Plants: influence of heat, =I=, 29;

effect of solar rays, =I=, 31–6, 500, 557;

chemical composition, =I=, 40–1;

heat generation, =I=, 47;

phosphorescence, =I=, 49;

electricity, =I=, 51;

sensible motion, =I=, 56–7, 58;

metabolism, =I=, 62–7, 70;

vital changes, =I=, 86, 87, 91, 94;

simulation by crystals, =I=, 96;

vital adjustments, =I=, 102;

length and complexity of life, =I=, 103–4;

biological classification, =I=, 125;

growth, =I=, 136, 138, 140, 143, 145–9, 153, 160–1; =II=, 401–2;

development, =I=, 163–5, 167–70, 272;

weight, temperature, and self-mobility, =I=, 174;

function, =I=, 174–8;

structure, =I=, 194–6; =II=, 21;

animal structure contrasted, =I=, 196;

function and structure, =I=, 200;

vicarious function, =I=, 208–9;

waste and repair, =I=, 213, 220;

physiological units, =I=, 225–6, 317, 360;

adaptation, =I=, 227;

what is an individual? =I=, 244–6, 250–1;

genesis, =I=, 270, 271, 272–3, 274, 276–8, 279–85;

relation of nutrition to growth and genesis, =I=, 284–9, 294,

295–300, 642; =II=, 39;

ovule homologues, =I=, 288;

natural selection, =I=, 294–8, 532, 533; =II=, 51;

heredity, =I=, 301–4, 308, 358–60;

variation, =I=, 320, 323–4, 325–6;

fertilization, =I=, 340–5;

classification, =I=, 377–80, 389–90;

distribution, =I=, 396–400, 401–3, 404–12, 478–9, 556;

special creation and parasitism, =I=, 428;

evolution hypothesis, =I=, 434, 443, 449–50;

rudimentary organs, =I=, 474, 475, 556;

varied media, =I=, 484; =II=, 32;

alien and native species in New Zealand, =I=, 477;

E. Darwin and Lamarck on evolution of, =I=, 490–8;

geologic changes affecting, =I=, 501–3, 557;

interdependence of animals and, =I=, 504–6, 514; =II=, 398;

complexity of influences affecting, =I=, 506;

direct equilibration, =I=, 523–5;

indirect, =I=, 532, 533;

seed distribution, =I=, 546;

wood development, =II=, 285–7, 289, 567–97;

interdependence, =II=, 402–3, 404;

insect relations, =II=, 406–7;

adaptation and multiplication, =II=, 411–6;

rhythm in numbers, =II=, 419;

growth and asexual genesis, =II=, 439–42;

growth and sexual genesis, =II=, 448–51;

expenditure, =II=, 467;

horticulture, nutrition, and genesis, =II=, 477;

tree development, =II=, 553;

circulation and wood formation, =II=, 567–92;

dye permeability and circulation, =II=, 569–74, 577–81, 584, 586;

_résumé_ on circulation and wood formation, =II=, 592–7.

(_See also_ Multiplication, Morphology, _and_ Physiology.)

Plasmodium, dissolution of, =I=, 185.

Plato, ἰδέα of, =II=, 550.

_Platyhelminthes_: transverse fission, =II=, 101;

segmented and non-segmented types, =II=, 102, 107;

symmetry, =II=, 195, 197;

multiplication and growth, =II=, 488–9.

Plethora, fertility and, =II=, 480–4, 511.

_Pleurococcaceæ_, unicellular form, =II=, 21, 134.

_Pleuronectidæ_: symmetry and location of eyes, =II=, 205;

outer tissue, =II=, 387.

_Plumatella_: metagenesis, =I=, 277;

symmetry, =II=, 195.

_Podostemaceæ_, undeveloped circulatory system, =II=, 274.

Polar bodies, hypothesis concerning extrusion of, =I=, 266–8.

Polarity, organic, of physiological units, =I=, 226, 315, 317, 332,

350–1, 701–6.

Polyatomic compounds (_see_ Chemistry).

_Polychætæ_, anomalous development in _Myrianida_, =I=, 361.

_Polycytharia_, integration, =II=, 90, 124.

_Polygastrica_, aggregation, =I=, 586.

Polymerism: of compounds, =I=, 9, 11, 25;

nerve tissue, =II=, 356.

_Polypori_, symmetry and environment, =II=, 139.

Polyps (see _Cœlenterata_).

_Polyzoa_: size, =I=, 140;

multiaxial development, =I=, 165;

structural indefiniteness, =I=, 173;

functional differentiation, =I=, 202;

trochophoral kinship, =I=, 447;

integration, =II=, 93–4, 96, 124;

symmetry, =II=, 194, 207;

vascular system, =II=, 340;

gemmation, =II=, 444.

Poor Laws, and natural selection, =II=, 532.

_Population, A Theory of_, =I=, 265, 577–601; =II=, 411.

Potato: simulated growth, =I=, 136;

vicarious function of tuber, =I=, 209; =II=, 255;

sub-species, =I=, 302;

dye absorption, =II=, 279.

Preservation: fertility and self-, =I=, 581; =II=, 423, 430;

nutrition, =II=, 493.

“Progress; its Law and Cause,” theory of species differentiation,

=I=, 568.

Projectiles, factors in flight of, =I=, 450–1.

Proteids: metabolic function, =I=, 67, 68, 69, 72, 76;

complexity of molecule, =I=, 122.

Protein: evolution, =I=, 23, 24;

isomerism, =I=, 700, 703, 704.

_Proteus_, degeneration of eye, =I=, 613.

_Protodrilus_, intestine segmentation, =II=, 125.

_Protophyta_: internal movements, =I=, 56;

limit of growth, =I=, 138;

development, =I=, 164;

structure, =I=, 173, 181–3;

self-mobility, =I=, 175;

individuality, =I=, 245;

multiplication, =I=, 270, 276, 279, 581, 584–5; =II=, 439, 462;

genesis and nutrition, =I=, 295;

unicellular, =II=, 21;

central aggregation, =II=, 24;

symmetry, =II=, 134;

tissues, =II=, 244, 249;

primary differentiation, =II=, 385;

primordial type, =II=, 398;

symbiosis, =II=, 400.

Protoplasm: self-increasing function of primordial, =I=, 63–4;

plant metabolism, =I=, 65–7;

complexity, =I=, 122, 253–5;

differentiation in simple organisms, =I=, 182–3;

continuity and inter-circulation, =I=, 190–2, 371, 629; =II=, 21,

620;

“streaming,” =I=, 253;

structure, =I=, 253–5.

(_See also_ Cell.)

_Protozoa_: inorganic components, =I=, 17;

locomotion, =I=, 58, 175; =II=, 14;

vital changes shown by, =I=, 94;

limitation of growth, =I=, 138;

development, =I=, 164;

structure, =I=, 173, 181–3;

incipient differentiation, =I=, 198, 391; =II=, 299, 309;

multiplication, =I=, 270, 276, 279, 280, 582, 584; =II=, 442,

451–2;

genesis and nutrition, =I=, 295;

distribution, =I=, 396;

parasites infesting, =I=, 427;

Weismann’s hypothesis of immortality, =I=, 637;

“spontaneous generation,” =I=, 697–701;

non-nucleated, =II=, 20;

primary aggregate, =II=, 86–7, 124;

progressing integration, =II=, 89–91, 124;

symmetry, =II=, 186;

primordial plant-animal type, =II=, 397–8;

symbiosis, =II=, 400.

Protyle, hypothetical chemical unit, =I=, 22, 23.

Pseud-axial development, vegetal, =II=, 28–9, 30.

Pseudo-foliar development, vegetal, =II=, 26–8, 30.

_Psychidæ_: parthenogenesis, =I=, 275;

sexual dimorphism, =I=, 683.

