STRUCTURE OF CLINOSTOMUM 211 



An observation made recently upon a worm from a frog cyst 

 seemed to be inconsistent with a circulatory movement of the 

 droplets as just described. The cyst attracted my attention 

 because of its small size, it being globular, compact and only 1.3 

 mm. in diameter, quite unlike frog cysts and much like those 

 found in the bass. When the worm had been liberated and ar- 

 ranged in a compressor for observation it was seen that the vessels 

 of the anterior region were filled with highly refractive droplets. 

 These droplets were not in a state of flux but were stationary. 

 The pulsations mentioned above and the flow of droplets were 

 seen in bass specimens in the posterior region. In the frog worm 

 the vessels of the posterior region were empty. It is possible that 

 this worm was a very recent arrival in the frog and that the move- 

 ments of the droplets had not yet begun to take place. 



A system of branches derived from the collecting vessel and 

 permeating the body in this way is very unusual in trematodes. 

 The usual structure is a network of minor vessels uniting to form 

 larger vessels which finally merge into a single collecting vessel. 

 In three widely separated forms however we find an arrangement 

 somewhat similar to that of Clinostomum. In a young stage of 

 D. echinatum Looss ('04, fig. 192) figures a collecting vessel much 

 resembling that of Clinostomum, especially in the anterior body 

 region where side branches are given off, the main vessel mean- 

 while continuing until it meets the ciliated recurrent vessel at the 

 extreme anterior end of the body. A comparison of Looss' fig. 192 

 with that of the younger stage shown in 191 indicates that the 

 branching is a late feature in the life history, a fact of interest since 

 it is uncommon in trematodes at large. In adults of D. echinatum 

 (Looss, '94, fig. 114) these vessels are very much branched but the 

 branches do not assume the form of a sub-cutaneous system like 

 the one so well developed in Clinostomum. In Cephalogonimus 

 also the excretory collecting vessel is branched. This point was 

 first noticed by Poirier ('85, fig. copied by Braun, '93, pi. 20, fig. 9) 

 who says ''Ces canaux lateraux comme le canal impar median, 

 emittant sur tout leur parcours des branches ramifies se dirigeant 

 vers le bords lateraux du corps. Ces ramifications s'entendent en 

 avant, jusque un peu au-dela du point de bifurcation de I'oesoph- 



