Chapter XXXVII: Epilogue (2)

[221] The appearance of “vacuolation” is a result of endosmosis or the diffusion of a less dense fluid into the denser plasma of the cell. _Caeteris paribus_, it is less apparent in marine organisms than in those of freshwater, and in many or most marine Ciliates and even Rhizopods a contractile vacuole has not been observed (Bütschli, in Bronn’s _Protozoa_, p. 1414); it is also absent, and probably for the same reason, in parasitic Protozoa, such as the Gregarines and the Entamoebae. Rossbach shewed that the contractile vacuole of ordinary freshwater Ciliates was very greatly diminished in a 5 per cent. solution of NaCl, and all but disappeared in a 1 per cent. solution of sugar (_Arb. z. z. Inst. Würzburg_, 1872, cf. Massart, _Arch. de Biol._ LX, p. 515, 1889). _Actinophrys sol_, when gradually acclimatised to sea-water, loses its vacuoles, and _vice versa_ (Gruber, _Biol. Centralbl._ IX, p. 22, 1889); and the same is true of Amoeba (Zuelzer, _Arch. f. Entw. Mech._ 1910, p. 632). The gradual enlargement of the contractile vacuole is precisely analogous to the change of size of a bubble until the gases on either side of the film are equally diffused, as described long ago by Draper (_Phil. Mag._ (n. s.), XI, p. 559, 1837). Rhumbler has shewn that contractile or pulsating vacuoles may be well imitated in chloroform-drops, suspended in water in which various substances are dissolved (_Arch. f. Entw. Mech._ VII, 1898, p. 103). The pressure within the contractile vacuole, always greater than without, diminishes with its size, being inversely proportional to its radius; and when it lies near the surface of the cell, as in a Heliozoon, it bursts as soon as it reaches a thinness which its viscosity or molecular cohesion no longer permits it to maintain.

[222] Cf. p. 660.

[223] The elongated or curved “macronucleus” of an Infusorian is to be looked upon as a single mass of chromatin, rather than as an aggregation of particles in a fluid drop, as in the case described. It has a shape of its own, in which ordinary surface-tension plays a very subordinate part.

[224] _Théorie physico-chimique de la Vie_, p. 73, 1910; _Mechanism of Life_, p. 56, 1911.

[225] Whence the name “mitosis” (Greek μίτος, a thread), applied first by Flemming to the whole phenomenon. Kollmann (_Biol. Centralbl._ II, p. 107, 1882) called it _divisio per fila_, or _divisio laqueis implicata_. Many of the earlier students, such as Van Beneden (Rech. sur la maturation de l’œuf, _Arch. de Biol._ IV, 1883), and Hermann (Zur Lehre v. d. Entstehung d. karyokinetischen Spindel, _Arch. f. mikrosk. Anat._ XXXVII, 1891) thought they recognised actual muscular threads, drawing the nuclear material asunder towards the respective foci or poles; and some such view was long maintained by other writers, Boveri, Heidenhain, Flemming, R. Hertwig, and many more. In fact, the existence of contractile threads, or the ascription to the spindle rather than to the poles or centrosomes of the active forces concerned in nuclear division, formed the main tenet of all those who declined to go beyond the “contractile properties of protoplasm” for an explanation of the phenomenon. (Cf. also J. W. Jenkinson, _Q. J. M. S._ XLVIII, p. 471, 1904.)

[226] Cf. Bütschli, O., Ueber die künstliche Nachahmung der karyokinetischen Figur, _Verh. Med. Nat. Ver. Heidelberg_, V, pp. 28–41 (1892), 1897.

[227] Arrhenius, in describing a typical colloid precipitate, does so in terms that are very closely applicable to the ordinary microscopic appearance of the protoplasm of the cell. The precipitate consists, he says, “en un réseau d’une substance solide contenant peu d’eau, dans les mailles duquel est inclus un fluide contenant un peu de colloide dans beaucoup d’eau ... Evidemment cette structure se forme à cause de la petite différence de poids spécifique des deux phases, et de la consistance gluante des particules séparées, qui s’attachent en forme de réseau.” _Rev. Scientifique_, Feb. 1911.

[228] F. Schwartz, in Cohn’s _Beitr. z. Biologie der Pflanzen_, V, p. 1, 1887.

[229] Fischer, _Anat. Anzeiger_, IX, p. 678, 1894, X, p. 769, 1895.

[230] See, in particular, W. B. Hardy, On the structure of Cell Protoplasm, _Journ. of Physiol._ XXIV, pp. 158–207, 1889; also Höber, _Physikalische Chemie der Zelle und der Gewebe_, 1902. Cf. (_int. al._) Flemming, _Zellsubstanz, Kern und Zelltheilung_ 1882, p. 51, etc.

[231] My description and diagrams (Figs 42–51) are based on those of Professor E. B. Wilson.

[232] If the word _permeability_ be deemed too directly suggestive of the phenomena of _magnetism_ we may replace it by the more general term of _specific inductive capacity_. This would cover the particular case, which is by no means an improbable one, of our phenomena being due to a “surface charge” borne by the nucleus itself and also by the chromosomes: this surface charge being in turn the result of a difference in inductive capacity between the body or particle and its surrounding medium. (Cf. footnote, p. 187.)

[233] On the effect of electrical influences in altering the surface-tensions of the colloid particles, see Bredig, _Anorganische Fermente_, pp. 15, 16, 1901.

[234] _The Cell_, etc. p. 66.

[235] Lillie, R. S., _Amer. J. of Physiol._ VIII, p. 282, 1903.

[236] We have not taken account in the above paragraphs of the obvious fact that the supposed symmetrical field of force is distorted by the presence in it of the more or less permeable bodies; nor is it necessary for us to do so, for to that distorted field the above argument continues to apply, word for word.

[237] M. Foster, _Lectures on the History of Physiology_, 1901, p. 62.

[238] _Op. cit._ pp. 110 and 91.

[239] Lamb, A. B., A new Explanation of the Mechanism of Mitosis, _Journ. Exp. Zool._ V, pp. 27–33, 1908.

[240] _Amer. J. of Physiol._ VIII, pp. 273–283, 1903 (_vide supra_, p. 181); cf. _ibid._ XV, pp. 46–84, 1905. Cf. also _Biological Bulletin_, IV, p. 175. 1903.

[241] In like manner Hardy has shewn that colloid particles migrate with the negative stream if the reaction of the surrounding fluid be alkaline, and _vice versa_. The whole subject is much wider than these brief allusions suggest, and is essentially part of Quincke’s theory of Electrical Diffusion or Endosmosis: according to which the particles and the fluid in which they float (or the fluid and the capillary walls through which it flows) each carry a charge, there being a discontinuity of potential at the surface of contact, and hence a field of force leading to powerful tangential or shearing stresses, communicating to the particles a velocity which varies with the density per unit area of the surface charge. See W. B. Hardy’s paper on Coagulation by Electricity, _Journ. of Physiol._ XXIV, p. 288–304, 1899, also Hardy and H. W. Harvey, Surface Electric Charges of Living Cells, _Proc. R. S._ LXXXIV (B), pp. 217–226, 1911, and papers quoted therein. Cf. also E. N. Harvey’s observations on the convection of unicellular organisms in an electric field (Studies on the Permeability of Cells, _Journ. of Exper. Zool._ X, pp. 508–556, 1911).

[242] On Differences in Electrical Potential in Developing Eggs, _Amer. Journ. of Physiol._ XII, pp. 241–275, 1905. This paper contains an excellent summary of various physical theories of the segmentation of the cell.

[243] Gray has recently demonstrated a temporary increase of electrical conductivity in sea-urchin eggs during the process of fertilisation (The Electrical Conductivity of fertilised and unfertilised Eggs, _Journ. Mar. Biol. Assoc._ X, pp. 50–59, 1913).