Psychology: reasoning and definition of life, =I=, 81–8;

correspondence shown by _recognition_, =I=, 95;

contrasted with physiology, =I=, 127;

departments of, =I=, 127–8;

vicarious function, =I=, 209;

waste and repair in sensory organs, =I=, 217;

sensory adaptability, =I=, 229, 231, 232;

inheritance of sensory defects, =I=, 306;

musical talent, =I=, 311–2;

intellectual progress and special creation hypothesis, =I=, 417;

special creation a pseud-idea, =I=, 420, 429, 433, 554;

legitimacy of evolution hypothesis, =I=, 433–5, 439, 554;

embryology of ideas, =I=, 450, 457;

persistent formative power unrepresentable, =I=, 492;

E. Darwin’s and Lamarck’s theory of desires, =I=, 494;

natural selection and brain evolution, =I=, 553;

genesis and cerebral activity, =I=, 594; =II=, 512–4, 516–9, 530;

heredity and distribution of tactual perceptiveness, =I=, 602–8,

646, 665–6, 672, 692;

inconceivability of the negation, =I=, 675;

vitiation of evidence, =II=, 88;

repetition and perception, =II=, 143;

differentiation of sensory organs, =II=, 317–20;

differentiation of nerve tissue, =II=, 355–61;

functional integration, =II=, 376;

also integration, =II=, 380–2;

equilibration of nerve discharge, =II=, 393;

human fertility and nerve development, =II=, 466, 532;

future human evolution, =II=, 523–5, 527;

human evolution and genesis, =II=, 529–31;

future mental development, =II=, 535;

origin of vertebrate type, =II=, 598–600.

_Pteridophyta_: size attained by, =I=, 138, 139;

homologies, =II=, 80–1, 82;

frond surface differentiation, =II=, 260.

_Pteropoda_: bilateral symmetry, =II=, 201;

dermal respiration, =II=, 310.

Ptyaline, metabolic function, =I=, 69.

Punjabis, inheritance of acquired osteological peculiarities, =I=,

689.

_Pyrosomidæ_: phosphorescence, =I=, 47;

integration, =I=, 588; =II=, 97.

Quagga, telegonic transmission of markings to offspring of mare,

=I=, 624, 627, 646.

Quills, development, =II=, 314–6.

Rabbit: activity and muscle colour, =II=, 365;

over-running checked by weasels, =II=, 405;

expenditure and genesis, =II=, 472.

Radial, definition, =II=, 148.

_Radiolaria_: unicentral development, =I=, 163;

secondary aggregation, =II=, 88;

symmetry, =II=, 187.

_Radula_, development of roots from leaflets, =II=, 34.

_Rafflesiaceæ_: homogenesis, =I=, 272;

tissue differentiation, =II=, 274;

nutrition and genesis, =II=, 486.

Rat (see _Rodentia_).

Rathke, H., on vertebrate embryo, =II=, 119.

Ray, J., plant classification, =I=, 378.

Reasoning, compared with assimilation, =I=, 81–7.

Recapitulation, embryological, =I=, 453.

Regeneration (_see_ Repair).

Rejuvenescence, and sexual fertilization, =I=, 637; =II=, 613.

Remak, R., vertebrate embryo, =II=, 120.

Repair: continuity of, =I=, 216–9;

animal injuries, =I=, 219, 222–4; =II=, 102, 611;

deductive interpretation, =I=, 221–2;

theories of heredity and regenerative phenomena, =I=, 360–1.

Repetition of like parts, =II=, 126.

Reproduction (_see_ Multiplication).

_Reptilia_: growth and expenditure of force, =I=, 142;

sizes of ova and adult, =I=, 144;

longevity of crocodile, =I=, 154;

temperature, =I=, 174;

waste, =I=, 214;

distinctive characters, =I=, 392;

distribution in time, =I=, 409, 412;

vertebral segmentation, =I=, 470;

rudimentary limbs of snakes, =I=, 473;

fertility and development, =I=, 583, 598, 599;

regeneration, =I=, 589;

elongated form, =II=, 15;

supernumerary vertebræ, =II=, 123, 564;

bilateral symmetry, =II=, 203, 204;

Cope on segmentation in extinct, =II=, 225, 226;

activity and muscular colour, =II=, 365;

functional integration, =II=, 375;

outer tissue differentiation, =II=, 387;

Owen on skeleton, =II=, 560.

Resistance of media to locomotion, =II=, 15.

Respiratory System: effect of light, =I=, 31;

organic re-arrangement, =I=, 37;

cutaneous, =I=, 209;

air-cells of lungs, =I=, 254;

embryonic branchiæ of salamander, =I=, 457;

differentiation, =II=, 310–1, 333–8;

physiological integration, =II=, 374–5, 382;

vascular differentiation and integration, =II=, 377.

Retrograde metamorphoses, in animals, =II=, 12.

Retzius, G., superficial nerve-endings, =I=, 666.

Reversed Selection, =I=, 611, 612.

Rhabdospheres, calcareous armour and dynamic element in life, =I=,

119.

Rhizoids, foliar expansions, =II=, 50.

_Rhizopoda_: structure, =I=, 173;

undifferentiated function, =I=, 200;

a primary aggregate, =II=, 86;

symmetry, =II=, 186;

tissue differentiated, =II=, 299, 385;

motion of sarcode, =II=, 356;

symbiosis, =II=, 400.

Rhythm: astronomic and organic, =I=, 499, 557;

law of equilibration, =I=, 520–1;

in multiplication, =II=, 419.

Richeraud, Baron A., definition of life, =I=, 79.

Riley, C. V., on telegony, =I=, 645;

_Termites_, =I=, 680, 681;

pouch of Honey-ants, =I=, 684.

_Rodentia_: incursions, =I=, 399;

American types, =I=, 403;

fertility and development, =I=, 583, 599.

Rivinus, plant classification, =I=, 377.

Rokitansky, on false joints, =I=, 230.

Romanes, G. J.: on “cessation of selection,” =I=, 560–2;

isolation and species differentiation, =I=, 569;

“physiological selection,” =I=, 569–71;

panmixia, =I=, 649, 667;

influence of a previous sire on progeny, =I=, 649.

Röntgen rays, =I=, 121; =II=, 621.

Roots: developed from leaflets, =II=, 34;

physiological differentiation, =II=, 253–5, 270;

nutrition from leaves, =II=, 274;

size and function, =II=, 276.

_Rotiferæ_: latent vitality of desiccated, =I=, 117;

trochopore, =II=, 108, 109;

molluscan relationship, =II=, 115;

fertility and size, =II=, 453, 459.

Roux, W.: “intra-selection,” =I=, 676;

functional adaptation, =II=, 354.

Rudimentary organs: the definition of life and, =I=, 112;

natural selection and eyes of cave fauna, =I=, 309, 612–4, 647–9,

693;

evolution hypothesis, =I=, 472–5, 556;

limbs of whale, =I=, 668–9, 685, 693.

Ruminants, alimentary canal development, =II=, 327–9.

Salamander, embryonic branchiæ, =I=, 457.

_Salmonidæ_, reproduction and growth, =I=, 291–3; =II=, 454.

_Salpidæ_: heterogenesis, =I=, 272, 277;

integration, =I=, 588; =II=, 97.

Sap (_see_ Vascular system).

_Sarcina_: central aggregation, =II=, 24;

fertility, =II=, 440.

Savage, Dr., on “Heredity and Neurosis,” =I=, 313.

_Scenedesmus_, individuation, =II=, 24.

Scent: natural selection and keenness of, =I=, 610;

floral fertilization, =II=, 268–9;

animal protection, =II=, 434.

Schelling, E. W. J. von, definition of life, =I=, 78, 178.

Schleiden, J. M., on individuality, =I=, 245;

on liverworts, =II=, 50, 52;

algal indefiniteness, =II=, 296.

Science, complex revelations of, =I=, 252, 369, 450.

_Scyphomedusæ_, strobilization, =II=, 108.

Sea: changes and movements in, =I=, 83;

life in, lower than terrestrial, =I=, 104;

distribution, =I=, 396, 517;

change of media caused by, =I=, 481;

geologic influence, =I=, 502.

