PEEFACE 



THE present volume is the " Third Part " in order of a com- 

 prehensive treatise on Zoology, which has been for some time 

 in preparation under my editorship. In this treatise each 

 of the larger groups of the Animal Kingdom is to be described 

 by a separate author; whilst, as far as possible, uniformity 

 in method and scope of treatment is aimed at. The authors 

 are, for the most part, graduates "of the University of Oxford, 

 though it may not be possible to maintain this limitation in 

 future sections of the work. 



The general aim of the treatise is to give a systematic 

 exposition of the characters of the classes and orders of the 

 Animal Kingdom, with a citation in due place of the families 

 and chief genera included in the groups discussed. The work 

 is addressed to the serious student of Zoology. To a large 

 extent the illustrations are original. A main purpose of the 

 Editor has been that the work shall be an independent and 

 trustworthy presentation, by means of the systematic survey, 

 or taxonomic method, of the main facts and conclusions of 

 Zoology, or, to speak more precisely, of Animal Morphography. 



The treatise will be completed in ten parts of the size of 

 the present one. It will at once be apparent that this 

 limitation necessitates brevity in treatment which, however, 

 will not, it is believed, be found inconsistent with the fulfil- 

 ment of the scope proposed or with the utility of the work 



