362 C. F. M. SWYNNERTON. 



(2). Elsewhere, usiiig cattle bait, we found usually either an approximate 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 77iorsitans area 

 (three at Kanyezi centre), but tEe proportion of females rose abruptly 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, the only day on which I had surpassed this figure being one (1st July) 

 on which the already weakened male cluster at and near which we were catching 

 had temporarily been obliterated by the passing through it of a buffalo. The 

 percentage of females for that day only was 30, and it was also the one day on 

 my first visit on which jMllidijpes (taken one here, one there) predominated, but 

 the total was in any case diminutive, not exceeding my daily catch minus morsitans 

 males. 



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 

 with a view to obtaining material for my marking and other experiments — ^I came 

 across no evidence at all which, properly analysed on the spot, suggested an actual 

 preponderance 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. 



Dr. Lawrence's numerous small sendings of flies, lasting over many months, 

 showed (in pallidipes) a remarkable equality of the sexes even in the individual 

 sendings. Here we have a locality in which game generally is rather scarce and 

 even wild pigs, it is stated, unusually so ; also no male fly crowds, in so far as I 

 have seen or heard, but mere individual attacks by single flies on natives passing 

 or working. In the stray individual flies of pallidipes and morsitans taken by my- 

 self over a far greater variety of country both east and west of the Sitatongas, 

 some of it with much game, the females amount approximately to one-third, but 

 a few stray flies taken on cattle (on 1st Aug. — ^females over 50 per cent.) are included 

 here. 



