PREFACE TO THE FIRST EDTTIO 



An understanding of structure, development, and relationships 

 of animals is essential as a basis for all lines of zoological study 

 and investigation. In the early history of the teaching of 

 zoology, a thorough grounding in these fundamental elements of 

 the science was the chief objective of the introductory courses 

 offered in colleges and universities. It was through an early 

 training of this sort that most of the prominent general zoologists 

 of the present and the preceding generations have passed. 

 Whether they remained in the older fields of general zoology or 

 entered as pioneers into virgin lines of investigation, this broad 

 training gave to them an understanding of animals which could 

 be gained by no other method. 



There is a growing practice of placing major emphasis upon 

 biological principles in the fundamental courses in college 

 zoology. There are many arguments in support of such training 

 based upon principles for beginners in the science. However, in 

 such a course students frequently have so httle knowledge of 

 animals that there is but limited opportunity for them to have 

 either a full understanding of the principles or capacity for 

 making applications of them. Under these conditions it becomes 

 essential that the introductory course be supplemented by a 

 systematic study of organisms. Even in the instances where the 

 initial course follows essentially the old type method of instruc- 

 tion, the number of forms covered is inadequate and should be 

 followed by further studies. 



Because of their relations to human anatomy and development 

 and as specific material for instruction of premedical students, 

 specialized courses in vertebrate zoology are very generally 

 given. For students who are seeking training either as teachers 

 or as investigators, there is fully as much need for specific courses 

 pertaining to the invertebrates. 



There have been some admirable large treatises dealing with 

 the invertebrates, and there have been several American labora- 

 tory guides intended for such a course but there have been few 

 books available as student textbooks. In the present work, the 

 writer has endeavored to collate materials which will serve as a 



