CORNELL UNIVERSITY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN I89I BY HENRY WILLIAMS SAGE Hing Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924024754487 THE EVOLUTION OF CONTINUITY IN THE NATURAL WORLD THE EVOLUTION of CONTINUITY in the NATURAL WORLD By DAVID RUSSELL, M.D. DIRECTOR OF THE BRITISH HOSPITAL, 4ND DOCTOR TO THE BRITISH LEGATION, LISBON LONDON : GEORGE ALLEN & UNWIN LTD. RUSKIN HOUSE, 40 MUSEUM STREET, W.C.1 yd 0 First published in 1922 (All rights reserved) PREFACE THis book is a modest attempt to show that there is one Evolutionary Principle ruling in all Nature; that, true to this principle, all Matter has, as it were, evolved into being, and the many fundamental species of dead and living Matter have been differentiated. Also, that the outstanding phenomena of living Growth and Reproduction reflect the action of the Common Factor behind all Evolution. The greater part of the book is, however, concerned with the evolution of living Species, and the development of the theory that this is based on our fundamental evolu- tionary principle, the Evolution of Continuity. It is curious that though the general principle of Natural Evolution is on an unshakeable basis, the bed- rock of the process has never been clearly displayed. Perhaps one explanation of this may be that all workers have been under the influence of the aphorism, ‘‘ Natura non facit saltum.” Thus, attention has been specially given to resemblances between nearly related types and, following Darwin’s lead, to the variation resulting from artificial selection ; it being taken for granted that if we could see all the past evolutionary road, this would be revealed as a continuous chain each of whose links was a step onwards in a more or less gradual transformation. The specially large gaps in the road are attributed to lost evidence, to an imperfect geological record, and their mystery has been accepted as impenetrable in the continued absence of new fossil discoveries. 5 6 THE EVOLUTION OF CONTINUITY While, no doubt, a more perfect geological record would provide us with wonderful information, yet it is suggested that very large gaps in the road would still remain to be explained. For it is our belief that Nature does take leaps, small and large, and our purpose is to show this. Modifica- tion is in its essence always sudden. It is the fundamental architectural plan of living types with which we shall deal, and the following questions serve to indicate the direction of our theory :— How is it that in Nature we have living Individuals composed of separate, independent cells or protoplasts, alongside of other Individuals composed of long filaments or single-celled series ? How is it that there are Individuals composed of many separate little cylinders or tubes, each built up of cells united in tissue-continuity ? Or how have been produced Individuals composed of many such tubes united together ? Or what of the organism with a central tube leading to radially arranged chambers, or of the colony composed of many such organisms united in continuity ? These are fundamental questions, and they can be answered in harmony with our common principle, and, be it noted, through a study of present-day living types and not through the geological record. It is through the Individual types of present-day living Continuity that the main features of Evolution’s main road can rise before us, a true classification of living organisms be made in terms of living Continuity, and the Fundamental be distinguished from the Sub-species. D. R. CONTENTS PAGE PREFACE . ‘ . ? J 2 : é 5 ‘ , 5 INTRODUCTION ’ , : 7 : : ‘ ; ; . 19 CuHaPTer I ATTRACTION AND REPULSION. : , ; : “ . 28 The recognition of Cause more important than that of Purpose— Relation between Growth and Reproduction—Attraction and Repulsion—The universality of the two opposing forces—The antithetic basis of a character—Equilibrium and Matter—Atoms and molecules—Dissociation and decomposition—The atomic cycle of Attraction—Repulsion—Attraction—Suggested definition of Life—All Growth is cyclical. Cuapter II Tue Unit GROWTH-CYCLE . : ' F ; : : . 82 The unit growth-cycle, an act of attraction followed by one of repulsion—The basis of all growth-cycles. Cuaprer III ProtorpLasM. THE INDIVIDUAL F : . F 2 . 85 Protoplasm a mixture—“ Basoplasm ’—All Growth is evolution on main and side paths—There are species of atoms, molecules, and cells, as well_as of organic types—The ‘‘ plasmolecule ’—The amceba—The plasmolecular cycle—Definition of the ‘“ Indi- vidual *—A unicellular Individual an improbability—The multi- cellular cycle—Suggested basic propositions regarding Growth. Caarrer IV THE DisconTINUOUSLY MULTICELLULAR INDIVIDUAL . . 42 Its general features—The malarial amceba—lIts asexual and sexual cycles not true cycles—Cycle-advance with each successive sporu- lation—The complete Individual all gametes; this because of Discontinuity—The size of the Individual must have its inevitable limits—The true hemamceba cycle—The law of “2 to the Nth "— Fundamental significance of branching—Spherella—A true gamete may develop vegetatively, without conjugation. 7 8 THE EVOLUTION OF CONTINUITY CuartrER V PAGE THe FILAMENTOUS INDIVIDUAL . . ; ; ‘ ‘ . 49 Cell-continuity in its simplest form—Continuity introduces Arrest —Environment and its wide significance—Always in terms of attraction or repulsion classifiable as suitable or unsuitable— The mutual attraction of cells has had no part in the evolution of cellular continuity—A special factor necessary as a compressing agency—Living Continuity has evolved by leaps and bounds— Temporary and Permanent cell-arrest—The price of Continuity is Cell-arrest—The four all-important laws of Growth—Spirogyra —tTheory of the development of its growth-cycle—Cell-intercala- tion—Sexes of filaments—Progressive diminution—A@dogonium supports Spirogyra theory—Parthenogenesis and Alternation of Generations—Alternation of Cycle-stages. CuHaPrer VI THE Ca:nocytic INDIVIDUAL . 3 ‘ ; F { . 59 Lateral Continuity—Ccenocytic Continuity not on main road of Continuity’s evolution—Mucor as an example of Ccenocytic Individual—Comparison of mycelial hypha with cell-filament— Mucor mucedo—Mycelial alternation of generations—‘ Torula” condition in Mucor—False Tissue; a multiplication of Continuity within the Individual, and connected with reproduction—In Eurotium ; in Agaricus. CHapter VII BactTERIA 4 ‘ . . : : ; ; . j . 67 Restricted sense in which the term is here employed—A bacterium probably not a unicellular ‘* Individual ’—The bacillary filament or cosnocyte ; its possible significance. Cuapter VIII Tue DIScONTINUOUSLY ZOOIDAL INDIVIDUAL g ‘ . 70 Its general characters—Serial and Lateral Continuity—The strict definition of a ‘“‘ zooid’’—The freshwater Hydra; its description —Discontinuous gemmation—-Sexual reproduction in Hydra— Possibility of zooidal progressive diminution—Effects of mutilation in Hydra—Discontinuity produces Release from Arrest—Alterna- tion of generations—Graphie representation of Continuity’s evolution up to the Discontinuously Zooidal Individual. CHapter IX Tue ContiNuOoUSLY ZOOIDAL INDIVIDUAL ; ; F e OT Demonstrates the further intensification of Continuity—Diagram showing this—Continuity produces Arrest—Zooidal arrest— Striking examples of alternation of generations offered by this type of Individual—Hydrozoal colonies—All Hydrozoa not Continuously Zooidal Individuals ; and many Hydrozoal colonies not strictly so; reason why—Terminal compression and ‘‘ mega- zooidal ” Continuity. CONTENTS 9 CHaprrr X PAGB MeEGazooma. INpIvVIDUALS. THE MoNoMEGAZOOIDAL INDrI- VIDUALS 7 r ‘ ‘ r F : a ‘ . 82 Summary of Continuity’s evolution up to the Megazooidal Indi- vidual—The alternation of Serial with Lateral Continuity—The three classes of Megazooidal Individual—The first is the Mono- megazooidal, and of it there are two types: (1) The Sea-anemone type—General description—Its megazooid represents a multiplication of Continuously Zooidal Continuity —Reasons supporting this view—Illustration of wax model— The multiplication of Continuity must have occurred during development. . (2) The Medusoid type—Its Continuity fundamentally similar to that of the Sea-anemone type—The two different plans ex- plained—Hydrozoal colonies and the formation of the sporosac —The evolution of the sporosac-gonoblastidium—The evolution of the medusiform ‘‘ gonophore”’ ; its structure—The sea-anemone contrasted with the medusoid type of megazooid—The “ open ccelom.” The Individual Medusa. CHapterR XI Tue DiscontTinuousty MercazooripaAL INDIVIDUAL. THE CoNTINUOUSLY MEGAZOOIDAL INDIVIDUAL . é . 102 Description of the Discontinuously Megazooidal Individual— Aurelia as an example—Development of Aurelia—Interpretation of the Continuity of the ‘ strobila.” The Continuously Megazooidal Individual—Compound Corals— Megazooidal serial Continuity. CuHapTerR XII THe RapiaTE INDIVIDUAL . é . 3 : ‘ . 107 Exemplified by Echinodermata—These have not evolved on Evo- lution’s main road—The Starfish—Difficult to classify the Echino- derms in terms of living Continuity ; they, however, show distinct evidences of medusoid derivation—The closed ccelom; the excre- tory anus—Suggestions regarding the evolution of the sea-urchin and starfish—Possibility of the Echinoderms being debased Segmental Individuals of a kind. CHaPreR XIII SEGMENTAL INDIVIDUALS. ; ‘ s : . z . 112 Segmental Individuals have not been divided into segments, but ‘built up” in segments—The significance of the ‘‘ segment — Segmental organisms not necessarily Individuals—Discontinuous and Continuous Segmental Individuals ; through the latter passed the main road of Evolution. The Continuous Segmental Individual—Example, the Earthworm ; brief description—Suggested theory of the Earthworm’s evolution, and explanation of the animal's Continuity—The different forms of living Continuity have appeared as the fundamental Acquired variations behind all living Evolution, 10 THE EVOLUTION OF CONTINUITY CHaprerR XIV PAGE ControL. ARREST , . ; i ‘ : 3 . 122 Control, and the preservation of Identity and Equilibrium—Atomic, plasmolecular, and nuclear control—Control in the ascending scale of Individual Continuity—Control cannot obtain apart from Con- tinuity. Arrest—Fundamentally, Environment produces Arrest—The limits to Environment's powers—The different ways in which Arrest is manifested—Temporary and Permanent Arrest—Nature is really not prodigal; in all but lower forms of Life, she arrests more than she releases from Arrest—The evolution of the fixed cell-species—Breach of Continuity and Release from Arrest— Restoration of lost parts—The interesting case of Amphioxus. CHAPTER XV Herepiry. NATURAL AND ACQUIRED VARIATIONS 5 . 133 Theory of transmission of parental characters—Always Variation in offspring—The two chief classes of Variations; the Natural, and the Acquired. Natural Variations; three main forms—Sex possibly a matter of natural variation—Fertilisation involves Variation. Acquired Variations—The acquisition of a variation is essentially a sudden process—Environment the basic factor at work in the acquisition of variations—Every acquired variation is ‘‘ adaptive,” and useful for life in the environmental conditions which produced it—Acquisition of variation implies environmental change of some sort—All natural characters originated in acquired variation— Life began as acquired variation—The basic variations acquired by Life were the successive multiplications of Continuity. Transmission of Acquired Variaticns—Reasons for holding that it can occur and has occurred—The case of the Tortoiseshell butterfly—For a variation to be acquired the modifying force must act during development—Experimental evidence that acquired variations can reappear in the offspring—Quoted explanation not satisfactory—The earlier the application of the modifying force on the devoloping growth-cycle, the more correct ought to be the “transmission ’’ of the resulting variations—A useless variation cannot be acquired—Recapitulation. CHarrer XVI THE EvoLutTion oF CONTINUITY ‘ : . 147 We must distinguish (1) the evolution of the different types of living Continuity from (2) the evolution of different species within each Continuity-type—Present chapter deals with former question —Probability that the main road of evolution, leading to Man, has not passed through any of the organisms actually known to us, past or present—The testimony of the rocks throws little light on the Evolution of Continuity—It is to the living world of the present time that we must turn for information. The formation of the Globe; a process of Continuity-intensifi- cation—The ‘‘ Nebular Hypothesis —The alternation of Attraction and Repulsion—The appearance of the first life on the globe must have marked a stage in the evolution of Continuity—The Living evolved from the Inorganic—Primitive Life enjoyed an aqueous environment—At the present day the waters of the globe provide examples of living Continuity which clearly indicate the past main road of Evolution—This road ran in an aqueous environment right CONTENTS 11 PAGE up to a high form of Segmental Continuity—The sea has been the great storehouse from which, from time to time, the earth has received its primitive terrestrial types—How the “gaps” in the evolutionary chain can be explained—The step from one form of Continuity to a higher form must always have been sudden. At each step a certain proportion of the Continuity-type in ques- tion developed as a new type with multiplied Continuity, while the remainder bred true to type as regards Continuity, or were ‘*permanently arrested” as regards Continuity—Parallel between growth-cycle evolution and that of Continuity-types in Nature’s body—The action of Environment in producing, maintaining, and intensifying Continuity—Force of Gravity—No multiplication of Continuity has taken place on land as it has in water, but the successive terrestrial Continuity-types are all probably derivatives and representatives of ancestral fixed marine Continuity-types. CHarter XVII Tue Evo.utTion or Continuity (continued) . . . . 158 The crust of the earth; its strata, and sections—Successive Con- tinuity-types do not regularly appear as fossil remains with successive strata—In the earliest ages all the known forms of Continuity had already evolved; this is known by the fossils found in Silurian rocks. Force of Attraction, as an indirectly compressing agency, has been the factor which produced the successive forms of living Continuity—Attraction has all along acted as Gravity, or terrestrial attraction—How Gravity may have produced its results—Relative density—Water-pressure—The production of Filamentous Con- tinuity—The diminution of cell-density with development—The evolution of the Zooid, and megazooid—Suggestion that the repeated multiplication of Continuity may have been due to the development of fertilised ova under higher water-pressure con- ditions than usually obtaining—The factor responsible for fertilised ova being brought to develop in these increased pressure con- ditions would be SEGREGATION, or Repulsion acting in special ways— Different forms of Segregation, and their probable effects—It may be that as many strata were laid down before the Silurian Period as have been deposited since that time, CHarrer XVIII Tue Evo.LuTIon oF PHANEZROGAMS . . 169 The main groups of the Vegetable Kingdom—Theory to the effect that each group may have a distinct derivation from a marine type which exhibited an identical form of Continuity—The chapter briefly deals with the origin of the Phanerogams—The views generally held at the present time regarding the evolution of Phanzrogams—Some new suggestions—Marine zooidal colonies ; their “‘ cones’ and “‘ flowers ”’—The sporosac ; the sporosac-gono- blastidium and the Gymnosperm cone—The evolution of the medu- siform gonophore, and of the gonoblastidium containing such gonophores—The Angiosperms came suddenly into existence ; probably not as an offshoot from the disappearing Cycadophytes, but as a new type suddenly derived from a primitive Hydrozoal type possessing some form of medusiform gonophore—The Gymno- sperms would be derived in an earlier age from a still more primi- tive Hydrozoal type which possessed sporosac-gonoblastidia—The homologies of the medusiform gonophore and the typical Angio- sperm flower. 12 THE EVOLUTION OF CONTINUITY Cuarter XIX PAGE THE EvoLuTION OF THE VERTEBRATE . ‘ js 5 . 180 What was probably the plan of the marine segmental type from which Man evolved ?—The megazooidal derivation this type must have had—The light which Aurelia throws on the subject—Man evolved from a primitive piscine type. The evolution of the typical Fish—How the Fish’s ancestry must have been serially-medusoid in structure—The evolution of the Fish’s respiratory and circulatory systems—The nectocalycine canals and the branchial arches—The formation of mouth and gill-clefts—Terminal compression—The probable factors which called for the formation of a heart and the institution of a circu- latory system—The closure of the vessel system—The first beats of the heart—The circulatory system of Senuris—The evolution of the Fish’s nervous system—The alimentary tract. CHarrer XX Tue EvoLuTIon oF THE ATYPICAL FisH ; . . 196 The ‘‘ Atypical Fish ” exemplified by the Cephalopod—The effects of the absence of locomotion in the primitive type—How ua ter- minally compressed head would come to be formed at the end which in the Typical Fish becomes the tail end—The formation of a primitive brain ; of gill-cleft, and of vascular and respiratory systems—The factor of the rhythmic contraction of body-walls— The branchial arches; the alimentary tube, and the formation of an anus—Support for foregoing suggestions from the structure of the present-day Cuttlefish—Its general anatomy—Further sup- port from the methods of Cuttlefish movement—Man has not evolved through a primitive Cephalopod type. CHapreR XXI Tue Evo.ution oF MATTER. . ; 4 ‘ ; . 204 Indications that Matter has evolved into being, and has done so through the Intensification of Continuity—Matter and Force— The possibility of the “ultimate unit” of Matter being an “ in- sulated ’’ force-system—Through the alternation of Attraction and Repulsion, the former force being dominant, an ascending scale of Matter-systems could have resulted, each manifesting a multiplication of its forerunner’s Continuity ; after the manner already shown to have occurred with living Continuity-types— Matter is Potential Energy Electrons, and Atoms—The different species of atoms and ele- ments—The significance of their distinctive atomic weights—The Periodic Law, or Law of Octaves—Probably a key to the problem— Some possibilities the Periodic Law suggests. Cnarter XXII Tur ORIGIN oF SPECIES . 2 ; P ‘ , 3 . 211 The term used here in the sense of the Origin of Sub-species within the Fundamental Species of Continuity. Rough outline of Darwin’s theory—Some objections to the theory— Several new propositions in connection with the Origin of Species— The Mutation Theory. CONTENTS 13 Cuaprer XXIII PAGE THE EVOLUTION OF SYMMETRY . P . ‘ Z . 217 Symmetry of Form accompanying Continuity is here dealt with— The result of special factor, and one necessarily exercising sym- metrical power—The symmetry of the Discontinuously Multi- cellular Individual is that of Numbers; this is not the basis of Symmetry of Form in cellularly-continuous organisms. Symmetry of Form finds its explanation in terms of Attraction and Repulsion—The action of the former force more important— Three ways in which Attraction has probably acted: as (1) Terres- trial, (2) as Solar, and (3) as Food Attraction—The different ways in which Terrestrial Attraction, or Gravity, has acted, and con- tinues to act—Directly—lIndirectly, as atmospheric and as water- pressure—Specific Gravity—Solar and Food attraction frequently compete with Gravity; Gravity also competes with itselfi—The share of Repulsion in producing Symmetry—Cells grow in Con- tinuity not as the result of mutual attraction, but owing to external compressing force; owing to Gravity—The production of the symmetry of the discontinuous Zooid; of the Megazooid. CHaPTteER XXIV SEGMENTAL BILATERAL SYMMETRY . 2 2 : . 224 Symmetry of Form in the Fish—Gravity, alone, could not have made the Fish symmetrical; Food-attraction has shared in the process—-Movement during development, in presence of water pressure, would give the developing primitive Fish a symmetrically tapering form, but could not unaided produce the bilateral sym- metry the body actually exhibits—The influence of the digestive tract and its contents in the matter—“ Ventral ballast ’’—In all vertebrates the abdominal viscera are pulled by Gravity to face the earth’s surface—The swimming-bladder and its functions ; its absence in flat fish—The loss of equilibrium in the developing flounder. CHarpTteR XXV SEGMENTAL BILATERAL SYMMETRY (continued) . . . 229 Terminal compression and the Fish’s brain—Why this organ develops at the anterior end of the organism—Sources of attraction or repulsion which call for the response of Locomotion demand that this be in as straight a line as possible to or from the source ; they call for No DEVvIATION—The attracting and repelling forces would demand the formation of locomotive appendages, and of a kind capable of exercising bilateral symmetry of power—The bilateral symmetry of site and shape of the fish’s fins would thus result. Repulsion induces movement as strongly as Attraction—Repulsion from one point is equivalent to attraction towards another—In movement the chief deviation to be corrected would be lateral— How such correction would demand a duplicate and bilaterally symmetrical brain—How the over-correction of deviation would be avoided—How a crossed motor nerve tract would be inevitable ; the decussation of pyramidal tracts—The call for crossed sensory tracts; the decussation of optic tracts—Why there is a spreading 14 THE EVOLUTION OF CONTINUITY PAGE out of nerve tracts towards the brain cortex—The situation of cortical motor areas in the vertebrate brain; suggested funda- mental explanation—The correction of deviation in Birds and Quadrupeds. CHAPTER XXVI ALTERNATION OF GENERATIONS. PARTHENOGENESIS . . 240 Alternation of generations: usual definition—Term itself inappro- priate—Alternation of intermediate and Terminal Cycle-stages— this alternation summarised in the successive types of Individual Continuity. Parthenogenesis—the common definition not satisfactory—The process can only be exhibited by a part of an Individual—Sug- gestion that the true parthenogenetic cell is never an ovum, but always an intermediate cycle-stage—Loeb’s experiment—‘“‘non- specific fertilisation.” CuapterR XXVII KARYOKINESIS ; i : . : - ‘ 3 ‘ . 248 The phenomena are exhibitions of Attraction and Repulsion in action—Three forms of Karyokinesis: with double chromosomes, with single chromosomes, and as it occurs in polar extrusion— Double chromosome karyokinesis; the three main stages of the process, and some suggestions regarding their significance. Extrusion of Polar Bodies, a form of Karyokinesis—the process described—its significance a mystery. CuarterR XXVIII ABNORMAL GRowTH. TUMOURS - . F . 260 The explanation of abnormal growth to be looked for in the light of the laws of normal growth—Two aspects of the question. Classification of Tumours—The characters of the main varieties— The problem viewed in the light of Arrest, and Release from Arrest—Natural Arrest—Unnatural Arrest. Tumours which are the result of Escape from Unnatural Arrest— (1) when the unnatural arrest is of late application; (2) when it is applied early—In the former case the tumours are typical, and their growth not completely uncontrolled; in the latter case growth is uncontrolled and atypical—The possibility of a ‘ tumour- oe aaa ” and of ‘‘ tumour-gametes ’—Cancer-bodies—Secondary growth. Tumours whose origin is due to Escape from Natural Arrest; their nature—The healing of wounds, and the regeneration of tissue—Natural Arrest and Control—The restraining influence of connective-tissue on overlying epithelium — Experiments of Champy—The origination of epitheliomata; some speculations— Cell-damage or breach of Continuity probably always precedes the formation of such tumours—The stroma of malignant tumours, INDEX J. Wl SA ay Wl “& Go wl Bi 53. DIAGRAM OF SUGGESTED THEORY OF PLANT-EVOLUTION. 4 . 178 54. THE DEVELOPMENT OF AURELIA e & j a , ‘ - 181 55. THE GILLS OF THE TYPICAL FISH : ‘ 3 3 f a » 182 56. THE BRANCHIAL CIROULATION OF TYPICAL FisH . F : - 183 57. (a) PLAN OF MEDUSOID ‘‘CIRCULATORY SYSTEM.” (b) THEMUL- TIPLICATION OF THIS IN CONTINUITY. (c) THE CIRCULATORY SYSTEM OF SZNURIS . : ; . : ‘ - F - 184 58. MovuTH-FORMATION, ETC., IN PRIMITIVE FISH . ‘ . 3 - 186 59. How THE DEVELOPMENT OF THE PRIMITIVE PISCINE MOUTH WOULD ENTAIL A CLOSED CIRCULATORY SYSTEM . : . « - 188 60. FoRMATION OF MOUTH AND GILL-CLEFTS IN PRIMITIVE FIsH - 189 61. THE EVOLUTION OF THE SEGMENTAL NERVE-CHAIN . ‘ - 192 62. EvoLUTIONARY SIGNIFICANCE OF THE PLANS OF THE INVER- TEBRATE AND VERTEBRATE NERVOUS SYSTEMS . . Z . 194 63-65. THE EVOLUTION OF THE ATYPICAL FisH ... - 197,198, 199 66. PLAN oF A CEPHALOPOD 5 ‘ : : 3 2 ‘i P - 200 67. TasBLE oF THE PERIODIC Law. ‘ F . 5 , . - 208 68. EFFECTS OF WATER-PRESSURE ON THE DEVELOPING EVOLVING PRIMITIVE FisH : ‘ ‘ ‘ ‘ F : is ‘ . 225 69. THe FisH’s CROSS-SECTION . ; ‘ ‘ 3 . 3 2 . 226 70. REPULSION FROM ONE DIRECTION IS EQUIVALENT TO ATTRACTION IN AN OPPOSITE ONE A . 3 ‘ is rs ‘ : .» 232 71, 72. CoRRECTION OF DEVIATION IN THE EVOLVING FisH - 232, 233 73. THE MAIN DIRECTIONS TAKEN BY LIGHT-WAVES PASSING TO THE PRIMITIVE FISH'S BRAIN. . . . . . . , . 234 74. THE COURSE OF FIBRES IN HUMAN OPTIC TRACTS . ‘ ‘ - 235 Fa. 15, 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. ILLUSTRATIONS 17 PAGB 76, THE NECESSITY FOR SENSORY DECUSSATION IN THE PRIMITIVE IRISH” ag Je os we ae we Sy) Ge. a Se ae SG THE NECESSITY OF CROSSED MOTOR OPTIC TRACTS . 5 . 237 THE FUNCTIONAL AREAS OF THE RIGHT HUMAN CEREBRAL HEMI- SPHERE . ri F ‘ . . 3 ‘ , e - 238 ALTERNATION OF CYCLE-STAGES WHERE THERE IS CELL-DISCON- TINUITY < ‘ ‘ 3 s ‘i x C ‘ , ‘ . 241 ALTERNATION OF CYCLE-STAGES IN FILAMENTOUS GROWTH . « 241 PROTOPLASTIC, CHNOCYTIC, AND MYCELIAL ALTERNATION OF CYCLE- STAGES . : : ‘ - F 4 ‘ , ‘ r . 242 ALTERNATION OF CYCLE-STAGES IN PRESENCE OF ZOOIDAL DIS- CONTINUITY % . z . P ‘ ‘5 ~ F * - 243 ALTERNATION OF CYCLE-STAGES IN ZOOIDAL CONTINUITY . - 243 CELLS WITH KARYOKINETIC CHROMATIN FIGURES . ‘ ‘ . 249 Tue “ MonasteR” AND “‘ DyasTER”’ ‘ ‘ F ; A . 249 THE LINES OF MAGNETIC FORCE OF A BAR MAGNET ¥ . . 251 THE MAGNETIC FIELD BETWEEN DISSIMILAR POLES. 252 THE MAGNETIC FIELD BETWEEN SIMILAR POLES 5 i 5 . 253 89-92. SUGGESTIONS CONCERNING SIGNIFICANCE OF KARYOKINETIC PHENOMENA ‘ ‘ : : F ; . , . 254, 255, 256 Formation oF Poztar Bopises IN ASTERIAS GLACIALIS ‘ « 257 93. THE EVOLUTION OF CONTINUITY INTRODUCTION BeErForeE developing our theory piece by piece it would be well to indicate what is meant by the phrase used in the title of this book—‘‘ The Evolution of Continuity.” At first sight, no doubt, the words will appear meaningless ; for one would naturally suppose that there could be no evolution from Discontinuity to Continuity ; that from the former to the latter there could be but one step. If, for example, we place two glass beads on a tray at a little distance from each other, the beads are in Discontinuity ; but if we bring them into close touch with each other, or thread them on a string in close contact, they are, we may say, in Continuity. And no matter how slowly we bring them together, there is but one step from Discontinuity to such Continuity as is roughly manifested in contact. We know that there is no such thing in reality as absolute continuity of matter, and that the very electrons which constitute the atom are separated from each other by space ; that the densest metal is in reality porous owing to inter- molecular spaces, and that the cells of our body tissues are not in absolute continuity... But for the purposes of our theory we shall neglect this fact, and the Continuity of which we shall speak, obtaining in the natural world, is the continuity of more or less firm attachment, or such as resists on the whole any forces making for its severance, or for dissipation into wide discontinuity. Thus, the atom preserves the relative continuity of its system of revolving electrons, the living cell its protoplasmic continuity, and our bodies their cellular and tissue continuity. 1 Similarly, Discontinuity is never absolute, in the sense of the com- plete isolation or dissociation of one entity from the rest of the Many. 19 20 THE EVOLUTION OF CONTINUITY What the phrase “ Evolution of Continuity” really indicates is that there are a number of different types, kinds, or species of living Continuity, and we shall presently try to show that this is the case; and also that, funda- mentally, natural living evolution has passed upwards through a regularly ascending scale of Continuity-types. How there can be different types of Continuity can easily be shown if we make use again of our beads. Let us place a large number on a tray. Each single bead has, it is true, its own Continuity which preserves its bead-identity and holds its bead-molecules together ; but we shall ignore this and take the single bead as our unit. First of all we begin by arranging the whole collection in a state of Discontinuity, no two beads touching each other. The beads are the discontinuous units. Our next step is to produce not only bead-continuity, but the humblest form of this as our “‘ primitive type,” and we find that our object is attained if we arrange the collection of beads in one continuous single chain, or thread it tightly on a fine wire. This gives us a ‘‘ bead-filament,” the simplest form of Continuity for the whole collection of beads, in that the terminal ones are in contact with but one bead, and the intermediate ones with never more than two. Any reduction of these contact proportions would bring about the discontinuity of the series. Now, if we followed no guiding principle we might proceed to form new bead arrangements of many sorts, all showing an intensification of “‘ bead-filament ” continuity ; or make patterns in which the number of points of bead-contact was greater. But unless we worked on a fixed principle we would not be evolving Continuity. This, however, we might do in many ways, and a simple one would be as follows :— We could regularly increase our unit. Thus, after making the single bead-chain we could take as our unit two beads joined in lateral continuity, and make a chain of such units, as in Fig. 1, c. After this we could make a chain in which four beads united in lateral continuity constituted the unit; and so on till, for a given number of beads, we would have the highest form of bead-continuity possible on the system followed. INTRODUCTION 21 The above, needless to say, is not the method followed by Nature in evolving living Continuity, but nevertheless it can be shown that a special form of progressive multi- plication of Continuity has been brought about by her. Also, that fundamentally the ‘‘evolution of species” has been the evolution of Continuity-types in an ascending scale, and that within each of these there has been origination of animal and vegetable species, as the term ‘‘ species ”’ is generally understood. The evolution of Living Continuity, whose attempted demonstration is the main object of this book, is, it may be remarked, only one aspect of an evolution of Continuity going on throughout creation. Any material system what- ee Ww OO O 0°? O Q O% a O06 4 ¢. a. Fig. 1.—An example of the evolution of Continuity on the principle of multiplying the unit. a, collection of discon- tinuous beads; 6, a continuous chain of single-bead units ; c, w similar chain of double-bead units; d, one of quadruple- bead units. If the original collection of beads numbered 16, the evolution of Continuity finishes with d, on the system followed. soever, be it that of the invisible atom, or that of the planet, or of a solar system, preserves its identity as a system owing to forces which have built up and maintain the (relative) continuity of its component parts. Matter owes its existence to the institution of Continuity. The natural evolution of non-living Matter has not, however, in terms of Continuity, advanced as far as the natural evolution of living Matter. Everywhere it has attained to the Con- tinuity of the molecule by what we may call an inevitable process, and then, except in one direction, has leapt to the varyingly multiplied and “ accidental” Continuity of Mass. The exception mentioned refers to crystallisation, where molecules of definite identity are naturally united in Con- 22 THE EVOLUTION OF CONTINUITY tinuity to form the beautiful structure which is the crystal. The amorphous mass has molecules as its highest units, the crystalline has definite bodies composed of many mole- cules in continuity. Artificially, Man can produce endless systems of Con- tinuity higher than molecular. For example, he can make a large number of similar bricks; can unite them together to form a house; can make a number of similar houses joined together in a row; can make a town composed of rows of tenements, and so on; but such action is not inevitable. CHAPTER I ATTRACTION AND REPULSION WHEN one is searching for the basic principles underlying any Growth process or phenomenon, it is wise to put aside completely all thoughts regarding the ‘“‘ purpose” mani- fested. One should presume that the elementary laws which are being sought for set in action and control a sequence of reactions which must inevitably have definite results ; these results being frequently the originators of similar sequences. We have to study our problem in the light of Causes and their Effects, and not of Purpose. On every hand in Nature we see what may truly be interpreted as the exhibition of beneficent Purpose, but, scientifically, we recognise Harmony: the phenomenon, whatever it may be, is the harmonious effect of a definite cause, or definite causes. Keeping in mind the object of our search, we shall be wise to relegate Purpose to behind the basic laws, and to regard all that follows from these laws as natural result, for there ean be no doubt that to look for Purpose often makes it difficult to see the Cause; we arrive at knowledge sooner by tracing back causes than by following purposes. To take an illustration. In the study of the multiplication of a unicellular organism by simple division it throws no light on fundamental processes to look for the purpose exhibited —for example, the avoidance of extinction, or the perpetua- tion of species. More will be learnt by ignoring Purpose and by reasoning somewhat as follows: that the organism is governed by, and is the result of relentlessly working laws; that it divides because it has to, owing to these laws ; that for certain discoverable reasons one part of the organism has to separate and withdraw itself from the remainder ; and that as a result of the constant application of the governing laws the organism in question does not 23 24 THE EVOLUTION OF CONTINUITY become extinct. Similarly, in the facultative mottling of certain flat fish, or the green colouring of certain insects, the detection of the purpose of protection or concealment in no way increases our knowledge. We wish to find causes, and conclude that in both the examples mentioned the colouring is ultimately the inevitable effect of environmental cause, and that the capacity for concealment is equally inevitable. Thinking on these lines, let us take the case of a multi- cellular animal. This grows as a potential Individual till it reproduces itself, or (as we shall see later) more correctly, till through its growth there occurs the reproduction of one or both of the original entities with whose fusion the growth-cycle began. We reason that the animal grows or enlarges because its component cells do likewise, and in a spurious way ‘reproduce ” themselves; and, taking it for granted that a fundamental law is at work, we may conclude that the growth and multiplication of the cell is the multiple expression of the growth of its component parts, and so backwards, till we stop at the multiplication of ultimate growth-units by a process of addition. At the present time we do not truly know what the ultimate material unit is, but in a series of progressive multiples any one of these serves as a common factor for those succeeding it, so that the matter is not of absolute importance. As a general statement it may be said that every living Individual in Nature grows to reproduce itself, but this is not literally correct, or is only half the truth; for while reproduction is the inevitable result of normal growth, it is not, strictly speaking, the Individual which is reproduced. The growth-cycle begins with the union of sexual elements, and it is these which are reproduced at the end of the cycle after having temporarily lost their identities. The Individual, as will be shown, is really the sum of the reactions involved in the restoration of the sexual elements, and the alternating loss and recovery of their identities in a given line of descent involves the reappearance of the intermediate ‘‘ reactions ” composing the evanescent Individual. Understanding this, however, we may call this reappearance “ reproduction,” and say that while from the loss of sexual element identity evolves the reproduction of the element, so also does the ATTRACTION AND REPULSION 25 Individual representing this evolution grow to reproduce itself. Growth being on the whole a matter of addition to existing substance, it may thus be said that every developing Individual, by additions from outside to its substance, is finally reproduced. And this brings us to the bed-rock of our theory, for the addition is the result of the action of one ubiquitous, fundamental force—the Force or ATTRAC- Tion. All vital processes manifest its action. But it does not rule alone; and indeed if it did there could be no growth. It is in constant strife with its anti- thesis, the Forcr oF REPULSION, and it will be shown as we go along that these two Forces—in reality, one force in two opposing aspects—are the basic factors in all Growth and its accompanying phenomena. Growth is a reaction, or series of reactions, running to a definite end, and with this peculiarity, that the series finishes definitely only when the original elements or sub- stances with which it started are restored or reproduced. In other words, living growth is a cycle which passes through many stages to arrive at the original starting-point—when a new cycle may begin. When we view the phenomena of Growth in complex organisms, what we see is the mass or multiple exhibition of component phenomena or processes, each of which is in turn a multiple exhibition of others more simple. That is, the Individual growth-cycle is composed of smaller cycles, and these of still smaller ones, till a unit cycle is reached, the basis of all. This unit cycle runs its course in obedience to the law of Attraction and Repulsion. ATTRACTION AND REPULSION. The forces of Attraction and Repulsion govern all matter, and there is every reason to believe that it is through their action that matter exists as matter. As we shall see, it has doubtless been through the action of attraction that the planet we inhabit assumed material form, and we know that, like the other planets of the solar system, it pursues its orbit under the influence of the sun’s attracting force ; in the same way the moon is subject to the attraction of the earth. It is through this force that the land and water composing the globe cohere in mass and to each other, 26 THE EVOLUTION OF CONTINUITY the attraction in mass being the sum total of the earth’s component molecular attractions. On the whole, the world may be regarded as a huge system of bound force, or as a mass of energy which is for the most part bound up “ potentially,” though frequently becoming “kinetic” or active. When, however, energy becomes kinetic it strives with all its might to return to the potential state, for Nature abhors disequilibrium ; her ideal, her goal, is equilibrium. It is with the upsetting of equilibrium in any system that energy is set free or becomes kinetic, and work is done while the lost equilibrium is being regained, the whole process showing itself as a series of reactions. All forms of kinetic energy are manifestations of the forces of Attraction and Repulsion in action, but it is important to recognise that kinetic energy can only be produced and disequilibrium manifested through Repulsion coming into play, for where Attraction alone obtains all is rest and equilibrium, all energy is potential, all is bound fast in the absence of the opposing force. This being so, and we ourselves observing that all kinetic inevitably trans- forms itself as quickly as possible into potential energy, we conclude that the dominant force in Nature is that of Attraction ; and it may be remarked that the truth of this will be borne out by the evolution of living Continuity. Equilibrium is, in truth, Nature’s ideal, and its attainment by any system shows that in that system the fundamental force is acting solely as force of Attraction; but whenever disequilibrium is produced, or whenever any of the potential energy becomes kinetic, then we are dealing with the manifestation of Repulsion. Further, such Repulsion is always induced; for Attraction induces Repulsion, and vice versa. The force which at one time binds in peace and rest, at others separates and repels, only, however, to bind once more. In the living world, where there is constant liberation of energy and resultant disequilibrium, the two opposing manifestations of the One Force are in constant strife, and their alternation clearly displayed, with Attrac- tion dominant. Wherever energy is liberated there is resultant move- ment; the movement of “ultimate particles,” atoms, molecules, or their multiples in mass ; there is a setting free, ATTRACTION AND REPULSION 27 an embarking on a period of unrest, and this is true whether the system in question be living or dead in nature. Every one of our mechanical contrivances exhibits throughout the action of the two universal forces. The matter of which the contrivance consists exists as matter by Force of Attrac- tion, and is shaped, adapted to and performs its work by means of, and in terms of this force and that of Repulsion ; and movement in some form inevitably represents the work done. The same is the case with living organisms, Life being always associated with movement, in which we can clearly recognise the action of one or both of the fundamental forces. For example, ameboid, ciliary, flagellar, and muscular movements, and those of any organism as a whole, are inevitably towards or away from any given point. We ourselves grasp or let go, advance or retire, unite in groups or separate from each other. The ovum is repelled from the ovary, the sperm is attracted to the ovum, the products