[244] Schewiakoff, Ueber die karyokinetische Kerntheilung der _Euglypha alveolata, Morph. Jahrb._ XIII, pp. 193–258, 1888 (see p. 216).

[245] Coe, W. R., Maturation and Fertilization of the Egg of Cerebratulus, _Zool. Jahrbücher_ (_Anat. Abth._), XII, pp. 425–476, 1899.

[246] Thus, for example, Farmer and Digby (On Dimensions of Chromosomes considered in relation to Phylogeny, _Phil. Trans._ (B), CCV, pp. 1–23, 1914) have been at pains to shew, in confutation of Meek (_ibid._ CCIII, pp. 1–74, 1912), that the width of the chromosomes cannot be correlated with the order of phylogeny.

[247] Cf. also _Arch. f. Entw. Mech._ X, p. 52, 1900.

[248] Cf. Loeb, _Am. J. of Physiol._ VI, p. 32, 1902; Erlanger, _Biol. Centralbl._ XVII, pp. 152, 339, 1897; Conklin, _Biol. Lectures_, _Woods Holl_, p. 69, etc. 1898–9.

[249] Robertson, T. B., Note on the Chemical Mechanics of Cell Division, _Arch. f. Entw. Mech._ XXVII, p. 29, 1909, XXXV, p. 692. 1913. Cf. R. S. Lillie, _J. Exp. Zool._ XXI, pp. 369–402, 1916.

[250] Cf. D’Arsonval, _Arch. de Physiol._ p. 460, 1889; Ida H. Hyde, _op. cit._ p. 242.

[251] Cf. Plateau’s remarks (_Statique des liquides_, II, p. 154) on the _tendency_ towards equilibrium, rather than actual equilibrium, in many of his systems of soap-films.

[252] But under artificial conditions, “polyspermy” may take place, e.g. under the action of dilute poisons, or of an abnormally high temperature, these being all, doubtless, conditions under which the surface-tension is diminished.

[253] Fol, H., _Recherches sur la fécondation_, 1879. Roux, W., Beiträge zur Entwickelungsmechanik des Embryo, _Arch. f. Mikr. Anat._ XIX, 1887. Whitman, C. O., Oökinesis, _Journ. of Morph._ I, 1887.

[254] Wilson. _The Cell_, p. 77.

[255] Eight and twelve are by much the commonest numbers, six and sixteen coming next in order. If we may judge by the list given by E. B. Wilson (_The Cell_, p. 206), over 80 % of the observed cases lie between 6 and 16, and nearly 60 % between 8 and 12.

[256] _Theory of Cells_, p. 191.

[257] _The Cell in Development_, etc. p. 59; cf. pp. 388, 413.

[258] E.g. Brücke, _Elementarorganismen_, p. 387: “Wir müssen in der Zelle einen kleinen Thierleib sehen, und dürfen die Analogien, welche zwischen ihr und den kleinsten Thierformen existiren, niemals aus den Augen lassen.”

[259] Whitman, C. O., The Inadequacy of the Cell-theory, _Journ. of Morphol._ VIII, pp. 639–658, 1893; Sedgwick, A., On the Inadequacy of the Cellular Theory of Development, _Q.J.M.S._ XXXVII, pp. 87–101, 1895, XXXVIII, pp. 331–337, 1896. Cf. Bourne, G. C., A Criticism of the Cell-theory; being an answer to Mr Sedgwick’s article, etc., _ibid._ XXXVIII, pp. 137–174, 1896.

[260] Cf. Hertwig, O., _Die Zelle und die Gewebe_, 1893, p. 1; “Die Zellen, in welche der Anatom die pflanzlichen und thierischen Organismen zerlegt, sind die Träger der Lebensfunktionen; sie sind, wie Virchow sich ausgedrückt hat, die ‘Lebenseinheiten.’ Von diesem Gesichtspunkt aus betrachtet, erscheint der Gesammtlebensprocess eines zusammengesetzten Organismus nichts Anderes zu sein als das höchst verwickelte Resultat der einzelnen Lebensprocesse seiner zahlreichen, verschieden functionirenden Zellen.”

[261] _Journ. of Morph._ VIII, p. 653, 1893.

[262] Neue Grundlegungen zur Kenntniss der Zelle, _Morph. Jahrb._ VIII, pp. 272, 313, 333, 1883.

[263] _Journ. of Morph._ II, p. 49, 1889.

[264] _Phil. Trans._ CLI, p. 183, 1861; _Researches_, ed. Angus Smith, 1877, p. 553.

[265] Cf. Kelvin, On the Molecular Tactics of a Crystal, _The Boyle Lecture_, Oxford, 1893, _Baltimore Lectures_, 1904, pp. 612–642. Here Kelvin was mainly following Bravais’s (and Frankenheim’s) theory of “space-lattices,” but he had been largely anticipated by the crystallographers. For an account of the development of the subject in modern crystallography, by Sohncke, von Fedorow, Schönfliess, Barlow and others, see Tutton’s _Crystallography_, chap. ix, pp. 118–134, 1911.

[266] In a homogeneous crystalline arrangement, _symmetry_ compels a locus of one property to be a plane or set of planes; the locus in this case being that of least surface potential energy.

[267] This is what Graham called the _water of gelatination_, on the analogy of _water of crystallisation_; _Chem. and Phys. Researches_, p. 597.

[268] Here, in a non-crystalline or random arrangement of particles, symmetry ensures that the potential energy shall be the same per unit area of all surfaces; and it follows from geometrical considerations that the total surface energy will be least if the surface be spherical.

[269] Lehmann, O., _Flüssige Krystalle, sowie Plasticität von Krystallen im allgemeinen_, etc., 264 pp. 39 pll., Leipsig, 1904. For a semi-popular, illustrated account, see Tutton’s _Crystals_ (Int. Sci. Series), 1911.

[270] As Graham said of an allied phenomenon (the so-called blood-crystals of Funke), it “illustrates the maxim that in nature there are no abrupt transitions, and that distinctions of class are never absolute.”

[271] Cf. Przibram, H., Kristall-analogien zur Entwickelungsmechanik der Organismen, _Arch. f. Entw. Mech._ XXII, p. 207, 1906 (with copious bibliography); Lehmann, Scheinbar lebende Kristalle und Myelinformen, _ibid._ XXVI, p. 483, 1908.

[272] The idea of a “surface-tension” in liquids was first enunciated by Segner, _De figuris superficierum fluidarum_, in _Comment. Soc. Roy. Göttingen_, 1751, p. 301. Hooke, in the _Micrographia_ (1665, Obs. VIII, etc.), had called attention to the globular or spherical form of the little morsels of steel struck off by a flint, and had shewn how to make a powder of such spherical grains, by heating fine filings to melting point. “This Phaenomenon” he said “proceeds from a propriety which belongs to all kinds of fluid Bodies more or less, and is caused by the Incongruity of the Ambient and included Fluid, which so acts and modulates each other, that they acquire, as neer as is possible, a _spherical_ or _globular_ form....”

[273] _Science of Mechanics_, 1902, p. 395; see also Mach’s article Ueber die physikalische Bedeutung der Gesetze der Symmetrie, _Lotos_, XXI, pp. 139–147, 1871.

[274] Similarly, Sir David Brewster and others made powerful lenses by simply dropping small drops of Canada balsam, castor oil, or other strongly refractive liquids, on to a glass plate: _On New Philosophical Instruments_ (Description of a new Fluid Microscope), Edinburgh, 1813, p. 413.

[275] Beiträge z. Physiologie d. Protoplasma, _Pflüger’s Archiv_, II, p. 307, 1869.

[276] _Poggend. Annalen_, XCIV, pp. 447–459, 1855. Cf. Strethill Wright, _Phil. Mag._ Feb. 1860.

