PREFACE vii 



acquaintance with the group. It has not appeared to me to be necessary 

 to go at great length into the history of erroneous views or of misstatements 

 of fact at any rate compression and omission here seemed to be more per- 

 missible than in other departments of the subject. I have deliberately omitted 

 to give any account of the early stages of the development of the Oligochaeta ; 

 the development of organs will be found treated of to a certain extent. 

 I determined to do this principally on account of Prof. Vejdovsky's recently 

 published ' Entwickelungsgeschichtliche Untersuchungen,' an elaborate and 

 finely-illustrated work, which goes into the matter with all details, and 

 treats of the rest of the literature in a most thorough fashion. Moreover, 

 I have personally no first-hand acquaintance with the early development 

 of the Oligochaeta another circumstance which leads me simply to refer to 

 the work already quoted those who are desirous of ascertaining what is known 

 about the embryology of the Oligochaeta. Another branch of the subject 

 which I have thought it well to abridge is the section dealing with 

 unrecognizable species. No name, I hope, has been omitted, and no reference ; 

 but I have not, except in a few instances, gone at any length into the endless 

 possibilities as to the identity of species imperfectly described and now 

 irrecoverable. 



While this work was in preparation two excellent revisions of two 

 families of the Oligochaeta have appeared : I refer to Dr. Rosa's detailed 

 account of the Lumbricidae, and to Dr. Michaelsen's ' Synopsis ' of the 

 Enchytraeidae. The appearance of these two valuable papers caused me to 

 hesitate a little before dealing with the respective families in this work. 

 I have, however, thought it best to incorporate both of them, not, I hope, 

 without critical examination. 



In the preparation of the systematic part of this monograph I received 

 the greatest assistance from M. Vaillant's work ; I gladly acknowledge that 

 it formed the basis of my preliminary (manuscript) account of many of the 

 species of Oligochaeta, and that it has saved me a vast amount of labour in 

 compilation ; I believe, however, that I have nowhere followed M. Vaillant's 

 descriptions and synonymies without careful verification and criticism. 



In the general sketch of the structure of the group I have only dealt 

 with generalities ; the details of particular genera, or it may be of species, 



