TEANSLATOB'S PBEFACB. 



The rapidly increasing recognition of the importance of Embryology 

 in all morphological studies makes it desirable that the most valuable 

 text-books upon the subject, in whatever language, be made available 

 for those who are beginning its study. Although the English-reading 

 student already has at command a number of text-books upon this 

 subject, it is evident to any one familiar with Hertwig's Lehrbuch der 

 Entwiohlungsgeschichte des Menschen und der Wirbelthiere that this 

 work covers the field of Vertebrate Embryology in a more complete 

 and satisfactory way than any book heretofore published in English. 



Two important objects to be accomplished in a text-book are : 

 first, a clear and methodical exposition of the well-established facts 

 of the science; and, secondly, such a presentation of unsettled 

 questions as shall stimulate the reader to further inquiry and re- 

 search. I believe it is far too common for the second of these aims 

 to be overlooked. The present work fulfils both requirements in an 

 eminent degree, and in its historical surveys exhibits an exceptional 

 fairness of treatment, notwithstanding the author has been one of 

 the foremost contestants in several of the fields reviewed. The 

 summaries which follow the discussions of the several topics serve a 

 useful purpose in directing attention to the more important conclu- 

 sions drawn from each subject. 



I have aimed to give a clear and accurate reproduction of the 

 author's ideas ; while I have endeavored — not always successfully — 

 to avoid awkward renderings and German idioms, I have preferred 

 to err on the side of a too literal rather than a too liberal translation. 

 There are a few points that demand a brief explanation. The German 

 word Ardage has heretofore been variously rendered into Enghsh 

 by rudiment, origin, beginning, basis, foundation, etc., while some 

 writers, recognising the inadequacy of any of these words to express 

 the idea, have incorporated the German word itself in their English. 



The Anlage of a structure is its beginning or its undifierentiated 

 state — ^the object in a simple condition which is destined to be 