Seals: nail-bearing toes, =I=, 473;

_vibrissæ_, =II=, 317.

Seasons: reproductive periodicity, =I=, 299;

variations of genesis with, =II=, 484–5.

Sedgwick, Adam: on continuity of protoplasm in animals, =I=, 190,

629; =II=, 21;

zoological classification, =I=, 387;

discrimination of species in embryonic stages, =I=, 461;

persistence of ancestral traits, =I=, 463–4;

Archiannelidan segmentation, =II=, 109.

Sedgwick, Wm.: heredity and sex, =I=, 305, 314;

telegonic transmission of hypospadias, =I=, 646.

Seeds: nitrogenous, =I=, 40;

temperature of germinating, =I=, 47; =II=, 615;

vitalism and latent vitality of, =I=, 116–7;

variation in environment, =I=, 327;

natural selection among, =I=, 532.

Segmentation (metameric): special creation hypothesis, =I=, 468–9;

Huxley on number of somites in higher articulates, _ib._;

in annulose animals, =II=, 98–110, 111–5, 601–5;

simulated molluscan, =II=, 116;

in vertebrates, =II=, 125–7, 225–7, 606–7;

in elasmobranchs, =II=, 126.

Segregation: of growth, =I=, 136;

of like units, =I=, 179;

organic repair, =I=, 221;

variation, =I=, 331, 334;

heterogeneity, and definiteness of evolution, =I=, 514–6, 517–8;

morphological development, =II=, 7–9;

physiological units, =II=, 616.

Self-fertilization, animal and vegetal, =I=, 341–4, 353.

Senses, the (_see_ Psychology).

Sex: in Ascidian colonies, =I=, 247;

limitation of heredity by, =I=, 314–6;

correlated traits, =I=, 371–2, 513;

nutrition and determination of, in social insects, =I=, 655–60,

678–84, 686–9;

neural and hæmal traits, =I=, 683;

differentiation of organs, =II=, 303;

castration and growth, =II=, 459;

Julin on “castration parasitaire” in crustaceans, =II=, 493–6;

the object of fertilization, =II=, 613.

(_See also_ Fertilization.)

Sexual Selection (_see_ Natural Selection).

Sharp, D.: on insect somites, =I=, 469;

food habits of _Termites_, =I=, 686–7.

Sheep: contrasted with oxen, =I=, 158, 160;

crossing of English and French breeds, =I=, 625;

nutrition and genesis, =II=, 480.

Sherrington, Prof., on effects of nerve severance, =I=, 349.

Ship-building, interdependence of social functions, =I=, 237–9,

241.

Shipley, A. E.: segmentation of _Microstomida_, =II=, 102;

_Protodrilus_, =II=, 125.

Silica, colloid and crystalloid, =I=, 16.

Silicic acid: properties, =I=, 16;

isomerism, =I=, 59.

Silicon, allotropic, =I=, 4.

Silkworm disease, =I=, 622–3.

Simulation: of homology by analogy, =II=, 14, 485;

of segmented structure by molluscs, =II=, 116.

_Siphonophora_, specialization of component polyps, =II=, 95.

_Sirenia_, simulated fish form, =I=, 485.

Size (_see_ Growth).

Skeleton, vertebrate (see _Vertebrata_).

Skin: respiratory function, =I=, 209;

adaptability, =I=, 228; =II=, 312–4, 387;

transmitted peculiarities, =I=, 306;

Wallace on distribution of sensitiveness, =I=, 646–7;

differentiation, =II=, 215, 217, 304–7;

tegumentary development, =II=, 314–6, 387;

differentiation of sensory organs, =II=, 317–20;

and mucous membrane, =II=, 303–4, 321–2, 389.

“Skin friction,” and locomotion of aquatic animals, =I=, 156.

Skull (see _Vertebrata_).

Sleep, repair favoured by, =I=, 216.

Small-pox, blood changes from, =I=, 221.

Smith, Prof. W., on fertility of _diatomaceæ_, =II=, 440.

Smith, W. P., on telegony in calves and foals, =I=, 645.

Smith, W. W., on habits of Tetramorium, =I=, 660.

Snakes (see _Reptilia_).

“Social organism,” author’s essay on, =I=, 363, 676.

Sociology: environment and degree of life, =I=, 105–6;

functional differentiation, =I=, 204;

division of labour, =I=, 207, 363–4, 367;

functional interdependence, =I=, 237–9, 240–2;

autogenous development of units in colonies, =I=, 364, 367–8;

=II=, 620;

belief in social evolution, =I=, 432;

natural selection, =I=, 553; =II=, 532;

integration and differentiation, =II=, 378–9;

effects of population, =II=, 535–6;

equilibration, =II=, 537.

Soil, dependence of plant evolution on, =II=, 402.

_Solanum jasminoides_, organs of attachment, =II=, 276.

Solar system, autogenous development illustrated by distribution

of forces in, =I=, 366.

Sole, symmetry and location of eyes, =II=, 205.

Soma-plasm, Weismann’s theory of differentiation from germ-plasm,

=I=, 357, 622, 628–30, 633–44.

Somites (_see_ Segmentation).

Special creation: and evolution, =I=, 412, 415, 431;

improbabilities, =I=, 418–9, 430, 439, 554;

inconceivability, =I=, 420, 429, 431, 554;

of individuals and species, =I=, 421–4;

the implication of beneficence, =I=, 425–9;

summary, =I=, 429, 554;

Von Baer’s formula, =I=, 451–6;

vertebrate skeleton, =II=, 551, 556, 565.

Species: adaptation and stability, =I=, 242;

hereditary transmission, =I=, 301–4;

variation in wild and cultivated, =I=, 323–5, 326, 693;

gamogenesis and life of, =I=, 347–9;

physiological units, =I=, 362, 364, 369–71, 458; =II=, 613;

indefiniteness, =I=, 389, 445, 572;

special creation, =I=, 422–4;

instability of homogeneous, and differentiation of, =I=, 509–11,

515, 517–8, 550, 557;

persistence of, =I=, 516, 518; =II=, 10–11;

natural selection and equilibration, =I=, 543–8, 553, 557;

non-adaptive characters, =I=, 565;

morbid products as marks of, =I=, 567;

migration and isolation as causes of differentiation, =I=, 568–9;

increasing multiformity of aggregate, =II=, 396.

Specific gravity, of organisms and environment, =I=, 174, 177.

Spermatozoa}

Sperm-cell } (_see_ Fertilization).

Sphere: tendency of units to form, =I=, 15;

the embryonic form, =I=, 177;

symmetry, =II=, 131.

Spheroid, symmetry, =II=, 132.

Spiders (see _Arachnida_).

Spine (see _Vertebrata_).

Sponge: structure and dynamic element in life, =I=, 119;

multicentral development, =I=, 164;

units and aggregate, =I=, 185;

reproductive tissue, =I=, 283;

integration, =I=, 586; =II=, 90, 383;

physiological differentiation, =II=, 300, 386;

development and genesis, =II=, 463;

analogy from, =II=, 576.

Spontaneous generation: and heterogenesis, =I=, 270;

and evolution, =I=, 696–701, 703.

Stag, horns and correlated structures, =I=, 567, 670, 676–7, 692.

Stamens, and foliar homology, =II=, 44.

Starches: properties, =I=, 11;

transformations, =I=, 66, 68, 69, 70; =II=, 593.

Star-fishes (see _Asteroidea_).

Statoblasts, of _Plumatella_, =I=, 277.

Steenstrup, on “Alternate Generation,” =I=, 592.

Sterility (_see_ Multiplication).

Stickleback: ova, =II=, 454;

_bothriocephalus_ in, =II=, 490.

Stomach (_see_ Alimentary canal).

Stomata, distribution, =II=, 260–1.

Straight line, and evolution hypothesis, =I=, 433.

Strain: compression and tension of, =I=, 151; =II=, 209–12;

relation to mass, =I=, 155–7;

vegetal structure, =II=, 574–88, 592–6;

origin of vertebrate type, =II=, 600.

