Nevertheless though we have been compelled to retreat from the speculative position to which scientific opinion had rashly advanced, the prospect of permanent progress is greatly better than it was. With the development of genetic research clear conceptions have at length been formed of the kind of knowledge required and of the methods by which it is to be attained. If we no longer see how varieties give rise to species, we may feel confident that a minute study of genetic physiology of varieties and species is the necessary beginning of any critical perception of their inter-relations. It is little more than a century since no valid distinction between a mechanical mixture and a chemical combination could be perceived, and in regard to the forms of life we may well be in a somewhat similar confusion.

As yet the genetic behaviour of animals and plants has only been sampled. When the work has been done on a scale so large as to provide generalisations, we may be in a position to declare whether specific difference is or is not a physiological reality.

INDEX OF SUBJECTS

PAGE
Abraxa grossulariata,[105], [193]
Aceras hircina, local variability,[123]
Achatinellidae, local forms of,[133]
Acquired characters, inheritance of,[188 et seq.], [217], [233]
Acronycta psi, melanic,[138]
Adaptation, problem of,[187], [234]
Agelaius, local forms,[120]
Agrotis, fixed and variable species,[ 25]
Alkaptonuria,[ 83]
Alpine Plants, growing larger, if protected,[183]
Alpine Varieties,[165]
Alytes obstetricans, Kammerer's experiments on,[199], [210]
Amblystoma, races of,[230]
Amphidasys betularia, melanic form,[136], [138]
 dimorphic larvae,[141]
Anodonta, polymorphism of,[130]
Antirrhinum, striped,[ 57]
 species-hybrids,[ 99]
 albinos,[110]
Apple, will not cross with pear,[239]
Arctia caja, effects of temperature,[192]
 larval variation in,[231]
Arctic varieties,[165]
Argynnis paphia and valesina in Italy,[121]
Armadillo, polyembryony,[ 42]
Artistic faculty,[ 89]
Arum, rights and lefts,[ 57]
Auriculas, short-styled selected,[236]
Axis of symmetry in hand and foot,[ 48]
Axolotl, alleged effect of conditions,[230]
Azalea, bud-sports,[ 55]

Bacillus anthracis, unsegmented form,
[ 71]
Bacillus prodigiosus, variation in,[213]
Bacteria, variation in,[212]
Bacterium coli, variation in,[214]
Baeolophus, geographical races of,[159]
Barley, right and left-handed,[ 58]
Basilarchia, geographical races of,[161]
Begonia phyllomaniaca,[ 50]
 hybrids,[ 51]
Bizarre Carnation, genetics of,[ 54]
Black, as a variation from red,[148]
Blackbird, varying,[150]
Black Cock, fixity of,[ 28]
Boarmia repandata, melanic form,[136]
 rhomboidaria,[137], [139]
Botrytis susceptibility to,[108]
Bovidae, hybrid,[242]
Brachydactyly,[ 89], [ 95]
Bradypus, vertebral variation,[ 68]
Bud-sports geometrically irregular,[54-57]
Buffalo, attempts to hybridize,[242]
Bullfinch, gynandromorph,[ 45]
Bulimus detritus, local variation of,[126]

Canary, asymmetrical markings in,
[154]
Canidae, hybrid,[241]
Capsella,[100]
Cardamine pratensis,[239]
Cat, Polydactylism,[ 53]
Carnation, Picotees and bizarres compared,[ 54], [ 58]
Cataract, hereditary,[ 89]
Certhiola, melanic,[142]
Chladni figures,[ 60]
Choloepus, vertebral variation in,[ 68]
 local variation in,[119]
Cinerarias, self-sterility in,[238]
Cistudo, local variation in,[119]
Climatic varieties,[164]
Coccaceae, variation in,[213]
Coenonympha arcania, climatic forms of,[179]
 satyrion,[180]
Coereba, melanic,[142]
Colaptes, geographical races,[147 et seq.]
 chrysoides,[154]
Colloids, growth in,[ 65]
Colorado beetles, experiments on,[218]
Colour blindness in twins,[ 44]
Continuous variation, possible example of,[173]
Coracias, geographical races of,[160]
Cotton, genetics of,[ 98], [100]
Coupling,[110]
Crab, extra claws,[ 74]
Crustacean appendages and Serial Homology,[ 63]
Crystals, analogy with,[ 78]
Cyclopian monsters, artificial,[ 50]

