The Principles Of Biology - free ebook by Herbert Spencer

Read as playlist

The Principles Of Biology

Herbert Spencer

97 chapters

32 hour read

Read as playlist

Selected Chapters

97 chapters

Preface to the Revised and Enlarged Edition.

Preface to the Revised and Enlarged Edition.

TO THE REVISED AND ENLARGED EDITION. Rapid in all directions, scientific progress has during the last generation been more rapid in the direction of Biology than in any other; and had this work been one dealing with Biology at large, the hope of bringing it up to date could not have been rationally entertained. But it is a work on the Principles of Biology; and to bring an exposition of these up to date, seemed not impossible with such small remnant of energy as is left me. Slowly, and often int

4 minute read

Read Chapter

THE PRINCIPLES OF BIOLOGY

THE PRINCIPLES OF BIOLOGY

BY HERBERT SPENCER IN TWO VOLUMES VOL. II REVISED AND ENLARGED EDITION 1899 NEW YORK D. APPLETON AND COMPANY 1900 Copyright , 1867, 1899, By D. APPLETON AND COMPANY....

14 minute read

Read Chapter

PREFACE TO THE REVISED AND ENLARGED EDITION OF VOL. II.

PREFACE TO THE REVISED AND ENLARGED EDITION OF VOL. II.

To the statements made in the preface to the first volume of this revised edition, there must here be added a few having special reference to this second volume. One of them is that the revision has not been carried out in quite the same way, but in a way somewhat less complete. When reviewing the first volume a friendly critic, Prof. Lloyd Morgan, said:— “But though the intellectual weight has also been augmented, it is an open question whether it would not have been wiser to leave intact a tre

4 minute read

Read Chapter

Preface.

Preface.

The aim of this work is to set forth the general truths of Biology, as illustrative of, and as interpreted by, the laws of Evolution: the special truths being introduced only so far as is needful for elucidation of the general truths. For aid in executing it, I owe many thanks to Prof. Huxley and Dr. Hooker. They have supplied me with information where my own was deficient; [1] and, in looking through the proof-sheets, have pointed out errors of detail into which I had fallen. By having kindly r

57 minute read

Read Chapter

I. Organic Matter.

I. Organic Matter.

ORGANIC MATTER. § 1 . Of the four chief elements which, in various combinations, make up living bodies, three are gaseous under all ordinary conditions and the fourth is a solid. Oxygen, hydrogen, and nitrogen are gases which for many years defied all attempts to liquefy them, and carbon is a solid except perhaps at the extremely high temperature of the electric arc. Only by intense pressures joined with extreme refrigerations have the three gases been reduced to the liquid form. [2] There is mu

40 minute read

Read Chapter

PREFACE TO VOL. II.

PREFACE TO VOL. II.

The proof sheets of this volume, like those of the last volume, have been looked through by Dr. Hooker and Prof. Huxley; and I have, as before, to thank them for their valuable criticisms, and for the trouble they have taken in checking the numerous statements of fact on which the arguments proceed. The consciousness that their many duties render time extremely precious to them, makes me feel how heavy is my obligation. Part IV., with which this volume commences, contains numerous figures. Nearl

1 minute read

Read Chapter

CHAPTER I. THE PROBLEMS OF MORPHOLOGY.

CHAPTER I. THE PROBLEMS OF MORPHOLOGY.

§ 175. The division of Morphology from Physiology, is one which may be tolerably-well preserved so long as we do not carry our inquiries beyond the empirical generalizations of their respective phenomena; but it is one which becomes in great measure nominal, when the phenomena are to be rationally interpreted. It would be possible, after analyzing our Solar System, to set down certain general truths respecting the sizes and distances of its primary and secondary members, omitting all mention of

16 minute read

Read Chapter

II. The Actions of Forces on Organic Matter.

II. The Actions of Forces on Organic Matter.

THE ACTIONS OF FORCES ON ORGANIC MATTER. § 10 . To some extent, the parts of every body are changed in their arrangement by any incident mechanical force. But in organic bodies, and especially in animal bodies, the changes of arrangement produced by mechanical forces are usually conspicuous. It is a distinctive mark of colloids that they readily yield to pressures and tensions, and that they recover, more or less completely, their original shapes, when the pressures or tensions cease. Evidently

28 minute read

Read Chapter

CHAPTER II. THE MORPHOLOGICAL COMPOSITION OF PLANTS.

CHAPTER II. THE MORPHOLOGICAL COMPOSITION OF PLANTS.

§ 180. Evolution implies insensible modifications and gradual transitions, which render definition difficult—which make it impossible to separate absolutely the phases of organization from one another. And this indefiniteness of distinction, to be expected à priori , we are compelled to recognize à posteriori , the moment we begin to group morphological phenomena into general propositions. Thus, on inquiring what is the morphological unit, whether of plants or of animals, we find that the facts

20 minute read

Read Chapter

III. The Re-actions of Organic Matter on Forces.

III. The Re-actions of Organic Matter on Forces.

THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. § 17 . Re-distributions of Matter imply concomitant re-distributions of Motion. That which under one of its aspects we contemplate as an alteration of arrangement among the parts of a body, is, under a correlative aspect, an alteration of arrangement among certain momenta, whereby these parts are impelled to their new positions. At the same time that a force, acting differently on the different units of an aggregate, changes their relations to one anot

27 minute read

Read Chapter

CHAPTER III. THE MORPHOLOGICAL COMPOSITION OF PLANTS, CONTINUED.

CHAPTER III. THE MORPHOLOGICAL COMPOSITION OF PLANTS, CONTINUED.

§ 187. That advanced composition arrived at in the Archegoniatæ , is carried still further in the Flowering Plants. In these most-elevated vegetal forms, aggregation of the third order is always distinctly displayed; and aggregates of the fourth, fifth, sixth, &amp;c., orders are very common. Our inquiry into the morphology of these flowering plants, may be advantageously commenced by studying the development of simple leaves into compound leaves. It is easy to trace the transition, as well

29 minute read

Read Chapter

IIIa. Metabolism.

IIIa. Metabolism.

METABOLISM. § 23 a . In the early forties the French chemist Dumas pointed out the opposed actions of the vegetal and animal kingdoms: the one having for its chief chemical effect the decomposition of carbon-dioxide, with accompanying assimilation of its carbon and liberation of its oxygen, and the other having for its chief chemical effect the oxidation of carbon and production of carbon-dioxide. Omitting those plants which contain no chlorophyll, all others de-oxidize carbon; while all animals

26 minute read

Read Chapter

CHAPTER IV. THE MORPHOLOGICAL COMPOSITION OF ANIMALS.

CHAPTER IV. THE MORPHOLOGICAL COMPOSITION OF ANIMALS.

