vi PREFACE 



to students. The immediate publication of the following 

 parts may be expected : 



Part I. Introduction and the Protozoa. 



Part II. Enterocoela and the Coelomocoela The Pori- 

 fera The Hydromedusae The Scypho- 

 medusae Th$ Anthozoa The Ctenophora 

 (the present volume). 



Part III. The Echinoderma (published in March 1900). 



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. This pro- 

 cedure 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 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. E. S. 



Goodrich, M.A.Oxon. 



E. RAY LANKESTER. 



August 1900. 



