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SHEEP GAD-FLY. 
The young grubs, as soon as they are deposited in the 
nostrils of the sheep, begin their migrations upwards into 
the dark passages of the nose and frontal sinuses. This 
movement is performed by means of hooks and spines, as the 
maggots do not possess any legs. Of course the use of such 
hooks and spines is very irritating to the sheep, and the 
poor victims make many attempts to get rid of their foes. 
The grubs remain about ten months in the nasal cavities 
of the sheep. During this period they undergo a number of 
molts; in the first stage they are white and almost trans- 
parent, and measure about 2mm. in length; in the second 
stage they are 6mm. in length, yellowish-white, and have 
no spines except a few near the mouth. In the third stage 
the fullsize and form is attained as shown in fig. 180, d. 
When mature the larve detach themselves from the mucous 
membrane, creep about, reach the nose, and are expelled by 
the violent snorting of their host. A day later the larval 
skin, which was thus far soft and of a reddish color, becomes 
contracted, and gradually turns brown and black, forming 
a puparium inside of which the future fly is formed. This 
pupal stage lasts from four to six weeks. If manylarve are 
present they cause in the sheep a catarrhal discharge on the 
affected side of the nose; this is commonly known as “Snot 
Nose.”” Neumann gives an excellent description of the Symp- 
toms: “Three or four larve of the Estrus are frequently found 
in the frontal sinuses of sheep which, during life, have never 
manifested any symptoms. It is only when the larve are 
numerous, and when they are quite well advanced in their 
development at the commencement of spring-time, that they 
occasion morbid troubles. The latter begin by a discharge, 
often unilateral, which is at first clear and serous, then 
thick and mucous. Frequently there is sneezing and snort- 
ing, accompanied by the expulsion of mucus and sometimes 
of hstrus larve. Later the animalsturn the head backward, 
often shake it, rub the nose against the ground or some 
other object within reach, or with their front feet. Ags the 
malady gradually advances the sheep go with lowered head, 
lifting the feet high as if they were walking in water. Some- 
times they quickly raise the head, carrying the nose to the 
