360 University of California Publications in Zoology [Vol. 19 



But even though the larger parts of the system have been long known, 

 yet for a considerable time they were confused with parts of the 

 digestive tract, the oviduct and other parts of the genital system 

 (Fraipont, 1880, pp. 415-420). The flame cell itself was perhaps first 

 seen by Biitschli in 1879, so it is improbable that earlier workers 

 thought of a unified system. Even after the flame cells and capillaries 

 had been found, they were considered for a time as distinct from the 

 larger tubules and bladder. That this confusion could readily exist 

 can now be well understood, because of the minuteness and complexity 

 of the parts of this system. 



In reviewing the literature on the excretory systems of cercariae 

 that have been completely worked out. the conclusion, I believe, can 

 be safely drawn that there is a definite plan of arrangement of the 

 collecting tubules and the accessory collecting tubules, when developed, 

 and that the capillaries and flame cells are found in groups, nearly 

 always of an equal number throughout the body. This grouping of 

 the flame cells, naturally can occur in cercariae only where the excre- 

 tory system in the cercaria approximates to the same condition as that 

 found in the adult, 



Looss, in 1892, thirteen years after the discovery of the first flame 

 cell in a digenetic trematode, worked out quite completely the excretory 

 system of " Amphistomum subclavatum." In the cercaria he found 

 the excretory system, as well as other parts, to be bilaterally sym- 

 metrical and the capillaries and flame cells to have a definite pattern. 

 Looss (1894) also found that the excretory system of the adult worm, 

 Allocreadium isoporum (Looss) was on a definite "2x6x4" plan; 

 that Opisthoglyphe ranae (Frol.) was built on the "2x6x3" plan; 

 that Haplometra cylindracea (Zeder) was also built on the "2x6x3" 

 plan. Several other species included in Looss' paper showed a definite 

 grouping of flame cells on each side as far as he could trace them. 

 Sometimes the anterior end and again the posterior end would be too 

 opaque to trace the fine capillaries. Again he found (Looss, 1896) in 

 Anchitn ma sanguineum (Sons.) a definite arrangement, although some 

 of the capillary groups are in twos while others are in threes. How- 

 ever, in each case both sides of the body are the same. Cort (1918a, 

 fig. 2) shows Agamodistomum marcianae (La Rue) to be built on the 

 "2 x 10 x 6" plan. Cort (1918c, pi. VII) shows Cercariaeum mutabile 

 to have a definite "2x8x4" plan. He (1919a) also shows Cercaria 

 polyadena to have a definite formula, namely "2x6x3." Dollfus 

 (1911, figs. 1 and 2) shows the excretory system of Gymnwphallus 



