Chapter XX: Part 20

Selection only gives rise to what is suited to its end; _beyond that it can call forth nothing_, as we have already emphasized on several occasions. I need only recall the protective leaf-marking of butterflies, which is never a botanically exact copy of a leaf, with all its lateral veins, but is comparable rather to an impressionist painting, in which it is not the reproduction of every detail that is of importance, but the total impression which it makes at a certain distance. If we apply this to the organs and capacities of Man, we shall only expect to find these developed as far as their development is of value for the preservation of his existence and no further. But this may perhaps seem a contradiction of what observation teaches us, that, for instance, our eyes can see to the infinite distance of the fixed stars, although this can be of no importance in relation to the struggle for existence. But this intensity of the power of vision has obviously not been acquired for the investigation of the starry heavens, but was of the greatest value in securing the existence of many of our animal ancestors, and was not less important for our own. In the same way our finely evolved musical ear might be regarded as a perfecting of the hearing apparatus far beyond the degree necessary to existence, but this is not really the case: our musical ear, too, has been inherited from our animal ancestors, and to them, as to primitive Man, it was a necessity of existence. It was quite necessary for the animals to distinguish the higher and lower notes of a long scale, sharply and certainly, in order to be able to evade an approaching enemy, or to recognize prey from afar. That we are able to make music is, so to speak, only an unintentional accessory power of the hearing organs, which were originally developed only for the preservation of existence, just as the human hand did not become what it is _in order to play the piano_, but to touch and seize, to make tools, and so on.

_Must this, then, be true also of the human mind?_ Can it, too, only be developed as far as its development is of advantage to Man's power of survival? I believe that this is certainly the case in a general way; the intellectual powers which are the common property of the human race will never rise beyond these limits, but this is not to say that certain individuals may not be more highly endowed. The possibility of a higher development of certain mental powers or of their combinations--whether it be intelligence, will, feeling, inventive power, or a talent for mathematics, music or painting--may be inferred with certainty from our own principles; for not only may the variational tendencies of individual groups of determinants in the germ-plasm be continued for a series of generations without becoming injurious, that is to say, without being put a stop to by personal selection, but sexual intermingling always opens up the possibility that some predominantly developed intellectual tendencies (_Anlagen_) may combine in one way or another, and so give rise to individuals of great mental superiority, in whatever direction. In this way, it seems to me, the geniuses of humanity have arisen--a Plato, a Shakespeare, a Goethe, a Beethoven. But they do not last; they do not transmit their greatness; if they leave descendants at all, these never inherit the _whole_ greatness of their father, and we can easily understand this, since the greatness does not depend upon a single character, but upon a particular combination of many high mental qualities (_Anlagen_). Geniuses, therefore, probably never raise the average of the race through their descendants; they raise the intellectual average only through their own performances, by increasing the knowledge and power handed on by tradition from generation to generation. But the raising of the average of mental capacity, which has undoubtedly taken place to a considerable degree from the Australasian aborigines to the civilized peoples of antiquity and of our own day, can only depend on the struggle for existence between individuals and races.

But if the human mind has been raised to its present level through the same slow process of selection by means of which all evolution has been directed and raised to the height necessary for the 'desired end,' we must see in this a definite indication that even the greatest mind among us can never see beyond the conditions which limit our capacity for existence, and that now and for all time we cannot hope to understand what is supernatural. We can recognize the stars in the heavens, it is true, and after thousands of years of work we have succeeded in determining their distance, their size, and gravity, as well as their movements and the materials of which they are composed, but we have been able to do all this with a thinking power created for the conditions of human existence upon the earth, that is to say, developed by them, just as we do not only grasp with our hands, but may also play the piano with them. But all that involves a higher thinking power that would enable us to recognize the pseudo-ideas of everlastingness and infinity, the limits of causality, in short, all that we do not know but regard as at best a riddle, will always remain sealed to us, because our intelligence did not, and does not, require this power to maintain our capacity for existence.

I say this in particular to those who imagine they have summed up the whole situation when they admit that much is still lacking to complete knowledge, say, to a true understanding of the powers of Nature or of the Psyche, but who do not feel that in spite of all our very considerably increased knowledge we stand before the world as a whole as before a great riddle. But I say it also to those who fear that the doctrine of evolution will be the overthrow of their faith. Let them not forget that truth can only be harmful, and may even be destructive, when we have only half grasped it, or when we try to evade it. If we follow it unafraid, we shall come now and in the future to the conclusion that a limit is set to our knowledge by our own minds, and that beyond this limit begins the region of faith, and this each must fashion for himself as suits his nature. In regard to ultimate things Goethe has given us the true formula, when the 'Nature-spirit' calls to Faust, 'Du gleichst dem Geist, den Du begreifst, nicht mir!' For all time Man must repeat this to himself, but the need for an ethical view of the world, a religion, will remain, though even this must change in its expression according to the advance of our knowledge of the world.

But we must not conclude these lectures in a spirit of mere resignation. Although we must content ourselves without being able to penetrate the arcana of this wonderful world, we must remain conscious, at the same time, that these unfathomable depths exist, and that we may 'still verehren was unerforschlich ist' (Goethe). But the other half of the world, I mean the part which is accessible to us, discloses to us such an inexhaustible wealth of phenomena, and such a deep and unfailing enjoyment in its beauty and the harmonious interaction of the innumerable wheels of its marvellous mechanism, that the investigation of it is quite worthy to fill our lives. And we need have no fear that there will ever be any lack of new questions and new problems to solve. Even if Mankind could continue for centuries quietly working on in the manifold and restless manner that has, for the first time in the history of human thought, characterized the century just gone, each new solution would raise new questions above and below, in the immeasurable space of the firmament, as in the world of microscopical or ultramicroscopical minuteness, new insight would be gained, new satisfaction won, and our enthusiasm over the marvel of this world-mechanism, so extraordinarily complex yet so beautifully simple in its operation, will never be extinguished, but will always flame up anew to warm and illumine our lives.