[277] Haycraft and Carlier pointed out (_Proc. R.S.E._ XV, pp. 220–224, 1888) that the amoeboid movements of a white blood-corpuscle are only manifested when the corpuscle is in contact with some solid substance: while floating freely in the plasma or serum of the blood, these corpuscles are spherical, that is to say they are at rest and in equilibrium. The same fact has recently been recorded anew by Ledingham (On Phagocytosis from an adsorptive point of view, _Journ. of Hygiene_, XII, p. 324, 1912). On the emission of pseudopodia as brought about by changes in surface tension, see also (_int. al._) Jensen, Ueber den Geotropismus niederer Organismen, _Pflüger’s Archiv_, LIII, 1893. Jensen remarks that in Orbitolites, the pseudopodia issuing through the pores of the shell first float freely, then as they grow longer bend over till they touch the ground, whereupon they begin to display amoeboid and streaming motions. Verworn indicates (_Allg. Physiol._ 1895, p. 429), and Davenport says (_Experim. Morphology_, II, p. 376) that “this persistent clinging to the substratum is a ‘thigmotropic’ reaction, and one which belongs clearly to the category of ‘response.’ ” (Cf. Pütter, Thigmotaxis bei Protisten, _A. f. Physiol._ 1900, Suppl. p. 247.) But it is not clear to my mind that to account for this simple phenomenon we need invoke other factors than gravity and surface-action.

[278] Cf. Pauli, _Allgemeine physikalische Chemie d. Zellen u. Gewebe_, in Asher-Spiro’s _Ergebnisse der Physiologie_, 1912; Przibram, _Vitalität_, 1913, p. 6.

[279] The surface-tension theory of protoplasmic movement has been denied by many. Cf. (e.g.), Jennings, H. S., Contributions to the Study of the Behaviour of the Lower Organisms, _Carnegie Inst._ 1904, pp. 130–230; Dellinger, O. P., Locomotion of Amoebae, etc. _Journ. Exp. Zool._ III, pp. 337–357, 1906; also various papers by Max Heidenhain, in _Anatom. Hefte_ (Merkel und Bonnet), etc.

[280] These various movements of a liquid surface, and other still more striking movements such as those of a piece of camphor floating on water, were at one time ascribed by certain physicists to a peculiar force, _sui generis_, the _force épipolique_ of Dutrochet: until van der Mensbrugghe shewed that differences of surface tension were enough to account for this whole series of phenomena (Sur la tension superficielle des liquides considérée au point de vue de certains mouvements observés à leur surface, _Mém. Cour. Acad. de Belgique_, XXXIV, 1869; cf. Plateau, p. 283).

[281] Cf. _infra_, p. 306.

[282] Cf. p. 32.

[283] Or, more strictly speaking, unless its thickness be less than twice the range of the molecular forces.

[284] It follows that the tension, depending only on the surface-conditions, is independent of the thickness of the film.

[285] This simple but immensely important formula is due to Laplace (_Mécanique Céleste_, Bk. x. suppl. _Théorie de l’action capillaire_, 1806).

[286] Sur la surface de révolution dont la courbure moyenne est constante, _Journ. de M. Liouville_, VI, p. 309, 1841.

[287] See _Liquid Drops and Globules_, 1914, p. 11. Robert Boyle used turpentine in much the same way. For other methods see Plateau, _op. cit._ p. 154.

[288] Felix Plateau recommends the use of a weighted thread, or plumb-line, drawn up out of a jar of water or oil; _Phil. Mag._ XXXIV, p. 246, 1867.

[289] Cf. Boys, C. V., On Quartz Fibres, _Nature_, July 11, 1889; Warburton, C., The Spinning Apparatus of Geometric Spiders, _Q.J.M.S._ XXXI, pp. 29–39, 1890.

[290] J. Blackwall, _Spiders of Great Britain_ (Ray Society), 1859, p. 10; _Trans. Linn. Soc._ XVI, p. 477, 1833.

[291] The intermediate spherules appear, with great regularity and beauty, whenever a liquid jet breaks up into drops; see the instantaneous photographs in Poynting and Thomson’s _Properties of Matter_, pp. 151, 152, (ed. 1907).

[292] Kühne, _Untersuchungen über das Protoplasma_, 1864, p. 75, etc.

[293] _A Study of Splashes_, 1908, p. 38, etc.; Segmentation of a Liquid Annulus, _Proc. Roy. Soc._ XXX, pp. 49–60, 1880.

[294] Cf. _ibid._ pp. 17, 77. The same phenomenon is beautifully and continuously evident when a strong jet of water from a tap impinges on a curved surface and then shoots off it.

[295] See a _Study of Splashes_, p. 54.

[296] A case which we have not specially considered, but which may be found to deserve consideration in biology, is that of a cell or drop suspended in a liquid of _varying_ density, for instance in the upper layers of a fluid (e.g. sea-water) at whose surface condensation is going on, so as to produce a steady density-gradient. In this case the normally spherical drop will be flattened into an oval form, with its maximum surface-curvature lying at the level where the densities of the drop and the surrounding liquid are just equal. The sectional outline of the drop has been shewn to be not a true oval or ellipse, but a somewhat complicated quartic curve. (Rice, _Phil. Mag._ Jan. 1915.)

[297] Indeed any non-isotropic _stiffness_, even though _T_ remained uniform, would simulate, and be indistinguishable from, a condition of non-stiffness and non-isotropic _T_.

[298] A non-symmetry of _T_ and _T′_ might also be capable of explanation as a result of “liquid crystallisation.” This hypothesis is referred to, in connection with the blood-corpuscles, on p. 272.

[299] The case of the snow-crystals is a particularly interesting one; for their “distribution” is in some ways analogous to what we find, for instance, among our microscopic skeletons of Radiolarians. That is to say, we may one day meet with myriads of some one particular form or species only, and another day with myriads of another; while at another time and place we may find species intermingled in inexhaustible variety. (Cf. e.g. J. Glaisher, _Ill. London News_, Feb. 17, 1855; _Q.J.M.S._ III, pp. 179–185, 1855).

[300] Cf. Bergson, _Creative Evolution_, p. 107: “Certain Foraminifera have not varied since the Silurian epoch. Unmoved witnesses of the innumerable revolutions that have upheaved our planet, the Lingulae are today what they were at the remotest times of the palaeozoic era.”

[301] Ray Lankester, _A.M.N.H._ (4), XI, p. 321, 1873.

[302] Leidy, Parasites of the Termites, _J. Nat. Sci., Philadelphia_, VIII, pp. 425–447, 1874–81; cf. Saville Kent’s _Infusoria_, II, p. 551.

[303] _Op. cit._ p. 79.

[304] Brady, _Challenger Monograph_, pl. XX, p. 233.

[305] That the Foraminifera not only can but do hang from the surface of the water is confirmed by the following apt quotation which I owe to Mr E. Heron-Allen: “Quand on place, comme il a été dit, le dépôt provenant du lavage des fucus dans un flacon que l’on remplit de nouvelle eau, on voit au bout d’une heure environ les animaux [_Gromia dujardinii_] se mettre en mouvement et commencer à grimper. Six heures après ils tapissent l’extérieur du flacon, de sorte que les plus élevés sont à trente-six ou quarante-deux millimetres du fond; le lendemain beaucoup d’entre eux, _après avoir atteint le niveau du liquide, ont continué à ramper à sa surface, en se laissant pendre au-dessous_ comme certains mollusques gastéropodes.” (Dujardin, F., Observations nouvelles sur les prétendus céphalopodes microscopiques, _Ann. des Sci. Nat._ (2), III, p. 312, 1835.)

[306] Cf. Boas, _Spolia Atlantica_, 1886, pl. 6.