Strawberry: multiaxial development, =I=, 166;

multiplication, =II=, 441.

Strength, a vital attribute, =I=, 578.

Structure: appliances for generating motion, =I=, 75–7;

biological classification, =I=, 125–7, 129;

size and organic, =I=, 137;

growth and complexity, =I=, 138, 145, 161;

relation to environment, =I=, 172–8, 195–6;

of unicellular organisms, =I=, 181–3;

multicellular, =I=, 183–96;

Hertwig’s classification of tissues, =I=, 189;

continuity of units, =I=, 190–2;

systems of organs, =I=, 192;

division into universal and particular, =I=, 193–4;

general truths, =I=, 194–5;

plant and animal, contrasted, =I=, 195–6;

precedence of function or, =I=, 197, 211;

correlative complexity of function and, =I=, 200, 211;

progressive concomitant differentiation, =I=, 201–4;

physiological units, =I=, 225–6, 362, 364, 369–71; =II=, 613;

social and organic interdependence, =I=, 235–42;

varied by function, =I=, 334, 535; =II=, 217 (_see_ Acquired

Characters);

zoological classification, =I=, 390–2;

equilibration, =I=, 521, 557;

progress of, and genesis, =I=, 590–1; =II=, 462;

co-operation with function, =II=, 3;

evolution and increased, =II=, 4;

retrograde metamorphosis, =II=, 12;

simulated homologies, =II=, 13–14;

earliest organic forms, =II=, 19;

cylindrical vegetal, =II=, 57–62;

permanence and complexity, =II=, 295, 296;

function and epidermic, =II=, 312–4, 387;

and muscular, =II=, 369, 391;

adaptation and equilibration, =II=, 392;

persistence of force and physiological adaptation, =II=, 394;

evolution, =II=, 501–4.

(_See also_ Morphology.)

Struggle, for nutriment among components of an organism, =I=, 562,

676;

for existence (_see_ Natural Selection).

Struthers, Sir J.: on heredity, =I=, 305, 314;

digital variation, =I=, 321;

rudimentary limbs of whale, =I=, 668.

Strychnine, effects of, =I=, 54, 55.

Sturgeon, size of ova and adult, =I=, 144.

Sugars: properties, =I=, 10–11;

transformations, =I=, 38, 40, 66, 69, 70; =II=, 593.

Suicide, hereditary tendency to, =I=, 307.

Sulphur: allotropic, =I=, 4, 59;

organic evolution, =I=, 703.

Sun (_see_ Light).

Survival of the Fittest, the expression, =I=, 530, 610.

(_See_ Natural Selection.)

Swan, vertebræ of neck, =II=, 123.

Swiftness, a vital attribute, =I=, 578.

_Syllis ramosa_, lateral branching, =I=, 166, 361; =II=, 105, 108.

Symbiosis, =II=, 399, 400.

Symmetry (_see_ Morphology).

Syphilis, hereditary transmission, =I=, 623.

Tactual, Perceptiveness, heredity and the distribution of, =I=,

602–8, 633, 665, 666, 672, 692.

_Tænia_ (see _Entozoa_).

Tansley, A. G., =I=, vi; =II=, vi;

adaptation of reproductive activity to conditions in _Algæ_, =I=,

288–9;

shapes of _Caulerpa_, =II=, 22;

stem-thickening in extinct Thallophytes, =II=, 56;

natural selection and leaf-distribution, =II=, 179.

Tape-worm (see _Entozoa_).

Taste, dependent on chemical action, =I=, 54.

Teeth: hereditary transmission, =I=, 306;

suppression of mammalian, =I=, 457;

of uncivilized and civilized, =I=, 541, 693.

Tegumentary organs, origin of, =I=, 314–6.

Telegony, or the Influence of a previous sire on offspring, =I=,

624–7, 644–6, 649–50.

Temperature (_see_ Heat).

Tension (_see_ Strain).

_Termites_: fertility, =I=, 583; =II=, 493;

late development of sexual organs, =I=, 680;

nutrition and differentiation of forms, =I=, 681.

_Tetramorium_, utilization of aphides by, =I=, 660–1.

_Thallophyta_: size, =I=, 138, 139;

low co-ordination of parts, =I=, 164;

pseudo-foliar, =II=, 28;

“transition place,” =II=, 30;

simulation of higher types, =II=, 32;

secondary thickening in extinct species, =II=, 56;

sexual and asexual genesis, =II=, 84.

(See also _Algæ_.)

Tickling, physiology of, =I=, 76.

Tide (_see_ Sea).

Time, as a factor in growth, =II=, 77.

Tissue, Hertwig’s classification, =I=, 189.

(_See_ Physiology.)

Tongue, perceptiveness of tip, =I=, 606–8, 665, 672–3.

Tortoise: contrasted life of dog and, =I=, 103–4;

natural selection and carapace, =I=, 534.

“Transcendental Physiology,” =I=, 176.

Tree, as symbolizing phylogeny, =I=, 428, 452–3.

(_See_ Plants.)

_Trematoda_: agamogenesis, =I=, 277;

parasitism, =I=, 428;

alternate generation, =I=, 592.

Trembley, A., on the polyp, =I=, 223.

Trichinosis, in Germany, =I=, 428.

Trochophore, phyletic relationships shown by, =I=, 447; =II=,

108–9.

_Tubicolæ_: development, =II=, 100;

bilateral symmetry, =II=, 197.

_Tunicata_: gemmation, =I=, 588; =II=, 445;

alternate generation, =I=, 592;

integration, =II=, 93–4;

tertiary aggregation, =II=, 124;

symmetry, =II=, 194–5.

Tunny, size of ova and adult, =I=, 144.

_Turbellaria_: segmentation, =II=, 102;

symbiosis, =II=, 400.

Turnip: chlorophyll in roots, =I=, 209; =II=, 254;

vascular system, =II=, 281, 284, 578, 591, 596.

Twins: similarity of, =I=, 324;

traits of women bearing, =II=, 457.

“Types, persistent,” Huxley on, =I=, 408.

Ulcer, dermal structure, =II=, 306.

Ultimate Reality, incomprehensibility of, =I=, 120.

_Ulva_: cell multiplication, =II=, 26;

outer tissue, =II=, 256.

_Umbelliferæ_: floral symmetry, =II=, 171;

axial and foliar organs, =II=, 541–6.

United States: cases of telegony, =I=, 644–5;

birth-rate, =II=, 520.

Units: differentiation and dissimilarity, =I=, 20;

“protyle,” =I=, 22–3;

shapes in higher types, =I=, 164;

differential assimilation, =I=, 180;

primordial organic, =I=, 181;

morphological composition, =I=, 184–7, 194, 252; =II=, 5, 7–9,

21, 79, 85–6;

segregation and organic repair, =I=, 221–2, 222–6;

chemical, morphological, and physiological, =I=, 225–6; =II=,

612;

stability, =I=, 339;

instability and heterogeneity of organic, =I=, 350;

Darwin’s gemmules, =I=, 356–60, 362, 372;

Weissmann’s germ-plasm (_q. v._) _ib._;

sociological comparison, =I=, 363–8;

specific proclivities in embryogeny, =I=, 458;

phænogamic, =II=, 73, 151;

annulose, =II=, 105;

incident force and homologous, =II=, 159;

morphological summary, =II=, 233.

(_See also_ Physiological Units.)

“Universal Postulate,” =I=, 675.

Unsymmetrical, definition, =II=, 131.

Urea, muscular energy and excretion, =I=, 72.

Van Beneden, P. J., on _Tænia_, =II=, 103.

