INTRODUCTION 



No monograph exists embracing the Nematoda as a whole, 

 and containing diagnoses either of genera, of famihes or of 

 higher groups, to which a worker who is not a specialist can 

 turn for assistance in the determination of specimens. It is 

 chiefly with the object of relieving this situation to some slight 

 extent that the present work has been undertaken. In the 

 labour of compiling it we have been very greatly assisted by 

 Stiles and Hassall's valuable Index-Catalogue of Medical and 

 Veterinary Zoology. Indeed, it is only the recent publication 

 (1920) of the subject- volume dealing with Roundworms that 

 has made it possible to gather together a collection of generic 

 diagnoses in any degree approaching completeness. Inciden- 

 tally, the attempt to collect these diagnoses has demonstrated 

 that a large proportion of those to be found in the literature 

 are totally inadequate, and in many instances it is doubtful 

 whether the genera concerned can ever again be recognized. 

 This statement, so far as the more modern literature is con- 

 cerned, refers particularly to the free-living forms. 



When the present work had already been in preparation 

 for some months, it came to our knowledge that Professor 

 Warrington Yorke and Dr. P. A. Maplestone, of the Liverpool 

 School of Tropical Medicine, were preparing a book on some- 

 what similar lines,* and that it was in a considerably more 

 advanced state than our own. We learnt, however, that it 

 was the authors' intention to deal only with the Nematodes 

 parasitic in Vertebrates. Professor Yorke, with the greatest 

 kindness and generosity, sent us the proofs of the book before 

 its publication, and allowed us to make use of them in com- 

 pleting our work. It was, however, unfortunately too late 

 for us to make full references to the book throughout the text, 

 and we have only done so where we have been particularly 

 indebted to it for fresh information. 



Our original plan was to confine our attention to genera 

 published before the end of the year 1923, and we have adhered 

 fairly strictly to this principle. It was found impossible to 

 obtain and consult all the literature necessary to keep pace 

 with the constant output of new genera since that date, and so 

 render the catalogue complete up to the moment of publica- 



♦ The Nematode Parasites of Vertebrates, London (192G). 



vii 



