VI PREFACE 



In the following pages I have endeavored to incorporate 

 such facts as are adapted to American college students or high 

 school students in their final years. The first two chapters are 

 devoted to a brief consideration of the more important general 

 principles underlying the biological sciences. While there is 

 much difference of opinion among teachers as to the best 

 method of presenting the subject of zoology to the adult stu- 

 dent, all are agreed that some knowledge of these principles 

 should be the first step; whether this knowledge should be 

 imparted as a preliminary part of the general subject of zoologv, 

 as in this book, or as a separate subject, — biology, — more or 

 less complete in itself, is comparatively immaterial perhaps ; 

 these chapters have been written for those who prefer the 

 former method, — recognizing that the student of zoology 

 wishes to get at the actual study of animal life as soon as pos- 

 sible, — with as brief an introduction as is necessary to make 

 the facts of the science intelligible ; they can readily be omitted 

 or rapidly reviewed, without affecting the usefulness of the book, 

 by those who prefer to begin the subject with a special text-book 

 of biology. This portion of the book, instead of giving a long 

 list of definitions of various biological sciences and a discussion 

 of cytological problems, briefly defines zoology, treats of the 

 phenomena of living matter in general, shows the relation of 

 protoplasm to the cell, the cell to the tissue, the tissue to the 

 organ, and the organ to the individual, and then gives the 

 fundamental principles of zoological classification. 



The second portion of the book is devoted to a description 

 of the various animal types. Here the chief object has been to 

 present such facts concerning the structure and life history of 

 the different groups as will enable the elementary student to 

 gain a conception of those characteristics which are fundament- 

 ally distinctive and yet, for the most part, easily recognized. 

 Thus, except in the lowest groups, it is the differences of 

 external structure which have been given the prominent place, 

 although in no case has the general internal anatomy been 

 ignored. The classification has in most instances been carried 

 as far as the orders ; occasionally suborders are mentioned. 

 While there are scarcely two zoologists who agree on the sub- 



