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Transactions of the Royal Society of South Africa. 
snail in which cercariae were noted, and repeated attempts to miest Limnaea 
iiatalensis from miracidia escaping from the ova of Schistosoma haematobium 
have uniformly proved negative. 
Limnaea natalensis is by far the most common snail that I have found 
in various parts of Natal, the Transvaal and the Cape. It has also proved 
the most easy to breed. In visiting an infected pool I have repeatedly 
found that only the most mature snails harbour the various cercariae for 
which I am looking ; however, I have sometimes come across a very young 
Physopsis harbouring the Bilharzia, and have found the infection present 
in a Physopsis which was only 13 mm. in length. 
On April 20, 1920, I placed 5 very young Physopses which I had 
]»red from eggs in water containing the miracidia of aS. haematobium. These 
snails were only 6 to 8 mm. in length, and showed no evidence of 
cercariae at the end of six weeks. They were probably too young to ingest 
the miracidia. 
Several F/njsojisis africana which had also been bred from eggs and 
safeguarded from other infection were placed in water containing the 
miracidia of S. haeniatobium on February 21, 1920. Six weeks later, on 
April 2, the mature cercariae of Schistosomavm haematobium were present 
in these snails. Other Physopses similarly treated on February 31 
showed the presence of similar cercariae on April 12, or eight weeks 
later, whilst 15 Physopses used as controls, and not exposed to miracidia, 
showed no infestation on Ajiril 28. They were about three and a half 
months old. 
On January 6, lO and 12, 26 Physopses which had been bred from 
eggs were exposed to water containing the miracidia of S. haematobium. 
On January 31 three contained very young sporocysts and cercariae, 
three were free from cercariae, and ten were dead. On February 13 
mature cercai'iae, resenil:)ling those of S. haematobium, were present in two 
specimens. Some of these sporocysts and cercariae were submitted to 
Dr. R. T. Leiper, who states, " The sporocysts and cercariae from Physopsis 
would appear to be those of Schistosoma." 
On February 13 and 16 about 20 Physopses were exposed to infection 
with the centrif ugalised deposit of urine containing the typical spine-pointed 
eggs of Schistosoma haematobium. 
Oil March 23 two were dead, but one contained a dark, branching 
sporocyst throughout the liver-substance, whilst the other contained a 
branching sporocyst with an immature cercaria possessing head, tail and 
prongs. On March 31 the typical Bilharzia cercaria was present in ten 
of these Physopses. 
Three of these Physopses were only 7 mm. long, two only 7*5 mm. 
long, and one only 6*5 mm., showing that Physopsis africana, when only 
about four months old, is capable of harbouring the Bilharzia parasite 
