PREFACE TO THE THIRD EDITION 



An unfortunate though inevitable result of advance in any field of 

 knowledge is the rapid obsolescence of textbooks. In cytology, the 

 years just past have witnessed the accumulation of a wealth of new 

 observations, including a number of significant discoveries calling for a 

 decided revision of certain concepts and statements which seemed 

 adequate when the second edition of this book was prepared. Many 

 of the questions troublesome at that time have received answers or 

 what is often fully as important, more precise formulation. New and 

 equally perplexing problems have arisen, but on the whole the cytological 

 picture, particularly those portions of interest to the geneticist, appear 

 notably clearer than they did eight years ago. 



Next to the desire to bring the book into better accord with the 

 present state of the subject in both text and illustration, the chief thought 

 in preparing this edition has been that of improving its adaptability to 

 the needs of students with comparatively little experience in the special 

 field of cytology, without, however, making it an elementary treatise. 

 To this end much of the material has been rearranged, the treatment of 

 many points has been simplified, and certain border-line topics have been 

 omitted altogether. Most of the citations to literature have been 

 transferred from the body of the text to footnotes, where they are still 

 available to the advanced student but need not confuse the beginner. 

 Instructors will often find it advisable to omit or rearrange certain 

 sections of the book in their class work. Much of the special matter in 

 the opening chapters, for example, might w^ell be considered later in 

 courses. In accordance with repeated recommendations from users of 

 the book, most of the former bibliography has been retained in spite of 

 its length. 



This edition, like the earlier ones, treats chiefly of the structural 

 and genetical aspects of cytology. An especially valuable complemental 

 work is J. Gray's A Textbook of Experimental Cytology, which deals at 

 length with the results of physical and chemical researches on the cell. 

 Among other recent general works of value to the student should be 

 mentioned Special Cytology, edited by E. V. Cowdry, K. Belaf's Die 

 Cytologischen Grundlagen der Vererhung, C. D. Darlington's Recent 

 Advances in Cytology, and Traite de Cytologic Vegetale by A. Guilliermond, 

 G. Mangenot, and L. Plantefol. Of special interest to readers of Japanese 

 are G. Yamaha's Saibo and Y. Sinoto's Japana Historio Citologia. 



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