80 
This Trematode is very small and inconspicuous, and with the 
exception of the eggs is quite colourless. The adult (Plate I., figs. 
1 — 2) measures 0-54 mm. to 1-30 mm. in length, and is flask- 
shaped, the broadest part which is about half the length occurring 
behind the ventral sucker. The anterior end narrows considerably, 
and after a short neck the body gradually broadens out, and is 
rounded posteriorly. In section it is nearly round, but slightly 
flattened dorso-ventrally, especially in front of the ventral sucker. 
The exceptionally large eggs have thick yellow shells which shine 
conspicuously through the colourless body. The whole worm is 
covered with sharp spines arranged in rows, somewhat flat and 
scale like in front, and becoming very sharp from the neck to 
about the posterior third of the body where they dwindle in size, 
although they never entirely disappear even at the extreme end. 
On the dorsal surface are two conspicuous eye-spots, one on 
each side of the pharynx, each composed of a dark brown central 
mass of pigment with smaller flecks radiating irregularly from it. 
These appear to be nearer or further from the oral sucker according 
to the amount of extension or retraction of the extremely mobile 
neck. 
The suckers are weakly developed and very nearly equal in size, 
the oral sucker in the adult being slightly the larger. In preserved 
material a specimen 0-35 mm. in length has the oral sucker 
globular and 0-06 mm. across, or it may be oval or oblong measur- 
ing 0-07 mm. by 0-05 mm. in a specimen of the same size, and 0-09 
mm. by 0-08 mm. in a specimen 0-54 mm. long. It grows with 
the worm. The aperture is almost terminal with a slight ventral 
inclination. The ventral sucker occurs just in front of the centre 
of the body, and is inconspicuous, and not so muscular as the oral 
sucker. It measures 0-06 mm. across in all the specimens 
examined, and does not appear to increase in size from the full- 
grown cercaria stage to the adult. 
The oral sucker leads to a narrow prepharynx so extremely 
contractile that it sometimes appears not to exist at all, its walls 
being flatly spread over the anterior part of the pharynx which 
telescopes into it, or it may reach a length of more than 0-08 mm., 
and then is seen to be narrow and thin-walled. Following this is 
a strongly muscular pharynx 007 mm. long and about two-tliirds 
as broad. This leads to a very short and broad oesophagus which 
branches immediately in front of the ventral sucker into two broad 
intestinal coeca reaching nearly to the posterior end of the body. 
