328 ERNEST CARROLL FAUST. 



possible to calculate the flame-cell formula of the cercaria from 

 the condition of the adult. 



The study of the flame-cell structure in the xiphidiocercariae 

 and comparison of the system with that of the related adult 

 flukes show in the first place that the fundamental basis of the 

 system is the number and disposition of the flame-cell groups. 

 Knowledge of the structure of the excretory system in the Plagior- 

 chiidae and Brachycceliidae makes it possible to state that this 

 fundament in these groups is a family or subfamily character. 

 The number of flame cells in each basic group is of lesser impor- 

 tance. Thus in the plagiorchiine species, where the species is 

 known, triad groups are the rule, but in the brachycceliine species 

 diad formation occurs in one subfamily and triad formation in 

 another. In the second place this study has caused the writer 

 to believe that this system is decidedly conservative in the xiphi- 

 diocercariae. 



A study of Cercaria trifurcata and C. candelabra shows these 

 species to have a flame-cell formula intermediate in form be- 

 tween that of the Brachycceliidse and the Plagiorchiidae. C. 

 trifurcata represents a type in which the anterior fundament is 

 brachycoeliine and the posterior fundament plagiorchiine, while 

 C. candelabra represents just the reversed condition. On account 

 of the large number of flame cells already present in the larva it 

 is highly probable that both of these species represent a condition 

 of flame-cell development which for the cercaria- is somewhat 

 more precocious than that of the larvae of the Brachycceliidae 

 and the Plagiorchiidae. The system in C. isocotylea has reached 

 a high degree of complexity which bears homologous relation- 

 ships to no other known system in larval or adult flukes. 



FURCOCERCARLE. 



The forked-tailed cercariae have secured more than ordinary 

 attention during the past few years because experimental evidence 

 has shown some of them to have a genetic relationship to the 

 three human blood flukes, Schistosoma hcsmatobitim, S. mansoni 

 and 5. japonicum. Cort (1918 )has made a careful analysis of 

 the excretory systems in five furcocercarise and the writer (iQiSa) 

 has previously published flame-cell data for the species C. gigas. 

 The writer's study of four additional species tends both to con- 



