38 Farmers’ Bulletin 1150. 
tract and get to the blood stream, leave the blood stream for the air 
passages of the lungs, crawl up the windpipe, and then pass down 
the esophagus or gullet, and thus reach the intestine again, where 
they continue their development to maturity. 
THE STOMACH WorRM." 
Location.—This worm is a parasite of the fourth stomach. It may 
be found elsewhere in the digestive tract, but such occurrences are 
of little significance. 3 
Appearance.—Stomach worms (fig. 24) are from one-half to 14 
inches long and about as thick as an ordinary pin. The females are 
the larger and have a spiral striping. In the rear half of the body 
of the female there is a projecting portion, which may be seen on 
close examination. The smaller male may be distinguished by the 
Iric. 24.—Stomach worms (Awmonchus contortus), Upper figure, 
male ; lower, female. Magnified five times. 
fact that the posterior or tail end of the body is flattened and ex- 
panded. ‘ 
Life history.—The eggs produced by the female worms pass out in 
the manure and hatch in a few hours under the most favorable con- 
ditions of warmth and moisture. Under less favorable conditions - 
hatching may require a number of days or even weeks. The embryo 
which leaves the egg undergoes further development until it becomes 
an ensheathed, infective larva. In this condition it is inclosed in a 
double skin and is very resistant. Whereas drying and low tempera- 
tures may kill the egg or embryo previous to this stage, the en- 
sheathed larva can withstand severe cold and long periods of dryness. 
When the grass is wet with rain or dew, these larve crawl up the 
blades. Here they are swallowed by sheep as they graze. In the 
stomach the. worms become mature in the course of two to three 
17 Hemonchus contortus. For additional information sce Department Circular 47 on 
“Stomach Worms in Sheep.” 
—— 2° 
