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* ^J^^' * • ** gl •v &fe ■roffir-n ' Mt^StL i5P ^•^"'tp* • i • jfc?%¥f ■ >--"" •* |ng^g *mL*2*M& ^K*g^' * -• lfe£^ ^3^ • % •^ fc -nHrirn *rf."r ^3Jfe* •ijaassgssjj Ekp'j Xfl W •« «r ir^s * *p. & - • t . ■'• .* ^..£ -^gsft '^;*^; ifflH^y -^-" ■ -j--y • I ^^ft." • ■' ■■' -^m^f': OF THK ^littuttsilg -of <$slif<rt|itt». H .No... p)/tl. Division , KJR Range Shelf.. - : Bxo^oSf reived ^jU*^<^ - '187 f LIBRARY * •« BIOLOGY By the Same Author. i. Second Edition, revised and enlarged. A MANUAL OF ZOOLOGY, FOR THE USE OF STUDENTS. WITH A GENERAL INTRODUCTION ON THE PRINCIPLES OF ZOOLOGY, AND GLOSSARY OF SCIENTIFIC TERMS. Crown 8vo, pp. 673, with 243 Engravings on Wood, 12s. 6d. 11. TEXT-BOOK OF ZOOLOGY, FOR THE USE OF SCHOOLS. Crown 8vo, pp. 340, with 153 Engravings on Wood, 6s. in. INTRODUCTORY TEXT-BOOK OF ZOOLOGY, FOR THE USE OF JUNIOR CLASSES. With 127 Engravings, 3s. 6d. IV. ESSAY ON THE GEOLOGY OF CUMBERLAND AND WESTMORELAND. Octavo, with Engravings, 3s. 6d. v. A MONOGRAPH of the BRITISH GRAPTOLITIDyE. Octavo, with Engravings, 5s. VI. A MANUAL OF PALAEONTOLOGY. FOR THE USE OF STUDENTS. WITH A GENERAL INTRODUCTION ON THE PRINCIPLES OF PALAEONTOLOGY. With Engravings. [In thefress. VII. TEXT-BOOK OF GEOLOGY, FOR SCHOOLS AND COLLEGES. Crown 8vo, with Illustrations. WILLIAM BLACKWOOD & SONS, Edinburgh and London ; and D. APPLETON & CO., New York. INTRODUCTION TO THE STUDY OF BIOLOGY H. ALLEYNE NICHOLSON M.D., D.Sc, M.A., Ph.D., F.R.S.E., F.G.S. &c. PROFESSOR OF NATURAL HISTORY AND BOTANY IN UNIVERSITY COLLEGE, TORONTO J FORMERLY LECTURER ON NATURAL HISTORY IN THE MEDICAL SCHOOL OF EDINBURGH ; ETC. ETC. Library* WILLIAM BLACKWOOD AND SONS EDINBURGH AND LONDON MDCCCLXXII Right of Translation is reserved N6> BIOLOGY LIBRARY G PREFACE. The present work is based chiefly upon the Intro- duction to the author's ' Manual of Zoology/ much of which is given here in an unaltered form. A con- siderable portion, however, of the Introduction has been here recast, whilst fully two-thirds of the work consists of new matter. Illustrations also have been introduced wherever such appeared to be necessary. Many important subjects have, of course, been ne- cessarily treated very superficially, or altogether omit- ted, as unsuitable for a merely elementary work. It is hoped, however, that most of those subjects are touched upon, a knowledge of which would be useful to the student of living or extinct forms of life, or to the general reader. Toronto, Canada, December 4, 1871. CONTENTS. CHAPTER I. PA Definition of Biology — Differences between dead and living bodies — Nature and conditions of life — Physical basis of life — Pro- toplasm — Connection between life and the matter of life — Or- ganisation — Light — Air — Temperature — Death — Use of the term "vital force," I- CHAPTER II. Differences between animals and plants — Regnum Protisticum of Haeckel — Higher plants distinguished from higher animals — Comparison of the lower animals with the lower plants — Form — Internal structure — Chemical composition — Power of locomotion — Nature of the food 19-25 CHAPTER III. Differences between different organisms— Morphology — Physiology — Specialisation of functions — Morphological type — Synopsis of the main divisions of the animal and vegetable kingdoms, 26.43 CHAPTER IV. Analogy — Homology— Serial Homology — Lateral Homology — Homogeny and Homoplasy — Homomorphism — Mimicry- Correlation of growth, 44-5 CONTENTS. Vll CHAPTER V. Principles of classification — Definition of Species — Genus — Family — Order — Class — Sub-kingdom — Impossibility of a linear clas- sification, 56-63 CHAPTER VI. Elementary chemistry of animals and plants — Chemistry of animals — Fats — Albumen — Fibrine — Caseine — Proteine of Mulder — Chemistry of vegetables — Starch — Cellulose — Sugar — Albuminous compounds of plants, .... 64-69 CHAPTER VII. Elementary structure of living bodies — Protoplasm or Bioplasm — Molecules — Cells— The cell-wall — The cell-contents — The nucleus — Cell-multiplication, 70-76 CHAPTER VIII. Physiological functions of animals and plants — Animal and vege- table functions — Unicellular plants — Foraminifera— Vital force as manifested in the digestive process of plants, . . 77-83 CHAPTER IX. General phenomena of nutrition — Assimilation — Death— Growth — Development — Transformation — Metamorphosis — Law of Quatrefages — Provisional organs of young animals — Absence of sexual reproduction in larval forms — Von Baer's law of. development — Retrograde development, . . . 84-96 CHAPTER X. Reproduction — Sexual reproduction — Non-sexual reproduction — General phenomena of gemmation and fission — Gemmation in the Foraminifera — Gemmation in the Sea-mat — Gemmation in Hydra — Fission in Paramcecium — Definition of the zoologi- cal individual — Zooids — Internal gemmation of Polyzoa — Al- ternation of generations — Reproduction of Hydractinia — Re- production of Clytia — Structure of free medusiform zooids — Reproduction of the Lucernarida — Parthenogenesis —Of Aph- ides—Of Bees — Law of Quatrefages — Antagonism between sexual reproduction and nutrition, .... 97-118 Vlil CONTENTS. CHAPTER XI. Reproduction in plants — Gemmation and fission — Resemblances be- tween plants and Hydroid zoophytes — Reproduction of Angio- spermous flowering plants — Reproduction of ferns, . j 19- 126 CHAPTER XII. Spontaneous generation — Development of living beings in organic infusions — Experiments of Dr Bastian, .... 