1. More than twenty new forms and variations of tsetse traps are described in this paper for trial, and rejection or improvement, by other investigators. The species of tsetse-flies that they have been tested against have been palpalis, pallidipes, morsitans and swynnertoni.2. The reactions of the various tsetse-flies to different forms of trap vary in a marked manner. Thus a trap (the Harris) that is excellent for pallidipes has appeared less good, though fair, for palpalis, poor (except at one season) for morsitans, and useless for swynnertoni. Another (the SS and the SSB) is particularly excellent for palpalis, excellent for pallidipes, mediocre for swynnertoni, and perfectly useless for morsilans.3. Tsetses, pallidipes in particular of the two species tested, have been found to react also most strongly to the scent of an invisible animal placed in a trap. It is not known yet whether this attracts at a distance or is merely a close-range attraction, inciting the flies that have arrived in any case to such effort as takes them in larger numbers into the traps, but the latter does undoubtedly happen.4. If the attraction be long-range, the flies do not readily distinguish between the source of the odour and conspicuous objects within its range. They go to and into a trap, even a trap that usually does not catch them, in greatly enhanced numbers when cattle are in its neighbourhood.