Daphnia, changed by environment,
[217]
Dasypus, polyembryony,[ 42]
Dianthoecia, fixed and variable species,[ 25]
Disease-resistance,[ 87]
Division, power of,
 a fundamental attribute of living things,[ 38]
 Genetics of,[ 46], [ 50]
Dogger Bank, large varieties on,[125]
Dogs, hybrid,[241]
Dominance, nature of,[ 95]
Dominants, origin of new,[ 88], [ 90], [ 95]
Double monsters,[ 42]
Draba, experiments with,[242]
Drosophila,[ 91]
 Payne's experiments on,[228]

Earthworm, regeneration,
[ 77]
Elephant, tusk segmented,[ 38]
Entelechy,[ 80]
Environmental treatment, effects of,[188 et seq.]
Enzymes and genetic factors,[ 86]
Epilepsy, inheritance of traumatic,[197]
Equidae, sterility of hybrid,[241]
Erophila, experiments with,[242]
 species,[249]
Exacum, right and left,[ 57]
Euphonia elegantissima, local forms,[120]
Eupithecia rectangulata, melanic form,[137]

Factors, new,
[ 88]
 loss of,[ 96]
Factorial representation of varieties,[158], [165]
Falcons, geographical races,[147]
Fasciation,[ 49]
Ferments, Boyle on,[ 54]
Finger-prints of twins,[ 44]
Fixity and Variability in species,[ 25]
Flax, climatic experiments,[197]
Fowl, Silky,[ 84]
 Leghorn,[ 85], [ 90]
 Dominant white,[ 94]
 Wyandotte,[ 97]
 Rumpless,[ 46]
Foxes, incompatibility with dogs,[241]
Free-martin,[ 44]
Fringillidae, sterility of hybrid,[241]
Fundulus, cyclopian,[ 50]

Gallus, invariability of wild species,
[ 13]
 and origin of poultry,[ 90], [ 97]
Genitalia, a basis for classification in insects,[ 13]
Gentians, climatic experiments,[197]
Geometrical structure and differentiation,[ 54], [ 56]
Geometrical distinction between germ-cells and somatic cells,[ 58]
Gladiolus, right and left,[ 57]
Gnophus obscurata, protective colouring,[141]
Goldfinch, geographical races,[147]
Gonioctena variabilis, variation in sexes of,[121]
Gouldian Finch, polymorphism,[148-149]
Gracilaria stigmatella, experiments on,[193]
Grantia, large varieties of,[125]
Ground-Squirrels, local forms of,[132]
Grouse, red, variation,[ 29]
Guillemot, Ringed,[150]
Guinea-pig, Brown-Séquard's experiments on,[198]
Gynandromorphs,[ 45]

Heliconius erato, forms of,
[122], [164]
Helix lapicida, local variation of,[126]
 striata,[127]
 Heripensis,[127]
 Caespitum,[127]
 trochoides,[127]
 nemoralis and hortensis,[128]
Helminthophila, geographical races of,[157]
Hemerophila abruptaria, melanic,[142]
Hepialus humuli, in Shetland,[119]
Heterostyle plants,[236]
Hieracium,[ 9]
Himantopus,[234]
Homoeosis,[ 68]
Hybernia progemmaria,[139]
Hybrids, sterility of,[233 et seq.]

