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.
XXXVIII. THE CONCEPTS AND THEORIES OF MODERN PHYSICS. By J. B. Stallo. $1.75.
XXXIX. THE BRAIN AND ITS FUNCTIONS. By J. Luys. $1.50.