Chapter LIX: Appendix: G (4)

[41] It is but just to the memory of Wolff, here to point out that he was immensely in advance of Goethe in his rationale of these metamorphoses. Whatever greater elaboration Goethe gave to the theory considered as an induction, seems to me more than counter-balanced by the irrationality of his deductive interpretation; which unites mediæval physiology with Platonic philosophy. A dominant idea with him is that leaves exist for the purpose of carrying off crude juices--that “as long as there are crude juices to be carried off, the plant must be provided with organs competent to effect the task”; that while “the less pure fluids are got rid of, purer ones are introduced” and that “if nourishment is withheld, that operation of nature (flowering) is facilitated and hastened; the organs of the nodes (leaves) become more refined in texture, the action of the purified juices becomes stronger, and the transformation of parts having now become possible, takes place without delay.” This being the proximate explanation, the ultimate explanation is, that Nature wishes to form flowers--that when a plant flowers it “attains the end prescribed to it by nature”; and that so “Nature at length attains her object.” Instead of vitiating his induction by a teleology that is as unwarranted in its assigned object as in its assigned means, Wolff ascribes the phenomena to a cause which, whether sufficient or not, is strictly scientific in its character. Variation of nutrition is unquestionably a “true cause” of variation in plant-structure. We have here no imaginary action of a fictitious agency; but an ascertained action of a known agency.

[42] The _Natural History Review_ for July, 1865, contained an article on the doctrine of morphological composition set forth in the foregoing Chaps. I. to III. In this article, which unites exposition and criticism in a way that is unhappily not common with reviewers, it is suggested that the spiral structure may be caused by natural selection. When this article appeared, the foregoing five pages were standing over in type, as surplus from No. 14, issued in June, 1865.

[43] A verifying comment on this paragraph runs as follows:--“In the Hypotricha Infusoria, which creep over solid surfaces, there is a differentiation between ventral and dorsal surface and an approach to bilateral symmetry. The ventral surface is provided with movable cilia, the dorsal with immobile setæ.”

[44] Criticisms on the above passage have shown the need for naming sundry complications. These complications chiefly, if not wholly, arise from changes in modes of life--changes from the locomotive to the stationary, and from the stationary to the locomotive. Referring to my statement that (ignoring the spherical) the radial type is the lowest and must be taken as antecedent to the bilateral type, it is alleged that all existing “radial animals above Protozoa are probably derived from free-swimming, bilaterally-symmetrical animals.” If this is intended to include the planulæ of the hydroid polyps, then it seems rather a straining of the evidence. These locomotive embryos, described as severally having the structure of a gastrula with a closed mouth, can be said to show bilateralness only because the first two tentacles make their appearance on opposite sides of the mouth--a bilateralness which lasts only till two other tentacles make their appearance in a plane at right angles, so giving the radial structure. I think the criticism applies only to cases furnished by Echinoderms. The larvæ of these creatures have bilaterally-symmetrical structures, which they retain as long as they swim about and which such of them as fix themselves lose by becoming similarly related to conditions all round: the radial structure being retained by those types which, becoming subsequently detached, move about miscellaneously. But, as happens in some of the Sea-urchins and still more among the Holothurians, the structure is again made bilaterally-symmetrical by a locomotive life pursued with one end foremost. Should it be contended that the conditions and the forms are reciprocally influential--that either may initiate the other, it still remains unquestionable that ordinarily the conditions are the antecedents, as is so abundantly shown by plants.

[45] Should it be proved that the Ascidian is a degraded vertebrate, then the argument will be strengthened; since loss of bilateral symmetry has gone along with change to asymmetrical conditions.

[46] A critical comment made on this sentence runs as follows:--“The aërial roots of most epiphytic orchids contain chlorophyll in their cortex throughout their length, but the cortex being covered by a ‘velamen’ of air-containing cells which break up and reflect incident light, the green colour is not visible through this opaque coat. When moistened the cells of the velamen take up water and the green colour immediately shows through. Such roots do not however possess stomata. The roots of certain species of _Angræcum_, however, contain the whole of the assimilating tissue of the plant.”

