426 VETEEINAEY HYGIENE 



plished by means of a proboscis, the skin being pierced by 

 lancets. 



The mosquito's hfe-history is briefly as follows: the 

 eggs are laid in a bunch in stagnant pools ; from the egg 

 hatches a larva, which, full fed, passes into the pupal stage. 

 Eespiration is accomplished by means of a projection in 

 the case of the larva and two horns in the case of the pupa, 

 which are thrust above the surface of the water. When 

 pupation is over the pupa skin ruptures and the fly 

 emerges. 



A knowledge of the life -history enables preventive 

 measures to be adopted for the eradication of mosquitoes 

 in malarial districts. The mosquito gets the malarial 



organism from man, but with- 

 out the mosquito it cannot 

 be transmitted ; therefore, if 

 mosquitoes are destroyed ma- 

 larial fever jeases. To attain 

 this end it is obvious the 

 breeding places of the insect 

 must be attacked ; pools should 

 Fig. m.—Tahanus bovis, the Ox ^^ filled in or drained ; while 



Gad-fly; natural size. , . i -n i 



any larvae in a pool will be 

 suffocated if a film of paraflin oil be allowed to form over 

 the surface. 



Tahanidce* Gad-flies or Breezeflies, so named from the 

 buzzing sound they make, attack both horses and cattle. 

 The females are blood-suckers, the mouth parts being 

 armed with six lancets for this purpose. This is a very 

 large family, and comprises many species. The best 

 known is Tahanus bovis, or the Ox 'Gad-fly' (Fig. 177), 

 the female of which worries cattle from the end of May 

 to the autumn. It is a big fly as much as an inch in 

 length, with a longitudinal row of whitish triangles along 



* The description given here of the various flies is taken from a 

 valuable paper, ' Insect Pests of Domesticated Aniraals,' by Dr. Stewart 

 MaoDougall, Consulting Entomologist, Highland and Agricultural 

 Society of Scotland. See Transactions, vol. xi., 5th series, 1899. See 

 also 'Plies ^^i^'^°^^Mh'b/^fms^m'°^' ^^'^^ 



