28 PARASITOLOGY. 
History.—Found in common with the Gastrophilus 
Equi in North America and Europe. 
Description.—Not so large as the Gastrophilus 
Equi. The thorax is covered with olive-gray hair; 
a black band is found in the middle. The abdomen 
is white in front, black in its median part, and orange 
red at the posterior end. 
Life Cycle.—The eggs are oval in shape and black 
in color. The larvae are taken into the mouth and 
swallowed, and then, by means of two hooklets, at- 
tach themselves to the mucous membrane of the 
digestive tract. They are found mostly in the right 
and left sacks of the stomach. They may loosen 
their hold and become attached at another point. 
They often become attached to the rectum, causing 
itching, and rubbing of the tail. The pupal stage 
lasts from four to six weeks, and is passed in the 
ground. 
Animal Attacked.—The horse. 
Parts Infested.— Stomach and intestines. 
OESTRUS Ovis (Oestrus—gad-fly; ovis—sheep). 
Synonyms.—Cephalemyia ovis (cephalo—head, 
myia—fly); sheep-bot; grub; 
head-maggot; sheep gad-fly. me 
Hiistory.—Found in Ameri- Qj 
ca, Europe, Asia, Africa and 
Australia. 
Description. igs Small, yel- Fig. 5—Orstrus Ovis Larva. 
lowish gray fly, slightly larger a, Side View. 
than the house-fly. Body >: Posterior view. 
covered with short fine hair. The abdomen is orna- 
mented with five rings; under side of head is white. 
