EXCRETORY SYSTEM IN DIGENEA. 



317 



main collecting tubule of each side is marked by a bifurcation. 

 The outer (posterior) fork remains free, but the inner (anterior) 

 one joins its mate of the opposite side and thus secures a phy- 

 siologically important connection between the excretory courses 

 of the two sides of the body. 



The flame cells have been carefully studied in living flukes. 

 In the mature cercaria they are naturally divided into three 



I 2 



FIG. I. Very young Cercaria convoluta, showing three flame cells on each side of 

 the body. X 250. 



FIG. 2. Four cell stage in development of excretory system of C. convoluta, X 225 . 



groups. At the anterior end, given off just after the collecting 

 tubule flexes caudad, there is a cluster of eight cells on each side 

 of the body. Midway down on the reflexed portion of the 

 tubule a single large flame cell is found. In the acetabulum the 

 outer (posterior) tubule of the posteriormost group terminates 

 in a cluster of eight cells. The inner (anterior) likewise gives 

 rise to a cluster of eight terminal flame cells. Analysis shows that 

 the cephalic group of eight cells and the two octet groups in 

 the acetabulum all have an orderly arrangement and are the 

 result of a regular development. Each consists of a quadruple 

 bifurcation of an originally single flame cell. Moreover, this 

 analysis is borne out by the successive stages in the development 

 of the system. The collecting system is originally composed 



