126 



CEPHALOCHORDATA 



pharynx (Fig. 71, br.f). There are, however, a large number 

 (about 100 pairs) of minute nephridia, discovered (1890) by 

 Weiss and by Boveri independently, lying at the sides of the 

 dorsal coelo'mic canals above the pharynx, which must be regarded 

 as the chief functional renal organs. These are bent tubules, 

 partly glandular and partly ciliated, each giving off several caecal 



FIG. 78. Branchiostoma lanceolatum. A nephridium of the left side with part of the 

 wall of the pharynx, as seen alive, highly magnified. (From Willey, after Boveri.) 



knobs (at first supposed to be open nephrostomes, one shown at 

 each end of the tubule and three along its upper surface in Fig. 

 78), which project into the coelom, and opening by one nephridio- 

 pore (on the lower surface, and opposite a tongue bar of the 

 pharynx) into the atrial cavity. The knobs, or closed nephro- 

 stomes, are surrounded by peculiar, slender, club-shaped tubular 

 and flagellated cells which Goodrich l has shown to correspond 

 to the " solenocytes " in the nephridia of Polychaete worms 

 (see Fig. 79). 



1 Quart. Journ. Micr. Sci. xlv. March 1902, p. 493. 



