Roubaud has recently recorded (cf. Sleeping Sickn. Bull., I l l, p. 419) that in West Africa G. morsitans is intolerant of high temperatures, as he has found that specimens exposed to 40° C. (104° F.) died within an hour. This species is however adapted to withstand such a temperature in the Luangwa Valley; for during the hot months of October and November the shade thermometer frequently registers from 106° to 108° F., seemingly without any ill results to the tsetses.