GAD-FLY. 
459 
the cattle for food. Such are the contingencies by 
which Nature has wisely prevented the too great in- 
crease of their numbers, and the total destruction of 
the animals they feed on. 
“ I have once seen the larva of this oestrus in 
the stomach of an ass ; indeed there is little reason 
to doubt their existence in the stomachs of all this 
tribe of animals. These larvae attach themselves 
to every part of the stomach, but are generally 
most numerous about the pylorus, and are some- 
times, though much less frequently, found in the 
intestines. Their numbers in the stomach are very 
various, often not more than half a dozen, at other 
times more than a hundred, and, if some accounts 
might be relied on, even a much greater number 
than this. They hang most commonly in clusters, 
being fixed by the small end to the inner mem- 
brane of the stomach, which they adhere to by 
means of two small hooks or tentacula. When 
they are removed from the stomach they will at- 
tach themselves to any loose membrane, and even 
to the skin of the hand. The body of the larva is 
composed of eleven segments, all of which, except 
the two last, are surrounded with a double row of 
horny bristles directed towards the truncated end, 
and are of a reddish colour, except the points, 
which are black. The larvae evidently receive their 
food at the small end, by a longitudinal aperture, 
which is situated between two hooks or tentacula. 
Their food is probably the chyle, which, being 
nearly pure aliment, may go wholly to the com- 
