The Origin and Development of the Nervous System

From this point of view the nervous system repre- sents physiologically the development and complication of these fundamental excitatory features of organismic pattern and their transmissive effects in those proto- plasms so constituted that such development is possible. Anatomically, the nervous system is the record in those protoplasms capable of developing and maintaining such a record, of the effects of the excitatory and transmissive processes upon the protoplasm. No other viewpoint yet attained affords any basis for the interpretation in physiological terms of the origin and development of the nervous system. If we maintain that organismic pattern is not fundamentally a relation of excitation and transmission, the appearance of the nervous system in development as the first definitive organ and its func- tion as the chief organ of integration and relation in the organism must remain scientifically completely insoluble problems. Such a conception of the organism, carried to its logical conclusion, practically forces us to regard the nervous system as functionally and structurally something new appearing in the organism at a certain stage and without any pre-existing physiological basis. In other words, from this viewpoint the nervous system appears essentially as a special creation superimposed upon the organism and falls into the same category with Driesch's entelechy and with certain theological concep- tions of the soul.

Such metaphysical difficulties are, however, avoided when we regard the nervous system as representing, on the one hand, the result and product of the primary excitation- transmission relations of organismic pattern, and, on the other, the further development of these relations. This conception gives us physiological con- tinuity from the beginning of the organism to the highest stages of nervous development attained in the individual, or, stated in still broader terms, from the simple physiological gradient to the ego. The domi- nance of the nervous system and its integrating function

in its various stages of development, up to the cerebral cortex of man, is in these terms a physiological conse- quence of the establishment of the physiological gradient or gradients in the cell or cell mass from which the indi- vidual develops. The distinction between pattern and material, between the physiological gradient and the hereditary constitution of the protoplasm in which it arises, has been pointed out repeatedly and may be emphasized once more. The course of events in relation to a gra- dient, for example, the particular kind of nervous sys- tem which develops in a particular organism is primarily a matter of hereditary constitution, but the gradients determine how the potentialities of the protoplasm as regards nervous development shall be realized.

This conception of organismic pattern and of the relation of nervous pattern to it is fundamentally a physiological conception and requires no assumptions nor special hypotheses concerning heredity and evo- lution, except in so far as it involves rejection of the more extreme preformistic types of theory. It does not, however, in any sense represent the extreme epi- genetic viewpoint. Moreover, it does not, as some of its critics have asserted, involve acceptance of Lamarck- ian doctrine, though it is possible of course to develop a Lamarckian conception of inheritance of organismic pattern from the conception of the physiological gradient. The gradient is primarily nothing more than an ordering and integrating factor in developmental physiology.

Objection may be, in fact has been, made to the use of the conception of the physiological gradient as the foundation of a theory of organismic and nervous pattern and integration on the grounds that, while various lines of evidence indicate the existence of these gradients, we do not yet know what they really are. As a matter of fact, we do not know what anything in the organism really is; we merely know more or less about it. Up to the present we have learned many things about the physiological gradients and many more remain to be learned. We can state, however, on grounds much more adequate than those on which many other scien- tific conclusions rest, that these gradients are primarily quantitative in character, that while they may persist through reproduction, i.e., be inherited, they arise pri- marily in relation to a quantitative differential in the action of an external factor on protoplasm, that they show all the characteristics of excitation-transmission gradients, and, finally, that they are of fundamental significance in the development and physiological inte- gration of the organism. The evidence for the existence of the physiological gradients and for their significance is based largely on experimental data and is therefore more definite and conclusive than much of the evidence on which various other current biological theories have been built up.

While experimental data concerning many features of nervous development are lacking, the main facts of its relation to the gradients are clear. As regards many points only suggestion, inference, or a weighing of proba- bilities is at present possible, but it has seemed desirable in the preceding chapters to follow through the line of thought developing from the experimental foundation and therefore to advance suggestions, to consider prob- abilities, and to draw tentative conclusions in many

cases. Such procedure is of value in two ways: first, it indicates to what extent the theory or working hypothesis may serve; and, second, the consideration of the various questions from a particular viewpoint may provide a basis for further investigation, which will confirm the suggestions or show them to be incorrect. Questions of detail aside, the general conception on which the book is based involves three main theses, which are, I believe, of fundamental importance for biological theory. These theses are: first, that devel- opment is a physiologically continuous process; second, that the problem of organismic pattern conceived in any other terms than those of relation to the external world becomes essentially a metaphysical rather than a scientific problem and it is necessary to postulate an entelechy, a soul, or some other metaphysical ordering and integrating factor; third, that in the excitatory relation between protoplasm and the external world and the effects of such excitation on protoplasm we have an adequate physiological basis for organismic pattern and for the physiological continuity of develop- ment. If the book contributes toward the establishment of these three theses as statements of fundamental bio- logical fact, it will have attained its chief purpose.