[307] This cellular pattern would seem to be related to the “cohesion figures” described by Tomlinson in various surface-films (_Phil. Mag._ 1861 to 1870); to the “tesselated structure” in liquids described by Professor James Thomson in 1882 (_Collected Papers_, p. 136); and to the _tourbillons cellulaires_ of Prof. H. Bénard (_Ann. de Chimie_ (7), XXIII, pp. 62–144, 1901, (8), XXIV, pp. 563–566, 1911), _Rev. génér. des Sci._ XI, p. 1268, 1900; cf. also E. H. Weber. (_Poggend. Ann._ XCIV, p. 452, 1855, etc.). The phenomenon is of great interest and various appearances have been referred to it, in biology, geology, metallurgy and even astronomy: for the flocculent clouds in the solar photosphere shew an analogous configuration. (See letters by Kerr Grant, Larmor, Wager and others, in _Nature_, April 16 to June 11, 1914.) In many instances, marked by strict symmetry or regularity, it is very possible that the interference of waves or ripples may play its part in the phenomenon. But in the majority of cases, it is fairly certain that localised centres of action, or of diminished tension, are present, such as might be provided by dust-particles in the case of Darling’s experiment (cf. _infra_, p. 590).

[308] Ueber physikalischen Eigenschaften dünner, fester Lamellen, _S.B. Berlin. Akad._ 1888, pp. 789, 790.

[309] Certain palaeontologists (e.g. Haeusler and Spandel) have maintained that in each family or genus the plain smooth-shelled forms are the primitive and ancient ones, and that the ribbed and otherwise ornamented shells make their appearance at later dates in the course of a definite evolution (cf. Rhumbler, _Foraminiferen der Plankton-Expedition_, 1911, i, p. 21). If this were true it would be of fundamental importance: but this book of mine would not deserve to be written.

[310] _A Study of Splashes_, p. 116.

[311] See _Silliman’s Journal_, II, p. 179, 1820; and cf. Plateau, _op. cit._ II, pp. 134, 461.

[312] The presence or absence of the contractile vacuole or vacuoles is one of the chief distinctions, in systematic zoology, between the Heliozoa and the Radiolaria. As we have seen on p. 165 (footnote), it is probably no more than a physical consequence of the different conditions of existence in fresh water and in salt.

[313] Cf. Doflein, _Lehrbuch der Protozoenkunde_, 1911, p. 422.

[314] Cf. Minchin, _Introduction to the Study of the Protozoa_, 1914 p. 293, Fig. 127.

[315] Cf. C. A. Kofoid and Olive Swezy, On Trichomonad Flagellates, etc. _Pr. Amer. Acad. of Arts and Sci._ LI, pp. 289–378, 1915.

[316] D. L. Mackinnon, Herpetomonads from the Alimentary Tract of certain Dungflies, _Parasitology_, III, p. 268, 1910.

[317] _Proc. Roy. Soc._ XII, pp. 251–257, 1862–3.

[318] Cf. (_int. al._) Lehmann, Ueber scheinbar lebende Kristalle und Myelinformen, _Arch. f. Entw. Mech._ XXVI, p. 483, 1908; _Ann. d. Physik_, XLIV, p. 969, 1914.

[319] Cf. B. Moore and H. C. Roaf, On the Osmotic Equilibrium of the Red Blood Corpuscle, _Biochem. Journal_, III, p. 55, 1908.

[320] For an attempt to explain the form of a blood-corpuscle by surface-tension alone, see Rice, _Phil. Mag._ Nov. 1914; but cf. Shorter, _ibid._ Jan. 1915.

[321] Koltzoff, N. K., Studien über die Gestalt der Zelle, _Arch. f. mikrosk. Anat._ LXVII, pp. 364–571, 1905; _Biol. Centralbl._ XXIII, pp. 680–696, 1903, XXVI, pp. 854–863, 1906; _Arch. f. Zellforschung_, II, pp. 1–65, 1908, VII, pp. 344–423, 1911; _Anat. Anzeiger_, XLI, pp. 183–206, 1912.

[322] Cf. _supra_, p. 129.

[323] As Bethe points out (Zellgestalt, Plateausche Flüssigkeitstigur und Neurofibrille, _Anat. Anz._ XL. p. 209, 1911), the spiral fibres of which Koltzoff speaks must lie _in the surface_, and not within the substance, of the cell whose conformation is affected by them.

[324] See for a further but still elementary account, Michaelis, _Dynamics of Surfaces_, 1914, p. 22 _seq._; Macallum, _Oberflächenspannung und Lebenserscheinungen_, in Asher-Spiro’s _Ergebnisse der Physiologie_, XI, pp. 598–658, 1911; see also W. W. Taylor’s _Chemistry of Colloids_, 1915, p. 221 _seq._, Wolfgang Ostwald, _Grundriss der Kolloidchemie_, 1909, and other text-books of physical chemistry; and Bayliss’s _Principles of General Physiology_, pp. 54–73, 1915.

[325] The first instance of what we now call an adsorptive phenomenon was observed in soap-bubbles. Leidenfrost, in 1756, was aware that the outer layer of the bubble was covered by an “oily” layer. A hundred years later Dupré shewed that in a soap-solution the soap tends to concentrate at the surface, so that the surface-tension of a very weak solution is very little different from that of a strong one (_Théorie mécanique de la chaleur_, 1869, p. 376; cf. Plateau, II, p. 100).

[326] This identical phenomenon was the basis of Quincke’s theory of amoeboid movement (Ueber periodische Ausbreitung von Flüssigkeitsoberflächen, etc., _SB. Berlin. Akad._ 1888, pp. 791–806; cf. _Pflüger’s Archiv_, 1879, p. 136).

[327] J. Willard Gibbs, Equilibrium of Heterogeneous Substances, _Tr. Conn. Acad._ III, pp. 380–400, 1876, also in _Collected Papers_, I, pp. 185–218, London, 1906; J. J. Thomson, _Applications of Dynamics to Physics and Chemistry_, 1888 (Surface tension of solutions), p. 190. See also (_int. al._) the various papers by C. M. Lewis, _Phil. Mag._ (6), XV, p. 499, 1908, XVII, p. 466, 1909, _Zeitschr. f. physik. Chemie_, LXX, p. 129, 1910; Milner, _Phil. Mag._ (6), XIII, p. 96, 1907, etc.

[328] G. F. FitzGerald, On the Theory of Muscular Contraction, _Brit. Ass. Rep._ 1878; also in _Scientific Writings_, ed. Larmor, 1902, pp. 34, 75. A. d’Arsonval, Relations entre l’électricité animale et la tension superficielle, _C. R._ CVI, p. 1740. 1888; cf. A. Imbert, Le mécanisme de la contraction musculaire, déduit de la considération des forces de tension superficielle, _Arch. de Phys._ (5), IX, pp. 289–301, 1897.

[329] Ueber die Natur der Bindung der Gase im Blut und in seinen Bestandtheilen, _Kolloid. Zeitschr._ II, pp. 264–272, 294–301, 1908; cf. Loewy, Dissociationsspannung des Oxyhaemoglobin im Blut, _Arch. f. Anat. und Physiol._ 1904, p. 231.

[330] We may trace the first steps in the study of this phenomenon to Melsens, who found that thin films of white of egg become firm and insoluble (Sur les modifications apportées à l’albumine ... par l’action purement mécanique, _C. R. Acad. Sci._ XXXIII, p. 247, 1851); and Harting made similar observations about the same time. Ramsden has investigated the same subject, and also the more general phenomenon of the formation of albuminoid and fatty membranes by adsorption: cf. Koagulierung der Eiweisskörper auf mechanischer Wege, _Arch. f. Anat. u. Phys._ (_Phys. Abth._) 1894, p. 517; Abscheidung fester Körper in Oberflächenschichten _Z. f. phys. Chem._ XLVII, p. 341, 1902; _Proc. R. S._ LXXII, p. 156, 1904. For a general review of the whole subject see H. Zangger, Ueber Membranen und Membranfunktionen, in Asher-Spiro’s _Ergebnisse der Physiologie_, VII, pp. 99–160, 1908.

