viii PREFACE 



tion in all biological branches, and this book is designed to be 

 used for constant reference, not only in connection with lectures 

 and recitations, but also in the laboratory and in museum and 

 field work. All of these methods of instruction should be 

 employed in an elementary college course in zoology. No 

 special directions for laboratory work have been given, for 

 teachers of this subject have all had such- laboratory training 

 that they are familiar with the methods best suited to the par- 

 ticular conditions under which they are teaching, while there 

 are, further, many excellent laboratory guides already in print. 

 I have for many years combined field work, particularly at the 

 seashore, and visits to museums with the other methods of 

 instruction, and believe that they are of great assistance to 

 the beginner and should be pursued more extensively than 

 they are at present in many colleges. 



No apology is necessary for the large number of illustrations ; 

 in a book of this type, which aims to give the student a general 

 survey over the entire field of animal life, illustrations are as 

 necessary as charts are to a lecture. In the laboratory the stu- 

 dent can, under the most favorable conditions, see only a rela- 

 tively few representative animals ; in the museum the smaller 

 animals are not the most striking and are soon forgotten, while 

 enlarged models of microscopic animals are rare ; the text-book, 

 then, must supply these deficiencies, hence the large number of 

 figures illustrating the external form of animals, supplemented 

 by some diagrams to illustrate types of internal structure and 

 occasionally embryological stages. 



It has been the purpose of this book to include in a single 

 volume of convenient size all that is necessary for an element- 

 ary course in zoology in our American colleges, suitable for 

 the general student and at the same time a proper introduction 

 for extended treatises, such as the text-book of Parker and 

 Haswell, or the books distinctively on comparative anatomv, 

 for the student who wishes to pursue the subject further. 

 There is at present no book on zoology that exactly meets this 

 need or that treats the subject in a way suited to the adult stu- 

 dent who is, to some extent, capable of thinking for himself and 

 forming his own judgments. Hence the treatment here is new ; 