1919. "Quantitative Studies on the Rate of Respiratory Metabolism in Planaria, I, Amer. Jour. Physiol., 1914. "Functional Variations in Contractions of Different Parts of the Small Intestine," Amer. Jour. Physiol., 19150. "The Motor Functions of the Intestine from a New Point of View," Jour. Amer. Med. Assoc., LXV. 19160. "IV. Differences in Rhythmicity and Tone in Dif- ferent Parts of the Wall of the Stomach," Amer. Jour. Physiol., XL. 19166. "V. Differences in Irritability and Latent Period in Different Parts of the Wall of the Stomach," Amer. Jour. Physiol., XLI.

19170. "VI. Differences in Latent Period and Form of the Contraction Curve in Muscle Strips from Different Parts of the Frog's Stomach," Amer. Jour. Physiol., 19176. "VII. Differences in Latent Period and Form of Contraction Curve in Muscle Strips from Different Parts of the Mammalian Stomach," Amer. Jour. Physiol., XLII. 19180. "X. Differences in Behavior of Segments from Dif- ferent Parts of the Intestine," Amer. Jour. Physiol., 19186. "XII. The Influence of Drugs on Intestinal Rhyth- micity," Amer. Jour. Physiol., XL VI.

I9i8c. "XVI. Differences in the Action of Drugs on Differ- ent Parts of the Bowel," Jour. Pharm. and Exp. Ther., XII. igiSa. "XL The Metabolic Gradient Underlying Intes- tinal Peristalsis," Amer. Jour. Physiol., XL VI. I9i8c. "XVII. The Metabolic Gradient Underlying Colonic Peristalsis," Amer. Jour. Physiol., XLVII. 19170. "The Effect of Temperature on the Rhythm of Ex- cised Segments from Different Parts of the Intes- tine," Amer. Jour. Physiol., XLIV.

19176. "Changes in Rhythmicity, Irritability and Tone in the Purged Intestine," Jour. Pharm. and Exp. Ther., X. 1918. Principles of General Physiology. Second edition. London. 1919. " Differential Susceptibility as a Basis for Modification and Control of Early Development in the Frog," Biol. Bull., XXXVII. 1907. Comparative Electro-Physiology. London. 1913. Researches on Irritability. London. anderter Furchung," Festschr. zum sechzigsten Geburts- tage R. Hertwigs, III.

1916. "Versuche an ausgeschnittenen und reimplantier- ten Flimmerschleimhautstiicken," Arch. f. d. ges. Anat. Anz., V. 1909. Histologie du systeme nerveux de Vhomme et des ver- Planaria," Arch.f. Entwickelungsmech.,XIXX,II Teil. 19106. "Further Experiments on Adventitious Reproduction and Polarity in Harenactis," Biol. Bull., XX. 19110. "Experimental Control of Morphogenesis in the Regulation of Planaria" Biol. Bull., XX. 19116. "Studies on the Dynamics of Morphogenesis and

Planaria dcrotocephala" Arch. f. Entwickelungs- mech., XXXVIII. igi6d. "Experimental Control and Modification of Larval Development in the Sea Urchin in Relation to the Axial Gradients," Jour. Morphol., XXVIII. 19160. "Further Observations on Susceptibility Gradients in Algae," Biol. Bull., XXXI. 19170. "Susceptibility Gradients in the Hairs of Certain Marine Algae," Bwl. Bull., XXXII. 19176. "Experimental Alteration of the Axial Gradient in the Alga, Griffithsia borneliana," Biol. Bull., XXXII.

19176. "The Gradient in Susceptibility to Cyanides in the Meridional Conducting Path of the Ctenophore, Mnemiopsis," Amer. Jour. Phsyiol., XLI. 191 7#\ "Differential Susceptibility and Differential Inhibi- tion in the Development of Polychaete Annelids," Jour. Morphol., XXX. Bull., XXXIV. 19190. "Demonstration of the Axial Gradients by Means of Potassium Permanganate," Biol. Bull., XXXVI. 19196. "The Axial Gradients in Hydrozoa, II," Biol. Bull.,

I9I9C. "The Effect of Cyanides on Carbon Dioxide Pro- duction and on Susceptibility to Lack of Oxygen in Planaria,'' Amer. Jour. PhysioL, XLIX. 1919^. "A Study of Susceptibility in Some Puget Sound Algae," Pub. Puget Sound Biol. Sta., II. 1920. "Studies on the Dynamics of Morphogenesis and Bryophyllum and Other Plants," Science, L. CHILD, C. M., and HYMAN, L. H. 1911. "The Central Nervous System in Teratophthalmic and Teratomorphic Forms of Planaria doroto- cephala," Biol. Bull., XXII.