Variation: digital, =I=, 331;

effects of parental conditions, =I=, 324;

of altered function, =I=, 325, 334, 693;

dissimilarity of initial conditions, =I=, 327–32, 333;

“spontaneous,” =I=, 328, 513, 697; =II=, 529;

persistence of force, =I=, 335;

physiological units, =I=, 348–54, 360, 369, 371–3; =II=, 614–7,

622–3;

Weismann’s germ-plasm theory, =I=, 357–8, 372–3, 671, 677; =II=,

622;

equilibration and vegetal, =I=, 523–5;

Weismann’s panmixia theory, =I=, 561–3, 649, 667–9, 671, 685;

reproductive organs, =I=, 570;

natural selection and concomitant, =I=, 614–21, 653, 664, 674,

692;

and disused organs, =I=, 648, 668;

plus and minus. =I=, 667, 685;

Masters on correlated, in plants, =II=, 298, 621–2;

equilibration of favourable, =II=, 394.

Vascular System: effects of vegeto-alkalies, =I=, 55;

nutrition, =I=, 146, 148;

embryonic development, =I=, 169;

structural traits, =I=, 192, 193;

function, =I=, 199;

of Ascidians. =I=, 202;

functional differentiation and integration, =I=, 205–6;

organic repair, =I=, 217, 221–2;

effect of function, =I=, 229, 234–5, 236;

equilibration, =I=, 535;

community in compound organisms, =I=, 588;

development of vegetal, =II=, 273–5, 279–84, 285–8, 388;

differentiation of, summary, =II=, 288–90, 388;

differentiation of animal, =II=, 339–44;

osseous development, =II=, 347–51;

muscularity, =II=, 364;

muscular colour, =II=, 365–9;

heart-motor apparatus, =II=, 374;

differentiation and integration in animal, =II=, 376–9, 383;

wood formation, =II=, 567–92;

_résumé_ of wood formation, =II=, 592–7.

_Vaucheria_, reproduction, =I=, 279, 289.

Vegetative System, co-ordination of actions in, =I=, 578.

Vegeto-alkalies, physiological effects of, =I=, 54–5.

Velocity, of moving bodies, =II=, 219–20.

_Vertebrata_: size, =I=, 139;

size at birth and maturity, =I=, 144;

axial structure, =I=, 165;

embryonic development and self-mobility, =I=, 175;

functional differentiation, =I=, 206, 591;

reparative power, =I=, 219, 223, 589;

homogenesis universal, =I=, 271;

distinctive traits, =I=, 392; =II=, 35;

distribution in time, =I=, 408;

classificatory value, =I=, 446;

embryonic mammalian respiratory system, =I=, 456;

embryological pre-adaptation, =I=, 461;

evolution and vertebral column, =I=, 470;

rudimentary organs, =I=, 473;

evolution and varied media, =I=, 479–85;

size of head and vertebræ, =I=, 512, 537;

segregation and evolution of vertebræ, =I=, 515;

fertility and development, =I=, 583, 598–9;

Weismann on reproductive cells, =I=, 635;

limb locomotion, =II=, 15;

adaptive segmentation, =II=, 117–23, 125–7, 223, 602, 605–7;

supernumerary vertebræ, =II=, 123;

bilateral symmetry, =II=, 203–6;

internal organic symmetry, =II=, 208;

genesis of rudimentary axis, =II=, 212–6;

natural selection and genesis of structure, =II=, 216, 227;

origin of notochord, =II=, 216–8;

spinal segmentation, =II=, 218–22, 224;

skull development, =II=, 222, 227;

_résumé_ of axis development, =II=, 224;

Cope on author’s theory, =II=, 225–7;

nerve differentiation, =II=, 304;

sensory organs, =II=, 318;

air-chambers, =II=, 334;

osseous differentiation, =II=, 344–55;

activity and muscular colour, =II=, 365–9;

heart-motor apparatus, =II=, 374;

cost of genesis, =II=, 436;

agamogenesis unknown, =II=, 445;

growth and genesis, =II=, 454;

heat expenditure and genesis, =II=, 468–9, 474;

Owen, theory of skeleton, =II=, 548–66;

evolution of vertebræ, =II=, 563–6;

origin of type, =II=, 598–600.

_Vestiges of Creation_, =I=, 491.

Vibrissæ, function of, =I=, 75.

Vitalism, hypothesis examined, =I=, 114–7.

Vittadini, C., on silkworm disease, =I=, 622–3.

Viviparons genesis, =I=, 271, 274–5, 278.

Voice, correlated sexual traits, =I=, 371–2.

Volcano, definition of life and, =I=, 85, 89.

_Volvocineæ_: unicentral development, =I=, 163;

individuality, =I=, 245;

disintegration of genesis, =I=, 276, 587;

spherical aggregation, =II=, 24;

symmetry, =II=, 137, 187;

fertility, =II=, 441.

Vomiting, alimentary canal development, =II=, 328.

_Vorticella_: secondary aggregate, =II=, 90;

symmetry, =II=, 188.

Wallace, A. R.: “The Origin of the Human Races,” =I=, 553;

the expression “Survival of the Fittest,” =I=, 530;

his association of natural with artificial selection, =I=, 609;

co-adaptation in giraffe, =I=, 615;

skin sensitiveness, =I=, 646.

Wasp: co-ordination of instincts in Mason-, =I=, 574, 679–80;

genesis of worker, =I=, 654–7.

Waste, animal, =I=, 69, 213–5, 228;

relation to activity, =I=, 196, 220–1;

in plants, =I=, 213, 220.

Water: properties, =I=, 7, 9;

colloidal affinity for, =I=, 28;

organic change from, =I=, 29;

organic need for, =I=, 147;

proportion in mammalian adult and fœtus, =I=, 154;

motion through, =I=, 156;

organic development and environment, =I=, 173, 177, 479;

terrestrial organisms inhabiting, =I=, 400;

adaptation of organisms to change of media, =I=, 479–85;

vegetal tissue differentiation, =II=, 253;

molecular re-arrangement, =II=, 359;

colloidal contraction, =II=, 361–2.

Water-weed, American, invasion of, =I=, 399.

Watts, Dr., on _The Principles of Biology_, =I=, ix.

Wax, foliar deposit, =II=, 260–1.

Weber, on tactual discriminativeness, =I=, 602.

Weight: relation to environment of organic, =I=, 174, 177;

varying as cube of dimensions, =I=, 151; =II=, 434, 470.

Weismann, Aug.: reproductive tissue in _Medusæ_, =I=, 281;

in _Daphnidæ_, =I=, 290;

his theory of the differentiated germ-plasm and its fundamental

units, =I=, 357, 622–3, 628–30, 633–44, 646; =II=, 618–9,

622;

the alleged differentiation and plant-phenomena, =I=, 359–60;

and regenerative processes, =I=, 360;

false joints, =I=, 362;

implied complexity of determinants, =I=, 370;

theory inadequate to explain correlation of sexual traits, =I=,

372;

and variations in peacock’s tail feather, =I=, 372–3, 695; =II=,

618;

his view of natural selection as sole factor in organic evolution,

=I=, 559;

the doctrine of panmixia, =I=, 561–3, 612, 632, 649, 667–9, 671,

685, 689;

arguments against inheritance of acquired characters, =I=, 612–3,

651–65, 669–71;

blindness of cave-animals, =I=, 613;

current acceptance of his views, =I=, 631, 690;

cannot explain the process of natural selection, =I=, 651;

the degradation of the little toe in man, =I=, 652, 669, 673;

caste gradations of social insects, =I=, 654, 658–65, 670, 675,

678–84, 685;

food-seeking instinct in Amazon ants, =I=, 660, 670;

the co-adaptation of co-operative parts, =I=, 663–4, 670, 674,

675, 676;

tactual discriminativeness, =I=, 665, 672;

intra-selection, =I=, 676–8;

effect of nutrition on fertility of blow-fly, =I=, 678–9.

Whale: weight of brain, =I=, 599;

rudimentary limbs, =I=, 668–9, 685, 693.

Wheat, adaptive variations, =II=, 298.

Whistling, definition of life and, =I=, 112.

White-Cooper, Mr., on inheritance of abnormal vision, =I=, 306.

Willow, nutrition and growth, =I=, 294.

Wilson, E. B.: composition of chromatin, =I=, 260;

separation of segmentation spheres of _Amphioxus_ ovum, =I=, 691.

