THIS BOOK HAS BEEN DEVELOPED FROM A SHORT LECTURE COURSE GIVEN to advanced undergraduate students as part of a general introduction to the subject of parasitology for zoologists. The book is written for the undergraduate who has no previous experience of parasitology and little background in either biochemistry or physiology. It is not a long book, and students will have to consult some of the more detailed textbooks in parasitology and physiology to gain a full understanding of the topics considered here. My objective in writing this book is to introduce the breadth of parasite physiology, leaving the reader to obtain a depth of knowledge by his own library research. Each chapter covers a single topic or related topics in physiological parasitology, and the variable length of the chapters reflects the amount of research interest that has been generated over the last few decades. It is to be hoped that by use of this book students will develop an interest in some of the more neglected areas and be stimulated to make good some of the more glaring deficiencies in our current knowledge. I should like to acknowledge with gratitude the assistance of my colleagues Dr 1. Barrett, Dr R. A. Klein, Dr A. W. Pike and Dr R. A.