127-133 CHAPTER XIII. Origin of species — Doctrine of Special Creation — Doctrine of Evol- ution — Views of Lamarck — The Darwinian hypothesis — Theory of natural selection — Sexual selection — Leading objec- tions to the theory of the evolution of species by natural selection, 134-143 CHAPTER XIV. Distribution in space — Geographical distribution — Zoological pro- vinces — Bathymetrical distribution — Discoveries in the deep sea— Conditions of life in the deep-sea animals, . . 144-150 .CHAPTER XV. Distribution in time — Laws of geological distribution — Chief divi- sions of the stratified series — Contemporaneity of strata — Geo- logical continuity— Imperfection of the palseontological re- cord, . 151-160 IX LIST OF ILLUSTRATIONS. 2. 3- 4. 5- 6. 7- 8. 9- 10. *3- 14. 15. 16. 17. 18. 19. 20. 21. 22. 23- 24. 25. 26. 27. 28. Nonionina and Gromia, .... Wheel-animalcule,. Ciliated spores of Plants, Volvox globator % and Euplotes Charon, Amoeba, ...... Actinia mesembryanthemum, and diagrammatic section of the same, *. Diagrammatic section of a Whelk, Gregarine, Rhizopod, and Infusorian, Hydra vulgaris, and diagrammatic section of the same, Holothurian and larva, .... Diagram of Annulose animal, Section of a Cephalopod, .... Skeleton of the Common Perch,. Fore-limb of Man, Fore-leg of Dog, and Wing of Bird, Fairy Shrimp, ..... Centipede, ...... Arm of Chimpanzee, .... Leg of Chimpanzee, .... Phyllium siccifolium, .... Yeast-plant, . . .. Cells of notochord of Lamprey,. Ovum of Ascaris nigovenosa, Germinating cells of Yeast-plant,. Metamorphoses of Butterfly, Young of water-breathing Gasteropod and adult Pteropod, Young of Achtheres, and adult LerncBa^. Diagram of Foraminifera, Flustra hispida, ..... Param&cium multiplying by fission, page 13 IS 21 29 30 3i 35 36 37 33 40 4i 45 46 46 47 47 53 72 73 75 7 6 90 95 96 99 100 10* X LIST OF ILLUSTRATIONS. 29. Group of Hydractinia echinaia, with gonophores, 30. Trophosome of Clytia Johnstoni % 31. Free Medusoid of Clytia Johnstom t 32. Development of A urelia,. 33. Generative zooid of Chrysaora, 34. Bean Aphis, .... 35. Male organs and pollen of Flowering Plants, 36. Female organs of Flowering Plants, 37. Fructifying Frond, Spore-cases, Spore, and Fern, ..... 38. Molecules and bacteria of organic infusions, 39. Ideal section of the Crust of the Earth,. ;s, 105 108 109 no. in : : 114 121 ProthaUus of a 122 125 128 iS3 ELEMENTS OF BIOLOGY. CHAPTER I. DEFINITION OF BIOLOGY. All natural objects admit of an obvious separation into two primary groups, according as they are dead or alive — according as they exhibit no phenomena except such as can readily be referred to the working of known physical and chemical laws, or as they present, in addition, the phe- nomena which we are accustomed to group together under the name of " vital." The studies which occupy themselves with dead bodies concern the physicist, the chemist, the geologist, and the mineralogist. The study of living be- ings, irrespective of the exact nature and position of these, is the province of Biology (Gr. bios, life ; logos, a discourse). All living beings, however, may be divided into the two kingdoms of animals and plants, the study of the former constituting the department of Zoology, whilst Botany is exclusively concerned with the latter. In accordance with this division, Biology splits up into the kindred sciences of Zoology and Botany, and properly includes both of these in all their details. Here, however, nothing more is aimed at than the presenting to the student in a concise form some A 2 ELEMENTS OF BIOLOGY. of the leading principles upon which the sciences of Zoology and Botany are based. With this view, technicalities will be as far as may be avoided; and on all matters which are still undecided the evidence on both sides will as far as possible be given, so that the reader may be enabled to form his own judgment as to the questions at issue. DIFFERENCES BETWEEN DEAD AND LIVING BODIES. In marking out the boundaries which limit the province of Biology, the first point is obviously to arrive at a clear conception as to the differences which separate all living bodies from those that are dead. The leading characters by which living bodies are distinguished from dead bodies may be summed up as follows : Firstly ', Every living body possesses the power of taking into its interior certain ma- terials foreign to those composing its own substance, and of converting these into the materials of which its body is built up. This constitutes the process of "assimilation," and it is in virtue of this that living bodies grow. In all cases alike, the materials to be assimilated are taken into the interior of the body, and the process of growth is, therefore, one depending upon the "intussusception" of foreign matter in contradistinction to its mere addition from the outside. When, on the other hand, dead bodies increase in size, as crystals do, the increase is produced simply by the addi- tion of fresh particles from the exterior, or, as it is techni- cally called, by the " accretion " of matter. This process cannot properly be considered as one of "growth," as being wholly destitute of the essential element of a pre- vious " assimilation." Secondly, All the actions of living beings are accompanied by a corresponding destruction of the matter by. which these actions are manifested. In other words, partial death is a constant accompaniment of life ; and the inces- sant loss of substance caused by vital action has to be DEAD AND LIVING BODIES. 