EXCRETORY SYSTEM IN DIGENEA. 327 



nov. spec., and C. candelabra nov. spec., both with an equal num- 

 ber of flame cells and with the same number to the group, but 

 with a different disposition of the groups anteriad and posteriad. 

 Thus the flame-cell formula of C. trifurcata is 15 ([3 + 3] 

 + [3 + 3 + 3l), while that of C. candelabra is 15 = ([3 + 3 + 31 



+ [3 + 3]). 

 Although these three species constitute the only known 



xiphidio-cercariae in which the flame-cell number and grouping 

 have been worked out to a certainty, very considerable light is 

 thrown on the subject by a comparison of these larval species 

 with related adult species. Allocreadium isoporum (Looss, 

 1894, Fig- J 03) has a flame-cell formula of 24 = ([4 + 4 + 4 + 4] 

 + [4 + 4]). The larva is a stylet cercaria with an unusually 

 large tail. The larva of Acrolichanus petalosa, belonging to the 

 same family, has the same fundamental flame-cell grouping but 

 reversed as regards number of units disposed anteriad and pos- 

 teriad. The formula is 12 = ([2 + 2] + [2 + 2 + 2 + 2]). An- 

 chitrema sanguineum (Looss, 1896, Fig. 77) has a flame-cell 

 formula of the same number of groups but different disposition 

 of the groups and different numbers of cells within the groups, 

 i. e., 16 = ([2 + 3 + 3] + [3 + 3 + 2]). 



Two plagiorchiine species, Haplometra cylindracea and Opistog- 

 lyphe endolobum (Looss, 1894, Figs. 29, 163) have larvae which 

 are typically xiphidiocercariae. Both of these adult species have 

 the same flame-cell formula, 18 = ([3 + 3 + 3] + [3 + 3 + 3]). 

 The very young distomulum of Opistoglyphe has a formula of 

 6 = ([i + i + i] + [i + i + i]), from which it is plainly to 

 be seen that the adult condition is derived by a triad splitting of 

 each fundamental group. That species in two different subfam- 

 ilies of the Plagiorchiidae should have identical flame-cell formulae 

 is quite significant. 



Again, certain subfamilies of the Brachycceliidse, in which 

 the larvae are thought to be xiphidiocercariae, have a flame-cell 

 formula of 12 = ([3 + 3] + [3 + 3]), while Microphallus opacus 

 (Wright, 1912), belonging to another subfamily of the Brachy- 

 cceliidae, has a formula of 8 = ([2 + 2] + [2 + 2]). Analysis 

 shows that these two species have a common larval denominator, 

 namely 4 = ([i + i] + [i + i]). In other words, the mathe- 

 matical exactness of flame-cell formation in this family makes it 



