272 
MR. YOUATT’s VETERINARY LECTURES. 
the mucus secreted by this membrane, from June or July to April 
or May. There are seldom more than three or four of these 
insects found in any sheep. When they have attained their 
full growth, and are ready to undergo their next mysterious 
change, they detach themselves from the sinus, and creep out 
through the circuitous course by which they first entered, and 
again they sadly annoy the sheep, who makes the most vio¬ 
lent efforts to dislodge his enemy. The grub having dropped 
from the nose, burrows into the ground, assumes the form of an 
oval and motionless chrysalis, from which in six weeks or two 
month bursts the perfect fly. It is found more particularly on 
the sides of copses, but is recognised by the shepherd on the 
walls and rails near the flock. The fly lives but a short time ; it 
has but one duty to perform, the propagation of its species. The 
male having accomplished this duty, immediately dies; indeed it 
takes no food, for it has not the organs by which it can either receive 
or digest it. The female lingers a little longer until her eggs are 
ripe, but she too eats not, but, impelled by powerful and unerring 
instinct, she seeks and persecutes the nearest flock of sheep, 
and finds, in the manner we have described, a habitation for her 
offspring. 
The larva having reached and fixed itself on the sinus, no 
longer annoys the animal: ten months pass, during which 
it is nourished by the mucus of the sinus, and produces 
neither disease nor inconvenience. In this respect it resembles 
the bot in the stomach of the horse, which, except existing in 
great numbers, is perfectly harmless. Nature would not have as¬ 
signed it this residence, if it did mischief there: the permanent 
comfort or health, or life of the sheep, would not have been sacri¬ 
ficed to so insignificant a being. The stories of nasal gleet, and 
vertigo, and phrenitis, and death, being occasioned by it, are all 
fabulous. It passes the longer but secluded portion of its life 
harmless in its destined abode : it then, for awhile, finds a darker 
home, and passes through a more torpid state of existence, until it 
bursts into perfect life only to propagate its species and to die. 
Spanish shepherds are said to use the trephine for it. They 
attribute various affections of the head to the worm which they 
are almost sure to find in the frontal sinus ; and they materially 
relieve or remove the complaint, not by the removal of the grub, 
but by the bleeding which is the necessary consequence of the 
operation. 
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