E. C. Faust 
261 
acidophilic glands. The former have mucoid content and the latter are 
granular. 
Only the reservoir elements of the excretory system have been studied. 
The median bladder is small, while the cornua are conspicuously large. The 
excretory pore is surrounded by a strong sphincter. 
The larva develops in a simple sporocyst. 
CeRCARIA C1RCUMSTRICTA nOV. Spec. 
(Plate XXII, Fig. 16.) 
The minute larva, for which the name Cercaria circumstricta is proposed, 
was found in 2 per cent, of Viviparus quadratics (Bens.) and in 2 per cent, of 
V . polyzonatus Frfld., examined in Wuchang in June, 1921. 
The body of the cercaria is broadly oval from the anterior aspect and 
truncate posteriorly, and measures 0-088 mm. in length by 0-074 mm. in 
broadest cross-section, while the tail is an elongate cone. The animal is pro¬ 
pelled by the sluggish lashing of the caudal organ. The body is covered with 
delicate spines. There is a constriction of the body just behind the oral sucker. 
The latter organ is 26 /x in diameter and is surrounded anteriad by a crown of 
20 sharp reversed hooks. No hooks or spines have been found in the region 
of the nuchal constriction. There is a short prepharynx anterior to the pharynx 
and an oesophagus mesad to the pharynx. The caeca arise from the oesophagus 
and extend to the subcaudal region of the body. The ventral sucker lies some¬ 
what behind the mid-region of the body and is only slightly smaller than the 
oral sucker. 
The excretory tract centres in a flattened bladder with postero-dorsal pore 
and with collecting tubes emptying into it from the antero-lateral aspect. 
These tubes are distended and contain concretions which are highly refractive. 
On reaching the region of the pharynx the tube becomes constricted and flexes 
backward, giving off in its course three secondary tubes. Each of these tubes 
leads into a series of three capillaries, each with a flame-cell at its head. The 
flame-cells are relatively large and have a few thick cilia. Thus the number 
of flame-cells for each side of the larva is 9 and the probable factoring is 
3 + (3 + 3), with the formula a + j3 n obtaining. Leading from the bladder 
into the tail is a conspicuous duct which forks in the proximal fourth and opens 
laterad about a fourth distance from the posterior end of the tail. 
A portion of the parenchyma is filled with cystogenous glands (eg) which 
contain minute elongate granules. These lie in two series on each side of the 
body. The intervening spaces are occupied with many cephalic glands, which 
empty through ducts around the oral sucker. It seems highly probable that 
the larva encysts by use of the former variety of secretory apparatus, 
while the latter serve in the digestion of host tissue after ingestion of 
the cyst. 
The generative anlagen were entirely obscured by the secretory glands. 
