VI PREFACE. 



Entoprocta, and the Brachiopoda have therefore been removed 

 from the end of Part III. (Vol. IV. of the English edition), 

 and placed at the commencement of Vol. II., which part 

 contains, in addition, the Crustacea proper and the Palaeostraca. 

 I do not think there can be any serious objection to this 

 change, inasmuch as the four groups mentioned probably find 

 a natural resting-place near to the Annelida, which were dealt 

 with in Part L, while they have little, if any, relation to the 

 Molluscan phylum treated in Part III. In all other respects 

 the original text has been adhered to as closely as possible ; 

 but it has occasionally been found necessary to rewrite certain 

 paragraphs which, when translated, appeared somewhat in- 

 volved and obscure. In such cases the motive of the original 

 has been adhered to as far as possible, the sentences, however, 

 being entirely recast. 



Additional notes have been added relating to the most 

 important of the many fresh observations which have been 

 made since the original work appeared. Such additional 

 matter has been placed in footnotes, distinguished from the 

 footnotes of the authors by being enclosed in square brackets. 

 A considerable number of additional references have also been 

 given; and these are placed with the Literature at the end 

 of each chapter under the form of Appendices, and, as in 

 Vol. I., numbered with Roman numerals. But even these 

 additions could now be added to. For instance, since going 

 to press a short note on the early development of PJioronis 

 by E. Schultz* has appeared, which might with advantage 

 have been incorporated in this work. 



Although desirous, as far as possible, to use the same 

 terminology as the translators of Vol. L, I have been compelled 

 to differ from them in the rendering of the ever-recurring word 

 " Anlage." This important term in Vol. I. is rendered by the 

 word " fundament." Exception, with which I concur, has already 



* " Ueber Mesoderm-bildung bei Phoronis," Otdyeln. Oppisk., Tryd. imp. 

 St. Petersburg, Obshch. estestv., T. xxviii., Vuip. 1. The author deals mainly 

 with the formation of the mesoderm, and controverts all Cald well's observations 

 relating to the origin of this layer, which he maintains is a mesenchyme, and 

 arises in the blastula and gastrula stages, most conspicuously in the latter, as 

 proliferations from the entoderm. He could not find Caldwell : s primitive groove, 

 and thinks that this observer described as his posterior coelomic sacs the 

 ventral invaginations which form the body-wall of the adult. 



