210 



fly scatters and therefore appears to decrease suddenly. The later, 

 therefore, that the rains are in coming, the greater is the insect's 

 capacity for increase. It follows that seasons of unusually heavy 

 rainfall are on the whole iaimical, while a series of years of low 

 rainfall is favourable to the fly. 



Many investigators have laid emphasis on the efiicacy of grass 

 fires in reducing the fly. The author has been unable to obtain the 

 slightest evidence in support of this theory, in fact the evidence to 

 the contrary appears almost conclusive. If the tsetse-fly could not 

 avoid grass fires, it would seem impossible that the species could 

 avoid extermination in parts of the country inhabited by natives. 

 The mopani belts, where the grass remains short, are probably a 

 convenient refuge from grass fires in the dry season, and are also 

 attractive to game in the wet season. 



The author is extremely sceptical concerning the fly's alleged 

 habit of migrating with game. During ten years' investigations 

 he has found no tendency on the part of the fly to migrate under 

 the stimulus of hunger or in company with game. There is, however, 

 always the seasonal scattering during the wet season, and sometimes 

 forced movements induced by destruction of the forest ; in the latter 

 case the fly naturally follows the receding shade. 



There has been a fairly generally accepted idea that G. morsitans 

 locates game and follows its movements more or less continuously, 

 at least within the limits of infested country. The author attempts 

 to show that this is not its general habit. Indications against the 

 theory are that female flies are apparently not known to follow to 

 any great distance at any time ; that gravid females seek seclusion 

 and are not likely to attempt to follow a moving herd ; that hungry 

 flies tend to feed fully and then abandon their hosts, which are unlikely 

 to remain in the vicinity imtil the flies recover ; and that the fly is 

 diurnal in habit, while game moves largely at night. It would seem, 

 therefore, that the only individuals capable of following game, even 

 for a few hours, are those that do not desire to feed. The probability 

 is that the fly neither ranges the forest in search of its host, nor follows 

 it when encountered for any length of time, but that it lies in ambush 

 waiting for the animal to come within the range of its perceptive 

 powers. The maximum distance at which a hungry fly readily 

 detects its hosts is a short one, possibly less than 100 yards, and 

 following on the part of females has only been proved up to about 

 400 yards. The situation in regard to certain fly-infested vleis during 

 1919 is discussed at some length. The maximum following distance 

 of females remains to be determined ; the author is not yet convinced 

 that the females seek animals and human beings only for the purpose 

 of feeding, though this appears probable. 



Payot(F.). Contribution a I'Etude CMPhthirus 'pubis{'LmnQ, Leach). 

 Morpion, Schamlaus, Filzlaus, Piattola, Crab-louse. — Bull. Soc. 

 Vaud. Sci. Nat., Lausanne, liii, no. 198, 15th September 1920, 

 pp. 127-161. 



The distribution, morphology and biology of Phthirus pubis and 

 the action of various substances on this louse are discussed in detail. 

 The life-cycle, which is compared with that of Pediculus humanus 



