Some South African Cercariae 201 



and C. pigmentosa, C. frondosa and C. carvstoni were observed 

 to encyst readily. 



Several little fish called '* millions " were observed to feed 

 greedily on the fork-tailed cercariae escaping from Ph^sopsis afri- 

 cana and on C. pigmentosa escaping from Limnaea natalensis. 

 In this way the fish might be used to keep down the infection in 

 semi-stagnant pools and in rivers. 



Strong solutions of salt, fresh lime and tartar emetic have each 

 been shown to destroy the free-swimming cercariae. 



Tiara tuberculata (Mlill.) is very prevalent amongst the water- 

 cress at Prospect Hall along the Natal North Coast. The snail 

 is provided with a stout oval operculum or lid, so that the animal 

 is able to close itself inside its shell as a protection against injury 

 or drought. Limnaea natalensis, Planorbis pfeifferi and Isidora 

 tropica — all fresh-water snails, also occur in these water-cress 

 beds, but Tiara tuberculata is the most prevalent. Some of 

 the shells are as much as 30 m.ms in length; but it is common to 

 find them eroded at their pointed extremity. Tiara tuberculata 

 is closely related to Blandfordia nosophora Robson of Japan, the 

 intermediary host of Schistosomum japonicum, and Dr. W. W. 

 Cort has recently shown that infested specimens can resist drying 

 for as much as 7 1 days — see Journal of Parasitology, vol. vi. pp. 

 84-88. I have found an interesting redia-produced cercaria in 

 some Tiara which I have collected from Prospect Hall. It is an 

 eye-spotted monostome with a long, slender tail armed with nu- 

 merous long spikes. The total length of the cercaria is : 7 mms., 

 the tail being slightly longer than the head. There is also a 

 small styletted distome cercaria infesting Tiara at Prospect Hall, 

 closely resembling C. caTvstoni Faust. We do not know the life- 

 history of either of these parasites ; but crabs cmd birds abound in 

 these water-cress beds. Tiara tuberculata also occurs close to 

 the Umgeni mouth. 



Cerithidea decollata L. is well-known to fishermen as a useful 

 bait. It is commonly seen on the trunks of trees growing in the 

 marshy surroundings of the lagoons near EHirban. The shell is 

 a stouter one than that of Tiara tuberculata, but the operculum is 



