Parasites and Parasitic Diseases of Sheep. 17 
ARTHROPODS. 
_ The arthropods include certain forms that live during a portion 
of their life as internal parasites of sheep, though most of the arthro- 
pod parasites of sheep are external parasites. 
The arthropods are forms which possess 6 or more leglike ap- 
pendages, such as the insects, which, in a limited sense of the word, 
include those forms with 6 legs, the spiders 
and spiderlike forms, which as adults have 8 
legs, and other forms having more than 8 legs, 
some of them having a considerable number. 
The life history of the arthropods varies so 
greatly in the case of different forms that it 
is hardly possible to give a general statement 
covering it. 
Fie. 11.—Grub in the head 
GRoD IN THE HEAD. Cia Sate? 
grub turned on its back. 
Location.—The erubs occur in the nostrils (From Osborn, 1896, 
‘ +. g A one after Riley.) 
and in such communicating cavities as the 
frontal sinus and the maxillary sinuses, cavities in the upper jawbone. 
Appearance.—The parasites appear as maggots which at first are 
less than 2 mm. (one-twelfth of an inch) long. When fully de- 
veloped in the sheep, they are usually over 2 em. (four-fifths of an 
inch) long and 7 mm. (almost one-third 
of an inch) wide, though the grub may 
contract or expand to a smaller or greater 
dimension. There are 11 segments, 
rather flattened on the ventral (lower) 
surface and arched on the dorsal (upper) 
surface. The ventral surface is spiny, 
the dorsal smooth. At first the grubs 
are white, later they become yellowish 
and darker, a band appearing on the 
dorsal side of the segments, and finally 
eT. meres ed. (cea becoming black (fig. 11). At the head 
ovis). (From Curtice, 1890.) end are two large hooks and at the tail 
end are two rounded breathing pores. 
Life history.—The adult fly (fig. 12), which looks something like 
an overgrown housefly, is active during the summer, usually in 
June and July. The female fly deposits a tiny grub on the edge of 
the sheep’s nostril. Sheep usually run when the fly attacks them 
™MHstrus ovis. 
184550°—20 3 
