VOLUME XIX.

THE INTERNATIONAL SCIENTIFIC SERIES.

_Works already Published._

I. FORMS OF WATER, IN CLOUDS, RAIN, RIVERS, ICE, AND GLACIERS. By Prof. JOHN TYNDALL, LL. D., F. R. S. 1 vol. Cloth. Price, $1.50.

II. PHYSICS AND POLITICS; OR, THOUGHTS ON THE APPLICATION OF THE PRINCIPLES OF "NATURAL SELECTION" AND "INHERITANCE" TO POLITICAL SOCIETY. By WALTER BAGEHOT, Esq., author of "The English Constitution," 1 vol. Cloth. Price, $1.50.

III. FOODS. By EDWARD SMITH, M. D., LL. B., F. R. S. 1 vol. Cloth. Price, $1.75.

IV. MIND AND BODY: THE THEORIES OF THEIR RELATIONS. By ALEX. BAIN, LL. D., Professor of Logic in the University of Aberdeen. 1 vol., 12mo. Cloth. Price, $1.50.

V. THE STUDY OF SOCIOLOGY. By HERBERT SPENCER. Price, $1.50.

VI. THE NEW CHEMISTRY. By Prof. JOSIAH P. COOKE, Jr., of Harvard University. 1 vol., 12mo. Cloth. Price, $2.00.

VII. THE CONSERVATION OF ENERGY. By Prof. BALFOUR STEWART, LL. D., F. R. S. 1 vol., 12mo. Cloth. Price, $1.50.

VIII. ANIMAL LOCOMOTION; OR, WALKING, SWIMMING, AND FLYING, WITH A DISSERTATION ON AËRONAUTICS. By J. BELL PETTIGREW, M. D., F. R. S. E., F. R. C. P. E. 1 vol., 12mo. Fully illustrated. Price, $1.75.

IX. RESPONSIBILITY IN MENTAL DISEASE. By HENRY MAUDSLEY, M. D. 1 vol., 12mo. Cloth. Price, $1.50.

X. THE SCIENCE OF LAW. By Prof. SHELDON AMOS. 1 vol., 12mo. Cloth. Price, $1.75.

XI. ANIMAL MECHANISM. A TREATISE ON TERRESTRIAL AND AËRIAL LOCOMOTION. By E. J. MAREY. With 117 Illustrations. Price, $1.75.

XII. THE HISTORY OF THE CONFLICT BETWEEN RELIGION AND SCIENCE. By JOHN WM. DRAPER, M. D., LL. D., author of "The Intellectual Development of Europe." Price, $1.75.

XIII. THE DOCTRINE OF DESCENT, AND DARWINISM. By Prof. OSCAR SCHMIDT, Strasburg University. Price, $1.50.

XIV. THE CHEMISTRY OF LIGHT AND PHOTOGRAPHY. IN ITS APPLICATION TO ART, SCIENCE, AND INDUSTRY. By Dr. HERMANN VOGEL. 100 Illustrations. Price, $2.00.

XV. FUNGI; THEIR NATURE, INFLUENCE, AND USES. By M. C. COOKE, M. A., LL. D. Edited by Rev. M. J. BERKELEY, M. A., F. L. S. With 109 Illustrations. Price, $1.50.

XVI. THE LIFE AND GROWTH OF LANGUAGE. By Prof. W. D. WHITNEY, of Yale College. Price, $1.50.

XVII. MONEY AND THE MECHANISM OF EXCHANGE. By W. STANLEY JEVONS, M. A., F. R. S., Professor of Logic and Political Economy in the Owens College, Manchester. Price, $1.75.

XVIII. THE NATURE OF LIGHT, WITH A GENERAL ACCOUNT OF PHYSICAL OPTICS. By Dr. EUGENE LOMMEL, Professor of Physics in the University of Erlangen. With 188 Illustrations and a Plate of Spectra in Chromolithography. Price, $2.00.

XIX. ANIMAL PARASITES AND MESSMATES. By Monsieur VAN BENEDEN, Professor of the University of Louvain, Correspondent of the Institute of France. With 83 Illustrations. (_In press._)

THE INTERNATIONAL SCIENTIFIC SERIES.

ANIMAL PARASITES AND MESSMATES.

BY

P. J. VAN BENEDEN,

PROFESSOR AT THE UNIVERSITY OF LOUVAIN, CORRESPONDENT OF THE INSTITUTE OF FRANCE.

_WITH EIGHTY-THREE ILLUSTRATIONS._

NEW YORK: D. APPLETON AND COMPANY, 549 & 551 BROADWAY. 1876.

CONTENTS. vii

PAGE

INTRODUCTION.

Adaptation of Food to Animals--Animal Manufacturers-- Brigands--Messmates--Mutualists--Theory of Spontaneous Generation xiii