Incompatibility between certain allied species,
[239]
Individual, geometrical independence of,[ 58]
Inhibiting Factors,[ 95]
Intermediates, nature of,[131], [135]
Isolation, consequences of,[118]

Lacerta muralis, Kammerer's experiments on,
[209]
 fiumana,[210]
Leptinotarsa, Power's experiments on,[218]
Limbs, extra, in pairs,[ 72]
Limnaea, sinistral,[134]
Linaria vulgaris, self-sterility,[239]
Loasa fruits, right and left,[ 57]
Lobster, extra claws,[ 76]
Locality, variation connected with,[ 14], [118], [146 et seq.], [208]
Lumbricus, regeneration,[ 77]
Lychnis dioica and vespertina, inter-relations of,[ 18]
 macrocarpa, possibly a common parent of,[ 19]

Machetes pugnax, polymorphism of male,
[ 28]
Maize, Blaringhem's experiments on,[229]
Maize, cumulative factors in,[116]
Malformations, dominants, arising de novo,[ 89]
Manx Cat, heredity,[ 46]
Matthiola,[ 84], [104], [113]
Melanic varieties,[135 et seq.]
Memory, analogy with heredity,[190]
Meristic variation,[ 69], [ 83], [ 86]
Mirabilis, striped,[ 57]
Models of segmentation,[ 59], [ 60]
"Modes," Coutagne's conception of,[126]
Mödling, peculiar race of Pieris napi at,[178]
Mole, albino,[27-28]
Mule, Linnaeus on,[ 8]
Mutation, Matthioli on,[ 4]
 in Mercurialis,[ 5]
 in Kales,[ 5]
 alleged in bulbs,[ 5]
 Theory,[ 97]
 periods of,[114]
 in Bacteria,[214]
Mutilation, consequences of,[ 71]
 alleged effect of, on offspring,[229]
Myxococcus, variation in,[213]

Narwhal, asymmetry of tusks,
[ 44]
Nemesia strumosa,[ 91]
Neuration, a basis for classification,[ 13]
Nicotiana, sterility of hybrid,[242]
Nightjars, varying,[150]
Noctuidae, fixity and variability,[ 25]
Noctua, polymorphic and fixed species,[ 25]
Noctua castanea, local forms of,[122]
Nomenclature, future of,[ 94], [245]
Notonecta, variations of,[130]

Odontoptera bidentata, melanic form,
[137]
Oedipodidae, protectively coloured,[140]
Oenothera, new dominant in,[ 92]
 rubricalyx and rubrinervis,[ 92], [ 95]
 Lamarckiana,[ 92], [101]
 origin of,[102], [244]
 has bad pollen-grains,[102]
 factorial analysis of,[103]
 pollen and egg-cells genetically dissimilar,[104]
Oenothera, "twin hybrids",[105]
 laeta and velutina,[105]
 reciprocal crosses in,[105 et seq.]
 possible coupling in,[111]
 dwarfs,[112], [114]
 "Triple hybrids",[114]
 alleged variation due to treatment,[227]
Ophrys, local variability,[125]
Orange, polyembryony,[ 45]
Osmotic growth,[ 65]
Overlapping forms,[146], [174]

Papilio, geographical races of,
[162]
Papilio turnus, variation of,[144]
Pararge egeria, geographical forms,[166 et seq.]
Parthenogenesis,[ 50]
Partula, local forms of,[133]
Passer domesticus and montanus, distinctions,[ 22]
Pea, round and wrinkled,[ 95]
Pear, will not cross with apple,[239]
Pelargonium, variegated,[ 55]
 bud-sports,[ 56]
Periodic phenomena in structure,[ 63]
Peronea, fixed and variable species,[ 26]
"Petites espèces",[248]
Petunia, double,[104]
Phalanger maculatus, local variation,[119]
Pheasant, fixity of,[ 29]
Phigalia pilosaria, melanic,[139-140]
Phratora vitellinae, experiments on,[193]
Phyllotaxis,[ 69]
Pied varieties common in Passer domesticus unknown in Montanus,[ 23]
Pieris napi and bryoniae,[174]
Pig, mule-footed,[ 46]
Pigeon, web-footed,[ 46], [ 49]
 Indian Rock, a recessive form,[ 98]
Pigments, nature of,[ 83]
Pisum humile, hybrids with culinary peas,[244]
 species,[246]
Planarian, regeneration of,[ 71], [ 77]
Plotheia frontalis, polymorphic,[ 26], [ 29]
Plusia, fixity and variation in,[ 26]
Poephila gouldiae, variation of,[148-149]
Polarity of individual,[ 44]
Polia chi, melanic,[138]
Polyanthus, short-styled selected,[236]
Polydactylism in Cat,[52-53]
Polyembryony,[ 45]
Potato, variation in,[ 91]
Poultry, evolution of,[ 90]
Primula obconica,[ 91]
Primula sinensis, flaked,[ 57]
 Leaf-shapes,[ 70]
 new dominant in,[ 92]
 sterility in,[236]
 "Giants",[236]
Primula, species-hybrids,[242]
Protective coloration,[140]
Pyrrhulagra, local forms,[120]
Python, twin-vertebrae,[ 60]

