9. Finally it may be urged, although the question has not been directly discussed in this volume, that no biologist is justified in the present state of knowledge in dogmatically teaching the lay public that gametogenic characters are alone worthy of attention in questions of eugenics and sociology. Hereditary or constitutional factors are of course of the highest importance, but there exists very good evidence that modifications due to external stimulus do not perish with the individual, but are in some degree handed on to succeeding generations, and that good qualities and improvement of the race are not exclusively due to mutations which are entirely independent of external stimuli and functional activity. It is important to produce good stock, but it is also necessary to exercise and develop the moral, mental, and physical qualities of that stock, not merely for the benefit of the individual, but for the benefit of succeeding generations and to prevent degeneration. INDEX _Abraxas groussularioun_ and _lacticolor_ Adaptations, origin of; evolution of _Agonus entaphractus_ Albinism Allantois Allurements _Alytes obstetricans_ _Amblyopsis_, eyes of _Amblystoma tigrinum_ Amnion _Anableps tetrophthalmus_ _Anas boscas_, crosses of _Anas tristis_, crosses Ancel and Bouin _Anguis fragilis_ _Antilocapra_ _Antirrhinum_, crossing of Antlers of stags Ants, heredity of sex in Aphidae, heredity of sex in Apoda Axolotl, albino; metamorphosis; influence of thyroid feeding Barred plumage in fowls Basoh Bateson Bees, heredity of sex in Bernard, Claude Berthold, A. A. Biedl and Konigstein Bionomies Blindness in cave animals _Bombyx mori_ Boring, Miss Born and Fränkel Brachydactyly Bresslau Brown-Séquard Bühler _Cambarus_, males of Capons Castle, experiments in grafting; on sex Castration; in ducks; of frog; of Lepidoptera Cats, heredity of colour in Cave animals, absence of pigment Cephalopoda Cetacea, absence of scrotum Chelonia _Chologaster agassixii_ Chromosomes; in mutations _Clevelandia_ _Colaptes_ Colour-blindness; heredity of Colours, origin of, in domesticated breeds Comb of fowls, uselessness of Corpora lutea, evolution of; in viviparous lower vertebrates; origin of _Corystes cassivelaunus_ Courtship, organs of Criss-cross inheritance Crossing over Cryptorchidism Cuttle-fishes Cyclostomes, absence of corpora lutea in Cytology Cytoplasm, in heredity _Dafila acuta_ crosses _Daphnia_, heredity of sex in Darwin _Dasyurus_; corpora lutea; lactation Davenport Determinants Determination of sex Dipnoi, fins Dog-fishes, oviparous and viviparous Dominant characters, origin of Doncaster; on heredity in cats _Drosophila_, blind mutation, heredity of sex, mutations Ducks, crosses of Dutch rabbit Earthworms, sex in Eclipse plumage Eigenmann Eimer Elasmobranchs; corpus luteum in Elephants, testes Eugenics Eunuch Evolution, evidence of