INFECTION IN THE LUANGWA VALLEY. 181 



this area were found only in localities suitable for the occurrence of p^lpalis, 

 it may be recalled that the physical conditions which are si)ecially suitable 

 for palpaUs are equally necessary for fusca. Moreover, although the non- 

 existence of palpalis in the Luangvva Valley is very far from being- 

 established, yet there are considerations which render such a conclusion at 

 least probable. For_, as Mr. S. A. Neave has pointed out (Journal of 

 Economic Biology, 1909, p. 110), the watershed, which in Northern Rhodesia 

 separates the river-system of tlie Congo from that of the Zambesi, also 

 constitutes a well-marked zoological boundary. The insect-fauna of the 

 country drained by the Congo presents a strong infusion of forms which 

 are peculiarly characteristic of Tropical West Africa ; while on the Zambesi 

 side of the watershed the insect life is thoroughly typical of the East 

 African fauna. Now, as Neave has remarked, wherever palpalis has been 

 found up to the present it has invariably been associated with an insect- 

 fauna of the West African type. From the large entomological col- 

 lections made by Neave himself in the Luangwa Valley, we are able 

 to say with some degree of certainty that the insect-fauna of that area is 

 purely East African in character, being quite similar to that of Northern 

 Mashonaland ; and the discovery of palpalis in such surroundings would 

 therefore be somewhat surprising. 



Early in July the Entomological Research Committee requested Mr. Neave 

 to proceed to the lower Luangwa for the express purpose of collecting and 

 observing the species of Glossina which may occur there. 



