358 C. F. M. SAVYNNERTON. 



and a few pallidipes beiiind the cattle was 820 paces quickly covered. The other 

 flies had already dropped off replete before that, in spite of the kicking and running 

 on the part of the cattle. 



The question of the females travelling, even on animals, is an important one 

 in relation to the question of possible control by barrier clearings, and is worthy 

 of more extended special experiQientation if long distances have not yet been 

 recorded for it.* In Simpson's experiments with marked male and female flies- 

 on the Yapi-Tamale road, in the Gold Coast, only one recaptured fly was found 

 more than two miles from the point of release, and all were retaken near the road, 

 on which there was considerable traffic. Unlucldly in stating the result he does 

 not separate the sexes or state the time that elapsed between release and recapture. 

 A female could readily cover two miles on successive journeys on man and animals, 

 especially if much disturbed in her feeding. In Lamborn's experiments only males 

 were retaken. 



It is obvious that a fly-belt can only extend definitely, whether its annual extension 

 into highly deciduous wooding is concerned, or a permanent extension into country 

 previously uninvaded, at the same rate as the females. This, if I am right in my 

 present belief that the females do not travel appreciably on their own initiative 

 or to any distance on animals, suggests that the extension wiU be slow and compact 

 and indicates a possible explanation for the alleged fact that the cause for the 

 division between fly and non-fly country is sometimes not to be found in any difler- 

 ence in the conditions of wooding. 



Living in a district that is right up against the fly I have come across no evidence 

 at all that either sex travels appreciably on its own initiative. There is on the 

 other hand, a very great deal of evidence to connect our local outbreaks of nagana 

 with the movements of big game. I do not think that a fly area will extend seriously 

 in the absence of game. 



Migration and Homing. 



The fact that the flies are found still in their centres in great numbers when food is 

 scarce, and even under such conditions of hunger as have been described by Maugham 

 and as, it is just possible, I saw myself in 1900, "j* tells against the theory of unassisted 

 outward migration, though the predilection of the " following " males for joining 

 other fly-clusters they may meet on the road amounts to unassisted migration of a kind. 

 It is also quite certain that in South Melsetter, with the fly right on our border for 

 20 years past and numerous herds of cattle grazing in and near Brachystegia bush 

 at relatively low elevations, we should have met with much indirect evidence of 

 migration were such to take place. 



* Against the obvious suggestion that the barrier could be narrow must be f placed 

 the possibility, to be referred to below, that females as well as males do not dismount 

 readily in uncongenial country once they have allowed themselves to be carried well [inta 

 it. This point needs testing also. 



i" I see from my journal of that time that the tsetses " swarmed and J were very 

 irritating." Game was not quite absent, but, with the exception of duikers, was very 

 scarce, having left this unburned country for the green patches on the basalt that had 

 been burnt earlier. 