3 compensated for by the simultaneous assimilation of an equivalent amount of fresh matter. Thirdly, If our observation be continued for a sufficient length of time, every living body has the power of repro- ducing its like. That is to say, every living body has the power, directly or indirectly, of giving rise to minute germSj which, under proper conditions, will be developed into the likeness of the parent. Fourthly, Dead bodies are subject to the physical and chemical forces of the universe, and have no power of suspending these forces, or modifying their action, even for a limited period. On the other hand, living bodies, whilst subject to the same forces, are the seat of something in virtue of which they can override, suspend, or modify the actions of the physical and chemical forces by which dead bodies are exclusively governed. Dead matter is com- pletely passive, unable to originate motion, and equally un- able to arrest it when once originated. Living matter, so long as it is living, is the seat of energy, and can overcome the primary law of the inertia of matter. However humble it may be, and even if permanently rooted to one place, every living body possesses, in some part or other, or at some period of its existence, the power of independent and spontaneous movement — a power possessed by nothing that is dead. Similarly, the chemical forces, which work unresisted amongst the particles of dead matter, are in the living organism directed harmoniously to given ends, their action regulated under definite laws, and their natural work- ing often strikingly modified, or even temporarily suspended, and this as effectually and as perfectly in the humblest as in the highest of created beings. As a result of this, dead bodies exhibit nothing but re- actions, and these purely* of a physical and chemical na- ture, whilst they show no tendency to pass through periodi- cal changes of state. On the other hand, living bod ies exhibit distinct actions, and are pre-eminently characterised by their 4 ELEMENTS OF BIOLOGY. tendency to pass through a series of cyclical changes, which follow one another in a regular and determinate. sequence. The above points are the leading characters by which living bodies are fundamentally separated from dead matter. There are, however, a few subordinate points in which some or all living bodies differ from those which are dead : — a. Che?nical Composition. — Dead bodies are composed of numerous elements, which exist either in an uncombined condition, or in a state of union. The combinations of these elements may be said to be naturally in a state of stable equilibrium, and they show no tendency to spon- taneous decomposition. Further, the combining elements unite with one another in low combining proportions, and the resulting compounds for the most part consist of no more than two or three elements. Living bodies, on the other hand, are composed of few chemical elements, and these are almost always in a state of combination. Furthermore, the combinations are always complex, consisting of three or four elements, and these elements are united with one another in high combining proportions. Finally, the chemical compounds of living bodies are invariably characterised by the presence of water, and are prone to spontaneous decomposition. Thus, the great organic compound, albumen, is composed of 144 atoms of carbon, no of hydrogen, 18 of nitrogen, 42 of oxygen, and two atoms of sulphur. Iron, however, exists in the blood, possibly in its elemental condition, and cop- per has been detected in the liver of certain of the Mam- malia, and largely in the colouring-matter of the feathers of certain birds. It is to be remembered, also, that certain mineral salts, well known as occurring in dead nature, are apparently absolutely indispensable to living bodies, at any rate as a general rule. Living bodies, therefore, whilst certainly presenting us with a peculiar group of chemical compounds, are to a certain extent built up of substances which commonly occur dissociated from vitality. NATURE AND CONDITIONS OF LIFE. 5 b. Arrangement of parts. — Dead bodies, when unmixed, are composed of an aggregation of similar and homogeneous parts which bear no definite and fixed relations to one another. Living bodies, on the other hand, are in the great majority of cases composed of dissimilar and heterogeneous parts, the relations of which amongst themselves are more or less definite. In other words, most living bodies are "organ- ised," being composed of separate parts or "organs," which have certain definite functions in the general economy. It must, however, be borne in mind, that organisation, though in the vast proportion of cases a concomitant of vitality, is not necessarily present in living bodies. Some living beings (such as the minute organisms known as the Foraminifera) ex- hibit no distinct parts or organs, and cannot therefore be said to be "organised" in any proper sense of the term, whilst they, nevertheless, exhibit all the essential phenomena of vitality. c. Form. — Dead bodies are either of no definite shape — when they are said to be " amorphous " — or they are crys- talline, in which case they are almost invariably bounded by straight lines and plane surfaces. Living bodies are almost always of a definite shape, presenting convex and concave surfaces, and being bounded by curved lines. Some living bodies, however, cannot be said to have any fixed form, but are extremely mutable in figure. In no case, however, could such be confounded with either the amorphous or the crystalline forms of