544 W. G. MacCallum, 



thin layer of epithelial cells wliose outline can be made out only 

 Avitli difflculty and wliose nuclei are very small and irregulär in 

 form and size and in fact look like chroraatin grannies. Usually 

 tliese cavities are empty but tliey may contain a coagulated fluid. 

 It is one of these sacs tliat practically surrounds the large ventral 

 sucker Avlnch appears almost to be suspended in it. Altliougli this 

 is obviously the excretory apparatus it is diflicult to make it appear 

 analogous in detail with that System in other trematodes for a search 

 for ciliated funnels etc. in this connection has been unsuccessful. 

 There exists however in the body a pair of structures Avhich may 

 explain this lack and which otherwise would themselves be diflicult 

 to explain. On each side of the large median excretory sac there 

 is a pear-shaped thin-walled sac lined with epithelium like that of 

 the central sac, the bnlbous end of which is directed forward; turning 

 on itself posteriorly it gives off on its outer side a tube which ruus 

 directly forward and soon divides into three branches each of which 

 continues to run forward. In the sections at my disposal I cannot 

 trace a communication between these lateral sacs and the median 

 one — they lie almost directly in contact with it so that in passing 

 from one section to the next, one sac disappears and the other begins, 

 but the walls seem to be complete. No communication exists be- 

 tween the lateral structures on tlie two sides — there are many 

 sections through the median portion of the body Avhich contain no 

 trace of either and no external opening can be found. It seems 

 therefore most probable that other sections (perhaps transverse) 

 might show a communication between the lateral sacs and the median 

 one and tlius constitute one excretory System. The canals which 

 run forward on each side from the point of branching are tortuous 

 thick-walled tubes with cuticle-like lining and surrounded by a 

 mantle of cells which look like secreting cells — one of the tubes 

 especially on each side is thickly surrounded by these large pink- 

 staining cells. These tubes run forward toward the anterior end 

 of the body wliere they beconie very thin-walled and finally dis- 

 appear in the parenchyma. Tliey are very little if at all branched 

 but they are continuous with delicate thin-walled tubules which 

 run backward through the parenchyma and which it is exceedingly 

 difficult to trace. The limited amount of material is perlia])s the 

 only excuse for so imperfect a study of these structures in which I 

 have nowhere been successful in tracing out and describing the 