§ 199. What was said in § 180 , respecting the ultimate structure of organisms, holds more manifestly of animals than of plants. That throughout the vegetal kingdom the cell is the morphological unit, is a proposition admitting of a better defence, than the proposition that the cell is the morphological unit throughout the animal kingdom. The qualifications with which, as we saw, the cell-doctrine must be taken, are qualifications thrust upon us more especially by the facts which zoologists have

31 minute read

Read Chapter

IV. Proximate Conception of Life.

IV. Proximate Conception of Life.

PROXIMATE CONCEPTION OF LIFE. § 24 . To those who accept the general doctrine of Evolution, it need scarcely be pointed out that classifications are subjective conceptions, which have no absolute demarcations in Nature corresponding to them. They are appliances by which we limit and arrange the matters under investigation; and so facilitate our thinking. Consequently, when we attempt to define anything complex, or make a generalization of facts other than the most simple, we can scarcely ever av

20 minute read

Read Chapter

CHAPTER V. THE MORPHOLOGICAL COMPOSITION OF ANIMALS, CONTINUED.

CHAPTER V. THE MORPHOLOGICAL COMPOSITION OF ANIMALS, CONTINUED.

§ 208. Insects, Arachnids, Crustaceans, and Myriapods, are all members of that higher division of the Annulosa [26] called Articulata or now more generally Arthropoda . Though in these creatures the formation of segments may be interpreted as a disguised gemmation; and though, in some of them, the number of segments increases by this modified budding after leaving the egg, as it does among the Annelids; yet the process is not nearly so dominant: the segments are usually much less numerous than w

22 minute read

Read Chapter

V. The Correspondence between Life and its Circumstances.

V. The Correspondence between Life and its Circumstances.

THE CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. § 27 . We habitually distinguish between a live object and a dead one, by observing whether a change which we make in the surrounding conditions, or one which Nature makes in them, is or is not followed by some perceptible change in the object. By discovering that certain things shrink when touched, or fly away when approached, or start when a noise is made, the child first roughly discriminates between the living and the not-living; and the

15 minute read

Read Chapter

CHAPTER VI. MORPHOLOGICAL DIFFERENTIATION IN PLANTS.

CHAPTER VI. MORPHOLOGICAL DIFFERENTIATION IN PLANTS.

§ 212. While, in the course of their evolution, plants and animals have displayed progressive integrations, there have at the same time gone on progressive differentiations of the resulting aggregates, both as wholes and in their parts. These differentiations and the interpretations of them, form the second class of morphological problems. We commence as before with plants. We have to consider, first, the several kinds of modification in shape they have undergone; and, second, the relations betw

8 minute read

Read Chapter

VI. The Degree of Life Varies as the Degree of Correspondence.

VI. The Degree of Life Varies as the Degree of Correspondence.

THE DEGREE OF LIFE VARIES AS THE DEGREE OF CORRESPONDENCE. § 31 . Already it has been shown respecting each other component of the foregoing definition, that the life is high in proportion as that component is conspicuous; and it is now to be remarked, that the same thing is especially true respecting this last component—the correspondence between internal and external relations. It is manifest, a priori , that since changes in the physical state of the environment, as also of those mechanical a

16 minute read

Read Chapter

CHAPTER VII. THE GENERAL SHAPES OF PLANTS.

CHAPTER VII. THE GENERAL SHAPES OF PLANTS.

§ 217. Among protophytes those exemplified by Pleurococcus vulgaris are by general consent considered the simplest. As shown in Fig. 1 , they are globular cells presenting no obvious differentiation save that between inner and outer parts. Their uniformity of figure co-exists with a mode of life involving the uniform exposure of all their sides to incident forces. For though each individual may have its external parts differently related to environing agencies, yet the new individuals produced b

15 minute read

Read Chapter

VIa. The Dynamic Element in Life.

VIa. The Dynamic Element in Life.

THE DYNAMIC ELEMENT IN LIFE. § 36 a . A critical comparison of the foregoing formula with the facts proves it to be deficient in more ways than one. Let us first look at vital phenomena which are not covered by it. Some irritant left by an insect's ovipositor, sets up on a plant the morbid growth named a gall. The processes in the gall do not correspond with any external co-existences or sequences relevant to the plant's life—show no internal relations adjusted to external relations. Yet we cann

22 minute read

Read Chapter

VII. The Scope of Biology.

VII. The Scope of Biology.

THE SCOPE OF BIOLOGY. § 37 . As ordinarily conceived, the science of Biology falls into two great divisions, the one dealing with animal life, called Zoology, and the other dealing with vegetal life, called Botany, or more properly to be called Phytology. But convenient as is this division, it is not that which arises if we follow the scientific method of including in one group all the phenomena of fundamentally the same order and putting separately in another group all the phenomena of a fundam

12 minute read

Read Chapter

CHAPTER VIII. THE SHAPES OF BRANCHES.

CHAPTER VIII. THE SHAPES OF BRANCHES.

§ 221. Aggregates of the first order supply a few examples of forms ramified in an approximately-regular manner, under conditions which subject their parts to approximately-regular distributions of forces. Some unicellular Algæ , becoming elaborately branched, assume very much the aspects of small trees; and show us in their branches analogous relations of forms to forces. Bryopsis plumosa may be instanced. Fig. 200 represents the end of one of its lateral ramifications, above and beneath which

9 minute read

Read Chapter

I. Growth.

I. Growth.

GROWTH. § 43 . Perhaps the widest and most familiar induction of Biology, is that organisms grow. While, however, this is a characteristic so uniformly and markedly displayed by plants and animals, as to be carelessly thought peculiar to them, it is really not so. Under appropriate conditions, increase of size takes place in inorganic aggregates, as well as in organic aggregates. Crystals grow; and often far more rapidly than living bodies. Where the requisite materials are supplied in the requi

48 minute read

Read Chapter

CHAPTER IX. THE SHAPES OF LEAVES.

CHAPTER IX. THE SHAPES OF LEAVES.

§ 228. Next in the descending order of composition come compound leaves. The relative sizes and distributions of their leaflets, as affecting their forms as wholes, have to be considered in their relations to conditions. Figs. 206, 207 , represent leaves of the common Oxalis and of the Marsilea , in which radial symmetry is as completely displayed as the small number of leaflets permits. This equal development of the leaflets on all sides, occurs where the foot-stalks, growing up vertically from

10 minute read

Read Chapter

II. Development.

II. Development.

DEVELOPMENT. [19] § 50 . Certain general aspects of Development may be studied apart from any examination of internal structures. These fundamental contrasts between the modes of arrangement of parts, originating, as they do, the leading external distinctions among the various forms of organization, will be best dealt with at the outset. If all organisms have arisen by Evolution, it is of course not to be expected that such several modes of development can be absolutely demarcated: we are sure t

32 minute read

Read Chapter

CHAPTER X. THE SHAPES OF FLOWERS.