1878. "Studien iiber Polypen und Quallen der Adria," Denkschr. d. Akad. d. Wiss. Wien., XXXVIII. 1909. "The Reaction to Tactile Stimuli and the Develop- ment of the Swimming Movement in Embryos of Diemyctylus lorosus Eschscholts," Bull, of Denison Univ., XIV. the Growth of the Nervous System of Amphibia, I," Jour. Comp. Neurol., XXIV. 1901. "Uber die Wirkung engbegrenzter Nervencompres- sion," Arch.f. d. ges. Physiol., LXXXIII. 1911. "Ein Beitrag zur Kenntniss des Ablaufes des Erre- gungsvorgangs im marklosen Warmbluternerven," Zeitschr. f. Biol., LVI.

1898. "The Regeneration of the Nervous System of Planaria torva and the Anatomy of Double-Headed Forms," Jour. Morphol., XIV. 1909. "The Influence of the Nervous System in Regenera- tion," Jour. Exp. Zool., VII. 1882. "Zur Physiologic des Flimmerepithels," Physiol. Studien. Leipzig. Protoplasmic Movement," Jour. Exp. Zool., IX. 1918. "Experiments on the Development of the Fore Limb of Amblystoma, a Self-differentiating Equipotential System," Jour. Exp. Zool., XXV.

1905. "The Central Gustatory Paths in the Brains of Bony Fishes," Jour. Comp. N enrol., XV. the Cerebral Cortex, "Jour. Animal Beh., May-June. 1918. An Introduction to Neurology. Second edition. Philadelphia. 1915. "The Development of Reflex Mechanisms in Ambly- stoma," Jour. Comp. Neurol., XXV. 1912. "Absence of Temperature Changes During the Transmission of a Nervous Impulse," Jour. PhysioL, 1900. "Developmental History of the Primary Segments of the Vertebrate Head," Zool. Jahrbiicher, Abt. f. Anat. und OnL, XIV. His, W.

1889. "Die Neuroblasten und deren Entstehung im embry- onalen Mark," Arch. f. Anat. u. Entwicklungsges., Jahrgang 1889. to the Mechanism of Amoeboid Movement," Jour. Exp. Zool., XXIV. 1917. "Further Contributions on Neurobiotaxis. IX. An Attempt to Compare the Phenomena of Neuro- biotaxis with Other Phenomena of Taxis and Tropism. The Dynamic Polarization of the Neu- ron," Jour. Comp. Neurol., XVII. 1910. "A Histological Study of Regeneration in Short Head Pieces of Planaria simplicissima," Arch. f. Ent- wickelungsmech., XXXI.

1904. "Uber Entstehung und Ausbreitung der Plasma- stromung in Folge von Wundreiz," Jahrbilcher f. wiss. Bot., XXXIX. 1901. "Notes on Regeneration and Regulation in Planarians, II," Amer. Jour. Physiol., VI. 19090. "On the Connection between Stimulation and Changes in the Permeability of the Plasma Mem- brane of the Irritable Element," Science, XXX. 19096. "On the Connection between Changes of Permea- bility and Stimulation and on the Significance of Changes in Permeability to Carbon Dioxide," Amer. Jour. Physiol., XXIV.

1909^. "The General Biological Significance of Changes in the Permeability of the Surface Layer of the Plasma Membrane of Living Cells," Biol. Bull., XVII. 1911. 'The Relation of Stimulation and Conduction in Irritable Tissues to Changes in the Permeability of the Limiting Membranes," Amer. Jour. Physiol., tion in Irritable Tissues and Especially in Nerve," Amer. Jour. Physiol., XXXIV. igi6a. "The Theory of Anesthesia," Biol. Bull., XXX. 19166. "The Conditions of Physiological Conduction in

Growths by Means of Electrolytic Local Action in Metals and the Physiological Significance and Con- trol of that Type of Action," Biol. Bull., XXXIII. Model of the Protoplasmic or Nervous Type of Transmission," Science, XL VIII. 1892. Untersuchungen zur physiologischen Morphologic der Tiere. II. Wiirzburg. 1917. " Some Factors Influencing the Respiration of Ground Nervous Tissue," Jour. Biol. Chem., XXXII. Carnegie Inst. Publ. No. 102. 1916. "Nerve Conduction and Other Reactions in Cas-

1906. Physiology of the Nervous System. English trans- lation. Chicago. 1901. "Factors That Determine Regeneration in Anten- nularia" Biol. Bull., II. 1904. "An Examination of the Problem of Physiological 'Polarity' and Electrical Polarity in the Earth- worm," Jour. Exp. Zoo'l., I. 1909. "The Origin of the Nervous System and Its Appro- priation of Effectors," Pop. Sci. Mo., 1909. 19100. "The Reactions of Sponges with a Consideration of Zool., VIII. 19106. "The Phylogenetic Origin of the Nervous System,"

