75 



ordinary way in morning and evening was 12 and 10 per cent., respec- 

 tively ; when taken at midday, mostly off trees, the proportion was 

 43-5 per cent. The following explanation is suggested for the varia- 

 tions observed in the proportion of males and females captured at 

 different times of the day : Males which have recently fed attend 

 man to await the females which come to feed. The female may be 

 secured by a male, or, if pregnant, may be driven off, and attempt to 

 feed later. After feeding, the female retires under cover of large trees 

 or to breeding places to protect itself from the males. It is almost 

 certain that the sexes exist in the same area in equal numbers. 



Writing with reference to the Gold Coast, Dr. J. J. Simpson (144) 

 agrees that a marked disparity exists in the proportion of the sexes 

 of Glossina, and states that, in explanation of the fact, there have been 

 advanced various hypotheses, such as the size of the river on which the 

 flies are caught, the time of capture, the number of inhabitants in a 

 given area, the season of the year, and meteorological conditions. To 

 these factors, in the opinion of this author, must be added the abundance 

 of game, and consequently food, which, by causing the retirement of 

 the gorged females, gives rise to an apparent disparity. 



Swynnerton's experience in Portuguese East Africa, in connection 

 with G. brevipalpis, G. morsitans and G. pallidipes, which is in harmony 

 with that of the authorities already referred to, strongly supports the 

 view that the numerical predominance of the males seen in captured 

 specimens is apparent rather than real, and is due to marked differences 

 in the habits of the two sexes. " G. brevipalpis," writes Swynnerton 

 (145), " may be found in the daytime scattered through all the little 

 thickets in the bush it frequents, two or three or more to each. Just 

 at sunset the males emerge from the thickets in the neighbourhood of 

 game and other paths and (where plentiful) distribute themselves at 

 short intervals along them, sometimes for a considerable distance. As 

 one walks each male moves on in front of one for at most a few feet, 

 evidently scanning the walker for any females that may be with him, 

 then falls behind. At one time, when a domestic matter called me 

 home from the Buzi, my police boy, left in charge of the work, captured 

 no less than 88 of these flies, every one a male, on three successive 

 evenings without the aid of cattle along the same stretch of path." 



" The males of G. morsitans, though occasionally seen like this on 

 game paths, were found mostly crowded together in the short grass 

 beside the path some of them on the path and were also (as events 

 each time fully proved) watching for females or carriers to take them 

 to the females. G. morsitans usually waited in a crowd, brevipalpis 

 always in a queue." 



On a subsequent page, when dealing specifically with the subject of 

 the present section, Swynnerton writes : " The following statements 

 represent the result of day-to-day observation and analysis in the 

 field the only reliable method. 



" (1) Wherever we had to deal with male crowds or queues awaiting 

 females, or, in the case of brevipalpis, the bush immediately bordering 

 on the path on which the male flies would line up at sunset, we took, 

 as might be expected, practically nothing but males. 



" (2) Elsewhere, using cattle bait, we found usually either an approxi- 

 mate equality of the sexes or a preponderance of females. 



(3) Many more females proportionally came to cattle than to man 

 and goats. 



' The cattle were with me only during my last four days in the 

 morsitans area .... but the proportion of females rose abruptly 



