Following the discovery, by Stokes, Bauer, and Hudson (13), of the susceptibility of Macacus rhesus to yellow fever, attempts were made to transmit the disease with a number of species of mosquito other than Aedes aegypti. In West Africa Bauer (1) and Philip (9, 10) incriminated five additional species of Aedes as well as Eretmopodites chrysogaster and Mansonia (Mansonioides) africanus, while Davis and Shannon (3, 4) showed experimental transmission with three other species of Aedes in Brazil. Next to Aedes aegypti, Mansonia (Mansonioides) africanus appeared to be the most important of the vectors demonstrated in Nigeria, because of its preference for human blood (2) and its house-haunting habits. Philip (12) also pointed out that Mansonia uniformis, although as yet untested, might eventually prove of considerable importance. Davis and Shannon in South America (5) made transmission experiments with the Brazilian species Mansonia fasciolata, Mansonia chrysonotum, and Mansonia albicosta.