INDEX

[References to vol. ii have the volume prefixed.]

Accessory idioplasm, 383.

Acræides, immunity of, 100.

Adaptation, in leaf butterflies, ii. 346;
of the sperm-cells to fertilization, 278, 279;
facultative, ii. 278;
functional, 244;
harmonious, ii. 80, 197;
not chance but necessity, ii. 346;
all evolution depends upon, ii. 347.

Affinities, vital, within the 'person,' ii. 36;
within the id, 374.

Agassiz, L., immutability of the species, 16.

Alcoholism, ii. 68.

Aldrovandi, 13.

Amixia, ii. 285, 286.

Ammon, O., the variation-playground, ii. 199, 202.

Amœba 'nests,' ii. 219.

Amphigony, 267;
as a factor in maintaining species, ii. 204.

Amphimixis, general significance of, ii. 192;
antiquity of, ii. 202;
Ammon's playground of variations, ii. 206;
Amœba 'nests' as a preliminary stage, ii. 219;
beginnings of, ii. 213;
parthenogenesis as self-fertilization, ii. 233;
in Coccidium, ii. 214, 216;
chromosomes in Protozoa, ii. 216;
the 'cycle' idea, 326;
increased stability due to, ii. 200;
continued inbreeding, ii. 231;
'formative' stimulus, ii. 229;
Galton's curves of frequency, ii. 206;
in relation to rudimentary organs, ii. 226;
immediate consequences of, ii. 224;
plastogamy as a preliminary stage of, ii. 222;
alters individuality, ii. 192;
and natural death, 335;
direct advantages of, ii. 198;
origin of, ii. 211;
association of, with reproduction, ii. 210;
increases power of adaptation, ii. 223;
preliminary stages of, ii. 213;
not a rejuvenescence in the sense of preserving life, ii. 221.

Ancestral plasm, ids of, ii. 38.

Ants, several kinds of ids in the germ-plasm of, 390;
harmonious adaptation of sterile forms, ii. 89;
degeneration of wings and ovaries in the workers, ii. 90;
transition forms between females and workers, ii. 92;
Wasmann's explanation of these, ii. 93;
_Polyergus rufescens_, ii. 95;
dimorphism of workers, ii. 96;
number of queens, ii. 98.

Apes, furred, in Tibet, ii. 269.

Arctic animals, sympathetic colouring in, 62.

Aristotle, 10.

Assimilation, ii. 371.

Auerbach, spindle-figure of the dividing cell-nucleus, 289.

Autotomy, self-amputation, ii. 18.

Baer, K. E. von, development of the chick in the egg, 25.

Barfurth, on the segmentation of the egg in the sea-urchin, 408.

Bates, discovery of mimicry, 91;
on the Sauba ant, ii. 96.

Beccari, _Amblyornis inornata_, 223.

Bees, harmonious adaptation in the workers, ii. 89;
influence of nutrition on the degeneration of the ovaries, ii. 92;
importance of the fact that there is only one queen, ii. 97.

Belt, plants and ants, 171.

Beneden, E. van, fertilization of the ovum of _Ascaris_, 295;
deutoplasm, 282;
theory of mitotic cell-division, 291.

Bickford, Elizabeth, experiments on regeneration, ii. 90.

Binswanger, on artificial epilepsy in guinea-pigs, ii. 68.

Biogenetic Law, Fritz Müller's view, ii. 160;
crustacean larvæ, ii. 161;
Haeckel's views, ii. 173;
markings of the caterpillars of the Sphingidæ, ii. 177;
shunting back of the stages in the ontogeny, ii. 177.

Biophors, the smallest vital units, 369;
struggle of the, ii. 52;
spontaneous generation of, 369.

Birds, adaptation in, ii. 315.

Blochmann, on the directive corpuscles in parthenogenetic ova, 304;
on the development of the ovum of the bee, 336;
on chromosomes in unicellulars, ii. 217.

Blumenbach, 'nisus formativus,' 352;
inheritance of mutilations, ii. 66.

Bois-Reymond, doubts as to the inheritance of functional
modifications, 242.

Bonnet, preformation theory, 350, 351.

Bordage, regeneration, ii. 20.

Borgert, proof of the splitting of the chromosomes in the division of
unicellulars, ii. 216.

Boveri, fertilization of non-nucleated pieces of ovum with nucleus of
another species, 341.

Brandes, on the extinction of _Machairodus_ species and the giant
armadillos, ii. 358, 359;
on the supposed transformation of the stomach in birds as a result
of nutrition, 267.

Brown-Séquard, artificial epilepsy in guinea-pigs, ii. 67.

Brücke, Ernst, organization of the living substance, 368.

Budding and division, ii. 1.

Bütschli, theories of amphimixis, 330;
discovery of the spindle-figure in nuclear division, 289.

Burdach, inheritance of mutilations, ii. 65.

Buttel-Reepen, Hugo von, on fertilization in the bee ovum, 306.

Butterflies, their enemies, 98;
aggressive colourings, 68, 70;
aberrations due to cold, ii. 274;
transmissibility of these, 275;
endemic species, 285;
polar and Alpine species, 285;
species of the Malay region, 291.

Butterflies, protective coloration in, 74.

Cænogenesis, ii. 173.

Calkins, conjugation of infusorians, 329.

Caterpillars, protective coloration in, 67.

_Catocala_, adaptive coloration in the various species, ii. 310.

Cell-division, integral and differential, 374;
differential in Ctenophores, 408;
proofs of differential, 377.

Centrospheres, 289, 309.

Ceratium, ii. 326.

Chance, elimination sometimes due to, 44, 47.

Characters, purely morphological, ii. 133.

Child, determination of, at fertilization, ii. 46.

Chromatin, the hereditary substance, 287;
grounds for the belief, 337-43.

Chromosomes, their occurrence in unicellulars, ii. 217;
simple and plurivalent (-idants), 349, 350;
individuality of, 349;
number of, in different species, 291;
indications of complexity of their structure, 292;
reasons for their existence, 303.

