[A]An interesting problem concerning the atmosphere is suggested by certain geological facts. In our buried coal-seams and other carbonaceous deposits a great quantity of carbon, for the most part abstracted from the atmosphere, has been stored away. Still greater quantities of carbon are imprisoned in the substance of our limestones, which contain, when pure, 44 per cent. of this element. A large quantity of oxygen has also been taken from the atmosphere to combine with other elements during their oxidation. The question is—Was the atmosphere, in the geological past, more richly laden with carbonic acid gas, of which some has entered into combination with lime to form limestone, while some has been decomposed by plants, the carbon being buried as coal, and the oxygen as products of oxidation? Or, has the atmosphere been furnished with continuous fresh supplies of carbonic acid gas?
[B]It has before been noticed that the organs themselves have their periods of rest. The rhythm of rest and repose in the heart is not that of the activity and sleep of the organism, but that of the contraction and relaxation of the organ itself.
[C]From a popular article of the author's on "Horns and Antlers," in Atalanta.
[D]It will be well here to introduce the technical terms for these changes. The general term for chemical actions occurring in the tissues of a living creature is metabolism; where the change is of such a nature that complex and unstable compounds are built up and stored for a while, it is called anabolism; where complex unstable compounds break up into less complex and relatively stable compounds, the term katabolism is applied. We shall speak of anabolic changes as constructive; katabolic, as disruptive, or sometimes, explosive.
[E]I do not mean, of course, to imply that there is no reconstruction during activity, but that it is then distinctly outbalanced by disruptive changes.
[F]Professor Geddes and Mr. J. Arthur Thomson, in their interesting work on "The Evolution of Sex," regard the ovum in especial, and the female in general, as preponderatingly anabolic (see note, p. 32); while the sperm in especial, and the male in general, are on their view preponderatingly katabolic. Regarding, as I do, the food-yolk as a katabolic product, I cannot altogether follow them. The differentiation seems to me to have taken place along divergent lines of katabolism. In the ovum, katabolism has given rise to storage products; in the sperm, to motor activities associated with a tendency to fission. The contrast is not between anabolic and katabolic tendencies, but between storage katabolism and motor katabolism. Nor do I think that "the essentially katabolic male-cell brings to the ovum a supply of characteristic waste products, or katastates, which stimulate the latter to division" (l.c., p. 162). I believe that it brings an inherited tendency to fission, and thus reintroduces into the fertilized ovum the tendency which, as ovum, it had renounced in favour of storage katabolism.
[G]On the other hand, three ova of the crustacean Apus are said to coalesce to form the single ovum from which one embryo develops.
[I]In some forms of life the opening of the cup marks the position of the future mouth: in others, of the future vent. In yet others it elongates into a slit, occupying the whole length of the embryo; the middle part of the slit closes up, and the opening at the far ends mark the position, the one of the future mouth, the other of the future vent.
[J]In technical language, the outer layer of cells is called the epiblast, the inner layer the hypoblast, and the mid-layer between them the mesoblast.
[K]In technical language, the opening by which the primitive digestive cavity (or mesenteron) communicates with the exterior is called the blastopore. When this closes, the new opening for the mouth is called the stomodœum; that for the vent, the proctodœum.
[L]We have seen that when volume tends to outrun surface, fission may take place, whereby the same volume has increased surface. But in unfavourable nutritive conditions, the same surface which had before been sufficient for nutrition may become, under the less favourable circumstances, insufficient, and fission may again take place to give a larger absorbent surface. Hence, possibly, the connection between insufficient nutriment and highly subdivided sperms.
[M]Samuel Butler in England, and Ewald Hering in Prague, have ingeniously likened this hereditary persistence to "organic memory." What are ordinarily called memory, habit, instinct, and embryonic reconstruction, are all referable to the memory of organic matter. The analogy, if used with due caution, is a helpful one, what we call memory being the psychical aspect (under certain special organic and neural conditions) of what under the physical aspect we call persistence.
[N]I have also to thank Mr. Edward Wilson for kindly giving me the measurements of three or four bats in the Bristol Museum.
