THE EXCRETORY SYSTEM IN DIGENEA. II. 

 ERNEST CARROLL FAUST. 



OBSERVATIONS ON THE EXCRETORY SYSTEM IN DISTOME 



CERCARLE. 1 



The diverse groups connoted by the term "distome cercariae" 

 are found to be decidedly heterogeneous when the reproductive 

 and excretory systems are examined. Even the nervous system 

 is extraordinarily modified in one family of this group, the Schis- 

 tosomatidse. Students of distome cercariae have commonly 

 made mention of the bladder and have frequently observed the 

 main collecting tubules of the excretory system. Only infre- 

 quently, however, have they traced out accurately the auxiliary 

 tubules and made an exact analysis of the flame cells at the distal 

 ends of the capillaries. Even as accurate an observer as Looss 

 has often been unable to analyze the system in material which 

 was available for study as living mounts. Failure to determine 

 the number of flame cells and their exact relationship to the 

 collecting tubules may be due to (i) paucity of material at hand, 

 (2) concealment of the cells by cysfogenous or mucin glands or 

 heavy and spinose integument, or (3) insufficient time to make 

 careful observations at the exact moment when the material is 

 best fitted for study. In general, mature free-swimming cer- 

 cariae are much the best for this study and freshly dissected 

 material is much better to work on than that which has been 

 standing for several hours. It is true, however, that material 

 may present seemingly insuperable difficulties for the study of the 

 excretory system at a certain time or when taken from a certain 

 place, while at another time or in another locality the study of the 

 same species may be one of comparative ease. 



Cort has frequently noted that the study of the excretory 

 system is both tedious and wearisome. The writer may add 

 that a successful analysis of the system requires greater care and 

 more poise of judgment than that of any other system of the fluke. 



1 Contributions from the Zoological Laboratory of the University of Illinois, 

 No. 131. 



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