THE FLIES: DIPTERA 63 



skin splits down the back and the imago works itself out of 

 its old skin, dries its wings, and flies away. Cold weather 

 retards these changes considerably. 



Great interest attaches to the mosquitoes by reason of the 

 recent indictment that some species transmit malaria and 

 yellow fever. Malaria is carried by mosquitoes belonging to 

 the genus Anoph'eles, 

 the females of which 

 may be distinguished 

 from the females of 

 Culex by the greater 

 length of the palpi FlG - 40 - Resting Positions of Anopheles and 



The males of both Culex ' Slightly enlarge(L < After Grassi) 

 genera can be distinguished from the females by their more 

 feathery antennae. Anopheles shows a tendency, especially 

 on horizontal surfaces, to alight with the hind end of the 

 body raised at a considerable angle to the surface ; Culex 

 holds the body parallel to the surface. In Anopheles the 

 body and beak are in the same plane no matter what the 

 position is ; Culex is humpbacked, with the beak pointing 

 downward. These various distinctions are well shown in 

 Fig. 40. The disease known as malaria is caused by the pres- 

 ence in the blood of a parasitic organism, one of the lowest 

 forms of animal life, known as Plasmo'dium mala' rice. Its rapid 

 development at certain stages produces the well-known fever 

 connected with the disease. The life-history of the organism 

 is described in Chapter XXI. The most extensive experi- 

 ments concerning the connection between the Anopheles 

 mosquito and malaria have been carried on by the British 

 Colonial Office and the British School of Tropical Medicine. 

 Two physicians, under the auspices of these institutions, estab- 

 lished themselves in the fever-infected Roman Campagna. 

 They took no special precaution against the disease, drinking 

 the water of the district and in other ways conforming to the 



