vi PREFACE 



of M. Vaillant, and one which should deal with the entire subject up to the 

 date of publication. As will be seen from the bibliography which I have 

 given in the Appendix, the literature of this subject is large and scattered ; 

 so that to bring together under one cover all of importance that is as yet 

 known about the group of the Oligochaeta will possibly be considered not to 

 have been a useless performance. In attempting this labour I have received 

 much kindly encouragement from Professor Ray Lankester, which I gratefully 

 acknowledge. I have been so fortunate, through the kind influence of 

 Dr. Burdon Sanderson, as to secure the assistance of the Clarendon Press, 

 to the Delegates of which institution I wish to express my great indebted- 

 ness. The cost of the necessary illustrations, which has been considerable, 

 has been largely defrayed by the generosity of Mr. J. P. Gassiot, F. Z. S., 

 who, at the suggestion of Mr. Sclater, has placed a sum of 100 at my 

 disposal for this purpose. Without this very liberal act of assistance on 

 Mr. Gassiot's part this work could hardly have been undertaken. 



I may now say a few words about the scope of this monograph. The 

 study of the group with which it deals is one which has occupied my leisure- 

 time for the past fifteen years ; I have had the opportunity of dissecting 

 and examining most, if not all, of the more important types ; so that while 

 a good part of the volume is necessarily derived from compilation, a con- 

 siderable proportion of it is the result of first-hand knowledge. Whilst 

 I have amalgamated my recent papers into the present work, I have also 

 incorporated with it a certain amount of new matter which I have not 

 published elsewhere, and I have given, in the systematic part, descriptions of 

 a few new species. I have not, however, made any lengthy investigations 

 for the express purpose of this monograph, but I have in several cases verified 

 the statements of others, and have corrected, in a few minor particulars, 

 errors of observation on the part of myself, as well as of other zoologists. 

 Those who have not followed closely the progress of knowledge in this group 

 of animals may be surprised at the large number of pages which it has taken 

 me to set down the facts : I have erred, however, rather on the side of 

 compression and omission than on that of undue prolixity. The omissions 

 (with a few exceptions to be noted immediately) will not be found, I trust, 

 to be of facts of much importance. They chiefly concern the progress of our 



