DEVELOPMENT OF NEPHRIDIA OF PHERBTIMA 51 



in the adult worm seemed to negative the ectodermal theory 

 of the Oligochaete nephridium, and to point to a mesodermal 

 origin of these nephridia of the new type. 



It thus became evident that interesting results would be 

 obtained from a study of the course of development of the 

 nephridial system of this worm, and accordingly I undertook 

 to investigate the problem and the following pages embody 

 the results obtained by me. 



The work was carried out in the Department of Comparative 

 Anatomy at Oxford, under the general supervision of Professor 

 E. S. Goodrich, to whom I am very much indebted for the 

 keen interest he has all along taken in my work and for his 

 valuable help and advice. 



2. Historical. 



The question of the origin of nephridia in Oligochaetes has 

 engaged the attention of many distinguished observers. The 

 early investigators, like Kowalewski (11), regarded the nephri- 

 dium as a tube connecting the coelom with the exterior, and 

 believed that a nephridium arose by a growth of the septal 

 wall of the coelom, that it gave rise to a chain of cells projecting 

 backwards, which eventually fused with the ectoderm and 

 then became hollowed out, so that the whole nephridium is to 

 be looked upon as a ' tail ' of the coelom. Moreover, since the 

 first trace of a cavity appears in the region of the funnel and 

 is a prolongation of the body-cavity, the cavity of the nephri- 

 dium might be said to be part of the coelom. Bergh (6) derives 

 the whole nephridium, including the funnel, of Criodrilus 

 and Lumbricus from a single large cell, the ' funnel-cell ', 

 lying close to the epiblast, between each successive pair of solid 

 mesoblastic somites. The origin of this ' funnel-cell ', from 

 which the whole nephridium develops, has been a matter of 

 considerable dispute. In a later paper on the subject (7) 

 Bergh denies the origin of the ' funnel-cell ' from the nephric 

 row in Criodrilus and Lumbricus, and asserts that the 

 funnel and the body of the nephridium have a separate and 

 different origin in K h y n c h e 1 m i s , the upper lip of the funnel 