dead matter. NATURE AND CONDITIONS OF LIFE. Life has been variously defined by different writers. Bichat defines life as " the sum total of the forces which resist death;" Treviranus, as "the constant uniformity of phenomena with diversity of external influences ; " Duges, as " the special activity of organised bodies f and Beclard, as " organisation in action." All these definitions, how- ever, are more or less objectionable, either because they really express nothing, or because the assumption under- 6 ELEMENTS OF BIOLOGY. lies them that life is inseparably connected with organisa- tion. More recently attempts have been made to prove that life is merely a form of energy or motion, in which case no difficulty should be found in giving it an exact defini- tion. In the meanwhile, however, this view certainly can- not be said to have been satisfactorily proved, and it does not appear that any rigid definition of life is possible. We may therefore employ the name life as a collective term for the tendency exhibited by certain forms of matter, under certain conditions, to pass through a series of changes in a more or less definite and determinate sequence. As regards the conditions under which alone life or vital activity can be manifested, we have to consider two sets of conditions : the intrinsic or indispensable conditions, with- out which no vital phenomena are possible; and the extrin- sic conditions, which are generally present, but which do not appear to be actually essential to living beings. Under the first head, we have only to consider the presence of a "physical basis;" under the second head, we may briefly look to the presence of organisation, light and air, and the necessity for a certain temperature. a. Protoplasm, — The first of the questions as to the con- ditions of life which it is necessary to consider, is whether the phenomena of vitality are necessarily associated with any particular form of matter, or with any special " physical basis," as it has been aptly termed. The answer to this question may with little hesitation be given in the affirma- tive. It does not at all appear that the phenomena of life can be manifested by any and every form of matter ; and a very little reflection ought Jo convince us that it would be very surprising if the reverse of this were the case. There is no physical or chemical force which can be rendered manifest to us by all and sundry forms of matter, and it would be indeed remarkable if the case were otherwise with the forces of the living organism. When, for example, we say that certain forms of matter, such as the metals, are NATURE AND CONDITIONS OF LIFE. J conductors of electricity, and certain other forms, such as glass, are non-conductors, we are in truth saying that elec- tricity requires for its manifestation a certain " physical basis." Upon merely theoretical grounds, therefore, we might have assumed the existence of a "matter of life," or a physical basis absolutely necessary for the manifestation of vital phenomena. This physical basis of life is known by the now notorious name of "protoplasm," or, as it is better termed by Dr Beale, " bioplasm." As regards its nature, protoplasm, though capable of being built up into the most complex structures, does not necessarily exhibit anything which can be looked upon as organisation or differentiation into distinct parts ; and its chemical composition is the only constant which can be approximately stated. It consists, namely, of carbon, oxy- gen, nitrogen, and hydrogen, united into a proximate com- pound to which Mulder applied the name of "proteine," and which is very nearly identical with albumen or white-of- egg. It further appears probable that all forms of proto- plasm can be made to contract by electricity, and "are liable to undergo that peculiar coagulation at a temperature of 4o°-5o° centigrade, which has been called ' heat-stirTen- ing ' " (Huxley). 8 ELEMENTS OF BIOLOGY. It seems certain, then, that no body is capable of mani- festing the marvellous phenomena of life, unless it be com- posed of some form or other of albuminous or protoplasmic matter. We know, at any rate, of no such body at present, and we are therefore justified in asserting that the presence of an albuminous basis is an essential condition of vitality. Most naturalists probably would subscribe to this state- ment ; but there are two different senses in which it would be received. Some eminent authorities insist that albumin- ous matter or protoplasm is not only a condition of vitality, but that it is its cause; or, in other words, that life is one of the properties of protoplasm. It is asserted, namely, that life is the result of the combined properties of the elements which form albuminous matter, just as the proper- ties of water are the resultant of the combined properties of its constituent hydrogen and oxygen ; and it is alleged that it is just as absurd to set down the phenomena of life to an assumed " vital force," as it would be to ascribe the properties of water to an assumed " aquosity." On the other hand, equally eminent philosophers would assert that the view just mentioned is one which confounds effect with cause, and that albuminous matter is at best but a condition of vitality, just as the presence of a conductor may be said to be an essential condition of electricity. Thje question as to which of these two opposing views has most in its favour is one of sufficient importance to warrant a brief exposition of the grounds upon which a decision may be arrived