Wind: and vegetal bilateral symmetry, =II=, 142;

and inner vegetal tissue differentiation, =II=, 275–9, 285, 288,

388;

and proliferation of _Bryophyllum_, =II=, 295;

and vegetal sap movement, =II=, 583, 584, 587;

_résumé_, 592–6.

Wolff, C.: vegetal fructification and nutrition, =I=, 283; =II=,

179–80;

vegetal vascular system, =II=, 283.

Women (_see_ Man).

Wood (_see_ Plants).

Yeast: fermentation, =I=, 38;

fertility, =I=, 581; =II=, 440;

linear aggregation, =I=, 587; =II=, 23.

Zebra marks in horses, =I=, 314.

Zoology, classification, =I=, 124–5, 380–9.

Zoophytes, structural indefiniteness, =I=, 173.

Zoospores, unit-life of, =I=, 185.

Zygote, of conjugating _Algæ_, =I=, 283.

THE END.

FOOTNOTES:

[1] It seems needful here to say, that allusion is made in this

paragraph to a proposition respecting the ultimate natures of Evolution

and Dissolution, which is contained in an essay on _The Classification

of the Sciences_, published in March, 1864. When the opportunity

comes, I hope to make the definition there arrived at, the basis of a

re-organization of the second part of _First Principles_: giving to

that work a higher development, and a greater cohesion, than it at

present possesses. [The intention here indicated was duly carried out

in 1867.]

[2] Let me here refer those who are interested in this question,

to Prof. Huxley’s criticism on the cell-doctrine, published in the

_Medico-Chirurgical Review_ in 1853.

A critic who thinks the above statements are “rather misleading”

admits that the lowest types of organisms yield them support, saying

that “there are certainly masses of protoplasm containing many nuclei,

but no trace of cellular structure, in both animals and plants. Such

non-cellular masses may exist during development and later become

separated up into cells, but there are certain low organisms in which

such masses exist in the adult state. They are called by some botanists

non-cellular, by others multi-nucleate cells. Clearly the difference

lies in the criteria of a cell. There are also some _Protozoa_, and

the _Bacteria_, in which no nucleus has certainly been demonstrated.

But it is usual to consider the bodies of such organisms as cells

nevertheless, and it is supposed that such cells represent a stage of

development in which the nucleus has not yet been evolved, though the

chemical substance ‘nuclein’ has been formed in some of them.”

Perhaps it will be most correct to say that, excluding the minute,

non-nucleated organisms, all the higher organisms--_Metazoa_ and

_Metaphyta_--are composed throughout of cells, or of tissues originally

cellular, or of materials which have in the course of development been

derived from cells. It must, however, be borne in mind that, according

to sundry leading biologists, cells in the strict sense are not the

immediate products either of the primitive fissions or of subsequent

fissions; but that the multiplying so-called cells are nucleated masses

of protoplasm which remain connected by strands of protoplasm, and

which acquire limiting membranes by a secondary process. So that, in

the view of Mr. Adam Sedgwick and others, the substance of an organism

is in fact a continuous mass of vacuolated protoplasm.

[3] In further illustration, Mr. Tansley names the fact that in

the genus _Caulerpa_ we have extremely complicated forms often of

considerable size produced in the same way. The various species

simulate very perfectly the members of different groups among the

higher plants, such as Horse-tails, Mosses, Cactuses, Conifers and the

like.

[4] It may be objected that in _Cladophora_ the separate compartments

of the thallus severally contain many nuclei, making it doubtful

whether they descend from uni-nucleate cells. If, however, they do not

they simply illustrate another form of integration.

[5] The great mass of early ancestral types--plant and

animal--consisting of soft tissues, have left no remains whatever, and

we have no reason to suppose that those which left remains fell within

the direct ancestral lines of any existing forms. Contrariwise, we have

reason to suppose that they fell within lines of evolution out of which

the lines ending in existing forms diverged. We must therefore infer

that the difficulties of affiliation which arise if we contemplate

divergent types now existing, would not arise if we had before us all

the early intermediate types. The Mammalia differ in sundry respects

from all other kinds of Vertebrata--Fishes, Reptiles, Birds; and if

the absence of hair, mammæ, and two occipital condyles, in these other

vertebrates were taken to imply a fundamental distinction, it might, in

the absence of any known fossil links, be inferred that the Mammalia

belonged to a separate phylum. But these differences are not held to

negative the assumed relationship. Similarly among plants. We must

not reject an hypothesis respecting a certain supposed type, because

the existing types it must have been akin to present traits which it

could not have had. We are justified in assuming, within limits, a

hypothetical type, unlike existing types in traits of some importance.

Hence results the answer to a criticism passed on the above argument,

that it implies relations between the undeveloped and developed forms

of the _Jungermanniaceæ_ such as the facts do not show us. This

objection is met on remembering that the types in which the supposed

transition took place disappeared myriads of years ago.

[6] There is much force in the criticism passed on the above paragraph,

and by implication on some preceding paragraphs, that though in plants

which tend to produce compound leaves the production is largely

dependent on the supply of nutriment, yet the unqualified statement of

this relation as a general one, is negatived by the existence of plants

which bear only simple leaves, however much high nutrition causes

growth. But mostly valid though this objection is, it is probably not

universally valid. I am led to say this by what occasionally occurs

in flowers. The flowering stem of the Hyacinth is single; but I have

seen a cultivated Hyacinth in which one of the flowers had developed

into a lateral spike. Still more striking evidence was once supplied

to me by Agrimony. All samples of this plant previously seen had

single flowering spikes, but some years ago I met with one, extremely

luxuriant, in which some flowers of the primitive spike were replaced

by lateral spikes; and I am not sure that some of these, again, did

not bear lateral spikes. Now if in plants which, in probably millions

of cases, have their flowering stems single, excessive nutrition

changes certain of their flowers into new spikes, it is a reasonable

supposition that in like manner plants which are thought invariably to

bear only single leaves, will, under kindred conditions, bear compound

leaves.

[7] See _British and Foreign Medico-Chirurgical Review_ for January,

1862.

[8] Schleiden, who chooses to regard as an axis that which Mr.

Berkeley, with more obvious truth, calls a mid-rib, says:--“The flat

stem of the Liverworts presents many varieties, consisting frequently

of one simple layer of thin-walled cells, or it exhibits in its

axis the elements of the ordinary stem.” This passage exemplifies

the wholly gratuitous hypotheses which men will sometimes espouse,

to escape hypotheses they dislike. Schleiden, with the positiveness

characteristic of him, asserts the primordial distinction between

axial organs and foliar organs. In the higher Archegoniates he sees an

undeniable stem. In the lower Archegoniates, clearly allied to them

by their fructification, there is no structure having the remotest

resemblance to a stem. But to save his hypothesis, Schleiden calls

that “a flat stem,” which is obviously a structure in which stem and

leaf are not differentiated. He is the more to be blamed for this

unphilosophical assumption, since he is merciless in his strictures on

the unphilosophical assumptions of other botanists.

[9] To this interpretation it is objected that “the more-developed

_Jungermanniaceæ_” do not appear to have arisen from the lower forms

of _Jungermanniaceæ_--that is to say, from such lower forms as are now

existing. It may, however, be contended that this fact does not exclude

the interpretation given; since the higher forms may well have been

evolved, not from any of the lower forms we now know, but from lower

forms which have become extinct. This, indeed, is the implication of

the evolutionary process as pointed out in the note to Chap. I. If then

we assume some early type of intermediate structure, the explanation

may not improbably hold.

[10] I am indebted to Dr. Hooker for pointing out further facts

supporting this view. In his _Flora Antarctica_, he describes the genus

_Lessonia_ (see Fig. 37), and especially _L. ovata_, as having a mode

of growth simulating that of the dicotyledonous trees, not only in

general form but in internal structure. The tall vertical stem thickens

as it grows, by the periodical addition of layers to its periphery.

That even Thallophytes should thus, under certain conditions, present

a transversely-increasing axis, shows that there is nothing absolutely

characteristic of Phanerogams in their habit of stem-thickening. Mr.

