
JOHNSTON AND BECKWITH—LARVAL TREMATODES S7\ 
commissure behind the ventral sucker, but have an exeretory formula identical 
with that of C, lessowi, The size, shape, proportions aud spination are similar. 
All haye four pairs of penetration glands, lit these are behind the ventral 
sucker, arranged either in two horizontal rows, as in the cetcaria of Apatemon 
gracilis, or in hwo groups of four, as in the others, Long, fine hair-like processes, 
like those of C. pygocytophora, ave shown on the sides of the tail-stem of the 
eercaria of A. gracilis, but no such processes were observed on C. lessoni. Byes 
are not recorded for C. burti. C. pseudoburti is very similar to C. lesson, but in 
the former, the lack of anterior commissure, the absence of spines at the posterior 
end of the body, as well as the disposition of the vland-cells, serve to distinguish 
it from our cerearia. 
To this group might be added €. ripani Brackett, 1939 (from Stagnicola) 
which agrees with the descriptions of the others, except that the glands, arranged 
like those of C. burli and C. pseudoburh, in two groups behind the ventral sucker, 
are given as only six in number. If these glands are of the same indistinet 
nature ag those of C. helvelica XX NT and (. lessoni, the diffiealty encountered in 
distinguishing the precise number world be e¢onsiderable, 
A tiumber of other cereariae appear to have some affinities with @. lessoni, 
though not so closely related as the six mentioned above. The cerearia of 
Apharyngostrigea pipientis Olivier (1940), from Plonorbula, has eyespots and 
four pairs of gland-cells rather like those of our Jarva; it alsa has two excretory 
commissures, though their relation to the rest of the excretory system is different. 
The exeretory system formula is 2[ (2+ 2) -+ (2-2 +4 (2))] —20, ie, it 
shows development of a greater complexity with the same pattern as that of 
C. lessont and its closest relatives. thr this connection it is interesting to note 
that the flame-cells in the tail of the eerearia of A, pipientis ave in the same 
position as those of the other group, and that the iwo flame-cells of each side are 
very closely connected, as though their division is very rerent. The size of the 
eerearia is of the same order, but it is very obviously distinguished from (. lessont 
by the peculiar nature of its tail, as well as by minor features sich as spination. 
The cerearia of Apharyngostriged- this Azim 1935 (from Planorbis, Physopsis 
and Pyrgophysa) is less similar to C. lessont in some respects than the cerearia 
of A. pimentis. The shape and size of the body are of the same order, and the 
spination probably similar, thongh the hair-like processes on the tail are a 
distinetion, and no pharynx is shown in .Avzim's figure. There appear to be, not 
four, but three pairs of gland cells arranged as in the cerearia of A. piptentis. 
The fureal exeretory tubes open at the tips of the furcae, unlike those of C. lessont 
and the related forms; the excretory system, so far as eau he determined from the 
diagram, possesses no comuussures; and though the flamne-cells are fourteen in 
