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x] The palpi are long, slightly grooved on their inner sides, and closely applied to the proboscis, which they almost entirely conceal, the only uncovered portion being a peculiar large bulb-like expansion at the base. The proboscis consists of three parts (Fig. 54), labrum, hypopharynx, and labium.

The genus Glossina belongs to the family. The nearest related genera are Stomoxys, Lyperosia, Hamatobia; but on account of its limitation to Africa, its peculiar structural features (bulb at the basis of proboscis, remarkable male genitalia, characteristic venation of wings), and its aberrant mode of reproduction, it presents a marked individuality.

The genus at present comprises fourteen species, though this number must not be considered final, as new species are discovered from time to time. Austen arranges the genus into four groups. (See the Table on p. 200.)

Distribution.—With the exception of one species, G. tachinoides, which occurs in the vicinage of Aden, tse-tse flies are confined to continental Africa. Some species, such as G. fusca and G. morsitans, have a very wide range throughout the greater part of intertropical Africa. G. palpalis is also widely distributed, ranging from the Senegal to Angola on the west, and throughout the Lualaba-Congo system to the Victoria Nyanza, Tanganyika, and Upper Nile at least as far north as Moolo in the Soudan. Glossina morsitans extends south in Bechuanaland, North-Eastern Transvaal, and Zululand. G. longipalpis ranges through West Africa as far south-west as the Senegal and south to the Katanga district on the Congo. G. pallidipes is found throughout East Africa from Zululand to the northern boundary of East Africa. Other species appear to be more restricted. G. longipennis is found in Somaliland and adjacent regions; G. tachinoides has a wide range in tropical Africa; G. pallicera ranges to the Ivory Coast; G. fusca ranges from Sierra Leone to Uganda; G. brevipalpis is common in South, Central, and East Africa; G. caliginea is found in Southern Nigeria. Knowledge of their topographical distribution is an important matter. The Glossing are never found on mountains; they are seldom seen above 3,000 feet; they are absent from extensive plains or other open places; they are rarely found in close cultivation. Their usual habitat is in the neighbourhood of open water along the banks of rivers, brooks, and springs, round the coasts of lakes, on low riverine islands, in swamps and mires, with open pools and sandy banks, especially at the foot of