of cell-growth repel each other in cell-division. And we are conscious of the action of the opposing forces within our- selves. We like or dislike, are pleased or pained, happy or sad; we affirm or deny; we unite into families and separate into communities. Our bodies assimilate and also excrete. In fact, a little thought will make it clear that there is nothing which happens which does not do so in terms of Attraction or Repulsion, that these factors rule everywhere in the living and dead worlds, and that they are the fundamental principles of creation. It is our purpose to show that they govern equally the formation of the atom and the origin of species. Furthermore, as everything in Nature exists and acts in terms of the opposing forces, so does everything possess its characters “‘ antithetically,” so to speak. There is no quality which has not its opposite quality, or which could exist as one had it not its antithesis. Truly, there could be no pleasure without pain, no content without discontent, no good but for the presence of evil. A line is straight in that it is not bent or crooked, or can only be described as bent because it is not straight. There is no adjective we can think of which has not its antithesis, or which exists except through its antithesis, and this is simply because the fundamental principle which is and rules 28 THE EVOLUTION OF CONTINUITY all things manifests its action in two opposing ways—as Force of Attraction and Force of Repulsion. An essential characteristic of inorganic matter is its comparative stability or equilibrium; putting on one side the question of radiation, its energy is naturally potential, and when on the upsetting of equilibrium it is converted into kinetic energy it returns as quickly as possible to the potential state. Living matter differs from inorganic in that although its activities similarly reflect the action of the basic forces, and though it is the scene of earnest strife for equilibrium, this goal is for all purposes never attained, or, if so, only temporarily. The very efforts of living matter to attain equilibrium at any point upset the advances towards this state at some other point. The attainment of lasting equilibrium implies death. As has been said, matter in any form owes its existence to the Force of Attraction. It is this which preserves Matter’s personality whether in large masses, in molecules, or in atoms. Indeed, if we are consistent, we must hold that our theoretical ultimate unit of matter retains its identity and personality through attracting force, and that were the unit’s equilibrium upset ‘the infinitesimally small particle would be dissipated. Into what we cannot safely say, though we may hazard the evasion of ‘‘ Power” or “* Force.” Until recent times the smallest particle of matter which could exist was held to be the ‘“‘ atom,” its name signifying that it could not be divided into anything smaller. Each one of the various elements was believed to possess unalter- able qualities owing to the ultimate nature of its atoms. But at the present day there is abundant proof that all atoms are complex systems of enormous numbers of smaller particles called “electrons,” and it is very possible that the different kinds of atoms reflect different electronic contents and “arrangements.” We know also that thé elements have not unalterable natures, and that atoms can break down and their electrons fly off in radiation, and that through the breaking down of some elements simpler ones may be formed. The atom which is stable owes its stability and the preservation of its identity to central attraction, which on the whole refuses to let its discontinuous and ATTRACTION AND REPULSION 29 revolving electrons fly away; on the other hand, in such atoms as break down, Repulsion has clearly become the dominant force.! The atom, then, is to be regarded as a multiple of electrons united in continuity to the extent that they are bound within the atomic system. But atoms themselves are brought into continuity by Attraction to form the higher system of the molecule. The number thus united may vary from two to a hundred, or more, according to the nature of the molecule, but in all cases the identity or personality of the molecule is maintained through the Force of Attraction. Now the molecules of any substance are, as long as this preserves its identity, also bound together by Force of Attraction, but the attachment is not absolute; there are ‘* spaces’? between the molecules, and spaces which can be made larger or smaller, the molecules moving past each other at a greater or slower speed. Thus, a given volume of water can be converted into steam by heat, when it occu- pies a vastly greater space owing to the dissociation or mutual repulsion of its molecules. The personality of each molecule is, however, preserved, and the steam can be made to condense so that there is water once more. On the other hand, by what is called chemical action, the molecules of a substance can be broken up, be decomposed, through the induction of Repulsion, and the dissociation of its contained atoms, which are set free to form molecules once more— it may be of a new kind. It is quite clear, then, that mole- cular decomposition is the same thing as atomic dissociation. This brings us to an important truth, namely, that in both cases we have a Cyclic Reaction, or the loss of a state followed by its recovery ; for if the state of water reflects association, and that of steam dissociation, the condensation of the steam into water represents re-association, and the cycle is a sequence of Attraction—Repulsion—Attraction, when a new cycle may conimence. Similarly, if we decom- pose water by electrolysis (water molecules being composed of 2 atoms of Hydrogen and 1 of Oxygen), the atoms are dissociated and the molecules broken up. We get the dis- 1 The revolving electrons in the atom are widely separate from each other. Their common attraction to the atomic centre induces their mutual repulsion, 30 THE EVOLUTION OF CONTINUITY tinct gases, Oxygen and Hydrogen, with their specific molecules. So that the cycle here is atomic Attraction— Repulsion—Attraction. What must be noted here is that in its true sense the word “‘cycle”’ always indicates the cycle of a state, or one leading to the reproduction, not of an actual entity, but of a manifestation or state of matter; not of actual particles, but of given particulate states. This, in our belief, is the law of reproduction in all creation, and we regard all cyclic development, whether of molecular systems or living Indi- viduals, in this light. The sexual element of the son is living matter in the same state (we may say) as was manifested by the sexual element of the father; it is obviously not the paternal element re-associated after dis- sociation. Similarly, when a Leyden jar discharges its electricity and is recharged to an exactly similar extent, there is reproduction, but not of the actual original charge of electricity. In the dead world we cannot predict how the reproduction of the lost identity of a substance will come about; we can foretell the results of given equations, but we cannot as a rule predict the terms of the equations. But the outstanding feature of the living growth-cycle is that though its real mechanism is unknown to us we can recognise it on the whole as a vast series of reactions which must end in the reproduction of a lost initial state along a definite road. While Life is not a matter of chemical reactions and inter-reactions in the ordinary sense, it is highly probable that, fundamentally, chemical and vital processes are the same. Life, we might say, is super-chemistry. When one considers that the world which evolved Life was once a molten inorganic mass, it seems clear that living matter is only a manifestation of special results produced by the laws governing the inorganic world along (it may be added) with everything.! There is no satisfactory definition of what Life is, but it can truthfully be said that Life is self- sustained perpetual disequilibrium ; self-sustained, that is, with the help of Environment. The paradox is that this 1 The probable evolution of living from inorganic matter is dealt with on a later page. ATTRACTION AND REPULSION 31 perpetual disequilibrium is the result of perpetual striving for equilibrium. Disequilibrium can only be maintained in presence of a more or less constant supply of foreign particles, and these by inducing atomic attractions and repulsions perpetuate unrest; failing such a supply, the living atomic inter-reactions will steadily diminish, Life will cease, and the comparative equilibrium of dead matter be established. But whatever one’s views regarding the nature of Life, the fundamental action of the One Force which acts as the opposing forces of Attraction and Repulsion must be admitted. These are the forces which actuate (and we might say are) all Growth whatsoever; which, whether living or dead in nature, is essentially cyclical. CHAPTER II THE UNIT GROWTH-CYCLE As has already been said, we do not really know what the ultimate unit of Matter is. It may be that the future will reveal it as a relatively ‘‘ insulated ’ revolving force-system, in a sense independent, and of definite ‘‘ charge,’’ and whose reaction must be one or the other of the two opposing reactions of the universal Force; that is, one of Attraction or of Repulsion. In other words, Matter may simply be potential energy. At the present time the smallest material particle recognised by science is the electron. It will make for greater simplicity and brevity, however, if we attribute ultimate characters to the atom, and take this complex particle as our growth-unit, and the atomic cycle as the unit growth-cycle. And we shall look for evidence that all higher growth-cycles are but multiple expressions of this unit growth-cycle. It is to be repeated that all cycles are essentially cycles of states or conditions, being represented by the diagram, hz: pete On Aepyi son but they may also be regarded as cycles of acts. Thus, although atoms do not exist in the free state, nevertheless they must be momentarily free when repelled or split oft from given attachments ; and in this sense it can be said that the Atomic Cycle begins with an act of attraction between two atoms which results in loss of independent identity, followed by an act of repulsion leading to the restoration or reproduction of independent identity—when 32 THE UNIT GROWTH-CYCLE 33 @ new cycle begins. That is, the unit-cycle of growth requires two units for its commencement, course, and conclusion. It is simply an act of attraction followed by one of repulsion, a unit diphasic reaction. The unit growth- cycle may therefore be represented as below. eerB son¥ Yo Here, A and B are two atoms mutually attracted. As a result there is unit growth, AB. Repulsion is induced between A and B, and each is restored or reproduced ; or better, their original independence is thus affected. They are now ready to begin a new cycle with each other, or two separate new cycles with two new units. It is to be noted that the repulsion which ‘‘ reproduces” A and B is induced. Were AB not interfered with, there would be no repulsion and no reproduction. For these to occur there must be present other atoms capable of upsetting the atomic attach- ment and equilibrium of AB. Thus, the figure might be drawn as below. Ker @->¢€ ae @-@ | Here the atom C, being stronger in attracting power on B than is A, induces the repulsion of A and attaches itself to B. As a result the independence of A is reproduced. Similarly, B may be reproduced in the presence of D, whose affinity for C is stronger than B’s. However, B At—>B + ( ace A B may be taken as the diagram of the unit growth-cycle, which, it is to be repeated, represents an Act oF ATTRAC- 34 THE EVOLUTION OF CONTINUITY TION FOLLOWED By AN Act oF REPULSION. This is offered here as the key to all growth-cycles, be they those of bacteria, plants, or animals, all higher cycles being but multiple expressions of this unit-cycle. Thus, we recognise in the act of attraction between A and B atomic “conjugation”; in AB, the unit “somatic tissue ’’; in the restoration of A and B, the ‘“ reproduc- tion’’ of the “‘atom-gametes,” whose union started the cycle. The diagram, in fact, would represent the growth- cycle of a complete bi-atomic “ Individual.’ CHAPTER III PROTOPLASM. THE INDIVIDUAL To the essential matter of all living organisms the name of Protoplasm has been given. The term, however, is not a very fortunate one, for what it is used to indicate is not a definite basic substance, but a fine mixture or emulsion of many substances in a fine state of suspension. At the same time it seems more than probable that amidst the many different molecular ‘species ’’ of the living cell there is always one representing the essential living matter of protoplasm. But beyond the fact that it is proteid in nature we know nothing definite of its composition, the insur- mountable difficulty being that its analysis involves its death ; and clearly living proteid must be a very different substance from dead proteid. To this essential living matter, whose molecule has received the name of “ biogen mole- cule,” we have ventured to apply the term “ basoplasm ”’ in order to distinguish it clearly from protoplasm. It can be well understood that there are many distinct varieties of protoplasm and species of basoplasm in the living world, reflections of different lines of evolution under differing environmental influence. All Growth is Evolution. From the conjugation of two gametes to their restoration at the end of the Individual cycle there is a straight path of evolution, and in the tissue differentiation of the higher-growth types we have the side-path evolution of cell-species; and similarly within each cell there are different species of substances, molecules, and atoms. In descriptions of simple or elementary protoplasm it has been customary to refer to one of the most structurally 35 36 THE EVOLUTION OF CONTINUITY simple of living organisms whose vital phenomena are at all observable—the freshwater Amosba; a tiny jelly-like particle possessing the power of changing its shape and position by protrusions and retractions of its substance. But the ameba is only comparatively simple ; it has evolved through ages to its present condition, and is the latest edition of some much more primitive prototype. We may imagine this to have been smaller and more homogeneous in structure, and unprovided with a nucleus, in the accepted sense of the term, though necessarily possessing some system of control. Nevertheless, the basoplasm of such an elemen- tary organism would be composed of highly complex ‘* plasmolecules,”’ and obedient to the forces of Attraction and Repulsion the component atoms of each, controlled by their attraction-centres, would unite, separate, and reunite in ceaseless change. There would be countless atomic cycles run, and through them each plasmolecule would all the time be trying to attain full satisfaction and complete equilibrium on a definite plan. THE PLASMOLECULAR CYOLE. The different characteristics of dead and living matter may reasonably be attributed to marked differences of molecular constitution or plan. They cannot be attributed to electronic or atomic differences, for the elementary atoms composing living matter are all found in non-vital combina- tions. Any analysis of living matter is impossible, as it involves death, and becomes the analysis of dead matter; but even so there is revealed a molecular complexity far higher than that of dead inorganic matter. The result of death is, moreover, inevitable Discontinuity or Decomposi- tion, the dead organism breaking up in its parts, tissues, cells, and molecules; and it is credible that the molecule of living basoplasm, the “‘ plasmolecule,”’ is a far more complex structure than that of dead proteid, which might be pictured as a part of its disintegration. And one is drawn to presume an extreme complexity of the basoplasmic molecule in order to explain certain phenomena of living growth, and especially why it is that so much cell-multiplication is required after a conjugation PROTOPLASM. THE INDIVIDUAL — 37 or fertilisation act before the originally combining elements are restored or reproduced. The development of the living Individual, whatever its kind, is a process of cell-multiplication and differentiation ; it is evolution. The undifferentiated embryonic cells become in their product the original elements, whose union started the Individual ; it is an evolution leading to the restoration of the original and temporarily lost sexual element “‘ plans,” a restoration depending, according to our suggestion, on that of the “‘ plans ”’ of their basoplasmic molecules. Where the Individual is cellularly continuous there is also a very obvious evolution in gradual somatic tissue-differentiation, and this must surely be based on progressive basoplasmic molecular change. In a word, our supposition is that as after sexual elements combine their identities disappear, so also is there a loss of identity of the respective basoplasmic molecules, the complete Individual representing all the growth-reactions necessary for the restoration of identity. We could picture the fusion of conjugating elements as entailing a fusion of their plasmolecules with resulting loss of plasmolecular identity, followed by the division of the enlarged plasmolecules, and finally the first act of cell- division. But a plasmolecule in either division-result would have an unstable constitution and resemble neither of the original plasmolecules whose fusion produced it. And it would try to recover its lost equilibrium and identity by growing; that is, by attaching to itself atoms from outside its personality, discarding many in the process. But before more than a slight advance had been made on the road to the recovery of lost identity or plan it would attain an enlargement which obliged it to divide into two, giving, in the mass, a renewed act of cell-division. And the process would go on till in a straight line of production a huge number of division acts ended in the recovery of lost plasmolecular plan and the restoration of one of the original sexual elements : leaving out of account the side-path evolution and tissue differentiation which occur in presence of cell-continuity. This in its broadest lines is the suggestion offered regarding the plasmolecular cycle. That when sexual ele- ments fuse, their plasmolecules do likewise; and that the plasmolecular cycle begins with an act of plasmolecular 38 THE EVOLUTION OF CONTINUITY attraction, and is continued through many acts of plasmole- cular repulsion or division till the original plasmolecular plans are restored in the sexual elements, This supposition does not seem unreasonable in view of the undoubted fact that the growth-cycles of living Individuals begin with the attraction of sexual elements, and are continued through many acts of cell-division (repulsion) till the elements are reproduced. Admittedly, it entails the acceptance of the living protoplast as essentially a multiple of plasmolecules, and makes cell-division the immediate sequence of plas- molecular division. As in cellularly continuous organisms the main road of evolution leading to sexual-element reproduction gives off many side-roads ending in the fixed tissue cells, s0 one may believe that in the cell, which is on the whole a molecularly continuous organism, the main road of plasmolecular evolu- tion gives off side-roads leading to the differentiation of fixed substances—the “‘ somatic substances’ of the cell. THE INDIVIDUAL. Before going farther it is necessary to define exactly what an “Individual” is, as the term will be constantly used, and always within the limits of the definition. Every independent living entity is not an Individual in the scientific sense of the term. Far from it. For example, a single aphis or greenfly is never one, nor is a queen bee, nor a drone. On the other hand, a worker bee always is, with rare exceptions. One rosebush may be a developing Individual, while another may not be. A malarial amoeba can never become an Individual, and no more can an independent alga cell. A living Individual may be defined as the Sum oF a CoMPLETE GROWTH-CYCLE, from its beginning up to where it finishes with the full possible reproduction of the originally combining elements. Two things follow from this. First, when the Individual cycle runs through many organisms, unicellular or multi- cellular, which enjoy a free and independent existence, as PROTOPLASM. THE INDIVIDUAL 39 in the case of Hydra or Aphis, no such organism even when producing sexual elements can be termed an Individual. A seedling rosebush is a potential Individual, but a rose- bush grown from a cutting can never be anything but a part of an Individual. In the second place, if the complete cycle comprises the Individual, one is not literally correct in applying the term to any organism—or group of organisms—before it has grown to its utmost limits and finished all its cell-cycles to the extent permissible to the class of Individual in ques- tion. A man can loosely be described as an Individual, but he is only potentially one as long as he can produce sexual elements and repair tissue loss. It is as indicating all the content of the living growth-cycle that the term ‘** Individual’ will be used in succeeding pages, and to denote this it will always be written with a capital “I.” It may well be questioned if there are such things as “unicellular Individuals.” Certainly, every unicellular organism is not an Individual, nor is there necessarily reproduction when a unicellular organism divides into two. There is reason for the belief that all unicellular organisms, whatever their kind and however marked their independence, are but parts of or stages in the development of some Discontinuously Multicellular Individual type. Our unit growth-cycle is an act of atomic attraction followed by one of repulsion, and our belief is that the repulsion manifested in the division of a unicellular organism, itself an atomic multiple, indicates that somewhere and sometime previously an act of unicellular attraction, or ‘‘ conjugation,” must have occurred. Our suggestion is, in fact, that the “ unicellular Indi- vidual”? is fundamentally on a par with the intermediate cell of the continuously multicellular organism, and that it is the independence due to discontinuity which is misleading and obscures the truth. On the other hand, the Individual composed of many unicellular organisms is common in Nature, the cycle always beginning with an act of attraction and the conjugation of two of the organisms, and ending with their multiple restoration or reproduction. And here one can but conclude 40 THE EVOLUTION OF CONTINUITY that the long series of cell-division acts which ocour before reproduction mark so many stages on the road to this goal. In its sum total, all the intermediate cell-growth of the Individual is the inconceivably immense number of atoms which must be supplied and incorporated from without to keep the process of restoration of the originally combining elements on the move. A very crude illustration might be used to make clear our interpretation of the multicellular Individual Cycle. Let us picture one sexual element, or “ gamete,” as a house built of bricks and on a definite plan, and the other as another house similarly constructed but on a different plan. The houses fuse together, breaking up into a large heap of bricks, with the loss of the original plans. The whole mass is then to be pictured as dividing into two masses, each of which obtains new bricks from outside, whose presence sets going a restoration of lost house structure. In time each mass doubles its size and divides, so that there are four masses, and each of these incorporates new bricks and the process repeats itself. But all the time, accompanying mass-enlargement there is a steady pro- gressive restoration of lost house plan of the one kind or the other, until a time is reached when instead of the original two houses there is a great multiple of them. In the living growth-cycle restoration proceeds by geometrical progression; one becoming two, two becoming four, four becoming eight, and so on; and we conclude that as two different sexual-element plans or identities have been lost and are striving for restoration, a stage in the process will occur when divergence must take place; in other words, when cells will be produced whose further product will be all “male” or all “‘ female.” i The propositions, then, which we put forward are :— I. All Growth, in every aspect, exhibits the action of One everywhere obtaining Power which manifests itself as the opposing forces of Attraction and Repulsior . II. All living Individuals are the product of a conjuga- tion act, or its equivalent. In other words, Conjugation Implies Multicellularity, or vice versa. PROTOPLASM. THE INDIVIDUAL 41 To these we shall have to add two others, namely, Environment produces Continuity, and Continuity produces Arrest, in order to throw light on the principles of Growth in living organisms, and the method of their evolution in the ascending scale. We shall now take one by one the main forms of living Continuity in the ascending scale, beginning with the Discontinuously Multicellular. It must be noted that the illustrative examples given are offered as iypes of Continuity, and that in no case is a given organism put forward as an actual milepost on Evolution’s main road, except in regard to its Continuity. The question of how the different types of Continuity probably evolved will be dealt with later in the chapters on EvoLurion. CHAPTER IV THE DISCONTINUOUSLY MULTICELLULAR INDIVIDUAL Tus we take as the simplest form of multicellular, if not of living Individual, and is all the product of two fused gametes. Its component cells! are not continuous or bound to each other, but are free to live as independent entities or pseudo-Individuals, in general contrast to those of Continuously Multicellular Individuals in whom the cells are bound together in one mass, or in several independent masses, and live for the good of the whole continuous number. The developing Discontinuously Multicellular Individual is composed of many free cells which are probably cycle-stages on the road leading to gamete formation, but the theoretical complete Individual is composed of nothing but terminal stages or gametes. The hemameeba of malaria will serve as our example. The malarial amceba, whatever the species, is usually described as having two distinct “life-cycles,” but it is to be noted that these are in no sense growth-cycles. One “‘ life- cycle” is in man—the “asexual cycle ’’—and the other in the body of the anopheles mosquito—the ‘sexual cycle.” But the so-called “ asexual cycle’ is only a cycle in that there is a repetition of immediate environmental conditions, while the ‘‘ sexual cycle” is not a true onein anysense. The diagram below shows the life-story of the amceba, and while correctly depicting the phenomena observed, it is nevertheless, as has been said, misleading from the growth-cycle point of view. 1 A “cell” is the term used to indicate a protoplasmic entity or “‘ pro- toplast ’ surrounded by distinct walls, and is not strictly applicable to an amceboid or an unwalled protoplast. But the word is employed here in the widest sense to indicate any protoplast, walled or unwalled. An alter- native heading to the chapter would be ‘The Discontinuous Polyproto- plestic Individual.” i DISC. MULTICELLULAR INDIVIDUAL 43 As is well known, when the human body is infected with malaria the amcebex, tiny unwalled protoplasmic masses, come to occupy the red blood corpuscles, where they increase in size, each finally dividing into a number of spores which varies with the class of infection. Each of the spores when liberated then enters a fresh blood corpuscle, becomes an amoeba, and the process is repeated. After a certain time, however, spores are produced which on entering corpuscles be al amoeba. git THe 20, Mee AS€xual Cyels, Oks BOX $a livary Gland of 0290/Te ai 4 Sporszortzs : THe Mos pyiTe ‘) genset aad Puase , or Stxu4L Cyc (s, C4 a Stomach wall «fF Mosquito é Fic. 2.—The life-cycle of the malarial parasite. (After Daniels.) do not grow to sporulate, but enlarge into male or female gametes. To quote Daniels :— “In the warm-blooded host reproduction takes place asexually by the breaking up of each organism into a number of young forms or spores. This is the endogenous or asexual cycle of development. The host during this cycle is the interme.iate host. The parasites which develop in this manner are known as sporocytes. Some of 44 THE EVOLUTION OF CONTINUITY the spores, however, instead of forming sporocytes assume the sexual or gamete form. These do not reproduce or undergo any change whilst in the intermediate host. If they are taken up by the definite host (mosquito) they become sexually active, conjugation takes place and further development follows. The product of conjugation, the fertilised female, increases in size and forms a cyst. The contents of the cyst divide into several masses, blastophores, from which small thread-like bodies, sporozoites, are formed. These bodies when introduced into a suitable animal—the intermediate host—become sporocytes. This cycle is a sexual one, and the host is therefore the definitive host.” Now our view is that these asexual and sexual cycles are not true cycles and that reproduction does not take place asexually. In one sense we can recognise an asexual cycle in that there is regular repetition of the phenomena of amceba— spores—ameebe, and the repetition of entering and leaving corpuscular immediate environment. But what we would call the “true” cycle is the Individual growth-cycle. This begins with gamete-conjugation and ends with gamete- reproduction or restoration. The products of the division of the “zygote,” or conjugated gametes, are the sporozoites mentioned, and these on entering the blood corpuscles become the first infecting amebe. And the point we wish to suggest is that no amcebe reproduce themselves in the amcebe resulting from their sporulation. Under the microscope, it is true, there are all the appearances of asexual “reproduction”; the amcebe resulting from one act of sporulation do appear to be identical with the amebe which became them; but it is very probable that this is purely a matter of appearances. Our belief is that each amceba is cyclically further advanced than that which grew to produce it, and that each ameba produced is, as it were, a stage in the cycle determining the reproduction of the original conjugating gametes. This reproduction is multiple ; more than one gamete of each sex is reproduced, and every ameeba resulting from the initial act of conjugation is the starting-point of a longer or shorter series of amceba-stages ending in gamete reproduction. According to our hypothesis such series will vary in length according to the situation in line of “ descent ”’ of the amceba originating them. It is the cellular Discontinuity of the Individual which allows every amceba produced to carry DISC. MULTICELLULAR INDIVIDUAL 45 on the growth-cycle to gamete-formation, or to the inevitable end, in the absence of special opposing factors. From this it would follow that the hemameba Individual is not indefinitely large, and there is reason for holding this to be true of all living Individuals. In fact, it is our belief that every living Individual, no matter its type or complexity, has a definite theoretical limit to its existence; the length of its existence under the most ideal conditions being the A. seo | i aa o> es @ : a 2a ayer ‘ er . BS Cz oo kc oF 7° BOOO0*Y Fic. 3.—The true hemameba growth-cycle ; diagrammatic. It begins at a. Only five sporulations are figured, and these in straight line of ‘ descent.” time necessary for the full determination of its contained cycles, within the limits permitted (as we shall see) by Con- tinuity to the Individual in question, plus, in higher types, the time occupied by the process of decline. In the case of the hemameeba the fullest determination of the contained cycles of the Individual is theoretically possible ; the whole Individual should, theoretically, come to be represented solely 46 THE EVOLUTION OF CONTINUITY by gametes, for the multicellularity is discontinuous. In the higher forms of Continuity the case is very different. To repeat ; the course Amceba—Spore—Ameeba does not constitute a growth-cycle, as the second ameeba is not reproduced but produced; it is not identical with its predecessor, but a stage nearer towards becoming, in its future product, gametes of one kind or the other. Nor does Spore—Gamete—Zygote—Spore represent a cycle, but two parts of different growth-cycles. The real growth-cycle is from conjugated gametes to restored gametes; the Individual cycle. The growth-cycle is therefore correctly figured as above. AAS NS MAA MANNIKNWYSS, Fic. 4.—To illustrate the law of “2 to the Nth minus 1.” The developing heamameba Individual increases by geometrical progression, as is shown in Fig. 4. Here the gametes are represented by the letter G, and all the stages leading to them are evanescent. B gives rise to, or becomes 32 gametes, while the intermediate stages, including B, number 31, The full number of gametes is equal to 2 to the Nth power, and that of the intermediate stages, alone, or with the addition of the gametes, equals 2 to the Nth minus 1. Thus the full Individual in our diagram would be X plus 126 stages plus 128 gametes, or 2 to the 8th minus 1. The true DISC. MULTICELLULAR INDIVIDUAL 47 Individual is, of course, 128 gametes ; for the stages are evanescent. It is interesting to draw the last figure in the form of a main line or stem of cell ‘‘ descent” with lateral branches, and this without really mutilating it in any respect. The significance of this will be evident when we come to con- sider the main stem and lateral branching plan of certain Individuals whose organic units are continuously multi- cellular. Here we notice a progressive diminution in the inter- mediate stage content of successive branches, whether ares x 7 Nor A A ' ee [ee wee c¢ \X\.6—*> Pm oP “a MwA, “so we / € ee’ FSS | ne” 26 F'e | E ae tI i S 4. ¢c D E F S 5. Fic. 9.—The formation of cell-caps in the light of proximal arrest. The process here is the same as in Fig. 7, with this difference, that when 4a becomes B, B, distal B will have one cap and proximal B none. Distal B becoming c, c, distal c will then have two caps and proximal o none; distal c becoming D, D, distal p will have three caps and proximal p none. In this way the process will go on till the series ends with distal @ possessing five caps, and in this cell is produced the gamete. 8, when released from arrest, will give rise to an intercalated series, Cc, D, E, F, G, the last being the game- tangium with four caps. giving rise to a purely asexual plant, produces a new gametophyte.”’ (Lowson.) But Spirogyra is surely not a “plant” in the strict sense of the term ; its continuity is more apparent than real ; it is a “‘cell-colony.”’ Its cells are virtually independent although attached in series, and each lives as an Individual although only part of one, and does so in spite of temporary arrest. The filament as a whole cannot therefore be compared to the gametophyte of the proper plant where there is true cell-continuity, for it is nothing more than a series of virtually 58 THE EVOLUTION OF CONTINUITY independent cell-units. It is to these that we must turn, and doing so we recognise that any asexual cell of the filament is a potential gametophyte, through its product. But the cell which divides to produce a gametangium may he regarded as the true gametophyte, and all preceding cell-stages of the cycle as sporophytes in that they divide into or produce “asexual” cells. The production of two cells by a simple act of division may, in fact, be regarded as elementary parthenogenesis, the commonly accepted and limited applica- tion of the term dealing only with the phenomenon when exhibited by a continuously multicellular organism, and not by a single cell. And in the fact that asexual cells must appear as stages on the road to the production of sexual cells or gametes we have the key to “ alternation of genera- tions.” It is not really an alternation of generations, but of intermediate or “‘ asexual’’ cycle-stages with terminal or “sexual ’”’ forms, CHAPTER VI THE CQ@NOCYTIC INDIVIDUAL WE naturally expect that the next step in the evolution of living Continuity will be the LaTrrat Continuity of filaments or single-cell series, and this we find to be the case. But Nature presents us with this intensification of Continuity in two distinct forms. One of these is what might be termed irregular, and occupies a place of its own, and it is to the Individuals exhibiting it that the term ‘‘ ccenocytic” has been here applied. It cannot be denied that Coenocytic manifest a higher form of Continuity than Filamentous Individuals, but at the same time there is every reason to believe that the evolution of the former has proceeded on a side-path, and that none of the higher forms of Continuity have evolved from the Cenocytic. No existing organism or Individual in Nature is, as it were, a milepost on the main road of evolution except in the matter of the Continuity it may exhibit, for fundamentally the evolution of the human species has been through primitive types which existed long ago and whose Continuity alone is still with us in certain present-day types. But a coonocytic was probably never one of these primitive types. Ccenocytic Continuity evolved on a side-path, and though possibly through the intensification of some form of primitive Fila- mentous Continuity, from it evolved no higher form. The truth of this will be more evident when later pages make it clear that Continuity has evolved by a process of steady multiplication, Serial alternating with Lateral Continuity. Ceenocytic Individuals are as a whole represented by those organisms called Fungi, though a few Algz are also ccenocytic ; and as examples we may briefly refer to the common moulds, of which Mucor is typical. 60 THE EVOLUTION OF CONTINUITY If one soaks a piece of bread in water and covers it with a glass dish, a good growth of Mucor is sure to develop within afew days. At first it appears as white dots on the surface of the bread, resembling moist spots of uncooked flour. Each of these spots is a growing ‘‘ mycelium” or network of mould which has originated from a spore—millions of which are everywhere about in the air and dust; and thus each mycelium is only a part of a Mucor Individual, though several Individuals may have been involved in the production of the spores producing the mycelia. For a day or two appearances remain more or less the same except for the extension of the mycelia, then with startling suddenness the bread becomes covered with a white swansdowny growth of exquisite fineness, which close inspec- tion shows to be composed of innumerable branching threads like the finest spun glass, while scattered over the surface are minute white dots. This is due to the development of aerial branches which are produced with the view to forming spores, the white dots being the “ sporangia,” or little cases full of spores, at the tips of the aerial branches or ‘‘ hyphe.”’ The spores are produced in enormous numbers, and every one which falls into a suitable environment can originate a new mycelium. Within a certain time the fluffy mass of mould, composed of how many mycelia it is impossible to say, so close is the interweaving, begins to look as if fine soot had fallen on it ; but regarding it with attention one can see that this is due to an immense number of black dots similar in size to the pre-existing sporangia. These are the ‘“‘ zygospores ”’ resulting from the conjugation of gametes which have been produced. Some varieties of Mucor, such as Mucor mucedo, produce gametes rather infrequently, and from this we infer that the growth-cycle is a long one and has to run through many mycelia (linked together by the discontinuous spores) before it ends with a gamete-forming mycelium. In the case of all moulds growth takes the form of a mycelium, and this is simply a species of filament which in growing gives off so many branches, and these so many others, that it becomes an intricate network of filamentous tubes or “hyphe.” But in addition to the fact that there is no THE CQ@NOCYTIC INDIVIDUAL 61 chlorophyll in it, the mould hypha differs in two important respects from the Spirogyra filament; in the first place, it is not a single-cell series, and in the second, lateral branching takes the place of intercalation. The hypha of the mould mycelium is not composed of separate cells shut off from each other by walls, but has a long tubular structure con- taining multinucleate contents, and divided or not divided at intervals by transverse septa. Each such non-septate mycelium, or segment of septate mycelium, is what is termed acenocyte. This, however, is not to be regarded as a species of long multinucleate cell. When we talk of the “cells” of Spirogyra we really refer to the separate nucleated protoplasmic entities or B. Ee hkoj eye} ¢. fe el wT ONT © ea OY [ ars ee y eee oh 2} “3 at plead ‘eps o e me Fic. 10.—Showing that cenocytic is higher than filamentous Continuity. a, diagram of a protoplast enclosed by walls, the whole being termed a “‘cell’’; B, part of a cell-series or filament of Spirogyra, presenting Srpiat Continuity; oc, ceenocyte of septate mycelium : in one respect a serial multiple of any cell of 8B, but containing as it does two parallel series of protoplasts, it presents us with the multiplication of 8’s serial into LaTeRAL Continuity. “protoplasts,” plus their containing walls, which compose the filament; but the walls are only containers, they are not essential parts of the entities, and the Spirogyra filament is simply a long succession of protoplasts separated from each other by partitions, whereas in mycelial growth there is an increase of Continuity which shows itself in two ways ; for between the septa or partitions of a ccenocyte there are many protoplasts in series as compared to one protoplast in the case of Spirogyra, and there is also the lateral con- tinuity of parallel protoplastic series running along the hypha (Fig. 10). The ceenocyte, in fact, might be looked on as the simplest of all forms of “ tissue,’’ were it not that we restrict this 62 THE EVOLUTION OF CONTINUITY word to denoting the serial and lateral continuity of proto- plasts provided with walls—in other words, of “cells”; for the multinucleate content of the hypha is really two or more parallel successions of protoplasts in lateral continuity, a fact which can be made out by carefully staining a specimen and examining it under a microscope (Fig. 11). In moulds of the Mucor type the hyphe are not as a rule divided by septa. As the result of continued growth, and as described on page 60, spores are formed in spore sacs borne at the ends of aerial branches. Each spore when set free can under suitable conditions develop into a new mycelium, which, if it is intermediate in the cycle, will likewise in time produce spores ; but sooner or later mycelia Fic. 11.