69 



bed had shady banks, but no water, the flies congregated there and did 

 not attempt to reach the river ; not a single tsetse was found in the 

 open bush bordering the road at a greater distance than 200 yards 

 from it, and there was practically no discrepancy in the proportion of 

 the sexes recaptured. 



TRAVELLING HABITS. 



It has been shown by Fiske (54) that individuals of G. palpalis, far 

 from remaining always at the same spot, are in constant movement 

 along lake shores and similar places. One of the experiments con- 

 ducted by the author in question on Lake Victoria, Uganda, consisted 

 in catching G. palpalis during five days, four of which were consecu- 

 tive, in November 1913, on a narrow spit of land (" Crocodile Point ") 

 at one extremity of Bulago Island. In the four consecutive days 

 " more than 2,000 flies were caught," but " neither density nor female 

 percentage underwent notable change." 



" Notwithstanding the semi-isolated position of Crocodile Point," 

 writes Fiske, " as many flies penetrated its area each day as were 

 caught on it, leaving no other conclusion possible than that, if no 

 flies had been caught, as many would have moved away -from it. 

 Otherwise stated, the fly population of this region was so far from 

 permanently fixed there that hardly any individuals sojourned there 

 for more than a single day. 



' The experiment of the 5th to 13th November 1913 was repeated 

 on the 17th to 22nd January 1914 . . . . and completely 

 confirmed it. The conclusions were subsequently confirmed in various 

 other ways, and there is no doubt that the flies of this species move 

 freely about from place to place, forming continuous streams of fly 

 traffic along the shores of lakes, banks of streams, and, it was subse- 

 quently ascertained, along the borders of woodland, game trails or 

 human pathways, etc." . 



Data furnished by the author show that by catching fly for consecu- 

 tive hours at points on the Lake shore the density of males was reduced, 

 but not that of active females, and Fiske observes : 



' The only conclusion that can be drawn is that the active females 

 habitually move along shore much more rapidly than the males, or 

 than many of the males. This is entirely in accord with the 

 conclusions reached through experiments .... that active 

 females are hungry, and actively seeking food, and that degree of 

 activity is correlated with abundance or scarcity of food. Their 

 movements along shore are stimulated by hunger. The movements 

 of the males are in part stimulated by hunger, but also in part 

 . . . by sex instinct. The object of the females and of such 

 males as require it is to seek food ; the object of many of the 

 males (forming a majority when females are inactive and the female 

 percentage low) is merely to seek the females, and this is accomplished 

 by loitering along the routes most freely followed by the food-hunting 

 flies." 



On two other occasions, on each of which catches of fly were made at 

 two different points close together, the character of the adjacent 

 shelter or type of vegetation, which differed in each case, was found to 

 have an extraordinary effect upon the percentage of females in the 

 catch. After giving statistics, Fiske observes that " in both cases the 

 high percentage of females is associated with a type of vegetation 

 known to be especially repugnant as shelter and the low percentage 

 with a type of vegetation known to be attractive. 