[O]A millimetre is about 1/25 of an inch, or more exactly .03937 inch.
[P]In nearly all cases the measurements were checked by comparing the two wings. In one or two instances there were differences of as much as two or three millimetres between the bones of the two sides of the body, but in most cases they exactly corresponded.
[Q]We are anxious to extend our observations and to compare series of bats from different localities. If any of my readers should feel disposed to help us, by sending specimens (with the locality duly indicated) to Mr. H. Charbonnier, 7, The Triangle South, Clifton, Bristol, we shall be grateful.
[R]Nature, vol. xli. p. 393. The variation in molluscs is often considerable. In one of the bays in the basement hall of the Natural History Museum is a series showing the variation in size, form, and sculpturing of Paludomus loricatus, which is found in the streams of Ceylon. These varieties have in former times been named as ten distinct species!
[S]More observations and fuller knowledge on this latter point and on the relative numbers of the sexes in different species are much to be desired. It is clear that the number of offspring mainly depends upon the number of females. But if it be true that good times and favourable conditions lead to an increased production of females, while hard times and unfavourable conditions lead to a relative increase of males, then it is evident that good times will lead to a more rapid increase and hard times to a less rapid increase of the species. Suppose, for example, in a particular district food and other conditions were especially favourable for frogs. Among the well-nourished tadpoles there would be a preponderance of females. In the next generation the many females would produce abundant offspring (for one male may fertilize the ova laid by several females). There would be a greater number of tadpoles to compete for the same amount of nutriment. They would be less nourished. There would be less females; and in the succeeding generation a diminished number of tadpoles. Thus to some extent a balance between the number of tadpoles and the amount of available nutrition would be maintained. These conclusions are, perhaps, too theoretical to be of much value, while the tendency here indicated would be but one factor among many.
[T]"Origin of Species," pp. 62, 63.
[U]"Animals and Plants under Domestication," vol. ii. p. 177.
[V]I may here draw attention to the fact that the bats whose wing-bone measurements were given above are those which have so far survived and escaped such elimination as is now in progress.
[W]"Origin of Species," p. 109.
[X]"Darwinism," p. 106.
[Y]Ibid. p. 106.
[Z]Proceedings Liverpool Biological Society, 1889.
[AA]Since this chapter was written, Mr. Poulton has published his interesting and valuable work on "The Colours of Animals," from which I have contrived to insert one or two additional examples.
[AB]Ann. and Mag. Nat. Hist., September, 1889, p. 209, quoted by Poulton, "Colours of Animals," p. 55.
[AC]Nature, vol. xxxv. p. 77.
[AD]Many other instances might be added. The hornet clear-wing moth (Sphecia apiformis) mimics the hornet or wasp; the narrow-bordered bee-hawk moth (Sesia bombyliformis) mimics a bumble-bee. These insects may be seen in the lepidoptera drawers in the Natural History Museum. But perhaps the most wonderful instance of insect-mimicry is that observed by Mr. W. L. Sclater, and given by Mr. E. B. Poulton, in his "Colours of Animals" (p. 252), where a (probably) homopterous insect mimics a leaf-cutting ant, together with its leafy burden—a membranous expansion in the mimic closely resembling the piece of leaf carried by the particular kind of ant he resembles.
[AE]The late Mr. H. W. Oakley first drew my attention to this snake. Since then Mr. Hammond Tooke has described the facts in Nature, vol. xxxiv. p. 547.
[AF]Nature, vol. xlii. p. 115.
[AG]Since the above was written and sent to press, there has been added, at the Natural History Museum, in the basement hall, a case illustrating the adaptation of external colouring to the conditions of life. All the animals, birds, etc., there grouped were collected in the Egyptian desert, whence also the rocks, stones, and sand on which they are placed were brought. Though somewhat crowded, they exemplify protective resemblance very well.
[AH]I have to thank Mr. H. A. Francis for drawing my attention to this, and showing me the insects in his cabinet.
[AI]"Colours of Animals," p. 73.
[AJ]"Origin of Species," p. 161.
[AK]"Descent of Man," summary of chap. xvi. pt. ii.
[AL]Ibid. chap. xiv.