—Examples of mould ccenocyte showing protoplastic series in lateral continuity. Greatly magnified. are formed which produce not spores but gametes. In fact, we have discontinuous mycelia taking the place of the independent cells of the Discontinuously Multicellular Individual in the growth-cycle sense. And as the Mucor cycle is composed of mycelial units which are stages on the road to sex, and others which become sexual, there is exhibited a mycelial alternation of generations. A fact of great interest is that at times the Mucor mycelium may go into a “torula”’ condition, developing chains of distinct cells after the manner of Yeast, or as lines of cells in filamentous series. This confirms the polyprotoplastic nature of the coenocyte. The converse of the phenomenon is to be seen in the cases of certain bacillus-Individuals THE CQ@NOCYTIC INDIVIDUAL 63 where the usually free bacilli may be produced in what is apparently ccenocytic or hyphal continuity. The Mucor Individual is all the product of gamete- conjugation; all the mycelia, asexual and sexual, which result from an original zygospore. Each mycelium in direct line of ‘‘descent”’ is, we presume, nearer to gamete- formation than that preceding it, till finally some appear which cannot produce spores but must produce gametes. Similarly, the successive protoplasts of a hypha may be regarded as successive “‘cell-stages”’ in the growth-cycle. The growth-cycle runs on through the spores, which are but links between successive mycelia. We might say that Coenocytic Individuals of mould type are, in contrast with Discontinuously Multicellular Individuals, Discontinuously Mycelial ; that in place of discontinuous cells or protoplasts the Individual is composed of discontinuous protoplast-multiples. In such moulds as are septate (e.g. Eurotium) we can recognise the multiplication of true Fila- mentous continuity ; for whereas in Spirogyra we are dealing with the serial continuity of single protoplasts enclosed within walls, in Eurotium we have the serial continuity of multiples of naked protoplasts enclosed within walls. The Spirogyra filament is a series of cells, the Eurotium hypha is a series of ceenocytes. On the other hand, while Spirogyra is a cell-colony, Eurotium is something more than a ceenocyte- colony; for the asexual cells of the Spirogyra series are only temporarily arrested, whereas in Eurotium great numbers of cceenocytes remain permanently arrested as vegetative supporting structure—the price of Continuity. Fase TISsvz. In certain of the higher Fungi there is, within the Individual, a multiplication of the lateral continuity of the cenocyte into a higher form of continuity, the discrete vegetative ccenocytes being joined laterally together to form the “false tissue’ of the reproductive organs. The effect is roughly what one would get by pressing together into &@ compact mass a fungus mycelium, and there can be little doubt that a physical compressing force was the factor at work in the evolution of primitive false tissue, the result showing a beautifully interwoven plan. 64 THE EVOLUTION OF CONTINUITY We may notice two examples of false tissue, and the first is that occurring in Eurotium. In this mould the end of a hypha becomes coiled in a close spiral forming what is called the archicarp or female organ; while from below it arise several thin hyphal branches, one of which, the pollinodium or male organ, curves over to enter the coiled archicarp and fertilise its contents. The remaining branches wrap round the archicarp and by repeated branching penetrate its coils and fill it with matted false tissue. The fertilised archicarp 1) nN rym. Meee _-Pallin od bios ‘ae a Gscogtaoys 6 ‘anch, ‘ Filing tissus. Fie. 12.—The sexual process in Eurotium. (After Lowson.) produces small buds whose tips become cut off by septa and form unicellular spore-sacs called asct. ‘‘The young ascus has at first two nuclei. These fuse together, and then by a process of free cell formation eight ascospores are formed inside the ascus”’ (Lowson). (Fig. 12.) Here we have a sudden change to a higher form of Continuity within the Individual, and it is to be noted that it occurs in connection with reproduction. A more striking case is that of Agaricus campestris, the common mushroom, where from the fine loosely matted THE CQ@NOCYTIC INDIVIDUAL 65 mycelium of the “spawn” there arises the so-called *‘ conidiophore,” or the part commonly called the mushroom. This is a stiff cylindrical column of many hyphe closely woven together, and these spread out to form the umbrella- like top, and terminate on the radiating gills on its under surface. It is true that Agaricus is commonly held by botanists lamsilae Hyminial layer Sushyminio m- Paraphys.is ™m Fic. 13.—Agaricus. 4, conidiophore with velum torn, showing lamella or gills. 8, section through one of lamella; enlarged. ©, marginal cells of lamella; further enlarged. (After Lowson.) to be so debased that it has lost all powers of sexual reproduc- tion, and can only reproduce itself vegetatively by the spores which fall from the gills of the conidiophore ; but it is our belief that such perpetual vegetative “reproduction” is impossible. For all cycles must end, and before the spores are formed there must occur a sexual act of some kind. No doubt this will be yet discovered, but it seems quite possible 5 66 THE EVOLUTION OF CONTINUITY that an act of nuclear fusion in the terminal basidiwm on the mushroom’s gill which occurs just before the formation of the spores is a sexual act. This view will without doubt be contested, but it is pertinent to ask, What other significance can nuclear fusion have? Why should the nuclei of two protoplasts fuse together, if the protoplasts are not terminal elements of the cycle 2 The whole principle of Individual growth is cell and nuclear division through which elements capable of fusion are restored or reproduced. If the reader refers again to the description of the fertilisation process in Eurotium he will see that here also there is a nuclear fusion in the young ascus, and the question arises, Is not this the true conjugation act here, and are not the ascogenous branches or buds pre- fertilisation phenomena? According to the quoted descrip- tion there is first gamete-fusion, then protoplast division, and then fusion again; a difficult sequence to comprehend. It might well be that the ascogenous buds contain the female gametes, and that the ascus contains the male and female gametes which lie together for a while before fusing. Our belief in any case is that the formation of false tissue is essentially concerned with sexual reproduction; and it may be remarked that “terminal compression” in the shape of the multiplication of preceding vegetative continuity has clearly this significance in higher types of organism, as will be shown when we come to treat of certain Hydrozoa and Phanerogams. CHAPTER VII BACTERIA Ir is necessary here to interpose a few remarks about a large Individual class whose characters are somewhat peculiar in that while the general habit is discontinuously multi- cellular, at times it is filamentous, or, possibly, ccenocytic. This class comprises what are known as Bacteria. It is to be noted, however, that the term is not used here in the wide sense in which it is sometimes applied. Bacteria are sometimes divided into the Lower and Higher Bacteria, the former including the free unicellular microorganisms such as micrococci, bacilli, or spirilla, and the latter, filamentous or ccenocytic growths such as, for example, the Ray Fungus. But as our present purpose deals with types of living Continuity, and as truly ceenocytic Individuals form a type by themselves, we confine the term “ bacterium ” solely to the unicellular microorganism. While a bacterium is essentially a unicellular organism, it does not follow that the common belief is true, namely, that it is a unicellular Individual ; or that when a bacterium divides it reproduces itself. It is indeed quite possible that the bacterial Individual is multicellular, and certain microbic growth-phenomena distinctly suggest this. It is common knowledge that while certain types of bacteria habitually multiply in discontinuity, each germ being free and independent, others tend if undisturbed to form con- tinuous bacterial series; to develop, in fact, as bacterial filaments (Fig. 14). te aed ae A. ya Fie. 14.—Examples of bacterial filament. a, streptococcal chain; 8B, anthrax beeillua “ filament.” 68 THE EVOLUTION OF CONTINUITY Sometimes there are all the appearances of filamentous branching (Fig. 15). In the figure below, the long bacillus with which the lowest branch commences is to be noted, and the suggestion it offers of the multiplication of filamentous into cceno- cytic continuity. The long bacillus might be really several bacillary protoplasts within one envelope. It is such long forms, chiefly observed in old cultures, which seem to link up the “lower” with the “higher” bacteria. They are usually termed “involution forms ” and regarded as degener- Fia. 15.—Bacillary growth from the urine of a case of bacilluria due to bacillus coli, and where under treatment the infection was disappearing. (Greatly magnified.) ative in nature, but under the term are included many peculiar bacterial shapes of distinctly different kinds, and probably of different significance, and it is questionable if degeneration is reflected in most cases, Thus the “ involution form ” of the plague bacillus is an oval, swollen, pale structure, very different from that of the typhoid bacillus, which is like a short thin mould hypha. There seems a probability that the latter form reflects not degeneration, but the imposition of Continuity, and that, far from being one overgrown bacillus, it is equivalent to a series of bacillary protoplasts enclosed in one envelope, and not separated from each other by transverse partitions. The reverse phenomenon would be that exhibited by Mucor mucedo (page 62) when BACTERIA 69 it adopts a bacillary habit and grows as chains of separate cells—the ‘‘torula ” condition. Following up this idea, we might imagine the presumed bacillary ccenocyte to be of growth-cycle significance, for it appears to be the rule that an increase of Continuity within the Individual is an indication of the approaching formation of sexual elements. This is clearly the case in the higher Fungi, and will be shown to be equally so in the case of Continuously Zooidal Individuals. It is true that the “lower” bacteria have not been observed to produce gametes, but that is no real objection to the supposition. It is the minute size of bacteria which makes them difficult to study, and as size after all is com- parative, the typhoid bacillus may well be as complex as the motile Chlamydomonas Alga cell, which it distinctly resembles, or the anthrax bacillus be on a level with the cell of the Spirogyra filament. Further, bacteria are known to produce “‘spores” at times. That is, they either become arrested and more resistent and assume a ‘‘resting-spore’’ condition, or what is called an “‘ endogenous ”’ spore is formed within the bacterial membrane. A spore is always due to environmental hostility in some form, and it is difficult to think otherwise than that in Bacteria the phenomenon is one of arrest on a road leading to gamete-formation through an immense bacterial product. CHAPTER VIII THE DISCONTINUOUSLY ZOOIDAL INDIVIDUAL TuE class of Individual now to be considered is probably the true successor to the Filamentous in the main road of Continuity’s evolution; the sequence so far being Dis- continuously Multicellular, Filamentous, Discontinuously Zooidal. It is as if we started with many separate beads, then united these in a single series, and next united many single series together in lateral continuity to form separate bead-masses on a given plan. Nature has not, of course, actually worked with already formed cells or cell-series, but, as will be shown elsewhere, has moulded the developing product of the zygote, resulting from a sexual act, on a new plan of Continuity. Thus, a zygote whose product would have been many discontinuous cells was obliged to produce this product in the form of a continuous filament, and a zygote with potential filamentous development has been obliged to have this realised as discontinuously zooidal development, at different times in past ages. The free zooid is a true multiple of the free cell, and the filament has been a necessary link between the two. In the filament we have serzal continuity of cells, in the zooid we have lateral continuity of cell-series. In the next type of Individual we shall see that we have the serial continuity of zooids, and as we go farther on the regular alternation of serial with lateral continuity will be clearly apparent. Thus, to repeat, while the Discontinuously Multicellular Individual is composed of separate, free cells, the Discon- tinuously Zooidal is composed of separate, free organisms made up of many cells closely united together. These organisms are in no sense cell-colonies, but possess real tissue-continuity, and sh cell performs a function 0 THE DISCONTINUOUSLY ZOOIDAL 71 for the organism of which it is a part, and which itself, though only part of an Individual, enjoys a free and independent existence. There are, however, Individual types, composed of many separate multicellular organisms, to whom the term “ dis- continuously zooidal’’ is not applicable; the reason being that in these cases the component organisms are not “‘ zooids,”’ but more complex than these, representing compressed zooid- multiples. For a ‘‘zooid’’ has a narrower definition than a living multicellular organism, part of an Individual. It is truly such an organism, but one built on a special and simple plan, being essentially a little cylindrical tube open at one end, whose walls are composed of two layers of cells. It represents the simplest form of multicellular organism in Nature composed of true tissue. So, from now onwards, “zooid’”’ and “ zooidal”’ will be used to indicate a special form of cellular continuity and a special structural plan, such as exhibited by the freshwater polypite, Hydra, which has been taken as our illustrative type. HypRa. The common Hydra is a minute little animal which is found with frequency in the water of ditches. In structure it is a tiny hollow cylinder of living tissue of a third or a quarter of an inch in length when its body is extended. At one end the cylindrical body is closed and a circular disc enables the organism to attach itself to twigs or other objects ; but at the other, the distal end, the cavity of the tubular body communicates directly with the surrounding water by an opening which is called the mouth and is provided with marginal tentacles. These are hollow and in communication with the body-cavity or ‘‘ccelenteron,” and being extensile and retractile, it is by their means that the little animal seizes its prey. The tissues of the Hydra zooid are on the whole adapted to simple functions, consisting largely of an outer layer of cells called the ectoderm, and an inner layer, the endoderm. Between these lies a very fine structureless layer or membrane called the mesoglea. At the same time there is wonderful cell-specialisation in the presence of stinging thread-cells here 72 THE EVOLUTION OF CONTINUITY and there in the ectoderm of the tentacles, the function doubtless being the paralysing of any prey seized; and there is also a very primitive communicating ‘‘ nervous system ”’ represented by small stellate cells whose branching processes communicate, and keep one part of the body in touch with the others. These nerve-cells lie between the ectoderm and endoderm. The Hydra zooid is only a part of the Hydra Individual, and during the Summer produces other zooids similar to itself by a process of budding or “‘gemmation.” The Fic. 16.—1. General plan of Hydra zooid, showing the cell- layers, and the production of a daughter-zooid by gemma- tion. The testis and ovary are also represented, though when these were present there would be no _ gemmation. ec, ectoderm; en, endoderm; ¢, tentacles; c, body-cavity ; d, disc of attachment ; g, developing budded zooid ; ta, testis; ov, ovary. (Partly after Shipley and MacBride.) 2. Hydra vulgaris, with several budded zooids about to be detached. (Nicholson.) budded zooid originates as a little protrusion of the body-wall enclosing a small diverticulum of the producing zooid’s body-cavity. It gradually elongates, a mouth opens at its distal end, tentacles arise around the mouth, and finally the new zooid becomes detached and is free to lead an in dependentexistence and to bud like its producer. But at the commencement of Winter this discontinuous gemmation ceases, and the zooids form sexual elements. These are male and female, the former being produced in numbers THE DISCONTINUOUSLY ZOOIDAL 73 by the ectoderm at a point near the distal end of the zooid in a little excrescence called the “‘ testis,’’ while the latter usually appear as a single ovum in a little sac nearer the proximal end of the zooid. Both spermatozoa and ovum are set free in the water and fertilisation occurs in this medium. The fertilised ovum lies in the mud till the return of warmer weather, when it proceeds to become the first zooid of a new Individual. The formation of a new zooid by gemmation is an act of production, not of reproduction, for the zooid is a part of, or a stage in the development of the Individual ; and while in a budded zooid there is a reproduction of structural plan, our belief is that each zooid represents a cyclic advance on its producer. We might say that the budded zooid carries on the cycle from where its producer temporarily halted, or that as each vegetative cell of the discontinuously multi- cellular Individual is a stage on the road towards the end of the cycle, so in a sense is each budded zooid, in a straight line of ‘‘ descent.’’ The compensation for the discontinuity of any growth-unit is the power of carrying the cycle to the end, or of becoming sexual, and thus each Zooid of the Hydra Individual should under favourable conditions attain to sex. But, on the other hand, the price of Continuity is Arrest, and thus it is that the great majority of the cells composing the zooid never become sexual, in their ‘‘ descend- ants ’’; they live not for themselves, but for the good of the zooid as a whole, and their arrest enables the zooid to persist and retain its identity. In Hydra only a certain number of cell-lines are allowed to terminate, and to do this along an interrupted path. And it is not unreasonable to suppose that it is through the cell- division involved in repeated gemmation that certain areas of a zooid finally produce sexual elements. For, in the first place, it is only through cell-growth, division, and multiplication, that sexual elements can ever appear in any cycle whatsoever. Again, nowhere, after zooidal maturity is reached, does repeated cell-division occur except at gemmation areas ; elsewhere there is cell-arrest. The natural conclusion one tends to arrive at is :— I. That a given zooid has to bud others in order to become 74 THE EVOLUTION OF CONTINUITY sexual; the number depending on the “stage” the zooid represents in the cycle. II. That the zooid’s sexual organs will finally appear in what we have called gemmation-areas. It is probable, how- ever, that gemmation is carried on with special frequency at two such areas. The interesting fact, that if a Hydra zooid be cut in pieces each piece grows to form a new and perfect zooid, illustrates well the law that whereas Continuity produces Arrest, Discontinuity produces Release from Arrest. The matter is one of breach of Continuity, and the artificial Fie. 17.—Possible zooidal progressive diminution a, an initial or intermediate zooid originates B; 8B originates c, and so on, till the line ends with the sexual zooid at r. The suc- cessive primary side-lines arising from the main line are repre- sented as progressively diminishing by one zooid. release from cell-arrest. Continuity being severed, the cells exposed are released to multiply till the parts lacking from the original zooidal plan are restored. It is also to be noted that “alternation of generations ” is exhibited in the Hydra cycle. There is cellular alternation in that asexual cells appear, and remain, as stages on the road to the final exhibition of sexual cells; and there is zooidal alternation in that temporarily asexual zooids become sexual in the end, and in this sense alternate with sexual zooids. It may be objected that this is not alternation of generations in the true sense, as for example in the case of the Hydrozoal colony, but in reality the cases are the same, the striking picture presented by the colony being the result of zooidal Continuity and Arrest. As, however, we shall THE DISCONTINUOUSLY ZOOIDAL 75 return to this in a later chapter, we shall not dwell further on it for the present. The question of space also prevents us from doing more than suggesting that the progressive diminution of the length of lines of cell-descent in the Discontinuously Multi- cellular Individual should find expression in cycles like that of Hydra’s (see page 47). One aspect of this is suggested in Fig. 17. We may close this chapter by recapitulating our theory of Continuity’s evolution up to the Individual type just considered. Our first Individual type was the Discontinuously Multi- cellular, and might be represented as o 0 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 0 Our second type was the Filamentous, and exhibited the simplest form of SzRIAL continuity, as in the next diagram :— In the type last considered the serial continuity of the fila- ment is as it were multiplied into the LaTERAL continuity of the independent zooid’s tissues, so that the preceding diagram becomes Thus we have our first exhibition of the alternation of Serial with Lateral Continuity in the evolution of living Individual growth-types. But it must not be supposed that Evolution has been through any existing Individuals manifesting the above forms of Continuity, for all these Individuals are at the most advanced points of ‘ species ”’ side-paths ; what is to be understood is that the main road of 76 THE EVOLUTION OF CONTINUITY Evolution has developed through a progressive intensification of Continuity similar to that which the illustrative examples given manifest. In other words, the main road of Evolution has passed through a primitive Discontinuously Multicellular to a primitive Filamentous and on to a primitive Dis- continuously Zooidal type, all of which were “‘ evanescent ”’ ; and every living species has evolved within a given type of Continuity. CHAPTER IX THE CONTINUOUSLY ZOOIDAL INDIVIDUAL Tuis type of Individual differs from the one last considered in that its component zooids, when budded, remain attached to each other, the Individual thus taking the form of a branching zooidal “‘colony.’’ In fact, it demonstrates for us the next inevitable step in the evolution of living Continuity. This may be illustrated by the addition of one more diagram to those given on page 75. d. core og Ee ES Fig. 18.—Diagram of Continuity’s evolution up to the Continuously Zooidal Individual. "eno In the figure above, A is the Discontinuously Multicellular Individual; each cell an independent organism. B is the Filamentous Individual whose cells are united in linear or Serial continuity. C is the Discontinuously Zooidal Individual in whom the equivalents of cell-series or filaments are united in Lateral continuity to form the tissues of dis- continuous and independent organisms, the zooids. D is the Continuously Zooidal Individual in whom, we may say, the separate zooids of C have been obliged to develop in Serial continuity. In other words, the discontinuity of A is “ multiplied ” into the serial continuity of B, which in turn is multiplied 78 THE EVOLUTION OF CONTINUITY into the lateral continuity of C. But it is to be noted that this is cellular continuity, and that in C the cellular discontinuity of A reappears as the discontinuity of the cell-multiple or zooid; and thus the next step in D is the evolution of serial zooidal continuity. We might say that as B is a cell-filament, so is D a zooidal filament. So it is that we can recognise in the figure an alternation of Dis- continuity with Continuity, as well as (in B,C,D) an alternation of serial with lateral continuity. We shall see that this alternation holds true for our next Continuity-type. It has already been put forward as a law that Con- tinuity Produces Arrest; and an outstanding feature of Continuously Zooidal Individuals is zooidal arrest. As the development of cells in serial continuity to make a filament or ‘‘ cell-colony ”’ entails cell-arrest, so does the development of zooids in series to form a zooidal colony entail zooidal arrest. In the discontinuous Hydra, when one zooid has budded another this is set free, and the gemmation area involved may commence straightway to bud again; but in the Con- tinuously Zooidal Individual, when one zooid has budded another the gemmation area involved is arrested for a con- siderable time, and it may be permanently. For the budded zooid remains attached, and it is by it that the next act of gemmation is performed, after which arrest is again imposed and further gemmation must come from the zooid last produced. Thus, as regards a given series, the process goes on till the end is reached with the production of a sexual zooid. At the same time the phenomenon of release from zooidal arrest is not uncommon, and a given gemmation area may later give rise to a second zooidal series. Perhaps the best examples of this are provided by flowering plants and trees (whose derivation, it can be shown, is clearly continuously zooidal, their special characters being the result of change to an aerial environment). In these organ- isms, where the stem or branch internode, or ‘‘ segment,” represents the ancestral zooid, a given budding-area may give rise to one branch only, or at considerable intervals of time originate several others, especially if encouragement is given by such procedures as pruning, heavy manuring, etc. Naturally, great variation in branching habit is exhibited by existing Continuously Zooidal Individuals, but on the THE CONTINUOUSLY ZOOIDAL 79 whole it may be said that zooidal continuity implies zooidal arrest. On the presumption that the growth-cycle advances on through the successive zooids of a series, it is clear that sooner or later sexual zooids, or ones in whom certain cell- cycles terminate, must be produced, and when this has occurred the growing Individual will offer the picture of a branching colony composed of two classes of zooids, one apparently devoted solely to nutritional and supporting functions, and the other to reproduction. It was this picture which gave to such zooidal colonies the special credit of exhibiting ‘‘ alternation of generations.”’ But the truth is that this phenomenon, in its proper wide sense, is exhibited in all living Individuals. Every intermediate zooid in a colony starts life, so to speak, with the intention of becoming sexual, and the fact that many cells and many zooids are permanently arrested and modified and never attain to sex does not affect the true significance of the “alternation of generations.” Fundamentally, it is Arrest, the product of Continuity, which brings it about that the Continuously Zooidal Individual gives a permanent exhibition of two kinds of zooids. If we look around for examples of Continuously Zooidal Individual we find them in considerable variety amongst the Hydrozoa—one of the two classes into which the Ceelen- terata are divided. All the Hydrozoa are not Continuously Zooidal Individuals, but those to whom the term is applicable are plant-like organisms inhabiting usually salt and rarely fresh water, and composed of many distinct zooids united by a branching framework, or ‘‘ ccenosare,”’ to form a zooidal colony. While we may regard the typical growth habit as essentially equivalent to what Hydra would exhibit were its budded zooids to remain attached to each other, and while we may hazard the guess that the original primitive Continuously Zooidal type presented this appearance, the Hydrozoal colony of present and recent times produces its zooids not directly from other zooids but from the hollow tubular framework just mentioned. The significance of the cosnosare is, however, very probably as roughly represented in the next diagram (Fig. 19); that is, it may be taken to represent the extension and narrowing of the basal or 80 THE EVOLUTION OF CONTINUITY proximal parts of ancestral zooids. Thus, in Fig. 19, A shows three zooids of Hydra type remaining in continuity, while B shows them as having developed narrow tubular connection with their producers. It is from the narrow con- nections that we presume gemmation habitually occurred in the primitive types, as it is from the ccenosarc that new zooids are budded in modern hydrozoal colonies. Such zooids as roughly drawn below are what is termed vegetative zooids; from their walls, as distinct from the connecting ccenosarc, they never bud other zooids, nor do they form sexual elements. Cyclically, they remain per- manently arrested, and the growth-cycle advances to its Fia. 19.—Suggested significance of the Hydrozoal colony’s ccenosare. z, zooids 3 eC, ectoderm; en, endoderm; ¢, tentacles ; b, body-cavity ; c, cenosarc ; xX, gemmation-areas. termination through ccenosarc gemmation, with the result that from some distal portion of the ccenosarc a sexual zooid ultimately appears. Naturally from any part of the ccenosare gemmation may take place and finally result in the pro- duction of sexua] zooids. There are several subclasses of Hydrozoa, and many orders in these, for an account of which the reader is referred to biological textbooks, but for our present purpose the general plan of Continuously Zooidal growth may be taken as is represented above in Fig. 19, B. It is to be emphasised that all Hydrozoa are not Continuously Zooidal Individuals. For example, Hydra is THE CONTINUOUSLY ZOOIDAL 8] zooidal but discontinuous. And there are even objections to classifying all Hydrozoal colonies as Continuously Zooidal ; for there are numerous examples which, while they may be so described as regards their vegetative or asexual structure, nevertheless manifest a higher form of Continuity in their sexual parts. Some Hydrozoal colonies are zooidal through- out, and their sexual organs are just zooids specially adapted for producing sexual elements, and in these types the whole colony may be said to exhibit Serial Zooidal Continuity. But there are others which, while serially zooidal in vegetative structure, exhibit in their sexual structure a “‘ multiplication ”’ of the serial into Lateral Continuity, with the result that the Individual is partly zooidal and partly ‘“‘ megazooidal.” This is a new term to be explained presently when we come to Individuals which are wholly ‘“‘ megazooidal,” but it may be said here that the sexual megazooid of Hydrozoa is another example of the “‘ terminal compression ’’ connected with reproduction. It has already been mentioned in the case of the higher Fungi, where it results in the production of “false tissue.’ Just as the Continuity of the false tissue is a multiplication of that of the loose mycelium, so is the sexual megazooid’s a multiplication of zooidal Continuity. It may also be remarked that amongst Hydrozoa there are commonly included the large Individual Meduse, or Jelly- fish, which directly reproduce themselves as Medusze. These are not in any sense Continuously Zooidal Individuals ; they are wholly Megazooidal. CHAPTER X MEGAZOOIDAL INDIVIDUALS. THE MONO- MEGAZOOIDAL INDIVIDUALS WE may begin this chapter with a summary of the stages of the evolution of living Continuity up to Megazooidal Individuals :— 1. In the independent unicellular organism of the Discontinuous Multicellular Individual there is, we may say, Protoplasmic Continuity. 2. In the Filamentous Individual there is a multiplica- tion of this Continuity in the attachment of single cells in linear series. There is little doubt that the main road of Evolution has passed through a primitive form of Filamentous Con- tinuity. It is equally probable, however, that it did not pass thence through any primitive Coenocytic type. For though the Coenocytic Individual has most likely evolved from some early polyprotoplastic type, its evolution has been along a side-path which has stopped dead at the false tissue of the higher Fungi. 3. Thus, passing on from Filamentous, or true cell- serial Continuity, we come to true Lateral Continuity, where the equivalents of many cell-series are compressed together in lateral Continuity to form the tissues of inde- pendent multicellular organisms. These organisms are developed typically on a simple plan, and we have reserved for them the name of “zooids.”’ In its simplest form the zooid is a little cylindrical tube, open at the distal end, and composed of two cell-layers; and when it leads an independent existence it forms part of the Discontinuously Zooidal Individual. It is this which represents our third stage, the independent “‘cell”’ of the first stage being here a continuous cell-multiple ; or it might be said that the MEGAZOOIDAL INDIVIDUALS 83 protoplasmic Continuity of stage 1 is multiplied into the cellular Continuity of the free zooid. 4, The next multiplication of Continuity exhibits itself serially. That is, we have the discontinuous zooids of stage 3 joined together in series to make the Continuously Zooidal Individual. Each zooid here is, as it were, a multiple of the cell of the Filamentous Individual: growth is in the form of a branching “ zooidal filament.” 5. In what we have termed the ‘‘ Megazooidal Individual ” Continuity is still further multiplied, and in a manner bearing out the previous statement that the evolution of living Continuity has proceeded by Serial and Lateral Alternation. For there are two main classes of Megazooidal Individual, one of which is represented by (1) Many discontinuous organisms, each equivalent to a number of zooids fused together in Lateral Continuity during development ; while the other is composed of (2) A number of such organisms, or many megazooids, joined in Serial Continuity. In both cases the megazooid represents an ancestral zooidal multiple compressed in its development, or during its attempts at realisation on the ancestral plan. In addi- tion to the two classes mentioned there is a third, in which the whole individual is represented by (3) One large megazooid. In other words, we have first of all separate cells; then serial cell-Continuity to form a filament or “cell-colony ” ; then cell-series growing in lateral Continuity to form the independent zooid; then a number of zooids united in serial Continuity to form a zooidal colony ; then a number of zooidal series fused or compressed in lateral Continuity to form the separate megazooid; and then a number of megazooids united in serial Continuity to form a mega- zooidal colony. 2 Although the intensification of Continuity has been traced above from the independent protoplast, it is to be understood that this itself must be a very high multiple of the ultimate growth-unit. The Continuity of the cell is a great advance on that of the atom. Under “The Evolution of Matter’ this is again referred to. 84 THE EVOLUTION OF CONTINUITY Megazooidal Individuals may be classed as follows :— (1) The Mono-megazooidal Individual, of which our examples are the Sea-anemone and the Indi- vidual Medusa or Jellyfish (there are jellyfish which are not Individuals). (2) The Discontinuously Megazooidal Individual, the example taken being one of the Acraspeda. (3) The Continuously Megazooidal Individual, exem- plified by the Compound Corals generally. Fie. 20.—Diagram of the evolution of living Continuity, beginning with the separate cell and stopping at the mega- zooidal colony. a, a free protoplast; 6, a cell-filament, a multiple of @ in serial Continuity; c, the Continuity of 6 multiplied into the lateral Continuity of the discontinuous zooid; d, zooidal serial Continuity; e, the free megazooid, equivalent to a number of zooids compressed in lateral Con- tinuity; ¥F, megazooidal serial Continuity. The figures are very diagrammatic. We shall begin by considering the Sea-anemone and the Medusa. THe MoNO-MEGAZOOIDAL INDIVIDUAL OF SEA-ANEMONE TYPE. The general appearance of the Sea-anemone is familiar to everyone. When its tentacles are extruded, the little animal has the form of a short broad cylinder. The mouth is a contractile opening centrally placed in the circular surface of the upper or distal end, while marginally placed are numerous strong tentacles in several rows. The base MEGAZOOIDAL INDIVIDUALS 85 of the body acts as a disc of attachment, muscular con- traction holding the organism fast to a submarine rock or shell. When the tentacles are wholly withdrawn the anemone has more the shape of a little bun, a cleft at summit indicating the region of the mouth (Fig. 21, a, b,c). Externally the Sea-anemone has the appearance of a large zooid, but its internal structure reveals no zooidal simplicity. The mouth does not lead into a simple body- cavity as in Hydra, but into an cesophagus or gullet. This passes downwards as a centrally placed tube half-way towards the base of the body, its lower end opening into a wide space, called the stomach, which in turn is in open com- munication with a number of chambers radially situated between the central esophagus and the body-wall. The Fic. 21.—Actinia mesembryanthemum (tigrina), &@ common sea-anemone. a, with tentacles half-extruded; 6, with them fully extruded, and mouth visible ; c, with tentacles withdrawn. chambers are separated from each other by vertical septa, or ‘ mesenteries,” which pass from the body-wall of the anemone to the csophageal tube, from the lower end of which they are continued downwards and outwards to the base of the stomach (Fig. 22). As in Hydra, there is an outer cell-layer of ectoderm, and an inner of endoderm, the latter lining the stomach and intermesenteric chambers. The gullet is lined with ectoderm (Fig. 22, A, B). Between these layers there is the connective tissue ‘‘ mesoderm.’ Underneath the ecto- derm there is also a layer of ganglionic nerve-cells and nerve fibres, which in lesser degree are present as well at the base of the endoderm. Certain of the septa are pro- vided with longitudinal muscles, and it is on the free edges 86 THE EVOLUTION OF CONTINUITY of the mesenteries that the reproductive organs are formed. The number of septa varies in different types of sea-anemone, though twelve is a common one—this statement referring to the “‘complete”’ septa which form the chambers; but “incomplete” septa are also present (Fig. 23, A) which do not stretch across to meet the esophagus. The chambers of the sea-anemone are roofed over by a continuation of the cell-layers of the body-wall, but fine pores in the septa allow a measure of direct communication. The endoderm lining the chambers is well provided with cilia which main- tain a circulation of the body contents. One sea-anemone, unless very rarely, comprises the whole Individual, and Fie. 22.—a, diagrammatic vertical section of sea-anemone drawn so as to show relations of cesophagus, stomach, septa, and mesenteries. ¢, tentacles: m, mouth; o, cesophagus ; 3, stomach; p, septa; and f, mesenteries. 8. transverse section at level of cesophagus. c, similar section below the level of the lower end of the gullet. ec, ectoderm; en, endo- derm; me, mesoderm; o, cesophagus; ic, interseptal chambers ; f, edges of mesenteries. produces, multiply be it noted, both male and female sexual organs. Possibly these few facts regarding the structure of the Sea-anemone have already enabled the reader to recognise in the organism the multiplication of Continuously Zooidal Continuity, and that its structural plan is the logical sequel, in the ascending scale of Continuity, to that of the Con- tinuously Zooidal Individual. The cross-section of Adamsia, in Fig. 23, shows dis- MEGAZOOIDAL INDIVIDUALS 87 tinctly a plan essentially equivalent to that of a continuous “circular ’’ series of tubular zooids whose body-walls are at times in close apposition, and at others incompletely developed. While centrally placed in the circular series, and supported by the best developed ‘“‘ zooidal*’ walls, is the short cesophagus, representing undoubtedly part of the “main-stem”’ of an ancestral branching zooidal system (Fig. 23, A). C7773 Fic. 23.—a, transverse section of a sea-anemone (Adamsia), slightly altered from O. and R. Hertwig. ec, the ectoderm (cross- shaded) ; 1, the mesodermal layer of connective-tissue (shaded dark); en, the endoderm (unshaded); Im, cross-section of one of the longitudinal septal muscles; s, cesophagus. B, a segment of the body of a sea-anemone (Cereus), traversing the column from the top to the disc (after R. Hertwig): 6, disc; #, tentacles: @, cesophagus hanging downwards; r, r, repro- ductive organs attached to the faces of the mesenteries, (After Nicholson.) As a help to make clear the nature of the Sea-anemones’ Continuity let us take the following illustration, admittedly a fanciful one, but, considering that evolutionary com- pression has been literally a physical compression during development, not so extravagant as it might at first appear to be. Let us picture a primitive Continuously Zooidal Indi- vidual to be modelled in wax, with its main-stem and 88 THE EVOLUTION OF CONTINUITY lateral branches formed as hollow tubes directly communi- eating with each other, and the branches arising from the stem in a spiral at regular intervals as in phanerogams. If we could soften and at the same time compress the main- stem so as to produce a short wide cylinder in place of the long series of narrow cylinders, or wax “‘ zooids ’? composing its length, and if we could simultaneously apply the same process to the branches, we would produce results some- what like those drawn in the figure below (Fig. 24). That \ A. e Fic. 24,—Diagram illustrating the probable derivation of the Sea-anemone’s structural plan. a, hollow tubular con- tinuously zooidal system of main-stem and branches. 