
570 RECORDS OF THE S.A, MUSEUM 
RELATIONSHIPS, 
Cercaria lessont 1s a longifureate, distome, pharyngeal cercaria whose nearest 
relative is C. helvetica XXXI (Dubois, 1929) from Limnaca and Planorbis, The 
measurements of the latter (body length, 120-140; tail-stem, 135-150; furea 
length, 160-180) show it to be a Little larger; but i is characteristic of this type of 
cerearia is to be ‘‘very contractile’? (Dubois 1929, 95), as the range of measure- 
ments of C. lessont indicate, so that this difference is probably of little importance, 
especially as Dubois’ method of fixing cerearia may have been different from 
ours, The shape and proportions of the body are closely similar; the excretory 
systems are identical, except that, in C. Jessoni, the commisgures are not always 
completely developed, and that the flame-eclls in the eaudal stem are placed 
higher than those of Dubois’ cerearia. The nature of the intestinal caeca jis 
apparently the same in both; those of (. /essoni were execedingly diffienlt to see, 
and Dubois was unable to follow those of CL helvetica XNAT to their termination. 
The most conspicuous difference is in the gland cells; in Dubois’ cereavia they are 
disposed in two longitudinal series, each of four cells, posterior to the ventral 
sucker, aud are sometvhat larger than those of C. lessuni; while im ‘the latter, 
the two longitudinal series have heeome pushed forward and le on either side of 
the ventral sucker. The gland cells of both have the same character, however, 
heing very indistinct, The only other differences are: firstly, that nmpigmented 
eyes are not recorded for Dubois’ cercaria, but these are in any ease not 
conspicuous features; secondly, that no mention is made of ininute scattered 
spines around the posterior part of the body, as in C. lessoni; and finally, that 
no island of Cort 1s indicated, but this again is a very inconspicuous feature. 
Another cerearia, (. pygocytophara Brown (1931), from Plamorhis, is very 
closely allied to C. helvetion XX XI, and to C, lesson. The flame-eell formula is 
the same, and spinatiou, caudal excretory system, body size and shape are all 
practically identical with those of the other two cercariae. The glands, eight 
in number, are arranged like those of C. helvetica NNXI, Apart from the latter 
difference, the only other distinctions between C. pygecylophorau and C. lesson, 
ave the presence of hair-like structures on the tail-stem of the former, and the 
nature of its exeretory commissures. The latter are apparently rather less 
completely developed even than those of (. lessoni; no trace of a posterior com- 
missure is shown, while (he branches of the anterior have not met in the cercarial 
stage, 
But for the presenee of the commissure anterior to the yentral sucker, 
C. lesson resembles closcly another group of eevearia, which includes the cerearia 
of Apatenon gracilis (from Bithynia). €. burti Miller (from Linnea and 
Planorbis), and C. pseudoburti Rankin (from Limnaea), These have only one 