[331] Cf. Taylor, _Chemistry of Colloids_, p. 252.

[332] Strasbürger, Ueber Cytoplasmastrukturen, etc. _Jahrb. f. wiss. Bot._ XXX, 1897; R. A. Harper, Kerntheilung und freie Zellbildung im Ascus, _ibid._; cf. Wilson, _The Cell in Development, etc._ pp. 53–55.

[333] Cf. A. Gurwitsch, _Morphologie und Biologie der Zelle_, 1904, pp. 169–185; Meves, Die Chondriosomen als Träger erblicher Anlagen, _Arch. f. mikrosk. Anat._ 1908, p. 72; J. O. W. Barratt, Changes in Chondriosomes, etc. _Q.J.M.S._ LVIII, pp. 553–566, 1913, etc.; A. Mathews, Changes in Structure of the Pancreas Cell, etc., _J. of Morph._ XV (Suppl.), pp. 171–222, 1899.

[334] The question whether chromosomes, chondriosomes or chromidia be the true vehicles or transmitters of “heredity” is not without its analogy to the older problem of whether the pineal gland or the pituitary body were the actual seat and domicile of the soul.

[335] Cf. C. C. Dobell, Chromidia and the Binuclearity Hypotheses; a review and a criticism, _Q.J.M.S._ LIII, 279–326, 1909; Prenant, A., Les Mitochondries et l’Ergastoplasme, _Journ. de l’Anat. et de la Physiol._ XLVI, pp. 217–285, 1910 (both with copious bibliography).

[336] Traube in particular has maintained that in differences of surface-tension we have the origin of the active force productive of osmotic currents, and that herein we find an explanation, or an approach to an explanation, of many phenomena which were formerly deemed peculiarly “vital” in their character. “Die Differenz der Oberflächenspannungen oder der Oberflächendruck eine Kraft darstellt, welche als treibende Kraft der Osmose, an die Stelle des nicht mit dem Oberflächendruck identischen osmotischen Druckes, zu setzen ist, etc.” (Oberflächendruck und seine Bedeutung im Organismus, _Pflüger’s Archiv_, CV, p. 559, 1904.) Cf. also Hardy (_Pr. Phys. Soc._ XXVIII, p. 116, 1916), “If the surface film of a colloid membrane separating two masses of fluid were to change in such a way as to lower the potential of the water in it, water would enter the region from both sides at once. But if the change of state were to be propagated as a wave of change, starting at one face and dying out at the other face, water would be carried along from one side of the membrane to the other. A succession of such waves would maintain a flow of fluid.”

[337] On the Distribution of Potassium in animal and vegetable Cells; _Journ. of Physiol._ XXXII, p. 95, 1905.

[338] The reader will recognise that there is a fundamental difference, and contrast, between such experiments as these of Professor Macallum’s and the ordinary staining processes of the histologist. The latter are (as a general rule) purely empirical, while the former endeavour to reveal the true microchemistry of the cell. “On peut dire que la microchimie n’est encore qu’à la période d’essai, et que l’avenir de l’histologie et spécialement de la cytologie est tout entier dans la microchimie” (Prenant, A., Méthodes et résultats de la Microchimie, _Journ. de l’Anat. et de la Physiol._ XLVI, pp. 343–404, 1910).

[339] Cf. Macallum, Presidential Address, Section I, _Brit. Ass. Rep._ (Sheffield), 1910, p. 744.

[340] In accordance with a simple _corollary_ to the Gibbs-Thomson law.

[341] It can easily be proved (by equating the increase of energy stored in an increased surface to the work done in increasing that surface), that the tension measured per unit breadth, _T__{_ab_}, is equal to the energy per unit area, _E__{_ab_}.

[342] The presence of this little liquid “bourrelet,” drawn from the material of which the partition-walls themselves are composed, is obviously tending to a reduction of the internal surface-area. And it may be that it is as well, or better, accounted for on this ground than on Plateau’s assumption that it represents a “surface of continuity.”

[343] A similar “bourrelet” is admirably seen at the line of junction between a floating bubble and the liquid on which it floats; in which case it constitutes a “masse annulaire,” whose mathematical properties and relation to the form of the _nearly_ hemispherical bubble, have been investigated by van der Mensbrugghe (cf. Plateau, _op. cit._, p. 386). The form of the superficial vacuoles in Actinophrys or Actinosphaerium involves an identical problem.

[344] In an actual calculation we must of course always take account of the tensions on _both sides_ of each film or membrane.

[345] Hofmeister, _Pringsheim’s Jahrb._ III, p. 272, 1863; _Hdb. d. physiol. Bot._ I, 1867, p. 129.

[346] Sachs, Ueber die Anordnung der Zellen in jüngsten Pflanzentheilen, _Verh. phys. med. Ges. Würzburg_, XI, pp. 219–242, 1877; Ueber Zellenanordnung und Wachsthum, _ibid._ XII, 1878; Ueber die durch Wachsthum bedingte Verschiebung kleinster Theilchen in trajectorischen Curven, _Monatsber. k. Akad. Wiss. Berlin_, 1880; _Physiology of Plants_, chap. xxvii, pp. 431–459, Oxford, 1887.

[347] Schwendener, Ueber den Bau und das Wachsthum des Flechtenthallus, _Naturf. Ges. Zürich_, Febr. 1860, pp. 272–296.

[348] Reinke, _Lehrbuch der Botanik_, 1880, p. 519.

[349] Cf. Leitgeb, _Unters. über die Lebermoose_, II, p. 4, Graz, 1881.

[350] Rauber, Neue Grundlegungen zur Kenntniss der Zelle, _Morph. Jahrb._ VIII, pp. 279, 334, 1882.

[351] _C. R. Acad. Sc._ XXXIII, p. 247, 1851; _Ann. de chimie et de phys._ (3), XXXIII, p. 170, 1851; _Bull. R. Acad. Belg._ XXIV, p. 531, 1857.

[352] Klebs, _Biolog. Centralbl._ VII, pp. 193–201, 1887.

[353] L. Errera, Sur une condition fondamentale d’équilibre des cellules vivantes, _C. R._, CIII, p. 822, 1886; _Bull. Soc. Belge de Microscopie_, XIII, Oct. 1886; _Recueil d’œuvres_ (_Physiologie générale_), 1910, pp. 201–205.

[354] L. Chabry, Embryologie des Ascidiens, _J. Anat. et Physiol._ XXIII, p. 266, 1887.

[355] Robert, Embryologie des Troques, _Arch. de Zool. exp. et gén._ (3), X, 1892.

[356] “Dass der Furchungsmodus etwas für das Zukünftige unwesentliches ist,” _Z. f. w. Z._ LV, 1893, p. 37. With this statement compare, or contrast, that of Conklin, quoted on p. 4; cf. also pp. 157, 348 (footnotes).

[357] de Wildeman, Etudes sur l’attache des cloisons cellulaires, _Mém. Couronn. de l’Acad. R. de Belgique_, LIII, 84 pp., 1893–4.

[358] It was so termed by Conklin in 1897, in his paper on Crepidula (_J. of Morph._ XIII, 1897). It is the _Querfurche_ of Rabl (_Morph. Jahrb._ V, 1879); the _Polarfurche_ of O. Hertwig (_Jen. Zeitschr._ XIV, 1880); the _Brechungslinie_ of Rauber (Neue Grundlage zur K. der Zelle, _M. Jb._ VIII, 1882). It is carefully discussed by Robert, Dév. des Troques, _Arch. de Zool. Exp. et Gén._ (3), X, 1892, p. 307 seq.