Chun, segmentation of the ovum in Ctenophores, 408;
Kerguelen cabbage and rabbits, ii. 362;
deep-sea investigation, ii. 322.

Cirrhipeds, ii. 241.

Climate, influence of, in causing variation, ii. 269.

Climatic varieties, ii. 269, 272.

Coadaptation, ii. 80;
in crustaceans, ii. 81;
in the markings of butterflies, ii. 87;
in the forelegs of the mole-cricket, ii. 86.

Cold aberrations in butterflies, transmissibility of, ii. 275.

Coloration, animal, its biological import, 58;
sympathetic in butterflies, 74;
in moths, 76;
of animals in green surrounding, 64;
of eggs, 60;
of nocturnal animals, of polar animals, 64;
water animals, 63.

Coloration, shunting backwards of, in the ontogeny, 73.

Colour-adaptation, double, 64, 73;
colour change in fishes, amphibians, reptiles and
Cephalopoda, ii. 278.

Combinations of determinants, ii. 40.

Conjugation, in Protozoa, 317;
in _Paramæcium_, 319.

Conklin, on the behaviour of the centrosphere in the ovum
of _Crepidula_, 309, ii. 41.

Connective tissue of vertebrates, 386.

Constancy and variability, periods of, ii. 294, 295;
degree of constancy of a character increases with its age, ii. 200.

Convergence, ii. 323.

Cope, supposed palæontological proofs for the Lamarckian
principle, ii. 77.

Copernicus, 13.

Copulation of _Coccidium proprium_, ii. 217.

Correlation of the parts of the body, 41;
of determinants of the germ-plasm, ii. 153.

Correns on Xenia, ii. 59.

Corsica, endemic butterflies of, ii. 285.

Crampton, segmentation in a marine snail, _Ilyanassa_, 409.

Crystal animals, sympathetic colouring, 63.

Cultivated plants, asexual reproduction in, ii. 261.

Cuvier, 16;
his dispute with St.-Hilaire, 24.

Dahl, the ants of the Bismarck Archipelago, ii. 101.

Danaides, immune butterflies, 94.

_Danais erippus_ and _Limenitis archippus_ (mimicry), 113, 114.

Darwin, Charles, first appearance of _The Origin of Species_, 28;
story of his life, 29.

Darwin, Erasmus, theory of evolution, 17.

Darwin and Nägeli, ii. 322.

Darwinian theory, dependence of the frequency of species on
enemies, 47;
on external circumstances, 45;
correlation of parts, 41;
races of pigeons, 34;
of domesticated animals, 31;
geometrical ratio of increase, 46;
struggle for existence, 47;
struggle between individuals of the same species, 52;
artificial selection, 39;
natural selection, 42;
affects all parts and stages, 54;
variation, 43;
summary, 55;
origin of flowers, 182;
pangenesis, ii. 62.

Death, natural, 260.

Degeneration of a typical organ not an ontogenetic but a phylogenetic
process, ii. 91;
of disused parts, ii. 116.

Delage, the germ-substance, 401;
'a portmanteau theory,' ii. 3;
experiments with sea-urchins, 342.

Desert animals, sympathetic colouring in, 62.

Determinants, active and passive state, 380;
controlling the cells, 381;
proofs of their existence, 361, 371, 408;
in limbs of Arthropods, 361;
liberation of, 382;
size and number, 369.

Determinates, 355.

Deutoplasm, 280.

Dewitz, degeneration of wings in the ontogeny of worker-ants, ii. 90.

Diatoms, ii. 324.

Dimorphism, sexual, its idioplasmatic cause, 388.

Disappearance of disused parts, ii. 135;
unequal rate of, ii. 129.

Dividing apparatus of the ovum, 288, 308.

Division, proof of differential nuclear division (_Phylloxera_), 377;
multiplication by division, ii. 1.

Dixon, isolation as a condition of species formation, ii. 284.

Döderlein, increase of characters in diluvial forms, ii. 139.

Dog, breeds of, 31;
attachment to man, ii. 73.

Driesch, 'prospective' importance of a cell, 378, 408.

Dzierzon, discovery of parthenogenesis in bees, 303.

Echinoderms, mesoderm cells of, 386, 387.

Ectocarpus, 334.

Egg-cell, form and structure, 280;
its migrations, 281.

Ehrlich, experiments with ricin and abrin, ii. 106.

Eigenmann, on blind cave-salamanders, ii. 347;
on species of Leptocephalus, ii. 133.

Eisig, on symbiosis, 162.

Elimination, ratio of, 47.

_Elymnias_, a genus of mimetic butterflies, 103.

Emery, on extinction of species, ii. 357;
on _Colobopsis truncata_, ii. 96;
on germinal selection, ii. 139;
'mixed' forms in ants, ii. 93;
variation of homologous parts, ii. 189.

Empedocles, 9;
ii. 370, 378.

Endemic species, ii. 283.

Endres, 'prospective' significance of the blastomeres of the ovum of
the frog, 407.

Epigenesis and evolution, 350.

Epilepsy, artificial, in guinea-pigs, ii. 67.

Equilibrium between species of a region, 49.

Evolution, phyletic, ii. 332;
paths of, ii. 381;
forces of, ii. 381;
mechanism of, 353;
facts of, 406.

Evolution, progressive, attempt of species to extend its
range, ii. 383;
unlimited diversity of forms of life, ii. 391;
parable of the traveller, ii. 386.

Evolution theory, general meaning of, 6;
'prospective' import of the cell, 378.

Exner, electric adaptation of the fur of mammals and feathers of
birds, ii. 316;
vision of insects, 216.

Eye-spots, 69;
ii. 179.

Falkland Islands, influence of climate on cattle and horses, ii. 268.

Feathers, regarded as an adaptation, ii. 316.