[47] The current doctrine that chlorophyll is _the_ special substance concerned in vegetal assimilation, either as an agent or as an incidental product, must be taken with considerable qualification. Besides the fact that among the _Algæ_ there are many red and brown kinds which thrive; and besides the fact that among the lower Archegoniates there are species which are purple or chocolate-coloured; there is the fact that Phænogams are not all green. We have the Copper-Beech, we have the black-purple _Coleus Verschaffeltii_, and we have the red variety of Cabbage, which seems to flourish as well as the other varieties. Chlorophyll, then, must be regarded simply as the most general of the colouring matters found in those parts of plants in which assimilation is being effected by the agency of light. Though it is always present _along with_ the red and brown pigments, yet there is much evidence to show that these are the actual assimilative pigments.

[48] This seems as fit a place as any for noting the fact, that the greater part of what we call beauty in the organic world, is in some way dependent on the sexual relation. It is not only so with the colours and odours of flowers. It is so, too, with the brilliant plumage of birds; and it is probable that the colours of the more conspicuous insects are in part similarly determined. The remarkable circumstance is, that these characteristics, which have originated by furthering the production of the best offspring, while they are naturally those which render the organisms possessing them attractive to one another, directly or indirectly, should also be those which are so generally attractive to us--those without which the fields and woods would lose half their charm. It is interesting, too, to observe how the conception of human beauty is in a considerable degree thus originated. And the trite observation that the element of beauty which grows out of the sexual relation is so predominant in æsthetic products--in music, in the drama, in fiction, in poetry--gains a new meaning when we see how deep down in organic nature this connexion extends.

[49] Students of vegetal physiology, familiar with the controversies respecting sundry points dealt with in this chapter, will probably be surprised to find taken for granted in it, propositions which they have habitually regarded as open to doubt. Hence it seems needful to say that the conclusions here set forth, have resulted from investigations undertaken for the purpose of forming opinions on several unsettled questions which I had to treat, but which I could find in books no adequate data for treating. The details of these investigations, and the entire argument of which this chapter is partly an abstract, will be found in Appendix C.

[50] To this implied inference it is objected that “excess of nutritive material does not necessarily lead to correspondingly increased growth.” My reply is that a concomitant factor is activity of the tissue, and that in its absence growth is not to be expected.

[51] In recent years (since 1890) Prof. Wilhelm Roux, in essays on functional adaptation, has set forth some views akin to the foregoing in respect to the general belief they imply, though differing in respect of the physiological processes he indicates. The following relevant passage has been translated for me from an article of his in the _Real-Encyclopädie der gesammten Heilkunde_:--“A more complete theory of functional adaptation by the author is founded on the assumption that the ‘functional’ stimulus, or ‘the act of exercising the function’ (in muscles and glands), and especially, in the case of bones, the concussion and tension caused by stress and strain, exert a ‘trophic’ stimulus on the cells, in consequence of which, and along with an increased absorption of nutriment, they grow and eventually increase (or the osteoblasts at the point of greater stimulus form more bone); while, conversely, with continued inactivity, by absence of these stimuli the nourishment of the cell declines so that the waste is insufficiently replaced (or otherwise that the bone-substance gradually loses its power of resistance to the osteoblasts formed as a result of inactivity”).

[52] An outline of the doctrine set forth in the following chapters, was originally published in the _Westminster Review_ for April, 1852, under the title--_A Theory of Population deduced from the General Law of Animal Fertility_; and was shortly afterwards republished with a prefatory note stating that it must be accepted as a sketch which I hoped at some future time to elaborate. In now revising and completing it, I have omitted a non-essential part of the argument, while I have expanded the remainder by adding to the number of facts put in evidence, by meeting objections which want of space before obliged me to pass over, and by drawing various secondary conclusions. The original paper, with omissions, will be found in Appendix A to Volume I of this work.