Quiscalus, geographical races of,
[156]

Rabbit, Angora,
[ 46]
 colours of,[ 93]
 Incompatibility with hare,[242]
Raimannia odorata, Macdougal's experiments on,[226]
Rats, Variation in,[248]
Recessives, origin of,[ 90]
Reciprocal crosses, giving distinct results,[105 et seq.]
Regeneration,[ 70]
Repulsion,[110]
Reversal on Regeneration,[ 77]
Rhamphocoelus, geographical forms,[159], [184]
Rhinoptera, variation in jaws of,[ 38]
Rhythm in repetition,[ 69]
Ribs, variation of,[ 68]
Rights and Lefts,[57-58]
Ripples, analogous to segments,[ 60], [ 66-67]
 regeneration of,[ 79]
Rollers, geographical races of,[160]
Ruff, polymorphism of male,[ 28]

Salamandra, maculosa and atra,
[182], [199], [203]
 spotted and striped,[207]
 geographical variation of,[208]
Segmentation, nature of,[ 63]
 simulated mechanically,[ 64]
 compared with rippling,[ 65]
 analogies with,[ 68]
Segmentation of normally unsegmented structures,[ 38]
Selection, Natural, an insufficient cause of definiteness of types,[ 17], [134], [142]
Sempervivum,[250]
Serial Homology, the true nature of,[ 62], [ 66]
Setina, Alpine varieties,[181]
Sex of Twins,[ 44]
Sex-factors, possible coupling of,[111]
Sexual characters, variation in,[119 et seq.]
Siamese twins,[ 44]
Silky Fowl,[84-85]
Simocephalus, changed by environment,[218]
Sinistral forms,[33-34]
Situs transversus,[ 43]
Skate's jaws, variation in,[ 38]
Sloths, vertebral variation,[ 68]
Species, conceptions of,[ 3], [ 94], [ 99], [240], [245]
 allied, distribution of,[185]
 alternative uses of the term,[245]
Specific difference, universality of,[ 12]
 of organisms compared with those of inorganic materials,[ 15]
 failure of theory of Selection to explain,[ 18], [134], [247]
Sphyropicus varius,[149], [156]
Spilosoma lubricipeda, varieties of,[181]
 Zatima, Heligoland form,[181]
Spinal nerves, segmentation of,[ 67]
Sporadic variation,[131], [134], [248]
Squashes, polymorphism of,[100]
Staphylococcus pyogenes, variation in,[213]
Sterility of hybrids, in general,[233]
 in Lychnis hybrids,[20 et seq.]
 in crossing forms of Draba,[243]
 Significance of,[244]
 Self,[238]
Stilt,[234]
Stocks,[ 84], [104], [113]
Striped varieties,[ 57]
Substantive variation,[ 84]
Subtraction-stages,[ 93]
Supernumerary limbs,[72-76]
Sweet pea, variation of,[ 91]
 sterile anthers in,[237]
Symmetry compared with heredity,[ 41]
Symmetry of body approximate,[ 78]
Syndactyly,[ 47]
 in foot,[ 48]
Synthetic formulae, in nomenclature,[ 94]

