PREFACE 



The purpose of this book is to provide the reader with a practical key 

 to the identification of land and fresh-water animals. We hope that it will 

 unlock the door to the great number of more technical or more detailed 

 treatises and thereby carry the inquiring student over the first and often most 

 difficult hurdle on the road to a knowledge of animals. Because the literature 

 of animal taxonomy is often not readily available and only too often not 

 readily comprehended by the general student of animal life, the idea has 

 become popular that only an expert can be expected to identify animals. 

 This unfortunate attitude has discouraged many a promising beginner from 

 attempting field work. We do not for one moment deny that the final verifica' 

 tion, in case of rare or peculiar animals or in scientific studies, should be made 

 by an authority on each group. We do feel, however, that the more common 

 animals can be identified with reasonable accuracy by any interested person 

 who is willing to follow up the use of keys, such as are given here, with a care 

 ful checking of the descriptions given in the references listed. The present 

 work is designed not to replace, but rather to serve as an introduction to, the 

 painstaking and detailed works of our zoologists. 



The type of key used is one that we have found, after much experimenta- 

 tion with students and long-suffering friends, to be the easiest to operate, 

 especially if one is holding a squirming animal in one hand meanwhile. 

 Wherever possible external and readily visible identification characters have 

 been used. For the finer details of classification a complete study of the 

 animal — external and internal anatomy and even physiology — is necessary, 

 but this book is intended for the use of those who are not yet expert zoologists. 

 It is also intended to serve as a field manual, where dissection facilities are 

 seldom available. Line drawings are included as the simplest way of picturing 

 the terms and characters used in the keys and to give the amateur an idea 

 of the likenesses and diversity to be found in each group. 



Not every species, or even every genus, can be included within the limits 

 of this book. The rarer forms not included will usually key to the most 

 nearly related of the included forms, and consultation of the literature will 

 usually clear up the difficulty. For groups about which a great deal of in- 

 formation is readily available, such as the birds and insects, only general 

 treatments have been considered necessary. Some groups, such as the Ostracods 

 and the smaller water Turbellaria, which are minute or require the knowledge 

 or dissection of certain parts beyond the skill of the amateur, are carried only 

 to the group or to the most common families or genera. 



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