[AM]"Darwinism," p. 108.
[AN]Its importance in artificial selection was emphasized by Darwin: "The prevention of free crossing, and the intentional matching of individual animals, are the corner-stones of the breeder's art" ("Animals and Plants under Domestication," ii. 62).
[AO]From the absence of interblending in some cases (to be considered shortly), both brown and green forms may be produced; and under certain circumstances, even a power of becoming either brown or green in the presence of appropriate stimuli.
[AP]Wallace, "Darwinism," p. 172, where other examples are cited.
[AQ]Ibid. pp. 217, et seq.
[AR]Journal of the Linnæan Society, vol. xix. No. 115: "Zoology."
[AS]"Animals and Plants under Domestication," p. 145.
[AT]Ibid. chap. xvii.
[AU]"Darwinism," p. 326.
[AV]"Animals and Plants under Domestication," vol. ii. p. 65. For Darwin's general conclusions on hybridism, see vol. ii. p. 162 of the same work.
[AW]"In every case there are two factors, namely, the nature of the organism and the nature of the conditions. The former seems to be much the more important; for nearly similar variations sometimes arise under, as far as we can judge dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform" ("Origin of Species," p. 6).
[AX]See "Evolution without Natural Selection," by Charles Dixon. This author's facts are valuable; his theories are ill digested.
[AY]Nature, vol. xlii. p. 136.
[AZ]We may here note, in passing, the fact that the changes of life-forms in a succession of beds points in nine cases out of ten rather to substitution through migration than to transmutation. Still, there are notable cases of transmutation, as in the fresh-water Planorbes of Steinhem, in Wittenberg (described, after Hilgendorf, by O. Schmidt, "The Doctrine of Descent," p. 96).
[BA]I would ask historians whether there have not been, in English history, good times of free and beneficial divergence exemplified in diverse intellectual activity, hard times of rigorous elimination, and intermediate times of placid, somewhat humdrum conservatism.
[BB]Two more technical examples may be noticed in a note. (1) Professor Haeckel has recently (Challenger Reports, vol. xxviii.) shown that the Siphonophora include two groups, closely resembling each other, but of different ancestry: (a) The Disconanthæ, traceable to trachomedusoid ancestors; (b) the Siphonanthæ, traceable to anthomedusoid ancestors like Sarsia. (2) M. Paul Pelseneer has been led to the conclusion that the pteropod molluscs also include two groups resembling each other, but of different ancestry: (a) The Thecosomes, traceable to tornatellid ancestors; (b) the Gymnosomes, traceable to aphysiid ancestors. In each case, the ancestral sea-slug has been modified for a free-swimming life.
[BC]For evidence in copious abundance, see Nicholson's "Manual of Palæontology," new edition, vol. i.: "Vertebrata," by R. Lydekker.
[BD]"Animals and Plants under Domestication," vol ii. p. 239.
[BE]Or in certain "physiological units" (Herbert Spencer), or "plastidules" (Haeckel), which may be regarded as organic molecules exhibiting their special properties under vital conditions.
[BF]Nature, vol. xxxix. p. 486.
[BG]Darwin, "Animals and Plants under Domestication," 2nd edit., vol. ii. chap. xxvii., from which the following description and quotations are taken.
[BH]For an excellent account of the genesis and growth of the modern views of heredity, see Mr. J. Arthur Thomson's paper on "The History and Theory of Heredity:" Proceedings of the Royal Society of Edinburgh, 1889.
[BI]Geddes and Thomson, "The Evolution of Sex," p. 92.
[BJ]Weismann, "Essays on Heredity," English translation, p. 173.
[BK]Weismann, "Essays on Heredity," p. 205.
[BL]A few pages earlier (p. 200) in the same essay, Professor Weismann says, "A sudden transformation of the nucleo-plasm of a somatic cell into that of a germ-cell would be almost as incredible as the transformation of a mammal into an amœba." This at first sight does not seem quite consistent with the subsequent sentence which I have quoted in the text; for here, at any rate, the daughters of "mammals" are said to be converted into "amœbæ." But this is no doubt because the amœbæ (germ-plasms) are contained in the mammals (body-cells). (See the quotations that follow in the text.)
