which may thus be inoculated in the tissues 
of the host. There are three ducts on each 
side, arranged like the strings of a cord (fig. 
63). They perforate the anterior sucker and 
are so wide and sinuous that the abdominal 
part might be mistaken for a coecum The 
ducts are connected with six or more relati- 
vely enormous cells with granulated proto- 
plasm, situated partly behind the ventral 
sucker and occupying a large space, characte- 
rized by transparency. They have a diameter 
of 0,03 mm, while that of the large nuclei 
is 0,01. The abdominal sucker with a diame- 
ter of 0,18 mm. looks very small; it is much 
nearer to the posterior end and may be re- 
tracted or protruded. Coloured preparations 
show behind the sucker an agglomeration 
of small and mostly elongate nuclei, other 
ones between the oral sucker and the large 
glandular cells and some round the suckers. 
The intestine is not easily distinguished; it 
seems to form a simple and short bag 
after the slightly visible, bulbless pharynx 
and oesophagus, Outlines of the genital system 
(which ought to be different according to 
sex) are hardly recognized. The numerous 
nuclei, seen in the cercariae, seem mostly 
connected with the muscular system; the 
others may belong to the glandular ducts, 
the nervous system, the intestine or the ru- 
diments of the genital organs, but they are 
so little differentiated that in spite of much 
work I could not obtain a clear insight. The 
tail and its transverse piece are formed by 
nucleate cells of a certain size, It moves in- 
dependently, even some time after it has been 
separated from the body, to which it is 
loosely attached by a kind of articulation. 
After penetration the schistosomulum (tig 
69) shows no more large glandular cell; they 
seem to vanish after having fulfilled their 
end. The ducts also seem to undergo invo- 
lution; for the rest we find the same structu- 
res. 
In this species the forked part consists 
of a separate spindleshaped piece at the trun- 
cate end of the tail. It may be bent in the 
middle so as to lie in the same axis or ho- 
121 
rizontally extended. This position is assumed 
while floating at the surface and supporting 
the body of the cercaria which hangs down. 
The extremities may also curl inwards (fig. 
55). The comparatively small body) and the 
rapid movement give to the cercariae, exa- 
mined under low power, a certain likeness 
with spermatozoa. 
Examination of infected snails show the 
cercariae formed in sporocysts, of which !ar- 
ge numbers are found in in the liver and the 
genital gland. In the infected liverfollicies 
the glandular epithelium disappears; this ex- 
plains the state of apathy and atrophy, so 
often seen in the infected snails. Of the in- 
fected Planorbis, the specimen, which lasted 
the longest, died after at three months, during 
which it furnished thousands of living cer- 
cariae. The production was diminishing to- 
wards the end of this period. 
Conditions under which the Cercariae 
leave the snails. 
In the complete absence of light, the 
ripe cercariae do not seem disposed to leave 
their host, even at temperatures of 30 to 31 
degrees, though they may accumulate in 
great quantities in the mucus expelled by 
snails. In the refrigerator, in intense cold 
and complete darkness, the free cercariae 
remain at the bottom of the water attached 
by the oral sucker; under these conditions 
they may live more than 24 and less than 
48 hours. When the snail retreats into the 
shell, as it does before death, the cercariae 
do not come out, so that, after the crushing 
of a shell, hundreds of live cercariae may 
pass into the water which was before abso- 
lutely free of them. 
Exposing the snails to the sun’s rays for 
several hours, we obtain a great number of 
cercariae, so that experimental infections are 
preferably made between three and four 
o’clock in the afternoon. Bathing at this time 
must therefore be considered as more dan- 
gerous than in the early morning. Light alo- 
ne, without corresponding heat, is not favo- 
rable to the coming out of the cercariae. 