Fertilization, process of, 286;
in lichens, 313;
in _Ascaris_, 296;
in the sea-urchin ovum, 293;
in Phanerogams, 313;
in higher plants, ii. 251;
importance of the chromatin, 290;
conjugation, 317;
the centrosphere the dividing apparatus of the cell, 289;
chromatin the hereditary substance, 287;
differentiation of individuals among the Protozoa, 322;
number of chromosomes reduced to half, 297;
rôle of the centrosphere, 308;
summary of process of fertilization, 343.

Fischel, segmentation, of the Ctenophore ovum, 408;
regeneration of the lens in Triton, ii. 20.

Fischer, E., experiments with butterfly pupæ in low
temperature, ii. 275.

Flowers, origin of, 179;
adaptation to insects, 189;
in _Aristolochia_, _Pinguicula_, and _Daphne_, 186;
colour as an attraction to insects, 195;
collecting apparatus of bee, 193;
cross-fertilization, means for securing, 182;
in _Salvia_, 183;
lousewort, 184;
flowers adapted to fly-visits, 185;
orchids, 187;
deceptive flowers, _Cypripedium_, 200;
fertilization of Yucca, 202;
imperfection of adaptation a proof of origin through selection, 204;
mouth-parts of insects, 189;
bee, 172;
butterfly, 193;
cockroach, 191;
wind-pollination, 182.

Forel, Auguste, alarm-signals in ants, ii. 83.

Fraisse, on regeneration, ii. 30.

Function, passively functioning parts in relation to the Lamarckian
principle, ii. 77;
harmonious adaptation in these, ii. 81.

Fungi, reproduction of, ii. 267.

Fur of mammals, adaptation to the conditions of life, ii. 269.

Galapagos Islands, fauna of, ii. 283, 292.

Galileo, Galilei, 13.

Galls, plant, 385;
ii. 271.

Gall-wasps, reproduction of, ii. 245.

Galton, Francis, on continuity of the germ-plasm, 411;
on inheritance of talents, ii. 150;
curves of frequency, ii. 206;
doubt of the Lamarckian principle, 242.

Genius, human, ii. 394.

Germ-cells, and somatic cells, 411;
development of, 410;
their mutual attraction, ii. 230.

Germinal infection, ii. 69.

Germinal Selection, ii. 113;
influenced by personal selection, ii. 155;
relation of determinants to determinates, ii. 153;
combination of mental gifts, ii. 150;
influence of amphimixis, ii. 125;
influence of the multiplicity of ids, ii. 124;
objections on the score of smallness of the substance of the
germ-plasm, ii. 156;
degeneration of a species through cultivation, ii. 144;
there are only plus and minus variations, ii. 151;
excessive increase of variations, ii. 139;
basis of sexual characters, ii. 135;
its sphere of operation, ii. 127;
small hands and feet in the higher classes, ii. 147;
climatic forms, ii. 134;
bud-variations, ii. 141;
play of forces in the determinant system, ii. 154;
artificial selection, ii. 123;
short-sight, ii. 146;
milk-glands, ii. 147;
deformities, ii. 137;
muscular weakness in the higher classes of men, ii. 147;
positive variation, ii. 122;
regulated by personal selection, ii. 131;
source of purely morphological characters, ii. 132;
disappearance of disused parts, ii. 119, 129;
self-regulation of the germ-plasm, ii. 128;
specific talents, ii. 149;
sport-variations, ii. 140;
spontaneous and induced, ii. 137;
excessive increase of a variation tendency, ii. 130;
preponderance of panmixia, ii. 120;
origin of secondary sexual characters, ii. 143.

Germinal vesicle, 295.

Germ-plasm, conception of, 410;
continuity of, 411;
at once variable and persistent, ii. 220;
disintegration of, in ontogeny, 379;
nutritive variations within the, 379;
structure of the, 373;
variation of, due to environment, ii. 267;
to nutrition, ii. 268.

Germ-plasm theory, 345;
accessory idioplasm, 383;
active and passive state of determinants, 379;
connective tissue-cells, 386;
determinants and determinates, 355;
lithium-larvæ, 383;
ids, conception of, 349;
idants, 349;
male end female ids, 389;
mesoderm cells of sea-urchin, 387;
plant-galls, 385;
polymorphism, 390;
proofs of existence of determinants (_Lycæna agestis_, insect
metamorphosis, &c.), 356;
sexual dimorphism, 388.

Germ-tracks, 411.

Gesner's _Book of Animals_, 13.

Godelmann, regeneration of Phasmids, ii. 28 _n._

Goebel, 269.

Goethe, archetypal animal and plant, 18.

Green animals, 64.

Gruber, A., regeneration experiments on the Protozoa, 340.

Guignard, fertilization of Phanerogams, 315.

Gulick, snails in the Sandwich Islands. ii. 329.

Haase, Erich, on Pharmacopagæ, 101;
on mimicry, 104.

Haberlandt, protection of leaves, ii. 133;
Auxo-spores, ii. 221.

Haeckel, Ernst, fundamental biogenetic law, ii. 173;
monogony and amphigony, 267;
palingenesis and cœnogenesis, ii. 173;
genealogical trees, ii. 388.

Häcker, Valentin, importance of the nucleolus, 287;
separateness of paternal and maternal nuclear substance during
development, ii. 42;
process of nuclear division, 291.

Hahnel, observations on the enemies of butterflies, 154;
lizards and birds as enemies of butterflies, 97, 98.

Haller, 267.

Harmony, pre-established, apparently existing in development, ii. 309.

Hartog, views on amphimixis, 334;
ii. 194.

Haycraft, on the equalizing effect of amphigony, ii. 203.

Heidenhain, theory of mitotic division, 291.

Heider, on the intimate processes of segmentation of the ovum,
'regulation' and 'mosaic' ova, 409.

Heliconiidæ, first example of immune butterflies, 91.

Henslow, on purely morphological specific differences, ii. 308.

Herbst, lithium-larvæ, 383;
ii. 277.

Hereditary sequence, alternation of, ii. 50.