Taeniocampa, fixed and variable species,
[ 25]
Tamias, local forms of,[132]
Tanagers, geographical races of,[159]
Teeth, variation in,[ 39], [ 67]
Tephrosia consortaria and consonaria,[137], [139], [140]
Tephrosia species, separated by season,[119]
Terminal members, variation of,[ 68]
Thais rumina, local variation in,[ 27]
Tolerance, persistence of diversity due to,[ 17], [134]
Tomato, number of cells in fruit,[ 46]
Transitional populations, rarity of,[165]
 an example,[178]
Tropaeolum, sterile anthers in,[237]
Trypanosomes, variation in,[215]
Tusk, of Elephant, segmented,[ 38]
 of Narwhal,[ 44]
Twinning,[ 41], [ 44], [ 71]
 heredity of,[ 45]
 in organs,[ 46]

Uria troile, variety of,
[150]

Vanessa urticae, effects of temperature,
[191]
Variation, a medley of phenomena,[14-15]
 sporadic,[131], [134]
 and locality,[118]
 Causes of genetic,[ 86], [ 87], [131], [212]
 Substantive and meristic,[ 83]
Veronica, specific difference in,[ 16]
 intermediates between species,[ 17]
Vertebrae, division in,[60-61]
 homologies of,[ 66]
Vespa, specific difference in,[ 23]
Vortex, living organism compared with,[ 40]

Wave-motion compared with repetition of parts,
[ 62], [ 67], [ 79]
Wheat, cumulative factors in,[116]
 climatic experiments on,[195]
Woodpecker,[234]

Zebra, pattern of stripes compared with ripples,
[ 38]

INDEX OF PERSONS

PAGE
Ackermann,[242]
Agar,[218]
Allen, J. A.,[132], [147], [159]
Annandale,[ 47]
Arrigoni degli Oddi,[167]

Backhouse,
[ 50]
Baker, G. T.,[166]
Bangs, Outram,[120], [142], [155]
Barrett,[ 26], [136], [167], [173], [178], [193]
Baur, E.,[ 55], [ 99]
Baur, G.,[119]
Beneden, van,[ 75]
Bentham, on species of Veronica,[ 16]
 Lychnis,[ 21]
 Primula,[ 22]
Bernadin,[ 42]
Bishop, L. B.,[153], [157]
Blaringhem,[229]
Bobart,[ 5]
Boisduval,[182]
Boissier,[ 19]
Borradaile,[74-75]
Boulenger, E. G.,[208]
Boulenger, G. A.,[182], [207], [209]
Boyle,[ 5], [ 54]
Brewster, W.,[149-150]
Britton,[227]
Brown, T. Graham,[198]
Brown-Séquard,[197 et seq.]
Bruant, P.,[ 51]
Buffon,[234]
Butler, S.,[189-190]

Candolle, de,
[245]
Carpenter, J. H.,[172]
Chapman, F. M.,[148], [156-158]
Chapman, T. A.,[ 13], [167], [182], [231]
Church, A. H.,[ 69]
Cieslar,[197]
Clark, Austin,[142], [144]
Cockayne, E. A.,[ 43]
Cockerell, T. D. A.,[224]
Compton, R. H.,[ 50], [ 58], [227]
Cope,[230]
Cory,[142]
Correns,[239]
Coutagne,[125 et seq.]

Darwin, on Variation,
[ 1], [ 2]
 Systematics,[ 10]
 Selection,[134], [139]
 Heterostyle plants,[236-237]
Darwin, F.,[190]
Darwin, Sir G.,[ 41]
Davenport,[ 46]
Davis, H. M.,[102]
Delcourt,[130]
Deschange,[181]
Dobell,[215]
Doncaster,[105], [121], [136]
Driesch,[80-81]
Duchartre,[ 51]

East,
[ 91], [116]
Edwards, W. H.,[162]
Ehrlich,[215]

Fellmer,
[215]
Field, W. L. W.,[161]
Fischer, E.,[192]
Fleck,[171], [174]
Fletcher, W. H. B.,[ 26], [181]
Foster, Sir N.,[ 39]

Gallé,
[123]
Garrod,[ 83]
Gates,[ 92], [ 95], [102]
Gayner, F.,[177]
Godron,[249]
Gold, E.,[196]
Goldschmidt,[116]
Goodwin, E.,[137]
Gortner,[226]
Greene, E. L.,[ 8]
Gregory, R. P.,[ 92], [100], [236]
Grenier,[249]
Grover,[173]
Gruber,[ 48]
Gulick,[119], [133]

