Acknowledgment of the principal sources of information has been made in footnotes, and a short list of leading authorities has been appended to the chapters on anatomy, for the use of students desirous to pursue the subject further. In the case of geographical distribution the authorities are too numerous and scattered to admit of a list being given. A special word of thanks is due to Mr. Edwin Wilson for his patient care in preparing the illustrations, the majority of which are taken from specimens in the University Museum of Zoology. Mr. Edgar Smith, besides affording the kind help which visitors to the British Museum always experience at his hands, has permitted me to use many specimens for the purposes of illustration. A. H. COOKE. KING’S COLLEGE, CAMBRIDGE, _20th December 1894_. CONTENTS SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK. MOLLUSCA CHAPTER I INTRODUCTION--POSITION OF MOLLUSCA IN THE ANIMAL KINGDOM--CLASSIFICATION--ORIGIN OF LAND AND FRESH-WATER MOLLUSCA 1 CHAPTER II LAND AND FRESH-WATER MOLLUSCA, THEIR HABITS AND GENERAL ECONOMY 23 CHAPTER III ENEMIES OF THE MOLLUSCA--MEANS OF DEFENCE--MIMICRY AND PROTECTIVE COLORATION--PARASITIC MOLLUSCA--COMMENSALISM--VARIATION 56 CHAPTER IV USES OF SHELLS FOR MONEY, ORNAMENT, AND FOOD--CULTIVATION OF THE OYSTER, MUSSEL, AND SNAIL--SNAILS AS MEDICINE--PRICES GIVEN FOR SHELLS 96 CHAPTER V REPRODUCTION--DEPOSITION OF EGGS--DEVELOPMENT OF THE FERTILISED OVUM--DIFFERENCES OF SEX--DIOECIOUS AND HERMAPHRODITE MOLLUSCA--DEVELOPMENT OF FRESH-WATER BIVALVES 123 CHAPTER VI RESPIRATION AND CIRCULATION--THE MANTLE 150 CHAPTER VII ORGANS OF SENSE: TOUCH, SIGHT, SMELL, HEARING--THE FOOT--THE NERVOUS SYSTEM 177 CHAPTER VIII THE DIGESTIVE ORGANS, JAW, AND RADULA: EXCRETORY ORGANS 209 CHAPTER IX THE SHELL, ITS FORM, COMPOSITION, AND GROWTH--DESIGNATION OF ITS VARIOUS PARTS 244 CHAPTER X GEOGRAPHICAL DISTRIBUTION OF LAND AND FRESH-WATER MOLLUSCA--THE PALAEARCTIC, ORIENTAL, AND AUSTRALASIAN REGIONS 277 CHAPTER XI