8B, the result obtained by steady, even, serial and lateral compres- sion in the experiment already mentioned. c, a vertical section showing how the compressed branches would com- municate basally with the central cylinder. The top, or cap of the central cylinder would require to be removed to form the mouth. is, we would have a central short cylinder with a ring of others springing from the region of its base, and directly communicating with it in this region. And if even, lateral, compression were exercised during the process the ring of short cylinders would form a closely fitting circular series around the central tube, and give us a wax model of the fundamental plan of the Sea-anemone. The central cylinder would represent the csophagus, whose walls would end abruptly where there was communi- cation with the lateral cylinders; that is, below the esophagus there would be a wide cavity bounded by MEGAZOOIDAL INDIVIDUALS 89 the external walls of the lateral cylinders and by the base of the central one. This would represent the stomach. The hollow interiors of the surrounding cylinders would repre- sent the intermesenteric chambers, and their contiguous walls would form the principal septa radiating from the esophagus of the experimental megazooid (Fig. 25). But the illustration of the wax model must not be taken too literally, for the compressed form and lateral Continuity of the earliest megazooid of Sea-anemone type must have evolved from the first development of a fertilised ovum of some primitive Continuously Zooidal type. This ovum must have had Continuously Zooidal potentialities, and these must have been modified (if we may so express it) as they strove to express themselves. In the evolution of the Fig. 25.—The evolutionary significance of the oesophagus (0), stomach (s), septa (sp), and intermesenteric chambers (ic), of the Sea-anemone. Sea-anemone type of megazooid there has been no com- pression of Continuously Zooidal structure already developed, such as has been pictured above ; but, bearing this in mind, we may be allowed to use the illustration. Consistently with the derivation of the Sea-anemone which has been offered, and the identification of the inter- mesenteric chambers with ancestral zooidal body-cavities, we expect to find that when sexual organs are formed they will reflect zooidal repetition. And we are not disap- pointed. The reproductive organs are multiple, and are placed on the face of the mesenteries. That is, each recog- nisable “tube ’’ of the megazooid produces its own sexual organs, ani this fact, alone, indicates clearly that the evolution of the Sea-anemone has been on the general lines 90 THE EVOLUTION OF CONTINUITY suggested. The megazooidal plan is clearly based on ancestral zooidal repetition (Fig. 26). The Sea-anemone is an Individual. It represents all the (realisable) product of the fertilised ovum, and does not produce other megazooids by gemmation or fission, and the theory we have to offer is that the organism represents the compression in lateral Continuity, in past ages, and during development, of some primitive Continuously Zooidal Indi- vidual type. That Environment in certain of its most powerful aspects has all along striven to compress serial into lateral Continuity is perfectly clear, and in later A B Fic. 26.—Diagram explaining the repetition of the sexual organs of the Sea-anemone. a, cross-section of a ring of zooids compressed round a centra’ stem; the section passing through the reproductive organs of the zooids, which are pre- sumed to be formed at a constant spot on the internal walls. On the supposition that the contiguous walls of the surround- ing zooids have gone to form the septa of the anemone-mega- zooid, we can see how a result such as pictured in B could take place, the sexual organs appearing on the free edges of the mesenteries. chapters we shall try to show what these aspects are. But from an examination of its structure, alone, we can hardly doubt that the Sea-anemone has been derived from a Continuously Zooidal ancestry. The anemonoid megazooid has not been a milestone on the road which passed on to the highest vertebrates. It represents a divergence from the main road, and one which came to a sudden stop. On the other hand, the megazooid of medusa type, about to be considered, has a structural plan which must closely resemble that of the primitive MEGAZOOIDAL INDIVIDUALS 91 megazooid from which was derived the vertebrate segment. It is in the medusoid plan that the origin of the ‘‘ celom ” of higher types can be recognised. THE MEDUSIFORM MEGAZOOID. To the casual observer there would seem to be few resemblances between a jellyfish and a sea-anemone, but the fact remains that in both cases the structural plan is mega- zooidal and originally of Continuously Zooidal derivation. How then are the divergences in form and habit to be explained ? The truth is that the differences depend on the different types of ancestral zooids which have been compressed in lateral Continuity. In the case of the sea-anemone the ancestral zooids have clearly been of typical cylindrical, tubular, or “ vegetative ’’ form, while in that of the jellyfish they have been of a structure whose characters reflected special adaptation for the function of reproduction. Here lies the whole crux of the matter, and it is of the greatest importance to grasp clearly the distinction just mentioned, as in no other way can we satisfactorily ex- plain the evolution of invertebrate and also vertebrate Segmental organisms. But here a few words of explanation are necessary. The present chapter deals with Megazooidal Individuals, and we have now to consider the Mono-megazooidal of medusiform or jellyfish type ; but to do so it is necessary to hark back to the Continuously Zooidal Individual, for it is only through the reproductive structure of the zooidal colony that the derivation of the medusiform megazooid can be made clear. As was stated on page 81, many marine zooidal colonies are zooidal throughout, the sexual elements being produced by structures which, though quite unlike the vegetative zooids in appearance, are zooids adapted for reproduction. But there are others in whom the sexual zooid is represented by a sexual megazooid of medusoid or jellyfish form in a state of imperfection or perfection, and in whom the Indi- vidual is partly zooidal and partly megazooidal. In certain colonies these sexual medusoids, or ‘‘ gonophores,” become 92 THE EVOLUTION OF CONTINUITY separated to lead an independent existence and grow into large jellyfish which fertilise their own ova and originate new sessile zooidal colonies; but such medusoids are, of course, not megazooidal Individuals. Apart, however, from matters of structural detail the plans of the gonophore and of the Individual Medusa are the same, and this is also true of their derivation. It is to be understood that the immediately following remarks deal with medusiform mega- zooids which are parts of Continuously Zooidal Individuals, and which offer themselves as links between the latter and Individual Medusz. THe EvotutTion or SzexvuaL STRUCTURE IN MaRINE ZOOIDAL COLONIES. In these colonies the fundamental vegetative structure is the tubular zooid, and this, specially adapted and altered, 4 a. en A. Fic. 27.—a, diagram of Hydrozoal sporosac. a, central hollow protrusion of the colonial ‘‘ body-cavity”; ec, ecto- derm; en, endoderm; «, sexual elements. 3B, diagram of a vegetative zooid for comparison. a is for all purposes like a B which has failed to form a mouth, and instead has formed sexual elements in its walls. is the basis of the various sexual structures exhibited. In its simplest form the sexual structure of the colony takes the form of a zooid which is not tubular nor possessed of a mouth leading to a body-cavity, but which has a globular form, has no external opening, and forms in the walls enclosing a blind protrusion of its producer’s somatic cavity the sexual elements. This special sexual zooid is termed a “ sporosac ”” (Fig. 27). From some primitive Hydrozoal type which produced MEGAZOOIDAL INDIVIDUALS 93 separate sporosacs a new type clearly evolved in which the successive sporosacs on a sexual branch suffered sufficient terminal compression during their development to form what is known as a “ gonoblastidium,” or a spray of sporosacs arising close to each other from a sexual stem, and enclosed in a capsule. This, in reality a manifestation of the intensi- fication of Continuity, is the form of sexual apparatus borne by certain Hydrozoa of the present time, and is diagram- matically represented in the next figure. lm = SS E p = ex es o= = \ Fie. 28.—Diagram of the sporosac-gonoblastidium of the Hydrozoal colony. But terminal compression had still further work to do, and by acting on some primitive sporosac-gonoblastidium (as this developed) it produced the medusiform gonophore. Elongation of the gonoblastidium stem bearing the sporosacs was not allowed to take place, but serial and lateral compression treated the whole system, as it tried to develop, roughly in the same way as they did the vege- tative zooidal system which became the primitive sea- anemone. In the case of the early sea-anemone a whole potential Individual system was compressed, whereas in the medusiform gonophore only a small part of one was so affected; but the real difference between the two cases is that in the former tubular vegetative zooids were involved, and in the latter sexual zooids of sporosac form. 94 THE EVOLUTION OF CONTINUITY Thus, the compression of the developing sporosac- gonoblastidium fused what should have otherwise become successive sporosacs, in lateral Continuity around a shortened and widened central stem whose hollow interior com- municated at the base with a varying number of radiating tubes, each representing the central spade of a sporosac. Between these tubes or canals the sporosac walls developed in lateral continuity, and thus would be formed the bell or umbrella of the medusiform gonophore, whose nourish- ment finally called for the formation round the bell-rim of Filamentous Discontinuously Zooidal Discontinuously weer Zooidal Vv Continuously ~~ — Zooidal © ——~ Continuously ae —~S Continuously Zooidal of Zooidal highly evolved type Discontinuously Megazooidal Discontinuously pee Megazooidal N Continuously Megazooidal Continuously wegen Megazooidal Segmental Pe Segmental Lae Simpler Segmental Higher Segmental Fia. 46. THE EVOLUTION OF CONTINUITY 153 have interfered to fix and preserve them for us up to the present time, a small proportion only of each new Continuity- type having been allowed to disappear in the origination of higher forms. The remaining proportion has suffered permanent arrest as regards Continuity, and further evolution has been a species of differentiation within the given Con- tinuity-type. In fact, we may say that the arrested types of Continuity are the “fixed tissue cells ” of the living body of Nature. The forces which produced each form of living Continuity have down to the present maintained it, any variation occurring being that of subordinate character. It is obvious that each new form of living Continuity must have appeared suddenly. From discontinuity to con- tinuity there is a sudden step, and the basis of Continuity’s evolution has been a species of multiplication. What we have to bear in mind is that all down the ages force of Attraction, as force working for continuity or compression, has been acting, and continues to act, in opposition to that of Repulsion, which works for decompression and discontinuity ; and that from time to time the former force has been able to dominate to an extent allowing it to compress still further the results of its previous action. These repeated intensifi- cations of Continuity took place, however, countless years ago on plastic evolving primitive types, and affected a limited number, or what we might call the ‘‘ main stem” of each Continuity group. The destiny of a certain number of organisms of a given new Continuity was to develop along an evolutionary road whose feature was the repeated multiplication of Continuity, much as the evolution of certain cell-lines of a developing Segmental Individual is along a main road leading to cycle-termination, or sexual elements. The parallel between the evolution of the Individual cycle and the evolution of the body of Nature is by no means far-fetched, for in both cases surely the same funda- mental laws must be at work. And as we can perceive that the arrest and differentiation of the human body’s somatic cells is for the maintenance of the body’s personality during life, and for its future reproduction, and that they reflect a state of equilibrium or balance, so may we take it that the fixation of Continuity types which occurred in past ages has been, and still is a necessity for the proper evolution of 154 THE EVOLUTION OF CONTINUITY the main road on which Continuity has been repeatedly multiplied. On all hands there is the process of Give and Take, of self-sacrifice and self-preservation; and as the cycle-career of the somatic cell has been sacrificed for the successful evolution of certain cell-lines towards sexual- element formation, so have the arrested forms of living Continuity been sacrificed in order that the remainder might advance on the main road of evolutionary destiny. This has been the inevitable result of Nature’s efforts towards equilibrium, themselves inevitable; remembering which, we may say it has been necessary for Nature’s equilibrium. Environment in the special aspect of evolutionary forces has worked to produce, maintain, and multiply Continuity, and even when, as in the Discontinuously Zooidal Individual, the built-up units composing the Individual remain separate and free, the matter is one of definite accomplishment rather than of defeat. For the Continuity is an advance on that of the preceding type and is a monument to definite results obtained. It is a matter of arrest on a side-path. Environ- ment, it is true, still continues to work for discontinuity, but it is a losing game. With the death of the Individual she shatters a given personality, but only to see it reproduced again. Force of Attraction inevitably dominates force of Repulsion. The manner in which Environment appears to have acted as a uniter and compressor will be suggested in the next chapter, and also when dealing with Symmetry. While new species of plants and animals have doubtless still to appear in this world, it does not seem probable that any existing types of Continuity are destined to be multiplied into higher ones. In any case it is difficult to see how the highest form, segmental, could be multiplied; it might be further intensified, traces of segmentation might disappear, but this would almost certainly involve, in man at any rate, loss of function, and be a matter of devolution. We have families and multiples of families of human beings respec- tively developing in relative continuity, but a ‘“‘ super- Individual ” equivalent to several Individuals united together is inconceivable. No doubt there have been cases of degeneration during the process of living evolution, and it may be that a given form of Continuity has at times been reduced to a lower THE EVOLUTION OF CONTINUITY 155 one, but such an occurrence would surely be exceptional, for on every hand we can see that Attraction is the dominant force, and higher and higher Continuity its goal. All these conjectures apart, the fact remains that we have the simplest known living type—the Discontinuously Multicellular—and all its successive multiplications, with us at the present time. This certainly shows that from the earliest ages the different forms of Continuity have remained arrested as regards their Continuity. Thus the world contains such diverse living types as amcebe, fungi, free zooids, zooidal colonies, meduse, corals, and vertebrates ; only a certain proportion of each newly evolved form of Continuity having been permitted to evolve to a higher form. The multiplication of living Continuity has not, however, been a process of moulding on new lines the already existing Individual, but of the developing Individual. For example, no actually existing series of primitive zooids was compressed to form the primitive sea-anemone—just as we know that no already formed terminal plant-shoots are compressed to form the plant flower ; but serial zooidal potentialities were compressed in their attempts at realisation, so that the megazooid resulted. Our conclusion is that the multiplica- tion of living Continuity has been due to compressing environ- mental force which acted on the first division-results of the zygote, or fertilised ovum, and all their subsequent product. Thus, the first megazooids of sea-anemone form would appear all at once, and we may picture with what comparative suddenness a stretch of primeval sea-bed would become studded over with a perfectly new living type, complete in structure from the first. Clearly a gap in the road of evolu- tion would be the result of this sudden leap to a higher form of Continuity. In a similar way we may picture the sudden appearance of filamentous Continuity, that of the tissues of , the primitive discontinuous zooid, that of the zooidal colony, or that of megazooids in series ; the last leading to primitive segmental Continuity and, like all the preceding forms, taking shape in a watery environment. But no similar evolution of Continuity has taken place on dry land. The different forms of Continuity which have appeared there have, we 156 THE EVOLUTION OF CONTINUITY believe, been separately derived from parallel aqueous types. The Continuity exhibited by terrestrial Individuals has been evolved in a watery environment, and minor special terrestrial characters are terrestrial modifications within each form of Continuity. In a rough way we might picture the process as having been somewhat as follows :— A. From a primitive Discontinuously Multicellular stock, whose environment was aqueous, a certain number of Individuals developed in Filamentous Continuity ; the rest breeding true through succeeding ages, and their further evolution being only that of Discontinuously Multicellular Species. From time to time the land would probably obtain “ primi- tive types’? from the fixed Discontinuously Multicellular class. Even on land, however, the environment would be largely aqueous. B. At some period a certain number of Filamentous Individuals would develop with the multiplied Continuity of the Discontinuously Zooidal Indi- vidual, while the rest continued to breed true as Filamentous Individuals, their further evolution being that of species. Probably from these would be obtained at a later date freshwater filamentous types. C. The evolution of Continuity would then, still in an aqueous environment, pass on to the Continuously Zooidal Individual type in a certain proportion, while in another it would remain arrested to preserve for us at the present day the free zooid ; that of Hydra being a modern species. It is most unlikely that any primitive terrestrial Discon- tinuously Zooidal Individual was ever derived from an aqueous type. D. Still in oceanic environment, the primitive Contin- uously Zooidal form would then pass on into the Discontinuously Megazooidal, and also continue to breed Individuals whose Continuity did not change to a higher form; and from these, at varying periods, we believe that the original types of the THE EVOLUTION OF CONTINUITY 157 higher terrestrial plants, existing and extinct, were derived. E. From the primitive Discontinuously Megazooidal would come the Continuously Megazooidal type, as well as all the different species of the former, extinct and existing. There is no evidence that any terrestrial Discontinuously Megazooidal Indi- viduals ever obtained. F. The highest form of Continuity would then be reached by the compression of primitive Continuously Megazooidal Continuity into primitive Segmental in one direction, while in another Megazooidal Continuity remained fixed to evolve species. None of these apparently ever supplied the earth with stock. G. It seems clear that from the primitive marine seg- mental type (or types it may be) many segmental ‘* sub-types ’’ evolved greatly differing in size and characters ; and it is probable that from these were separately derived the chief original terrestrial forms of segmental Individual. Thus, the centipede is segmental, and so also is the bird, but it seems unlikely that these share one common terrestrial primitive ancestry or derivation. Each has been derived from a distinct aqueous type, and the common ancestor was probably megazooidal. In the above summary the Ccenocytic and Radiate Individuals are not included, as these have not evolved on the main road of Continuity-multiplication. CHAPTER XVII THE EVOLUTION OF CONTINUITY (continued) WHILE the geological record does not supply the key to the evolution of living Continuity, yet it throws valuable light on the subject. The part of the earth in which we are interested is the ‘crust,’ and lies superficially to the crystalline or Archean rocks, regarding whose origin geologists are still uncertain, and which contain no traces of past life in any form. The crust of the globe is composed of more or less distinct rock layers or strata which have been successively deposited through inconceivable stretches of time, and which contain evidences of past life in the shape of fossil forms or casts of plants and animals. These strata from below upwards are divided into four great sections, namely, the Paleozoic or Primary, the Mesozoic or Secondary, the Cainozoic or Tertiary, and the Post-Tertiary or Quarternary; the adjectives being also used to denote the periods of geological time during which the rock-systems were being deposited and the living types represented in their fossils flourished. Each section is further divided into systems of strata or formations. The following table shows the sections and systems ; the numerous strata not being included :— SEcTIONS. Systems. Nature or Rocks, Post-Tertiary sete Pleisto- cene or Glacial } Sand, gravel, clay Pliocene Tertiary Miocene Sands, gravels, clays, marls, Oligocene limestones Eocene Mesozoic Jurassic Limestone, sands, clays Triassic Marls, sandstones, limestone 158 Secondary or { ders Limestone, chalk, sands THE EVOLUTION OF CONTINUITY 159 SxEcrrons. Systems. Nature oF Rocks. Penney Sands, limestone, slate P ‘arboniferous Coal, limestones Primary or Devonian Old red sandstone Paleozoic Silurian Cambeian } Sands, gravel, shale, slate Archean Archzan Granites, schists Sandstone, limestone, and chalk strata have been laid down at the bottom of the sea, or on the beds of inland lakes, during immense periods of time, and have been derived from the siliceous skeletons and calcareous shells of endless generations of marine organisms. Shales and slates, which are practically indurated muds, have also been deposited under water, but presumably shallow water at the mouths of rivers and estuaries. The origin of coal measures from paleozoic vegetation is common knowledge. There is clear proof that from time to time in the past there have been great elevations of the sea-bed above water level, alternating with subsidences, for we find the Devonian old red sandstone of submarine origin followed by the carboniferous system representing ages of terrestrial plant- life, and this in turn followed by the submarine deposition of sands, limestone and chalk. Elevation has alternated with subsidence. Our knowledge of the forms of life abound- ing in past ages is gathered from the fossils found in the various strata, and it is noteworthy that from below upwards there is an increasing complexity of type. In certain layers new organisms suddenly appear as if their evolution had been a sudden process, while others plentiful in lower strata may completely be wanting. But, while this is so, we do not find the successive Continuity-types appearing with successive strata. On the contrary, we find that as far back as the Silurian period segmental Individuals were in existence. In the Silurian rocks fossils have been discovered of Algze, Hydrozoa, Corals, Starfish, Crustaceans, Brachiopods, Cephalopods, Insects, and Fishes. That is, at this comparatively “‘early age” all the forms of living Continuity had evolved. If we accept the Cambrian system as the first of the earth’s crust, we would naturally conclude that evolution was a more rapid process when the world was younger than in later ages ; 160 THE EVOLUTION OF CONTINUITY but it may well be that the Archean rocks represent many strata which have been crushed out of recognisability and which may have contained fossils showing the progressive evolution of living Continuity. Be this as it may, there can be little doubt that, as a matter of acquired variation, transmissible be it noted, each new form of living Continuity must have appeared suddenly. To repeat ; as regards the fundamental forms of Continurty we have advanced nothing since the Silurian period. During the time that the presumed first strata of the globe were forming, the highest form of Continuity known to us, the Segmental, had already evolved. As has been said, however, the Archean rocks may represent many “‘ lost ”’ strata. It can hardly be doubted that the factor at work in the formation of the successive types of Continuity has been a compressing agency. It has been Force of Attraction acting in special ways. For it is necessary to point out that Force of Attraction does not solely imply either the attrac- tion of one entity to another, or the mutual attraction of two entities. The force is essentially directly attracting in its action, it is true, but it may indirectly produce the compression of objects not directly affected. If we turn, for example, to the evolution of the megazooid of sea-anemone fourm (page 88, Figs. 24, 25) we must attribute the results produced to steady vertical and lateral pressure on all the development of a zygote which originally possessed branching continuously zooidal potentialities. And the pressure must have been constantly applied. In fact, the compressing agency which produced the different forms of living Continuity must have acted evenly and constantly from age to age. It is not implied that the degree of com- pression which produced filamentous Continuity was the same as that which produced the megazooid, but that variations in the degree constantly and inexorably conformed to natural laws. The only attracting and compressing force to which we can attribute constant action according to Law; which could compress evenly in vertical and lateral directions ; which could originate the successive forms of Continuity and maintain them after formation, appears to us to be the THE EVOLUTION OF CONTINUITY 161 attraction force which caused the first formation of this globe, and its progressive contraction and solidification : the force, in fact, which caused, we believe, Life itself to originate. This force is Terrestrial Attraction, or Gravity. When we realise that owing to terrestrial attraction the electronic Continuity of the atom, the atomic Continuity of the inorganic molecule, and the higher atomic Continuity of the living molecule were successively realised, and that Life, once called into being, had to continue its existence and multiply in presence of the constantly acting force, we can see how the first form of living Continuity would inevitably come to be multiplied again and again. All the forms of living Continuity evolved in aqueous environment, and Gravity would act in two main ways as the compressor of developing living systems. (1) Directly ; by pulling the system against the earth’s surface. (2) Indirectly ; in the form of WaTER-PRESSURE. The question of relative densities of a living entity and its watery environment would, in the absence of means of locomotion, decide whether the entity sank to the bottom, remained suspended, or floated to the surface, and therefore the degree of water-pressure to which it would be subjected. Did it sink, it would be subjected to direct force of Gravity plus the pressure of overlying and surrounding water, whose weight, apart from the added one of superincumbenié atmos- phere, would always be the measure of its attraction to the earth. Naturally, were the entity to move habitually under the water, new pressure factors would appear. Now water-pressure varies according to the depth of the water, but at a given depth it is constant, and it is clear that the results of compression obtained at one depth would be more marked at a greater one. One has only to postulate that it is the Individual’s development from the zygote which has been compressed, to realise how the progressive multiplication of living Continuity could take place. We do not suggest that water-pressure was the only factor at work; for example, the temperature and salinity of the water, and the food of the developing organism, could all affect the density of its cells; while light, as a factor pulling away from the earth would enter into the question. ll 162 THE EVOLUTION OF CONTINUITY But, though it is possible that without the aid of water- pressure cells might have developed in serial filamentous continuity, nevertheless it is difficult to see how the pro- gressive multiplication of Continuity in the manner which has occurred could have taken place in the absence of water- pressure. One cannot, in fact, resist the impression that compres- sion during development has been the constant process in the evolution of the different forms of living Continuity. In no other way, it is suggested, could the structural plan of the sea-anemone or the medusoid be explained, nor the intensified Continuity of the segmental Individuals. And regarding this compression to be but an indirect result of the action of everywhere-obtaining terrestrial attraction (attracted water being the compressor of our theory), we are consistently recognising the work of one factor all up the scale. The force which binds the electrons in the atomic whole, binds the atoms of the molecule; the molecules of the mass; mass to mass; and in binding masses of water to the earth has compressed into existence the primitive protoplast and all succeeding forms of Continuity. We cannot pretend to explain the actual way in which water-pressure produced its results, but we get some hints from the structural plans of the Individual types. If primitive Filamentous Continuity appeared as an acquired variation in a discontinuously multicellular Indi- vidual type, and was due to compression during develop- ment, it is clear that rest under the body of compressing water would be a necessity. This could only occur if the zygote about to develop as a filament were of greater density than the water. This might well represent the initial acquired variation, and be due itself to increased water- pressure ; an agency such as a strong current carrying the fertilised ovum to depths where the pressure by diminishing volume increased density. Be this as it may, if it be given that a fertilised ovum, or zygote, with discontinuously multicellular potentialities, were dense enough to remain at the bottom under unusual water-pressure, then its development as a filament might be expected for the following reasons: The zygote’s density, THE EVOLUTION OF CONTINUITY 163 and the water-pressure would make for rest in situ of the zygote and its division results, and conceivably for attach- ment. The result of attachment would presumably be proximal cell-arrest, with distal cell-multiplication and serial growth. But there is reason to suppose that as cell succeeded cell there would be a slight diminution in density, with a resultant slight pull towards the surface of the water. Light-attraction might also act by stimulating distal growth and drawing the filament towards the surface. This supposed diminution in density is not fanciful, for it obviously occurs in the development of present-day alge such as Spirogyra, whose zygote develops in under- water attachment, and whose filament floats to the surface. Another example is the bladder-wrack, which, attached to some rock or stone, strains towards the surface when submerged ; diminishing density here taking the special form of air-floats. Hydrozoal colonies, and stalked crinoids, are other examples of organisms whose zygotes are denser than the water, and in whose development diminishing density may be presumed from the fact that growth is upwards and away from attachment. Naturally, in the sudden evolution of filamentous growth we presume a very faint diminution of density with extension; just sufficient to cause upward growth in face of even lateral water-pressure. In the evolution of the zooid we have to presume that a fertilised ovum, or its equivalent, with filamentous potentialities, came to develop in water-pressure conditions severe enough to institute a higher form of Continuity ; the result being, on the whole, as if several beginnings of branching filaments were squeezed together, as they grew, into a little mass by water-pressure. If the multiplying cells of such a mass regularly diminished in density, a spherical form, then a pear-shaped one, and finally a cylindrical form, could result, as accompaniments of upward growth. Another result of gradual diminution in cell-density could be the formation of a hollow interior in the mass. In this connection it may be noted that if a liquid heavier than water—chloroform, for example—be placed in small amount under water, it takes the form of one or more discrete flattened globes. Gravity and overlying pressure try to spread the chloroform out as a film on the bottom, but lateral 164 THE EVOLUTION OF CONTINUITY water-pressure resists. The density of the chloroform is, however, such that a drop under water cannot assume a spherical form. Calamifes To 5 —| > Cyeadaphytss, re Nii aad Sym Doshirms. Single madusifor gree preenie sprees vilhiow anne ot 0° —=—B Angiosherms, 5 pacaie wun = —7 5fo =2 Angiosperms. Fic. 53.—Suggested scheme of plant evolution. sporosac came the sporosac “‘raceme” or gonoblastidium ; from this evolved the medusiform gonophore ; and finally, from this last, the gonoblastidium containing many medusoid gonophores. The four primitive Hydrozoal types distin- guished by the mentioned forms of sexual structure appeared in the sea at long intervals of time, we may believe; and each one, it seems almost certain, stocked the land at long EVOLUTION OF PHANEROGAMS 179 distant periods with a new primitive form of terrestrial plant-life. It is true that it is difficult to do more than guess the plant type which was derived from the single sporosac primitive hydrozoon, though it may have been possibly the Ferns with their little sporangia; but we feel surer in concluding that coniferous plants generally have been derived from a hydrozoal type or types bearing sporosac- gonoblastidia. The Angiosperms we hold to have appeared at a much later date, because their marine primitive type was much later in its evolution. Its distinguishing feature was the attached medusiform gonophore, and this, it is suggested, finds representation in the flower of the present-day Angio- sperm. The medusoid-containing gonoblastidium would logically be represented in the Angiosperm flower raceme. Fig. 53 is a rough outline diagram of our theory of plant evolution. CHAPTER XIX THE EVOLUTION OF THE VERTEBRATE THE megazooidal precursor of the primitive segmental type through which the highest segmental organisms evolved must not unly have exhibited serial megazooidal repetition, but must also have possessed strong locomotive powers. And if we turn to the megazooidal types known to us we find that the only ones distinctly motile are medusoid in plan. It is through these that we can explain the evolu- tion of the present-day typical Fish, and thus picture the evolution of the primitive piscine type from which, without doubt, sprang the higher vertebrates. It is clear that an organism like the Fish could not have evolved from a primitive type in which one medusa composed the Individual; we have to imagine a type in which the Individual would be represented by a series of medusoids ; for a series must be presumed in order to account for the Fish’s segmental repetition. Now the only existing medusoid Individuals in whom there is anything approaching a serial medusoid plan are certain members of the Siphono- phora and of the Acraspeda, and it is the latter which throw light on our subject. There are two classes of Acraspedote Individual. One is represented by a single large Medusa, and for this reason can be put on one side; but the other develops as a great number of medusiform gonophores which are successively set free from the distal end of a long developing series. This class has been already considered under the name of Dis- continuously Megazooidal Individual (page 103), with Aurelia as the example, and the reader is requested to refer to the description already given. It is the strobila which interests us, as it represents a long series of medusoids developing in close continuity. 180 EVOLUTION OF THE VERTEBRATE 181 It is true that in Aurelia they all end by becoming discon- tinuous, but it requires no great effort of imagination to picture a primitive type in which the successive medusiform parts of the strobila did not separate, but were obliged to develop in close continuity, so that a series of interdependent segments was the result. Such development in close con- tinuity would in fact produce a primitive piscine organism ; and we propose to try to show how a mouth, gills, brain and cord, and closed circulatory system, such as possessed by the typical Fish, would be almost inevitable consequence. It cannot be emphasised too strongly that the primitive Fish must have originated suddenly, and that its mature plan was the result of forces moulding and guiding on new lines the development of a fertilised ovum originally serially- We Fic. 54.—The development of Aurelia. a, Scyphistoma ; 6, further stage; c, strobilation begins; d, strobila; e, free- swimming Ephyra. (After Claus.) medusoid in its potentialities. Thus we are not to picture the modification of a strobilar plan already realised, but the moulding, on new lines, of developing tissue whose original idea was to realise a strobilar plan. The umbrella or bell of a medusoid is not only a locomotive but also a respiratory organ. In humbler forms of aquatic life the digestive is also the respiratory system, as in the Hydra zooid, where the body-cavity not only receives food for digestion but also oxygenated water for respiration; but in a medusoid, equivalent to a number of zooids united closely in lateral Continuity, there is neces- sarily more specialisation. For the somatic cavity, while a simple tube to begin with, expands to form a dilatation 182 THE EVOLUTION OF CONTINUITY from which radiate the nectocalycine canals to join the circular canal in the rim of the bell. In this way the diges- tive canal is continued as a water-vascular system. The canals, in fact, act as primitive bloodvessels in that they convey to all parts of the organism oxygen for respiration, in addition to nutritive substances from the digestive cavity proper. In all probability bell contractions and relaxations are the chief agencies in maintaining a proper canal circulation, the former causing the expulsion of fluid bearing impurities, and the latter causing an inflow of fresh water bearing oxygen and food. The regularly recurring accumulation of waste-products no doubt stimulate the nerve-ganglia in the bell-rim to call for bell-contraction, and thus it is that in the free-swimming medusoid there appears for the first Fic. 55.—a, diagram of the gills on the left side of a typical Fish. 3, diagram of uw pair of lamine. a, the artery which gives off little branches which are linked up through capillaries with the little venules leading to the vein, 6. (After Nicholson.) time in the ascending scale of types rhythmic respiration due to muscular action. In the typical Fish this bell-contraction is represented by gill-contraction, and when we examine the vascular anatomy of the Fish’s respiratory system we get some light on the mode of evolution followed. It is not to be supposed that the head of the Fish represents an ancestral medusoid ; in reality it represents an ancestral series terminally com- pressed so that the segments are indistinguishable; the result of development while moving forward in the face of water-pressure, and reflected in the formation of the brain- mass, as will be shown. It is common knowledge that the Fish breathes by EVOLUTION OF THE VERTEBRATE 183 admitting water into its mouth and then forcing it past the gills to escape at the gill-slits; the capillaries in the mucous membrane of the lamine of the gills absorbing oxygen from the water as it passes through, and giving up carbonic acid. The Fish’s heart drives the venous blood of the general circulation through the branchial arteries (a in figure) to the gill capillaries, where, having got rid of its carbonic acid, it absorbs oxygen and returns through the branchial veins (b) to the aorta. The branchial circulation is thus to all purposes composed of a number of vascular rings, usually four, each formed by the junction of a right and Fic. 56.—Diagram of the branchial circulation of the typical Fish. The venous part of the system is shaded, including the arterial bulb. The capillaries would link up the shaded with the unshaded half of each ring at x. left arching bloodvessel, the points of junction being the arterial bulb and the aorta (Fig. 56). Consistently with our theory that the Fish has evolved from a primitive “ serio-medusoid ’’ organism, we recognise in the branchial rings ancestral medusoid canal repetition ; each ring representing, as it were, the circular canal which runs round the rim of the medusoid bell. Derivatively, the rings are in the Fish what the loop-hearts are in the Worm (page 117), though the Vertebrate and the Invertebrate have evolved on quite separate paths from their primitive serio- 184 THE EVOLUTION OF CONTINUITY medusoid types. So, taking Fig. 57, A, to represent the plan of the medusoid canal system, a series of such systems joined up together through the intensification of megazooidal serial Continuity would give a diagrammatic canal-plan such as is drawn in Fig. 57, B. In humbler forms of segmental Individual, for example, in some Annelids (from which, however, the Fish has not Fia. 57.