DIPTERA 



157 



these germs unless it has been infected with them itself. Stegom'yia 

 fascia' t a (Fig. 127) is the yellow-fever-carrying species, so much dreaded in 

 our southern states. It has been 

 ostablishcil by observation and ex- 

 periment ' t hat these mosquitoes, if 

 they have bitten persons affected by 

 malaria or yellow fever, actually 

 carry these diseases, also that Steg- 

 omyia fascia' ta and Cu'lex fati'gans, 

 var. skusii, and Anoph'eles rossii 

 carry certain forms of filariasis. 

 These organisms belong to the 

 round worms or Nematoda (see 

 p. 41). The most common form of 

 filariasis is elephantiasis. In this 

 disease the legs and arms are af- 

 fected. One leg may become so 

 enlarged as to weigh as much as 

 the rest of the body, or the arm 

 may become a foot thick and horri- 

 bly repulsive. In Samoa, says Kel- 

 logg, fully one-third of the natives 

 are attacked by this incurable dis- 

 ease, which, though slow and almost 

 painless, is certainly fatal. Ma- 

 laria, so widespread in the United 

 States, becomes even more prevalent and more often fatal in the tropics. 

 Millions die from it every year. In a single year five million persons died 

 of malaria in India alone. Hence the mosquito is to be classed not sim- 

 ply as a great annoyance, but as an insidious foe to health and life. 



Fig. 127. — Stegom'yia fasci'ata (en- 

 larged). (Howard, Bull. U. S. Dept. 

 of Agriculture, 1902.) 



Fig. 128. — The common harmless Fig. 129. — The malarial mosquito 



mosquito stands this way on a ver- stands with its head pointing down- 

 tical or horizontal svu-face. (From ward at an angle of from 20 to 30 

 Hampton Leaflet.) degrees from a vertical or horizontal 



surface. (From Hampton Leaflet.) 



The common mosquito, Culex (Fig. 128), maybe distinguished from the 

 malaria-carrying form (Fig. 129) in several ways. The female Culex has 



1 Kellogg, pp. 617, 630. 