CHAPTER X. THE SHAPES OF FLOWERS.

§ 232. Following an order like that of preceding chapters, let us first note a few typical facts respecting the forms of clusters of flowers, apart from the forms of the flowers themselves. Two kindred kinds of Leguminosæ serve to show how the members of clusters are distributed in an all-sided manner or in a two-sided manner, according as the circumstances are alike on all sides or alike on only two sides. In Hippocrepis , represented in Fig. 226 , the flowers growing at the end of a vertical s

18 minute read

Read Chapter

CHAPTER XI. THE SHAPES OF VEGETAL CELLS.

CHAPTER XI. THE SHAPES OF VEGETAL CELLS.

§ 237. We come now to aggregates of the lowest order. Already something has been said ( § 217 ) concerning the forms of those morphological units which exist as independent plants. But it is here requisite briefly to note the modifications undergone by them where they become components of larger plants. Fig. 254. Of the numerous cell-forms which are found in the tissues of the higher plants, it will suffice to give, in Fig. 254 , representing a section of a leaf, a single example. In this it wil

3 minute read

Read Chapter

IIa. Structure.

IIa. Structure.

STRUCTURE. [21] § 54 a . As, in the course of evolution, we rise from the smallest to the largest aggregates by a process of integration, so do we rise by a process of differentiation from the simplest to the most complex aggregates. The initial types of life are at once extremely small and almost structureless. Passing over those which swarm in the air, the water, and the soil, and are now some of them found to be causes of diseases, we may set out with those ordinarily called Protozoa and Prot

28 minute read

Read Chapter

III. Function.

III. Function.

FUNCTION. § 55 . Does Structure originate Function, or does Function originate Structure? is a question about which there has been disagreement. Using the word Function in its widest signification, as the totality of all vital actions, the question amounts to this—does Life produce Organization, or does Organization produce Life? To answer this question is not easy, since we habitually find the two so associated that neither seems possible without the other; and they appear uniformly to increase

26 minute read

Read Chapter

CHAPTER XII. CHANGES OF SHAPE OTHERWISE CAUSED.

CHAPTER XII. CHANGES OF SHAPE OTHERWISE CAUSED.

§ 238. Besides the more special causes of modification in the shapes of plants and of their parts, certain more general causes must be briefly noticed. These may be described as consequences of variations in the total quantities of the matters and forces furnished to plants by their environments. Some of the changes of form so produced are displayed by plants as wholes, and others only by their parts. We will glance at them in this order. § 239. It is a familiar fact that luxuriant shoots have r

3 minute read

Read Chapter

IV. Waste and Repair.

IV. Waste and Repair.

WASTE AND REPAIR. § 62 . Throughout the vegetal kingdom, the processes of Waste and Repair are comparatively insignificant in their amounts. Though all parts of plants save the leaves, or other parts which are green, give out carbonic acid; yet this carbonic acid, assuming it to indicate consumption of tissue, or rather of the protoplasm contained in the tissue, indicates but a small consumption. Of course if there is little waste there can be but little repair—that is, little of the interstitia

24 minute read

Read Chapter

CHAPTER XIII. MORPHOLOGICAL DIFFERENTIATION IN ANIMALS.

CHAPTER XIII. MORPHOLOGICAL DIFFERENTIATION IN ANIMALS.

§ 242. The general considerations which preluded our inquiry into the shapes of plants and their parts, equally serve, so far as they go, to prelude an inquiry into the shapes of animals and their parts. Among animals, as among plants, the formation of aggregates greater in bulk or higher in degree of composition, or both, is accompanied by changes of form in the aggregates as wholes as well as by changes of form in their parts; and the processes of morphological differentiation conform to the s

3 minute read

Read Chapter

CHAPTER XIV. THE GENERAL SHAPES OF ANIMALS.

CHAPTER XIV. THE GENERAL SHAPES OF ANIMALS.

§ 244. Certain of the Protozoa are quite indefinite in their shapes, and quite inconstant in those indefinite shapes which they have—the relations of their parts are indeterminate both in space and time. In one of the simpler Rhizopods, at least during the active stage of its existence, no permanent distinction of inside and outside is established; and hence there can arise no established correspondence between the shape of the outside and the distribution of environing actions. But when the rel

30 minute read

Read Chapter

V. Adaptation.

V. Adaptation.

ADAPTATION. § 67 . In plants waste and repair being scarcely appreciable, there are not likely to arise appreciable changes in the proportions of already-formed parts. The only divergences from the average structures of a species, which we may expect particular conditions to produce, are those producible by the action of these conditions on parts in course of formation; and such divergences we do find. We know that a tree which, standing alone in an exposed position, has a short and thick stem,

28 minute read

Read Chapter

CHAPTER XV. THE SHAPES OF VERTEBRATE SKELETONS.

CHAPTER XV. THE SHAPES OF VERTEBRATE SKELETONS.

§ 254. When an elongated mass of any substance is transversely strained, different parts of the mass are exposed to forces of opposite kinds. If, for example, a bar of metal or wood is supported at its two ends, as shown in Fig. 281 , and has to bear a weight on its centre, its lower part is thrown into a state of tension, while its upper part is thrown into a state of compression. As will be manifest to any one who observes what happens on breaking a stick across his knee, the greatest degree o

28 minute read

Read Chapter

VI. Individuality.

VI. Individuality.

INDIVIDUALITY. § 72 . What is an individual? is a question which many readers will think it easy to answer. Yet it is a question that has led to much controversy among Zoologists and Botanists, and no quite satisfactory reply to it seems possible. As applied to a man, or to any one of the higher animals, which are all sharply-defined and independent, the word individual has a clear meaning: though even here, when we turn from average cases to exceptional cases—as a calf with two heads and two pa

12 minute read

Read Chapter

VIa. Cell-Life and Cell-Multiplication.

VIa. Cell-Life and Cell-Multiplication.

CELL-LIFE AND CELL-MULTIPLICATION. § 74 a . The progress of science is simultaneously towards simplification and towards complication. Analysis simplifies its conceptions by resolving phenomena into their factors, and by then showing how each simple mode of action may be traced under multitudinous forms; while, at the same time, synthesis shows how each factor, by cooperation with various other factors in countless modes and degrees, produces different results innumerable in their amounts and va

27 minute read

Read Chapter

CHAPTER XVI. THE SHAPES OF ANIMAL CELLS.

CHAPTER XVI. THE SHAPES OF ANIMAL CELLS.