—a, diagram of circulation of a medusa; 8, the result of linking up a series of forms like a (leaving out the manu- brium) ; c, diagram of the circulation of Saenuris, an Annelid, for comparison ; h, heart. evolved), circulatory arch repetition is very regular down the length of the animal, as is shown in C above. But in a medusoid the canal system is continuous with the digestive tube, and communicates through this with the mouth of the organism ; whereas in the Fish, while the respiratory circulation is in close touch with part of the digestive tract, all the bloodvessels are completely shut off from this. And here we come to the crux of the question. The medusoid has one opening which acts both as mouth and anus, whereas in the primitive Fish an additional EVOLUTION OF THE VERTEBRATE 185 opening to that at the end of a series of medusoids inevitably had to be formed. This new opening became the mouth of the organism. In segmental organisms the mouth develops at what is termed the anterior end of the body; that is, at the end where the controlling nerve-centre develops, and which habitually leads the way when the organism responds to a source of attraction by moving towards it. The nerve- centre itself, a mass of nerve-ganglia compressed together, takes form as the result of terminal segmental compression during development, this in turn being caused by resistance encountered in movement under water-pressure. Now, in our hypothetical primitive serio-medusoid type it is clear that bell-contractions would be the means employed for active locomotion, and the convex end of the series would be that which led the way during movement. A developing embryo, therefore, which started life with serio-medusoid potentialities, would inherit, so to speak, this method of movement, and as a result its developing serial segments would from the first encounter end-on re- sistance at what we may call its convex extremity. Hence, at this extremity terminal compression would be a feature of development, and with it the massing of ganglia to form a brain. Thus, while the mouth forms at the anterior end where the brain takes shape, the brain forms at the end of the organism, which for ancestral reasons has to lead the way during movement. The development of a series of medusoids in such close continuity as to become segments would produce an embry- onic organism of a long, somewhat tubular shape, whose walls, representing a continuity of medusoid bells, would have the power of muscular contraction. Down the centre of the body, suspended in the celomic space, equivalent to the successive spaces between ancestral medusoid bells and manubrial structure, would run an alimentary tube. This would represent the development in continuity of the manubria of successive medusoids. The “inherited ”’ opening of this tube would be at the posterior or “concave” end of the organism (Fig. 58). Such an organism as that drawn below could never take shape, given motile powers and ever-present water-pressure. 186 THE EVOLUTION OF CONTINUITY In the first place, forward movement in water-pressure conditions would inevitably mould the body on stream-lines (see Fig. 68, in chapter on Symmetry), and cause a tapering of form towards the posterior end. But, more important than this, the systems of digestion, respiration, and circula- tion, suitable for a single medusoid, would never suffice for a long series of medusoidally derived segments. The medusoid’s mouth is also its anus, and the stomach and canals can be filled and emptied through the one opening, but it is clear that one long manubrium with one terminal orifice could never admit the nourishment necessary for a long series of segments, nor allow the escape of impurities ; especially so when it is remembered that the whole series Fic. 58.—Diagram in connection with mouth formation in the primitive Fish. Showing how the “inherited ’’ mouth would be at the posterior end of the developing organism, special factors apart. A, anterior end with terminally compressed developing segments and mouth; 6, brain mass; w, con- tractile walls, the segments, s, of which represent ancestral medusoid bells; c, celom; m, digestive tract, whose one inherited opening is at the concave posterior end, Pp. This diagram is not offered as a developmental stage. of linked-up canal systems would only communicate with the digestive tube by the radial canals of the terminal leading segment (Fig. 59, A). Further, the development of tapering form would reduce the manubrial orifice to a minimum. Our conclusion is that the inherited manubrial orifice became, or developed as, the anus of the primitive Fish. It is to be remembered that the primitive Fish must have evolved suddenly; that a fertilised ovum with “‘ strobilar ” potentialities must have been so acted on during its development that new characters appeared all at once. Thus, during its development, the elongating embryonic mass would be compressed in close segmental Continuity, and as it moved with its convex end leading there would EVOLUTION OF THE VERTEBRATE 187 come into play powerful physical forces. There would be a moulding of the developing and plastic, not of the mature and rigid. There would not be a narrowing and tapering of an already formed Fish-like structure, nor of an already formed manubrial orifice, but a moulding of form and orifice during development. As serio-medusoid potentialities tried to realise themselves the new plan would be made to evolve, and modification, once started, would itself be active in causing further modification. For example, the commencing tapering of body form and the narrowing of the inherited orifice of the digestive tube would result in the accumulation of impurities, which in turn would induce strong contractions of the body-wall segments. And these contractions would raise the pressure in the celom and in its contained digestive tube. We can thus not unreasonably picture the rise of pressure in the digestive tube (increased by the insufficient size of the outlet at the posterior end), resulting in a breach in the tube walls and the body-walls at the junction of certain developing segments. That is, the very need for oxygen would bring about gill-formation. In addition, the same internal pressure might result in the formation of a new opening at the anterior end of the organism, whose alimen- tary tract would now have a mouth as well as an anus; though it is possible that the mouth was formed not by positive pressure from within during body-wall contraction, but by external water-resistance on the anterior end during movement, assisted by internal negative pressure during body-wall relaxation: was pushed and sucked in, and not pushed out. At the same time, the compression of the anterior developing segments would be going on, a nerve- centre taking shape, and all the modifications occurring which would exert a mutual balancing influence while evolving to become new characters. The formation of the mouth and gill-slits or branchial clefts of the developing embryo would have important resuits. For in the first place the muscular relaxation of the walls of the anterior segments would suck in water at the new mouth-opening, and this water would pass but a short distance down the alimentary tract to escape at the gill-slits. The escape would be assisted by the muscular 188 THE EVOLUTION OF CONTINUITY contraction following relaxation. In the second place, the formation of an anterior mouth would bring about the closure of the developing circulatory system. This system in a continuous medusoid series would be the linked-up canal-systems of the successive medusoids, and would only communicate with the manubrial tube in the convexity of the anterior terminal medusoid-segment, and it seems clear that the formation of a mouth at this spot would cut off the terminal communicating radial canals from the digestive tube, and leave the embryo with a developing closed vascular system. This can be made clearer in the next figure (Fig. 59). It may well be that terminal compression of the leading segments would assist in closing the circulatory system ; 4 * Fic. 59.—a, diagram of “circulatory system” of imaginary serio-medusoid organism, showing how the manubrial digestive tube would only communicate with the linked-up canal-systems at the anterior extremity. 3B, showing how the formation of an anterior mouth could cut off the radial canals. m, m, the digestive tube; 1, r, the radial canals at anterior end of the organism. and it also occurs to one that this factor might assist in the formation of gill-clefts, the compressed developing anterior segments exercising specially strong contractions on the digestive tube and celom in their neighbourhood. This apart, however, the point to which we return is that the formation of an anterior mouth would close the developing vascular system, and that the indrawn water of respiration would of necessity pass over and not through the primitive branchial vascular rings (Fig. 60). But simple branchial loops, such as in the diagram, would not offer a sufficiently large surface for the absorption of the oxygen passing over them, and it is quite probable that the gas itself would directly stimulate vascular branching and the formation of branchial capillaries. This alone, EVOLUTION OF THE VERTEBRATE 189 however, would not suffice for the needs of the developing organism, for not only would oxygen have to be absorbed in large quantity, but it would have to be carried to the tissues of the segments anterior and posterior to the gill- clefts. Moreover, impurities in the closed circulation would have to be borne to the branchial vessels for excretion. Thus a circulation of the contents of the closed vessel-system would be called for. No doubt the developing primitive Fish would help to maintain a circulation in its vessels by serial body-wall contractions, but this means would be aii Wty Fic. 60.—Formation of mouth, and gill-clefts, of primitive Fish. nz, L, right and left sides of head which represents many compressed segments, whose circular and longitudinal canals have become bv, bloodvessels of a closed circulation. The powerful contractions of posterior R and L are supposed to have caused dilatation of the digestive tube and finally breaches at the site of the arrows. The branchial loops, 1, represent ancestral circular canals, across which, instead of through which (as in medusoids) the respiratory water passes. Posterior to them is the representative of an ancestral circular canal adapted for tissue nourishment. The figure is ultra-diagram- matic. insufficient and spasmodic. The organism would develop a heart. We seem to get a hint of the acting causes behind heart formation from the free-swimming medusoid, for it would appear that the regularly recurring accumulation of waste- products, carbonic acid, etc., in the medusoid canal system is the exciting cause of the bell-contractions, and it is reasonable to suppose that the same factor in the closed vessel-system of the developing primitive Fish would produce parallel results. These can be recognised in the regular gill-contractions, but as we have seen that gill action alone 1909 THE EVOLUTION OF CONTINUITY could not supply the Fish with oxygen, it may well be that the accumulation of impurities within the closed vessels brought on recurring contractions of part of the vessels themselves. The primitive heart, and the arterial pulse, would on this supposition originate as wave-like ‘“ convul- sive’ spasms of the walls of part of the vessel system, the spasms being the result of waste-product accumulation, and recurring regularly owing to the regularly recurring accumulation of waste-products. In a similar way, it may be remarked, we might account for the first beats of the human fetal heart ; for, as develop- ment proceeds, the maternal circulation alone is insufficient for the removal of the impurities and poisons of fetal metabolism, and these substances may well directly force the foetal circulation to evolve its own driving powers. It is to be noted that when the mother’s excretory functions fail to act properly spasmodic contractions of her muscular system, in the form of eclampsic convulsions, can occur. With respect to the systemic circulation of the Fish we would detect in the main branches arising from the main venous and arterial trunks ancestral megazooidal circular canals. So far we have tried to show how the primitive Fish’s respiratory and circulatory systems would evolve, an anterior mouth being formed at the same time; and if our theory is reasonable it should help to explain the evolution of the Fish’s nervous system. In Invertebrate segmental organisms, such as the earth- worm, it has been shown (page 120) that terminal compression provided a primitive form of brain by bringing together the ganglia of successive anterior segments; while pos- teriorly the ganglia of successive uncompressed segments formed for the animal a ganglionic chain or primitive cord. The anterior ganglionic mass is situated above the mouth, or dorsally, but the chain runs ventrally or below the alimentary canal, a connecting nerve-collar encircling the esophagus. On the other hand, in Vertebrates the brain and spinal cord occupy a dorsal position, and when it is presumed that the vertebrates have evolved from some primitive inverte- EVOLUTION OF THE VERTEBRATE 191 brate type this change in the position of the cord is clearly a very puzzling matter. The theory of Gaskell is at the present time generally held to explain satisfactorily how the invertebrate ventral cord came to take a dorsal position, being roughly to the effect that in some primitive invertebrate type, possessing annelid characters, the nerve-ganglia composing the ventral chain increased in size and grew upwards so as to surround or encase the overlying alimentary canal, the lumen of this finally becoming the ventricles of the brain and the central canal of the cord. Also that in place of the original digestive canal a new one was formed underneath the cord. We cannot pretend to find this theory in any way satisfactory, and it is here suggested that there lies at hand a much simpler one, and one completely in harmony with the theory of the evolution of Continuity. There is more reason to believe that vertebrates have not evolved from any annelid type, or one possessing a ventral chain and esophageal collar ; and that the primitive Fish evolved on a line of its own from a special continuously medusoid type, while the annelids did the same from another. Our firm belief is that the Vertebrates sprang suddenly into existence with the primitive Fish, and that the spinal cord was dorsal from the start. That an inherited alimentary canal should come to take on the duties of a spinal central canal, as Gaskell’s theory suggests, is, to say the least, improbable. It would be a sudden modification of a kind which completely ignored the inheritance of func- tion and plan. Did we entertain the suggestion as possible, it could only be by picturing it as occurring during develop- ment; but we would ask how a new alimentary tract could be formed from developing tissues whose potentialities had been decided in simpler living types countless ages before. It is true that we can recognise the evolution of the closed vascular system of the vertebrate from the hollow tubular interiors of ancestral sporosacs, but this is a different question altogether, for it is a harmonious evolution by steps which are the repeated multiplications of Continuity. We can see how the digestive cavity of the zooid was multi- plied in the medusoid into a digestive cavity with thin radial branches, whose contents bearing oxygen and nourishment, 192 THE EVOLUTION OF CONTINUITY and necessitating circulation, were a primitive blood of sorts just as the canals were primitive bloodvessels com- municating with the stomach cavity. The development in continuity of successive medusoid canal systems, and the cutting these off from communication with the digestive canal resulted in the closed circulation of the segmental organism. But this is, we might say, inevitable evolution. But Gaskell’s theory pictures a nervous system (which had evolved harmoniously with the digestive and other systems of the body it governed) as suddenly overgrowing and practically obliterating the all-important alimentary tract on which its own normal development depended. This might occur as uncontrolled growth, or as a nervous neoplasm, but not as a modification, inevitable, and necessary for evolutionary advance. We cannot believe that Nature 5 7 by 5’ Fic. 61.—The evolution of the segmental nerve-chain. g, the ganglia of successive medusoid rings linked together. could make a new alimentary tract where no inherited alimentary tissues or potentialities were present. A simple explanation of the dorsal position of the vertebrate cord offers itself through the theory that Vertebrates and organisms of Annelid type, while both of medusoid ancestry, evolved on separate lines from the beginning. In a word, it is to the effect that the method followed in the “ linking up ”’ in continuity of the developing representatives of successive medusoidal ganglia has differed in the two cases. The nerve-ganglia of a medusoid are situated in the bell-rim, and the linking up of the successive ganglia in a continuous medusoid series would make a number of longitudinal ganglionic chains, as in Fig. 61. This we take to be the basic plan on which depended alike the evolution of the Annelid and the Vertebrate. In a medusoid the ganglionic ring in the bell-rim surrounds EVOLUTION OF THE VERTEBRATE 193 the manubrium near the mouth, and in a continuous medu- soid series the continuous manubrial tube or gut would be surrounded by all the successive nerve-rings. In the evolution of the Annelid type we can thus account for the circum-pharyngeal nerve-collar, and would conclude that this alone remains to represent the ancestral nerve- rings in complete circle. Dorsally on the nerve-collar terminal compression has massed together several ganglia to form a primitive brain, while ventrally a smaller ganglionic mass obtains as a ‘‘sub-brain.”’ Posteriorly to this the nerve-rings are only represented by one ganglionic mass for each segment, plus the nerves given off laterally, and the linking up of these ventral ganglia has given the ventral cord. In the primitive Vertebrate the same state of affairs could, we may say, have possibly resulted. But here terminal compression massed together a greater number of ganglia to form a dorsal brain, the ancestral nerve-rings altogether failing to surround the alimentary tract as rings or collars, but being represented by the right and left cranial nerves. Posteriorly to the brain the nerve-rings were represented by a ganglion mass with lateral nerves in each segment, but these developed from the first dorsally. The next figure illustrates our suggestions. It seems clear that terminal compression was the chief factor at work in the evolution of the Vertebrate brain ; the developing evolving type habitually presenting its anterior segments towards sources of attraction as it moved to them in the face of water resistance. That the compressed brain- mass is bilaterally symmetrical, as is also the spinal cord, is a matter to be dealt with in the chapter on Symmetry, being essentially connected with the demand by attraction- sources for undeviating movement-response, or for the correction of deviation. But it may be noted here that such a demand would call for the representation in the central nervous tract of two ancestral ganglionic chains, such as are roughly drawn in Fig. 62, I. Further, the call for a motor and sensory tract on each side of the body would be inevitable, and this inclines one to suppose that the vertebrate brain and cord represent, so to speak, four ancestral ganglionic chains which have developed in close lateral continuity, and in a dorsal position. 13 194 THE EVOLUTION OF CONTINUITY As we have said, a few pages back, we cannot accept Gaskell’s theory of the derivation of the vertebrate brain ventricles and spinal canal from an enclosed alimentary tract; and if our own theory respecting the evolution of brain and cord be consistently applied we are driven to suggest that the ventricles and canal arose as follows :— The development in dorsal lateral continuity of the four ancestral ganglionic chains involved their enclosing a 1 \e) by ne Fic. 62.—The significance of the plans of the Vertebrate and Invertebrate nervous systems. JI. Imaginary serially medu- soid organism with successive nerve-rings surrounding the alimentary tract; their ganglia being linked together in parallel lines. This may be taken to stand for the inherited nervous potentialities of the developing primitive Invertebrate and Vertebrate alike. mn, nerve-rings; g, ganglia; a, ali- mentary canal. II. How the plan in I was realised in the primitive Invertebrate. Dp, dorsal, v, ventral surfaces ; cs compressed anterior segments; 8B, primitive brain ; we, nerve-collar surrounding cesophagus; va, ventral ganglia which with their nerves alone represent the nerve- rings of I. III. How the plan in I was realised in the primitive Vertebrate. cn, cranial nerves, representatives of nw in I; sc, spinal cord, dorsally placed, otherwise of similar significance to the ventral chain in II, the nerve-rings being represented by the spinal nerves passing out to right and left. The other letters same as in II. dorsally situated ancestral medusoid radial canal-system in all its length as this developed (see Fig. 59, A, upper 7). When the usual position of nerve-ganglia in the rim of the medusoid bell is remembered, this supposition does not seem unnatural, and is much less fanciful than that which would make a ventrally situated nervous system grow round and almost obliterate an alimentary tract of long pedigree. The fact that in the developing Amphioxus the neural canal temporarily communicates posteriorly with the EVOLUTION OF THE VERTEBRATE 195 alimentary tract does not lend real support to Gaskell’s theory, in our opinion. In fact, we believe that the phe- nomena of early development are not safe guides to the derivation of mature structure. Thus, for example, in the same case of Amphioxus, the celom is usually described as arising from the developing alimentary tract in the form of two outgrowths or protrusions. Our belief, as already clearly stated, is that in no living organism can the celom be regarded as having been derived in the evolutionary sense from alimentary structure; and the most we are entitled to say is that in the developing Amphioxus there is at first a common cavity from which is formed both celom and alimentary tract. It is not suggested that the study of early development is not of the greatest value in the case of different species within a given type of Continuity, but our suggestion is that where the question is the evolu- tion of a given type of Continuity from a lower one the comparison of mature structure is the safer guide. As regards the Vertebrate alimentary tract, this we believe represents ancestral medusoid manubria united in serial continuity ; in harmony with the explanations already given of the evolution of the vascular and nervous systems. The abdominal cavity, or cewlomic space, in which the digestive tract is loosely suspended, would thus be equivalent to a number of medusoid “‘ open celoms ”’ merged in serial continuity (see page 186); the “‘open celom”’ being the space obtaining between the medusoid’s manubrium and inner bell-surface. The significance of the true celom has already been mentioned in connection with the earthworm and the echinoderm. CHAPTER XX THE EVOLUTION OF THE ATYPICAL FISH THE typical Fish’s characters are largely the result of the active locomotive powers possessed by its developing primitive type. But there exists at the present time what may be called the “‘ atypical Fish,”’ and its structural plan would seem to indicate that the primitive type from which it evolved had no motile powers. Examples of atypical Fish are presented by the Mollusca generally, but it is in the class called Cephalopods that we get the clearest hints as to the way this type of organism evolved. Although possessing no vertebral column, and for this reason biologically classified as an Invertebrate, the Cepha- lopod shows no signs of having been derived from primitive Annelid invertebrate stock. In fact, though invertebrate, the Cephalopod probably has a closer relationship to the typical Fish than to the Annelid. Our supposition is that, like the typical Fish, the Cephalopod has been derived from a primitive serially-medusoid form of Continuity, and that the absence of locomotive powers in this ancestral type resulted in the evolution of characters greatly different from those of the typical Fish. The serially-medusoid type from which it has been suggested came the typical Fish, moved along actively with its convex end leading, and thus it was that in the evolving Fish the head, mouth, and brain took form in this, so to speak, potential region; while the potentially concave end developed a tapering form, and the inherited alimentary opening became the anus. All this was due to movement during development, in face of constant water-pressure, and with the convex end leading. But if the ancestral serially-medusoid type had not been free-swimming, but had lived attached to the bottom of the sea, can we picture what structural segmental plan 196 EVOLUTION OF THE ATYPICAL FISH 197 would have resulted when development under compression took place? With the help of the modern cuttlefish we can, to a certain extent. Let us start, then, with our primitive serially-medusoid type, noting that it was not motile, but most probably attached to the sea-bed at its convex extremity. This requires no stretch of imagination, for in the developing Aurelia (Fig. 54) we have practically such an organism. If a fertilised ovum, with developmental potentialities of a strobilar kind, such as Aurelia possesses, were obliged to develop under strong pressure conditions, the Cephalopod’s Fic. 63.—Terminal compression in the evolving atypical Fish. A, the inherited developmental potentialities of the fertilised ovum which was caused to develop under special pressure conditions. The figure is virtually a ‘‘ strobila,” anchored to the sea-bed at b. m, the digestive tube of manubrial deriva- tion, communicating with the water-vascular system, ¢, at d. Terminal compression during development, as indicated by the arrows, could, other results apart, give the result shown in B. plan would, it is suggested, be the result. In the absence of movement with convex developing end leading there would be no terminal compression of this region as in typical Fish evolution; but the concave end would be the one to suffer compression. For as the strobilar plan tried to realise itself through growth towards the surface of the water, the potentially concave end would be subjected to overlying and surrounding water-pressure, and it would be this region which would be terminally compressed in its development. In other words, a head would take shape at what would represent the tail end in the evolving typical Fish (Fig. 63). 198 THE EVOLUTION OF CONTINUITY The terminally compressed segments would take the form of a solid tissue mass surrounding the distal part of the digestive tube with its inherited opening. There would be a narrowing of the tube in the compressed region, and at the same time the nerve ganglia of successive compressed segments would develop in close continuity to form a primitive brain. Terminal compression would also probably provide strong thick tentacles representing growth from the several compressed segments forming the head (Fig. 64). But all parts of the new type would be evolving in their Fig. 64.—Terminal compression in the evolving atypical Fish. The diagram does not, of course, represent an actual stage of evolution, but is merely meant to show how inherited poten- tialities would be affected by pressure in their attempts at realisation. u, the head-region, with narrow csophagus, o, passing through it. wu is composed of several compressed segments, whose successive nerve-ganglia are compressed to form g, the compound ganglion or primitive brain. Below the head is a comparatively uncompressed body with wide digestive tract, drawn as communicating at the convex base with the water-vascular system. development at the same time—an impossible thing to describe or figure—and this is where our difficulty comes in. For while the parts mentioned would be taking shape, others would be evolving in their company, moreover influenced by them and influencing them. While the head and narrow gullet were forming, accompanying alimentary, respiratory, and circulatory novelties would be developing. As a mass of solid tissues, the developing head would not rhythmically contract, but below it there would be taking shape a sac-like body whose walls would contract in a wave- like manner—a gift from ancestral medusoid bells. These EVOLUTION OF THE ATYPICAL FISH 199 contractions would be stopped sharply at the junction of body-sac and head; and the fluid contents between the digestive tube and body-walls, being unable under pressure to escape because of the obstructing head, would force an opening by which to issue. The most likely spot to give way would be where the body joined the head, for here the pressure would be greatest. As a result of the breach, seawater would then pass in and out to circulate round the digestive tube suspended in the celomic cavity (Fig. 65). That is, we suppose the same forces to have been at work in the formation of the developing primitive Cephalopod’s gill-clefts as in the case of the evolving Fish; the difference Fig. 65.—The evolution of the Cephalopod’s gill-cleft. Show- ing how, as development proceeded, the body-wall contrac- tions, by acting on the fluid contents of the body-sac, would cause @ rupture in the region indicated as x. a represents the state of relaxation; 8, the effects of contraction. being that the clefts took shape at what we might call the opposite ends of the ancestral medusoid-series. As in the case of the evolving primitive Fish, the vascular system of the Cephalopod would be ancestral water-vascular canal systems which had been cut off in their development from all communication with the alimen- tary tube; and in the region of the gill-cleft the indrawn oxygenated water would stimulate representatives of ancestral circular canals to act as branchial loops, and to form the fine capillaries of primitive gills. In the primitive Fish a mouth had to take form which communicated with the gill-clefts ; the inherited alimentary 200 THE EVOLUTION OF CONTINUITY orifice developing as the anus. In the primitive Cephalopod the inherited orifice developed as the mouth, and it was the anus which appeared as the new alimentary opening, and it communicated with the gill-cleft. It is difficult to say what forces caused the formation of the anus, but no doubt they were pressure forces, possibly the result of peristaltic or contractile movement of the developing gut, and it may be partly due to body-wall contractions, and the outflow of water at the gill-cleft. In any case, the current of the escaping water would doubtless cause the terminal part of the alimentary tube to develop with the anus presenting towards the gill-cleft, the excreta being thus carried outside with the water of expiration. This is what we presume from the anatomy of the present-day Cepha- lopod in the next figure. Fic. 66.—Plan of a typical Cephalopod. (After Nicholson.) The notes beneath will help to explain the figure. “The body in the Cephalopods is bilaterally symmetrical, and the cephalic region (prosoma) is conspicuously marked out, and is separated from the visceral region (metasoma) which is enclosed in the mantle. The mantle cavity is situated on the under side of the body, when the animal is placed in its natural position. The head is very distinct, bearing a pair of large globular eyes, and having the mouth in its centre. The mouth is surrounded by a circle of eight, ten, or more long muscular processes or arms which are generally provided with rows of stalked or sessile suckers. . . . In all the Decapod, and in some of the Octopod forms, the sides of the body are produced into muscular expansions or fins with which the animal swims head foremost. In all the Cephalopods, also, the lateral margins of the foot (‘epipodia’) are either placed in apposition (Nautilus) or are actually united (Cuttlefishes) in such a manner as to form a muscular tube known as the ‘ funnel.’ EVOLUTION OF THE ATYPICAL FISH 201 ** The funnel (Fig. 66, f), is placed on the lower surface of the body, with its anterior extremity projecting beyond the mantle, while it opens behind into the pallial chamber. It serves for the elimination of the water which has been used in respiration, and the outgoing currents also carry with them the excretions of the kidneys and of the ink-sac, together with the feces. By the contractions of the mantle, the water contained in the pallial sac can also be driven through the funnel in a succession of jets, driving the animal backwards through the water. . . . The circulatory organs consist of a central ventricle, into which the aerated blood from the gills is poured by two laterally placed auricles developed on the branchial veins where they leave the branchie. ... The respiratory organs are in the form of two (Cuttlefishes) or four (Nautilus) plume-like gills, placed symmetrically on the sides of the body within the pallial sac . . . the necessary respiratory currents are maintained by the alternate contractions and expansions of the muscular walls of the mantle-sac. In each expansion the water finds its way into the pallial chamber by the opening between the rim of the mantle and the neck; and in each contraction it is expelled through the tube of the funnel, which is so constructed as to allow of the egress but to prevent the ingress of the water. The central nervous system consists of the three normal pairs of ganglia . . . but these are aggregated to form an cesophageal collar (Fig. 66,ng). ... The great cesophageal nerve-collar is pro- tected by a cartilaginous plate which foreshadows the cranium of the Vertebrata. ...? (Nicholson.) It will be noticed that most Cephalopods are able to move forwards by the action of lateral fin-fringes, but that when alarmed or desiring to move with speed they move in a backward direction by ejecting water strongly from the mantle sac. In the latter case the advancing end of the animal is that which in the typical Fish has become the anterior; and the fact that backward movement is more efficient than forward in the Cephalopod, and also the method of the movement’s production, clearly reflect the serial-medusoid derivation of the organism. The ejection of water through the funnel is due to “wall-contractions ” which represent ancestral serial-medusoid contractions, and, as in the case of medusoids, the mechanism of locomotion is here also that of respiration. In the common Octopus backward movement is also obtained by additional means representing ancestral bell-contractions ; for the organism expands and contracts the fringe which bears the tentacles, these being drawn behind the head to be thrown forwards immediately afterwards. 202 THE EVOLUTION OF CONTINUITY The mantle-sac of the Cephalopod is equivalent to the celom or abdominal cavity of the typical Fish, in that both represent the space enclosed by a continuous series of medusoid walls; the viscera lying suspended as we would expect a continuous manubrial structure to be in a medusoid series. We have suggested that in contrast with the primitive Fish the primitive Cephalopod evolved from a stationary or attached type of strobilar plan, and we have to presume that on full development the organism became humbly motile. This might well have happened as a result of gill-formation, and the strain on the organism’s “‘ moor- ings’ during the expulsion of respiratory water. The Cephalopod could never hope to evolve rapid continuous movement like that of the typical Fish, for it evolved two separate locomotive mechanisms, which acted in opposite directions. It did its best with fin-fringes, assisted by grasping tentacles, to develop forward move- ment, but the contractions necessary for respiration of the walls of the mantle-sac have more or less defeated its purpose. It may be remarked that in the typical Fish we find the water current of expiration trying to defeat voluntary movement in a different way; for if the Fish desires to remain motionless, or to move backwards, it has to counter- act the forward drive of gill-contraction. This can be well observed in the case of a stationary goldfish in a glass globe. The main road of Evolution leading to Man has not passed through any primitive Cephalopod type, but through one whose features were roughly those of the present-day typical Fish. And it is well here to repeat that the truth seems to be that no living organism in this world represents an actual past type on the main road of Evolution. In the light of the ConrinuiTy they exhibit we can clearly recognise through known organisms what the outstanding features of the main road have been, but the actual road has been wiped out. Moreover, the side-roads have also been wiped out; and as Man is all that remains to represent the main road, so is a given animal or plant species all that remains of the actual side-road leading to it. The road of the Evolution of Continuity has, however, been preserved to the present day. Side-path evolution has been a matter of modification EVOLUTION OF THE ATYPICAL FISH 203 or variation within a given Continuity-type; and each new form of Continuity which evolved suddenly in the past has remained arrested to produce its appropriate species, with the exception of such representatives as were destined to carry on the main road of Evolution through the further multiplication of Continuity. The foregoing conjectures are very superficial, but the intention has simply been to outline the Evolution of living Continuity ; to make clear the fundamental principles of Evolution, and to show how there must be “‘gaps’’ in the evolutionary record. CHAPTER XXI THE EVOLUTION OF MATTER It would be easier to speculate regarding its evolution if one were aware of the ultimate nature of Matter; but even without this knowledge there are distinct indications that what is termed “ Matter ’’ has evolved into being, and that its evolution has been based on the intensification of Continuity. Any hypothesis that can be put forward regarding the nature of Matter must clearly include one concerning the nature of Matter’s “ antithesis’—Force; but this is a question equally obscure. Our own inclination is to regard Matter as a Force manifestation, or as Force in a special aspect. The outstanding characters of Matter are form, weight, and visibility, whereas what we designate as Force is form- less, intangible, and invisible Power, perceptible by us only through its effects ; and our perception of Matter’s character is nothing else than the reception of Force-impressions of various sorts by the Matter which we are. Thus, as far as we are concerned as living beings, Force would be non- existent but for Matter, and Matter non-existent but for Force. On the whole, though it does not take us very far, it might be said that Force is the power to produce perceptible effects, and that these can only be perceived by Matter, and through Matter, which is possibly Force in a special aspect. It might be said that if this is so, then Force is Matter in a special aspect ; but the question is, Did Force originate from Matter, or Matter from Force? It is reasonable to conclude that Force did not originate from Matter; for if we give the former an ultimate material nature it is clear that it must be ultimately particulate ; and for the preserva- tion of the identity of the ultimate particle, and for its move- 304 THE EVOLUTION OF MATTER 205 ment on given lines, Force would be absolutely necessary. On the other hand, if one pictures Matter as having been derived from Force there is no such difficulty. Our real difficulty is in conceiving Force or Power in the absence of Matter, or before Matter evolved ; and it is only possible to try to imagine vaguely Force as the Force of Attraction, and in “ pre-creation”’ days sustaining some all-containing system of equilibrium and unity. Our speculative theory is that the All-containing cycle started from such a non-material state of unity and attraction, and that the cycle itself could only start its course through the transformation of attractive into repulsive force, with as a result disequilibrium, separation, and division. There would be a chaos of Force, and a shattering of previously obtaining oneness to its utmost limits. This shattering, however, we suppose to have been followed by the first step towards the restoration of lost oneness through the re-induction of Force of Attraction ; that is, the lost equi- librium immediately began to be regained through a gradually evolving dominance of Attraction. This belief is based on the revelation of all natural growth-cycles, where we can recognise that Attraction induces Repulsion, and vice versa, but all with the inevitable end that Attraction gains the victory. And our next supposition is also based on the revelation of natural law. For as we can trace the constant battle between Attraction and Repulsion, and the dominance of the former force, in the evolution of living Continuity, so we might picture the first victory of Attraction over Repul- sion to take the form of inconceivably small “‘ force-systems ”’ which, like the original all-containing System, would have distinct and complete identity of personality. Repulsion would keep apart, and prevent the coalescence of these ‘‘ ultimate particles,’ or “potential force-units,” but their actual existence would indicate a victory for Attraction. The particles would be insulated in the sense that Force of Attraction would prevent their dissolution, while Force of Repulsion would for the time being prevent their aggregation into larger systems. This is to picture the ultimate particle of Matter as a force system, bound in attraction round some mysterious 206 THE EVOLUTION OF CONTINUITY force-centre. The particle would have definite quantity and size, and as a repellible or attractable unit could be said to have weight. In other words, through the binding and “insulation” of an infinitesimally small “amount” of kinetic force the phenomenon of Matter may have first appeared. If, then, we suppose that the first act of “ Creation” was the formation of this bound force-system through the commencing substitution of Force of Attraction for chaos- producing Repulsion, the rest of our theory puts a smaller strain on the imagination. For the alternating mutual induction of Attraction and Repulsion—the former force maintaining and increasing its dominance in the process— could result in the aggregation of ultimate particles into larger systems, as well as the separation or independence of these systems. Thus, the discontinuity of the ultimate particle could be followed by the first form of particu- late Continuity. These multiparticulate systems might be capable of disintegration as the result of special action of Force of Repulsion, and their component particles set free ; but re-formation would keep pace with disintegration, and the loss of one identity go towards the formation of another —possibly one of higher Continuity. In any case, by the steady multiplication of Continuity we could account for the evolution of more and more complex systems up through the atomic to the living segmental. At the present day the atom is regarded as being a system of ultimate particles to which the name electrons has been given. But atoms are clearly of different fixed species, and if the electron is truly ultimate, it follows that the special characters of atoms must depend on the quantities and “arrangement ’”’ of component electrons; that is, on the form of Continuity obtaining. For the atoms of the different elements are distinguish- able by one marked feature This is their ‘‘ atomic weight.” The atomic weight of an element is the weight of its atom as compared with that of an atom of Hydrogen, taken as 1. So the different species of elements are the different species of atoms, and these vary fundamentally in the matter of weight, or in the degree in which they are attracted towards the earth’s centre. THE EVOLUTION OF MATTER — 207 We know that the earth was once a molten inorganic mass; that it was derived from the evolving sun; and that the sun probably took shape through the condensation of some enormous diffuse “‘nebula’’; and we are led to wonder at what stage of the evolution of the solar system the elements evolved. Had all the known elements evolved before this globe took shape, or before the crust of the earth began to form? We do not know, but it seems clear that some elements had already evolved when the earth was still molten; for the spectroscope reveals that the sun, of which the earth is a fragment, has, although it is still molten or incandescent, certain known elements in its substance ; for example, Hydrogen, Iron, and Sodium. It may well be that further cooling, condensation, or compres- sion have to take place before the sun can evolve the elements of high atomic weight. And perhaps towards the centre of the comparatively cold earth the evolution of elements of higher atomic weight than any known to us is at present going on, or is to take place, as the result of increasing contraction or condensation. ‘On the whole it is reasonable to suppose that a pre- elemental stage of evolution once obtained, and that the known elements evolved through the Intensification of Continuity ; and we get a certain measure of support for this presumption from what is known as the Periodic Law, or the Law of Octaves (Fig. 67). This law is to the effect that if the elements be arranged in the ascending order of their atomic weights, any given element in the series is found to resemble the eighth, six- teenth, twenty-fourth, etc., succeeding it, or preceding it; the resemblance being that of general properties, and also in the matter of highest oxides and hydrides. The following table, taken from Bloxham’s “Chemistry,’’ shows this. One cannot but feel that this table is a species of key to the evolution of the elements, if we could but use it aright. But in spite of our inability to do so, we can see in it indications of past elemental evolution through some form of Continuity intensification. 