[53] I was here thinking only of the cases which are general among insects, but it seems that vertebrate animals, too, furnish cases. Mr. Cunningham writes:--“There is a curious instance of this in the Conger: the female grows to 6 or 7 feet long and a weight of 60 lbs. and upwards and then ceases to feed for 6 months while the eggs develop, and when the eggs are shed dies.”

[54] I say “normal” for the purpose of excluding not only morbid growths but excess of fat.

[55] To meet a possible criticism it should be remarked that this calculation assumes that the power of asexual reproduction is not exhausted by the end of the month. It has been found that “the successive fissions of _Paramœcium_ cannot continue indefinitely. After some hundreds of generations the products of fission are small, have no mouth, and die unless before this they have been allowed to conjugate with individuals of another brood.” It may, however, be fairly taken for granted that “some hundreds of generations” would take longer than a month.

[56] Even this number is far exceeded. Dr. Edward Klein, in a lecture he gave at the Royal Institution on June 2, 1898, asserted that 246 bacteria in a cubic centimetre of nutritive liquid would multiply to 20,000,000 in the course of twenty-four hours: a rate which, at the end of the _third_ day, would give, as the offspring of one individual, 537,367,797,000,000.

[57] It has since been shown that in _Myrianida fasciata_ as many as 29 attached groups exist. See _Cambridge Natural History_, Vol. II, _Worms, Rotifers and Polyzoa_, p. 280.

[58] To this passage Prof. MacBride appends the remark:--“This is quite proven now, and the statement as it stands is quite correct; but far better and more minutely worked out cases are to be found amongst the _Infusoria_. In _Paramœcium_ for example, there are normally present a large macronucleus and a small micronucleus lying alongside of it. When two individuals adhere preparatory to conjugation, the macronucleus breaks up into fragments which are absorbed: the micronucleus--which has some time previously divided into two--begins to break up further and eventually forms eight bodies; all of these except one disappear; this last piece then divides into two; of these two one represents a male genital cell, for it passes over into the body of the other _Paramœcium_ and fuses with one of the two corresponding nuclei there; thus each of the two individuals which adhere fertilizes the other. The two individuals then separate and the nucleus (result of fusion of male and female nuclei) in each divides into four. Of these, two move to one end of the animal and two to the other. The animal then divides into two transversely--each of the products thus having two nuclei which form the micro-and macronucleus of it. Thus it appears that the function of sexual union is simply to give increased vigour to all the vital processes _including fission_. Since as mentioned above (p. 443) if it is prevented, the products of fission are eventually unable to feed themselves.”

[59] A passage translated for me from the German may be here given in verification. Dr. Dionys Hellin in an essay on the origin of Multiparity and Twin-births, refers to the thesis above set forth, and says that “the fact that it is generally women of small growth who bear twins is in complete agreement with it.” He adds that “Puech is right in his opinion that twin pregnancies are a direct result of relatively large ovaries (_i.e._, in comparison with the whole body). He has observed that for the same size of body the ovarium of a pluriparous animal is always of greater volume than that of a uniparous animal ... a sow has ovaries as large as a cow’s; but while the latter bears only one calf [at a time], the sow brings forth 6–15 at each litter. Even in animals of the same species but belonging to different races these relations may be verified,” _e.g._, Barbary sheep and ordinary sheep.

[60] When, after having held for some years the general doctrine elaborated in these chapters, I agreed, early in 1852, to prepare an outline of it for the _Westminster Review_, I consulted, among other works, the just-issued third edition of Dr. Carpenter’s _Principles of Physiology, General and Comparative_--seeking in it for facts illustrating the different degrees of fertility of different organisms, I met with a passage, quoted above in § 339, which seemed tacitly to assert that individual aggrandizement is at variance with the propagation of the race; but nowhere found a distinct enunciation of this truth. I did not then read the Chapter entitled “General View of the Functions,” which held out no promise of such evidence as I was looking for. But on since referring to this chapter, I discovered in it the definite statement that--“there is a certain degree of antagonism between the Nutritive and Reproductive functions, the one being executed at the expense of the other. The reproductive apparatus derives the materials of its operations through the nutritive system, and is entirely dependent upon it for the continuance of its function. If, therefore, it be in a state of excessive activity, it will necessarily draw off from the individual fabric some portion of the aliment destined for its maintenance. It may be universally observed that, when the nutritive functions are particularly active in supporting the _individual_, the reproductive system is in a corresponding degree undeveloped,--and _vice versâ_.” P. 592.

