224 Gastrotliylax hubalis 
Cross section of atrium triangular with apex directed ventrally : 
synethes, elongatus, mancupatiis, cohholdi and minutus. 
Cross section of atrium circular : sjKitiosus. 
This system of classification is not quite reliable, for in one specimen 
of G. h'uhalis, of which serial sections were made, the atrium frequently 
changed its shape. Fig. 8 shows a few of the changes presented by it 
in cross section. 
The genital organs lie in front of the posterior sucker and may be, 
as is usually the case, placed fairly near the body wall. They may also 
be placed nearer the centre. The size of the ovary and of the shell 
gland varies in the different species, while their proximity to each other 
also differs. In C. wenyoni a notable characteristic is found, and one 
which is unique in the genus. The duct of the excretory vesicle and 
Laurer’s canal unite to form a single short duct opening to the exterior. 
The uterus may or may not be clumped. The testes are large, paired 
organs, situated in front of the posterior sucker, and their position in 
relation to each other may be specific. The excretory vesicle is placed at 
the posterior end slightly in front, and at the side of, the large sucker. 
The size and outline vary. In G. hubalis it is exceedingly large and 
irregular and in one specimen the entire vesicle was filled with a large, 
glassy, lens-like body which did not stain and which quite changed its 
shape. Its duct, larger than Laurer’s canal, opens separately in all the 
species except G. wenyoni. The gut divides into two a little below the 
genital aperture, and the level to which the two limbs pass backward 
is of specific value, since in certain species the gut branches reach only 
to a third of the body length. The gut pockets are blind sacs and 
usually exhibit convolutions. 
The yolk follicles have no special arrangement, being generally in 
the form of widely distributed net formations. 
The life-histories of the species of Gastrotliylax are not known, but 
probably the intermediate host is some freshwater snail and the cyple 
like that of the sheep trematode— Fasciola Iwpatica. 
The following is a brief summary of the known species of Gastrotliylax, 
with their distinguishing features other than the shape of the atrium. 
(1) G. crumenifer, Creplin 1847. 
Gut branches are long and tortuous, extending to the level of the testes ; testes 
are placed laterally and close to the body wall. Length 12-18 mm. 
(2) G. compressus, Braudes 1898. 
Gut branches are short, and do not reach the level of the testes. Length 9-11 
mm. 
