PREFACE. 



IN the preparation of this Treatise, the Author has kept 

 -steadily in view the objects at which he has aimed in the 

 preceding volumes, and in the attainment of which he 

 trusts that he has been in some degree successful ; namely, 

 the exposition of the principles of Science in their simplest 

 form, and the illustration of these by the most useful and 

 interesting examples. He has so fully explained his views 

 on the utility of the study of Zoology, and on the mode in 

 which it may be most advantageously pursued, in the Intro- 

 duction and First Chapter of the present volume, that 

 he considers any further remarks on these subjects here 

 uncalled for. 



The general account of the Classes is translated, with some 

 additions and modifications, from the " Cours Elernentaire 

 de Zoologie "of M. Milne-Edwards ; a work adopted by 

 the French Government as the Text-Book of instruction, 

 in the Colleges connected with the University of Paris ; 

 and the whole of the beautiful illustrations prepared for 

 that Treatise, will be found in the present volumes. For 

 the more detailed accounts of the Orders, Families, &c., 

 as well as for the first Two Chapters, the Author is solely 

 responsible. In the preparation of these portions of the 

 work, he has availed himself of the best and most recent 



