SHEEP GAD FLY. 303 
That part of the hard skin, or shell, 
■which is nearest to the head, is attached 
hy a slender filament, or thread, as the lid 
of a box is by the hinge ; this filament 
yields to a very slight pressure from 
within, the door opens, and the fly es- 
capes. 
Lucy, Are horned cattle the only 
creatures which the gad fly attacks ? 
Mother, There are three species,^ 
which deposit their eggs on the coat of the 
horse ; two of these, by a wonderful in- 
stinct, place them on his lips, or within 
reach of his tongue ; when licked in, 
and unconsciously swallowed, they are 
hatched by the heat of his stomach. The 
oestrus ovis *, or sheep gad fly, is a dreadi- 
ful pest to sheep ; it lays its eggs in their 
nostrils, from whence the maggots creep 
into the interior of the head, and afflict 
those poor animals with such pain, that 
they seem to fall into a sort of frenzy; 
* From Ovis, a sheep. 