§ 260. Among animals as among plants, the laws of morphological differentiation must be conformed to by the morphological units, as well as by the larger parts and by the wholes formed of them. It remains here to point out that the conformity is traceable where the conditions are simple. Fig. 294. In the shapes assumed by those rapidly-multiplying cells out of which each animal is developed, there is a conspicuous subordination to the surrounding actions. Fig. 294 represents the cellular embryon

2 minute read

Read Chapter

CHAPTER XVII. SUMMARY OF MORPHOLOGICAL DEVELOPMENT.

CHAPTER XVII. SUMMARY OF MORPHOLOGICAL DEVELOPMENT.

§ 262. That any formula should be capable of expressing a common character in the shapes of things so unlike as a tree and a cow, a flower and a centipede, is a remarkable fact; and is a fact which affords strong primâ facie evidence of truth. For in proportion to the diversity and multiplicity of the cases to which any statement applies, is the probability that it sets forth the essential relations. Those connexions which remain constant under all varieties of manifestation, are most likely to

6 minute read

Read Chapter

VII. Genesis.

VII. Genesis.

GENESIS. § 75 . Having, in the last chapter but one, concluded what constitutes an individual, and having, in the last chapter, contemplated the histological process which initiates a new individual, we are in a position to deal with the multiplication of individuals. For this, the title Genesis is here chosen as being the most comprehensive title—the least specialized in its meaning. By some biologists Generation has been used to signify one method of multiplication, and Reproduction to signify

51 minute read

Read Chapter

CHAPTER I. THE PROBLEMS OF PHYSIOLOGY.

CHAPTER I. THE PROBLEMS OF PHYSIOLOGY.

§ 265. The questions to be treated under the above title are widely different from those which it ordinarily expresses. We have no alternative, however, but to use Physiology in a sense co-extensive with that in which we have used Morphology. We must here consider the facts of function in a manner parallel to that in which we have, in the foregoing Part, considered the facts of structure. As, hitherto, we have concerned ourselves with those most general phenomena of organic form which, holding i

6 minute read

Read Chapter

VIII. Heredity.

VIII. Heredity.

HEREDITY. § 80 . Already, in the last two chapters, the law of hereditary transmission has been tacitly assumed; as, indeed, it unavoidably is in all such discussions. Understood in its entirety, the law is that each plant or animal, if it reproduces, gives origin to others like itself: the likeness consisting, not so much in the repetition of individual traits as in the assumption of the same general structure. This truth has been rendered so familiar by daily illustration as almost to have los

32 minute read

Read Chapter

IX. Variation.

IX. Variation.

VARIATION. § 85 . Equally conspicuous with the truth that every organism bears a general likeness to its parents, is the truth that no organism is exactly like either parent. Though similar to both in generic and specific traits, and usually, too, in those traits which distinguish the variety, it diverges in numerous traits of minor importance. No two plants are indistinguishable; and no two animals are without differences. Variation is co-extensive with Heredity. The degrees of variation have a

26 minute read

Read Chapter

CHAPTER II. DIFFERENTIATIONS BETWEEN THE OUTER AND INNER TISSUES OF PLANTS.

CHAPTER II. DIFFERENTIATIONS BETWEEN THE OUTER AND INNER TISSUES OF PLANTS.

§ 268. The simplest plant presents a contrast between its peripheral substance and its central substance. In each protophyte, be it a spherical cell or a branched tube, or such a more-specialized form as a Desmid, a marked unlikeness exists between the limiting layer and that which it limits. These vegetal aggregates of the first order may differ widely from one another in the natures of their outer coats and in the natures of their contents. As in the Palmella-form of one of the lower Algæ , th

9 minute read

Read Chapter

X. Genesis, Heredity, and Variation.

X. Genesis, Heredity, and Variation.

GENESIS, HEREDITY, AND VARIATION. § 92 . A question raised, and hypothetically answered, in §§ 78 and 79 , was there postponed until we had dealt with the topics of Heredity and Variation. Let us now resume the consideration of this question, in connexion with sundry others which the facts suggest. After contemplating the several methods by which the multiplication of organisms is carried on—after ranging them under the two heads of Homogenesis, in which the successive generations are similarly

31 minute read

Read Chapter

CHAPTER III. DIFFERENTIATIONS AMONG THE OUTER TISSUES OF PLANTS.

CHAPTER III. DIFFERENTIATIONS AMONG THE OUTER TISSUES OF PLANTS.

§ 272. The motionless protococcoid forms of lower Algæ , which do not permanently expose any parts of their surfaces to actions unlike those which other parts are exposed to, have no parts of their surfaces unlike the rest in function and composition. This is what the hypothesis prepares us for. If physiological differentiations are determined by differences in the incidence of forces, then there will be no such differentiations where there are no such differences. Contrariwise, it is to be expe

28 minute read

Read Chapter

Xa. Genesis, Heredity, and Variation (concluded)

Xa. Genesis, Heredity, and Variation (concluded)

GENESIS, HEREDITY, AND VARIATION CONCLUDED . § 97 a . Since the foregoing four chapters were written, thirty-four years ago, the topics with which they deal have been widely discussed and many views propounded. Ancient hypotheses have been abandoned, and other hypotheses, referring tacitly or avowedly to the cell-doctrine, have been set forth. Before proceeding it will be well to describe the chief among these. Most if not all of them proceed on the assumption, shown in § 66 to be needful, that

31 minute read

Read Chapter

CHAPTER IV. DIFFERENTIATIONS AMONG THE INNER TISSUES OF PLANTS.[49]

CHAPTER IV. DIFFERENTIATIONS AMONG THE INNER TISSUES OF PLANTS.[49]

§ 277. In passing from plants formed of threads or thin laminæ, to plants having some massiveness, we find that after the external and internal parts have become distinguished from one another, there arise distinctions among the internal parts themselves, as well as among the external parts themselves: the primarily-differentiated parts are both re-differentiated. From types of very low organisation illustrations of this may be drawn. In the thinner kinds of Laminaria there exists but the single

29 minute read

Read Chapter

XI. Classification.

XI. Classification.

CLASSIFICATION. § 98 . That orderly arrangement of objects called Classification has two purposes, which, though not absolutely distinct, are distinct in great part. It may be employed to facilitate identification, or it may be employed to organize our knowledge. If a librarian places his books in the alphabetical succession of the author's names, he places them in such way that any particular book may easily be found, but not in such way that books of a given nature stand together. When, otherw

28 minute read

Read Chapter

CHAPTER V. PHYSIOLOGICAL INTEGRATION IN PLANTS.

CHAPTER V. PHYSIOLOGICAL INTEGRATION IN PLANTS.

