346 University of California Publications in Zoology [Vol. 19 



The excretory system of the redia (fig. 31) is difficult to see and 

 I found it impossible to analyse it completely. The most difficult part 

 to make out proved to be the capillaries and smaller tubules at either 

 end of the collecting tubules. The excretory pore is located on the 

 side and slightly in front of the posterior projection of the body. 

 Immediately underneath is a small bladder, which gives off two 

 branches, the collecting tubes, one extending posteriorly and the other 

 anteriorly. Close around the posterior protrusion eighteen flame cells 

 were seen. No plan of branching or attachment of the capillaries could 

 be made out, due to the extreme coiling. At the anterior end, a short 

 distance behind the intestinal sac seventeen flame cells were seen. 

 These capillaries and accessory collecting tubes were also much coiled 

 and so the pattern could not be determined here either. Possibly 

 other flame cells are to be found at either end. It is quite probable 

 that this condition of the excretory system prevails on both sides 

 although in a given specimen it was never so seen. Other rediae, 

 whose excretory system has been worked out. show it to be bilateral 

 and the pattern to be quite definite. This bilaterality is described by 

 Looss (1896, p. 199) in the redia of Cercaria distomatosa Sons. This 

 redia also has its capillaries and flame cells arranged in groups of 

 threes. He also shows the young redia of "Amphistomum conicum" 

 Rud. (fig. 130) arranged in a definite plan. Again Looss (1892, pi. XX, 

 fig. 9) shows the redia of "Amphistomum subclavatum" to be bilateral, 

 having two flame cells on a side. Cort (1918c, pi. VII, fig. 2) also 

 finds Cercariaeum mutabile to be bilateral and as far as he could 

 make out, with definite capillary arrangement. From this evidence it 

 seems safe to say that probably the excretory systems in all rediae are 

 bilaterally symmetrical and may have a definite grouping of the 

 capillaries and flame cells. 



CERCARIAE 



The fully developed cercariae of Echinostoma revolutum has a total 

 length of from 0.82 to 1.25 mm., according to the degree of contrac- 

 tion, averaging about 1 mm. when moderately extended and from 

 0.19 to 0.30 mm. in width, averaging about 0.25 mm. at its widest part. 

 The body alone varies in length from 0.39 to 0.63 mm., depending on 

 the amount of contraction; the tail from 0.43 to 0.62mm., depending . 

 on the same condition. Occasionally in extreme contraction or expan- 

 sion of the body and tail there is an even greater range of variation. 