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THE EVOLUTION OF MATTER 209 result of a process of condensation or aggregation due to the steady action of Force of Attraction. Several possibilities suggest themselves. I. That no element evolved from a preceding one in the table, but that each case came from some primitive element-type which has disappeared. That the known elements are fixed species at the ends of side-paths. II. That each element did actually evolve from some preceding one in the list. III. That each group (vertical series in the table) indicates, or is a special line of, past evolution. IV. That in the ascending order of their atomic weights the elements represent links in a past evolutionary line. It may be noted with respect to the third possibility that Lithium can be obtained from Copper in group 1; and Thorium and Zirconium can be made to produce Carbon in group 4. But, on the other hand, Radium can give rise to Helium, and Thorium to Helium, in both cases to an element of a different group. It is not unreasonable to conclude that the recurring similarity of characters in every eighth element is based on some recurring similarity of atomic internal plan or arrange- ment. There is, so to speak, a repeating cycle of general characters. This is indicated in the matter of the hydrides, for in a given series of eight elements the difference in hydrogen combination increases to its highest in the fourth element, and then decreases by regular steps till the eighth is reached, whose highest hydride is the same as that of the first element of the series. In a different way the oxides also indicate a character cycle which may well be based on a repetition of internal atomic plan. Experiments which have been made with floating magnets of various numbers, and all of similar polarity, give distinct colour to the supposi- tion. For when controlled by a bar magnet of opposite polarity, held above the water, the floating magnets take most interesting arrangements according to their numbers ; and if the numbers are steadily increased, past arrangements reappear on a larger scale. The Periodic Law would certainly seem to indicate that the elements have evolved, and that a feature of this evolution has been the larger and larger aggregation of 14 210 THE EVOLUTION OF CONTINUITY electrons composing atoms. The plan on which the elec- trons became aggregated would seem, however, to decide elemental character, and the character-repetition of the Periodic Law may well indicate a repetition of internal plan whose basic principle is the multiplication of Continuity through addition. CHAPTER XXII THE ORIGIN OF SPECIES THis chapter deals with the origin of sub-species within the different classes or fundamental Species of living Con- tinuity. The latter question has already been considered, and the conclusion has been suggested that the fundamental Species did not originate through any process of Natural Selection in the Darwinian sense, but was a matter of direct modification during development, at the hands of Environment; a process of repeated compression, assisted by the factor of Segregation in its various forms. And we would likewise attribute the origination of sub-species to the same fundamental cause, namely, environmental action. Each new type of living Continuity first appeared as an acquired variation from established plan, and it is our belief that sub-species have originated in the same manner. It must be emphasised that the variation to which we would attribute the origin of sub-species was not “from whatever cause arising’? (Darwin), but was acquired; acquired from Environment. And the acquisition must have been sudden. Natura non facit saltum is clearly untrue, as the gaps between the successive Continuity-types show, and it is difficult not to believe that any variation con- cerned in the origination of sub-species must have been suddenly acquired or imposed. Thus, if we were to accept Darwin’s supposition of slow and gradual change during great stretches of time, it would only be in the sense that the final result had been gradually attained as the sum of very many suddenly acquired variations imposed at intervals. At the present day Darwin’s theory of Natural Selec- tion, although not wholly satisfactory, holds the field, and its only rival may be said to be the Mutation Theory of De Vries. 21 212 THE EVOLUTION OF CONTINUITY It is clear that behind all Darwin’s theory was the crossing of selected Individuals as practised by man in originating new varieties; and that accepting it as certain that in Nature new species must have originated in variation, he had to solve the problem of how Nature could similarly select Individuals possessing given variations, so that interbreeding could take place without interference from Individuals not possessing the variations. As it was imperative that the Individuals possessing the variations should survive, it seemed inevitable to him that those not possessing the variations should be destroyed or weeded out, or removed in some way. He felt that he had the key to the whole problem in his hands when he recognised that of any type of Individual born only a small portion could survive owing to the ‘struggle for existence.”” For he had only to suppose that the variations in question were peculiarly favourable for the perpetuation of the species to account for the destruction or disappearance of the Individuals not possessing these variations. The survivors were in his words “ the fittest,”’ the non-survivors the “unfit.” The Natural Selection was thus obtained by weeding out all but the specially fit, whose fitness was the possession of variations peculiarly suitable for continued existence. There is here an intermingling of truth and fallacy which is difficult to disentangle, and yet the fallacy can be clearly discerned. But it is not our purpose to do more here than give a bare outline of our own theory regarding sub-species origination, and this is done in the form of the following propositions which, incidentally, show where the weak points are in Darwin’s great theory. The propositions are :— The fundamental factor in sub-species origination has been Environment. This it is which in innumerable forms has modified development so that transmissible variation has resulted. It has produced the Acquired Variation. Life itself first appeared as Variation at the call of, or by the force of Environment, and all the variations of Life appeared through the influence of the same factor. The acquired variation is not “from whatever cause THE ORIGIN OF SPECIES 213 proceeding”’; it is distinct from the natural variation present in every offspring the result of fusion of distinct male and female elements. It is direct modification, and harmonious with the modifying force or forces. Any acquired variation must be peculiarly favourable for the life of the organism possessing it, or eminently suit- able for life in the environmental conditions which produced the variation; but not for the continued existence of the species generally, and without regard to environment. Environment varies between extreme hostility and extreme friendliness, and it is clear that in its innumerable forms it can destroy, hinder, or push on development. But whether an Individual is weeded out or perishes, or survives to wax great and multiply, is not owing to the absence or presence of variations peculiarly favourable for the preserva- tion of the species as a whole, but is fundamentally a question of environmental fitness. It is wrong to classify living Individuals as Fit and Unfit. The adjectives should have an environmental appli- cation. The matter is one of Fit and Unfit environments. The first life on this globe must have sprung into being as the fittest response to the environmental forces which produced it. But these forces being themselves variable in nature and action, developing multiplying Life must have harmoniously responded to their influence by exhibiting acquired variation. In fact, no sooner can Life have originated than Environment must have begun to weed it out as well as have continued to encourage it. The Bible parable of the Sower illustrates our meaning well. The seed was all fit to begin with, but its fate depended on the nature of the environment into which it fell. That which fell into good ground and sprang up an hundredfold was initially no better than that which fell upon stony ground, or amongst thorns. The fitness or unfitness was the environment’s. ‘‘ Those on whom the tower of Siloam fell’? were no worse than their neighbours ; they had the misfortune to enter a hostile environment. Man, it is true, can select and cross Individuals possessing transmissible variations, and in this way fix new varieties ; but man here only acts as a selector of Individuals, and it is not really his selection which produces the new varieties. 214 THE EVOLUTION OF CONTINUITY His interference only results in the production of one hundred per cent. pure-breds as compared with a smaller but equally inevitable number in Mendelian proportions. And he cannot prevent a certain proportion of the true- breds (showing the variation) from appearing, even if he try by intercrossing with Individuals not possessing it to delete the variation. Mendel’s experiments with the ‘tall and dwarf sweet-pea plants exemplifies this point. It seems clear that Individual selection is not necessary for the preservation of the transmissible variation, but that the use of the process is to increase the percentage of ‘* preserveds.”’ Environment imprints the variation and preserves it. Darwin pictured a selection or segregation of Individuals possessing a given variation “from whatever cause pro- ceeding ’’; the segregation being in essence a weeding out of the Individuals not possessing the variation. The more reasonable proposition would seem to us to be that Environ- ment selected or segrated developing Individuals of normal developmental potentiality in order to imprint the variations ; or, to put it better, so that the developing Individuals came under the play of new environmental forces which imposed the variation ; the variation being a harmonious response to the new environment’s influence. In a word, Environment used Segregation of Individuals (in posse) in order to produce acquired variation. Like Man, Environment has clearly segregated at times Individuals possessing a variation, but as has been pointed out, this has not been necessary for the preservation of the variation, though assisting ‘‘numerically”’ in its preservation. The survival of the fittest is only the survival of the hereditarily normal in suitable environment; though, of course, one capable of producing variation. The struggle for existence only reflects the law that nothing is gained, or thrives, without some corresponding loss or sacrifice in surrounding Nature; and also that the potentially fit becomes the unfit when forced to develop in hostile environ- ment. At the basis of things, Nature has not worked by means of tragedies, but in spite of them. Tragedies are taken into account, and have their influence in the universal THE ORIGIN OF SPECIES 215 balance, but the ruling principle is the survival of the normal in suitable environment. It is clear that if selection of Individuals has not been the basic factor in the origination of species as the preserver of transmissible variation, we must look for some other form of selection. This offers itself in the Segregation or the Growth-cycle. For the growth-cycle begins with an act of attraction or “aggregation”? between two sexual elements with a resulting temporary loss of identities, and ends in the restoration and segregation of the elements once more. And just as the fused elements inevitably segregate at the end of the cycle, so do the characters potential in them segregate cleanly in Individual descendants. It is true that a crossing over of characters takes place on Mendelian lines, but, as experiment has clearly shown, intercrossing by itself cannot delete a character. Thus, it is the selection or segregation of the growth-cycle, and not that of Individuals, which preserves the transmissible variation as a fixed character. Our main argument may thus be summed up in the following way: All characters have originated as acquired variation under the influence of Environment. Life itself originated as an example of such variation. Experiment has clearly shown that acquired variations can be transmitted, and when this happens they become characters. But apart from this, there is clear evidence that each succeeding form of living Continuity appeared as an acquired variation of ancestral plan, which has been preserved through countless years to the present day. Environment, which has moulded all characters, has itself been always evolving, and by acting in innumerable ways has produced the innumerable variations of Life. Environment has been the one and only producer of new characters, and growth-cycle segregation has been the factor which has all along worked for their preservation. Naturally, the persistence of the environmental forces which produced a new character would, of itself, cause the reappearance of the character in the offspring, if not add to character’s intensity. Individual segregation to new environment, or the equivalent, the imposition of new environmental conditions, 216 THE EVOLUTION OF CONTINUITY would be necessary for the production of acquired varia- tion; but natural selection would not at all be necessary for the preservation of the acquired variation. By its action in insuring the fullest percentage of true-breds it could, however, on occasion, help to preserve a new species in certain conditions of the struggle for existence. In the Mutation Theory, to which reference has been made, De Vries holds that new species originate through sudden change and not by gradual transformation. The sudden changes he calls “‘ mutations,”’ and his belief is that all simple characters have originated inthem. The commonly termed “sport”? is an example of an organism exhibiting mutations. ‘In our opinion the mutation can only be acquired variation, and if this be accepted, then our theory is in fundamental agreement with that of De Vries. For our view is that all simple characters of plants and animals have originated as acquired variations. Clearly, the natural variation, or “‘ fluctuation,’’ exhibited in the transmission of fixed hereditary characters is quite distinct from acquired variation, and being in no sense a matter of modification, cannot be held to have any influence in the origination of new species. CHAPTER XXIII THE EVOLUTION OF SYMMETRY THE subject of Symmetry is a very wide one, including as it does symmetry of Form, of Power, of Time, and of Numbers ; but what we are concerned with is the evolution of Symmetry of Form in cellularly-continuous organisms. It is symmetry of form accompanying Continuity. There is, it is true, a symmetry of form which may accompany Discontinuity, in the sense that free and inde- pendent organisms could be symmetrical with each other. Thus, the measurements of one fish could, in all directions, be exactly those of another. This, however, we may put on one side as of no interest ; our attention being taken up with the fact that the fish, an organism built up of many cells in close continuity, is itself bilaterally symmetrical. It is quite clear that symmetry of form need not be the accompaniment of Continuity, for just as a very asymmet- tical house may be built up with a number of similar bricks, so might the union of many cells result in an asymmetrical organism. In fact, we may say that asymmetry of form would be the inevitable accompaniment of Continuity unless the uniting factor so worked as to produce symmetrical results, or exercised symmetrical power. In the following brief remarks regarding the evolution of living symmetry the independent protoplast, or cell, of the Discontinuous Multicellular Individual has been taken as the unit, or “ brick,’’ with which Nature has worked to produce its balanced effects. The cell, of course, is itself a wonderful organism with a living Continuity of its own, and it may be of symmetrical measurements, or it may not ; but it is evident that the symmetry of form of cellularly- continuous organisms is in no way due to cell-symmetry. The cells of living tissues show endless variation in details of size and shape, and can only be described as being similar to each other. They are not really comparable with “ bricks.”’ a17 218 THE EVOLUTION OF CONTINUITY If the independent protoplast or cell is our unit, it is obvious that in the Discontinuous Multicellular Individual we recognise no symmetry of form, for our subject is the Symmetry of Continuity. At the same time this Individual type, when theoretically complete, or composed of nothing but gametes, may lay claim to Symmetry of Numbers ; for the complete Individual should be equal to 2 to the Nth, a number exactly divisible by 2, or multiples of 2. This symmetry of numbers is, however, in no way concerned in the production of symmetry of form in organisms composed of many cells, for without some special factor we could not expect the continuity of 2 to the Nth to make a symmetrical organism, or a number of such organisms. And it may also be remarked that cell-division into 2, 4, 8, 16 cells, and so on, can have no real influence in producing a sym- metrical organism, though in the early stages of development it doubtless assists the work of the moulding factor. Our proposition may be summed up as follows: That symmetry of form in living organisms has appeared as the result of the action of symmetrical or evenly balanced external forces on the developing new type; that such symmetry as we can recognise in the ascending scale of Continuity has been the inevitable accompaniment of the Continuity exhibited ; that Environment, in many aspects, was the moulder, her material being the plastic, similar, Many; and that numbers, not symmetrical numbers, was all that Environment required for her task. It is in harmony with foregoing pages that we put forward forces acting in terms of Attraction and Repulsion as the producers of symmetry of living form. That is, the same forces which have been opposed to each other in the evolution of Continuity ; and, as in that matter, it is to the dominance of Attraction that most of the credit is due. As the producer of Symmetry, Attraction may be said to have acted in three main ways. I. As Terrestrial Attraction. II. As Solar Attraction. III. As Food-attraction, and other forms of attraction acting in a similar way. THE EVOLUTION OF SYMMETRY 219 Of these three the most important is undoubtedly the first—the Force of Gravity. Through its action this globe first took shape, and to its continued action may be attributed not only the evolution of inorganic, but also of living matter. Whatever moulding Environment may do in other ways than through the force of Gravity has to be done in sub- servience to this force; and this must always have been so. And the result, as a contribution to the equilibrium of personality, is maintained with Gravity’s assistance, or in the face of its action. In evolving this material world, and all within it, as so many different works of Continuity, Gravity, however, inevitably brought into action innumerable force-manifesta- tions whose action as often as not opposed its direct pull. Thus, the intensification of Continuity resulting in the formation of the various elements with their different atomic weights is fundamentally responsible for the varying density of Matter, varying degrees of terrestrial attractability, and even for induced terrestrial repulsion. So it is that the cork or the air-bubble moves away from the earth to the surface of the water, and so it is that Gravity constantly defeats itself. In fact, the movement eternally associated with Life, as well as that of the electron in its orbit, may have its basis in Gravity’s constant contest with itself. In spite of this, Gravity is dominantly an attracting force ; one which directly draws and binds objects to the earth, and compresses them by the pull it exerts on their superincumbent atmosphere, aqueous or aerial. As it is certain that all the road of Continuity’s evolution up to Segmental Continuity took place in aqueous environment, we are thus bound to recognise what an important compress- ing factor water-pressure must have been in the evolution of the successive Individual types. The three chief ways in which Gravity could affect living development are thus: (1) As a force directly attracting towards the earth’s surface ; (2) as a vertically and laterally compressing force by means of the direct pull it exerted on the developing organism’s overlying atmosphere—in other words, as water-pressure. This would come into play when the organism’s density was greater than that of the water. (3) As a force repelling away from the earth’s 220 THE EVOLUTION OF CONTINUITY surface. This would happen when the organism was less dense than the water. It would be indirect repulsion, a matter of displacement by the more strongly attracted water. Gravity acts in the same three ways when the atmos- phere is aerial and not watery. The natural effect of Gravity being to keep an organism at rest in a fixed position, we may conclude that the question of an organism’s being fixed or motile in character will be determined fundamentally by the manner and degree in which it is acted on by competing attraction-forces ; for all movement, except such as is towards the earth, takes place in spite of the direct action of Gravity. Living organisms may be divided into the motile and the non-motile ; that is, such as have the power of moving from place to place, and such as remain fixed in position. It is unnecessary to point out that the increase in bulk accompanying growth involves movement, though in no way connected with motility. Itis, so to speak, a movement of extension, and may be horizontal or vertical in its direc- tion, or at any angle from the perpendicular. The plan on which bulk increases varies according to the Continuity the growing organism exhibits, and it is when this is serial in nature, and growth takes the form of linear extension, that the movement of growth is most detectable. This serial extension, especially if in an upward direction away from the surface of the earth, indicates a certain degree of successful competition by some force acting in an opposite direction to the direct force of Gravity. The competing force may be Gravity itself acting indirectly as a repellent, causing the growing organism to pull upwards more or less as a string of corks would do if fastened by one end to the bed of a pond, and as exemplified by certain sea-weeds and hydrozoal colonies. It may be that the little air-floats of the bladder-wrack originated through Gravity, gases from all parts of the growing “plant” having percolated upwards in the direction of the surface of the water to form little imprisoned collections in terminal situations. But it is very probable that in the origination, and maintenance, of serial growth away from the earth a force THE EVOLUTION OF SYMMETRY 221 directly opposing and distinct from Gravity was a factor, namely, Solar Attraction. Moreover, this force would be a factor calculated to work for immobility. As regards submarine life, it is true that its power would vary inversely with the depth of the water, but in shallow depths it would be considerable. Its full power would come into play in aerial environment, and its results are visible in the immobility and habit of existing plants and trees. For solar attraction at its strongest is at right angles to the earth’s surface, and a developing organism peculiarly sensi- tive to its action would during its growth be subjected to attraction in opposite directions. Thus, in the case of the plant, Gravity is pulling along a line towards the earth’s centre, while the sun is pulling in an exactly opposite direction. Other things apart, this would make for serial extension, and also for immobility. Assisting Gravity in producing and maintaining immobility in the case of the plant, there would, of course, be the attraction exercised by water and nourishment in the earth on the root. Solar attraction, however, is not the only force competing with Gravity, and is probably not the fundamental one upon whose action the motility or immobility of evolved organisms has depended ; for this we believe to have been Food-attraction, and minor forms of local attraction. When an organism has a fixed habit, its food invariably surrounds it, or is brought within its reach by causes external to the organism. In such cases, Food-attraction, as a force demanding the response of motility, does not exist for the organism, and Gravity and solar attraction successfully hold the organism in situ. But in many cases the attracting food is not brought within reach of the organism, and may itself be immobile; it may be patchy in its distribution, and the patches may be situated at considerable distances from each other. The organism then, as the attracted entity, has to respond to the source of attraction by calling into play its locomotive powers, which themselves originally evolved through this habitual call for responsive movement. And responsive movement of this sort has invariably to be manifested in the “ presence” of the force of Gravity. Clearly, Gravity might assist movement, but in many ways it would always be trying to prevent it. On the whole, 222 THE EVOLUTION OF CONTINUITY we may say that the motility displayed by so many living organisms, in spite of any opposition which Gravity and Solar attraction can offer, is proof that Food-attraction can defeat both these forces. Naturally, Food-attraction, though probably the most powerful of factors calling for motility, is only one of many; and sources of repulsive force could demand movement away from their neighbourhood. As we shall see, there is a Symmetry associated with immobility, and a Symmetry associated with motility, and they are distinct. It is not the purpose here to take one by one the different types of Individual Continuity in our brief survey. Certain of these can be ruled out as asymmetrical; for as Individuals they develop as colonies, growing in serial and lateral extension, and branching irregularly. Thus we exclude the Filamentous, Ccenocytic, Continuously Zooidal, and Continuously Megazooidal Individuals. And such as the Discontinuously Zooidal, Megazooidal, and Segmental can have no symmetry of form, owing to their component units being free and independent. The problem, in fact, narrows itself down to the Symmetry of certain organisms which may, as in the distinct zooid, be part of an Individual, or as in the higher segmental organism be the whole Individual. It is the problem of the symmetry of the zooid, the megazooid, and the segmental organism. It is to the last of these, and its bilateral symmetry, that most attention shall be given. We may credit a zooid, such as the Hydra zooid, with being built on a symmetrical plan, though the contractile powers of the organism tend to obscure it. For all purposes it has the symmetry of a cylinder. It is impossible to say definitely how this cylindrical form had to take shape, though on page 164 we have made a few speculations on the matter; but we would attribute the tubular form of the zooid to the effects of water-pressure on the development of a zygote whose inherited potentialities were filamentous. So that an inherited power of developing as discrete branching series of cells was realised as lines of cells united in lateral continuity. It is not difficult to see how even water-pressure acting on all sides could give and maintain a cylindrical THE EVOLUTION OF SYMMETRY — 223 external form to the developing new type, but the hollow interior is not so easy of explanation. It may be that the factor of diminishing density mentioned on page 164 was involved. The cylindrical tube the zooid represents is the basis of megazooidal symmetry. There are two types of mega- zooid, the anemonoid and the medusoid, the former prac- tically immobile, and the latter free-swimming, and in both there is an external symmetry of form, and an internal symmetry of parts. In the anemonoid megazooid the external symmetry is that of a short cylinder, and it reflects the internal symmetry of structure. The theory offered on page 88, and the accom- panying figures, explaining the evolution of the anemone- megazooid, serve to show how the organism came to be radially symmetrical, and to avoid repetition the reader is requested to refer to them. We would only point out once more that the new form of Continuity constituted by the megazooid was the result of compression during develop- ment. The fertilised ovum had the power of becoming many tubular zooids on a colonial plan, and an evenly compressing force, which we believe to have been water- pressure, accepted the hereditary gift of the zooidal tubes, but caused them to develop in close lateral continuity round a central stem, and the megazooid was the result. The radial symmetry of the medusoid-megazooid is to be explained in a similar way (page 94), the hereditary gift being here sporosacs or sexual zooids, and not tubular vegetative zooids. CHAPTER XXIV SEGMENTAL BILATERAL SYMMETRY Tuis is well illustrated by the typical Fish, and by terrestrial vertebrates generally ; and as the latter have undoubtedly derived their bilateral symmetry from some primitive piscine type, it is to the modern typical Fish that we shall turn our attention. In Chapter XIX it has been suggested that the segment of the Fish has a medusoid derivation, and that the primitive Fish was equivalent to a continuous series of medusoids which, as the series tried to develop, were compressed to become indivisible segments of one organism (see Figs. 57 to 62). As the plan of a medusoid is radially symmetrical, it is not difficult to see that here we have the basis of piscine symmetry. That is, we may regard the primitive Fish as having had hereditarily transmitted to it the capacity of developing as a cylindrical tube built up of segments, each radially symmetrical. If this be admitted, the problem which then remains is how such capacity or potentiality came to be realised as the bilaterally symmetrical Fish, The explanation which we have to offer is that Environment, as modifying force, evolved the Fish’s tapering form and bilateral symmetry ; and that the two main ways in which Environment acted were probably as Gravity, and sources of attraction competing with this force. The force of Gravity, acting directly and in the form of water-pressure, could never have evolved the piscine form without the interference of other forces. Gravity, uninter- fered with, would have gifted the results of its compression with immobility, and while capable of moulding development on some cylindrical plan, as in the case of the zooid and anemone-megazooid, could never alone have produced bilateral symmetry. But the primitive Fish must have been actively motile from the first, and it is to this motility 224 Sera east IE : PO TNTETAIAS Vex SEGMENTAL BILATERAL SYMMETRY 225 in the face of gravitation forces working for immobility that the shape of the typical Fish is due. To a certain extent the Fish’s locomotive powers are based on those of ancestral medusoids; but only to a certain extent. The jelly-tissue in the bell of the medusoid has been the forerunner of the Fish’s muscle-tissue. But, on the other hand, locomotion in a medusoid is almost, we might say, a side-result; bell-contractions being due to the demand for a regular radial-canal circulation. The medusoid’s food surrounds it on all sides, and the organism does not move along owing to direct-food-attraction, but rather as the result of bell-contractions produced by the intake of food and accumulation of impurities. In the developing primitive Fish, however, the case would be <—— Fic. 68.—Showing how movement in the face of water-pressure would produce a torpedo-like form in the evolving Fish. A, a diagram representing the developing primitive Fish at rest, evenly pressed on all sides by surrounding water. B, roughly shows the lines of water-pressure a would experience if moving through the water in the direction of the large arrow. a being plastic, its elongating form would be made to take the shape enclosed by the dotted lines in B; that is, it would become c. different, for its food would not be in a fine state of suspension in the water of respiration, but was, we may presume, coarsely particulate and scattered in its distribution. The young Fish had therefore to develop the power of moving in a definite line towards a localised source of food-attraction. It would develop, in fact, a voluntary muscular system. And it is to be noted that all voluntary movement would be in the face of ever-acting gravity and water-pressure. The young evolving Fish would always have the same part of its body leading the way as it moved through the water, and during movement this part would encounter strong resistance or friction. During rest the water would press evenly on all parts of the body, but during movement 15 226 THE EVOLUTION OF CONTINUITY special compressing force would play on the developing organism with inevitable moulding results. It would cause the development of a tapering form like that of a torpedo (Fig. 68). It is interesting to note that the form which engineers give to an object, such as a torpedo, so that as it moves through the water friction shall be reduced to a minimum, is the actual form which water-friction forces a plastic body to take when moving through the water. But while water-friction could give the elongating primitive Fish (its hereditary symmetrical gifts being re- membered) a tapering symmetrical form with a circular cross-section, it could not unaided mould it on bilaterally symmetrical lines (Fig. 69). a. v. Fic. 69.—aA, cross-section of Fish ; d, dorsal; v, ventral aspect ; dv is the only dividing line which can give symmetrical results. B, cross-section of a torpedo, divisible into symmetrical halves by any diameter. While terminal compression of the developing anterior segments of the primitive Fish was going on the anterior mouth was formed (see page 186), the food entering by it passing towards the primitive anus at the opposite end of the organism. This food would be more bulky or coarsely particulate than that enjoyed by the ancestral medusoid, and it would not stream through the alimentary canal, but collect in the stomach to be digested before slowly passing down the intestine. Thus the Fish would, as it were, always carry a load of food material inside it. On the presumption, then, that the digestive contents would be of greater density than the water, their attraction towards the earth would have its influence on the young Fish’s physical equilibrium. We are led to this conclusion, moreover, when we examine SEGMENTAL BILATERAL SYMMETRY 227 the present-day Fish’s anatomy. Apparently the digestive load was strongly attracted to the earth, and the alimentary tube, instead of being suspended in the general somatic cavity, sank down to be as near the earth as possible, where with its contents it became so much “ ballast” in the body of the Fish. And as alimentary development proceeded, with the elongation of intestines and the formation of associated organs such as the liver, the digestible parts would form a bulky and heavy mass. The fact that the cross- section of the Fish is not circular, in spite of even friction forces having played during development on all parts of the circumference, but shaped as below, can hardly be attributed to anything else than the pull of Gravity on the digestive tract. That is, the region where this tract is situated, termed the ventral region, came habitually to face the earth through the Force of Gravity, and the density of the digestive organs and contents was so relatively high as to resist the forces making for a circular cross-section and gave the Fish its ventral fulness. It may be remarked that in all vertebrates the ventral surface is invariably that which is habitually turned towards the earth, and this inclines us to believe that the digestive viscera and their contents have always tended to be of greater specific gravity, or to be more strongly attracted towards the earth, than the nervous, muscular, and supporting tissues of animals. Exceptional cases, such as those of the sloth, or of man, only reflect the late adoption of peculiar posture. The viscera of the developing primitive Fish would thus act as so much ballast, which, by exerting pressure down- wards and outwards at the call of Gravity, would give the Fish a pear-shaped instead of a circular cross-section, and 228 THE EVOLUTION OF CONTINUITY thus be a factor in the production of bilateral symmetry. The ballast would work for the maintenance of a habitual poise, and tend to prevent rolling when the organism moved through the water, and by its resistance to water-pressure forces trying to produce a torpedo form would bring about the compromise of streamline and bilateral symmetry. Assisting in the maintenance of an even keel in the majority of known typical fishes (the exceptions being flat fish, marsipobranchs, and elasmobranchs) there is a structure known as the swimming bladder ; this lying beneath the vertebral column, and being a species of sac whose contents are nitrogen in freshwater fishes, and oxygen in those inhabiting salt water. Although in the Mudfishes (Dipnoi) it appears to have evolved respiratory functions and to act as a facul- tative lung, there can be little doubt that its presence in all other eases is concerned with physical equilibrium. The gas the swimming bladder contains seems to come from the fine bloodvessels ramifying in its walls, and one is inclined to suppose that the organ was originally produced as the direct result of water-pressure which caused the escape of gas from the blood. The gas would naturally tend to collect in the highest region of the fish, thus increasing the ballast effect of the abdominal organs. On this supposition, the deeper the fish would go the more gas would be in the bladder, and the nearer the surface the reverse would be the case. The absence of a swimming bladder in flat fish, such as the flounder, is interesting in relation to the body asymmetry exhibited. For the flounder in its early days is bilaterally symmetrical, and swims on an even keel after the manner of typical fish ; but as growth proceeds, the animal generally takes to lying on one side on the sea-bottom, finally adopting this pose permanently, and living and swimming with one side uppermost. Thus, what appears to be the back or dorsum of the flounder was originally the side. With the adoption of the new position, one of the eyes finds itself applied to the sand and temporarily useless, but it at once begins to work its way towards the dorsal surface and comes to lie asymmetrically alongside of the unaffected eye. Similarly, the mouth becomes twisted in adapting itself to the new position. The body is also asymmetrical, the under white surface being flatter than the dark dorsal one. It is safe to say that the developing flounder fell over because it lost its previously maintained state of physical equilibrium, and our suggestion is that this was at first preserved by the ballast of the digestive tract. It might be that the falling over was the result of relative decrease in weight of the visceral organs and contents owing to the growing fish taking to a food of low density; but it is also interesting to note that the failure to develop a swimming bladder could help to bring about the accident. On the other hand, elasmo- branchs and marsupobranchs have not this organ, and they are not flat fish. CHAPTER XXV SEGMENTAL BILATERAL SYMMETRY (continued) WHILE the development of ventral ballast was proceeding in the evolving primitive Fish, other factors were working to produce bilateral symmetry of form. The bilaterally symmetrical brain was developing in response to a demand for symmetry of power in all it controlled, and this brain symmetry had its own influence in producing and main- taining that of the Fish’s body and appendages. The development of a brain was one of the results of terminal compression (page 193). For a given part of the developing Fish was constantly obliged to lead the way when the organism moved through the water, and thus became the region which received with fullest force all attracting or repelling influences acting along the line of its course. This leading or anterior part was, in fact, called on to register and distribute the influences to the rest of the body, and, as an inevitable result of the water-resistance encountered during movement, the anterior segments were massed together as they developed, and the ancestrally derived ganglia took shape as the registering and controlling brain-mass. The young primitive Fish would be stimulated to develop its locomotive powers through Food-attraction, and also through sources of repulsion; and while the weight of the abdominal viscera would, as we have seen, assist in the maintenance of physical equilibrium, it is clear that this could be easily upset by suddenly acting external forces, and that means would require to evolve to correct this. Moreover, if the locomotive appendages formed by the Fish were not capable of exerting symmetrical power, they them- selves would upset equilibrium. 