§ 283. A good deal has been implied on this topic in the preceding chapters. Here, however, we must for a brief space turn our attention immediately to it. Plants do not display integration in such distinct and multiplied ways as do animals. But its advance may be traced both directly and indirectly—directly in the increasing co-ordination of actions, and indirectly in the effect of this upon the powers and habits. Let us group the facts under these heads: ascending in both cases from the lower

10 minute read

Read Chapter

XII. Distribution.

XII. Distribution.

DISTRIBUTION. § 104 . There is a distribution of organisms in Space, and there is a distribution of organisms in Time. Looking first at their distribution in Space, we observe in it two different classes of facts. On the one hand, the plants and animals of each species have their habitats limited by external conditions: they are necessarily restricted to spaces in which their vital actions can be performed. On the other hand, the existence of certain conditions does not determine the presence of

30 minute read

Read Chapter

CHAPTER VI. DIFFERENTIATIONS BETWEEN THE OUTER AND INNER TISSUES OF ANIMALS.

CHAPTER VI. DIFFERENTIATIONS BETWEEN THE OUTER AND INNER TISSUES OF ANIMALS.

§ 287. What was said respecting the primary physiological differentiation in plants, applies with little beyond change of terms to animals. Among Protozoa , as among Protophyta , the first definite contrast of parts is that between outside and inside. The speck of jelly or sarcode which appears to constitute the simplest animal, proves, on closer examination, to be a mass of substance containing a nucleus—a periplast in the midst of which there is a minute endoplast, consisting of a spherical me

13 minute read

Read Chapter

I. Preliminary.

I. Preliminary.

PRELIMINARY. § 109 . In the foregoing Part, we have contemplated the most important of the generalizations to which biologists have been led by observation of organisms; as well as some others which contemplation of the facts has suggested to me. These Inductions of Biology have also been severally glanced at on their deductive sides; for the purpose of noting the harmony existing between them and those primordial truths set forth in First Principles . Having thus studied the leading phenomena o

1 minute read

Read Chapter

CHAPTER VII. DIFFERENTIATIONS AMONG THE OUTER TISSUES OF ANIMALS.

CHAPTER VII. DIFFERENTIATIONS AMONG THE OUTER TISSUES OF ANIMALS.

§ 291. The outer tissues of animals, originally homogeneous over their whole surfaces, pass into a heterogeneity which fits their respective parts to their respective conditions. So numerous and varied are the implied differentiations, that it is impracticable here to deal with them all even in outline. To trace them up through classes of animals of increasing degrees of aggregation, would carry us into undue detail. Did space permit, it would be possible to point out among the Protozoa , variou

21 minute read

Read Chapter

CHAPTER VIII. DIFFERENTIATIONS AMONG THE INNER TISSUES OF ANIMALS.

CHAPTER VIII. DIFFERENTIATIONS AMONG THE INNER TISSUES OF ANIMALS.

§ 297. The change from the outside of the lips to their inside, introduces us to a new series of interesting and instructive facts, joining on to those with which the last chapter closed. They concern the differentiations of those coats of the alimentary canal which, as we have seen, are physiologically outer, though physically inner. These coats are greatly modified at different parts; and their modifications vary greatly in different animals. In the lower types, where they compose a simple tub

48 minute read

Read Chapter

II. General Aspects of the Special-Creation-Hypothesis.

II. General Aspects of the Special-Creation-Hypothesis.

GENERAL ASPECTS OF THE SPECIAL-CREATION-HYPOTHESIS. [45] § 110 . Early ideas are not usually true ideas. Undeveloped intellect, be it that of an individual or that of the race, forms conclusions which require to be revised and re-revised, before they reach a tolerable correspondence with realities. Were it otherwise there would be no discovery, no increase of intelligence. What we call the progress of knowledge, is the bringing of Thoughts into harmony with Things; and it implies that the first

24 minute read

Read Chapter

III. General Aspects of the Evolution-Hypothesis.

III. General Aspects of the Evolution-Hypothesis.

GENERAL ASPECTS OF THE EVOLUTION-HYPOTHESIS. § 116 . Just as the supposition that races of organisms have been specially created, is discredited by its origin; so, conversely, the supposition that races of organisms have been evolved, is credited by its origin. Instead of being a conception suggested and accepted when mankind were profoundly ignorant, it is a conception born in times of comparative enlightenment. Moreover, the belief that plants and animals have arisen in pursuance of uniform la

16 minute read

Read Chapter

CHAPTER IX. PHYSIOLOGICAL INTEGRATION IN ANIMALS.

CHAPTER IX. PHYSIOLOGICAL INTEGRATION IN ANIMALS.

§ 305. Physiological differentiation and physiological integration, are correlatives that vary together. We have but to recollect the familiar parallel between the division of labour in a society and the physiological division of labour, to see that as fast as the kinds of work performed by the component parts of an organism become more numerous, and as fast as each part becomes more restricted to its own work, so fast must the parts have their actions combined in such ways that no one can go on

15 minute read

Read Chapter

CHAPTER X. SUMMARY OF PHYSIOLOGICAL DEVELOPMENT.

CHAPTER X. SUMMARY OF PHYSIOLOGICAL DEVELOPMENT.

§ 310. Intercourse between each part and the particular conditions to which it is exposed, either habitually in the individual or occasionally in the race, thus appears to be the origin of physiological development; as we found it to be the origin of morphological development. The unlikenesses of form that arise among members of an aggregate that were originally alike, we traced to unlikenesses in the incident forces. And in the foregoing chapters we have traced to unlikenesses in the incident f

16 minute read

Read Chapter

IV. The Arguments from Classification.

IV. The Arguments from Classification.

THE ARGUMENTS FROM CLASSIFICATION. § 122 . In § 103 , we saw that the relations which exist among the species, genera, orders, and classes of organisms, are not interpretable as results of any such causes as have usually been assigned. We will here consider whether they are interpretable as the results of evolution. Let us first contemplate some familiar facts. The Norwegians, Swedes, Danes, Germans, Dutch, and Anglo-Saxons, form together a group of Scandinavian races, which are but slightly div

13 minute read

Read Chapter

CHAPTER XA. THE INTEGRATION OF THE ORGANIC WORLD.

CHAPTER XA. THE INTEGRATION OF THE ORGANIC WORLD.

