1919] Cort: Excretory System of a Stylet Cercaria 279 



to the narrower polyaclenous group (Cort, 1915, p. 57), of which 

 Cercaria polyadena is the type. Of the other adult distomes with 

 the "2X6X3" type of excretory system only the cercaria of Haplo- 

 metra cylindracea is known, which is also a stylet cercaria belonging 

 to the Cercariae armatae group. The adult into which Cercaria poly- 

 adena develops is not known, but the homologies described above 

 place it in the family Plagiorchiidae close to Opisthioglyphe. 



So little is known of the excretory system in the stylet cercariae 

 that it is not possible in the present state of our knowledge to draw 

 any conclusions in regard to the prevalence and modifications of the 

 "2X6X3" type of excretory system in the whole group. It 

 seems very probable as suggested by Faust (1918, p. 104) that the 

 stylet cercariae do not represent a closely related group of trematodes. 

 The Y-shaped type of excretory bladder, however, is quite common 

 among stylet cercariae (Looss, 1896; Cort, 1915; Faust, 1918 and 

 1918a). Faust (1918 and 1918a) has partially worked out this 

 excretory system in a number of stylet cercariae. In most cases, 

 however, it is difficult to determine from his drawings and descrip- 

 tions the number of flame cells or the pattern of the finer vessels. 

 His description of the system in Cercaria isocotylea Cort, also placed 

 in the polyadenous group, is more complete (Faust, 1918, p. 103, fig. 

 20). In this form he describes a system strikingly different from 

 that of Cercaria polyadena. He finds a total of twenty-two flame 

 cells on a side, and shows capillary groups of both two and three. 



In every stylet cercaria of which Faust describes the excretory 

 system he shows branches extending into the tail. Magath (1917, 

 pi. 1, fig. 3) shows a branch of the excretory system of the stylet 

 cercaria of Lissorchis f airport i Magath in the tail. I have made exam- 

 inations of the excretory systems of eight different stylet cercariae 

 and have never seen any trace of excretory tubules in the tail. 

 Unfortunately I have never had the opportunity of studying the 

 excretory system of any of the stylet cercariae in which Faust shows 

 this peculiarity. The excretory tubules which Faust figures in the 

 tails of his stylet cercariae vary from a simple tube to a very much 

 branched tube (cf. Faust, 1918a, figs. 18 and 20). He never shows 

 flame cells in the tail nor does he show tubules opening to the out- 

 side. In my studies on the excretory system of cercariae I have seen 

 only two parts of the excretory system invading the tail: either 

 extensions of the bladder which form usually two larval excretory 



