vi PREFACE 



to students. The immediate publication of the following 

 parts may be expected : 



Part I. Introduction and the Protozoa. 



Part II. General Discussion of the Metazoa The Pori- 

 fera The Hydromedusae The Scypho- 

 medus^e The Anthozoa The Ctenophora. 



Part III. The Echinoderma (the present volume). 



Part IV. The Mesozoa The Platyhelmia The Nemer- 

 tini. 



These parts will be issued, without reference to logical 

 sequence, as soon as they are ready for the press. In accord- 

 ance with this procedure, which to some extent evades the 

 injustice of making an author, whose work is finished, wait 

 for publication until other more tardy writers have completed 

 their tasks, the present volume, which is Part III., is the first 

 to make its appearance. 



The following authors have undertaken portions of the 

 work : Professor Poulton, F.R.S., M.A. Oxon. ; Professor 

 Weldon, F.R.S., M.A. Oxon. ; Professor Benham, D.Sc., M.A. 

 Oxon.; Mr. G. C. Bourne, M.A. Oxon. ; Mr. G. H. Fowler, 

 M.A. Oxon. ; Professor Minchin, M.A. Oxon. ; Mr. F. A. Bather, 

 M.A. Oxon. ; Professor J. W. Gregory, D.Sc. ; and Mr. K S. 

 Goodrich, M.A. Oxon. 



E. RAY LANKESTER. 



February 1900. 



