VI. PREFACE 



appearance. For the sake of reference an index has been 

 prepared and a separate pagination has been given above 

 the original pagination, which was retained for the sake of 

 the cross references in the text of the separate parts. The 

 original numbering of the plates has been retained, and as 

 the plates of each part are to be found immediately following 

 that part no difficulty should be experienced in referring to 

 the figures. 



This work was carried out while I was a member of the 

 Zoological Staff of the Manchester University, and I should 

 like again to express my sincere thanks to my former 

 teacher, Prof. Sydney J. Hicksdn, and to the Council of the 

 University for the opportunities which they gave me for 

 the prosecution of my studies. I would also take this 

 opportunity of thanking Sir Ray Lankester for his help in 



the matter of publication. 



C. GORDON HEWITT. 