Hamling,
[142]
Hampson, Sir G.,[ 26]
Harris,[142]
Hartlaub,[182]
Herbst,[ 42]
Heribert-Nilsson,[116]
Hewett,[182]
Honing,[105]
Hunter, John,[ 44]

Jakowatz,
[197]
Janet,[ 24]
Jeans,[ 41]
Jenkinson,[ 40]
Jentink,[120]
Johannsen,[195]
Jordan,[185], [242], [249]

Kammere,
[199 et seq.]
Keeble,[236]
Klebs,[250]
Krancher,[182]
Küchenmeister,[ 44]
Kudicke,[215]

Lamarck,
[ 9]
Lang, A.,[128]
Lawrence, W. N.,[142], [145]
Leake, H. Martin,[ 98], [100]
Leavitt,[185]
Lecoq,[ 99]
Lederer,[167]
Leduc,[ 64-65], [ 80]
Leydig,[182]
Linden, M. von,[192]
Linnaeus,[6-8]
Lloyd, R. E.,[248]
Locard,[130]
Lock, R. H.,[242], [244]
Loeb,[ 42], [ 45], [ 50], [ 71], [ 77]
Lotsy,[ 99]
Lowe, P. R.,[143]

Macdougal, W. T.,
[102], [226]
Marchant,[ 7]
Mathew,[171]
Matthioli,[ 4]
Mayer, A. G.,[133]
Mendel, Rediscovery of,[ 2]
 On Fasciation,[ 49]
Merrifield,[169], [172]
Miller, W. D.,[120], [149]
Morgan,[ 71], [ 77], [ 91], [198]
Moggridge,[125]

Nathusius, S.,
[242]
Nettleship,[ 44]
Newman, H. H.,[ 42]
Newsholme,[ 48]
Nilsson-Ehle,[116], [169]
Norman, A. M.,[125], [156]

Ober,
[142]
Oberthür,[168], [170], [193]
Oliver, J.,[ 45]

Page, H. E.,
[167], [180]
Patterson, J. T.,[ 42]
Payne, F.,[229]
Pellew,[236]
Poll,[ 45]
Porritt,[136]
Poulton,[141]
Powers, J. H.,[230]
Pringsheim, H.,[213]
Przibram,[ 72], [ 78], [178], [194], [197], [199]
Punnett,[110]

Ray,
[4-5]
Raynor,[105]
Ridgway,[ 10], [120]
Roedelius,[195]
Rolfe,[ 20]
Rosen, F.,[242]
Rosner,[ 42]
Rowland-Brown, H.,[167], [180]

Sargent,
[185]
Saunders, E. R.,[ 84], [104], [112]
Schima,[177]
Schröder,[193-194]
Schübeler,[195]
Semon, R.,[190 et seq.]
Sharrock,[ 5]
Shull,[100]
Speyer, A.,[166], [170], [181]
Spillman,[ 47]
Standfuss,[135], [181], [191]
Staples-Browne,[ 49], [ 98]
Staudinger,[170], [179]
Stockard,[ 50], [ 71]
Sutton,[236], [244]

Tornier,
[ 72]
Tower, W. L.,[218-226]
Trechmann,[133]
Tugwell,[181]
Tutt, J. W. On Definiteness of Species,[ 13]
 On Plusia interrogationis,[ 26]
 On Tephrosia,[119]
 On N. castanea,[122]
 On Pararge egeria,[167 et seq.]

Verity, R.,
[171], [177]
Vries, H. de,[101-115], [222], [239]

Walker, G,
[ 49]
Weir, Jenner,[119]
Weismann,[176], [188]
Wendelstadt,[215]
Werbitzki,[215]
Werner,[209]
Wettstein,[197]
Wheeler, G.,[168], [171]
Wheldale,[ 83]
Wilder,[ 44]
Wille,[197]
Williams, H.,[167], [172]
Windle, B. C. A.,[ 43]
Winslow,[213]
Wolf, F.,[213]
Woodforde,[123]
Woltereck,[215]

Zeijlstra,
[114]