Tansley gives me further verification by the statement that “it is

also now certain that members of the _Equisetineæ_ and _Lycopodineæ_,

as well as some Ferns which flourished in Carboniferous times, had

secondary thickening in their stems quite comparable to that of modern

Dicotyledonous trees.”

[11] See note at the end of the chapter.

[12] Since this paragraph was put in type [this refers to the first

edition], I have observed that in some varieties of _Cineraria_, as

probably in other plants, a single individual furnishes all these forms

of leaves--all gradations between unstipulated leaves on long petioles,

and leaves that embrace the axis. It may be added that the distribution

of these various forms is quite in harmony with the rationale above

given.

[13] Since these figures were put on the block, it has occurred to

me that the relations would be still clearer, were the primary frond

represented as not taking part in these processes of modification,

which have been described as giving rise to the erect form; as,

indeed, the rooting of its under surface will prevent it from doing

in any considerable degree. In such case, each of the Figs. 111 to

117, should have a horizontal rooted frond at its base, homologous

with the pro-embryo among Acrogens. This primary frond would then more

manifestly stand in the same relation to the rest, as the cotyledon

does to the plumule--both by position, and as a supplier of nutriment.

Fig. 117_a_, which I am enabled to add, shows that this would complete

the interpretation. Of the dicotyledonous series, it is needful to add

no further explanation than that the difference in habit of growth,

will permit the second frond to root itself as well as the first; and

so to become an additional source of nutriment, similarly circumstanced

to the first and equal with it.

[14] How the element of time modifies the result, is shown by the

familiar fact that crystals rapidly formed are small, and become

relatively large when left to form more slowly. If the quantity of

molecules contained in a solution is relatively great, so that the

mutual polarities of the molecules crowded together in every place

throughout the solution are intense, there arises a crystalline

aggregation around local axes; whereas, in proportion as the local

action of molecules on one another is rendered less intense by their

wider dispersion, they become relatively more subordinate to the forces

exerted on them by the larger aggregates of molecules that are at

greater distances, and thus are left to arrange themselves round fewer

axes into larger crystals.

[15] It is objected that these transformations should be much

commoner than they are, were they caused solely by the variations of

nutrition described. The reply is that they are comparatively rare

in uncultivated plants, where such variations are not frequent. The

occurrence of them is chiefly among cultivated plants which, being

artificially manured, are specially liable to immense accessions of

nutriment, caused now by sudden supplies of fertilizing matters, and

now by sudden arrival of the roots at such matters already deposited in

the soil. It is to these great _changes_ of nutrition, especially apt

to take place in gardens, that these monstrosities are ascribed; and it

seems to me that they are as frequent as may be expected.

[16] Since this paragraph was published in 1865, much has been learned

concerning cell-structure, as is shown in Chapter VI^A of Part I.

While some assert that there exist portions of living protoplasm

without nuclei, others assert that a nucleus is in every case present,

and that where it does not exist in a definite aggregated form it

exists in a dispersed form. As remarked in the chapter named, “the

evidence is somewhat strained to justify this dogma.” Words are taken

in their non-natural senses, if one which connotes an individualized

body is applied to the widely-diffused components of such a body; and

this perverting of proper meanings leads to obscuration of what may

perhaps be an essential truth. As argued in the chapter named (§§

74_e_, 74_f_), nuclear matter is, as shown by its chemical character,

an extremely unstable substance, the molecular changes of which,

perpetually going on, initiate shocks, producing changes all around.

In the earlier stages of cell-evolution this unstable substance is

dispersed throughout the cytoplasm; whereas in the more advanced stages

it is gathered together in one mass. If so, instead of saying there is

a dispersed nucleus we should say there are the materials of a nucleus

not yet integrated.

[17] This statement seems at variance with the figure; but the figure

is very inaccurate. Its inaccuracy curiously illustrates the vitiation

of evidence. When I saw the drawing on the block, I pointed out to

the draughtsman, that he had made the surrounding curves much more

obviously related to the contained bodies, than they were in the

original (in Dr. Carpenter’s _Foraminifera_); and having looked on

while he in great measure remedied this defect, thought no further

care was needed. Now, however, on seeing the figure in the printer’s

proof, I find that the engraver, swayed by the same supposition as the

draughtsman that such a relation was meant to be shown, has made his

lines represent it still more decidedly than those of the draughtsman

before they were corrected. Thus, vague linear representations, like

vague verbal ones, are apt to grow more definite when repeated.

Hypothesis warps perceptions as it warps thoughts.

[18] Though the subdivision into chambers of the shell does not

correspond to the subdivision into cell-units it may still be held

that since in the solitary types the subdivision of the nucleus is

followed by formation of new individuals which separate, and since in

the compound types the subdivision of the nucleus is followed by growth

and formation of new chambers, the compound type must be regarded as an

aggregate of the second order.

[19] A critic says the question is “what are the forces internal

or external which produce union or separation.” A proximate reply

is--degree of nutrition. As in a plant new individuals or rudiments of

them are cast off where nutrition is failing, so in a compound animal.

The connecting part dwindles if it ceases to carry nutriment.

[20] It has been pointed out that I have here understated the evidence

of physiological integration. An instance of it among _Hydrozoa_ is

shown in Fig. 151, but by a strange oversight I have forgotten to

name the various cases furnished by the _Siphonophora_ in which the

individual polypes of a compound aggregate are greatly specialized in

adaptation to different functions.

[21] Recently Mr. T. H. Morgan has made elaborate experiments which

show that _Planaria Maculata_ may be cut into many pieces from various

parts and of various shapes--even a slice out of the side--and each, if

not too small, will produce a perfect animal.

[22] Since this was written in 1865 there has come to light evidence

more completely to the point than any at that time known. In the

subdivision of _Platyhelminthes_ known as _Turbellaria_, there are

some, the _Microstomida_ which, by a process of segmentation form

“chains of 4, then 8, then 16, and sometimes even 32 individuals.”

“Each forms a mouth [lateral] and for some time the chain persists, but

the individuals ultimately become sexually matured and then separate.”

(Shipley, _Zoology of the Invertebrata_, p. 92.) Here it should be

remarked that the lateral mouths enable the members of a string to feed

separately, and that nutrition not being interfered with they doubtless

gain some advantage by temporary maintenance of their union--probably

in creeping.

[23] I find that the reasons for regarding the segment of a _Tænia_

as answering to an individual of the second order of aggregation, are

much stronger than I supposed when writing the above. Van Beneden

says:--“Le Proglottis (segment) ayant acquis tout son développement,

se détache ordinairement de la colonie et continue encore à croître

dans l’intestin du même animal; il change même souvent de forme et

semble doué d’une nouvelle vie; ses angles s’effacent, tout le corps

s’arrondit, et il nage comme une Planaire au milieu des muscosités

intestinales.”

[24] Though this was doubtful in 1865 it is no longer doubtful. In

an individual _Ctenodrilus monostylus_, which multiplies by dividing

and subdividing itself, “parts arise which are destitute of both head

and anus and at times consist of only a single segment.” In another

species, _C. pardalis_, there is separation into many segments; and

each segment before separating forms a budding zone out of which other

segments are afterwards produced, completing the animal (Korschelt and

Heider, _Embryology_, i, 301–2).

[25] In place of those originally here instanced about which there

are disputes, I may give an undoubted one described by McIntosh, the

_Syllis ramosa_, a species of chætopod living in hexactinellid sponges

from the Arafura Sea, which branches laterally repeatedly so as to

extend in all directions through the canals of the sponge. In most

cases the buds terminate in oval segments with two long cirri each.

But male and female buds were found, provided each with a head, and

containing ovaries and testes. Sometimes these sexual buds had become

separate from the branched stock.

[26] The name _Annulosa_, once used to embrace the _Annelida_ and

_Arthropoda_, has of late ceased to be used. It seems to me better than

_Appendiculata_, both as being more obviously descriptive and as being

more exclusive.

