330 



ERNEST CARROLL FAUST. 



a type with a slightly more complex formula, 6 = (3 + 3). 

 The fundament is, however, just the same, 2 = (i + i), so that 

 these two may be considered two subdivisions of one larger 

 group, all members of which have the same basic formula. 



A simple condition of a stage in advance of this primitive 

 group cited above is expressed in the excretory system of Cer- 

 caria furcicanda nov. spec. (Fig. 6), in which there are three 



FIG. 8. Cercaria quattuor-solenata nov. spec., ventral view, showing excretory 

 and digestive systems. X 105. 



FIG. 9. Cercaria rhabdocaeca nov. spec., ventral view, showing excretory and 

 digestive systems. X 330. 



instead of two basic groups. The formula for the flame cells in 

 this species is 6 = (2+2+2). One of these flame cells is in 

 the tail. Two species, evidently differing in minor characters 

 but bound together by the same number and arrangement of 

 flame cells are C. emarginattz and C. douglasi. These differ from 



