The book is entirely rewritten by different authors each of them is a specialist in their own fields. It is a complete revised edition of the first volume of the book originally written by Professors Parker and Haswell in 1898. An up to date and authoritative account of the whole field of comparative invertebrate zoology is covered in this book. The book is of great significance for academicians and scholars and value to literature. This forms a part of the knowledge base for future generations. A relatively conventional sequence of subjects is followed. Explanations are clear and detailed, with adequate coverage of each topic. Diagrams are beautifully drawn with utmost clarity.