320 ERNEST CARROLL FAUST. 



mature cercaria. In Cercaria convoluta, on the other hand, a 

 distinct three-cell stage is passed through. The four-cell stage 

 is found only after the acetabular cell has divided. Then 

 by successive divisions eight cells are formed from the cephalic 

 and each of the acetabular groups, while the cell in the mid region 

 of the body fails to divide. Thus in the mature cercaria of 

 Diplodiscus subclavatus there are fifteen or sixteen flame cells on 

 each side of the body while in the writer's species twenty five 

 flame cells have been consistently found. 



In spite of the less pronounced symmetry of division of flame 

 cells in Cercaria diplodisci subdavati it is nevertheless highly 

 probable that the grouping is of a fourfold character both in 

 redia and cercaria, just as the arrangement in C. convoluta is 

 threefold. Thus within a relatively small subfamily there exists 

 a fundamental difference of arrangement of a relatively conserva- 

 tive system. 



SUMMARY. 



1. Cercaria convoluta, a new species belonging to the Diplo- 

 discinse, is described. 



2. The development of flame cells in both redia and cercaria 

 of this species is based on a three-fold division of a primitively 

 single flame cell on each side of the body. 



3. A study of the development of flame cells in C. diplodisci 

 subdavati, based on Looss's study, shows a four-fold group 

 arrangement but with less exact symmetry. 



4. A comparison of these two forms shows a fundamental 

 difference of arrangement of a relatively conservative system 

 within the same subfamily. 



REFERENCES CITED. 

 Cort, W. W. 



'18 Homologies of the Excretory System of the Forked-Tailed Cercariae. 



Jour. Parasit., 4, 49-57. 



'i8a The Excretory System of Agamodistomum Marcianae (La Rue), the 

 Agamodistome Stage of a Forked-Tailed Cercaria. Jour. Parasit., 4, 

 130-134. 

 Faust, E. C. 



'18 Life History Studies on Montana Trematodes. 111. Biol. Monogr., 4, 



1-120, 9 pi. 

 'i8a Studies on Illinois Cercariae. Jour. Parasit., 4, 93-110, 2 pi. 



