TRANSLATORS' PREFACE 



The value of the Lehrbuch der vergleichsnden Entwicklungs- 

 geschichte der wirhsllosen Thiere for students of animal 

 morphology is too well understood by those who are familiar 

 with its scope and execution to require any statement of our 

 aims in undertaking an English translation of it. 



In presenting to zoologists the First Part of this work 

 we consider ourselves fortunate in having had the valuable 

 aid of the authors in supplementing the original text by 

 numerous additions, made desirable by the rapid advance of 

 the science since the date of first publication. Although the 

 scope of the work has permitted the addition of only the 

 most succinct statement of the results reached by embryo- 

 logists in the last five years, these additions must prove 

 to be of assistance to all students, and will, we believe, be 

 especially acceptable to those who are already familiar with 

 the original edition. 



In order to spare the reader the labor of comparing 

 original and translation for the purpose of ascertaining 

 what is new, the plan has been adopted of enclosing ill 

 brackets [ ] all new matter, which, so far as practicable, 

 has been put in the form of footnotes. Each of these addi- 

 tions is followed by the initial of the author, or by the word 

 " Translators," to indicate the persons responsible for the new 

 matter. Owing to an oversight, the initial has been omitted 

 from several of the additions in the earlier chapters. It 

 should be stated, therefore, that, unless otherwise indicated, 

 the additions to Chapters I. — III. were made by Professor 

 Heider, those to Chapters IV. — XIV. by Professor Korschelt. 

 Brackets have also been freely used in the text to enclose 

 such words or brief explanations as the translators deemed 