[BM]Weismann, "Essays on Heredity," p. 207.
[BN]Weismann, "Essays on Heredity," p. 179.
[BO]It will, of course, be understood that a minute fragment of germ-plasm is capable of almost unlimited growth by assimilation of nutritive material, its properties remaining unchanged during such growth.
[BP]Latency is here neglected. Mr. Francis Galton has shown, statistically, that the offspring, among human folk, inherit 1/4 from each parent, 1/16 from each grandparent, and the remaining 1/4 from more remote ancestors. In domesticated animals, reversion to characters of distant ancestors sometimes occurs. This, however, does not invalidate the argument in the text, which is that sexual admixture tends towards the mean of the race (ancestors included), and cannot be credited with new and unusually favourable variations. The prepotency of one parent is also here neglected.
[BQ]See his valuable paper on "Divergent Evolution," Lin. Soc. Zool., No. cxx.
[BR]One parthenogenetic form—the drone—has been shown by Blochmann to extrude a second polar cell. This observation is in serious opposition to Dr. Weismann's theory.
[BS]Weismann, "Essays on Heredity," pp. 355, 378.
[BT]The law of compensation of growth or balancement was suggested at nearly the same time by Goethe and Geoffrey Saint-Hilaire. The application in the text has not, so far as I know, been before suggested.
[BU]Darwin spoke of changed conditions acting "directly on the organization or indirectly through the reproductive system." Now, since Professor Weismann has taught us to reconsider these questions, we speak of such conditions as acting directly on the germ or indirectly through the body. The germ is no longer subordinate to the body, but the body to the germ.
[BV]July 15, 1876. Since reprinted in "The Advancement of Science," p. 273.
[BW]Herbert Spencer, "Principles of Biology," vol. i. p. 256.
[BX]Mr. J. A. Thomson has published a most valuable "Synthetic Summary of the Influence of the Environment upon the Organism" (Proceedings Royal Physiological Society, Edinburgh: vol. ix. pt. 3, 1888). The case of the Amazonian parrots was communicated to Darwin by Mr. Wallace ("Animals and Plants under Domestication," vol. ii. p. 269).
[BY]St. George Mivart, "On Truth," p. 378.
[BZ]Op. cit., p. 47. I venture to say, "with some assurance," because Charles Darwin, who had also considered this matter, writes, "Who will pretend to decide how far the thick fur of Arctic animals, or their white colour, is due to the direct action of a severe climate, and how far to the preservation of the best-protected individuals during a long succession of generations?" ("Animals and Plants under Domestication," p. 415).
[CA]"Organic Evolution," English translation, p. 88.
[CB]"Contributions to Natural Selection," p. 197.
[CC]Since this was written, Mr. Poulton has described his results in an interesting volume on "The Colours of Animals" (q.v.).
[CD]See Journal of Anatomy and Physiology, vol. xxii. p. 215.
[CE]See Professor Herdman's Inaugural Address, Liverpool Biological Society, 1888.
[CF]Francis Galton, "Inquiries into Human Faculty," p. 216.
[CG]That the epidermis is thicker on the palms of the hands and the soles of the feet in the infant long before birth, may be attributable to the inherited effects of use or pressure. It can hardly be held that the thickening of the skin in these parts is of elimination value.
[CH]The instances cited are from "Animals and Plants under Domestication."
[CI]It is beyond the scope of this book to give the evidences of evolution. Such evidence from embryology, from distribution, and from palæontology, is now abundant. For palæontological evidence, see Nicholson's "Manual of Palæontology," 3rd edit., especially the second volume on "Vertebrates," by R. Lydekker.
[CJ]Weismann, "Essays on Heredity," p. 24.
[CK]Ibid. p. 140.
[CL]Weismann, "Essays on Heredity," p. 90.
[CM]Ibid. p. 292. See also a discussion in Nature, in which Mr. Romanes and Professor Ray Lankester took part, beginning vol. xli. p. 437.
[CN]Weismann, "Essay on Heredity," p. 140.
