It is a fact that insects very frequently fail to notice odors which we perceive as intense, and even while these are present, detect odors which are imperceptible to our olfactories. We must explain this as due to the fact that the olfactory papillæ of different species of animals are especially adapted to perceiving very different substances. All biological observations favor this view, and our psycho-chemical theories will have to make due allowance for the fact.] THE OPEN COURT PUBLISHING CO., CHICAGO. Biology, Evolution, Etc. [Illustration: CHARLES DARWIN, 1809-1882 From a private photograph taken in Darwin’s prime.] Darwin and After Darwin An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions. By GEORGE JOHN ROMANES, LL. D., F. R. S. Part I. The Darwinian Theory Pp. xiv., 460. 125 illustrations. Second Edition. With portrait of Darwin. Cloth, $2.00. “A brilliantly written work.”--Review of Reviews. “The best single volume on the general subject since Darwin’s time.”--American Naturalist. “The most lucid and masterly presentation of the Darwinian theory yet written.”--Public Opinion. “The best modern handbook of evolution.”--The Nation. Part II. Post-Darwinian Questions. Heredity and Utility Pp. xii., 344. With portrait of Romanes. Cloth, $1.50. “The clearest and simplest book that has appeared in the sphere of the problems it discusses.”--Chicago Dial. “Contains the ripest results of deep study of the evolutionary problem.... No student of the subject can afford to neglect this last volume of Romanes.”--Bibliotheca Sacra. Part III. Post-Darwinian Questions Isolation and Physiological Selection Pp. 181. With portrait of Mr. Gulick. Cloth, $1.00. The three volumes of “Darwin and After Darwin” supplied to one order $4.00 net. Darwinism Illustrated (Reprint of illustrations from Darwin and After Darwin, Part I.) Wood engravings explanatory of the Theory of Evolution, selected by and drawn under the direction of Prof. G. J. Romanes. Designed for use in class and home instruction. Pp. 94. Paper, $1.00. [Illustration: AUGUST WEISMANN Professor in the University of Freiburg in Breisgau. (Born January 17, 1834.)] An Examination of Weismannism By GEORGE JOHN ROMANES. With Portrait of Weismann, and a Glossary of Scientific Terms. Thoroughly indexed. Pp. ix., 221. Cloth, $1.00 net. “The best criticism of the subject in our language.”--The Outlook, N. Y. “The reader of this work will appreciate from this discussion, better than from the writings of Weismann himself, the significance of the final position adopted by Weismann.”--Science. [Illustration: E. D. COPE. 1840-1897. “One of the Great Men of Science of the World.” --Science,New York, Sept., 1896.] The Primary Factors of Organic Evolution