§ 314 a . That from the beginning of life there has been an ever-increasing heterogeneity in the Earth’s Flora and Fauna, is a truth recognized by all biologists who accept the doctrine of evolution. In discussing the origin of species Mr. Darwin and others have been mainly occupied in explaining the genesis of now this and now that form of organism, considered as a member of one or other series, and regarded as becoming differentiated from its allies. But by implication, if not avowedly, there

19 minute read

Read Chapter

V. The Arguments from Embryology.

V. The Arguments from Embryology.

THE ARGUMENTS FROM EMBRYOLOGY. § 127 a . Already I have emphasized the truth that Nature is always more complex than we suppose ( § 74 a )—that there are complexities within complexities. Here we find illustrated this truth under another aspect. When seeking to formulate the arguments from Embryology, we are shown that the facts as presented in Nature are not to be expressed in the simple generalizations we at first make. While we recognize this truth we must also recognize the truth that only b

30 minute read

Read Chapter

VI. The Arguments from Morphology.

VI. The Arguments from Morphology.

THE ARGUMENTS FROM MORPHOLOGY. § 133 . Leaving out of consideration those parallelisms among their modes of development which characterize organisms belonging to each group, that community of plan which exists among them when mature is extremely remarkable and extremely suggestive. As before shown ( § 103 ), neither the supposition that these combinations of attributes which unite classes are fortuitous, nor the supposition that no other combinations were practicable, nor the supposition of adhe

12 minute read

Read Chapter

CHAPTER I. THE FACTORS.[52]

CHAPTER I. THE FACTORS.[52]

§ 315. If organisms have been evolved, their respective powers of multiplication must have been determined by natural causes. Grant that the countless specialities of structure and function in plants and animals, have arisen from the actions and reactions between them and their environments, continued from generation to generation; and it follows that from these actions and reactions have also arisen those countless degrees of fertility which we see among them. As in all other respects an adapta

7 minute read

Read Chapter

VII. The Arguments from Distribution.

VII. The Arguments from Distribution.

THE ARGUMENTS FROM DISTRIBUTION. § 137 . In §§ 105 and 106 , we contemplated the phenomena of distribution in Space. The general conclusions reached, in great part based on the evidence brought together by Mr. Darwin, were that, "on the one hand, we have similarly-conditioned, and sometimes nearly-adjacent, areas, occupied by quite different Faunas. On the other hand, we have areas remote from each other in latitude, and contrasted in soil as well as climate, which are occupied by closely-allied

24 minute read

Read Chapter

CHAPTER II. À PRIORI PRINCIPLE.

CHAPTER II. À PRIORI PRINCIPLE.

§ 319. The number of a species must at any time be either decreasing or stationary or increasing. If, generation after generation, its members die faster than others are born, the species must dwindle and finally disappear. If its rate of multiplication is equal to its rate of mortality, there can be no numerical change in it. And if the deductions by death are fewer than the additions by birth, the species must become more abundant. These we may safely set down as necessities. The forces destru

9 minute read

Read Chapter

VIII. How is Organic Evolution Caused?

VIII. How is Organic Evolution Caused?

HOW IS ORGANIC EVOLUTION CAUSED? § 143 . Already it has been necessary to speak of the causes of organic evolution in general terms; and now we are prepared for considering them specifically. The task before us is to affiliate the leading facts of organic evolution, on those same first principles conformed to by evolution at large. Before attempting this, however, it will be instructive to glance at the causes of organic evolution which have been from time to time alleged. § 144 . The theory tha

13 minute read

Read Chapter

CHAPTER III. OBVERSE À PRIORI PRINCIPLE.

CHAPTER III. OBVERSE À PRIORI PRINCIPLE.

Conversely, the continued aggregation of materials into one organism, renders impossible the formation of other organisms out of those materials. As much assimilated food as is united into a single whole, is so much assimilated food withheld from a plurality of wholes which might else have been produced. Given the absorbed nutriment as a constant quantity, and the longer the building of it up into a concrete shape goes on, the longer must be postponed any building of it up into discrete shapes.

10 minute read

Read Chapter

CHAPTER IV. DIFFICULTIES OF INDUCTIVE VERIFICATION.

CHAPTER IV. DIFFICULTIES OF INDUCTIVE VERIFICATION.

§ 329. Were all species subject to the same kinds and amounts of destructive forces, it would be easy, by comparing different species, to test the inverse variation of Individuation and Genesis. Or if either the power of self-preservation or the power of multiplication were constant, there would be little difficulty in seeing how the other changed as the destroying forces changed. But comparisons are nearly always partially vitiated by some want of parity. Each factor, besides being variable as

9 minute read

Read Chapter

IX. External Factors.

IX. External Factors.

EXTERNAL FACTORS. § 148 . When illustrating the rhythm of motion ( First Principles , § 83) it was pointed out that besides the daily and annual alternations in the quantities of light and heat which any portion of the Earth's surface receives from the Sun, there are alternations which require immensely-greater periods to complete. Reference was made to the fact that "every planet, during a certain long period, presents more of its northern than of its southern hemisphere to the Sun at the time

13 minute read

Read Chapter

CHAPTER V. ANTAGONISM BETWEEN GROWTH AND ASEXUAL GENESIS.

CHAPTER V. ANTAGONISM BETWEEN GROWTH AND ASEXUAL GENESIS.

§ 334. When illustrating, in Part IV, the morphological composition of plants and animals, there were set down in groups, numerous facts which we have here to look at from another point of view. Then we saw how, by union of small simple aggregates, there are produced large compound aggregates. Now we have to observe the reactive effect of this process on the relative numbers of the aggregates. Our present subject is the antagonism of Individuation and Genesis as seen under its simplest form, in

11 minute read

Read Chapter

X. Internal Factors.

X. Internal Factors.

INTERNAL FACTORS. § 153 . We saw at the outset ( §§ 10 - 16 ), that organic matter is built up of molecules so unstable, that the slightest variation in their conditions destroys their equilibrium, and causes them either to assume altered structures or to decompose. But a substance which is beyond all others changeable by the actions and reactions of the forces liberated from instant to instant within its own mass, must be a substance which is beyond all others changeable by the forces acting on

17 minute read

Read Chapter

CHAPTER VI. ANTAGONISM BETWEEN GROWTH AND SEXUAL GENESIS.

CHAPTER VI. ANTAGONISM BETWEEN GROWTH AND SEXUAL GENESIS.

§ 338. In so far as it is a process of separation, sexual genesis is like asexual genesis; and is therefore, equally with asexual genesis, opposed to that aggregation which results in growth. Whether deduction is made from one parent or from two, whether it is made from any part of the body indifferently or from a specialized part, or whether it is made directly or indirectly, it remains in any case a deduction; and in proportion as it is great, or frequent, or both, it must restrain the increas

16 minute read

Read Chapter

XI. Direct Equilibration.

XI. Direct Equilibration.

DIRECT EQUILIBRATION. § 159 . Every change is towards a balance of forces; and of necessity can never cease until a balance of forces is reached. When treating of equilibration under its general aspects ( First Principles , Part II., Chap. xxii.), we saw that every aggregate having compound movements tends continually towards a moving equilibrium; since any unequilibrated force to which such an aggregate is subject, if not of a kind to overthrow it altogether, must continue modifying its state u

17 minute read

Read Chapter

CHAPTER VII. THE ANTAGONISM BETWEEN DEVELOPMENT AND GENESIS, ASEXUAL AND SEXUAL.

