398 MEDICAL ENTOMOLOGY 



longitudinal markings reduced to streaks. Abdomen buff, with a brown 

 spot at the lateral margins of the second segment ; third to sixth seg- 

 ments inclusive with a brown transverse band, not reaching to the 

 middle line. Antenna without a fringe of hairs. A distinctly marked 

 fly, not likely to be mistaken for any other species. 



This species is widely distributed in Western and Central Africa, 



having a range considerably wider than that of palpalis. According to 



Austen it is found from Senegambia on the west coast 



Geographical Distribu- (16 N>) to the sout h er n part of Kordofan (12 N.) ; on the 



south it extends from Southern Abyssinia in a south- 

 westerly direction to the Bechuanaland Protectorate, and is present in the 

 northern part of Rhodesia. It is a common fly in most of the places in 

 which it occurs, and is probably the one which was referred to by the 

 older travellers as the ' tsetse ', the presence of which in certain regions 

 led to their being termed fly belts. 



As a cause of disease inorsitans ranks next to palpalis. Long before 

 the etiology of trypanosome diseases was understood the presence of this 



fly was associated, by natives of the country and Euro- 

 Relations to disease J 1-1 i XT e i i- r 

 pean travellers alike, with Nagana, a fatal disease of 



domestic stock. It w r as Bruce's discovery that the trypanosome which is 

 the causal agent in this disease is transmitted to the animals by the bite 

 of the fly which directed attention to the genus in relation to human 

 trypanosomiasis. Within the last year or two the species has come into 

 prominence owing to its occurrence in areas in which, although palpalis 

 was absent, cases of human trypanosomiasis were found. Its connec- 

 tion with Sleeping Sickness is now accepted as proved. Taute, working 

 at Lake Tanganyika, has shown it to be capable of transmitting a human 

 trypanosome, probably T. gambiense. More recently Kinghorn and 

 Yorke, working in the Luanga valley, have conducted a series of experi- 

 ments on the same lines as those which established the role of palpalis, 

 and have shown that morsitans can transmit T. rhodesiense Stephens 

 and Fantham, to monkeys and other animals. The species has thus come 

 to have a very great importance in those regions, such as Rhodesia, in 

 which cases of Sleeping Sickness have recently come to light, and in 

 which palpalis does not occur. 



The kind of country frequented by this species is very different 

 to that in which palpalis is found, and it jis rare to find the two in the 



u ,_*. *. J .. ... same locality, a fact which is not surprising in view of 

 Habitat and Habits J 



the very narrow limits within which the latter species 



can thrive. Whereas palpalis is restricted to the close neighbourhood of 