Hering, his reasons for assuming the inheritance of functional
modifications, ii. 110.

Hermaphroditism in flowers, ii. 250;
in animals, ii. 239;
advantages of, ii. 239.

Herrich-Schäfer, on mimicry, 105.

Hertwig, O., fertilization of sea-urchin eggs, 293;
theory of development, 354;
differential cell-division, 376;
inheritance of functional modifications, ii. 106;
maturation divisions of the sperm-cells, 300.

Hertwig, R., chromosomes in Actinosphærium, ii. 216.

Heterogony, ii. 244.

Heteromorphosis, Loeb on, ii. 7.

Heterostylism, ii. 254.

Heterotopia, 365, 367.

Hirasé, fertilization of Phanerogams, 313.

Histonal selection, 240;
and personal selection, 280.

Hübner, O., experiments on regeneration in _Volvox_, ii. 4.

Humming-birds, species fixed by isolation, ii. 290.

Hyatt, Alpheus, the snail-strata of Steinheim, ii. 305.

Hybrids, ii. 60;
of pigeons, 34;
plant, ii. 57.

Hydra, regeneration in, ii. 4.

Hydroid polyps, development of germ-cells in, 411.

Idants, 349.

Ids, 349;
male and female, 389;
mimicry a proof of the existence of, 390.

Immortality, potential, of the Protozoa, 260.

Immunity of butterflies, 99.

Imperfection of adaptation, 203.

Inbreeding, evil consequences of, ii. 231.

Infection of the germ, ii. 69.

Infusorians, experiments of Maupas on, 328;
Calkins on, 329;
differentiation of nucleus into macro-and micro-nucleus a means of
compelling conjugation, 334.

Inheritance, of acquired characters, ii. 62 (_see_ also Lamarckian
principle);
of functional modifications, ii. 64;
of mutilations disproved, ii. 65;
from parent to child, ii. 38;
hereditary substance, 288, 341;
preponderance of one parent, ii. 47;
alternation in ontogeny, ii. 48.

Instinct, 141, ii. 70;
will and, 152.

Instincts, aberrant, 149;
attachment of dog, ii. 73;
change of, in _Eristalis_, &c., 150;
egg-laying of butterfly, 159;
exercised only once, 155;
ii. 75;
'feigning death,' 145;
imperfectly adapted, 152;
inheritance of, ii. 72;
masking of crabs, 145;
material basis of, 142;
monophagy of caterpillars, 146;
new in domesticated animals, ii. 73;
nutritive, 146;
in Ephemerids and sea-cucumbers, 148;
in predatory fishes, 149;
origin of, ii. 70;
pupation of butterflies, 156;
self-preservation of, 144;
wild animals on lonely islands, ii. 73.

Intra-selection (histonal selection), 240.

Ischikawa, on chromosomes in unicellulars, ii. 216;
on the conjugation of _Noctiluca_, 317;
ii. 42.

Island faunas, ii. 283.

Isolated regions, ii. 284.

Isolation, favours species-formation, ii. 383;
relative, ii. 350;
snails on the Sandwich Islands, ii. 292.

Jäger, G., on the continuity of the germ-plasm, 411.

Japanese cock, 356.

Kaleidoscope, transformation resembles a, ii. 307.

Kallima, mimicry of leaf, 83, 236, 237.

Karyokinesis, 290.

Kathariner, birds as enemies of butterflies, 97.

Kennel, birds as enemies of butterflies, 97.

Kerner von Marilaun, Alpine plants, 122;
influence of hybridization on the formation of new species, ii. 352.

Knowledge, limits of, ii. 392.

Köhler, on scent-scales in the Lycænidæ, 370.

Koshewnikow, on the influence of royal food on drone-larvæ, ii. 92.

Kükenthal, on the fur of aquatic mammals, ii. 270.

Lamarck, theory of development, 21;
on limits of genera and species, ii. 306.

Lamarckian principle, ii. 62;
Lamarck regarded inheritance of functional modifications as a matter
of course, 241;
cleaning apparatus of bees, ii. 84;
claw of crustacean, ii. 85;
Darwin's attitude to, 242;
facts (foreleg of mole, cricket, &c.), ii. 86;
Galton's attitude to, 242;
Hering's view, ii. 109;
O. Hertwig's view, ii. 106;
neuters among ants and bees, ii. 89;
phyletic development, ii. 77;
skeleton of Arthropods, ii. 82;
stridulating organs, ii. 83;
theoretical impossibility of, ii. 107;
variation of passive parts, ii. 77;
venation of butterfly's wing, ii. 87;
Zehnder's defence of, ii. 99.

_Lathræa_, 135.

Lauterborn, on amphimixis in diatoms, ii. 216.

Leaf-imitation, in Locustidæ, 88;
in moths, 87;
in butterflies, 83, 357-61;
in Anæa species, ii. 310.

_Lepus variabilis_, 62;
ii. 344, 350.

Leeuwenhoek, first use of the microscope, 14.

Leuckart, _Trichosomum crassicauda_, with dwarf males, 227;
structure of snails, ii. 301.

Leuckart and von Siebold, 333.

Leydig, regeneration of the lizard's tail, ii. 30.

Liberation of the determinants in ontogeny, 382-6;
quality of nutrition as a liberating stimulus in bees and
ants, ii. 92.

Liebig, theory of the origin of life, ii. 365.

Limits of knowledge determined by selection, ii. 394.

Linné, conception of species, 14.

Lloyd Morgan, artificially induced instincts, ii. 72.

Loeb, experiments on regeneration, ii. 6, 7;
the cell-nucleus as an organ for oxidation, ii. 31.

Luminous organs in deep-sea animals, ii. 321.

MacCullock, autotomy, ii. 19.

_Machairodus_, ii. 358.

Mammals, adaptation to aquatic life, ii. 333.

Maturation divisions, ii. 40;
in plants, 315;
in the ovum, 298;
in the sperm, 301;
influence of, ii. 44.

Maupas, intimate processes of conjugation, 319;
conjugation of Infusorians, 329.