CHAPTER VII. THE ANTAGONISM BETWEEN DEVELOPMENT AND GENESIS, ASEXUAL AND SEXUAL.

Besides the direct opposition between that continual disintegration which rapid genesis implies, and the fulfilment of that pre-requisite to extensive organization—the formation of an extensive aggregate, there is an indirect opposition which we may recognize under several aspects. The change from homogeneity to heterogeneity takes time; and time taken in transforming a relatively-structureless mass into a developed individual, delays the period of reproduction. Usually this time is merged in th

6 minute read

Read Chapter

XII. Indirect Equilibration.

XII. Indirect Equilibration.

INDIRECT EQUILIBRATION. § 164 . Besides those perturbations produced in any organism by special disturbing forces, there are ever going on many others—the reverberating effects of disturbing forces previously experienced by the individual, or by ancestors; and the multiplied deviations of function so caused imply multiplied deviations of structure. In § 155 there was re-illustrated the truth, set forth at length when treating of Adaptation ( § 69 ), that an organism in a state of moving equilibr

33 minute read

Read Chapter

XIII. The Co-operation of the Factors.

XIII. The Co-operation of the Factors.

THE CO-OPERATION OF THE FACTORS. § 169 . Thus the phenomena of Organic Evolution may be interpreted in the same way as the phenomena of all other Evolution. Fully to see this, it will be needful for us to contemplate in their ensemble , the several processes separately described in the four preceding chapters. If the forces acting on any aggregate remain the same, the changes produced by them will presently reach a limit, at which the outer forces are balanced by the inner forces; and thereafter

5 minute read

Read Chapter

CHAPTER VIII. ANTAGONISM BETWEEN EXPENDITURE AND GENESIS.

CHAPTER VIII. ANTAGONISM BETWEEN EXPENDITURE AND GENESIS.

§ 347. Under this head we have to set down no evidence derived from the vegetal kingdom. Plants are not expenders of force in such degrees as to affect the general relations with which we are dealing. They have not to maintain a heat above that of their environment, nor have they to generate motion; and hence consumption for these two purposes does not diminish the stock of material which serves on the one hand for growth and on the other hand for propagation. It will be well, too, if we pass ov

12 minute read

Read Chapter

XIV. The Convergence of the Evidences.

XIV. The Convergence of the Evidences.

THE CONVERGENCE OF THE EVIDENCES. § 171 . Of the three classes of evidences that have been assigned in proof of Evolution, the à priori , which we took first, were partly negative, partly positive. On considering the "General Aspects of the Special-creation hypothesis," we discovered it to be worthless. Discredited by its origin, and wholly without any basis of observed fact, we found that it was not even a thinkable hypothesis; and, while thus intellectually illusive, it turned out to have mora

6 minute read

Read Chapter

CHAPTER IX. COINCIDENCE BETWEEN HIGH NUTRITION AND GENESIS.

CHAPTER IX. COINCIDENCE BETWEEN HIGH NUTRITION AND GENESIS.

§ 352. Under this head may be grouped various facts which, in another way, tell the same tale as those contained in the last chapter. The evidence there put together went to show that increased cost of self-maintenance entailed decreased power of propagation. The evidence to be set down here, will go to show that power of propagation is augmented by making self-maintenance unusually easy. For into this may be translated the effect of abundant food. To put the proposition more specifically—we hav

12 minute read

Read Chapter

CHAPTER X. SPECIALITIES OF THESE RELATIONS.

CHAPTER X. SPECIALITIES OF THESE RELATIONS.

§ 356. Tests of the general doctrines set forth in preceding chapters, are afforded by organisms having modes of life which diverge widely from ordinary modes. Here, as elsewhere, aberrant cases yield crucial proofs. If certain organisms are so circumstanced that highly-nutritive matter is supplied to them without stint, and they have nothing to do but absorb it, we may infer that their powers of propagation will be enormous. If there are classes of creatures which expend very little for self-su

15 minute read

Read Chapter

XIVa. Recent Criticisms and Hypotheses.

XIVa. Recent Criticisms and Hypotheses.

RECENT CRITICISMS AND HYPOTHESES. § 174 a . Since the first edition of this work was published, and more especially since the death of Mr. Darwin, an active discussion of the Evolution hypothesis has led to some significant results. That organic evolution has been going on from the dawn of life down to the present time, is now a belief almost universally accepted by zoologists and botanists—"almost universally," I say, because the surviving influence of Cuvier prevents acceptance of it by some o

26 minute read

Read Chapter

CHAPTER XI. INTERPRETATION AND QUALIFICATION.

CHAPTER XI. INTERPRETATION AND QUALIFICATION.

§ 362. Considering the difficulties of inductive verification, we have, I think, as clear a correspondence between the à priori and à posteriori conclusions, as can be expected. The many factors co-operating to bring about the result in every case, are so variable in their absolute and relative amounts, that we can rarely disentangle the effect of each one, and have usually to be content with qualified inferences. Though in the mass organisms show us an unmistakable relation between great size a

12 minute read

Read Chapter

A. The General Law of Animal Fertility.

A. The General Law of Animal Fertility.

THE GENERAL LAW OF ANIMAL FERTILITY. [ In the Westminster Review for April, 1852, I published an essay under the title "A Theory of Population deduced from the General Law of Animal Fertility." That essay was the germ of Part VI of this work, "The Laws of Multiplication," in which its essential theses are fully developed. When developing them, I omitted some portions of the original essay—one which was not directly relevant, and another which contained a speculation open to criticism. As indicat

55 minute read

Read Chapter

B. The Inadequacy of Natural Selection, etc., etc.

B. The Inadequacy of Natural Selection, etc., etc.

THE INADEQUACY OF NATURAL SELECTION, ETC., ETC. [ In this Appendix are included four essays originally published in the Contemporary Review and subsequently republished as pamphlets. The first appeared under the above title in February and March, 1893; the second in May of that year under the title "Prof. Weismann's Theories;" the third in December of that year under the title "A Rejoinder to Prof. Weismann;" and the fourth in October, 1894, under the title "Weismannism Once More." As these succ

54 minute read

Read Chapter

CHAPTER XII. MULTIPLICATION OF THE HUMAN RACE.

CHAPTER XII. MULTIPLICATION OF THE HUMAN RACE.

§ 365. The relative fertility of Man considered as a species, and those changes in Man’s fertility which occur under changed conditions, must conform to the laws which we have traced thus far. As a matter of course, the inverse variation between Individuation and Genesis holds of him as of all other organized beings. His extremely low rate of multiplication—far below that of all terrestrial Mammals except the Elephant, (which though otherwise less evolved is, in extent of integration, more evolv

20 minute read

Read Chapter

CHAPTER XIII. HUMAN POPULATION IN THE FUTURE.

CHAPTER XIII. HUMAN POPULATION IN THE FUTURE.