[359] Thus Wilson (_J. of Morph._ VIII, 1895) declared that in Amphioxus the polar furrow was occasionally absent, and Driesch took occasion to criticise and to throw doubt upon the statement (_Arch. f. Entw. Mech._ I, 1895, p. 418).

[360] Precisely the same remark was made long ago by Driesch: “Das so oft sehematisch gezeichnete Vierzellenstadium mit zwei sich in zwei Punkten scheidende Medianen kann man wohl getrost aus der Reihe des Existierenden streichen,” _Entw. mech. Studien, Z. f. w. Z._ LIII, p. 166, 1892. Cf. also his _Math. mechanische Bedeutung morphologischer Probleme der Biologie_, Jena, 59 pp. 1891.

[361] Compare, however, p. 299.

[362] _Ricreatione dell’ occhio e della mente, nell’ Osservatione delle Chiocciole_, Roma, 1681.

[363] Cf. some of J. H. Vincent’s photographs of ripples, in _Phil. Mag._ 1897–1899; or those of F. R. Watson, in _Phys. Review_, 1897, 1901, 1916. The appearance will depend on the rate of the wave, and in turn on the surface-tension; with a low tension one would probably see only a moving “jabble.” FitzGerald thought diatom-patterns might be due to electromagnetic vibrations (_Works_, p. 503, 1902).

[364] Cushman, J. A. and Henderson, W. P., _Amer. Nat._ XL, pp. 797–802, 1906.

[365] This does not merely neglect the _broken_ ones but _all_ whose centres lie between this circle and a hexagon inscribed in it.

[366] For more detailed calculations see a paper by “H.M.” [? H. Munro], in _Q. J. M. S._ VI, p. 83, 1858.

[367] Cf. Hartog, The Dual Force of the Dividing Cell, _Science Progress_ (n.s.), I, Oct. 1907, and other papers. Also Baltzer, _Ueber mehrpolige Mitosen bei Seeigeleiern_, Inaug. Diss. 1908.

[368] Observations sur les Abeilles, _Mém. Acad. Sc. Paris_, 1712, p. 299.

[369] As explained by Leslie Ellis, in his essay “On the Form of Bees’ Cells,” in _Mathematical and other Writings_, 1853, p. 353; cf. O. Terquem, _Nouv. Ann. Math._ 1856, p. 178.

[370] _Phil. Trans._ XLII, 1743, pp. 565–571.

[371] _Mém. de l’Acad. de Berlin_, 1781.

[372] Cf. Gregory, _Examples_, p. 106, Wood’s _Homes without Hands_, 1865, p. 428, Mach, _Science of Mechanics_, 1902, p. 453, etc., etc.

[373] _Origin of Species_, ch. VIII (6th ed., p. 221). The cells of various bees, humble-bees and social wasps have been described and mathematically investigated by K. Müllenhoff, _Pflüger’s Archiv_ XXXII, p. 589, 1883; but his many interesting results are too complex to epitomise. For figures of various nests and combs see (e.g.) von Büttel-Reepen, _Biol. Centralbl._ XXXIII, pp. 4, 89, 129, 183, 1903.

[374] Darwin had a somewhat similar idea, though he allowed more play to the bee’s instinct or conscious intention. Thus, when he noticed certain half-completed cell-walls to be concave on one side and convex on the other, but to become perfectly flat when restored for a short time to the hive, he says: “It was absolutely impossible, from the extreme thinness of the little plate, that they could have effected this by gnawing away the convex side; and I suspect that the bees in such cases stand on opposite sides and push and bend the ductile and warm wax (which as I have tried is easily done) into its proper intermediate plane, and thus flatten it.”

[375] Since writing the above, I see that Müllenhoff gives the same explanation, and declares that the waxen wall is actually a _Flüssigkeitshäutchen_, or liquid film.

[376] Bonnet criticised Buffon’s explanation, on the ground that his description was incomplete; for Buffon took no account of the Maraldi pyramids.

[377] Buffon, _Histoire Naturelle_, IV, p. 99. Among many other papers on the Bee’s cell, see Barclay, _Mem. Wernerian Soc._ II, p. 259 (1812), 1818; Sharpe, _Phil. Mag._ IV, 1828, pp. 19–21; L. Lalanne, _Ann. Sci. Nat._ (2) Zool. XIII, pp. 358–374, 1840; Haughton, _Ann. Mag. Nat. Hist._ (3), XI, pp. 415–429, 1863; A. R. Wallace, _ibid._ XII, p. 303, 1863; Jeffries Wyman. _Pr. Amer. Acad. of Arts and Sc._ VII, pp. 68–83, 1868; Chauncey Wright, _ibid._ IV, p. 432, 1860.

[378] Sir W. Thomson, On the Division of Space with Minimum Partitional Area, _Phil. Mag._ (5), XXIV, pp. 503–514, Dec. 1887; cf. _Baltimore Lectures_, 1904, p. 615.

[379] Also discovered independently by Sir David Brewster, _Trans. R.S.E._ XXIV, p. 505, 1867, XXV, p. 115, 1869.

[380] Von Fedorow had already described (in Russian) the same figure, under the name of cubo-octahedron, or hepta-parallelohedron, limited however to the case where all the faces are plane. This figure, together with the cube, the hexagonal prism, the rhombic dodecahedron and the “elongated dodecahedron,” constituted the five plane-faced, parallel-sided figures by which space is capable of being completely filled and symmetrically partitioned; the series so forming the foundation of Von Fedorow’s theory of crystalline structure. The elongated dodecahedron is, essentially, the figure of the bee’s cell.

[381] F. R. Lillie, Embryology of the Unionidae, _Journ. of Morphology_, X, p. 12, 1895.

[382] E. B. Wilson, The Cell-lineage of Nereis, _Journ. of Morphology_, VI, p. 452, 1892.

[383] It is highly probable, and we may reasonably assume, that the two little triangles do not actually meet at an apical _point_, but merge into one another by a twist, or minute surface of complex curvature, so as not to contravene the normal conditions of equilibrium.

[384] Professor Peddie has given me this interesting and important result, but the mathematical reasoning is too lengthy to be set forth here.

[385] Cf. Rhumbler, _Arch. f. Entw. Mech._ XIV, p. 401, 1902; Assheton, _ibid._ XXXI, pp. 46–78, 1910.

[386] M. Robert (_l. c._ p. 305) has compiled a long list of cases among the molluscs and the worms, where the initial segmentation of the egg proceeds by equal or unequal division. The two cases are about equally numerous. But like many other writers, he would ascribe this equality or inequality rather to a provision for the future than to a direct effect of immediate physical causation: “Il semble assez probable, comme on l’a dit souvent, que la plus grande taille d’un blastomère est liée à l’importance et au développement précoce des parties du corps qui doivent en naître: il y aurait là une sorte de reflet des stades postérieures du développement sur les premières phénomènes, ce que M. Ray Lankester appelle _precocious segregation_. Il faut avouer pourtant qu’on est parfois assez embarrassé pour assigner une cause à pareilles différences.”

[387] The principle is well illustrated in an experiment of Sir David Brewster’s (_Trans. R.S.E._ XXV, p. 111, 1869). A soap-film is drawn over the rim of a wine-glass, and then covered by a watch-glass. The film is inclined or shaken till it becomes attached to the glass covering, and it then immediately changes place, leaving its transverse position to take up that of a spherical segment extending from one side of the wine-glass to its cover, and so enclosing the same volume of air as formerly but with a great economy of surface, precisely as in the case of our spherical partition cutting off one corner of a cube.

[388] Cf. Wildeman, _Attache des Cloisons_, etc., pls. 1, 2.

