The Life History of Distoma luteum n. sp., with Notes on some Cercariae and Rediae found in S. Africa

Abstract

Some years ago, in endeavouring to obtain various stages in the life history of the liver-fluke in South Africa for teaching purposes, I found that, although the parasite is fairly common on some farms in this country, the intermediate host had not yet been definitely ascertained. In Europe, as is well known, the intermediate host is the fresh-water snail Limnaea truncatula, but this species has not been recorded with certainty from South Africa. The commonest fresh-water snail here is Physa (Isidora) tropica and a preliminary examination of a few specimens of this mollusc from Muizenberg Lake revealed abundant stages of fluke very closely resembling those of the liver-fluke. Additional specimens procured from the neighbourhood also afforded abundant material of the same stages. The only difficulty in accepting this as a solution of the problem was that, though placed in the most favourable conditions, the free swimming form (cercaria) was never observed to encyst.