THE SHEEP-TICK. 141 
nourished by a milky secretion produced in special glands, 
also shown in illustration, until the larva has attained its 
full size, when it is born. Such a larva is white, but it soon 
turns brown and becomes a puparium, as shown in fig. 122. 
To prevent this puparium from dropping from the host it is 
fastened to it by means of a sticky material. Here it remains 
for sometime, when the matureinsect emerges by forcing off a 
round lid from one end of the dry and glassy puparium. The 
illustration (fig. 122) shows such a puparium; the upper and 
pointed end was connected with a membrane through which 
the larva obtained food; below are seen the spiracles, and to 
the right a young larva removed from the mother fly. 
All louse-flies seldom remain attached to the skin longer 
than to fill themselves with blood. They areactive and try to 
escape by runningina peculiar sideways fashion among hairs 
and feathers. They can move forward withequal ease, and act 
somewhat like acrab. Those equipped with wings fly away 
when disturbed, and leave their host, as do those found up- 
on birds of prey as soon as the body of the dead bird becomes 
stiff and cold. 
Only two species of louse-flies infest our domesticated 
animals, and the best known of all the external parasites of 
the sheep, the so-called ‘‘sheep-tick,”’ is one of them. 
THE SHEEP-TICK. 
(Melophagus ovinus Lann). 
It is not a true tick, which possesses eight legs, as illus- 
trated elsewhere, but a true six-legged insect. It is less than 
a quarter of an inch long (4.4mm.), with a short, flattened, 
tough and leathery body covered with hairs. The illus- 
stration (fig. 120) shows this insect, and some of its struc- 
tural details. 
It is a veritable pest, especially in spring, to the younger 
animals it infests. Sheep always kept in stables are almost 
free from such parasites, which seem to require conditions 
only found upon pastures. When we consider that a female 
of this parasite only produces one offspring at a time, and 
perhaps only four to five during her whole existence, it is 