Medium, influence of, ii. 267.

Mendel's Law, ii. 57.

Merogony, fertilization of non-nucleated pieces of ovum, 343.

Merrifield, temperature-experiments with _Polyommatus
phlæas_, ii. 273;
cold experiments with _Vanessa_, ii. 274.

Meyer, Hermann, architecture of the bone spongiosa, 246.

Mimicry, 91;
in beetles, bees, ants, &c., 116;
in butterflies does not affect caterpillar or pupa, 104;
in both sexes, 96;
in vertebrates, 117;
degree of resemblance to model, 104;
_Elymnias undularis_, 106;
_Papilio merope_, 108;
_P. turnus_, 110;
same effect produced in different ways, 105;
several imitators of one immune species, 101;
species of genera which need protection imitate different immune
models, 102;
'rings' of mimetic species, 112;
rarity of mimetic species, 108;
wide divergence of mimetic species from their congeners, 115.

Mitosis, 288.

Möbius, 296.

Monism, 393.

Monogony, 266.

Montgomery, on reduction of the chromosomes, ii. 43.

Morgan, experiments on regeneration, ii. 15.

Morphological characters, dependent on germinal selection, ii. 132;
discussion as to indifferent characters, ii. 132, 309.

Mortality of multicellular organisms, 260;
causes of this, 263.

Morton, Thomas, on degeneration in the children of alcoholics, ii. 69.

Moths, protective coloration in, 80.

Müller, Fritz, scent-scales, 217;
on mimicry, 111;
plants and ants, 171;
relation between ontogeny and phylogeny, ii. 160.

Müller, Johannes, the vision of insects, 216.

Musical sense in man, ii. 148.

Mutation theory of de Vries, ii. 317.

Mutilations, supposed inheritance of, ii. 65.

Mutual sterility, of no great importance in connexion with lasting
variation, 349.

Nägeli, Carl von, on the definite directions of
variations, ii. 306, 385;
objection to origin of flowers through selection, 198;
on the difference in size between egg and sperm, 337;
his _Hieracium_ experiments, ii. 272;
Nägeli's view and Darwin's reconciled through germinal
selection, ii. 334;
number of smallest vital units in a 'moneron,' ii. 368.

Nathusius, inbreeding experiments, ii. 231.

Natural Selection, not directly observable, 58;
under the influence of isolation, ii. 292.

Neo-Lamarckism, 243.

Neotaxis, ii. 40.

Nerve-tracks in relation to instincts, ii. 71.

Normal number of a species, 45.

_Notodonta_, protective coloration in, 80.

Nuclear division, process of, 289;
integral and differential, 374, 377.

Nussbaum, M., regeneration-experiments in Protozoa, 340;
on the continuity of the germ-cells, 411;
infection of the ovum in Hydra, ii. 68.

Nutrition, influence of, on variation, ii. 267;
relation between nutrition and the number in a species, 45.

Oken's 'Naturphilosophie,' 21.

Omnipotence of selection, ii. 348.

Ontogenesis, relation to phylogenesis, ii. 159;
shunting back of the phyletic stages in embryogenesis, ii. 176;
condensation of phylogeny in ontogeny, ii. 186.

Orchids, fertilization of, ii. 256.

Organs, rudimentary, ii. 226.

Origin of flowers, _see_ Flowers.

Osborn, supposed palæontological proofs for the Lamarckian
principle, ii. 77.

Ovaries, 282.

Ovogenic determinants, 388.

Ovum, maturation of, 295.

Packard, disappearance of useless parts, 129.

Palingenesis, ii. 173.

_Pandorina_, reproduction of, 257, 293.

Pangenesis, ii. 62.

Panmixia, ii. 114.

_Papilio meriones_, 108, 427;
_P. turnus_, 110.

Parasites, power of adaptation in, ii. 384.

Parthenogenesis, discovery of, 303;
exceptional and artificial, 307;
facultative in bees, ii. 235;
receptaculum seminis in Cypris-species without males, 326, ii. 234;
advantages of, ii. 243;
its effects compared with those of inbreeding, ii. 233;
alternation of, with bisexual generations (heterogony), ii. 243.

Personal selection, indirect effects of, ii. 200.

Petrunkewitsch, A., maturing divisions in the ovum of the
bee, 306, 336.

Pfeffer, rôle of malic acid in the fertilization of ferns, 273.

Pflüger and Born, experiments in hybridization, ii. 232.

Phasmids, regeneration in, ii. 17.

_Phylloxera_, reproduction in, ii. 249.

Phylogenetic variation of butterfly and caterpillar independent of
each other, 362.

Phylogeny, condensation of, in ontogeny, ii. 186.

_Physiologus_, 11.

Pictet, turban eyes in male Ephemerids, 229.

Pigeons, breeds of, 34.

Plants, fertilization of the higher, ii. 250;
carnivorous, 132;
_Aldrovandia_, 138;
_Dionæa_, 138;
_Drosera_, 136;
_Lathræa_, 135;
_Nepenthes_, 134;
_Pinguicula_, 135;
_Utricularia_, 133.

Plant-galls, ii. 270.

Plastogamy a preliminary stage to fertilization, ii. 220.

Pliny, 11.

Polar bodies, 294.

Polymorphism, its idioplasmic roots, 390.

_Polyommatus phlæas_, dimorphism of caterpillars, 363;
climatic varieties, ii. 272.

Postgeneration (Roux), 407.

Pouchet, spontaneous generation, ii. 366.

Poulton, on facultative colour adaptation in caterpillars, ii. 278;
on mimicry, 105.

Prediction on the basis of the evolution theory, 3.

Preformation and Epigenesis, 351.

Primordial males among Cirrhipeds, ii. 242.

Protective arrangements in plants, 119;
Alpine plants, 126;
chemical substances, 128;
ethereal oils, 128;
hairs, 122;
poisons, 120;
Raphides, 129;
'Prigana scrub,' 126;
against small enemies, 127;
Tragacanth, 124.

