PREFACE 



In presenting the second part of my work on Zoology to the 

 public I must apologise for the delay in its appearance and 

 for the fact that I am not keeping to the undertaking which 

 I gave in the preface to my first volume that the work would 

 be completed in two volumes The delay in pubUcation 

 has been caused in part at least by the fact that the Verte- 

 brata compel a lengthier and more detailed treatment than 

 the other groups. Not only is more known about them, 

 but they excite greater interest, and their palaeontological 

 history has been more completely worked out than in the 

 case of any other phylum. The result has been the present 

 bulky volume which deals only with them and with Amphi- 

 oxus. 



Embryology is of course excluded, except in the case of 

 Amphioxus, but I have endeavoured to deal fairly fully 

 with anatomy, habits, and classification. In the systematic 

 portions I have probably been too ambitious, but the 

 usefulness of a book of this kind depends largely upon its 

 completeness in this respect, and in cases of doubt I have 

 generally included rather than excluded. In Aves alone 

 have I made a selection ; for there are many excellent 

 works devoted to them and it would be impossible to give 

 anything like a complete list of their genera. 



In judging the anatomical portions I would ask the reader 

 to remember that this is not exclusively a work on Compara- 

 tive Anatomy, and limitations of space forbid an exhaustive 

 treatment. This branch of the subject has not, however, 

 been neglected, and questions of general interest have usually 

 been at least touched upon. 



Considerable space has been given to extinct forms. 



