280 University of California Publications in Zoology [Vol.19 



pores, one on each side of the tail as in echinostome cerceriae, aniphi- 

 stome cercariae or schistosome cercariae, or flame cells which are con- 

 nected with accessory collecting tubes extending back into the tail 

 from the body as in the various types of fork-tailed cercariae. In 

 Faust's (1918a, pi. 2, fig. 18) figure of Cercaria stilifera he draws 

 twenty-one subdivisions of the excretory-branch in the tail which 

 appear to correspond to capillaries of the body. If this representation 

 is correct there should be twenty-one flame cells in the tail of this 

 form although Faust does not figure any. 



Since the study of the tails of stylet cercariae is very difficult in 

 the living condition, which is the only way in which the finer tubules 

 of the excretory system can be seen, I feel that many more careful 

 studies on this point will have to be made before final judgment can 

 be passed on the differences noted above. 



The finding of such fundamental homologies in the excretory 

 systems in such a wide variety of forms is very suggestive and must 

 in my opinion indicate some degree of relationship between the groups 

 to which these species belong. I prefer, however, not to attempt to 

 draw any far-reaching conclusions in regard to relationships since the 

 excretory systems of so few species are known. Such a comparison, 

 however, emphasizes the great importance of further studies on the 

 excretory systems both of cercariae and adult trematodes for the 

 determination of the relationship of the larger groups and the estab- 

 lishment of a natural classification. 



