26 INSECTS AND HUMAN WELFARE 



more remote. As is well known, sleeping sickness depends 

 for its spread entirely upon certain biting flies known as 



FIG. 11. Tsetse-flies. Above, Glossina palpalis, the carrier of human sleeping sick- 

 ness; below another species of Glossina with a more enlarged view of the head and 

 blood-sucking mouth parts. 



tsetse-flies belonging to the same family as our common house- 

 fly and stable-fly. The genus Glossina (Fig. 11) in which 