at. In the first place, when we come to sum up the actual data upon which such a decision should be formed, it is clear that we know two factors only of the case. We recog- nise certain phenomena which we call " vital, " as being exclusively manifested by living beings. We recognise, further, that these phenomena are never manifested except by certain forms of matter, or, it may be, by but a single form of matter. We conclude, therefore, that there must be NATURE AND CONDITIONS OF LIFE. 9 an intimate connection between vital phenomena and the " matter of life ; " but we can go no further than this, and the premisses do not in any way warrant the assertion that life is the result of living matter, or one of its properties. We know the succession of phenomena, but we know no more, and it is not possible to decide dogmatically which phenomenon precedes the other in point of time. It is therefore just as reasonable to believe that the matter of life is the result of vital forces as the reverse ; and, as far as mere logic is concerned, neither view can claim the smallest advantage over the other. If we take such a microscopic animalcule as the Amoeba, or, still better, one of the yet more humble organisms which are known as Foraminifera, we are presented with a little speck of animal matter, a little particle of albumen, almost or quite destitute of structure, and yet exhibiting all the essential phenomena of vitality. Such a particle of living matter is undoubtedly the seat of certain forces which render it different from any and every collocation of mere dead particles. . Whether we call these forces "vital" or not matters little ; but we certainly are not at present justified, by any evidence in our hands, in asserting that they are merely a form of energy or motion. No one has hitherto succeeded in demonstrating how any form or any combina- tion of any of the known physical or chemical forces should produce the vital phenomena which are seen to occur in the albuminous matter of even the most humble of animals. Until such a demonstration can be brought forward, we are not only justified, but we are bound, to look at the forces at work in living matter as something outside and beyond the mere physical forces. We may call these forces "vital" or not, ' as we choose, but the fact will either way remain the same. Again, every one will willingly admit that all compound substances possess certain properties which are the result of the combined properties of their component elements. Water, for example, is composed of hydrogen and oxygen, 10 ELEMENTS OF BIOLOGY, and its properties are the resultant of the combined proper- ties of these two gases. It is a definite chemical compound, having definite and constant properties, and there is no kind of necessity for ascribing the properties of water to any assumed principle of "aquosity." It is to be remembered, however, that there is only one kind of water, and its pro- perties are universally the same. In the same way, albumi- nous matter, or protoplasm, is a chemical compound which unquestionably possesses certain properties as the result- ant of the combined properties of its component elements. But this is dead protoplasm of which this is true, and unless this be granted it is difficult to see how to avoid having to deny that dead protoplasm can exist at all. It is conceiv- able — nay, more, it is one of the splendid possibilities of the future — that the chemist should succeed in forcing the ele- ments of albuminous matter to combine with one another, and thus in manufacturing protoplasm artificially in the laboratory. But this would be dead albuminous matter; and it is wholly inconceivable that the utmost advances of con- structive chemistry should ever lead to the manufacture of living protoplasm. Dead albuminous matter may be re- garded as a tolerably definite and uniform chemical com- pound, and its properties are, beyond doubt, the resultant of those of its component elements. Like water, therefore, dead protoplasm has universally the same physical and chemical properties. Living protoplasm, on the other hand, though still unchanged in chemical composition and physi- cal characters, exhibits the most varied properties, accord- ing as its forms enter into the composition of different ani- mals. If, then, we are to ascribe vital phenomena to the inherent constitution of living matter — in the sense that the properties of water are those of its component gases — we are left to account, as best we may, for the utterly immea- surable differences between the vital phenomena of a man and of a sponge, both of which may be regarded as com- posed fundamentally of the same materials. NATURE AND CONDITIONS OF LIFE. II The more philosophical view, then, as to the nature of the connection between life and its material basis, is the one which regards vitality as something superadded and foreign to the matter by which vital phenomena are manifested. Protoplasm is essential as the physical medium through which vital action may be manifested ; just as a conductor is essential to the manifestation of electric phenomena, or just as a paint-brush and colours are essential to the artist. Because metal conducts the electric current, and renders it perceptible to our senses, no one thinks of therefore assert- ing that electricity is one of the inherent properties of a metal, any more than one would feel inclined to assert that the power of painting was inherent in the camel's hair or in the dead pigments. Behind the material