[389] _Nova Acta K. Leop. Akad._ XI, 1, pl. IV.

[390] Cf. _Protoplasmamechanik_, p. 229: “Insofern liegen also die Verhältnisse hier wesentlich anders als bei der Zertheilung hohler Körperformen durch flüssige Lamellen. Wenn die Membran bei der Zelltheilung die von dem Prinzip der kleinsten Flächen geforderte Lage und Krümmung annimmt, so werden wir den Grund dafür in andrer Weise abzuleiten haben.”

[391] There is, I think, some ambiguity or disagreement among botanists as to the use of this latter term: the sense in which I am using it, viz. for any partition which meets the outer or peripheral wall at right angles (the strictly _radial_ partition being for the present excluded), is, however, clear.

[392] _Cit._ Plateau, _Statique des Liquides_, i, p. 358.

[393] Even in a Protozoon (_Euglena viridis_), when kept alive under artificial compression, Ryder found a process of cell-division to occur which he compares to the segmenting blastoderm of a fish’s egg, and which corresponds in its essential features with that here described. _Contrib. Zool. Lab. Univ. Pennsylvania_, I, pp. 37–50, 1893.

[394] This, like many similar figures, is manifestly drawn under the influence of Sachs’s theoretical views, or assumptions, regarding orthogonal trajectories, coaxial circles, confocal ellipses, etc.

[395] Such preconceptions as Rauber entertained were all in a direction likely to lead him away from such phenomena as he has faithfully depicted. Rauber had no idea whatsoever of the principles by which we are guided in this discussion, nor does he introduce at all the analogy of surface-tension, or any other purely physical concept. But he was deeply under the influence of Sachs’s rule of rectangular intersection; and he was accordingly disposed to look upon the configuration represented above in Fig. 168, 6, as the most typical or most primitive.

[396] Cf. Rauber, Neue Grundlage z. K. der Zelle, _Morph. Jahrb._ VIII, 1883, pp. 273, 274:

“Ich betone noch, dass unter meinen Figuren diejenige gar nicht enthalten ist, welche zum Typus der Batrachierfurchung gehörig am meisten bekannt ist .... Es haben so ausgezeichnete Beobachter sie als vorhanden beschrieben, dass es mir nicht einfallen kann, sie überhaupt nicht anzuerkennen.”

[397] Roux’s experiments were performed with drops of paraffin suspended in dilute alcohol, to which a little calcium acetate was added to form a soapy pellicle over the drops and prevent them from reuniting with one another.

[398] Cf. (e.g.) Clerk Maxwell, On Reciprocal Figures, etc., _Trans. R. S. E._ XXVI, p. 9, 1870.

[399] See Greville, K. R., Monograph of the Genus Asterolampra, _Q.J.M.S._ VIII, (Trans.), pp. 102–124, 1860; cf. IBID. (n.s.), II, pp. 41–55, 1862.

[400] The same is true of the insect’s wing; but in this case I do not hazard a conjectural explanation.

[401] _Ann. Mag. N. H._ (2), III, p. 126, 1849.

[402] _Phil. Trans._ CLVII, pp. 643–656, 1867.

[403] Sachs, _Pflanzenphysiologie_ (_Vorlesung_ XXIV), 1882; cf. Rauber, Neue Grundlage zur Kenntniss der Zelle, _Morphol. Jahrb._ VIII, p. 303 _seq._, 1883; E. B. Wilson, Cell-lineage of Nereis, _Journ. of Morphology_, VI, p. 448, 1892, etc.

[404] In the following account I follow closely on the lines laid down by Berthold; _Protoplasmamechanik_, cap. vii. Many botanical phenomena identical and similar to those here dealt with, are elaborately discussed by Sachs in his _Physiology of Plants_ (chap. xxvii, pp. 431–459, Oxford, 1887); and in his earlier papers, Ueber die Anordnung der Zellen in jüngsten Pflanzentheilen, and Ueber Zellenanordnung und Wachsthum (_Arb. d. botan. Inst. Würzburg_, 1878, 1879). But Sachs’s treatment differs entirely from that which I adopt and advocate here: his explanations being based on his “law” of rectangular succession, and involving complicated systems of confocal conics, with their orthogonally intersecting ellipses and hyperbolas.

[405] Cf. p. 369.

[406] There is much information regarding the chemical composition and mineralogical structure of shells and other organic products in H. C. Sorby’s Presidential Address to the Geological Society (_Proc. Geol. Soc._ 1879, pp. 56–93); but Sorby failed to recognise that association with “organic” matter, or with colloid matter whether living or dead, introduced a new series of purely physical phenomena.

[407] Vesque, _Ann. des Sc. Nat._ (_Bot._) (5), XIX, p. 310, 1874.

[408] Cf. Kölliker, _Icones Histiologicae_, 1864, pp. 119, etc.

[409] In an interesting paper by Irvine and Sims Woodhead on the “Secretion of Carbonate of Lime by Animals” (_Proc. R. S. E._ XVI, 1889, p. 351) it is asserted that “lime salts, of whatever form, are deposited _only_ in vitally inactive tissue.”

[410] The tube of Teredo shews no trace of organic matter, but consists of irregular prismatic crystals: the whole structure “being identical with that of small veins of calcite, such as are seen in thin sections of rocks” (Sorby, _Proc. Geol. Soc._ 1879, p. 58). This, then, would seem to be a somewhat exceptional case of a shell laid down completely outside of the animal’s external layer of organic or colloid substance.

[411] _C. R. Soc. Biol. Paris_ (9), I, pp. 17–20, 1889; _C. R. Ac. Sc._ CVIII, pp. 196–8, 1889.

[412] Cf. Heron-Allen, _Phil. Trans._ (B), vol. CCVI, p. 262, 1915.

[413] See Leduc, _Mechanism of Life_ (1911), ch. X, for copious references to other works on the artificial production of “organic” forms.

[414] Lectures on the Molecular Asymmetry of Natural Organic Compounds, _Chemical Soc. of Paris_, 1860, and also in Ostwald’s _Klassiker d. ex. Wiss._ No. 28, and in _Alembic Club Reprints_, No. 14, Edinburgh, 1897; cf. Richardson, G. M., _Foundations of Stereochemistry_, N. Y. 1901.

[415] Japp, Stereometry and Vitalism, _Brit. Ass. Rep._ (Bristol), p. 813, 1898; cf. also a voluminous discussion in _Nature_, 1898–9.

[416] They represent the general theorem of which particular cases are found, for instance, in the asymmetry of the ferments (or _enzymes_) which act upon asymmetrical bodies, the one fitting the other, according to Emil Fischer’s well-known phrase, as lock and key. Cf. his Bedeutung der Stereochemie für die Physiologie, _Z. f. physiol. Chemie_, V, p. 60, 1899, and various papers in the _Ber. d. d. chem. Ges._ from 1894.

[417] In accordance with Emil Fischer’s conception of “asymmetric synthesis,” it is now held to be more likely that the process is synthetic than analytic: more likely, that is to say, that the plant builds up from the first one asymmetric body to the exclusion of the other, than that it “selects” or “picks out” (as Japp supposed) the right-handed or the left-handed molecules from an original, optically inactive, mixture of the two; cf. A. McKenzie, Studies in Asymmetric Synthesis, _Journ. Chem. Soc._ (Trans.), LXXXV, p. 1249, 1904.

[418] See for a fuller discussion, Hans Przibram, _Vitalität_, 1913, Kap. iv, Stoffwechsel (Assimilation und Katalyse).

[419] Cf. Cotton, _Ann. de Chim. et de Phys._ (7), VIII, pp. 347–432 (cf. p. 373), 1896.

