Transcriber's note: Text enclosed by underscores is in italics (_italics_). A single underscore introduces a subscript (CO_2), and a caret a superscript (B^1). Page numbers enclosed by curly braces (for example: {25}) have been incorporated to facilitate the use of the Alphabetical Index and other page references in the text. * * * * * THE CAMBRIDGE NATURAL HISTORY EDITED BY S. F. HARMER, M.A., Fellow of King's College, Cambridge; Superintendent of the University Museum of Zoology AND A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge; University Lecturer on the Morphology of Invertebrates VOLUME II [Illustration] FLATWORMS AND MESOZOA By F. W. GAMBLE, M.Sc. (Vict.), Owens College NEMERTINES By Miss L. SHELDON, Newnham College, Cambridge THREAD-WORMS AND SAGITTA By A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge ROTIFERS By MARCUS HARTOG, M.A., Trinity College, Cambridge (D.Sc. Lond.), Professor of Natural History in the Queen's College, Cork POLYCHAET WORMS By W. BLAXLAND BENHAM, D.Sc. (Lond.), Hon. M.A. (Oxon.), Aldrichian Demonstrator of Comparative Anatomy in the University of Oxford EARTHWORMS AND LEECHES By F. E. BEDDARD, M.A. (Oxon.), F.R.S., Prosector to the Zoological Society, London GEPHYREA AND PHORONIS By A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge POLYZOA By S. F. HARMER, M.A., Fellow of King's College, Cambridge London MACMILLAN AND CO., LIMITED NEW YORK: THE MACMILLAN COMPANY 1901 _All rights reserved_ 'Nous allons faire des vers ensemble' ANDRÉ DE CHÉNIER _First Edition 1896. Reprinted 1901_ CONTENTS PAGE SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK ix PLATYHELMINTHES AND MESOZOA CHAPTER I TURBELLARIA INTRODUCTION—DESCRIPTION OF THE POLYCLAD _LEPTOPLANA TREMELLARIS_ —APPEARANCE—HABITS—STRUCTURE: POLYCLADIDA—CLASSIFICATION—HABITS —ANATOMY—DEVELOPMENT: TRICLADIDA—OCCURRENCE—STRUCTURE —CLASSIFICATION: RHABDOCOELIDA—OCCURRENCE—HABITS—REPRODUCTION —CLASSIFICATION 3 CHAPTER II TREMATODA CHARACTERS OF TREMATODES—HABITS AND STRUCTURE OF TREMATODA ECTOPARASITICA (MONOGENEA)—LIFE-HISTORIES OF _POLYSTOMUM INTEGERRIMUM_, _DIPLOZOON PARADOXUM_, AND _GYRODACTYLUS ELEGANS_ —TREMATODA ENDOPARASITICA (DIGENEA)—OCCURRENCE AND HABITS OF DIGENEA —LIFE-HISTORY OF _DISTOMUM MACROSTOMUM_—_DISTOMUM HEPATICUM_ AND ITS EFFECTS—_BILHARZIA HAEMATOBIA_—BISEXUAL TREMATODES—TABLE OF HOSTS —CLASSIFICATION 51 CHAPTER III CESTODA