250 W. A. LAMBORN. 



bushes not of a thorny nature, while the grass is so high that for seven or eight miles 

 one simply tunnels through it, with no possibility at all of seeing the surrounding 

 country (Plate iv, fig. 2). Thorn trees then gradually appear and the grass gets 

 lower, till at the end of another two or three miles one gets into thorn bush country, 

 where there are few other trees. The soil here is inclined to be hard and clayey, 

 though areas containing a considerable amount of sand are seen from time to time. 

 With a gradual rise of the ground, beginning at about fifteen miles from the Lake, 

 rocky outcrops appear, the thorn bushes becoming twisted and stunted in growth 

 (Plate V. fig. 1) ; and j&nally, at an altitude of about 3,000 feet, only a few 

 scattered shrubs are to be seen, so that practically open country is reached. 



In all these varied regions, except the last, G. morsitans is to be met with, though 

 in greatest abundance where the thorn bushes and the large trees are thickest. 



When the grass is high, the flies, like the ticks, are most numerous along game and 

 native paths ; though, as is the case when the grass is low, their distribution varies 

 from day to day. 



Proportion of the Sexes. 



My experience in this matter is the same as that of other observers, namely, that 

 when the flies are bred out from pupae, the sexes emerge in almost equal proportions ; 

 and when the flies are captured, the males far outnumber the females. A theory 

 which might account for this is that the females have different feeding habits from 

 the males, possibly feeding better with an overhead sun, or when the sun's rays are 

 more oblique. To test this a series of captures were made for several days at three 

 different periods of the day, viz. : from 8 to 11, from 12 to 3, and from 3 to 6. The 

 proportion of the sexes was found to be practically the same in each case. 



A further theory which then occurred to me was that the distribution of the sexes 

 in a given area might not be quite the same, and this theory seems to some extent 

 to be supported by actual facts. Differential captures at the centre of a tsetse 

 area, and at its margins where the flies are more scanty, do show, though statistics 

 are as yet meagre, that the females are more abundant at the outskirts ; and in 

 the search for pupae in regions which the fly has temporarily vacated, it has been 

 my frequent experience to be assailed by a solitary pregnant female. 



Theie are very definite reasons why the female flies should to some extent shun 

 the society of the males. As I have before remarked, and have since repeatedly 

 observed, coitus takes place as a result of capture without preliminary courtship. 

 Moreover, when, as often happens, little knots of flies in a confused buzzing swarm 

 of four and five appear suddenly in one's vicinity, repeated captures have shown 

 the group to contain one female, and one only, the obvious interpretation being 

 that the female wishing to feed, has been chased by the males. Furthermore, on 

 putting a newly emerged female, even with its wings still flaccid, into a jar containing 

 males and an adequate supply of the other sex, it is almost the rule for the female 

 to be seized immediately by one of the males, which sooner or later after a struggle 

 accompanied by loud protest effects coitus ; and it occasionally happens that two 

 males will seize the same female. 



In captivity even females in an advanced state of pregnancy are not secure from 

 the violence of the males, and as abortion is so frequent with captive females, it seems 



