This text is a general introduction to zoology at the college and university level. The subject matter is arranged to facilitate readings with either lectures or laboratory work and for reference use. Part I deals with general principles of animal biology. The first chapters deal with the finer structures of the body and their organization into special systems that carry on essential life processes. Succeeding chapters consider the more general phases of animal existence reproduction, heredity, distribution and evolution. The synopses of classification, a special feature of the book, have been prepared from recent publications with the help of specialists and organized on a uniform pattern. They show the extent, diversity, and relationships of animals constituting each of the larger groups and something of their mode of occurrence. They may also aid in identification of a specimens as to phylum, class or order.