substratum, in all cases, is the active and living force ; and we have no right to assume that the force ceases to exist when its physical basis is removed, though it is no longer perceptible to our senses. It is, on the contrary, quite conceivable theoreti- cally that the vital forces of an organism should suffer no change by the destruction of the physical basis, just as elec- tricity would continue to subsist in a world composed uni- versally of non-conductors. In neither case could the force manifest its presence, or be brought into any perceptible relation with the outer world; but in neither case should we have the smallest ground for assuming that the power was necessarily non-extant. b. Organisation. — Having decided that the presence of a certain physical basis or peculiar form of matter is essential to the manifestation of vital phenomena, we may next pass on to consider whether organisation, or the presence of a certain de- finite structure, is one of the essential conditions of vitality. It is a very common thing to speak of animals as if they were so many machines, and from one limited point of view the comparison is a fair and useful one. Every machine, however simple, is composed of certain definite parts which have cer- tain definite relations to one another; and every machine, 12 ELEMENTS OF BIOLOGY. therefore, has what in the case of an animal would be spoken of as " organisation." Each part or "organ" of the machine has certain definite functions, and the machine carries out its appointed work, when supplied with the necessary force, in virtue of the harmonious combination and interaction of its several parts. Most animals, in the same way, consist of definite parts or organs, with fixed relations to one ano- ther, and each discharging its own work or function in the general economy. So far the comparison is a good one, but it may be, and has been, carried too far. It is the very essence of a machine that it should consist of definite parts. It does not matter whether we are dealing with a toasting- fork or a steam-engine, we have in all cases a body com- posed of different parts performing different functions ; and no work can be got out of the machine unless by the invo- cation of a separate factor to supply the necessary force. It has been hastily assumed that the case is the same with animals, and the common simile has gone far to foster and diffuse this belief. It has, in fact, been unhesitatingly laid down that life is inseparably connected with organisation ; nay, more, it has even been asserted that life is the result of organisation. The falsity of this belief, however, is conclu- sively shown by the study of the minute creatures known as the Foraminifera (fig. i). These little animals possess the power of secreting a very beautiful and elaborate external envelope or shell, and they thus obtain a spurious kind of complexity which is very strikingly at variance with their real simplicity. In point of fact, the bodies of the Foram- inifera exhibit nothing which could truly be termed "organ- isation." They consist simply of formless and structureless albuminous matter. They are not composed of definite parts or organs, and they are in no proper sense to be com- pared to machines. Nevertheless, they live, assimilate nourishment, grow, maintain their existence against hostile forces, have certain relations with the outer world, and reproduce their like. The highest animal, regarded merely NATURE AND CONDITIONS OF LIFE. 13 as an animal, can do no more than this ; and yet the Foram- inifera attain this end without possessing a single organ of Fig. 1. — Foraminifera. a The animal of Nonionina, after the shell has been removed by a weak acid ; b Gromia (after Schultze), showing the shell surrounded by a network of filaments derived from the body-substance. any kind. These minute animalcules, therefore, show in an extremely beautiful and instructive manner, that organisa- tion is only a result of life, and not even a necessary result. In other words, we learn that an animal is organised, or possesses structure, because it is alive; it does not live because it is organised. c. Light — In one sense light may be regarded as one of 14 ELEMENTS OF BIOLOGY. the essential conditions of vitality ; but from another point of view it is wholly unnecessary. Light, namely, is neces- sary for animated nature as a whole, but is by no means essential to all living beings regarded as individuals. Many animals spend a great part of their existence in total dark- ness, and some pass their entire life without "access to the rays of the sun. Regarded, however, from a deeper point of view, light is seen to be absolutely essential to life, since vegetable life can only be carried on under the influence of sun-force. All animals, as we shall subsequently see, are dependent, mediately or immediately, upon plants for their food ; since plants alone possess the power of building up organic compounds out of inorganic materials. Plants, however, can perform this feat of vital chemistry only when supplied with the light-giving and chemical rays of the sun, so that light is an absolute prerequisite for life. The im- portance of light as one of the conditions of life, will, how- ever, be spoken of at greater length in treating of the food of animals and plants, and the distribution of animal life at great depths in the ocean. d. Air. — The presence of atmospheric air, or rather of free oxygen, appears to be essential to animal life, and a supply of oxygen may therefore be regarded as one of the extrinsic conditions of vitality. It would seem, however, that certain low vegetable organisms (vibriones and bacte- ria) flourish in an atmosphere of carbonic acid ; so that free oxygen cannot be looked upon as being an indispensable requisite of life. e. Temperature. — In a general way, the higher manifesta- tions of life are only possible between certain limited ranges of temperature, which may be stated as varying from near the freezing-point to 120 or 130 Fahrenheit. Some of the lower forms of life, however, can unquestionably endure temperatures much more extreme than these; and it would appear that life in its lowest grades is not impossible at tem- peratures considerably below the freezing-point, and rising DEATH. 