PARASITES OF ANIMALS. 23 
or turning of the head, inclination to butt and push with the 
head, fits of frenzy, and general appearance of suffering and 
weakness, which sometimes goes so far as to render the animal 
unable to rise, when death generally results. The gums, back 
part of mouth, and lining of the nasal cavities are often red and 
inflamed. Sometimes the larve even force their way, by the 
openings through which the nerves pass, into the brain, when 
death quickly follows. 
These larvee, when full grown (Figure 24) are about an 
inch long, and have lost more or less of the white color which 
they had when younger, and each ring is crossed above by two 
dark brown bands; there are also small, round, raised brown 
spots on the sides of each segment. The small end, or head, 
has two sharp hooks and two papille; but the posterior seg- 
ment bears two small brown plates, in which the spiracles 
are placed, and this segment can be drawn into and con- 
cealed by the next, which give a truncated appearance to 
the posterior end. The under side is flattish, and each seg- 
ment has a median row of minute brown spines, which are 
directed backward. 
When full grown, they descend from the nostrils and fall 
to the earth, where, in the soil or among the roots of grass, 
they change to pup in about two days. They remain in 
this state from six weeks to two months, when a sort of lid is 
forced off from one end of the pupe cases, and the mature 
flies come forth, pair, and immediately proceed with the work 
of perpetuating the race, for in the winged state they seem to 
have no other instinct ; and not having any mouth, they take 
no food. When not engaged in depositing the eggs, they 
seem sluggish and lazy. The flies appear irregularly in June, 
July, and August, and larve of all sizes may be found at one 
time in the same sheep. Each female produces several hun- 
dreds of young. According to Mr. Riley, * over 300 living 
larve have been taken from one female fly, by Mr. Cockrill. 
The amount of injury which these insects do to the sheep 
has long been a matter of discussion among veterinary sur- 
geons and others; but it appears to be the universal testi- 
. o, : +p. 164. i 
* First Annual Report on I a NY, loxions Ansects af Missonri, p. 164, in Report of 
Roard of Agriculture, 1868. 
