I have tried in this book to present the subject in a way that will interest the student who does not intend to follow a career in the parasitology. I hope also this book will interest those with some experience in the parasitology. It is therefore my earnest hope that readers will read this book not with their eyes but with their minds , to try and get at the fundamentals of the various problems. Finally, I gratefully acknowledge my indebtedness to my husband (Dr. Alfageh, Z. A.) for his continuous intellectual, guidance and moral support to me.