Protective colouring, rôle of light in, 78;
_Kallima_, 83;
_Notodonta_, 80;
_Xylina_, 82.

Protective marking in caterpillars, 67.

Protozoa, chromosomes in, ii. 216.

Quetelet, amphigony preserves the mean of the species, ii. 204.

Races, development of, depending on adaptation, ii. 335;
dependent on germinal selection, ii. 144.

Radiolarians, skeleton of, ii. 324.

Rand, experiments on regeneration in Hydra, ii. 5.

Rath, O. von, on the influence of royal food on drone-larvæ, ii. 91.

Ray, John, conception of 'species,' 14.

Reactions, primary and secondary, ii. 277.

Reducing divisions, _see_ Maturation divisions.

Regeneration, ii. 1;
atavistic, ii. 30;
autotomy, ii. 16;
in birds, ii. 14;
in Hydra, ii. 4;
in Hydroid polyps, ii. 9;
in plants, ii. 9, 32;
in Planarians, ii. 6, 13;
in starfishes, ii. 30;
in Vertebrates, ii. 10;
of the lens in Triton, ii. 19;
a phenomenon of adaptation, ii. 9;
nuclear substance the first organ of, ii. 31;
phyletic origin of, ii. 23;
disappearance of the power of, ii. 16;
and budding, ii. 31;
relation of, to liability of part to injury, ii. 7;
not always purposive, ii. 25.

Reinke, objections to the 'machine theory' of life, 402;
on regeneration, 32.

Rejuvenescence, theory of, 325-8.

Reproduction, adaptation of the germ-cells, 277;
asexual, ii. 259;
structure of the ovum, 280;
of the bird's egg, 285;
zoosperm, 273;
in Amœbæ, 253;
in Infusorians, 254;
in _Pandorina morum_, 257, 269;
in fungi, 267;
by means of germ-cells, 266;
differentiation of germ-cells into male and female, 267;
by division, 264;
two kinds of eggs in same species, 282;
nutritive ovum cells, 283;
introduction of death into the living world, 261;
contrast between reproductive and body cells in the Metazoa, 256;
budding and division in the Metazoa, 264;
potential immortality of the Protozoa, 260;
sperm and ovum in Algæ, 272;
in _Volvox_, 265, 271;
zoosperms of Ostracods, 275;
different kinds of spermatozoa, 278.

Reproductive cells, development of, 410;
in Diptera, 411;
in Hydroid polyps, 413.

Reversion, ii. 53;
in doves, ii. 55;
in the horse, ii. 55.

Riley, fertilization of the Yucca by a moth, 202.

Ritzema Bos, experiments on mice, ii. 65, 66.

Romanes, isolation theory, ii. 284;
physiological selection, ii. 337;
panmixia, ii. 115.

Rosenthal, experiments with mice, ii. 65, 66.

Roux, Wilhelm, Mosaic theory, 379;
struggle of the parts, 244;
postgeneration, 407.

Rückert, the nuclear substances in Copepods, ii. 42.

Rudimentary organs in man, ii. 226.

St.-Hilaire, unity of type, 18.

Samassa, segmentation of the frog's egg, 407.

Sarasin, snails of Celebes, ii. 299.

_Saturnia_, pupation of, 158.

Schaudinn, fertilization in Coccidia, ii. 214;
maturing division in Sun-animalcule, 318.

Schimper, plants and ants, 171.

Schleiden and Schwann, discovery of the cell, 26.

Schmankewitsch, experiments with _Artemia_, ii. 277.

Schmidt, Oscar, ii. 324.

Schneider, discovery of the 'spindle-figure' of nuclear division, 289.

Schütt, Diatoms, ii. 325.

Schwarz, Ostracods, 276.

Segmentation-cells in animal ova, their prospective importance, 406.

Seitz, a case of mimicry, 114.

Selection-processes, grades of, ii. 265;
evolution guided by, ii. 298.

Selection, sexual, 210-39;
absence of secondary sexual characters in the lower animals, 231;
adaptations for seizing the females, 229;
choice on the part of the females, 214;
odours and scent-scales, 217;
song of cicadas and birds, 221;
superfluity of males, 213;
weapons for the struggle for mates, 228;
summary, 238.

Selection value, ii. 132, 311.

Self-fertilization in plants, ii. 252;
continued influence of, ii. 257;
alternation of self- with cross-fertilization, ii. 241.

Self-preservation, instinct of, 144.

Sex-cells, mutual attraction of, ii. 228.

Sex, determination of, 377;
ii. 44.

Sexual characters, secondary, have their roots in germinal
selection, ii. 130, 143, 289-91, 378.

Sexual selection, _see_ Selection, sexual.

Sexual selection through isolation, ii. 289.

Short-sight, ii. 146.

Siedlecky, copulation in _Coccidium proprium_, ii. 218.

Simroth, ii. 302.

Slevogt, on birds as enemies of butterflies, 97.

Sluiter, on symbiosis, 167.

Smerinthus, markings of the caterpillars, ii. 177, 184.

Snail-strata of Steinheim, ii. 305.

Sommer, on artificial epilepsy in guinea-pigs, ii. 68.

Special investigation, period of, 25.

Species, the, a complex of adaptations and variations, ii. 307.

Species-colonies, ii. 280.

Species, extinction of, ii. 357;
dying out of the large animals of Central Europe, ii. 361;
extinction due to cultivation, ii. 360;
to unlimited variation, ii. 357;
_Machairodus_, ii. 358;
lower types more capable of adaptation than higher, ii. 359;
extinction of flightless birds, ii. 360.

Species-formation, ii. 299;
favoured by isolation, ii. 284;
snails of Celebes, ii. 219;
without amphigony in lichens, ii. 343;
without isolation in _Lepus variabilis_, ii. 344;
Peridineæ, ii. 325;
protective coloration in butterflies, ii. 310;
the Steinheim snail-strata, ii. 315;
telescope eyes in deep-sea animals, ii. 323;
typical species, ii. 304;
variation in definite directions, ii. 306;
the bird as a complex of adaptations, ii. 316;
the whale as a complex of adaptations, ii. 313;
mutual fertility between many plant-species, ii. 340.

