Rabbits, lactation in, Recapitulation, absence of, and mutations, Reptiles, corpora lutea in, Reversal, in Flat-fishes, _Rhinoderma darwinii_, Ribbert, Rieger, Rodents, testes, Romanes, GJ Röntgen rays, effect on testes, Rose comb, in fowls, Rotifers, heredity of sex in, _Rubricalyx, Oenothera_, _Rubrinervis, Oenothera_, _Sacculina_, Salamanders, transplantation of eye, Sandes, Schuster, Edgar, Scrotum, origin, of, Sea-horse, Secondary sexual characters, Selheim, _Semilata, Oenothera_, Sertoli's cells, Sex, chromosomes; Mendelian theory of, Sex-Linked heredity, _Sexual Dimorphism_, Sexual dimorphism, in Rajidae, in Plaice, Shattock and Seligmann, Silkworm, Silky fowl, plumage of, Sirenia, absence of scrotum, Slow-worm, Smith, Geoffrey, Snakes, absence of limbs, Sociology, Somatic sexual characters, Species, conception of, origin of, characters of, sterility and hybridism, Spermatogenesis, in man, Starling and Lane-Claypon, on lactation, Steinach, heredity of milk glands, Sternum, carina of, Swallows, Sweet Pea, Swifts, Tadpoles, effect of thyroid in Tandler and Gross Taxonomies Teleosteans; corpora lutea in; ovarian follicles Testes, descent of Tetraploidy Thayer Thumb-pad of frog Thyroid-gland feeding Tortoise-shell colour in cats Tosa fowls, Japanese Transplantation of gonads _Typhiogobius_ Uhlenhuth Urodela, larva Variations _Vespa vulgaris_; _germanica_ Vries, De Wallart Wasps; heredity of sex in Weapons, organs used as Weismann Whale, paddle of White Leghorn, crosses Wilson, E. B. Wing, development of Winiwarter, von Witch Wood, T. B., on crossing of sheep Woodland, W. Woodpecker X chromosome _Zeugopterus_ _Zoaea_ End of Project Gutenberg's Hormones and Heredity, by J. T. Cunningham