66 
THE INSECT WORLD. 
which the fly gets rid of when it is in a fit state to come into the 
open air.” 




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Fig. 47.—Imago of 
Bot-fly emerging. 
Fig. 47, taken from drawings in Réaumur’s 
memoirs, represents the imago of the Gstrus 
leaving the cocoon. 
The reader is, most likely, desirous to know 
- i ‘ with the aid of what instrument the Cstrus is 
able to pierce the thick skin of the ox. 
The female only is possessed of this instru- 
ment, which is situated in the posterior ex- 
tremity of the body. It is of a shiny blackish 
brown colour, and as it were covered with scales. 
By pressing the abdomen of the fly between 
one’s two fingers it is thrust out. Réaumur 
observed that it was formed of four tubes, which 
could be drawn the one into the other, like the tubes of a telescope 
(Fig. 48). The last of these appears to terminate in five small 
scaly knobs, which are not placed on the same line, 






















Fig. 48.—Ovi- 
but are the ends of five different parts. Three of 
these knobs are furnished with points, which form an 
instrument well fitted to operate upon a hard thick 
skin. United together, they form a cavity similar to 
that of an auger, and terminating in the form of a 
spoon. 
The Gad-fly, or Breeze-fly of the sheep, Mstrus 
(Cephalemyia) ovis, has obtained notoriety on account 
of its attacking those animals. , 
Even at the sight of this insect the sheep feels the 
ea ereatest terror. As soon as one of them appears, the 
(Gistrus bovis.) flock becomes disturbed, the sheep that is attacked 
shakes its head when it feels the fly on its nostril, and at the 
same time strikes the ground violently with its fore-feet ; it then 
commences to run here and there, holding its nose near the 
ground, smelling the grass, and looking about anxiously to see if 
it is still pursued. 
It is to avoid the attacks of the Cephalemyia that during the 
hot days of summer sheep le down with their nostrils buried in 
dusty ruts, or stand up with their heads lowered between their 