[61] The climate, the locality, and the kind of food, are of course all factors; and hence, probably, the differences between the statements of different authorities concerning these several cases. Prof. MacBride writes:--

“According to Flower (_Mammals, Living and Extinct_) the Ferret is a domesticated variety of the common polecat, which has 3 to 8 young. Darwin (_Animals and Plants_) says that the wild sow often breeds twice a year and produces a litter of 4 to 8, and sometimes even 12. The domestic sow breeds twice and would breed oftener if permitted, and if any good at all produces 8 in litter.”

[62] It is worth while inquiring whether unfitness of the food given to them, is not the chief cause of that sterility which, as Mr. Darwin says, “is the great bar to the domestication of animals.” He remarks that “when animals and plants are removed from their natural conditions, they are extremely liable to have their reproductive systems seriously affected.” Possibly the relative or absolute arrest of genesis, is less due to a direct effect on the reproductive system, than to a changed nutrition of which the reproductive system most clearly shows the results. The matters required for forming an embryo are in a greater proportion nitrogenous than are the matters required for maintaining an adult. Hence, an animal forced to live on insufficiently-nitrogenized food, may have its surplus for reproduction cut off, but still have a sufficiency to keep its own tissues in repair, and appear to be in good health--meanwhile increasing in bulk from excess of the non-nitrogenous matters it eats.

[63] Huxley, _Anatomy of Invertebrated Animals_, p. 274.

[64] Shipley, _Zoology of Invertebrata_, p. 112.

[65] I am told that “Wagner, who described the larva, found that it bored into the bark of trees. It attacks also the wheat plant, and is a most destructive parasite.” Apparently this statement is at variance with the foregoing inference. It is clear, however, that since these heaps of nitrogenous refuse in which it has been found are artificial and recent, they cannot be its natural habitats; and it seems not improbable that these larvæ, suddenly supplied with a more nutritive food in unlimited amount, may have as a consequence acquired this habit of agamogenetic multiplication which did not characterize the species under its natural conditions and relatively low nutrition.

[66] This is exactly the reverse of Mr. Doubleday’s doctrine; which is that throughout both the animal and vegetable kingdoms, “over-feeding checks increase; whilst, on the other hand, a limited or deficient nutriment stimulates and adds to it.” Or, as he elsewhere says--“Be the range of the natural power to increase in any species what it may, the _plethoric_ state invariably checks it, and the _deplethoric_ state invariably develops it; and this happens in the exact ratio of the intensity and completeness of each state, until each state be carried so far as to bring about the actual death of the animal or plant itself.”

I have space here only to indicate the misinterpretations on which Mr. Doubleday has based his argument.

In the first place, he has confounded normal plethora with what I have, in § 355, distinguished as abnormal plethora. The cases of infertility accompanying fatness, which he cites in proof that over-feeding checks increase, are not cases of high nutrition properly so-called; but cases of such defective absorption or assimilation as constitutes low nutrition. In Chap. IX, abundant proof was given that a truly plethoric state is an unusually fertile state. It may be added that much of the evidence by which Mr. Doubleday seeks to show that among men, highly-fed classes are infertile classes, may be out-balanced by counter-evidence. Many years ago Mr. G. H. Lewes pointed this out: extracting from a book on the peerage, the names of 16 peers who had, at that time, 186 children; giving an average of 11·6 in a family.

Mr. Doubleday insists much on the support given to his theory by the barrenness of very luxuriant plants, and the fruitfulness produced in plants by depletion. Had he been aware that the change from barrenness to fruitfulness in plants, is a change from agamogenesis to gamogenesis--had it been as well known at the time when he wrote as it is now, that a tree which goes on putting out sexless shoots, is thus producing new individuals; and that when it begins to bear fruit, it simply begins to produce new individuals after another manner--he would have perceived that facts of this class do not tell in his favour.

