E. C. Faust 253 
organ then secrete a protective layer around the essential body, under which 
circumstances the larva could be transferred to the next host. 
Cercaria serpens nov. spec. 
(Plate XXI, Fig. 4.) 
* 
The larva, for which the name Cercaria serpens is proposed, was found in 
3 per cent, of Viviparus quadratus (Bens.) examined at Wuchang during June 
and July, 1921. 
The worm is a slowly moving larva, with a body measuring 0-1 mm. long 
by 0-06 mm. wide, and a broad tail nearly equal in length to the body. The 
body is entirely covered with minute spines and has a collar constriction with 
an interrupted series of 26 blunt spines. The tail has lamellate margins ex¬ 
tending from the proximal region almost to the tip. In contracted specimens 
these have a fluted appearance. 
The oral sucker is small, measuring 28/x in outer diameter and tapering 
inwardly like a caper-fig. The acetabulum is nearly isometrical but is sunken 
into a deep outer disc-like pocket ( oa ). The oral sucker leads into a long narrow 
pxepharynx. The pharynx lies in the plane of the collar spines and measures 
10/x in transection. Leading inward from the pharynx the oesophagus is seen 
to consist of glandular epithelium with granular cytoplasm and clear-cut 
nuclei. This structure extends into the caeca which continue to the subdistal 
region of the body. The cephalic glands are situated just behind the aceta¬ 
bulum. They are numerous, with granular cytoplasm and clear nuclei and are 
acidophilic in reaction. The conspicuous elements of the excretory system 
consist of a rhomboidal bladder with a well-marked pore (ep), collecting 
tubules arising on the anterior side of the bladder and enlarging in the pre- 
acetabular region to accommodate the excretory concrement there, and the 
tubule system in the tail. The collecting tubules of the body become con¬ 
stricted in the region of the oesophagus and are flexed backward just posterior 
to the pharynx, to continue backward as the secondary tubules. These secondary 
tubules are provided with ciliated walls in the vicinity of the acetabulum. At 
the plane of the bladder the tubules are flexed forward, to continue as the 
tertiary tubules. On account of the closely massed cystogenous glands through¬ 
out the entire body of the larva the details of flame-cell structure could not 
be made out. Proceeding from the bladder into the tail one observes a short 
median shank which forks almost immediately to proceed to the lateral margins 
of the tail, there to open through large pores (see Fig. 4). 
Ihe redia possesses a pair of small “feet” which are situated near the 
posterior end of the body, a collar, a birth-pore, a conspicuous pharynx and 
an elongate gut with yellowish-brown opalescent content. Although none of 
t e specimens of cercariae observed demonstrated the phenomenon of encyst- 
ment, this method of transfer evidently obtains, in view of the large number 
of cystogenous glands in the body of the cercaria. 
Parasitology xiv 
17 
