36 MOSQUITO WORK IN KHARTOUM, ETC.

The sudd as a factor in

mosquito distribution

Daniels1 has suggested that larvse protected by floating sudd may be earned long distances, and that new genera and species may in this way reach Egypt. The first part of this hypothesis may well be true, but as regards the second,

I would point out that little, if any, sudd finds its way even so far north as Khartoum. Floating islands of sudd are rarely encountered north of Dueim on the White Nile. They get caught by the reedy river banks and the low islands, and are at all times liable to be broken up and dispersed by the paddle floats of steamers. As a matter of fact, the distribution of mosquitoes indicated on the map is, on the whole, an argument adverse to the ingenious theory of this able

observer.

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1 Laboratory Studies in Tropical Medicine, 1903