PREFACE 



In English speaking countries the leeches are a neglected group 

 of animals. Very few zoologists study them and apart from the 

 volume in the " Fauna of British India" series there is no book in 

 English devoted to them. In Germany and the central European 

 countries the Hirudinea are much better known. Antrum (1939) 

 lists over 2500 research papers, most of them in German, and 

 leech biology has been summarized in several extensive works. 



The purpose of this volume is to present a fairly concise account 

 of the Hirudinea at a level appropriate to the honours student of 

 zoology at a university. It is hoped that a summary of present 

 knowledge, particularly in the realm of physiology, will also be of 

 value to more senior zoologists, so references to the original papers 

 have been given where appropriate. The guiding principle in 

 determining to what extent the text need be interrupted by 

 references has been that work summarized in the Hirudinea 

 volume of Bronns: Klassen und Ordnungen des Tierreichs (1936-9) 

 should be quoted without extensive references, while results 

 published since 1939 and here reviewed for the first time should 

 be fully documented. 



The first three chapters are intended as an introduction to the 

 group for beginners. For this purpose it has been thought best 

 to give a fairly thorough description of Hirudo medicinalis as a type 

 species rather than an account of the group in general or compara- 

 tive terms. After this there follows a chapter in which the main 

 features of the various families are set out. 



The reader whose prime interest is physiological may pass 

 straight to Chapter 4, using the previous chapters only as a source 

 of reference when unexplained morphological or taxonomic terms 

 are encountered. 



