XVI. THE LIFE AND GROWTH OF LANGUAGE. By Professor WILLIAM DWIGHT WHITNEY, of Yale College. $1.50. XVII. MONEY AND THE MECHANISM OF EXCHANGE. By W. STANLEY JEVONS, M. A., F. R. S. $1.75. XVIII. THE NATURE OF LIGHT, with a General Account of Physical Optics. By Dr. EUGENE LOMMEL. With 188 Illustrations and a Table of Spectra in Chromo-lithography. $2.00. XIX. ANIMAL PARASITES AND MESSMATES. By Monsieur VAN BENEDEN. With 83 Illustrations. $1.50. XX. FERMENTATION. By Professor SCHÜTZENBERGER. With 28 Illustrations. $1.50. XXI. THE FIVE SENSES OF MAN. By Professor BERNSTEIN. With 91 Illustrations. $1.75. XXII. THE THEORY OF SOUND IN ITS RELATION TO MUSIC. By Professor PIETRO BLASERNA. With numerous Illustrations. $1.50. XXIII. STUDIES IN SPECTRUM ANALYSIS. By J. NORMAN LOCKYER, F. R. S. With Six Photographic Illustrations of Spectra, and numerous Engravings on Wood. $2.50. XXIV. A HISTORY OF THE GROWTH OF THE STEAM-ENGINE. By Professor R. H. THURSTON. With 163 Illustrations. $2.50. XXV. EDUCATION AS A SCIENCE. By ALEXANDER BAIN, LL. D. $1.75. XXVI. STUDENTS' TEXT-BOOK OF COLOR, OR, MODERN CHROMATICS. With Applications to Art and Industry. By Professor OGDEN N. ROOD, Columbia College. New edition. With 130 Illustrations. $2.00. XXVII. THE HUMAN SPECIES. By Professor A. DE QUATREFAGES, Membre de l'Institut. $2.00. XXVIII. THE CRAYFISH: an Introduction to the Study of Zoölogy. By T. H. HUXLEY, F. R. S. With 82 Illustrations. $1.75. XXIX. THE ATOMIC THEORY. By Professor A. WURTZ. Translated by E. CLEMINSHAW, F. C. S. $1.50. XXX. ANIMAL LIFE AS AFFECTED BY THE NATURAL CONDITIONS OF EXISTENCE. By KARL SEMPER. With Two Maps and 106 Woodcuts. $2.00. XXXI. SIGHT: An Exposition of the Principles of Monocular and Binocular Vision. By JOSEPH LE CONTE, LL. D. With 132 Illustrations. $1.50. XXXII. GENERAL PHYSIOLOGY OF MUSCLES AND NERVES. By Professor J. ROSENTHAL. With 75 Illustrations. $1.50. XXXIII. ILLUSIONS: A Psychological Study. By JAMES SULLY. $1.50. XXXIV. THE SUN. By C. A. YOUNG, Professor of Astronomy in the College of New Jersey. With numerous Illustrations. $2.00. XXXV. VOLCANOES: What they Are and what they Teach. By JOHN W. JUDD, F. R. S., Professor of Geology in the Royal School of Mines. With 96 Illustrations. $2.00. XXXVI. SUICIDE: An Essay in Comparative Moral Statistics. By HENRY MORSELLI, M. D., Professor of Psychological Medicine, Royal University, Turin. $1.75. XXXVII. THE FORMATION OF VEGETABLE MOULD, THROUGH THE ACTION OF WORMS. With Observations on their Habits. By CHARLES DARWIN, LL. D., F. R. S., author of "On the Origin of Species," etc., etc. With Illustrations. $1.50.