76 



on their arrival. It amounted now to from 35 to 40 per cent., in spite- 

 of the fact that the cattle were used very largely at a strong male cluster 

 in order to obtain the material for certain experiments. Previously 

 7 per cent, had constituted a good day . . . ." 



" Bagshawe's result (more male palpalis where crocodiles were, 

 present, more females where not) and McConnell's (more palpalis 

 females on the small tributaries where food is doubtless scarcer 

 more males on the main Nile) appear to be completely explained by 

 observation No. 3 above. Bequaert's observation (more males in 

 uninhabited regions, where non-human food would be more abundant) 

 would appear to be the same, had not Graham (quoted by Bagshawe) 

 noted that, in Ashanti, palpalis prefers human blood to that of cattle. 

 But both Graham and Zupitza (also quoted by Bagshawe) observed 

 that when flies bite readily males are not in excess. 



" In spite of a heavy preponderance of males in my total takings 

 the inevitable result of following paths and of special attention to all 

 male crowds or queues .... I came across no evidence at all 

 which, properly analysed on the spot, suggested an actual preponder- 

 ance of the male sex. Rather the reverse ; and it was likely, both 

 in view of the systematic attack by birds which I found taking place 

 on a conspicuous male crowd and from a consideration of the breeding 

 habits (which are such as to allow for much male wastage), that, at 

 a given moment and apart even from the freer dispersal of the males,, 

 the females are more numerous than the latter, though they will show 

 themselves in their true proportions only when hungry." 



Lastly, after stating that G. brevipalpis is " very loth to feed on man," 

 and that " the female sex comes primarily to feed," Swynnerton adds : 

 " My results would seem .... to show clearly that the apparent 

 scarcity in the presence of game of the females of the three flies chiefly 

 investigated is probably due to a relative dislike of man." 



In North Katanga, Belgian Congo, it was found by Schwetz (132) 

 that, " contrary to what happens in the case of G. brevipalpis, and even 

 G. pallidipes, among captured specimens of G.jusca, whether taken on 

 the wing or resting upon trees and lianas, females occur in large numbers, 

 and constitute nearly one-half of the total." 



To conclude this short statement, we append a few of the observa- 

 tions made by various entomologists with reference to the relative 

 proportion of the sexes in G. palpalis, G. morsitans and G. brevipalpis. 



In the report on his investigations in Uganda upon the biology of 

 G. palpalis vax.fnscipes, Dr. G. D. H. Carpenter (25) notes the propor- 

 tion of the sexes of this Tsetse-fly in three localities. At Jinja, on 

 the shore of Lake Victoria, 12,773 flies yielded 55 7 per cent, of females ; 

 in Damba Island, Lake Victoria, among 6,000 flies, females formed 21 -6 

 per cent., and in Bugalla Island 20 6 per cent, among 56,775 flies. Since 

 in breeding experiments he obtained the two sexes in approximately 

 equal numbers, Dr. Carpenter thinks that it is possible that in nature 

 female pupae die in consequence of variations in temperature, humidity, 

 etc., which do not occur under laboratory conditions. 



On the other hand, Mr. LI. Lloyd, Entomologist to the Luangwa 

 Sleeping Sickness Commission, in describing his observations on 

 G. morsitans in the Luangwa Valley, Northern Rhodesia, writes (88) :- 

 " Much difficulty was experienced at first in obtaining sufficient 

 females for breeding purposes. Frequently only three or four females 

 were brought in amongst two or three hundred males. Later, the . 

 boys were shown the differences between the males and females, and 



