PREFACE TO THE FIFTH EDITION. 



THE present edition of this work, in its general ground-plan, 

 is essentially identical with those which have preceded it ; but 

 it has, nevertheless, been subjected to very considerable modi- 

 fications in detail. The original aim of the work was to give, 

 in as clear and concise a form as possible, the chief parts of 

 Systematic Zoology, and to give only such a selection from 

 these as could be readily made available by ordinary students. 

 In the present edition this aim has been faithfully adhered to, 

 and, it is hoped, has been more thoroughly carried out than 

 on previous occasions. 



While in the main preserving its original basis, the entire 

 work has been submitted to careful revision, and large portions 

 of it have been almost entirely rewritten. A very considerable 

 amount of new matter has been added ; but an undue increase 

 in the size of the book has been prevented by the expedient 

 of printing portions of the text in small type. Some space 

 has also been gained by the omission of the synoptical tables 

 of the families of the various orders and classes of the animal 

 kingdom, which were inserted in former editions; and the 

 space thus gained has been largely taken by bibliographical 

 lists, indicating for each great division of animals the more 

 important sources to which the student may look for original 

 information. 



Much of the increase in the bulk of this edition is further 

 due to the fact that nearly one hundred additional illustrations 

 have been introduced, which, it is believed, will materially 

 assist in the comprehension of the text. In connection with 



