304 ON SOME TRBMATODE PARASITES OF AUSTRALIAN FROGS, 



where, is a thick-walled muscular bulb (wanting, however, in 

 the (jroryoderiiut, and a few others), which is almost univer- 

 sally called the pharynx. The exact position of this pharynx 

 is subject to a good deal of variation ; in most Fasciolidce, fol- 

 lowing almost immediately upon the oral sucker ; in many 

 others, e.g., the Lepoderrnatuut, Dolichosuccus, Brachysaccus, 

 the pharynx is placed further back, a thin-walled section, the 

 prepharynx, being interposed between the pharynx and the 

 oral sucker (Fig. 43). In others, again, the pharynx is placed 

 much further back as, for instance, in M icroscaphidium (55, 

 p. 691), where it opens directly into the intestine. Just in 

 this position does a well-marked pharynx lie in JJiplodiscus, 

 as the photographs 36, and 34 and 35, of transverse and horizon, 

 tal longitudinal sections respectively, show. The wide, short, 

 intestinal limbs are circular in transverse section, and reach 

 just past the middle of the body. The posterior sucker is, in 

 life, ventrally directed, but in most preserved specimens it 

 faces postero- ventrally. In form, it presents a quoit-like rim 

 and a deep central cavity, in the centre of which, concentric 

 with the outer rim, is the second quoit-like ring, the meaning 

 of which has given rise to so much discussion (Braun 4, p. 693). 

 Its centre is often deeply depressed from the exterior, while a 

 cylindrical plug of parenchyma cells projects towards its centre 

 from within, the two opposing depressions making the thick- 

 ness of the sucker, in this region, much less than elsewhere 

 (Figs. 32, 33). Through this depression, there is no opening 

 of the excretory system nor of any other system of ducts or 

 vessels. The muscular ring is entirely an accessory part of 

 the sucker, and, no doubt, is of considerable assistance in per- 

 fecting the clinging action of the whole sucker. When the 

 sucker is being fastened on to the wall of the frog's bladder or 

 any othar surface, this central plug would assist in making 

 the expulsion of the air (or gas, or whatever its contents may 

 be) from the cavity of the sucker much more complete, in 

 just the same way as the column?e carnese and musculi pecti- 

 nati of the mammalian heart assist in expelling the last drop 



