V 



PREFACE. 



IN preparing the present work I have heen actuated 

 mainly by the desire to place before English students 

 of Zoology a treatise in which the subject was dealt with 

 on the lines followed with so much advantage by Glaus 

 and his predecessors in their works on Zoology. My original 

 intention was to bring out a new edition of Glaus' Lchrbuch, 

 revised and brought up to date, and a trace of this intention 

 may be seen in a few pages of the present volume. But 

 this plan was, for various reasons, soon given up, and the 

 present treatise is, with the exception of about twenty pages, 

 an entirely new work. 



For a successful study of Zoology it is necessary that the 

 student should begin by making a thorough examination of 

 individual animals, of their structure, of the functions of 

 their parts, of their relation to the external world and to 

 each other. This method of study by types, which was largely 

 introduced into this country by Huxley, and is admirably 

 exemplified by that author's book on the Crayfish, is absolutely 

 necessary as a preliminary to any thorough study of Zoology. 

 I'.y pursuing it the student acquires, if the animals are 

 properly selected, a knowledge of the principal forms of 

 animal life, and a basis from which more extended studies 

 can be made. It is to assist these more extended studies 

 that the present work is designed. At the same time it is 

 hoped that the book will be of value to all interested in 

 Natural History, whether professedly students of Zoology or 

 jjot, if in no other way than as a handy book of reference in 

 which, by means of the index, information may be gained of 



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