254 
Larval Flukes from China 
Cercaria crista cantiia nov. spec. 
(Plate XXI, Figs. 5, 6.) 
This species, for which the name Cercaria cristacantha is proposed, was found 
in 0-4 per cent, of Vivijparus quadratics (Bens.), examined in Peking in the 
spring of 1921. It has an elongate body, 0-68 mm. in length by 0*25 mm. in 
width, and a tail somewhat longer, broad and stubby. The entire body is 
studded with a large number of minute spines and is beset with 24stylet spines 
in an interrupted series around the collar. The tail is aspinose. 
The oral sucker measures about 50 /x in diameter. The ventral sucker, which 
lies in the middle of the body, may reach a diameter of 100/x, although it more 
usually averages about 80 /x in transection. Within the oral sucker is a short 
prepharynx which is soon replaced by the pharynx, an oval sphincter about 
30/x in transverse diameter. Behind the pharynx is a long oesophagus which 
leads backward as far as the pre-acetabular region, where it forks in a charac¬ 
teristic manner, with the furci extending to the subdistal region of the body. 
The cephalic glands are many and heavily massed. They lie in the middle 
half of the body, mesad to the excretory tubules. They contain a chromophobic 
mucoid substance and have small basophilic nuclei. They empty through 
capillary ducts ( cgd ) lateral to the oral sucker. The genital anlagen consist of 
two clumps of cells lying mesad, one over the anterior region of the acetabulum, 
the other anterior to the bladder, with a connecting chain of cells. This system 
is, indeed, very undifferentiated in the cercaria. The body is provided with 
cystogenous glands. 
The redia is a typical parthenita of the echinostome group, with birth- 
pore and collar prominence, pharynx and gut. The ‘‘feet are present but 
are not conspicuous. The region of the integument surrounding the pharynx 
is studded with coarse sharp spines. Encystment of the cercaria is readily 
effected by decaudation and the elaborate secretion of cystogenous material 
to form the heavy cyst wall. The cyst is found throughout the winter and early 
spring months, long after motile cercaria have disappeared. It is an adapta¬ 
tion, no doubt, for prolonging the period of transmission to the next host. 
The Excretory System of C. cristacantha. 
The main features of the excretory system of this species conform to type. 
There is an oval bladder, with a posterior pore and a pair of large collecting 
tubules running cephalad. Just anterior to the acetabulum each tubule 
enlarges to permit of the collection of excretory granules in this region ( eg , 
Fig. 5). The tubule bends and is directed posteriad as the secondary tubule. 
As it again resumes its direction anteriad it gives off the capillaries of the 
system. The tubule system in the tail suggests an inverted Y, with the median 
shank and laterals of approximately equal length. It is the ultimate branching 
of the capillary system that deserves special attention. 
