GAD-FLY. 
455 
From about the middle of June till the same 
time in August the insect continues in the form of 
a chrysalis, when the fly arrives at its last and per- 
fect state, and escapes from its shell by opening a 
very singular triangular lid, which, according to the 
observation of Mr. Clark, may be traced in the skin 
of the larva, and is situated on the side of the small 
end. The ox gad-fly is the largest of the European 
species, and is very beautiful. 
Heifers, steers, and younger cattle are said to be 
most frequently attacked by this gad-fly, and to 
have in general a greater number of hots, as they 
are called, than others : as the insects always select 
the strongest and most healthy of the beasts to lay 
their eggs in, the number of their marks in a hide 
has become a criterion of goodness in much esteem 
with the dealers in cattle. The tanners likewise are 
aware of this fact, and observe that the best and 
strongest hides have the greatest number of bot- 
holes in them. 
The care and attention which is paid to that 
noble and valuable animal the horse, has caused, 
perhaps, more inquiry to be made into the natural 
history of the kind of bot that infests his intestines, 
than if the same insect had inhabited the bowels of 
any creature of inferior note. This troublesome 
maggot derives its being from another species of 
the same genus, the QLstrus equi, or horse gad-fly, 
the history of whose introduction into, and passage 
through, the alimentary canal of the horse, has 
