.TRANSLATORS' PREFACE 



THE fact that this second volume of the translation appears four years 

 after the first is due partly to the delay in the issue of the third and 

 fourth German parts of which it is composed, and partly to the 

 increased difficulty in the work of translation. A comparison of the 

 two volumes will show at a glance that the work has developed 

 under the hands of the author: the treatment has become more 

 elaborate. The two " chapters " which practically fill this volume are 

 in reality more like comprehensive treatises on the groups with 

 which they deal, and as such could only be adequately translated from 

 the German by some one with a very special knowledge of both 

 groups. There are probably few zoologists who have attempted to 

 make a special study of two such heterogeneous phyla as the Mollusca 

 and the Echinodermata. In addition, therefore, to frequent references 

 to the original literature and to constant applications to kind friends, 

 the whole of the text relating to the two chief groups was submitted 

 to specialists for revision. The translators beg to tender their 

 warmest thanks to their friends who kindly undertook this laborious 

 task. Mr. B. B. Woodward read the text of the chapter dealing 

 with the Mollusca, revising the terminology, and suggesting slight 

 alterations, which have been either adopted without comment in the 

 text or else placed in short footnotes. Mr. W. Percy Sladen and Mr. 

 F. A. Bather revised the text dealing with the Echinodermata, each 

 with special reference to the group with which his name is most asso- 

 ciated. Thanks are also due to Professor Jeffery Bell for his kind 

 assistance in the solution of difficulties. We have no hesitation in 

 saying that it is to the generous help of these gentlemen that 



