412 



GEORGE W. TANNREUTHER 



often show protruding cilia and communicate directly with the 

 body cavity (text fig. s) . In the later stages, however, the open 

 tags are rare and exhibit closed ends with pending cilia (text fig. 

 u). Tags are never formed on the recurrent tubules. 



The systems of excretory tubules on either side do not com- 

 municate at their anterior ends, but at their posterior ends they 

 connect with the urinary bladder. The urogenital sinus, as 

 stated above, arises as a solid ingrowth of the ectoderm at the 



Figs, o and p Median longitudinal sections, to show the early formation of 

 the excretory system; note the nephridial bands on the ventral side within the 

 ectoderm. 



Fig. q Horizontal section of the same stage as above; the section shows the 

 rows of nephridial cells and their connections with the extoderm at different 

 intervals; these connections become the controlling muscle fibers. 



Fig. r A horizontal section of a later state; shows the early lumen in the 

 formation of the excretory tubules. 



ABBREVIATIONS 



■a., anterior 

 b.c, body cavity 

 d, dorsal 

 m.c, muscle cell 

 m.f., muscle fiber 

 mo, mouth 



n.b., nephridial band 

 ph., pharynx 

 sto, stomodaeum 

 ur.s., urogenital sinus 

 t', ventral 



