62 
hoidalis, by occasionally closing over, and cleaning the horny 
plate, from the mucus and pus of the membranes, with which it 
is subject to be smeared and prevented from performing its office. 
When this margin opens after closing over the plate, it occasions 
frequently a slight snap from the sudden admission of the air. 
They move with considerable quickness, holding with the ten- 
tacula as a fixed point, and drawing up the body towards them. 
On the under side of the larva is placed a broad line of dots, 
which, on examination with glasses, appear to be rough points, 
serving perhaps the double purpose of assisting their passage 
over the smooth and lubricated surfaces of these membranes, and 
of exciting a degree of inflammation in them where they rest, so 
as to cause a secretion of lymph or pus for their food. 
I have mostly found these animals in the horns and frontal 
sinuses, though I have remarked, that the membranes lining 
these cavities were hardly at all inflamed, while those of the 
maxillary sinuses were highly so. From this I am led to suspect 
they inhabit the maxillary sinuses, and crawl, on the death of 
the animal, into these situations in the horns and frontal sinuses. 
The breeds of these, like the CE. Bovis, do not appear con¬ 
fined to any particular season, for quite young and full-grown 
larvrn may be found in the sinuses at the same time. 
When full-grown they fall through the nostrils, and change to 
the pupa state, lying on the earth, or adhering by the side to a 
blade of grass. See fig. 18. 
The fly bursts the shell of the pupa in about two months. 
See fig. 19, 20, and the veins of the wing, fig. 21. 
On their Effects. The sheep are particularly subject to verti¬ 
ginous diseases, which the agitations and irritations these ani¬ 
mals occasion may tend to prevent. In the sheep it will be 
much more difficult than in horses to prevent or destroy them, 
particularly if they are seated in the maxillary sinuses: in this 
l 
