1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 91 
found in considerable numbers in the intestine or stomach of wild and 
domestic vertebrates. Species of Paramphistomum are especially common 
in African herbivores. But little is known thus far of their life-cycle.! 
According to Cawston, the usual Paramphistomum of South African cattle 
and sheep has the snail Bulinus schackoi (Jickeli) as intermediate host.2 
In Japan, China, and other Oriental countries a very serious disease 
is caused in man by a lung fluke, Paragonimus ringeri (Cobbold) (= pul- 
monale Balz; westermani Kerbert), which, moreover, also infects dogs 
and pigs. In this case it was shown experimentally that the mira- 
cidia enter certain water snails, particularly a species referred to as 
“Melania”’ libertina Gould, where they produce sporocysts.2 Ando’s? 
later experiments, though not eliminating all possible sources of error, | 
render it probable that the cercarie eventually migrate from ‘‘ Melania”’ 
to fresh-water crabs (Potamon and Eriocheir), where they encyst, and 
that they finally reach their vertebrate host, mostly following the con- 
sumption of uncooked crustaceans.° | 
In Africa the most important parasitic trematodes are the blood 
flukes, species of the genus Schistosoma’ that live in the large blood-vessels 
of the abdominal cavity of man, producing a disease known as bilharziosis 
or schistosomatosis. In Schistosoma the two sexes are separate, the adult 
male worm carrying the adult female in a ventral groove. Two species 
of the genus are restricted to man, at least as natural infections. 
Of these, Schistosoma hematobium (Bilharz) [=S. capense (Harley) | is 
common in Lower Egypt, Asia Minor, southern Asia, and the eastern 
half of Africa and has also been found in Morocco and Portugal.’ The 
1J. D. F. Gilchrist (1918, Parasitology, X, pp. 311-319) has shown that the cercarize of Distoma 
luteum Gilchrist, a common intestinal fluke of South African frogs (Rana and Xenopus), develop in 
Bulinus tropicus (Krauss); the cercarise emitted by infested Bulinus, after swimming about for some 
time, reenter the body of the same species of snail by the nephridial opening and encyst in the peri- 
cardium; snails thus infested with cysts are later eaten by the frogs. Another interesting case is that of 
certain trematode larve that have on several occasions been found in mosquito larve, whence they may 
pass into the adult insect. In the case of an Indian species, M. B. Soparkar (1918, Indian Jl. Med. 
Res., V, pp. 512-515) was able to show that cercarie derived from Planorbis exustus infect larve of 
Anopheles rossi and Culex fatigans; the next stage of the fluke, which is related to Clinostomum, is found 
in certain fresh-water fish; but it is possible that the fully mature form of the worm develops in a fourth 
host, namely some aquatic bird. 
2Cawston, F. G. 1923. ‘South African larval trematodes and their intermediary hosts.’ Trans. 
Roy. Soc. South Africa, XI, 2, pp. 119-130. 
’3Nakagawa, Koan. 1919. ‘Further notes on the study of the human lung distome, Paragenimus 
westermani. Journ. of Parasitology, VI, pp. 39-43. It is not clear from this paper that the life-history 
is as yet completely elucidated. 
‘Ando, R. 1920. (‘The first intermediate host of Paragonimus westermant.’) Tokyo Iji Shinshi, 
Nos. 2175-78, 21 pp., 1 Pl. (in Japanese; reviewed in Tropical Diseases Bull., X VII, 1921, p. 51). 
sAccording to Iturbe and Gonzalez |1919. ‘Quelques obsevations sur les cercaires de la vallée de 
Caracas.’ (Caracas), 20 pp., 7 Pls., P. ringert occurs also in Venezuela, where its intermediate hosts 
are, they claim, the snail Pomacea luteostoma (Swainson) and the fresh-water crab Pseudothelphusa 
aturbet Rathbun. Se 
6Schistosoma Weinland, 1858 =Bilharzia Cobbold, 1859; Gynzcophorus Diesing, 1858;. Thecosoma 
Moquin-Tandon, 1860. : 
70. C. Chesterman (1923, ‘Note sur la bilharziose dans la région de Stanleyville.’ Ann. Soc. Belge 
Méd. Tropic., III, pp. 73-75, Pl.) has recently reported cases of intestinal bilharziosis from the region 
of Stanleyville, Belgian Congo. They appear to be due to S. hematobium, although the eggs found in the 
feeces are larger and narrower at the ends than in the Egyptian S. hematobium. The few adults examined 
seemed identical in every respect with S. hematobium. The intermediate host of this parasite was found 
to be near Stanleyville Physopsis africana (erroneously called Bulinus contortus in Chesterman’s paper). 
