PREFACE TO THE FIRST EDITIO 



ON account of its clearness and breadth of view, its comparatively 

 simple character and moderate size, Professor Richard Hertwig's 

 'Lehrbuch der Zoologie' has for ten years held the foremost place 

 in German schools. The first or general part of the work was trans- 

 lated in 1896 by Dr. George W. Field, and the cordial reception which 

 this has had in America has led to the present reproduction of the whole. 



This American edition is not an exact translation. With the consent 

 of the author the whole text has been edited and modified in places to 

 accord with American usage. For these changes the translator alone 

 can be held responsible. Some of the alterations are slight, but others 

 are very considerable. Thus the group of Vermes of the original has 

 been broken up and its members distributed among several phyla; the 

 account of the Arthropoda has been largely rewritten and the classification 

 materially altered; while the Tunicata and the Enteropneusti have been 

 removed from their position as appendices to the Vermes and united 

 with the Vertebrata to form the phylum Chordata. Other changes, like 

 those in the classification of the Reptilia and the nephridial system of the 

 vertebrates, are of less importance. 



A large number of illustrations have been added, either to make 

 clearer points of structure or to aid in the identification of American 

 forms. Except in the Protozoa, American genera have in most cases 

 been indicated by an asterisk. Numerous genera have been mentioned 

 so that the student may see the relationships of forms described in 

 morphological literature. 



In the translation the word Anlage, meaning the embryonic material 

 from which an organ or a part is developed, has been transferred directly. 

 As our language is Germanic in its genius, there can be no valid objection 

 to the adoption of the word. 



As this work is intended for beginners, no bibliography has been 

 given. A list of literature to be of much value would have been so 

 large as materially to increase the size of the volume. Experience has 

 shown that beginners rarely go to the original sources. This omission 

 it the less important since in all schools where the book is likely to be 

 used other works containing good bibliographies are accessible. Refer- 



