PREFACE 



THE authors have long felt the need of one book in the 

 hands of the student which would give not only the salient 

 facts of structural Zoology and the development of the various 

 branches of animals, but also such facts of natural history or 

 the life and habits of animals as to show the interrelations of 

 structure, habit, and environment. For we believe that a 

 knowledge of both structure and life-history is necessary before 

 any suggestions or discoveries can be made concerning the prin- 

 ciples which underlie and control all animal life, including that 

 of man. For it is principles and their application for which we 

 are searching. 



This book is an attempt to supply this need. It is especi- 

 ally designed to accompany the " Field and Laboratory Guide " 

 (Part I). 



For the sake of the natural history many examples have 

 been included. To reduce the size of the book it has been 

 necessary to print this natural history in smaller type, but 

 that in no way implies that it is of minor importance, and it is 

 by far the most interesting portion of the subject. The scien- 

 tific names need not, in all cases, be learned. They have been 

 used because common names are so often misleading. 



