1920] Johnson: Life Cycle of Echinostoma Revolutum (Froclich) 353 



In the cercaria of Echinostoma revolutum sometimes the collecting 

 tubules and again the accessory collecting tubules are much reduced 

 or have entirely disappeared, as shown in figure 47, 3c. This reduction 

 or loss is probably due to several causes, which might all be summed 

 up by calling it adaptation to the position they occupy in the cer- 

 caria 's body or to the position they will eventually occupy in the body 

 of the adult echinostome. 



la, caudal division of bladder; 

 lb, muscular sac of bladder; lc, 

 muscular descending tube of blad- 

 der; Id, concretional descending 

 tube of bladder; le, ascending tube 

 of bladder; 2a, 2b, 2c 2d, collecting 

 tubules; 3a, 3b, 3c, 3d, 3e, Sf. 

 3h, accessory collecting tubules; 

 1-24, flame cells. 



Pig. 1. A diagrammatic drawing showing the probable arrangement of the 

 excretory system of the primitive echinostome cercaria. 



The above figure represents graphically what I consider to be 

 the generalized system of an echinostome cercaria from which the 

 present system probably arose. The comparison of this diagram with 

 figure 47 illustrates a method by which the capillary grouping of a 

 system could be progressively modified until the exact pattern is 

 somewhat obscured. 



The drawing (text fig. No. 1) shows particularly what I think has 

 happened to the accessory collecting tubule (3c), to which are attached 

 the capillaries draining flame cells 7, 8, and 9. Compare with figure 47 



