The books to which direct reference is made are marked with an asterisk. BIOLOGICAL PART *AUDUBON: Scenes de la nature dans les Etats Unis (_French trans._). Ornithological Biography: an Account of the Habits of the Birds of the United States of America. BATESON, W.: Materials for the Study of Variation. Mendel's Principles of Heredity. *BONHOTE, J. LEWIS: Birds of Britain. BREHM: Tierleben. Ornithology, or the Science of Birds. (_From the text of Brehm._) BROOKS, W.K.: The Law of Heredity. The Foundations of Zoology. *BUeCHNER: Mind in Animals (_Eng. trans._). Liebe und Liebesleben in der Tierwelt. *BUTLER, SAMUEL: Life and Habit. Evolution Old and New. *DARWIN, CHARLES: The Descent of Man. The Origin of Species. The Variation of Animals and Plants under Domestication. The Expression of the Emotions in Men and Animals. *DARWIN, FRANCIS: Life and Letters of Charles Darwin. *ELLIS, HAVELOCK: Psychology of Sex. Vol. III. *ESPINAS: Societes animales. FABRE, J. HENRI: Moeurs des insectes. Life and Love of Insects (_trans._). Insect Life (_trans._). Social Life in the Insect World (_trans._). *FORBES, H.O.: A Naturalist's Wanderings. *GALTON, FRANCIS: Natural Inheritance. Average Contribution of Each Several Ancestor to the Total Heritage of the Offspring. _Pro. Roy. Soc., London, LXI._ *GEDDES, PATRICK: _Articles_: "Reproduction," "Sex," "Variation" and "Selection": _Encycl. Brit._ *GEDDES AND TOMPSON, A.J.: The Evolution of Sex. (_Cont. Sci. Series._) _Rev. ed._ Problems of Sex. *HAeCKER: Der Gesang der Voegel. *HAECKEL: Generelle Morphologie der Organismen. Evolution of Man (_trans._ by J. McCabe). HERTWIG: The Biological Problem of To-day (_trans._ by P. Chalmers Mitchell). HOUZEAU: Etudes sur les facultes mentales des animaux compares a celles de l'homme. *HUDSON, W.H.: Argentine Ornithology. The Naturalist in La Plata. Birds and Man. *HUXLEY, T.H.: A Manual of Invertebrate Animals. KELLOGG: Studies of Variation in Insects. Evidence as to Man's Place in Nature. LETOURNEAU: Evolution of Marriage. (_Cont. Sci. Series._) *MILNE-EDWARDS, HERNI: Lecons sur la physiologie et l'anatomie comparee de l'homme et des animaux. A Manual of Zoology (_trans._). Histoire naturelle des insectes. MIVART, ST. GEORGE: Lessons from Nature as manifested in Mind and Matter. The Common Frog. (_Nat. Series._) Man and Apes: an Exposition of Structural Resemblance upon the Questions of Affinity and Origin. On the Genesis of Species. *MORGAN, C. LLOYD: Animal Life and Intelligence. Habit and Instinct. Animal Behaviour. POULTON, E.B.: The Colours of Animals. PUNNETT, R.C.: On Nutrition and Sex-determination in Man. (_Proc. Cambridge Phil. Soc._, XII.) RIBOT, TH.: Heredity (_Eng. trans._).