DEVELOPMENT OP NBPHRIDIA OF PHBRETIMA 



91 



a dorso-lateral instead of its usual ventral position ? That 

 it travels dorsalwards can be seen easily from figs. 13 and 14, 

 and that this is very unusual can be realized from the fact that 



comm 



snv. 



sn.r 



A series of four diagrams showing how the commissural vessel 

 elongates with the migration dorsalwards of the dorsal vessel 

 and how the nephridial rudiment on the septum is carried to its 

 dorso-lateral position. d.i\, dorsal vessel (double in A, B, and C) ; 

 V.V., ventral vessel ; n.c, nerve-cord ; snA\, subneural vessel ; 

 i.s,, intersegmental septum ; i.n., integumentary nephridium ; 

 s.n.r., rudiment of a septal nephridium ; h.uK, body-wall. 



ordinarily the funnel in a nephridium is the most ventral part 

 of it and lies almost next to the ventral nerve-cord. But 

 although away from the nerve-cord, the position of the primary 

 septal nephridia is not very unusual if we bear in mind the 



NO, 261 H 