229 230 THE EVOLUTION OF CONTINUITY But sources of Attraction and Repulsion would, in demanding the formation of the Fish’s fins, also demand that these should be symmetrical in shape and situation, and for the following reasons: Lines of attraction or repul- sion are for all purposes straight lines, and unhindered response along them in the form of movement towards the source of attraction or away from that of repulsion must be undeviating movement. Thus, the above forces, in inducing through evolving nerve-centres the development of motor appendages, demanded that these should in the first place develop symmetry of power calculated to prevent deviation. Such symmetry of power could be exerted by two appendages, or sets of these, asymmetrical in form and position; but in the case of the developing primitive Fish the body which was called on not to deviate was already moulding on bilaterally symmetrical lines, so that the lateral fins would naturally appear in symmetrical positions, and each pair be symmetrical in form. The asymmetrical would not be allowed to appear. In a word, local sources of attraction and repulsion would cause the developing Fish to move, and to do this to or from them in as straight a line as possible; and it would be they who made the Fish produce fins, and caused these to appear in symmetrical pairs. During the responsive movements of the developing Fish external physical forces would constantly try to produce deviation from the line of attraction or repulsion, and this would call for correction ; and it would be the source of attraction or repulsion itself which would correct such deviation as soon as it occurred, and do so by means of a bilaterally symmetrical brain and nervous system. We have indicated Food-attraction as the chief of the local attractions which, in the face of, or at times with the help of Gravity must have called for locomotion. But sources of direct repulsion must also have been a powerful factor. Repulsion is, however, but reversed attraction. If the nerve-centre at the anterior end of a Fish is affected by force of repulsion acting directly on it, it moves away from the source as quickly as possible ; the organism swings round, presents its tail to the source of disgust, and moves SEGMENTAL BILATERAL SYMMETRY 231 away ; and it does so in as straight a line as possible. This is what the force of repulsion demands. The Fish could naturally deviate abruptly from this straight line to move in @ new one at the call of some laterally situated new source of repulsion, or one of attraction ; but whether this occurred or not, the point to note is that repulsion from one source or direction is equivalent to attraction in the opposite direction. This may seem rather obvious, but it is none the less important (Fig. 70). Naturally the deviation to be corrected could be either upwards or downwards, or to the right or left, but we shall fr a_i oA. t ar U) Fic. 70.—To illustrate how repulsion from one direction is equivalent to attraction in the opposite one. 1, 2, repulsion acting from R on the brain B of the organism, causes its attrac. tion in the opposite direction along a straight lme. From this line, however, there might be deviation at the call of some definite source of attraction, as in 3. confine our remarks to the correction of lateral deviation when the Fish is moving on an even keel in a given plane. This correction would demand the formation of a bilaterally symmetrical brain. If we draw the developing Fish as lying obliquely across a line of attraction, as in Fig. 71, it is clear that the force would be most strongly exerted on the right side of the anterior end of the organism ; and similarly, in 2, it would be most strongly felt on the left side. In either case the immediate result would be asymmetrical power response. If the Fish were a rigid inanimate object something 232 THE EVOLUTION OF CONTINUITY like a torpedo in shape, and had a brain-equivalent in the form of a steel nose; and if this were to receive obliquely the attracting force of a strong magnet, then the object would swing forwards into the direct line of force and con- tinue to move without deviation. But the Fish’s movement is not passive response, and the attracting force calls for active fish movements. If we confine our attention to the lateral fins as pro- pelling agencies, it is clear that the Fish in the last figure, if called to swing to the right to get in the main line of attraction, would have to drive with the fins of the left side, or that furthest from the source of attraction. Conversely, if it had to swing to the left, it would have to work the fins of the right side of the body. But in either case the immediate effect would be that the Fish would swing beyond Fie, 71 the straight line of attraction unless something prevented this. The next figure shows how swinging past the straight line is obviated. Thus it will be evident that the Fish’s brain would be called on to have two similar parts which would evenly balance each other and so prevent deviation; and which could also correct deviation when this occurred. An interesting point is to be noticed here. If responsive movement to the right involves left fin movement, and vice versa, it is clear that the messages sent from the brain to the fins must cross the body; in other words, that the motor nerve-tracts would require to be crossed. This is the logical conclusion, and the fact is that in the typical Fish, as in all true vertebrates (these having evolved through some primitive piscine type), a crossing of main motor nerve-paths always takes place. In Man, SEGMENTAL BILATERAL SYMMETRY 233 for example, the supreme motor centres are situated in the cortex of the right and left cerebral hemispheres. From these centres the right and left motor tracts pass down through the substance of the brain, converging as they do so, to the upper part of the spinal cord called the medulla, ‘SA "SA SA iy A B ms ay A (3). R R R. Fic. 72.—Correction of deviation in the evolving Fish. R-sa is the straight line of attraction leading to sa the source ; P, Q, are the left and right sides of the developing brain; a, B, the left and right lateral fins. In position (1) the attracting force affects side g of the brain more strongly than side Pp, and in demanding movement forwards into the line R-sa can only obtain this by obliging the left fins, a, to drive strongly. If side P is unaffected by the force at first, the swinging of the Fish into R-sa4 soon brings P under sa’s influence, when the right fins, B, also drive. And they do so with increasing power until, when the long axis of the Fish is in the line R-sa, both sides of the brain are equally affected by sa, and the symmetrical drive of the right and left fins produces straight forward move- ment towards sa. A similar drawing could be made with the Fish subjected to force of repulsion from an antero-laterally situated source R. In this case the Fish would be attracted to a posteriorly laterally situated source of attraction, sa, and have a greater distance to swing round to move in the line leading from R to SA. where, anteriorly situated, they are visible as the “ pyramids.” Immediately below the pyramids the majority of the con- ducting fibres of the right side cross over to run down the left side of the cord, while the majority of those on the left 234 THE EVOLUTION OF CONTINUITY cross over to the right. In both cases the remainder continue down the cord anteriorly, but at intervals give off fibres to run down the opposite side, and this goes on till finally decussation or crossing is complete. Thus it is that the right side of the brain controls the movements of the left side of the body, and the severance of the right pyramid would cause left-sided paralysis; the reverse occurring if the left pyramid were severed. In the last figures, it will be noticed that the lines of attracting force which call for deviation into the straight pass through the near side of the brain to the side of the body whose fins are called on to act strongly; and there is some reason for supposing that the habitual crossing of Fic. 73.—The main directions taken by light-waves passing to the brain of the developing primitive Fish. 0, 0, objects straight ahead to all purposes; 0’, o’, objects situated well to the right or left; 3B, the brain; J, 1, direction of light-waves. force-lines from before backwards was a factor in deter- mining crossed nerve-tracts. But the brain is not an exposed organ, and force-waves have to pass to the brain along what are called sensory paths or nerve-tracts. No matter where the source of the waves is situated, these require a sensory path to conduct them to the brain cortex, from whence motor impulses pass down to the fins, and this has to be understood with respect to preceding figures. While the bilaterally symmetrical brain was taking shape, sensory conducting paths leading to it would also be developing, and these may, for our purpose, be divided into three main classes: (1) those conducting waves from sources situated somewhere in front of the brain; (2) from SEGMENTAL BILATERAL SYMMETRY 235 sources somewhere behind ; (3) from sources directly to the right or left. As examples of the first we shall take the optical sensory paths. In Fig. 73 there is represented the anterior end of a developing primitive Fish, and the main directions in which light waves would pass to the brain from objects situated anteriorly. Now our suggestion is that the rays of light have Fic. 74.—Diagram of the course of the fibres in the human optic tracts. R, right eye; L, left eye; o, c, crossed tracts ; 8, Ss, straight tracts. The crossed tract of the right eye, coming from the nasal half of the right retina, passes through the chiasma to run to the left hemisphere in company with the straight tract of the left eye, coming from the temporal half of the left retina. The dotted lines suggest fibres crossing over between the corpora quadrigemina (cQ), or further back towards the cortex. LH, RH, left and right hemispheres. demanded sensory paths to lead them to the brain, and also demanded that these paths should follow the direction the rays themselves habitually take; and that as a result of this a crossed sensory optic tract has inevitably been formed in the typical Fish. In the next figure the plan of the human optic chiasma is given for comparison (Fig. 74). The next diagram deals with tactile impressions from sources situated behind the brain, and we can see how in every case the strongest waves the brain would receive 236 THE EVOLUTION OF CONTINUITY would be those crossing to the opposite side of the brain (Fig. 75). Naturally it is to be remembered that our evolving Fish had as an ancestral gift a nervous system somewhat as in Mua a 3 Se Soe sam thee TY Fic: 75.—Diagram illustrating how tactile impressions behind the brain would demand crossed sensory tracts to conduct them to the brain. If we imagine the evolving primitive Fish to be constantly receiving tactile impressions on the surface of its body at different points, as in the figure, we can see that the main lines of force would be always across the body, and that of those passing in the direction of the brain the strongest would be the ones reaching the hemisphere of the opposite side. Fig. 61 on page 192, and that this plan would, as it were, only require modification in its attempts at realisation. But our suggestion is that the method of this modification Fie. 76.—A suggested explanation of sensory decussation in the cord and medulla. c, cord; »P, P, points of decussation in the cord ; D, great decussation in the medulla ; s, the spreading out on the cortex of the brain; 1, 1, lines of force whose direc- tion may have determined the course of the nerve-tracts; B, brain. was fundamentally due to the impressions which the evolv- ing organism came habitually to receive. Is it not possible that the decussation of force lines as pictured in the last SEGMENTAL BILATERAL SYMMETRY 237 figure was the cause of the great decussation of the sensory tracts occurring in the Fish and higher vertebrates in the region of the medulla, and also of the spreading out of these to reach the cortex of the brain? Might it not also explain the minor decussation at intervals all up the cord, as suggested in Fig. 76 2 From this figure it is clear that a painful impression at, say, R would be equivalent to attraction towards A, the continuation of the line from R, and the proper motor response would be an extra strong drive of the fins on the @ Fic. 77.—Diagram of the crossed motor tract which causes the human eyes to move towards a source of attraction on the right. 1, left external rectus; 2, left internal rectus muscle; 3, right internal rectus; 4, right external rectus ; 5, 6, nuclei of left and right 3rd nerves; 7, 8, tracts from 6th nerve to opposite 3rd nerve; 9, 10, nuclei of left and right 6th nerves; 11, 12, left and right cortical centres. A motor impulse from 11 would cross over to 10 and cause 2 and 4 to contract, the eyes thus moving to the right where the attract- ing object was situated. There is really double decussation here. (After Swanzy.) same side as R; the motor impulse coming down a crossed motor tract. If R were a pleasant impression, the reverse would be the case. With regard to sight sensations, in order that the eyes turn towards the source of light a crossed motor tract would also be necessary as the complement of the crossed sensory optic tract, and the next figure shows how this occurs in the human brain. Crossed motor tracts here produce the expected result. But if we take the response of fin-movement to bring the body towards the source of light attraction, it becomes 238 THE EVOLUTION OF CONTINUITY apparent that a crossed motor tract leading to a right fin would, if this drove with vigour, cause the Fish to move away from the source. The fin would have to backwater to help in the proper response. Clearly the brain is such a complicated organ, and its communicating paths so imperfectly known, and the body’s responses so multiple and complex, and mutually influential, that no more than superficial suggestions have been offered above. But our main point remains to be emphasised, namely, that the avoidance, or correction, of deviation in fish locomotion Fie. 78.—Diagram of fissures, convolutions, and functional areas of human right hemisphere. (After Jacobson and Steward.) would demand a bilaterally symmetrical nervous system, and that local habitually acting sources of attraction and repulsion calling for undeviating response would be the ground factors in the production of the duplicate brain. The bilateral symmetry of birds and quadrupeds has clearly been derived in the first place from the primitive Fish. Like the fish, the typical bird is able to leave the surface of the earth and move through its surrounding atmosphere in spite of the direct pull of Gravity; the difference being that the atmosphere of the bird is air, and wings take the place of lateral fins. On the whole, however, SEGMENTAL BILATERAL SYMMETRY 239 Gravity is victorious, and the larger part of the bird’s existence is spent on the earth, or on the water. For moving on the surface of the earth the bird has two symmetrical legs, and as in the case of the wings this symmetry reflects the call for undeviating responsive movement towards any point of attraction, or away from any source of repulsion. In the case of quadrupeds, it may be said that, with the exception of such as live in trees or live an amphibious existence, the only possible form of deviation is lateral— to the right or the left. The body-mass is, as it were, slung on four upright supports, symmetrically paired, with the abdominal contents invariably sagging downwards in the middle towards the earth’s surface. Man is after all but a quadruped who has learnt to go about constantly on his hind legs, and moving as he does on the earth’s surface the deviation he has to avoid or correct is lateral. It is interesting to note that the situation of the cortical centres in man’s brain tend to confirm the supposition already mentioned, that the direction of habitual force-lines impinging on the evolving primitive Fish could determine the direction of the main nerve-tracts. For if we turn to Fig. 76, and compare it with the next below, we can see that the lines from the region of the posterior limbs, or fins, pass to the mesial and anterior part of the opposite hemisphere ; those from the anterior limbs to a point farther out and behind; while any from the head region would pass to a still more external or posterior part of the cortex. CHAPTER XXVI ALTERNATION OF GENERATIONS. PARTHENOGENESIS ALTERNATION of Generations is usually defined as the appearance in any Individual of two kinds of component organism, actually or virtually independent, one of which is sexless and whose chief functions are those of nutrition or support, while the other develops sexual organs with a view to the perpetuation of the species. But while such a definition is correct as far as it goes, it only describes one limited aspect of a phenomenon exhibited in all living Individuals. For our contention is that Alternation of Generations in the generally accepted sense is simply one aspect of the everywhere-obtaining Alternation of Inter- mediate and Terminal Cycle-stages. In itself the term “‘ Alternation of Generations” is not appropriate to the phenomena exhibited, for these take place within the Individual, which is one generation and no more; nor are the asexual organisms produced by any act of generation, but by gemmation or fission. This is obvious if we turn to the alternation as it is displayed by a hydrozoal colony. The development of the normal Individual is for the restoration of the lost personalities of the originally com- bining elements, and it is just because this restoration is a very gradual process that cycle-stages of the Individual in which it is going on can be recognised, to contrast with the terminal or sexual stages marking restoration. Naturally, where the Individual develops in cellular discontinuity the sexless or intermediate cycle-stages are evanescent, and the alternation is not strikingly apparent ; but where Continuity unites and arrests definite numbers of cell-stages of the Individual to form zooids or higher 240 ALTERNATION OF GENERATIONS 241 continuous cell-multiples, which may be free or may remain attached to each other, the alternation may attract atten- tion. For the arrest accompanying Continuity here prevents sexless or intermediate cells, or their multiples, from ever becoming sexual, and these thus remain in lasting contrast with the ultimately appearing sexual forms. Regarding, then, Alternation of Generations as essen- tially Alternation of Cycle-stages, we might summarise the ways in which it is exhibited in the ascending Individual scale. I. The Discontinuously Multicellular Individual.—Fig. 79 represents diagrammatically such an Individual developing as so many sexless unicellular organisms, each an evanescent intermediate stage in the cycle, and drawn as a number of ‘‘o’s.”’ When this Individual is theoretically complete it is composed of nothing but gametes (x, x). 0 0 ® 0 4 x c& | =| 2 2 & o oO GO OD 86 xX xX xX - xX & «= becomes oO 9 0 OD @ x{ =& & =X A =X = 0 0000 x xX x x x x x plus— Fic. 79. For example, an examination of the blood of a person affected with malaria will, in the early days, reveal only amceboid or “‘ sexless ’’ forms of the parasite ; but at a later date gametes or sexual forms may be discovered. The former are stages on the road to gamete production, and become gametes in their future product. Discontinuity is [aoe TeT=T=1- Tel t t game eed ells Zamcte. Fie. 80.—Diagram of filamentous growth (as in Spirogyra), exhibiting cellular alternation of cycle-stages. here the factor which, other things being equal, allows this to occur. When the Individual is truly complete, the inter- mediate or ‘‘sexless”’ stages should all have vanished, and no alternation would be observable. Il. The Filamentous Individual.—Here there is the same 16 242 THE EVOLUTION OF CONTINUITY alternation as in I, but as there is filamentous Continuity, and as a result, temporary cell-arrest, the phenomenon is more clearly observable; a given filament displaying at the same time sexless intermediate cells and sexual cells or gametes (Fig. 80). III. The Cenocytic Individual.—In this no less than three forms of the alternation may be offered. (a) Protoplastic ; there being protoplasts which, arrested on the road to become sexual, contrast with forms which as gametes are sexual. (b) Coenocytic; whole sections of mycelium con- taining sexless protoplasts contrast with sections which, as gametangia, contain gametes. (c) Mycelial; as where an Samtts om famttangton. F ene” Fa; spore” er ee eo Troteblest A. B. Fic. 81.—a, Protoplastic and Cenocytic alternation of cycle- stages; the protoplasts alternating with the gametes, and the ceenocyte with the gametangium. s, Mycelial alternation, the mycelium bearing spores alternating with that producing gametes. original mycelium produces only spores, and the mycelia arising from these produce gametes. IV. The Discontinuously Zooidal Individual._—In such (e.g. Hydra), there is the alternation of the sexless body-cell with the sexual element. But in addition there is zooidal alternation. But as the zooids are discontinuous, the sexless condition is temporary. It is the alternation of the dis- continuously multicellular Individual in a higher form (Fig. 82). V. The Continuously Zooidal Individual._—Here also the alternation is cellular and zooidal; but as many zooids are permanently arrested owing to Continuity, and adapta- tion to special function, the sexless and reproductive zooids form a striking and enduring contrast, heightened by the ALTERNATION OF GENERATIONS 243 peculiar structure of the latter. Frequently the repro- ductive entity is a megazooid and not a zooid (Fig. 83). Byebsa st Fic. 82.—Alternation of cycle-stages in the Discontinuously Zooidal Individual. VI. The Discontinuously Megazooidal Individual.—Owing to discontinuity, the sexless megazooids all ultimately Fic. 83.—Alternation of cycle-stages in the Continuously Zooidal Individual. In a, the vegetative zooid, v, contrasts with the sexual zooid, or sporosac, s. In B, the contrast is with a sexual megazooid, or gonophore, g. become sexual (as in I and IV). The alternation is cellular and megazooidal; the example being Aurelia (page 103). 244 THE EVOLUTION OF CONTINUITY VII. The Continuously Megazooidal Individual.—The alternation here is sometimes as in VI; but in certain compound corals, such as Alcyonaria, some megazooids are permanently arrested for special function and never become sexual; the phenomenon being very striking. VIII. The Radiate Individual.—The only alternation is cellular, the Individual being one cellularly-continuous organism. IX. The Discontinuous Segmental Individual.—In what might be called a typical case, such as Aphis, the alter- nation is generally similar to that in I, IV, and VI; that is, it is cellular, and also the alternation of a sexless with a sexual cell-multiple. The discontinuity of the “ neuter” aphis would lead one to suppose that were life prolonged enough, repeated ‘‘ gemmation”’ would end in the produc- tion of sexual elements. But the presumably permanent arrest of the neuters makes these contrast strikingly with the final sexual forms. The case of the honey-bee is peculiar, for there are three classes of Bee-Individual. In one of these, the sterile worker, there is no alternation of any sort, because no sexual elements are produced. In a second, the occasionally drone-producing worker, this insect alternates with the sexual males formed from it. In the drone itself there is cellular alternation. In the third, the queen-bee Individual, the somatic cells of the queen alternate with her true ova, and the somatic cells of the drones she produces alternate with the drones’ male elements. X. The Continuously Segmental Individual.—Cellular alternation alone is exhibited. It is true that certain segments contain no sexual organs and alternate with those that do, but owing to close continuity the segment cannot as a rule be strictly delimited. In an organism like the earthworm we might say there was segmental alternation. In the above sense it is therefore suggested that “ alter- nation of generations’ is a phenomenon exhibited in some form in all living Individuals; and that it is truly the alternation of intermediate cycle-stages with terminal sexual forms as affected by varying intensifications of Continuity. ALTERNATION OF GENERATIONS 245 PAaRTHENOGENESIS. Parthenogenesis has been defined as the production of new organisms by virgin females, without the intervention of males. Owen, who originated the term, gave it, however, a wider meaning, and applied it to all processes of gemmation exhibited by sexless beings or virgin females. In our opinion Owen’s definition is to be preferred, though we would modify it to ‘“‘all processes of gemmation by temporarily or permanently sexless beings which are always parts of Individuals.” This is to widen the definition in one direction and to narrow it in another, making it include phenomena which are not usually held to be parthenogenetic, and ruling out the development of the unfertilised female element as not true parthenogenesis. Many, no doubt, would rule out the former and include the latter, but this apart, one thing is obvious, that the term should not be so widely applied as to embrace two such distinct phenomena as the unaided development of the unconjugated gamete or unfertilised ovum, and the production by gemmation of a Hydra zooid, a coral megazooid, or an aphis. And for this reason: that in the first cases we are dealing with the abnormal origination of a new Individual, whereas in the second the matter is one of the production of a further portion of an Individual. The gamete is a sexual element, but the cell from which arises a neuter aphis can surely not be classed as such. Were it to be so, then each successive neuter aphis would be a new Individual of unusual sort and represent a new generation. We would, in fact, limit the application of the term “ Parthenogenesis” to the production of new organisms from cells which are not terminal or sexual cells, but sexless intermediate cells ; the producer of the new organism being part of an Individual, and its product (and antecedent producers, if any) the remainder. The development of an unconjugated gamete or an unfertilised ovum is abnormal, and where, as with certain Alge, it occurs in Nature, one is inclined to presume that accidental special factors have interfered to upset the equilibrium of the gamete in the absence of the specific 246 THE EVOLUTION OF CONTINUITY upsetter. Certainly, in the classic experiments of Loeb this was apparently the case. Loeb found that solely by pricking with a very fine needle the unfertilised ovum of the frog he could make development start and proceed in an apparently natural manner. The unfertilised ova of the sea-urchin can also be made to develop by exposing them to the action of chemical solutions. As in both cases the development of a true sexual element occurs, in our view this is not par- thenogenesis ; but apart from this it is justifiable to say that in neither case was there unaided development. We might well say that the matter was one of “ non-specific fertilisation.” The needle enters the ovum and withdraws; it leaves none of its substance in the ovum, but it does something, and the presumption is that the results which follow are due to the physical effects of the puncture. The main effect is the breach of Continuity, and it seems possible that, in accordance with the general rule, the breaking of Continuity by causing release from Arrest is responsible for the unexpected development of the ovum. The reactions of the growth-cycle have terminated in the ovum which is in a state of arrest in that it is in equilibrium. Repulsion, the force causing and sustaining disequilibrium, is not active init. And on the theory that the immediate result of normal fertilisation is the loss of sexual-element “identity ’ or internal “‘ plan,” we believe that ensuing development is due to the shattering of this “plan”? and the production of disequilibrium, through active force of Repulsion. There is, we might say, living chaos followed by creation, all subsequent growth being for the reproduction of the lost “‘plans’’ and lost specific equilibrium. It is conceivable that the breach of Continuity effected by the needle in the frog experiment is just an abnormal way of producing the results of fertilisation, and that in the same way may be explained the action of chemicals on the egg of the sea-urchin. The resulting Individual is clearly abnormal, and it is difficult to understand how it could show any except female sex, for no true male element has been concerned in the fertilisation. Certain recent ALTERNATION OF GENERATIONS 247 experiments, however, would appear to show that male tadpoles can result from Loeb’s experiment. If fully con- firmed, this will upset many preconceived ideas. But to repeat; ‘‘non-specific fertilisation” clearly starts a new Individual, whereas Parthenogenesis never does, in our opinion; the parthenogenetically produced organism being always part of an Individual. Parthenogenesis would appear to go hand in hand with Alternation of ‘‘ generations,’ as previously defined. All gemmation is based on intermediate cell-division, and one division-half may be said to bud the other just as a yeast cell buds a small part of its substance. It is varying forms of living Continuity which, in Individuals developing as separate cell-multiples, confuse the recognition of the common underlying principle. Thus, it is suggested that a succession of unicellular organisms ending in gamete-formation has its multiple expression in a succession of asexual zooids or of neuter aphides ending in sexual forms. We regard cell-division as fundamental Parthenogenesis. When the Individual is discontinuous and its cells inde- pendent, or when we are dealing with the growth of a tissue, Parthenogenesis is not obvious; but when a division-result leaves a tissue of an organism to repeat the organism’s structure the phenomenon is striking. Yet all is but a matter of what form of Continuity is imposed on the pro- ducts of cell-division. Thus, while the Fern spore is in many ways different from the parthenogenetic cell of an aphis, still both are similar in that they are intermediate cells on the evolutionary road leading to sex, and link together cell-multiples of the Individual. The parthenogenetic cells of the queen bee are not, in our opinion, ova in any sense, but rather “‘ animal spores,” whose further development makes in the drone a male gonophore of sorts ; just as the fern spore becomes a herma- phrodite gonophore. The cells destined to become drones could not, we believe, be fertilised by male elements even if the queen bee allowed it. Are they not certain cells evolving on roads to become male elements when others have already evolved to become female elements ? Is it not that the former have to finish the road outside the queen’s body, while the latter manage to do this inside her body ? CHAPTER XXVII KARYOKINESIS THE phenomena of Karyokinesis are essentially exhibitions of Force of Attraction and Repulsion in action within the confines of the enlarged cell, and it is owing to the act of mass-repulsion finishing the process of division that con- tinued growth, and advance towards the restoration of the sexual elements, are made possible. The restoration is a very gradual process, judging from the large number of division acts preceding it, but while this is so, there seem to be certain definite stages attained on the road which are indicated by variations in the nuclear division-phenomena exhibited. Thus, in the main road of the growth-cycle three forms of Karyokinesis can be observed :— I. Karyokinesis with double chromosomes. IJ. Karyokinesis with single chromosomes. III. Karyokinesis as exhibited in the extrusion of Polar Bodies. Karyokinesis with double chromosomes may be described briefly as follows :— The nucleus of the cell about to divide loses its retiform character and takes the appearance of a thick convoluted chromatin thread, coiled compactly (Fig. 84, c). The nuclear membrane and nucleolus disappear. The convoluted thread disentangles itself to a certain extent, and breaks into a number of short lengths (the number being fixed for the organism in question), each of which becomes bent to form a loop. The loops arrange themselves in the equatorial plane of the cell with their.free ends pointing outwards, forming thus a species of rosette. This is called the ‘“‘ monaster ” stage (Fig. 84, e). Meanwhile at the opposite poles of the cell a point defines 248 KARYOKINESIS 249 itself as a centre from which fine lines radiate to the equator, forming the so-called “spindle” (Fig. 85). Each loop of chromatin then splits longitudinally, and the resulting halves retire to opposite poles of the cell along the lines Fria, 84, of the spindle, so that the cell now contains two rosettes, composed of loops whose free ends point outwards (Fig. 84, 7). This is the “‘ dyaster”’ stage. The protoplasm of the cell then divides equatorially ; the rosettes of each resulting cell revert to the appearance of the original nucleus; and finally a nucleolus appears in both cases. 250 THE EVOLUTION OF CONTINUITY The above is the condensed description of karyokinesis with double chromosomes, each loop splitting longitudinally into two. In karyokinesis with single chromosomes the process exhibited is the same, except that the loops do not split. In the first variety each dyaster has the same number of chromosomes as the monaster; in the second each dyaster has half this number. For this reason ‘reduction of chromosomes ”’ is said to occur when splitting ceases to take place. The process of cell-division has, in effect, three stages : the nucleolar, the nuclear, and the protoplasmic. In the first the nucleolus divides, and as a result each half then takes with it the nuclear substance which it controls; that is, the nucleus then also divides. Then when the nuclear halves have segregated, each draws to it the protoplasm controlled by, or in sympathy with it. The whole process is clearly an exhibition of alternating attraction and repulsion. Cell enlargement as a whole is due to attraction; and it induces or is followed by the mass-repulsion of cell-division. The nucleolar division with which the process starts is due to repulsion, and each repelled half would seem by its attraction exerted on the nuclear chromatin to induce the repulsion causing nuclear division. In the same way it would appear that the mutual repulsion of the protoplasmic ‘‘halves”’ is induced by attraction towards the opposing nuclear halves. Thus, the suggestion offered is that to the attraction exerted by the mutually repellent nucleolar halves nuclear and protoplasmic division are ultimately due. In support of this suggestion the following points may be noted :— There is the initial disappearance of the nucleolus, and at the same time the appearance at opposite poles of the cell of two achromatic points. It is not unreasonable to conclude that these two achromatic points are the ‘‘ division- halves”? of the enlarged true nucleolus, whose position during the growth of the cell was indicated by a special area of chromatin concentration, capable of demonstration by staining. KARYOKINESIS 251 Between the two points the spindle takes shape, and we can recognise in it radiating lines of attraction leading towards the opposing points. That is, the spindle is not a structure ; in fact, it is not properly a “spindle” at all. Its lines are surely not anything else than the arrangement of protoplasmic granules along the force-lines leading to the poles—a purely temporary phenomenon. Further, the steady divergence of the spindle lines towards the equator ie Ls eae . MASHED IO: re EQUATOR. . . ' i « eg eg 4 ey ie re tee a” 7 es ES > seiere nk oe. mies a ne e = ‘ eT * : fe oR 3 Fie. 86.—a, lines of magnetic force of a bar magnet. N, north pole; s, south pole. 3B, the lines issuing from the surface of the north end of a cylindrical bar magnet. of the cell would prove, as is shown above, that they are not continuous from one pole to the other, but are indica- tions of mutual polar repulsion. Lying suspended between the achromatic poles is the nuclear chromatin, stationary because attracted towards both by reason of its containing blended closely together “elements ”’ peculiarly attractable to the opposing poles. Thus the lines of mutual polar repulsion are also the lines 252 THE EVOLUTION OF CONTINUITY of attraction acting on the nuclear chromatin. In other words, it is suggested that we have in the spindle what might be termed a “ magnetic field,’ and in the achromatic poles two magnetic points of “similar polarity.” This can be made clearer by reference to the well-known experiment of iron filings in a magnetic field (Figs. 86, 87, 88). Here the lines of magnetic force of a bar magnet have been made evident by means of iron filings. If two bar magnets like the above be brought near each other, so that the south pole of the one faces the north pole of the other, the two will experience strong mutual attraction, and the force lines will pass directly from the north pole of the one to the south pole of the other. By Fic. 87.—Diagram of the lines of force between dissimilar magnetic poles. means of iron filings this can be made evident, as in Fig. 87, which shows the magnetic field between dissimilar poles. But if the north pole of one magnet be brought to face the north pole of the other, there is no attraction, but repulsion, and the magnetic field as made visible by iron filings takes quite a different appearance (Fig. 88). Here the lines of magnetic force issuing from the poles antagonise and repel each other. There is no passing across, but where they meet a sharp angle is formed. The lines do not lie in one plane as the figure suggests, but radiate in all directions from the poles. Thus, the diamond-shaped space is really of cubic dimensions, being enclosed by a false ‘‘ spindle.” In karyokinesis the achromatic nucleoli appear to act KARYOKINESIS 253 like two little magnets with similar poles facing; the resultant lines of opposing force being made evident by protoplasmic granules, in much the same way as occurs with iron filings in the field between the opposing similar poles of two steel bar magnets. And now if we imagine an object, composed of two classes of elements closely blended together, one of which is peculiarly attractable to one pole and the other to its opponent, to be placed in the equator of the magnetic field; and if we take it that the ‘‘ elements” are evenly represented and that the poles attract with equal force ; then it is clear that the object would remain suspended, as it were, at the equator. But if in addition we suppose that though closely Fic. 88.—Diagram of the magnetic field between similar poles, blended the two varieties of “‘ elements ”’ were free to move within the confines of the object, then the result would be a determination of one variety to the aspect of the object facing one pole, and of the other variety to the opposite side. This is represented very diagrammatically in Fig. 89. It is suggested that this imaginary experiment supplies us with an explanation of the phenomena of karyokinesis, and that although the exact nature of the nuclear separation process must remain a mystery, it is according to the principle illustrated that chromosome splitting occurs. It is also possible to explain roughly on the same lines the nuclear phenomena preceding chromosome splitting. The nucleus is not a flat object, but a more or less spherical one ; and it is not unlikely that the first effects of achromatic 254 THE EVOLUTION OF CONTINUITY polar attraction would be that the chromatin would seek to arrange itself in the lines of attracting force. That is, that ErSTsS ss . : RBP Agen co =a . gh 24d Octo ace . EeEEEa aa Lerner en, ee oe RS swe Fecrccrsea A. 8. Fic. 89.—TIllustrating a theory of chromosome splitting. In a the object remains suspended between the opposing poles, each of which attracts its peculiar subject “elements.” As a result of this attraction the condition in B would presumably occur, and ultimately a separation, as in c, with withdrawal in opposite directions. owing to the steady attraction along these lines the chromatin would gradually take the form of a convoluted thread. The achromatic poles being equal and similar, one half of the chromatin would lie on one side of the equatorial Fic. 90.—Diagram illustrating how the nuclear chromatin could become a convoluted thread, by attraction along the lines leading to the opposing poles. plane and the other half on the other side; so that a situation diagrammatically illustrated as above would result (Fig. 90). KARYOKINESIS 255 The “pull” exercised in opposite directions would in time produce a continuous looping as in the above figure, and the equatorial plane would be the situation where division would be expected to result from the continued pull (Fig. 91). Without being able to explain why, we must presume that the loops when formed are still attractable to both poles, for they remain at the equator. (We are speaking of double chromosome karyokinesis.) And we would suggest that the ‘‘ monaster ”’ is due to the loops adjusting themselves to the radiating planes of force-lines which meet at the iy ae ee ng, hee WTemsilee Fic. 91.