The present edition is completely revised and rewritten by the author. It is a perfect book for B.Sc. and M.Sc. students of Zoology. Explanations are clear and detailed, with adequate coverage of each topic. Close attention has been paid to cross-referencing, the detailed tables of contents and illustrations. Diagrams are beautifully drawn with utmost clarity. An innovation in the present edition is the inclusion of the elements of a classification under each illustration of a whole, or almost whole, animal. This will help the student more or less painlessly to familiarize himself with animal's systematic position. Attempt has been made to retain the basic morphology and yet at the same time emphasise functional aspects and where possible, present animals as living creatures rather than a laboratory specimens. Scholars believe, and we concur, that this book is important enough to be preserved, reproduced, and should be available to the public. This work has been republished using a format that seamlessly blends the original graphical elements with text in an easy-to-read typeface.