PARASITES OF ANIMALS. QT 
two last segments do not show the spines, and the posterior 
end of the body is rather truncate, with two fleshy lobes, 
which cover, more or less completely, a chitinous plate, in 
which the spiracles are situated. The mouth is at the small 
end, between the hooks, which represent the maxille; the 
mandibles, above and between these, are small and slender. 
At the. places where they attach themselves there are found 
small pits or depressions ; but they do not appear to cause 
ordinarily much irritation or inflammation, unless in great 
numbers, as they sometimes are. They have been accused of 
perforating the walls of the stomach, and this may possibly 
be the case in very rare instances; but the perforations of 
the stomach, so often found in post-mortem examinations, 
are generally caused by the digestive action of the gastric 
juice after the death of the animal; for after death this fluid 
will attack the stomach as quickly as any other flesh. 
When full grown they loosen their hold, and passing 
through the intestine, fall to the earth. But they often fix 
themselves for a few days upon the lining of the intestine, 
and then cause considerable irritation and pain. Probably 
most of the acute symptoms of “ bots’’ in horses are caused 
in this way. They often attach themselves in and about the 
anal orifice, and in that situation cause much suffering and 
trouble to the horses, which under these circumstances, re- 
fuse to travel rapidly, and even after whipping, soon relapse 
into a slow walk, as if lazy. But the bots can be easily re- 
moved from this location, much to the relief of the horse. 
The bot-larve get their growth and leave the horses from the 
latter part of May to July, or even later. They enter the 
surface of the soil and change to pups within the shrunken 
skins of the larve. They remain in the pupa state forty or 
fifty days, and emerge in the same way as the preceding spe- 
cies; consequently the flies may occur from the last of June 
till September, or later. 
The amount of injury caused by the bots of horses has long 
been a matter of dispute, many writers claiming that they are 
very injurious, and even at times, fatal ; while others deny this, 
and consider them as harmless, or even beneficial. This can 
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