52 
as the ninth month, or September, which must have produced 
their Flies as late as November or December, or perhaps not till 
the ensuing summer. 
’The larva after being immured in the chrysalis a sufficient' 
time, and its soft members dry and in a degree hardened, bursts 
from its confinement by. forcing open a very remarkable triangu¬ 
lar lid or operculum, see Plate II. fig. 7 . and makes its way out at 
the small end, a. The position and appearance this Fly makes in 
the chrysalis is also given. 
The larva at the period of making its way from the back of 
the beast is weak and tender, and exposed to imminent danger, 
if on land, of being trod on by the cattle or picked up by birds; 
if on the water, where the cattle stand during great part of the 
day at this hot season of the year, it perishes by drowning or 
becomes the food of fishes. 
It is worthy of remark, that Reaumur has stated that its escape 
from the back of the beast usually takes places at a very early 
hour of the morning, at two or three o’clock, or at sun-rise, now 
if it be so it is remarkable that in this way much of the danger is 
avoided, as the animals at this time would most probably be 
upon dry land, and in a more quiet state than at mid-day, and 
the birds also would not then be present. 
The Fly thus singularly produced, is large and handsomely 
coloured, see fig. 8. and 9- Plate II. and its description at the 
conclusion of this Essay ; its wings and tendons, fig. 10. and the 
abdominal stylus of the female for depositing the eggs, according 
to Reaumur’s drawing, fig. 11. To the extremity of the abdo¬ 
men of a specimen of the Oestrus Bovis which I possess, there 
is something visible like a hard white stylus, or rather spine, of 
whose nature 1 am not assured. 
As to theii efiects, they may be perhaps not inaptly considered 
as the living rowels of the ox, producing in all respects the same 
