PREFACE TO THE SECOND EDITION 



THIS edition contains descriptions for the study of a few 

 forms and a rather simple literature list that were not included 

 in the first edition. There has been no attempt to make the 

 literature list at all complete, but it seems desirable to refer 

 students to some of the available papers, for by consulting 

 them in connection with their laboratory work they become 

 acquainted with methods of work and develop the spirit of 

 research that is the beginning of real understanding. 



Certain text-books should be used freely for reference. 

 These have not been mentioned under the special heads, as they 

 apply to practically all groups. Among these may be men- 

 tioned Parker and Harwell's "Text-book of Zoology," Macmil- 

 lan; Lankester's "A Treatise on Zoology/' Black; Harmer and 

 Shipley's "The Cambridge Natural History," Macmillan; 

 Lang's "Lehrbuch der Vergleichenden Anatomic," Fischer; or 

 the English translation, Macmillan; Korschelt and Heider's 

 "Lehrbuch der Vergleichenden Entwicklungsgeschichte," Fis- 

 cher; or the English translation, Macmillan; and Delage et 

 Herouard's "Traite" de Zoologie Concrete," Schmidt. 



For the many suggestions and criticisms from zoological 

 friends the author is deeply grateful. To Dr. Lorande L. 

 Woodruff, who has given much attention to the revision of 

 the Protozoa, and to Dr. Winterton C. Curtis and Dr. Caswell 

 Grave, who, with the men associated with them as instructors 

 in the Zoology Course at the Marine Biological Laboratory, 

 have given much attention to corrections and additions through- 

 out the manual, special acknowledgments are due, for they have 

 not only saved the author much labor, but have added mate- 

 rially to the value of the revision. 



THE AUTHOR. 

 July, 1913. 



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