PREFACE 



This book is intended for the use of students who have com- 

 pleted a year's study of the principles of zoology and of the 

 anatomy and physiology of a series of invertebrate types such as 

 is provided by any of several elementary textbooks in use in this 

 country. The types commonly included in these books — ^various 

 Protozoa, Hydra, Ascaris, and the Liver Fluke, Earthworm, 

 Leech, Crayfish, Cockroach, Pond Mussel, and Starfish — are not 

 here described in detail. We have endeavoured to provide the 

 student with a classification of the Invertebrata which proceeds 

 as far as is usual in an honours course, with a concise statement 

 of the characteristic features of each of the groups mentioned, 

 and with a more detailed statement and discussion of matters of 

 importance or interest concerning them. The choice of examples 

 has been difficult, and we have not always been able to include 

 all those we should have wished, but a fairly full account of 

 certain representative genera has been given. 



The writing of the book has been shared among us as follows : 

 Chapters I-IV, X, XI (except Onychophora), XII, XVIII and 

 XIX have been written by L. A. Borradaile, Chapters V (except 

 Ctenophora), VII-IX, XIII, XV-XVII, and the Onychophora 

 in Chapter XI by F. A. Potts, Chapter VI and the Ctenophora in 

 Chapter V by J. T. Saunders, and Chapter XIV jointly by F. A. 

 Potts and L. E. S. Eastham, but each of us has read and criti- 

 cized the work of the others. 



We desire to express our grateful thanks for valuable advice 

 and criticism to Dr S. J. Hickson, Professor D. Keilin and 

 Dr S. M. Manton ; for much care bestowed upon the illustrations 

 to Messrs A. P. Hayle, J. F. Henderson, and C. F. Pond; 

 and for valuable assistance in the preparation of the index 

 and in other matters to Mr B. Newman. 



For permission to reproduce illustrations acknowledgment is 

 due to Messrs Geo. Allen & Unwin, Ltd. (Textbook of Zoology y 

 Sedgwick); Messrs A. & C. Black, Ltd. (Treatise on Zoology, 

 Lankester); the Council of the Cambridge Philosophical 