Anat. Rec., IV. 1911. "The Origin and Significance of the Primitive Nervous System," Proc. Amer. Phil. Soc., L. 1914. "The Origin and Evolution of the Nervous System," igiyd. "Actinian Behavior," Jour. Exp. Zool., XXII. igi'je. "The Sources of Nervous Activity," Science, XLV. 191 7/. "The Activities of Corymorpha," Jour. Exp. Zool., 1916. "The Structure of Metridium (Actinoloba) marginatus Milne-Edwards with Special Reference to Its Neuro- 1909. "The Differentiation and Specificity of Correspond- ing Proteins and Other Vital Substances in Relation to Biological Classification and Organic Evolution. The Crystallography of Hemoglobins," Carnegie Inst. Publ. No. 116.

1905. "Aus dem Liickengebiet zwischen organismischer und anorganismischer Materie," Ergebn. d. Anat. u. 1919. "Action of Salts upon the Metabolism of Nerve," Jour. Biol. Chem., XXXIX. 1909. "Halocynthia Johnsoni n. sp. A Comprehensive Inquiry As to the Extent of Law and Order That Prevails in a Single Animal Species," Univ. Cat. Publ., ZooL, VI. 191 1. "The Growth and Differentiation of the Chain of Cyclosalpa affinis Charnisso," Jour. MorphoL, XXII. ROBBINS, H. S., and CHILD, C. M.

1920. "Carbon Dioxide Production in Relation to Regen- eration in Planaria dorotocephala" Biol. Bull., 1904. "t)ber den Zusammenhang von Muskel und Nerv bei den Siphonophoren," Mitt, naturwiss. Ges. Win- ter thur, Jahrgang 1903-4. on the Differentiation of the Neuroblasts," Jour. Exp. ZooL, VII. 1885. "t)ber den Einfluss der Beleuchtungsrichtung auf die Teilung der Equisetumsporen," Berichte deutsch. lot. Ges:, III. 1902. "Regeneration in Antennularia ramosa" Arch. j. Entwickelungsmech., XV.

1907. "The Artificial Production of a Single Median Cyclopian Eye in the Fish Embryo by Means of Sea Water Solutions of Magnesium Chloride," Arch. f. Entwickelungsmech.j XXIII. malities and An Analysis of the Development of the Primary Parts of the Eye," Arch. /. vergl. Ophthalmol., I. 1914. "The Metabolic Gradient in the Nerve Fiber," Proc. Amer. Physiol. Soc., Amer. Jour. Physiol., XXXIII. 19150. "The Metabolism of Resting Nerve and Its Correla- tion with the Direction and Rate of Nerve Impulse," Proc. Amer. Physiol. Soc., Amer. Jour. Physiol.,

1917. "The Effect of Temperature on the Excised Seg- ments of Different Parts of the Intestine," Amer. Jour. Physiol., XLIV. erungen und Vervielfachungen des Medullarrohres (Polymyelie) bei Hiihnerembryonen," Arch. f. Entwickelungsmech . , XXXVIII . 1907. "On Some Phenomena of Coalescence and Regenera- tion in Sponges," Jour. Exp. ZooL, V. 1911. "Development of Sponges from Dissociated Tissue Cells," Bull. Bur. Fish., XXX. bei Bryopsis," Jahrb.f. wiss. Bot., XXXV. i9oo&. " Uber den Einfluss ausserer Faktoren auf die Teilung

NOTE — References give the number of the page on which the matter referred to begins. Acclimation: in relation to physio- logical condition, 31; differen-" tial, 36 Adjuster: as part of reflex arc, 233; adaptive function of, 237; localization of, 249. See also Arcs, reflex Amphibia: physiological gradients in, 33 ; circulation in ovarian egg of, 56; susceptibility in early development of, 135 Annelids: susceptibility in, 34; electrical gradient in, 45 ; origin of segments in, 132; centraliza- tion in, 146; physiological domi- nance in, 249. See also Segmen- tation

Arcs, excitation : definition of , 236; different degrees of develop- ment of, in same individual, 242; functional axiation in, 242, 245; structural axiation in, 247. See also Excitation; Transmis- sion higher animals, 251; in amphib- ian development, 252; spinal paths of, in higher vertebrates, 259. See also Arcs, excitation; Gradients, excitation. Centralization, nervous; defini- tion of, 142; in relation to or- ganismic pattern, 144; charac- teristic of all nervous systems, 144; evolutionary changes in,