3G2 
OESTRUS. 
moisture is sufficient to bring forth in an instant 
the latent larva. At this time, if the tongue of 
the horse touches the egg, its operculum is thrown 
open, and a sn'all active worm is produced, which 
readily adheres to the moist surface of the tongue, 
and is from thence conveyed with the food to the 
stomach. If the egg itself be taken up by acci- 
dent, it may pass on to the intestinal canal before 
it hatches; in which case its existence to the full 
growth is more precarious, and certainly not so 
agreeable, as it is exposed to the bitterness of the 
bile. I have often with a pair of scissars clipped 
oh' some hairs with eggs on them from the horse, 
and on placing them in the hand, moistened with 
saliva, they have hatched in a few seconds. At 
other times, when not perfectly ripe, the larva 
would not appear, though held in the hand under 
the same circumstances for several hours; a suf- 
ficient proof that the eggs themselves are not con- 
veyed to the stomach. It is fortunate for the ani- 
mals infested by these insects that their numbers 
' are limited by the hazards they are exposed to. I 
should suspect near a hundred are lost for one that 
arrives at the perfect state of a fly. The eggs, in 
the first place, when ripe, often hatch of them- 
selves, and the larva, without a nidus, crawls 
about till it dies; others are washed off by the 
water, or are hatched by the sun and moisture, 
thus applied together. When in the mouth of the 
animal, they have the dreadful ordeal of the teeth 
and mastication to pass through. On their arrival 
at the stomach, they may pass, mixed with the 
