On South African Paramphistomidae (Fisch.). 
185 
observations, it was quite certain that the snails from which the cerceriae 
had escaped to encyst on the grass used in my feeding experiment harboured 
only these particular dark-coloured cerceriae. In the locality selected 
there were no other species of fresh-water snails to be found ; animal life 
in the pools, as far as vertebrates are concerned, was confined to the develop- 
ment of tadpoles that died off as soon as the pools began to dry up. The 
cerceriae encyst very readily, and in the laboratory I caused a large number 
to encyst on grass stems placed in a wide tube of water into which the 
cerceriae of infected snails were removed. Such grass was also used as a 
feed. I was therefore perfectly sure that my experimental animals were fed 
only on the cysts of the cerceriae under observation. 
A few months after the first feed I found on examination that my 
experimental animals were heavily infected with Paramphistomids. In 
some cases these flesh-coloured and cream-coloured parasites were found in 
all four divisions of the stomach, and a large number had found their way 
down to the small intestine. The death of one of the young sheep towards 
the end of the second month was evidently due to a confined life and an 
abnormal heavy infection which was revealed on a post-mortem examination. 
The adult parasite I identified as Paramphistomum calicophorum 
.5 
Fig. 6. 