[420] Byk, A., Zur Frage der Spaltbarkeit von Razemverbindungen durch Zirkularpolarisiertes Licht, ein Beitrag zur primären Entstehung optisch-activer Substanzen, _Zeitsch. f. physikal. Chemie_, XLIX, p. 641, 1904. It must be admitted that further positive evidence on these lines is still awanting.

[421] Cf. (_int. al._) Emil Fischer, _Untersuchungen über Aminosäuren, Proteine_, etc. Berlin, 1906.

[422] Japp, _l. c._ p. 828.

[423] Rainey, G., On the Elementary Formation of the Skeletons of Animals, and other Hard Structures formed in connection with Living Tissue, _Brit. For. Med. Ch. Rev._ XX, pp. 451–476, 1857; published separately with additions, 8vo. London, 1858. For other papers by Rainey on kindred subjects see _Q. J. M. S._ VI (_Tr. Microsc. Soc._), pp. 41–50, 1858, VII, pp. 212–225, 1859, VIII, pp. 1–10, 1860, I (n. s.), pp. 23–32, 1861. Cf. also Ord, W. M., On Molecular Coalescence, and on the influence exercised by Colloids upon the Forms of Inorganic Matter, _Q. J. M. S._ XII, pp. 219–239, 1872; and also the early but still interesting observations of Mr Charles Hatchett, Chemical Experiments on Zoophytes; with some observations on the component parts of Membrane, _Phil. Trans._ 1800. pp. 327–402.

[424] Cf. Quincke, Ueber unsichtbare Flüssigkeitsschichten, _Ann. der Physik_, 1902.

[425] See for instance other excellent illustrations in Carpenter’s article “Shell,” in Todd’s _Cyclopædia_, vol. IV. pp. 550–571, 1847–49. According to Carpenter, the shells of the mollusca (and also of the crustacea) are “essentially composed of _cells_, consolidated by a deposit of carbonate of lime in their interior.” That is to say, Carpenter supposed that the spherulites, or calcospherites of Harting, were, to begin with, just so many living protoplasmic cells. Soon afterwards however, Huxley pointed out that the mode of formation, while at first sight “irresistibly suggesting a cellular structure, ... is in reality nothing of the kind,” but “is simply the result of the concretionary manner in which the calcareous matter is deposited”; _ibid._ art. “Tegumentary Organs,” vol. V, p. 487, 1859. Quekett (_Lectures on Histology_, vol. II, p. 393, 1854, and _Q. J. M. S._ XI, pp. 95–104, 1863) supported Carpenter; but Williamson (Histological Features in the Shells of the Crustacea, _Q. J. M. S._ VIII, pp. 35–47, 1860) amply confirmed Huxley’s view, which in the end Carpenter himself adopted (_The Microscope_, 1862, p. 604). A like controversy arose later in regard to corals. Mrs Gordon (M. M. Ogilvie) asserted that the coral was built up “of successive layers of calcified cells, which hang together at first by their cell-walls, and ultimately, as crystalline changes continue, form the individual laminae of the skeletal structures” (_Phil. Trans._ CLXXXVII, p. 102, 1896): whereas v. Koch had figured the coral as formed out of a mass of “Kalkconcremente” or “crystalline spheroids,” laid down outside the ectoderm, and precisely similar both in their early rounded and later polygonal stages (though von Koch was not aware of the fact) to the calcospherites of Harting (Entw. d. Kalkskelettes von Asteroides, _Mitth. Zool. St. Neapel_, III, pp. 284–290, pl. XX, 1882). Lastly Duerden shewed that external to, and apparently secreted by the ectoderm lies a homogeneous organic matrix or membrane, “in which the minute calcareous crystals forming the skeleton are laid down” (The Coral _Siderastraea radians_, etc., _Carnegie Inst. Washington_, 1904, p. 34). Cf. also M. M. Ogilvie-Gordon, _Q. J. M. S._ XLIX, p. 203, 1905, etc.

[426] Cf. Claparède, _Z. f. w. Z._ XIX, p. 604, 1869.

[427] Spicules extremely like those of the Alcyonaria occur also in a few sponges; cf. (e.g.), Vaughan Jennings, _Journ. Linn. Soc._ XXIII, p. 531, pl. 13, fig. 8, 1891.

[428] _Mem. Manchester Lit. and Phil. Soc._ LX, p. 11, 1916.

[429] Mummery, J. H., On Calcification in Enamel and Dentine, _Phil. Trans._ CCV (B), pp. 95–111, 1914.

[430] The artificial concretion represented in Fig. 202 is identical in appearance with the concretions found in the kidney of Nautilus, as figured by Willey (_Zoological Results_, p. lxxvi, Fig. 2, 1902).

[431] Cf. Taylor’s _Chemistry of Colloids_, p. 18, etc., 1915.

[432] This rule, undreamed of by Errera, supports and justifies the cardinal assumption (of which we have had so much to say in discussing the forms of cells and tissues) that the _incipient_ cell-wall behaves as, and indeed actually is, a liquid film (cf. p. 306).

[433] Cf. p. 254.

[434] Cf. Harting, _op. cit._, pp. 22, 50: “J’avais cru d’abord que ces couches concentriques étaient produites par l’alternance de la chaleur ou de la lumière, pendant le jour et la nuit. Mais l’expérience, expressément instituée pour examiner cette question, y a répondu négativement.”

[435] Liesegang, R. E., _Ueber die Schichtungen bei Diffusionen_, Leipzig, 1907, and other earlier papers.

[436] Cf. Taylor’s _Chemistry of Colloids_, pp. 146–148, 1915.

[437] Cf. S. C. Bradford, The Liesegang Phenomenon and Concretionary Structure in Rocks, _Nature_, XCVII, p. 80, 1916; cf. _Sci. Progress_, X, p. 369, 1916.

[438] Cf. Faraday, On Ice of Irregular Fusibility, _Phil. Trans._, 1858, p. 228; _Researches in Chemistry, etc._, 1859, p. 374; Tyndall, _Forms of Water_, p. 178, 1872; Tomlinson, C., On some effects of small Quantities of Foreign Matter on Crystallisation, _Phil. Mag._ (5) XXXI, p. 393, 1891, and other papers.

[439] A Study in Crystallisation, _J. of Soc. of Chem. Industry_, XXV, p. 143, 1906.

[440] _Ueber Zonenbildung in kolloidalen Medien_, Jena, 1913.

[441] _Verh. d. d. Zool. Gesellsch._ p. 179, 1912.

[442] _Descent of Man_, II, pp. 132–153, 1871.

[443] As a matter of fact, the phenomena associated with the development of an “ocellus” are or may be of great complexity, inasmuch as they involve not only a graded distribution of pigment, but also, in “optical” coloration, a symmetrical distribution of structure or form. The subject therefore deserves very careful discussion, such as Bateson gives to it (_Variation_, chap. xii). This, by the way, is one of the very rare cases in which Bateson appears inclined to suggest a purely physical explanation of an organic phenomenon: “The suggestion is strong that the whole series of rings (in _Morpho_) may have been formed by some one central disturbance, somewhat as a series of concentric waves may be formed by the splash of a stone thrown into a pool, etc.”

[444] Cf. also Sir D. Brewster, On optical properties of Mother of Pearl, _Phil. Trans._ 1814, p. 397.

[445] Biedermann, W., Ueber die Bedeutung von Kristallisationsprozessen der Skelette wirbelloser Thiere, namentlich der Molluskenschalen, _Z. f. allg. Physiol._ I, p. 154, 1902; Ueber Bau und Entstehung der Molluskenschale, _Jen. Zeitschr._ XXXVI, pp. 1–164, 1902. Cf. also Steinmann, Ueber Schale und Kalksteinbildungen, _Ber. Naturf. Ges. Freiburg i. Br_ IV, 1889; Liesegang, _Naturw. Wochenschr._ p. 641, 1910.