15 S6-- d far above the boiling-point of water (from 20 up to 300 F.) This subject, however, will be treated of at greater length in speaking of the alleged development of living beings de novo (Spontaneous Generation). f. Water, — Lastly, it may be remarked that no vital pro- cesses can be carried on except in the presence of water. This, however, truly depends upon the fact that water is an essential constituent of protoplasmic or albuminous matter in its living state. The necessity, therefore, for a "physical basis " of life, carries with it the necessary presence of water. Life, however, may remain in a dormant condition during long periods, even in the total ab- j|^|r sence of water. ^F DEATH. The non-fulfilment of any of the above-named conditions for any length of time, as a rule, causes death, or the cessation of vitality ; but, as just remarked, life may sometimes remain in a dormant or " potential" condi- tion for an apparently indefinite length of time. An excellent illustration of this is afforded by the eggs of some animals, and the seeds of many plants ; but a more striking example is to be found in the Rotifera or "Wheel-animalcules" (fig. 2). The Rotifers are minute, mostly microscopic creatures, which inhabit almost all our ponds and streams. Diminu- tive as they are, they are nevertheless, comparatively speak- Fig. 2. — Rotifera. Eospkora aurita* one of the Wheel-animalcules. En- larged about 250 diameters. (After Gosse.) 1 6 ELEMENTS OF BIOLOGY. ing, of a very high grade of organisation. They possess a mouth, masticatory organs, a stomach, and alimentary canal, a distinct and well-developed nervous system, a differen- tiated reproductive apparatus, and even organs of vision. Repeated experiments, however, have shown the remarkable fact, that, with their aquatic habits and complex organisa- tion, the Rotifers are capable of submitting to an apparently indefinite deprivation of the necessary conditions of their existence, without thereby losing their vitality. They may be dried and reduced to dust, and may be kept in this state for a period of many years ; nevertheless, the addition of a little water will, at any time, restore them to their pristine vigour and activity. It follows, therefore, that an organism may be deprived of all power of manifesting any of the phenomena which constitute what we call life, without los- ing its hold upon the vital forces which belong to it It seems, however, hardly necessary to add that this is a mere instance of revival and not of revitalisation. The desiccated Rotifers are not truly dead, but are merely in a state of sus- pended animation. USE OF THE TERM VITAL FORCE. If, in conclusion, it be asked whether the term "vital force " is any longer permissible in the mouth of a scientific man, the question must, I think, be answered in the affirma- tive. Formerly, no doubt, the progress of science was retarded and its growth checked by a too exclusive reference of natural phenomena to a so-called vital force. Equally unquestionable is the fact that the development of Biological science has progressed contemporaneously with the succes- sive victories gained by the physicists over the vitalists. Still, no physicist has hitherto succeeded in explaining any fundamental vital phenomenon upon purely physical and chemical principles. The simplest vital phenomenon has in it something over and above the merely chemical and physical forces which we can demonstrate in the laboratory. USE OF THE TERM VITAL FORCE. 1 7 It is easy, for example, to say that the action of the gastric juice is a chemical one, and doubtless the discovery of this fact was a great step in physiological science. Neverthe- less, in spite of the most searching investigations, it is cer- tain that digestion presents phenomena which are as yet inexplicable upon any chemical theory. This is exemplified in its most striking form, when we look at a simple organism like the Amoeba. This animalcule, which is structurally little more than a mobile lump of jelly, digests as perfectly — as far as the result to itself is concerned — as does the most highly organised animal with the most complex diges- tive apparatus. It takes food into its interior, it digests it without the presence of a single organ for the purpose ; and still more, it possesses that inexplicable selective power by which it assimilates out of its food such constituents as it needs, whilst it rejects the remainder. In the present state of our knowledge, therefore, we must conclude that even in the process of digestion as exhibited in the Amoeba there is something that is not merely physical or chemical. Simi- larly, any organism when just dead consists of the same protoplasm as before, in the same forms, and with the same arrangement ; but it has most unquestionably lost a some- thing by which all its properties and actions were modified, and some of them were produced. What that something is we do not know, and perhaps never shall know ; and it is possible, though highly improbable, that future discoveries may demonstrate that it is merely a subtle modification of some physical force. In the meanwhile, as all vital actions exhibit this mysterious something, it would appear unphilo- sophical to ignore its existence altogether, and the term "vital force" may therefore be retained with advantage. In using this term, however, it must not be forgotten that we are simply employing a convenient expression for an unknown quantity, for that residual portion of every vital action which cannot at present be referred to the operation of any known physical force. B 1 8 ELEMENTS OF BIOLOGY. It must, however, also be borne in mind that this residuum is probably not to be ascribed to our ignorance, but that it has a real existence. It appears, namely, in the highest degree probable that every vital action has in it something which is not merely physical and chemical, but which is conditioned by an unknown force, higher in its nature and distinct in kind as compared with all other forces. The presence of this " vital force " maybe recognised even in the simplest phenomena of nutrition ; and no attempt even has hitherto been made to explain the phenomena of reproduc- tion by the working of any known physical or chemical force. 19 CHAPTER II. DIFFERENCES BETWEEN ANIMALS AND PLANTS.* Having now arrived at some definite notion as to the essen- tial characters of living beings in general, we have next to consider what are the characteristics of the two great divi- sions of animated nature. What are the characters which induce us to place any given organism in either the animal or vegetable kingdom ? What, in short, are the differences between animals and plants ? It is generally admitted that all bodies which exhibit vital phenomena are capable of being referred to one of the two great kingdoms of organic nature. At the same time it is often extremely difficult in individual cases to come to any decision as to the kingdom to which a given organism should be referred, and in many cases the determination is purely arbitrary. So strongly, in fact, has this difficulty been felt, that some observers have established an intermediate king- dom, a sort of no-man's-land, for the reception of those debatable organisms which cannot be definitely and posi- tively classed either amongst vegetables or amongst animals. Thus, Dr Ernst Hseckel has proposed to form an intermediate kingdom, which he calls the Regnum Protisticum^ for the reception of all doubtful organisms. Even such a cautious observer as Dr Rolleston, whilst questioning the propriety of this step, is forced to conclude that " there are organisms 20 ELEMENTS OF BIOLOGY. which at one period of their life exhibit an aggregate of phenomena such as to justify us in speaking of them as animals, whilst at another they appear to be as distinctly vegetable." In the case of the higher animals and plants there is no difficulty; the former being at once distinguished by the possession of a nervous system, of motor power which can be voluntarily exercised, and of an internal cavity fitted for the reception and digestion of solid food. The higher plants, on the other hand, possess no nervous system or organs of sense, are incapable of independent locomotion, and are not provided with an internal digestive cavity, their food being wholly fluid or gaseous. These distinctions, however, do not hold good as regards the lower and less highly organised members of the two kingdoms, many ani- mals having no nervous system or internal digestive cavity, whilst many plants possess the power of locomotion; so that we are compelled to institute a closer comparison in the case of these lower forms of life. a. Form. — As regards external configuration, of all char- acters the most obvious, it must be admitted that no abso- lute distinction can be laid down between plants and ani- mals. Many of our ordinary zoophytes, such as the Hydroid Polypes, the sea-shrubs and corals — as, indeed, the name zoo- phyte implies — are so similar in external appearance to plants that they were long described as such. Amongst the Mol- luscoida, the common sea-mat (Flustra) is invariably re- garded by sea-side visitors as a sea-weed. Many of the Protozoa are equally like some of the lower plants (Proto- phyta); and even at the present day there are not wanting those who look upon the sponges as belonging to the vege- table kingdom. On the other hand, the embryonic forms, or " zoospores," of certain undoubted plants (such as the Protococcus nivalis, Vaucheria, &c), are provided with ciliated processes with which they swim about, thus coming so closely to resemble some of the Infusorian animalcules as DIFFERENCES BETWEEN ANIMALS AND PLANTS. 21 to have been referred to that division of the Protozoa. This is also the case with some adult plants, such as Volvox globator (fig. 3). Fig. 3. — Algae and Infusoria, a Ciliated zoospores of Conferva; b Ciliated zoospore of Vauckeria; c Volvox globator ; magnified; d Euplotes Charon, one of the Infusoria, magnified. b. Internal Structure. — Here, again, no line of demarcation can be drawn between the animal and vegetable kingdoms. In this respect all plants and animals are fundamentally- similar, being alike composed of molecular, cellular, and fibrous tissues. 