TRANSLATOR'S PREFACE. 



THIS volume comprises the First or General Part of 

 Professor Richard Hertwig's " Lehrbuch der Zoologie," 

 which embodies the results of his long and eminently suc- 

 cessful experience in teaching. The translation has been 

 made with his consent and active cooperation and thus really 

 constitutes a fourth edition. When the "Lehrbuch" was 

 prepared, the author did not contemplate the contingency 

 of a separate publication of the General Part, but it is 

 believed that his masterly treatment of the larger generaliza- 

 tions of the subject will be of service by itself to teacher, 

 student, and general reader. 



The term "Anlage" has been rendered "rudiment," 

 in the sense that rudimentary organs are such as are in 

 process of development. Conversely, organs in process of 

 disappearance are termed "vestigial organs." The adjec- 

 tive "vegetal," as corresponding with "animal," has been 

 used in preference to " vegetative"; e.g., the vegetal and 

 the animal pole of the egg. 



It is too much to hope that errors have not crept in, 

 and as the most satisfactory text-books result from the co- 

 operation of many workers, the editor invites such correc- 

 tions and suggestions as may tend to widen the usefulness 

 of the work. In reading proof much assistance has been 

 given by Miss Ada G. Wing, a graduate student of Biology 

 in Brown University, and to her the translator is indebted 

 for many valuable suggestions. Go W. F. 



BROWN UNIVERSITY, July 15, 1896. 



iii 



