43 
P. Manson-Bahr and ^ t . H. Fairley 
most active cercariae, so it may safely be assumed that they die on reaching 
the stomach. 
After penetrating the skin or mucosa, the cercariae are conveyed by the 
venous system to the right heart and so to the lungs. Here they may con¬ 
ceivably be temporarily held up in the pulmonary capillary bed, but eventually 
reach the portal vein and liver. 
The lung of a monkey exposed to heavy infection three days previously 
showed no cercariae on section. 
Once having reached the portal venules, the cercariae develop into adult 
male and female worms; the latter being then enveloped in the gynaecophoric 
canal of the former. Subsequently the paired worms travel against the portal 
blood stream to their ultimate destinations. 
The different distribution of the paired worms in the two species of in¬ 
festations is of considerable interest. In S. mansoni infestations, the habitat of 
the worm in infested monkeys was the inferior and superior mesenteric veins, 
and the portal veins of the liver. 
In S. haematobium infestations, paired worms were found in portal veins 
of the liver, as well as in the inferior and superior mesenteric veins, i.e. 
the vesical and uterine branches. From here many wandered into the inferior 
vena cava, and were filtered out into the lung. This tendency was never 
noted in S. mansoni , though their lateral spined eggs have been found in those 
situations. 
Morphology of Adult Parasites. 
General characteristics common to both species of worms. 
The male schistosomes are 1-1*5 cm. in length. The greatest breadth pos¬ 
terior to the ventral sucker is 1 mm. The anterior truncated portion is short, 
narrow and cylindrical, and bears suckers; the posterior part is flat and leaf¬ 
like; more posteriorly the lateral margins of this fold inwards and overlap, 
forming the gynaecophoric canal in which the female lies. The ventral sucker 
is situated just anterior to the junction of the fold. Posterior to the ventral 
sucker, the body of the male is covered with wart-like projections. The 
suckers are two in number, and are covered with papillae. The oral sucker 
is situated anteriorly and is funnel-shaped, with the dorsal lip larger than the 
ventral and communicating with the mouth. 
The ventral sucker is longer than the oral, is somewhat triangular in shape, 
and the apex of the triangle forms the stalk of the attachment. 
The function of this particular sucker would appear to be to fix the worm 
in a stable position while that of the oral sucker is essentially prehensile and 
alimentary. 
The excretory pore is placed posteriorly and is dorsal in position. The 
genital opening lies just posterior to the ventral sucker in the median line. 
The alimentary canal presents a mouth opening into the oral sucker and 
a short straight oesophagus which bifurcates just posteriorly to the ventral 
