MUSCIDAE TSE-TSE FLY 



513 



It bites man and animals in South Africa, and if it have 



previously bitten an animal 

 whose blood was charged with 

 the Haematozoa that really con- 

 stitute the disease called Nagana 

 (fly-disease), it inoculates the 

 healthy animal with the dis- 

 ease ; fortunately only some 

 species are susceptible, and man 

 is not amongst them. It has 

 recently been shown by Surgeon 

 Bruce l that this fly multiplies 

 by producing, one at a time, a 

 full-grown larva, which irnme- 



FIG. 244. The Tse-tse fly (Glossina morsi- 



tans). A, The fly with three divisions diately changes to a pupa, as 



larva c r u S a CiS pr jecting ' B ' adult do the members of the series 



Pupipara. There are already 



known other Muscid flies with peculiarities in their modes of 

 reproduction, so that it is far from impossible that the various con- 

 ditions between ordinary egg-laying and full-grown larva- or pupa- 

 production may be found to exist. Although it has been supposed 

 that the Tse-tse fly is a formidable obstacle to the occupation of 

 Africa by civilised men, there is reason to suppose that this will 

 not ultimately prove to be the case. It only produces disease when 

 this pre-exists in animals in the neighbourhood ; only certain 

 species are liable to it ; and there is some evidence to the effect 

 that even these may in the course of a succession of generations 

 become capable of resisting the disease inoculated by the fly. As 

 long ago as 1878 Dr. Drysdale suggested 2 that this fly only pro- 

 duces disease by inoculating a blood-parasite, and all the evidence 

 that has since been received tends to show that his idea is correct. 

 Although the facts we have mentioned above would lead to 

 the supposition that Muscidae are unmitigated nuisances, yet it 

 is probable that such an idea is the reverse of the truth, and 

 that on the whole their operations are beneficial. It would be 

 difficult to overestimate their value as scavengers. And in 

 addition to this they destroy injurious creatures. Thus in 

 Algeria Idia fasciata, a fly like the House - fly, destroys the 



VOL. VI 



1 Prelimitiary Report on the Tse-tse Fly Disease, 1895. 

 2 P. Liverpool Soc. xxxiii. 1878, p. 13, note. 



2 L 