[27] The fusion of the segments forming the Arthropod head and the

extreme changes, or perhaps in some cases disappearances, of their

appendages, put great difficulties in the way of identification;

so that there are differences of opinion respecting the number of

included segments. Prof. MacBride writes:--“It is highly probable that

a primary head (præoral lobe or præstomium) has been derived from

annelid ancestors, but the secondary fusion of body-segments with this

head, in other words the formation of a secondary head, has gone on

independently in the different classes of the phylum _Arthropoda_,

viz., _Arachnida_, _Crustacea_, and _Tracheata_ (including Insects and

Myriapods). Judged by the number of appendages (which gives an inferior

limit) the head of a malacostracous Crustacean consists of præstomium

and 8 segments; the head of an insect of præstomium and 4 segments; the

head of a Myriapod of præstomium and 3 segments; and the head of an

Arachnid of præstomium and 3 segments.” Again, the comment of Mr. J. T.

Cunningham is:--“According to Claus and most modern authorities there

are only 5 segments in the head of an Arthropod, the eyes not counting

as appendages; and further it should be noted that the second pair of

antennæ are wanting in Insects.”

Of course difference of opinion respecting the number of somites in the

head involves difference of opinion respecting the number constituting

the entire body, which, in the higher Arthropods, is said by some to

be 19 and by others 20. But those who thus differ in detail, agree in

regarding all the segments of head and body as homologous, and this is

the essential point with which we are here concerned.

[28] Prof. MacBride corrects this statement by saying that “The

ctenidia or gills (which in _Mollusca_ generally are represented only

by a single pair) are here represented by a large number of pairs;

they do not, however, correspond in either number or position to the

shell plates.” It may, I think, be contended that if these had any

morphological significance, they would not differ in arrangement from

the shell plates, and would not be limited to this special type of

Mollusc.

[29] Though it is alleged that at a later stage the posterior part

of the skull is formed by fusion of divisions which are assumed to

represent vertebræ, yet it is admitted that the anterior part of the

skull never shows any signs of such division. Moreover in both parts

the bones show no trace of primitive segmentation.

[30] See note at the end of the chapter.

[31] A qualifying fact should be named. When the production of

vertebral segments has become constitutionally established, so that

there is an innate tendency to form them, there arises a liability to

form supernumerary ones; and this, from time to time recurring, may

lengthen the series, as in the body of a snake or the neck of a swan.

This qualification, however, affects equally the hypothesis of an ideal

type and the hypothesis of mechanical genesis.

[32] Here and throughout, the word _radial_ is applied equally to the

spiral and the whorled structures. These, as being alike on all sides,

are similarly distinguished from arrangements that are alike on two

sides only.

[33] It should be added that this change of distribution is not due to

change in the relative positions of the insertions of the leaves but to

their twistings.

[34] We may note that some of these leaves, as those of the Lime,

furnish indications of the ratio which exists between the effects of

individual circumstances and those of typical tendencies. On the one

hand, the leaves borne by these drooping branches of the Lime are

with hardly an exception unsymmetrical more or less decidedly, even

in positions where the causes of unsymmetry are not in action: a fact

showing us the repetition of the type irrespective of the conditions.

On the other hand, the degree of deviation from symmetry is extremely

variable, even on the same shoot: a fact proving that the circumstances

of the individual leaf are influential in modifying its form. But the

most striking evidence of this direct modification is afforded by the

suckers of the Lime. Growing, as these do, in approximately upright

attitudes, the leaves they bear do not stand to one another in the way

above described, and the causes of unsymmetry are not in action; and

here, though there is a general leaning to the unsymmetrical form, a

large proportion of the leaves become quite symmetrical.

[35] It was by an observation on the forms of leaves, that I was first

led to the views set forth in the preceding and succeeding chapters

on the morphological differentiation of plants and animals. In the

year 1851, during a country ramble in which the structures of plants

had been a topic of conversation with a friend--Mr. G. H. Lewes--I

happened to pick up the leaf of a buttercup, and, drawing it by its

foot-stalk through my fingers so as to thrust together its deeply-cleft

divisions, observed that its palmate and almost radial form was changed

into a bilateral one; and that were the divisions to grow together in

this new position, an ordinary bilateral leaf would result. Joining

this observation with the familiar fact that leaves, in common with

the larger members of plants, habitually turn themselves to the

light, it occurred to me that a natural change in the circumstances

of the leaf might readily cause such a modification of form as that

which I had produced artificially. If, as they often do with plants,

soil and climate were greatly to change the habit of the buttercup,

making it branched and shrub-like; and if these palmate leaves were

thus much overshadowed by one another; would not the inner segments

of the leaves grow towards the periphery of the plant where the light

was greatest, and so change the palmate form into a more decidedly

bilateral form? Immediately I began to look round for evidence of the

relation between the forms of leaves and the general characters of the

plants they belong to; and soon found some signs of connexion. Certain

anomalies, or seeming anomalies, however, prevented me from then

pursuing the inquiry much further. But consideration cleared up these

difficulties; and the idea afterwards widened into the general doctrine

here elaborated. Occupation with other things prevented me from giving

expression to this general doctrine until Jan. 1859; when I published

an outline of it in the _Medico-Chirugical Review_.

[36] It is objected to the above interpretation that “many flowers of

sizes intermediate between the Hollyhock and the Agrimony are radially

symmetrical and yet grow sideways. I may mention various _Liliaceæ_,

e.g. _Chlorophytum_, _Eucomis_, _Muscari_, _Anthericum_. _Sagittaria_,

also, has many of its flowers in this position. Further, if the higher

insects alight on flowers in a definite way, as they do, the parts

of the flower must bear different relations to the visiting insect,

however large, so that flowers unvisited ought all to be zygomorphic.”

My reply is that in the sense which here concerns us, the different

petals of the Hollyhock-flower do not bear different relations to the

visiting insect; since, practically, the upper and lateral petals

bear no physical relations at all: in so far as the visiting bee is

concerned they are non-existent. The argument implies that change in

the form of a flower from the radial to the bilateral is likely to take

place only when the contact-relations of the petals to the visiting

insect, are such as to make some forms facilitate its action more than

others; and the large petals of the Hollyhock cannot facilitate its

action at all. In respect of the _Liliaceæ_ instanced, it is needful

to inquire whether the structures are such that this alleged cause of

bilateral symmetry can come into play.

[37] I had intended here to insert a figure exhibiting these

differences; but as the Cow-parsnip does not flower till July, and as

I can find no drawing of the umbel which adequately represents its

details, I am obliged to take another instance.

[38] It has been pointed out to me that “the extreme development of the

corolla so often found in the outer flowers or on the outer side of the

outer flowers in closely-packed inflorescences, associated as it often

is with disappearance of stamens or carpels or both, is usually put

down to specialization of these outer flowers for attractive purposes.

Since the whole inflorescence is increased in conspicuousness by such

a modification, it is supposed that natural selection favoured those

plants which sacrificed a portion of their seed-bearing capacity for

the supposed greater advantage of securing more insect visits.” But

granting this interpretation, it may still be held that increase of

attractiveness due to increase of area must be achieved by florets at

the periphery, and that their ability to achieve it depends on their

having an outer, unoccupied, space which the inner florets have not;

so that, though in a more indirect way, their different development is

determined by different exposure to conditions.

[39] One of my critics writes:--“This chapter might of course be

enormously extended, not only as in the preceding ones by citation of

quite similar cases, but by the introduction of fresh groups of cases.”

[40] Natural selection may have operated in establishing a

constitutional tendency to other sudden abridgments. Mr. Tansley

alleges that this is a part-cause of the varying distribution of

leaves. He says:--“I have myself made some observations on the length

of internodes in the Beech, and am satisfied that it follows quite

other laws, connected with the suitable disposition of the leaves on

the branch. Although I have not had the opportunity of following up

this line of work so as in any way to generalize the results, I suspect

that ‘indirect equilibration’ is a widespread cause of such variation.”

[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=.