1920] Johnson: Life Cycle of Echinostoma Revolutum (Froelich) 359 



Concerning any of the criticisms of Faust's work, I will say in fair- 

 ness to him, that since none of his species has been studied. I may have 

 carried my criticisms based on comparison too far. It must be said, 

 however, that his arrangement of the excretory parts violates some of 

 the most fundamental homologies of excretory systems. Also since 

 details are so lacking in Faust's work the conclusion is reached that 

 he really did not completely solve the pattern of the excretory system 

 of any one of the four echinostome cercariae. 



Because of the numerous flame cells,* the complexity of the 

 arrangement of the collecting tubules and accessory collecting tubules 

 and the definite arrangement into capillary groups throughout the 

 body, it seems quite probable that the excretory system of the 

 echinostome cercariae represents much more closely the adult condition 

 than the condition found in the schistosomes or fork-tailed cercariae, 

 in which the flame cells arise singly and are few in number, and in 

 which the pattern is quite simple. 



The general knowledge of the excretory system of trematodes is 

 comparatively meager. In nearly every cercaria described, the bladder 

 and larger tubules are shown, whereas the collecting tubules, acces- 

 sory collecting tubules, capillaries and flame cells are missing or nearly 

 so. This is. as stated before, due to working on preserved material. 



* Shortly after this manuscript was completed, Faust published in the Bio- 

 logical Bulletin for May, 1919, an article which included data on the excretory 

 system of echinostome cercariae. In the summary of this article, "The Excre- 

 tory System in Digenea, II," he makes the following statements: 



1. ''The number and distribution of groups of flame cells is the fundamental 

 basis of structure of the excretory system of the distomes. " This agrees with 

 my findings in all cercariae that I have studied. 



2. "The group of flame cells is typical of all members of a family or at least 

 of a sub-family." My work also suggests the fundamental significance of the 

 capillary group. 



3. "Seven new species of distome cercariae are described, which are of 

 special importance in affording evidence of the orderliness of the excretory 

 system of the Digenea." This statement also is substantiated not only by my 

 study of E. revolutum but also by unpublished work on fork-tailed, stylet, and 

 monostome cercariae. If the above statement concerning the orderliness of the 

 excretory system is universally true, then much of the previous work on this 

 system in Digenea indicates incompleteness. 



The descriptions of the excretory systems of echinostome cercariae in this 

 paper agree more closely with my findings in E. revolutum than did Faust's 

 earlier work. Cercaria eomplexa, which he figures, shows the tail arrangement 

 of the excretory system to be identical with that of E. revolutum. The flame 

 cells of C. eomplexa likewise are arranged much like those of E. revolutum. 

 Probably a larger number of flame cells are present in C. eomplexa than are 

 shown and would have been seen except for the numerous heavy cystogenous 

 glands. The arrangement of the flame cells at the anterior end of C. eomplexa 

 is particularly like that of E. revolutum. I should expect, upon thorough study 

 of other echinostome cercariae to find that the anterior grouping of flame cells 

 is very similar in them to that in C. eomplexa and E. revolutum. 



It is interesting to note that as more thorough studies of the excretory 

 system in Digenea are made, more uniform results are obtained. 