—A further stage of Fig. 90. The convoluted thread broken at the equatorial plane, looped chromosomes being the result. equator, somewhat as represented in Fig. 92. This is the position preceding splitting. In single chromosome karyokinesis the chromosomes do not split, but as soon as they are formed one half retires to one pole, and the other half to the other. After the dyaster stage has been reached the cell divides ; the chromosomes retire to their special poles, and do so along the lines of attracting force. As th2 achromatic poles induced equatorial nuclear division, so probably do the chromosomes induce equatorial protoplasmic division. The cell has now divided, and is controlled by a single 256 THE EVOLUTION OF CONTINUITY nucleolar centre. This gathers all around it in its efforts to restore equilibrium. Thus, the chromosomes fuse to form a new nucleus, and the nucleolus indicates its govern- ing position by a special concentration of chromatin around it. We do not know why at a certain stage of growth-cycle advance the chromosomes cease to split, though it is clearly an indication that the cycle is about to terminate in sexual elements. But one might perhaps venture the suggestion that as the growth-cycle starts with a fusing of two distinct elements, and as their identities, though lost, are potentially present in the fertilised ovum, a point in cell multiplication must be reached sooner or later when there is “‘ divergence.” That is, when, through the institution of what might be Fic. 92.—a, diagram of chromosomes lying in the equatorial plane; B, showing the limbs of the loops adjusting themselves to the force-planes leading to the pole. called “‘ predominance,” a given cell on the road leading to sex is destined to give rise in its product to one class alone of sexual element. We do not say that this point coincides with chromosome reduction, but it is a faint possibility. In some plants the reduction occurs with the first division processes of the spore, the chromosomes of the gametophyte never splitting. In other forms of plant life where no separation into sporophyte and gametophyte obtains, reduction does not take place until the sexual elements are about to be formed. In a general way reduction suggests a simplification in the mysterious processes leading to the restoration of the lost identity of the sexual element. KARYOKINESIS 257 Tur Exrrvusion or Potar Bovis. Extrusion of Polar Bodies may be described as follows :— Immediately before actual fertilisation—though the spermatozoon may have entered the ovum—the germinal vesicle, or nucleus of the ovum, begins to lose its definite form and to move towards the periphery of the ovum. Gradually the germinal spot and vesicle disappear, and two “star-like ’’ arrangements united to form the poles of H H = a I\\ — Oe “ys ais : | ats a : ie Fic. 93.—Formation of Polar Bodies in Asterias glacialis. I. The nuclear spindle approaches the surface. II, One half of the spindle is projected in an elevation. III. The elevation is separated as the first polar body, Pl, and the inner half of the original spindle becomes again a complete spindle. IV. This spindle is protruded to half its extent. V. The protrusion becomes the second polar body, P2. VI. The deep part of the spindle becomes the nucleus, m, of the ovum. (After Hertwig.) a spindle make their appearance in connection with the germinal vesicle, and one pole turns round till it comes in contact with the surface of the yelk and is gradually separated by constriction from the other half, constituting what is called the “ first polar body.” “The remaining half of the spindle is again converted into a complete spindle, and a second time one half is pro- jected from the surface of the yelk and separated to produce 17 258 THE EVOLUTION OF CONTINUITY the second polar body. From the half of the spindle which remains within the yelk after the extrusion of the second polar body, a small nucleus is formed which retires towards the centre of the yelk and remains as the nucleus of the unimpregnated ovum, the female pronucleus of V. Beneden, a structure comparable in size rather to the germinal spot than to the germinal vesicle.” (Cleland and Mackay.) After polar extrusion the final nucleus of the ovum is ready to unite with the male pronucleus; this latter being what remains (it is reasonable to suppose) after the sperma- tozoal head has itself performed what seems to be a form of polar extrusion. For on entering the ovum the sperma- tozoon first of all loses its tail, and then a small globule, “the seminal granule,” is discarded by what remains. The result is the male pronucleus. The protoplasm surrounding this then assumes a markedly radiating appearance, and the male and female pronuclei approach each other, fusion takes place, and fertilisation is complete. Polar extrusion apparently represents the second modi- fication of karyokinesis occurring in the growth-cycle, the first being reduction of chromosomes. For the phenomena seem clearly to be karyokinetic. Achromatic poles oppose each other and draw to themselves their subject chromo- somes, though this is done in a simpler manner than in ordinary karyokinesis. There is no monaster formation, and apparently no loops are formed, but straight rods which lie between the poles in the lines of attraction revealed by the spindle, and which divide transversely at the equatorial plane. When the two pronuclei approach each other a new kind of spindle formation occurs along the lines of mutual attrac- tion. It is exactly the opposite of that exhibited in karyo- kinesis, for the pronuclei represent, so to speak, dissimilar poles, and the lines of force pass directly without break from the male pronucleus to the female, exactly as repre- sented in Fig. 87 of two dissimilar magnetic poles facing each other. The true significance of polar extrusion is not known, but it is reasonable to regard the phenomena as those of two final acts of cell-division. It is not equal division in KARYOKINESIS 259 as far as the ovum’s protoplasm is concerned, and suggests the discarding of an ‘‘impurity,’”’ necessary before complete restoration of the female sexual element. Perhaps this ‘‘ impurity ’’ may represent remaining traces of the attempted restoration of the original male element which helped to start the Individual cycle. CHAPTER XXVIII ABNORMAL GROWTH. TUMOURS Up to the present time tumour formation has not been satisfactorily explained, in spite of the enormous amount of work which has been done on the subject. It is quite probable, however, that a proper understanding of abnormal growth will not be arrived at until the fundamental processes of normal growth are fully understood. No doubt there are many who believe that at any moment in these days a definite specific agency responsible for the formation of tumours may be discovered, but while this may possibly happen, it does not seem probable. The question has really two aspects, one being the nature of tumour formation, and the other the factor or factors inducing it, and the object of the following remarks is to suggest that all neoplasms are exhibitions of one morbid process which can be excited by several different hostile agencies. Tumours are divided into two main classes—Simple or Innocent tumours, and Malignant tumours : this is a clinical classification based on the effects produced by them in living organisms. Tumours are also classified as Typical or Atypical, according as their structure conforms to that of normal tissue or not. If the tumour tissue is similar in character to that in which it arises, it is said to be homo- logous ; if of a different type, it is described as heterologous. Thus a lipoma, or fat tumour, growing subcutaneously, is typical, innocent, and homologous, while a cartilaginous tumour arising in bone is innocent, typical, and heterologous. A cancer or sarcoma, on the other hand, no matter where it arises, is malignant, atypical, and heterologous. A tumour shows its innocence in that, apart from secon- dary trouble the result of increasing size, pressure effects, 260 ABNORMAL GROWTH. TUMOURS 261 inflammation, etc., it is not dangerous to life but remains a local abnormality. It does not give rise to tumours in other parts of the body. Its innocence is frequently emphasised in the formation of a distinct capsule which shuts it off from the surrounding tissue, though at other times such a capsule is absent, and any demarcation between normal and tumour tissue difficult to recognise. Examples of innocent tumours are: Lipoma (composed of fat tissue) ; Fibroma (of fibrous tissue); Chondroma (of cartilage) ; Osteoma (of bone); Myoma (of muscle tissue); Neuroma (of nerve tissue); Adenoma (of glandular tissue). The Malignant tumour does not remain localised, but infiltrates the surrounding tissues, displacing and destroying their cells; this is termed “local malignancy.” But in addition the growth almost always exhibits ‘general malignancy ” in that it gives rise to other tumours, similarly malignant, in other parts of the body. The two main classes of malignant tumours are the Sarcomas and Carcinomas ; the former originating in connective tissue and to some extent resembling it in structure at times, while the latter develop in one of the many situations where epithelium is present in the body. It is to be noted that innocent tumours may, though rarely, develop malignant characters, and also that a tumour with all the microscopic appearances of malignant nature may behave like an innocent one. The two chief factors commonly held to predispose to tumour formation are Age, and Injury in some form or another. In the evolution of the living growth-cycle two sexual elements unite and lose their identities, and all subsequent cell-multiplication composing the Individual is the wonderful “reaction”? which must end inevitably in the multiple restoration of the lost sexual-element identities. Where the cells of the Individual are produced in dis- continuity, the theoretically complete Individual ought to be an enormous number of gametes; but where the Indi- vidual’s cells are produced in close continuity this is far from being so. For as part of the Individual develops on 262 THE EVOLUTION OF CONTINUITY a main evolutionary road, there is an accompanying side- evolution of cell-species for the performance of special function. And these species when fixed, or fully differen- tiated, represent so many arrested evolutionary lines of the Individual, repeated cell-multiplication never in their case ending in the restoration of sexual elements. It is through this fundamental interpretation of the living growth-cycle that a theory of tumour formation can be offered capable of embracing tumours innocent and malignant. This is to the effect that the problem centres in ARREST, and RELEASE FROM ARREST. Fundamentally, Arrest may be UNNATURAL, or NATURAL. Unnatural Arrest is the premature arrest of cells of the developing Individual, and it may occur in two forms. (1) At a very early stage of development, long before tissue differentiation has occurred, or the fixed cell-species of the body have evolved. (2) At a later stage, when full differen- tiation is about to be accomplished. It represents the absolute arrest of cell multiplication, and also of given lines of cell-species evolution. Natural Arrest, on the other hand, is the normal arrest of cell multiplication which occurs when maturity is reached. In one sense it is not absolute, for all through life cell- multiplication goes on in most tissues to make good damage or loss, and for the needs of the organism. But in the sense that, in the normal body, this multiplication is rigidly controlled and limited for the preservation of the Individual’s size and personality, we may say that cell-multiplication in contrast with that during development is arrested. At the same time, naturally arrested tissues are composed of fixed cell-species which as species are absolutely arrested, and under normal control cannot change their characters. Thus a fat cell can only become two fat cells when it divides. Given, then, these forms of Arrest, it is obvious that were the controlling or arresting influences removed different results would follow—different types of growth abnormal and unprovided for in the body; all, however, would be similar in the selfish “individuality ” they manifested. ABNORMAL GROWTH. TUMOURS 263 TUMOURS WHICH ARE THE RESULT or ESCAPE FROM UNNATURAL ARREST. 1. Where the Arrest was comparatively late in appli- cation. Let us suppose that in a certain region of a developing embryo cell-differentiation from mucous tissue into fat tissue was about to commence, and that several of the cells were unnaturally arrested and remained isolated amidst the multiplying evolving fat cells. On the attainment of maturity the normal fat tissue in the region mentioned would consist of cells naturally arrested, while in their midst would be those unnaturally arrested, both as regards multiplication and species-evolution. If now these latter cells started to multiply, their product would be unexpected, for the lack of their product earlier in the life of the Individual would have been made good by the extra proliferation of the unarrested cells. The new growth would now try to fulfil the destiny originally potential in the unnaturally arrested cells, but would find no place for itself in the fully developed body- plan; and as a result an innocent tumour would develop myxomatous or fatty in nature, or it might be exhibiting both characters, according to whether the unnatural arrest preceded or coincided with fat-tissue differentiation. If the latter was the case, the tumour would be a lipoma with fat cells apparently identical to those of the surrounding fatty tissue. In reality, however, the tumour cells would be less highly evolved than the cells of the normal fat-tissue, and presumably only after much cell-multiplication would they become “equivalent” to these. At the same time this multiplication would take place in a mature body environment, and not in that of the developing body, as ought to have occurred. That the tumour cells are fat cells suggests that their development is controlled as regards character, and it may be that the surrounding environment of normal fat tissue exerts the influence. At the same time it is to be remem- bered that when the unnatural arrest occurred the destiny of the cells affected was already largely fulfilled. On the 264 THE EVOLUTION OF CONTINUITY whole we may regard such a lipoma as representing the late development of unnaturally arrested young somatic tissue at a time when it is not wanted, and long after its absence has been made good. It is young tissue which arrives late when there is no place for it in the well-balanced cell-republic of the body. But as regards the size the tumour may grow to, two possibilities offer themselves. (1) That the tumour may grow to an indefinite size, being, with respect to multiplica- tion of its cells, completely independent of the balancing restraint imposed on normal tissue. (2) That this complete independence does not obtain, but that the product of the unnaturally arrested cells is only free to multiply till it fulfils its thwarted destiny, or to become the cells it would have become had there been no unnatural arrest. Experience does not lead us to expect that a lipoma after reaching a certain size will stop growing. The lipoma mentioned is an example of a homologous tumour. One simple and heterologous may be exemplified by a myxoma arising in fat tissue, or a chondroma in bone. Here—and so far our theory is more or less that of Conheim—we presume the same unnatural or premature arrest to have occurred, but at a slightly earlier stage of development, before fat or bone differentiation had taken place; the release from arrest occurring after maturity. In such cases there may at times be additional evidence of character-control, for sometimes the mucous cells of the myxoma give rise later on to fat cells, or the chondroma may begin to form bone; mucous tissue being the normal precursor of fat, as cartilage is of bone. In contrast with this, fat tumours have been known to degenerate and produce mucous cells. If this be true degeneration, it must then indicate diminishing control, and conceivably if degeneration went far enough embryonic cell-character would appear and malignancy be exhibited. But the possibility of some mucous cells having been un- naturally arrested along with fat cells must be borne in mind. It is reasonable to suppose that no single factor is constantly at work in causing the release from unnatural ABNORMAL GROWTH. TUMOURS 265 arrest. An increase in local blood-supply might perhaps sometimes account for it. Local injury or breach of con- tinuity from various causes, physical or bacterial, could conceivably set free the cells from their unnatural arrest. Another factor appears to be Age. The majority of tumours generally, and a great number of innocent tumours, appear when the sexual life of the Individual is drawing to a close; and it might well be that at such a time there is a call for the development of any arrested potentialities, or perhaps a weakening of certain inhibiting influences which the normal tissues exercised over the unnaturally arrested cells in previous years. Internal secretion might be involved in the matter in various ways. 2. Where the Unnatural Arrest is applied early in development. The unnatural arrest here occurs long before tissue differentiation has taken place, and release from arrest produces different results. There is tumour growth, but it is atypical. The supposition is (like Conheim’s) that some of the undifferentiated cells of the early embryo, by being shut off or separated from their companions during the infolding of cell strata, or in some other way, find them- selves in unnatural or uncongenial surroundings, and become arrested. They are not wanted in their locality, and they miss the growth-regulating and exciting impulses which they would receive if normally situated. Environment is hostile, and they assume, as it were, the characters of rest- ing spores, awaiting better conditions for their further development. The embryo so affected develops, and in time the organism reaches maturity with its various somatic tissues apparently normal in every respect; yet in a certain one there lies unnaturally arrested or quiescent a little group of early embryonic cells. The body has developed without their assistance, they perform no function, and are not really part of the body except in that they are continuous with it. If these cells escape from arrest when the body is mature or begins to decline, they proceed to multiply actively. But the product of their division is not typical of any 266 THE EVOLUTION OF CONTINUITY of the body tissues; it has the characters of embryonic tissue ; and as cell multiplication goes on there will be no signs of approaching differentiation, for the growth is uncontrolled, and the influences which guided the normal evolution of the unnaturally arrested cells’ original com- panions do not now exist. The body does not expect this new development, and its system of growth-control is in all aspects adapted for mature differentiated tissues. Further, while there is nothing to influence cell-character there is also nothing to restrain the amount of cell-multiplication— in the absence of special accidental factors. The tumour cells are young, and youth will be served; they invade, push aside, crush and destroy the normal tissues which, to all purposes permanently arrested, can offer no com- petition. The growing mass spreads and infiltrates in all directions; in fact, a malignant tumour develops—in the case pictured, a sarcoma. Such a tumour represents an organism unlike any occurring in the normal living scale; an organism, part of the Individual, and living parasitically on the remainder of the Individual. In it every cell lives for itself, and performs no special function for the good of the tumour, behaving just as if produced in discontinuity. Viewed as an organism—and it is clearly not a part of the real individual—the tumour is unique in Nature as an example of cell-growth-in-Continuity with not the slightest signs of cell-differentiation. The malignant tumour’s Con- tinuity is not therefore true, and normal cell-arrest is not exhibited. This being so, one is justified in supposing that our sarcoma’s celis may go on multiplying until some form of gamete is produced. This is only logical, for the original tumour cells are part of the product of the original fertilised ovum, and in the absence of arrest and differentiation they are free to carry on their cycles to the end. And to carry our suggestion a stage further: the con- jugation of the hypothetical “tumour gametes” should give rise to a new tumour similar in characters to the parent growth. Such a new tumour might start to grow alongside of the original one, or ‘‘ gametes”? might be set free into a lymph channel, or into the blood stream and thus be carried to some distance where their conjugation would give ABNORMAL GROWTH. TUMOURS 267 rise to a secondary tumour. This would be a potential Individual, whereas the primary tumour would only be a small part of an Individual—the Individual attacked. These presumptions involve us in a strange state of affairs. The body is attacked by an unnaturally arrested part of itself which has escaped arrest; and this part, owing to the complete absence of control and guidance, develops as an amorphous parasite, capable of forming sexual elements and originating a new tumour as a tumour- Individual. In this connection it seems just possible that the so-called “‘ cancer-bodies ”’ discovered some years ago, and considered by some observers to be parasitic in nature and possibly causal agents of the disease, may be “‘ tumour- gametes.” At the same time, there is no reason to doubt that a primary malignant tumour may give rise to a secondary one by vegetative production, and that tumour cells which are not “gametes”? may be separated from the original mass and carried to new situations; a species of trans- plantation by cuttings. We may believe that early unnatural arrest does occur in the developing embryo, for congenital moles and warts can be explained in no other way. Moreover, these little masses of unnaturally arrested cells not infrequently escape from arrest and give rise to malignant growths, usually sarcomatous, but at times epitheliomatous. It will be observed that this theory that benign and certain malignant tumours are exhibitions of Escape from Unnatural Arrest is practically Conheim’s theory, and that, like his, it does not explain the origin of all tumours. But Unnatural Arrest is only one form of arrest, and it is with the help of its opposite, Natural Arrest, that our theory is made all-including. TUMOURS WHOSE ORIGIN 18 Dur TO EscaPE FROM NatuRsaL ARREST. Such tumours are the product of cells composing normal differentiated tissues which exhibit the final arrest charac- teristic of adaptation to special function. They do not seem to arise so spontaneously as the tumours which have just 268 THE EVOLUTION OF CONTINUITY been considered ; that is, there is a more gradual assumption of tumour characters. And our suggestion is that a tem- porary release from Natural Arrest gradually becomes a permanent and uncontrolled release. It is common knowledge that a large number of tumours arise in situations where chronic irritation, inflammation, or ulceration has obtained for some time, and where there are no reasons for supposing that any unnaturally arrested cells have been lying dormant. These tumours are invariably malignant in nature, and chiefly arise in epithelial tissue ; this, no doubt, being largely due to the fact that surfaces exposed to chronic irritation are always covered by one or more layers of epithelium. And in this connection it is necessary to recall what happens in the healing of wounds and the regeneration of tissue. With the destruction of a localised area of mature tissue, or on its wounding or severance, the exposed cells are released from arrest and multiply until the tissue loss is made good and local tissue-balance regained. If the wound be clean, and the edges can be brought in close apposition, release from arrest is shown at a minimum and the wound heals by “first intention.”” But where damage or loss of substance is great, rapid healing is impossible, and tissue restoration requires a considerable and sustained exhibition of release from arrest. In such a case it is chiefly the cells of the connective tissue which by multiplying heal the wound, and this is said to heal by “granulation.” The so-called granulation tissue is composed of newly formed cells, at first embryonic in character, but later assuming a spindle shape and largely conforming to the ordinary connective tissue cell-type. It is also rich in newly formed bloodvessels, but contains no nerves. When healing by granulation proceeds normally, as soon as the granulation tissue has restored the loss or filled the gap the surface epithelium grows across, continuity is complete, and arrest again obtains. But when the wound is unhealthy or septic, or when healing is prevented by the continued action of an irritating agency, two things may happen: (a) unhealthy granulations are produced in excess, so that the marginal epithelium is prevented from growing across, or is destroyed in its attempts to do so ; or (0) hardly ABNORMAL GROWTH. TUMOURS 269 any granulations are formed at all, or if formed are imme- diately destroyed, and the wound assumes the appearance of an ulcer, which remains stationary in size or gradually grows larger. In the latter case there is no bed formed for epithelial new growth. Under proper treatment, and in healthy subjects, such wounds heal sooner or later, but as long as healing is delayed we may recognise a theoretical risk of uncontrolled escape from arrest. Theoretically, all that prevents a granulating wound from originating tumour tissue is Control. The ‘ proud flesh ’’ of an unhealthy wound is in certain respects abnormal growth ; it is a hyper-production of cells, a release from arrest far greater than is necessary for the healing of the wound ; it is, so to speak, temporary tumour tissue. As a matter of fact, however, we know that the danger is not that granulation tissue, whether excessive or deficient, will become tumour tissue ; it is in the marginal epithelium that this danger arises, and particularly in chronic sores which fail to granulate. It is the epithelium which is specially liable to grow atypically, probably through being deprived of normal connective tissue influences which should locally control its typical development. In every living organism there is Equilibrium of Per- sonality ; there is balance of function for the preservation of identity and personality, and this balance reflects itself in the proportionate development of the different somatic tissues and organs. Thus the size of the stomach, the liver, the kidneys, the amount of fat, connective tissue, muscle, or skin in an organism, primarily reflects in each case the degree of development necessary for the preservation of the organism’s identity and its equilibrium of personality. In a sense, therefore, one organ, or one tissue, may be said to control the development of another, and we may accept this influence to be exercised indirectly through the central nervous system, and also more directly by means of secre- tions passed into the blood stream. The case of epithelial or endothelial tissue is peculiar among the body-tissues in that it always covers surfaces, This is so, whether we are dealing with skin, pleura, peri- toneum, or secreting cells. It is thus always especially subject to damage or wear and tear on what may be called 270 THE EVOLUTION OF CONTINUITY its external aspect. The other outstanding point is that the unexposed surface is always in contact with connective tissue. The free epithelial surface is very liable—and specially so in the case of skin or mucous membrane—to be wounded, severed, or have its continuity broken by many hostile agencies, and its normal functions may involve a continual cell loss. On the other hand, on the connective tissue side the blood and lymph may bring to the cells toxic substances which can wound or destroy as thoroughly as externally acting physical agencies. When the lesion heals, it does so through the release of cells from arrest, which, their purpose accomplished, become re-arrested ; but it may happen that the arrest, once broken, is never re-imposed and that tumour growth results. The theory of Waldeyer and Thiersch presumes that the underlying connective tissue exercises normally a restraint on its covering epithelium, and that malignant epithelial tumours might arise through the removal of this restraint with advancing age. Advancing age may well be only one factor, but this apart, the influence of connective tissue on its epithelium would seem to be proved by experiments which have been performed in vitro. Those of Champy are very suggestive. He found that on growing in culture a piece of embryo rabbit’s kidney, tubules were soon produced of a primitive type, and finally these merged into an unformed mass of undifferentiated embryonic cells. Smooth muscle cultivated outside the body also gave rise to embryonic cells, this being specially noteworthy because smooth muscle cells do not divide when in the body. Champy’s most interesting discovery was, however, that when a portion of attached connective tissue was included in the culture the epithelial cells multiplied typically. It would thus seem clear that if tissues are removed from the body and grown in culture the amount of growth is uncontrolled ; and this because the tissues in question are no longer a part of the body’s personality. And it is clear, in addition, that in the case of epithelium if no attached connective tissue be included, the character of the epithelial growth is also uncontrolled. One cannot but conclude that the connective tissue exerts the influence which keeps ABNORMAL GROWTH. TUMOURS 271 the growth of its epithelium typical. Naturally, one would not expect the connective tissue to exert its power for very long in vitro, as it itself is removed from the normal growth influences of the body. Prolonged growth in vitro could never be accompanied by re-differentiation, but only to atypical cells with characters harmonious with the artificial environment; but in time some form of debased gamete would presumably be produced. What we may then conclude is that epithelium in the living body cannot grow typically in amount and character unless it is in touch with the supporting connective tissue which is its normal immediate ‘internal’’ environment, and from which it receives certain normal growth influences. And this conclusion is one we could arrive at from what we see in the healing of a granulating wound, for the epithelium will not grow across bare muscle, bone, or cartilage, or bridge a space; it requires to advance in touch with new connective tissue in the form of healthy granulations. The skin graft exhibits the same phenomenon, for it will only “take” if placed on or in its proper immediate environment, healthy granulation tissue. Let us take the case of an epithelioma of the lip or the tongue, developing at the site of some chronic irritation. Regarding the onset of malignancy several possibilities- suggest themselves. (1) That the marginal epithelium comes to grow out of touch with its restraining connective tissue, so that the growing edge gradually escapes from control. (2) The connective tissue granulations may become so unhealthy owing to the continued action of the irritant that as an immediate environment they cease to have a proper restraining influence. (3) In the absence of granu- lations of any kind the epithelium may insist in growing without any restraining influence. (4) Through advancing age, or other general cause, affecting the body as a whole, the controlling power of the connective tissue is weakened and breaks down. The absence of granulations in ulcers which become malignant is a common phenomenon, and the long processes of malignant cells which burrow down into the base of an epithelioma, and the curling cell-nests as observed in such a tumour in the lip, strongly suggest that in the absence 272 THE EVOLUTION OF CONTINUITY of granulations the marginal epithelium has dipped down in an attempt to cover the wound; that as the epithelial processes grew longer, not only did their advancing ends fail to find normal restraining granulations, but such in- fluences as originally passed from the healthy connective tissue near the ulcer would become weaker and weaker till they were not. felt. For normally the connective tissue restrains a few layers of epithelium, and could not be expected to control a process equivalent to a hundred layers in depth. In the light of Champy’s experiments one other possi- bility suggests itself, namely, that epithelial cells might break away from the margin and multiply, as it were, in culture in the serum of the ulcer. All carcinomata do not develop in elderly people, though these are specially liable to be attacked, and there is not always an ulcer preceding the tumour; but where the tumour arises in normally arrested tissues it is probable that it always follows on a breach of Continuity of some sort, due to physical injury or inflammation. There is this peculiarity about all epithelium, and especially such as is glandular: while we may say that as a tissue it is permanently arrested in the sense that it never gives rise to sexual elements, its cells, under normal condi- tions, are constantly being released from the arrest of multiplication, owing to friction, wear and tear, etc. More- over, the very function of glandular epithelium entails constant cell loss and fresh cell-division. Thus, epithelial tissue as a whole is not so rigidly arrested as the other tissues of the body, and we might suppose that on this account it was specially apt to break away from control, and that with advancing years its confirmed “habit” of cell-multiplication became a danger to the body. We have taken epithelial tumours as examples of com- plete escape from the control of Natural Arrest, but it may well be that at times connective-tissue cells may also break away from all control and originate sarcomatous tumours. An interesting question is that of the stroma of certain cancerous tumours. This could sometimes be interpreted as no more than cirrhotic connective-tissue due to the breaches of connective-tissue continuity caused by the ABNORMAL GROWTH. TUMOURS 273 multiplying epithelial cells; an attempt at repair, or to form internal scar-tissue. But, on the other hand, not infrequently the stroma acts as widely spreading malignant tissue, and even to the extent of almost crushing out the malignant epithelial cells. The foregoing suggestions are admittedly superficial, and deal with the significance of tumour-formation rather than with the actual exciting agency, or agencies at work. Our own belief may, however, be repeated, that tumour- formation is abnormal growth, a morbid process which may be excited by several diverse agencies; and that these probably all act by causing an initial breach of cellular continuity whereby cell-arrest is broken. There can be no normal growth without Arrest and Control in cellularly- continuous organisms; no cell species or animal species could be maintained but for these factors, and they are the handmaidens of Continuity. 18 INDEX A Acquired variations, transmission of, 142 Adamsia, 86 AEdogonium, 55 Agaricus campestris, 64 Alga cell, 38 Alternation of Discontinuity with Continuity, 78 Alternation of Generations, elemen- tary, 48; in filament, 58; mycelial, 62 ; zooidal, 74 ; general summary, 240 Alternation of Serial with Lateral Continuity, 70, 75, 77, 81, 83 Ameeba, 36; amceba-stages, 44 Amphioxus, 131, 144, 195 Angiosperms, 171, 174; the flower, 175 Antithetic characters, 27 Aphis, 38, 113, 244 Archean rocks, 160, 168 Archicarp, 64 Arrest, 127; permanent, of Con- tinuity-types, 133 Asci, ascospores, 64, 66 Asexual cycle of malarial ameba, 42, 44 Atom, 28, 29; atomic cycle, 32, 33 ; atomic conjugation, 34; atomic species, 35 Attraction, the basic Force of, 25, 27; its dominance, 26, 52 Atypical Fish, 196 Aurelia, 102, 116, 180, 197 121, 139; B Bacteria, 67 Bar-magnet experiments, 252 Basidium, 66 Basoplasm, 35 Biogen molecule, 35 Blastophores, 44 Bryophytes, 169 Calamite, 173 Cause and Effect, 23 Cell, continuity of, 51; cells and protoplasts, 61; cell-arrest and Continuity, 49, 52; cell-arrest, release from, 74, 131; cell-caps, 56; cell-colony, 57 : Cephalopods, 159, 196; evolution of, 198, 200; anatomy of, 201 Champy’s experiments, 270 Chlamydomonas alga cell, 69 Chromosomes, 250 Circular canal, of medusoid, 95; of echinoderm, 107 Ceelenteron, 71 Ceelomata, 98 Ceelom, 91; calom ‘‘ open,” 98, 110, 195; ccelom of echinoderm, 107, 109; of earthworm, 114, 120 Ceenocyte, 61 : Ceenocytic Individual, 59 Ccenosare, 79 Colorado beetle, 145 Conidiophore, 65 Continuity of Matter, 21; Con- tinuity’s intensification within the Individual, 69, 95; Continuity, breach of, 129; evolution of, 20, 147 Continuously Zooidal Individual, 77 Control, 122 Coral, 105, 159 Cortical centres, 239 Crossed motor and sensory tracts, 233-7 Cycle, true, 30; of acts, 32; cyclic reaction, molecular, 29 D Decomposition of water, 29 Deviation, avoidance of, 231 De Vries’ theory, 211, 216 275 276 THE EVOLUTION OF CONTINUITY Discontinuity, 19; after death, 36; independence due to, 39 ; cellular, and gamete-formation, 44; price of, 151 Discontinuously Multicellular Indi- vidual, 39; definition, 42 Discontinuously Zooidal Individual, 70 Drone, 38 Dyaster, 249 E Earth, its crust and strata, 158; its evolution, 207 Earthworm, 114 Echinodermata, 107; larve of, 110 Ectoderm, 71, 85, 95, 98 Electrons, 28, 29, 32, 206 Endoderm, 71, 85, 98 Energy, 26 Environment, general, 49; basic varieties, 50, 51; as physical force in relation to Continuity, 51, 52, 87; Environment and Variation, 140; as segregator, 167; as originator of species, 154, 214 Equilibrium, and Nature, 26; of inorganic matter, 28; of dead matter, 31; physical, of Fish, 229; of personality, 269 Eurotium, 63 : Evolution, of living Individual, 37; of somatic tissue, 37; main road of, 59, 76, 150, 202; evolution of sexual structure in zooidal colonies, 92; gaps in chain of evolution, 151, 203 F False tissue, 63; in Eurotium, 64 Ferns, 171 Fertilisation, non-specific, 246 Filamentous Individual, 49 Fish, evolution of, 181; circulation of, 183; nervous system of, 185 ; alimentary tract of, 186; mouth and gill formation, 187; respira- tory system, 188; symmetry of, 227; fins, 230 Fishes, 159 Flounder, 228 Flowering plants, and arrest, 78 Food-attraction, 218, 221, 229 Frog, puncture of unfertilised ovum, 48, 246 Fungi, 59 G Gametes, of malarial ameba, 44; of lower bacteria, 69 Gametangium, 58 Gametophyte, 57, 58 Ganglia, 115; ganglionic nerve cells, 85 Gaskell’s theory, 191, 194 Gemmation, zooidal, 71, 78, 80 Geometrical progression and growth- cycle, 40; in hemameeba, 46 Gonoblastidium, 93 Gonophores, 91; 166 Gravity, its evolutionary action, 161 ; as factor in Symmetry, 219 Growth, 25, 35 Gymnosperms, 169; the cone, 173 medusiform, 94, H Hemamoba of malaria, 42, 43; size of Individual, 45 Healing of wounds, 269 Heredity, 133 Honey-bee, 113 Hydra, 39, 71 Hydra-tuba, 103 Hydrozoa, 74, 80, 104, 172 Hyphe, 60 159, 163, I Incomplete septa, 86 Individual, the, 38 ; size of living, 45 Intercalation in Spirogyra, 55 Intermesenteric chambers, 85, 89, 101 Involution forms, 68 J Jelly-fish, 81, 91, 95 Jelly tissue, 98, 108 INDEX K Karyokinesis, 248 L Lateral Continuity, of protoplasts, 59; of hyphe, 63; of zooids, 70 Law of ‘‘2 to the Nth,” 46, 218; of Octaves, 207 Laws of Growth, 52 Life, general definition of, 30. First Life, 148 Lucernarida, 102 M Malarial amoeba, 38, 42 Man, as an Individual, 39 Manubrium, 95, 101 Matter, inorganic and living, 28; ultimate unit of, 32, 205. Evolu- tion of Matter, 204 Medusa, 81, 98 Megazooidal Individuals, 82. Mega- zooid, 83; medusiform, 91; Discontinuously, 102; and Con- tinuouslyMegazooidal Individuals 105 Memory, 138 Mesenteries, 85 Mesoderm, 85 Mesogla@a, 71 Micrococci, 67 Molecule, the, 29. Molecular disso- ciation and decomposition, 29; molecular species, 35 Mollusea, 196 Monaster, 248 Mucor, 59, 603; 62 Mudfish, 228 Multicellular Individual cycle, meta- phor of, 40 Mutation Theory, 211, 216 Mycelium, 60 Mucor mucedo, 60, N Natural Selection, 211 277 Nervous system, of Hydra, 72; of medusoid, 119, 192; of star-fish, 108; of earthworm, 115, 119; of phanerogam, 124; of Fish, 185. Nervous system and Con- trol, 125-7 Nuclear fusion, 66 Oo Origin of Species, 211 P Parthenogenesis, elementary, 58; summary of, 245 Periodic Law, 207 Phanezrogams, evolution of, 169 Plasmolecules, 30; Plasmolecular cycle, 36 Polar Bodies, 257 Pollinodium, 64 Polypite, 71 Progressive diminution in Discon- tinuously Multicellular Individual, 47; in Discontinuously Zooidal Individual, 74 Propositions, basic, regarding Growth, 40, 41 Protoplasm, 35 Protoplasts, 61, 62 Proximal cell-arrest, 56, 57 Pteridophytes, 169 Purpose, 23 Pyloric sac, and ceca, 107 Q Queen Bee, 38, 136, 247 R Radial canals, medusoid, 95, 97, 101 ; in starfish, 108 Radiate Individual, 107 Ray-fungus, 67 Reproduction, 24 Repulsion, basic Force of, 25, 27£ in cell-division, 51; in karyo- kinesis, 251 Rosebush, 39 278 THE EVOLUTION OF CONTINUITY 8 Scyphistoma, 103 Sea-anemone, 84; primitive, 155 Sea-urchin, chemical fertilisation of eggs, 48, 246 Segmental Individuals, 112; tinuously Segmental, 113 Segregation, 166, 214 Serial Continuity, of cells, 59; of zooids, 70 Sexual cycle of malarial amceba, 42, 44 Sexual element “ plans,” 37, 40; in Variation, 137 Side-roads of Evolution, 38, 59, 76, 134 Sieve-tubes, 124 Silurian Period, 159, 168 Solar Attraction, 218, 221 Spherella, 48 Spirilla, 67 Spirogyra, 53, 163; theory of fila- ment’s development, 54 Sporangia, 60 Spores, of malarial amoeba, bacterial, 69 Sporocytes, 43 Sporophyte, 57, 58 Sporosac, 92, 173 Sporosac-gonoblastidium, 93, 96, 100, 104, 173 Sporozooites, 44 Starfish, 107 Strobila, 116 Swimming-bladder, 218 Con- 43; T Tentacles, of Hydra, 71; medusoid, 96 ; of cephalopod, 198 Terminal compression, in Fungi, 66, 81; in Continuously Zooidal _ Individuals, 81; in evolving Fish, 185, 226, 229 Testis of Hydra, 73 Thallophytes, 169 Thread cells, 71 Tissue-continuity, 70 Tortoiseshell butterfly, 142 Torula condition, 62, 69 Trachymeduse, 99 Transmission of characters, 134 Tumours, 260; due to escape from unnatural arrest, 263; to escape from natural arrest, 268 Types of Continuity, 41; evolution within, 76 U Unicellular Individual, 39, 67; Uni- cellular organisms, 39 Unit cycle, 25; Unit Growth-cycle, 32, 33 Unit “‘ somatic tissue,” 34 Vv Variation, 134; Natural variations, 135; Life the Great Variation, 149 Velum, 96 Vertebrate, evolution of, 180 Ww Waldeyer and Thiersch, theory of, 270 Water-friction, 226 Water-pressure, 161, 185, 225 Water-vascular system, 107 Worker-bee, 38 Z Zooid, definition of, 71, 82. 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