KLEINENBERG ON DEVELOPMENT OE LOPADOLtHYNCIlUS. 531 



Kleinenberg on the Development of 

 Lopadorhynchus. 



By 



G. C. Bourne, B.A., F. ¥>.«.. 



Fellow of New College, Oxford, and Assistant to the Linacre Professor in 

 the University. 



It is now more than a year since Professor Kleinenberg 

 published, in the 'Zeitschrift furWissenschaftliche Zoologie/ a 

 long account of the development of a polychaete Annelid, Lopa- 

 dorhynchus. Whether it is because of the extreme length of 

 the paper, which extends over 225 pages, that the work has not 

 attracted the attention it deserves, or because the very nume- 

 rous illustrations include no diagrams, but are invariably exact 

 drawings of the sections studied by the author, and require to 

 be laboriously re-interpreted by the reader, or because the 

 facts and views expressed are so novel and so much opposed to 

 all preconceived notions of what mesoblast ought to be, the 

 fact remains that this paper is little known by English 

 readers. 



The morphological importance of the questions raised by 

 Kleinenberg concerning the origin of the mesoblast is so great, 

 that a reproduction of those parts of his paper which deal espe- 

 cially with this subject calls for no excuse. 



In an introductory chapter, the consideration of which I 

 shall defer until the facts of the development of Lopadorhyn- 

 chus have been presented to the reader, the author lays down 

 the proposition that there is no such thing as a mesoblast as a 

 specially differentiated germ layer. The existence of two 

 primary germ layers in the Ccelomata, ectoderm and endo- 

 derm, homologous with the similarly-named layers in Cceleu- 



