TSETSE-FLIES AND COLONISATION 211 



great, and several species are so strikingly similar in this 

 respect as to render their specific determination a matter of 

 great difficulty and doubt. On the other hand, a careful 

 study of the male armature has revealed the fact that all the 

 species hitherto described can be determined with comparative 

 ease by a study of these appendages. 



The genera] colour varies from dark brown or blackish 

 brown to yellowish brown or dusky yellow. In certain species 

 the abdomen is more or less uniformly dark brown or blackish 

 (Glossina palpcdis), in others yellowish brown with dark, 

 interrupted transverse bands (G. morsitans), or dark brown 

 with the first and second segments often paler (G. brevipalpis, 

 etc.). The thoracic markings (see Fig. 1) are very similar in 

 many species, but may be reduced to spots, as in G. longi- 

 pennis ; or the markings may vary inter se in a single species 

 (G. palpalis). They vary in size, the smallest species being 

 a little larger than a house-fly, the largest about the size of 

 a queen bee (7-13-5 mm.). 



The most salient characteristics of a tsetse-fly are (a) the 

 long, thin proboscis, which, when at rest, is completely en- 

 sheathed by the spiny palpi, and (6) the unique venation of 

 the wings, in which the fourth vein is curved abruptly upwards 

 near the centre of the wing-area. Sexual dimorphism is well 

 marked, the males being easily distinguished by the gibbose 

 hypopygium at the apex of the abdomen on the ventral 

 surface ; in the females this structure is entirely wanting. 



The life-cycle or mode of reproduction is unique among the 

 members of the group (Muscidae = house-flies, etc.) to which 

 the tsetse-flies belong, as the female, instead of laying eggs, 

 gives birth to a single fully developed larva or maggot at 

 intervals of a few days, given favourable conditions as to 

 temperature, humidity and an efficient pabulum. During its 

 intra-uterine life the larva is nourished by the secretion of 

 specially developed glands ; two moults take place, the effete 

 skins being generally extruded with the fully developed 

 larva during the act of parturition. 



The larva is footless and rather faintly segmented, and 

 when at rest its body assumes a cylindrical form. Its colour 



P2 



