E, C. Faust 249 
high, probably because climatic conditions as well as the large areas covered 
by lakes and the large amount of irrigated land tend to foster the development 
of an enormous number of snails. But since fluke infection in all groups of 
vertebrates is unusually high in the Central Yangtze Valley, it is very 
probable that, of the larval flukes found in the samplings secured in this area, 
there are more that represent indigenous species than do those collected from 
North China. The absence in this collection of larvae of a large share of the 
well-known trematodes of man and domestic animals of Central China may 
be explained on the basis of chance distribution of many species of parasites 
in a tremendous number of host individuals. Random sampling explains why 
repeated examinations from various habitats in three centres (Wuchang, 
Changsha, Kiukiang) have not revealed more larvae of mammalian species; 
while the disproportionally large number of molluscs compared with definitive 
hosts in the area tends to reduce the percentage of infection. Furthermore, 
one needs to remember that certain species, such as Clonorchis , require a 
second intermediate host, which requirement necessarily reduces the number 
of individuals of the species that can “ carry on.” In addition to these data 
there is the fact that certain infections of man, such as schistosomiasis japonica, 
although present in various centres of the Central Yangtze Valley, are not 
ubiquitous, but definitely localised. It is quite necessary, then, to consider 
both groups of limiting factors in comparing the infection-incidence of larval 
trematodes in two areas as dissimilar as North and Central China admittedly 
are. 
Certain species have been observed in both North and Central China. These 
include Aspidogaster conchicola, observed in two unrelated species of mollusc, 
as well as in Amyda sinensis and Leuciscus aethiops ; Cercaria pekinensis ; and 
Cercariacum mutabile. 
In all, 26 species of flukes have been observed from molluscan hosts, which 
are included in the following groups: 
Group No. of species 
Aspidobothridae ... ... i 
Holostomata ... ... ... \ 
Monostomata ... ... ... 2 
Amphistomata. 2 
Distomata, divided as follows: 
echinostome larvae... ... 4 
xiphidio-cercariae ... ... 8 
cystophorous cercariae ... 1 
cystocercous cercariae ... 1 
leptocercous cercariae ... 3 
microcercous cercariae ... 1 
furcocercous cercariae ... 1 
Cercariaeum ( C . mutabile) ... 1 