[CO]"Origin of Species," p. 110.
[CP]With regard to blind cave-fish, Professor Ray Lankester has suggested that some selection has been effected. Those animals whose sight-sensitiveness enabled them to detect a glimmer of light would escape to the exterior, leaving those with congenitally weak sight to remain and procreate in the darkness of the cave.
[CQ]Darwin, "Descent of Man," pt. ii. chap. viii.
[CR]"Darwinism," chap. x.
[CS]"Darwinism," p. 295. Messrs. Geddes and Thomson, "The Evolution of Sex," p. 28, also contend that "combative energy and sexual beauty rise pari passu with male katabolism."
[CT]"Darwinism," p. 293.
[CU]Mr. Poulton, who takes a similar line of argument in his "Colours of Animals," lays special stress upon the production of white (see p. 326).
[CV]See Chapter VIII.
[CW]"Darwinism," p. 172.
[CX]See "Animals and Plants under Domestication," vol. ii. p. 80.
[CY]"Darwinism," p. 332.
[CZ]"The Colour-Sense," by Grant Allen, p. 95.
[DA]That on "The Emotions of Animals" (X.).
[DB]"Darwinism," p. 318.
[DC]Natural History Society of Wisconsin, vol. i. (1889).
[DD]"Darwinism," p. 286.
[DE]On the negative character of disuse, see p. 196.
[DF]Cope, "Origin of the Fittest," p. 374.
[DG]It would appear, from certain passages of his "Darwinism," that Mr. A. R. Wallace (e.g. p. 139, note) holds or held similar views. "The genera Ateles and Colobus," he says, "are two of the most purely arboreal types of monkeys, and it is not difficult to conceive that the constant use of the elongated fingers for climbing from tree to tree, and catching on to branches while making great leaps, might require all the nervous energy and muscular growth to be directed to the fingers, the small thumb remaining useless." I should also have quoted Mr. Wallace's account of the twisting round of the eyes of flat-fishes—where he says that the constant repetition of the effort of twisting the eye towards the upper side of the head, when the bony structure is still soft and flexible, causes the eye gradually to move round the head till it comes to the upper side—had he not subsequently disclaimed this explanation (see Nature, vol. xl. p. 619). It is possible that Mr. Wallace, notwithstanding the words "constant use" in the passage I have quoted, merely intends to imply that the elongated fingers are of advantage in climbing, and are thus subject to natural selection, the thumb diminishing through economy of growth.
[DH]I find, on rereading one of his articles, that I have here unwittingly adopted one of Mr. Romance's arguments (see Nature, vol. xxxvi. p. 406). The instance Mr. Romanes cites is the curious habit of dogs turning round before they lie down.
[DI]Mr. Darwin, while contending that the modifications need not all have been simultaneous, says, "Although natural selection would thus tend to give the male elk its present structure, yet it is probable that the inherited effects of use, and of the mutual action of part on part, have been equally or more important" ("Animals and Plants under Domestication," vol. ii. p. 328).
[DJ]Midland Naturalist, November, 1889.
[DK]See ante, p. 52.
[DL]Nature, vol. xli. p. 511.
[DM]"Animals and Plants under Domestication," vol. ii. p. 291.
[DN]In the third chapter we saw that in such cases not only are there an enormous number of ova produced, but that (e.g. in aurelia and the liver-fluke) each ovum produces, through the intervention of asexual multiplication, many individuals.
[DO]Cope, "Origin of the Fittest," pp. 226, 125, and 297.
[DP]"Animals and Plants under Domestication," vol. ii. p. 313.
[DQ]Ibid. p. 56.
[DR]Nature, vol. xxxvi. p. 592.
[DS]Quoted from "Medical Notes and Reflections," 1855, p. 267, by Darwin, "Animals and Plants under Domestication," vol. i. p. 446.
[DT]Darwin, "Animals and Plants under Domestication," vol. i. p. 465.
[DU]"Natural Inheritance," p. 12.
[DV]Darwin, "Animals and Plants under Domestication," vol. ii. p. 70.
[DW]"Organic Evolution," Mr. Cunningham's translation, p. 76.