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Summary.

An account is given of the entozoal fauna found in certain South African snakes, including members of the Boidae, Colubridae, Elapidae and Viperidae.

Of the 89 snakes examined, 60 harboured Entozoa, 58 different associations of parasites having been found. These assemblages are detailed. Of these infected snakes, 33 were males and 27 females, of which 12 only were young. The majority of those without Entozoa at the time of examination were also young specimens.

A systematic statement of the entozoal assemblages of each infected snake is given, the distribution of the parasites within the hosts being noted. Mature snakes usually contained more species than younger ones and numerically more entozoal individuals were found in full-grown snakes in poor condition. Flagellates were numerically dominant in most cases.

A number of new species of Flagellata, Ciliata and Plasmodia occurring in these hosts are described and their systematic positions discussed. Other parasitic organisms of special interest, but less well known, are also described.

The effects of certain Entozoa on their ophidian hosts are described. These include spontaneous intestinal and hepatic amoebiasis, found in members of each of the ophidian families examined, conditions due to ciliate infections, coccidiosis of the intestine and of the gall bladder, pressure effects of cysticerci, intestinal obstruction by helminths, haemorrhagic conditions and hypersecretion of mucus by the lungs due to the presence of helminths, one case of gall stones associated with a trematode infection, and blood conditions, In connection with blood conditions due to Entozoa, the percentage of erythrocytes infectcd with haemogregarines and the alterations of the host cells due to them and to Plasmodium spp. are stated. Mononuclear leucocytosis was found in snakes suffering from liver abscess. The pereentage of eosinophiles associated with single or multiple helminth infestations in some of the snakes is tabulated.

A brief comparison is made of the entozoal fauna of these snakes examined in South Africa and of the same species of snakes from West Africa. Distinct similarity is disclosed.

The interelations of the hosts and parasites are briefly indicated and their economic significancc stated.