoologico Italiano, 15, No. 249-56. On the basis of the figures and descriptions of the SARASINS, the author compares the ‘‘Vebenohren,” or accessory lateral line organs on the head of Ichthyophis with the ampullae of LORENzINI of elasmo- branchs, concluding that the organs are strictly homologous, thus strengthening the current belief in the archaic character of the Gymno- phiona. It will be recalled that the reviewer has suggested (this /owrnad/, vol. 13, p. 135) a similar homology between the ampullae of LOREN- ZINI and a type of ‘‘small pit organs” found in the skin of the North American siluroid fishes, though the evidence for this relationship is not regarded as conclusive GJ, He Freidenfelt. T. Ueber den feineren Bau des Visceralganglions von Anodonta. Lunds Universitets Arsskrift, Bd, 40, Afd. 2. Nr. 5. Lund, 1905. A detailed description of the neurones of the visceral ganglion and their connections, after methylene blue preparations, illustrated by four good plates. The author finds no true net-work (protoplasmic continuity of the older authors) in the neuropil, but refrains from ex- pressing an opinion on the question of continuity of the neuro-fibrils of ApAruy and BETHE. (oa ae = Tumors of the Cerebellum. Under the above title, the A. R. Elliott publishing Co., of New York, has re-printed six papers by Drs. MILts, FRAZIER, DE SCHWEIN- Itz, WEISENBURG and LopHoiz. While the clinical and surgical detai!s do not fall within our limits, we call attention to the cases reported and to the summaries of literature as important contributions to the theory of cerebellar functions. CN H: Banchi, Arturo. Di un cervello senze commessure e con funzioni apparente- mente normali. Archivio di Fisiologia. Vol. 1, pp. 614-618, 1904. A brief statement of a remarkable case of cerebral malformation where the mental life seemed perfectly normal. An extended account of the case will shortly appear in the Archivio Italiano di Anatomia e di Embriologia j