EXCRETORY SYSTEM IN DIGENEA. 



341 



cercaria amounts to 12, or 6 on each side of the median line 

 (Fig. 2). Since the two cells on each side of the body, arising 

 from the bifurcation of the original cell, are the key to the further 

 development of the system, the general flame-cell formula may be 

 represented as a + a" = 4 + 2 or 6. 



Data on the excretory system in the redia of Cercaria spatula 

 furnish additional evidence in favor of the belief that this formula 

 is valid for the excretory system in this species. In the very 



FIG. i. Cercaria spatula, dorsal view, showing eye-spots, pigmentation, and 

 genital cells. X 170. 



FIG. 2. C. spatula, dorsal view, showing digestive and excretory systems. 

 X 170. 



young redia a single flame cell is found on each side of the body, 

 at the end of a coiled tubule which opens to the outside through 

 an inconspicuous pore. Later a single bifurcation of the flame 

 cell and the distal end of the coiled tubule occurs so that in the 

 mature redia the two collecting tubules on each side open outward 