In the law which Mr. Doubleday alleges, he sees a guarantee for the maintenance of species. He argues that the plethoric state of the individuals constituting any race of organisms, presupposes conditions so favourable to life that the race can be in no danger; and that rapidity of multiplication becomes needless. Conversely, he argues that a deplethoric state implies unfavourable conditions--implies, consequently, unusual mortality; that is--implies a necessity for increased fertility to prevent the race from dying out. It may be readily shown, however, that such an arrangement would be the reverse of self-adjusting. Suppose a species, too numerous for its food, to be in the resulting deplethoric state. It will, according to Mr. Doubleday, become unusually fertile; and the next generation will be more numerous rather than less numerous. For, by the hypothesis, the unusual fertility due to the deplethoric state, is the cause of undue increase of population. But if the next generation is more numerous while the supply of food has not increased in proportion, then this next generation will be in a still more deplethoric state, and will be still more fertile. Thus there will go on an ever-increasing rate of multiplication, and an ever-decreasing share of food, for each person, until the species disappears. Suppose, on the other hand, the members of a species to be in an unusually plethoric state. Their rate of multiplication, ordinarily sufficient to maintain their numbers, will become insufficient to maintain their numbers. In the next generation, therefore, there will be fewer to eat the already abundant food, which becoming relatively still more abundant, will render the fewer members of the species still more plethoric, and still less fertile, than their parents. And the actions and reactions continuing, the species will presently die out from absolute barrenness.

[67] A good deal of this chapter retains its original form; and the above paragraph is reprinted verbatim from the _Westminster Review_ for April, 1852, in which the views developed in the foregoing hundred pages were first sketched out. This paragraph shows how near one may be to a great generalization without seeing it. Though the struggle for life is the alleged motive force; though the process of natural selection is recognized; and though to it is ascribed a share in the evolution of a higher type; yet the conception is not that which Mr. Darwin has worked out with such wonderful skill and knowledge. In the first place, natural selection is here described only as furthering direct adaptation--only as aiding progress by the preservation of individuals in whom functionally-produced modifications have gone on most favourably. In the second place, there is no trace of the idea that natural selection may by co-operation with the cause assigned, or with other causes, produce _divergences_ of structure; and of course, in the absence of this idea, there is no implication that natural selection has anything to do with the origin of species. And in the third place, the all-important factor of variation--“spontaneous,” or incidental as we may otherwise call it--is wholly ignored. Though use and disuse are, I think, much more potent causes of organic modification than Mr. Darwin supposes--though, while pursuing the inquiry in detail, I have been led to believe that direct equilibration has played a more active part even than I had myself at one time thought; yet I hold Mr. Darwin to have shown beyond question, that a great part of the facts--perhaps the greater part--are explicable only as resulting from the survival of individuals which have deviated in some indirectly-caused way from the ancestral type. Thus, the above paragraph contains merely a passing recognition of the selective process; and indicates no suspicion of the enormous range of its effects, or of the conditions under which a large part of its effects are produced.

[68] For the information of those who may wish to examine metamorphoses of these kinds, I may here state that I have found nearly all the examples described, in the neighbourhood of the sea--the last-named, on the shore of Locheil, near Fort William. Whether it is that I have sought more diligently for cases when in such localities, or whether it is that the sea-air favours that excessive nutrition whence these transformations result, I am unable to say.

[69] These two dyes have affinities for different components of the tissues, and may be advantageously used in different cases. Magenta is rapidly taken up by woody matter and other secondary deposits; while logwood colours the cell-membranes, and takes but reluctantly to the substances seized by magenta. By trying both of them on the same structure, we may guard ourselves against any error arising from selective combination.

