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 mature insect 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 w^as connected with a membrane through w^hich 

 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 are active and try to 

 escape by running in a peculiar sideways fashion among hairs 

 and feathers. They can move forward with equal ease, and act 

 somewhat like a crab. Those equipped with wings fly away 

 w^hen 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. 

 {Melojyhagus ovinus Linn). 



It is not a true tick, wdiich 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 w^e 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 



