EXCRETORY SYSTEM IN DIGENEA. 323 



It is the purpose of this paper to present data on the excretory 

 system of three distinct groups of distome cercariae, the echi- 

 nostome cercariae, the xiphidiocercariae and the furco-cercariae, 

 and to show how these data may be used to supplement the 

 anatomical relationships based on other fundamental systems 

 of these platodes. 



ECHINOSTOME CERCARIAE. 



These cercariae, frequently designated as the offspring of 

 rediae, with a collar of spines at the anterior end of the body, may 

 be as readily recognized by the pair of heavy collecting tubules 

 extending from the bladder to the region of the pharynx, where 

 they become constricted and reflex on themselves in triangular 

 fashion (see Figs. I and 2). The manner in which the flame cells 

 are disposed, together with their number, and the course of the 

 tubule in the tail offer a method for separating larval echino- 

 stomes into two quite distinct groups. 



The more simple of these groups, as illustrated in Fig. i, shows 

 the collecting tubule ending in the triangular flexure and only 

 three flame cells for each half of the body. The cells are situated 

 at the ends of small capillaries whfch empty, the one at the end, 

 the others at the sides of the triangle. No other flame cells 

 occur along the entire course of the tubules. In the tail a single 

 median tubule runs from the distal end forward into the bladder. 

 Of the cercariae in which the flame-cell count has been satis- 

 factorily worked out, two species fall into this group, Cercaria 

 chisolenata Faust, 1918, and C. trisolenata Faust, 1917. 



The second or more complex type is one in which the constricted 

 tubule does not end in the region of the triangular flexure lateral 

 to the pharynx but continues caudad to the posterior region of 

 the body. Commonly (Fig. 2), when this secondary portion of 

 the tubule reaches the posterior region of the body, it bends 

 forward and continues to the region of the pharynx. Numerous 

 flame cells, constant for each species, are connected by minute 

 capillaries with this tertiary portion of the tubule. In Cercaria 

 acanthostoma Faust, 1918, sixteen flame cells occur along each 

 tubule. In Cercaria complexa nov. spec, the number is fifteen. 

 In this type also the main collecting tubule of the tail, after cours- 

 ing distad for a short distance, bifurcates and opens on each side 

 through a simple pore. To this type belong C. trivolvis Cort 