[70] Those who repeat these experiments must be prepared for great irregularities in the rates of absorption. Succulent structures in general absorb much more slowly than others, and sometimes will scarcely take up the dye at all. The differences between different structures, and the same structure at different times, probably depend on the degrees in which the tissues are charged with liquid and the rates at which they are losing it by evaporation.

[71] It may be added here that, on considering the mechanical actions that must go on, we are enabled in some measure to understand both how such inosculating channels are initiated, and how the structures of their component cells are explicable. What must happen to one of these elongated prosenchyma-cells if, in the course of its development, it is subject to intermittent compressions? Its squeezed-out liquid while partially escaping laterally, will more largely escape upwards and downwards; and while repeated lateral escape will tend to form lateral channels communicating with laterally-adjacent cells, repeated longitudinal escape will tend to form channels communicating with longitudinally-adjacent cells--so producing continuous though irregular longitudinal canals. Meanwhile each cell into and out of which the nutritive liquid is from time to time squeezed through small openings in its walls, cannot thicken internally in an even manner: deposition will be interfered with by the passage of the currents through the pores. The rush to or from each pore will tend to maintain a funnel-shaped depression in the deposit around; and the opening from cell to cell will so acquire just that shape which the microscope shows up--two hollow cones with their apices meeting at the point where the cell-membranes are in contact. Moreover, as confirming this interpretation, it may be remarked that we are thus supplied with a reason for the differences of shape between these passages from one pitted cell to another, and the analogous passages that exist between cells otherwise formed and otherwise conditioned. In the cells of the medulla, and others which are but little exposed to compression, the passages are severally formed more like a tube with two trumpet-mouths, one in each cell. This is just the form which might be expected where the nutritive fluid passes from cell to cell in moderate currents, and not by the violent rushes caused by intermittent pressures. Of course it is not meant that in each individual cell these structures are determined by these mechanical actions. The facts clearly negative any such conclusion, showing us, as they in many cases do, that these structures are assumed in advance of these mechanical actions. The implication is, that such mechanical actions initiated modifications that have, with the aid of natural selection, been accumulated from generation to generation; until, in conformity with ordinary embryological laws, the cells of the parts exposed to such actions assume these special structures irrespective of the actions--the actions, however, still serving to aid and complete the assumption of the inherited type.

[72] Some exceptions to this occur in plants that have retrograded in the character of their tissues towards the simpler vegetal types. Certain very succulent leaves, such as those of _Sempervivum_, in which the cellular tissue is immensely developed in comparison with the vascular tissue, seem to have resumed to a considerable extent what we must regard as the primitive form of vegetal circulation--simple absorption from cell to cell. These, when they have lost much of their water, will take up the dye to some distance through their general substance, or rather through its interstices, even neglecting the vessels. At other times, in the same leaves, the vessels will become charged while comparatively little absorption takes place through the cellular tissue. Even in these exceptional cases, however, the movement through cellular tissue is nothing like as fast as the movement through vessels.

[73] It seems probable, however, that osmotic distention is here, especially, the more important of the two factors. The rising of the sap in spring may indirectly result, like the sprouting of the seed, from the transformation of starch into sugar. During germination, this change of an oxy-hydro-carbon from an insoluble into a soluble form, leads to rapid endosmose; consequently to great distention of the seed; and therefore to a force which thrusts the contained liquids into the plumule and radicle, and gives them power to displace the soil in their way: it sets up an active internal movement when neither evaporation nor the change which light produces can be operative. And similarly, if, in the spring, the starch stored-up in the roots of a tree passes into the form of sugar, the unusual osmotic absorption that arises will cause an unusual distention--a distention which, being resisted by the tough bark of the roots and stem, will result in a powerful upward thrust of the contained liquid.

Transcriber’s Note:

1. Obvious printers’, spelling and punctuation errors have been silently corrected.

2. Where appropriate, original spelling has been retained.

3. Both hyphenated and non-hyphenated versions of the same words have been retained where deemed appropriate.

4. Superscripts are represented using the caret character, e.g. D^r.

5. Italics are shown as _xxx_, bold print is shown as =xxx=.