THE EXCRETORY SYSTEM IN DIGENEA. III. 



ERNEST CARROLL FAUST. 



NOTES ON THE EXCRETORY SYSTEM IN A MONOSTOME LARVA, 

 Cercaria spatula NOV. SPEC. 1 



In two previous papers of this series (Faust, 1919, 19193) the 

 writer has discussed the excretory system of an amphistome 

 larva, Cercaria convoluta, and significant types of this system in 

 distome larvae. This paper presents data on the development 

 and structure of the excretory system in a monostome larva, 

 Cercaria spatula nov. spec. The system w r ill be best presented 

 by first tracing its development. 



At the time when the cercaria germ-ball begins to differentiate 

 and the tail portion becomes distinguishable from the body, the 

 excretory system is recognizable as a pair of tubules running 

 nearly the length of the animal. Soon the portion in the pos- 

 terior part of the body proper draws together and fuses to form 

 the bladder. Sometime after this the tail tubules coalesce to 

 form the single median tubule of the mature larva. Meanwhile 

 the tubules anterior to the bladder fuse with one another at their 

 anteriormost ends, thus forming a circuitous tubule from one 

 side to another. 



At the earliest stage there is a single flame cell for each side 

 of the body. This is situated at the anterior end of the body. 

 Later this cell wanders backward along the lateral tubule so that 

 at the time when the tubular circuit becomes closed the flame 

 cell occupies a place halfway between the anterior end of the 

 system and the bladder. It then divides into two flame cells, 

 the fundaments of the system. The anterior one wanders for- 

 ward and by a two-fold bifurcation gives rise to four flame cells. 

 The posterior one wanders backward and by a single bifurcation 

 forms two cells. Thus the flame-cell number of the mature 



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

 No. 132. 



340 