§ 371. Any further evolution in the most highly-evolved of terrestrial beings, Man, must be of the same nature as evolution in general. Structurally considered, it may consist in greater integration, or greater differentiation, or both—augmented bulk, or increased heterogeneity and definiteness, or a combination of the two. Functionally considered, it may consist in a larger sum of actions, or more multiplied varieties of actions, or both—a larger amount of sensible and insensible motion generat

21 minute read

Read Chapter

C. The Inheritance of Functionally-Wrought Modifications: A Summary.

C. The Inheritance of Functionally-Wrought Modifications: A Summary.

THE INHERITANCE OF FUNCTIONALLY-WROUGHT MODIFICATIONS: A SUMMARY. The assertion that changes of structure caused by changes of function are transmitted to descendants is continually met by the question—Where is the evidence? When some facts are assigned in proof, they are pooh-poohed as insufficient. If after a time the question is raised afresh and other facts are named, there is a like supercilious treatment of them. Successively rejected in this way, the evidences do not accumulate in the min

8 minute read

Read Chapter

D. On Alleged Spontaneous Generation, and on the Hypothesis of Physiological Units.

D. On Alleged Spontaneous Generation, and on the Hypothesis of Physiological Units.

ON ALLEGED "SPONTANEOUS GENERATION," AND ON THE HYPOTHESIS OF PHYSIOLOGICAL UNITS. [ The following letter, originally written for publication in the North American Review, but declined by the Editor in pursuance of a general rule, and eventually otherwise published in the United States, I have thought well to append to this first volume of the Principles of Biology. I do this because the questions which it discusses are dealt with in this volume; and because the further explanations it furnishes

10 minute read

Read Chapter

APPENDIX A. SUBSTITUTION OF AXIAL FOR FOLIAR ORGANS IN PLANTS.

APPENDIX A. SUBSTITUTION OF AXIAL FOR FOLIAR ORGANS IN PLANTS.

I append here the evidences referred to in § 190 . The most numerous and striking I have met with among the Umbelliferæ . Monstrosities having the alleged implication, are frequent in the common Cow-Parsnep—so frequent that they must be familiar to botanists; and wild Angelica supplies many over-developments of like meaning. Omitting numerous cases of more or less significance, I will limit myself to two. Fig. 69. One of them is that of a terminal umbel, in which nine of the outer umbellules are

12 minute read

Read Chapter

APPENDIX B. A CRITICISM ON PROF. OWEN’S THEORY OF THE VERTEBRATE SKELETON.

APPENDIX B. A CRITICISM ON PROF. OWEN’S THEORY OF THE VERTEBRATE SKELETON.

[ From the British &amp; Foreign Medico-Chirurgical Review for Oct., 1858. ] I. On the Archetype and Homologies of the Vertebrate Skeleton. By Richard Owen , F.R.S. — London , 1848. pp. 172. II. Principes d’Ostéologie Comparée, ou Recherches sur l’Archétype et les Homologies du Squelette Vertébré. Par Richard Owen .— Paris. Principles of Comparative Osteology; or, Researches on the Archetype and the Homologies of the Vertebrate Skeleton. By Richard Owen . III. On the Nature of Limbs. A Disco

40 minute read

Read Chapter

APPENDIX C.

APPENDIX C.

[ From the Transactions of the Linnean Society, vol. xxv .] XV. On Circulation and the Formation of Wood in Plants. By Herbert Spencer , Esq. Communicated by George Busk , Esq., F.R.S., Sec. L.S. Read March 1st, 1866. Opinions respecting the functions of the vascular tissues in plants appear to make but little progress towards agreement. The supposition that these vessels and strings of partially-united cells, lined with spiral, annular, reticulated, or other frameworks, are carriers of the plan

59 minute read

Read Chapter

APPENDIX D. ON THE ORIGIN OF THE VERTEBRATE TYPE.

APPENDIX D. ON THE ORIGIN OF THE VERTEBRATE TYPE.

[ When studying the development of the vertebrate skeleton, there occurred to me the following idea respecting the possible origin of the notochord. I was eventually led to omit the few pages of Appendix in which I had expressed this idea, because it was unsupported by developmental evidence. The developmental evidence recently discovered, however, has led Professor Haeckel and others to analogous views respecting the affiliation of the Vertebrata on the Molluscoida. Having fortunately preserved

4 minute read

Read Chapter

APPENDIX D 2. THE ANNULOSE TYPE.

APPENDIX D 2. THE ANNULOSE TYPE.

The production of a segmental structure by undulatory movements, suggested in Appendix D, as also in B (first published in 1858) as explaining the vertebral column, has been recently suggested by Prof. Korschelt as the cause of that segmentation of the annulose type which gives the name to it. He espouses a— “view which is based upon the assumption that at first an unsegmented, elongated ancestral form was produced by terminal growth, whereupon the entire body became separated at once into a lar

10 minute read

Read Chapter

APPENDIX E. THE SHAPES AND ARRANGEMENTS OF FLOWERS.

APPENDIX E. THE SHAPES AND ARRANGEMENTS OF FLOWERS.

In Part IV., Chapter X., under the title of “The Shapes of Flowers,” I have, after describing their several kinds of symmetry, as habitually related to their positions, made some remarks by way of interpretation. The truth that flowers exhibit a radial symmetry when they are so placed as to be equally affected all round by incident forces, having been exemplified, and also the truth that they assume a bilateral symmetry when they are so placed that their two sides are conditioned in ways differe

6 minute read

Read Chapter

APPENDIX F. PHYSIOLOGICAL (OR CONSTITUTIONAL) UNITS.

APPENDIX F. PHYSIOLOGICAL (OR CONSTITUTIONAL) UNITS.

There has recently come before me a fact which has a significant bearing on the hypothesis of Constitutional units: serving, indeed, to give an apparently conclusive proof of its truth. Before stating it, however, I may with advantage re-state the several evidences already assigned in support of it. 1. First comes the à priori reason. These units in the germ of an organism which cause development into a special structure, cannot be chemical units—cannot be simply molecules of proteid substance i

9 minute read

Read Chapter

APPENDIX G. THE INHERITANCE OF FUNCTIONALLY-CAUSED MODIFICATIONS.

APPENDIX G. THE INHERITANCE OF FUNCTIONALLY-CAUSED MODIFICATIONS.

In Part II, Chapter X A , I have confessed that the process by which a structure changed by use or disuse affects the sperm-cells or germ-cells whence arise descendants, is unimaginable: without, however, inferring that therefore such a process does not exist. With others it seems different. Some three years ago the following expression of opinion came to me from a zoological expert:— “Many zoologists—most of us here at Cambridge—are intensely opposed to the doctrine of the inheritability of acq

10 minute read

Read Chapter