PREFACE TO THE FOURTH EDITION 



The present revision of this manual has been made by the 

 staff of the Invertebrate Zoology course as of 1926 at the Marine 

 Biological Laboratory, Woods Hole, Massachusetts, for the 

 purpose of bringing the subject matter of the third revised 

 edition more up to date. Where it has seemed advisable the 

 classification, literature lists, and especially the nomenclature 

 have been changed to accord with more modern usage. Such 

 few errors as had crept into earlier editions, it is hoped, have 

 been eliminated. In a number of instances the directions for 

 laboratory work have been modified in favor of exercises which 

 have proved valuable in the work of the Invertebrate Zoology 

 course at the Marine Biological Laboratory. 



J. A. Dawson. 



June, 1928. 



