DEVELOPMENT OF NEPHRIDIA OP PHERETIMA 81 



on the other hand, both conditions prevail— the funnel is pre- 

 septal in some cases and post-septal in others. Both conditions 

 are represented in fig. 15 a and b. In the adult Pheretima 

 it was found that while a large majority of nephridia have 

 their funnels in the same segment there are some with pre- 

 septal funnels. The statement that all the septal nephridia 

 have funnels in their own segments is therefore not quite 

 universally true, as I thought before. We may note, however, 

 that in the case of those nephridia which have the funnel in 

 the same segment, all that happens is that the ' funnel-cell ' 

 and the cells going to form the body of the nephridium project 

 in the same direction, either pre-septal or post-septal. 



When the first secondary nephridium is fully formed, its 

 terminal duct running along the septum meets that of the 

 primary nephridium dorsal to it, and, similarly, the ducts of 

 all the succeeding nephridia join those of the preceding ones, 

 and that is how we get the formation of the septal excretory 

 canal running parallel and internal to the commissural vessel 

 (dorso-sous-nervien, 2). We may note that, like the septal 

 nephridia themselves, the septal excretory canal is also inter- 

 peritoneal. 



(6) Secondary Integumentary Nephridia. 



The secondary integumentary nephridia, in their early 

 rudimentary condition, can be seen in older embryos about 

 to hatch out of the cocoon. In whole mounts, as shown in 

 Text-fig. 7, they can be distinguished as small solid deeply- 

 staining masses on the side of and between the setal sacs. The 

 setal sacs at this stage have not yet developed full-grown 

 setae in them, and rudiments of secondary nephridia in sections 

 (fig. 17) can be made out lying beneath the coelomic epithelium 

 between the inner ends of two adjoining setal sacs. They arise 

 at almost any place on the body-wall, like the primary 

 nephridia ; in some segments they are found near the dorsal 

 vessel, in others on each side of the nerve-cord (fig. 17). 

 Whether the secondary nephridia develop from some of the 

 nephridial cells, lying beneath the somatic peritoneum, that 