Species, variable and constant, ii. 286.

Specific type, its occurrence favoured by germinal
variation, ii. 333, 334;
by natural selection, ii. 334;
origin of the, ii. 299, 332-5.

Spencer, Herbert, germinal substance composed of homogeneous
particles, 355;
on 'units,' the smallest vital particles, 369;
protective adaptations in plants to be referred to
selection, ii. 77.

Spermaries, 282.

Spermatozoa, _see_ Zoosperms.

Sperm-cells, 272.

Spermogenic determinants, 388.

Sphingidæ, caterpillars of the, biological value of their
markings, 73;
ontogeny and phylogeny of the markings, ii. 177.

_Sphinx convolvuli_, double adaptation of the caterpillar, 71, 72;
_S. euphorbiæ_, var. _Nicæa_, purely local form of caterpillar, 362.

Spontaneous generation, 410;
conditions necessary, ii. 370;
only possible as regards invisible minute organisms, ii. 369;
the 'where' of, ii. 371;
impossibility of proving or disproving it experimentally, ii. 366.

Sprengel, fertilization of flowers, 180.

Standfuss, cold experiments with butterfly pupæ, ii. 275.

Steinheim snail-strata, ii. 305.

Steller's sea-cow (_Rhytina stelleri_), ii. 74.

Stick-insects, 88.

Strasburger, fertilization of Phanerogams, 314.

Stuhlmann, zoosperms in Ostracods, 276.

Swammerdam, 14.

Symbiosis, candelabra trees and ants, 171;
hermit-crabs and Hydroid polyps, 163;
hermit-crabs and sea-anemones, 162;
origin of symbiosis, 176;
lichens, 173;
fishes and sea-anemones, 167;
green Amœbæ, 170;
green fresh-water polyp (_Hydra viridis_), 168;
_Nostoc_ and _Azolla_, 177;
sea-anemones and yellow Algæ, 171;
root-fungi, 175.

Talents, specific, of man referred to germinal selection, ii. 149;
depend on a combination of mental gifts, ii. 150.

Tichomiroff, artificial parthenogenesis, 307, 333.

Thorn-bugs, 89.

Transparent winged butterflies, 106.

Treviranus, as founder of the evolution theory, 18;
on generic differences, ii. 306.

Trimen, observations on the immunity of the Acræidæ, 100.

Tropism in plants, ii. 276.

Twins, identical, ii. 44.

_Vanessa_, endemic species of, with protective colouring, 75.

Variability, fluctuating, ii. 327.

Variation, all ultimately quantitative, ii. 151;
in a definite direction, ii. 118;
double roots of, ii. 195;
ascending, ii. 122;
sports or saltatory variations, ii. 140;
roots of hereditary, ii. 118.

Variation of individual characters, ii. 336;
not always due to adaptation, ii. 197.

Variation, periods of, ii. 294.

Vital force, ii. 369.

Vitalism, ii. 369.

Virchow, Rudolf, on the inheritance of mutilations, ii. 65.

Vöchting, influence of light on the production of flowers, ii. 276;
on regeneration, ii. 32.

Voigt, Walter, experiments in regeneration, ii. 6;
on Planarians, ii. 25.

Voit, Carl von, influence of nutrition on bodily size, ii. 268.

Volvocineæ, reproduction in, 257.

Vries, de, asymmetrical curves of frequency, ii. 234;
theory of mutations, ii. 317;
Pangen theory, 380.

Wagner, Franz von, regeneration in _Lumbriculus_, ii. 27.

Wagner, Moriz, on the influence of isolation, ii. 284.

Wahl, Bruno, on the development of _Eristalis_, 399.

Wallace, on the immunity of Heliconiidæ, 99;
on the causes of the coloration of butterflies, 211.

Wasmann, Erich, on transition forms in ants, ii. 93;
on sounds produced by ants, ii. 83.

Weaver birds, ii. 290.

Whales, their origin through adaptation, ii. 313.

Wheeler, rôle of the centrosphere in the ovum, 309.

Wiedersheim, rudimentary organs in man, ii. 226.

Wiesner, the smallest vital particles, 369.

Wing-primordia in insects, 364.

Winkler, Hans, experiments on artificial parthenogenesis, 307, 333;
on merogony, 343.

Wolff, G., regeneration of the lens in Triton, ii. 19.

Wolff, K. v., the founder of the epigenetic theory of evolution, 352.

Wroughton, Robert, production of sounds by Indian ants, ii. 95.

Würtemberger, form-series of ammonites, ii. 176.

Xenia, ii. 58.

_Xylina_, protective colouring of, 82.

Yolk of egg, 282.

Zehnder, the living substance made up of fistellæ, ii. 217;
polymorphism in ants, ii. 99;
on the Lamarckian principle, ii. 99-106;
on the skeleton of Arthropods, ii. 103;
effect of amphimixis, ii. 223.

Ziegler, Ernst, on deformities, ii. 138.

Ziegler, H. E., experiments on merogony in sea-urchin ova, 342.

Zoja, experiments with the ova of Medusæ, 407.

Zoosperms, 273, 278, 279.

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Transcriber's Notes:

Italics are shown thus: _sloping_.

Punctuation has been retained as published.

Variations in spelling and hyphenation are retained.

Illustrations have been moved out of mid-paragraph.

Figures repeated from Volume I have been added to the
Table of Illustrations.

On page 246 (Fig. 125, B and C) has been corrected to
Fig. 124, B and C).

On page 216 Fig. 118, D, has been corrected to Fig. 122,D.

In the index, Reproductive cells, development of, in Diptera,
has been corrected from 471 to 411.

In the index, Spontaneous generation, ii. has been corrected
to Spontaneous generation, and thus refers to volume I.