Parasites and Parasitic Diseases of Sheep. 45 
cleaned frequently to keep it free from litter and manure, thereby 
preventing the development of the eggs in the manure in the: yards. 
As in most parasitic diseases, the young animals suffer more than 
older ones and measures must be directed especially to the protection 
of the lambs. If persisted in, these measures and pasture rotation 
- should keep the infestation down to a point where it does little 
damage. 
THE SHEEP HOOKWORM.® 
Location.—Hookworms of sheep are found in the small intestine. 
Appearance.—The female hookworm attains a length of 2.6 cm. 
(about 1 inch), the male attaining a maximum length of 1.7 cm. (fig. 
28). The worms are about one-half to three-fourths as thick as an 
ordinary pin. At the head 7 
end is a mouth capsule 
armed with teeth. The 
tail end of the male is ex- 
panded and flattened. 
Life history.—The life 
history of the sheep hook- 
worm has received little 
attention, but, judging 
from the life history of 
related forms, it is prob- 
ably about as follows: 
The eggs produced by the 
female worm in the intes- 
tine of the sheep pass out 
in the manure and hatch 
on the pasture. Under fa- I'ig. 28.—Sheep hookworm (Bunostomum trigo- 
ee nocephalum). Female at right; male at left. 
vorable conditions of tem- Magnified. (From Ransom, 1911.) 
perature and moisture the 
young worms develop to a resistant form capable of infecting sheep. 
Possibly most of the infection takes place by way of the skin, the 
larval worms boring through the skin of the lower part of the legs and 
making their way to the near-by blood vessels. In the blood the worms 
would be carried to the lungs, where they would escape from the 
blood and get into the air passages. Here they would make their way 
up the windpipe and then down the gullet into the stomach and intes- 
tine. When they reach the intestine they develop to adult worms and 
the two sexes mate. In addition to the possible entrance of larvee 
through the skin, many of the infective larve on the pasture are un- 
doubtedly swallowed by the sheep in food or water, but even in this 
case it is possible that the larvee make their way to the blood stream 
™ Bunostomum trigonocephalum. Synonym, Monodontus trigonocephalus. 
