The =Armed Palisade Worm=, or =Strongyle= (_Strongylus armatus_), four-fifths of an inch to two inches long, one twenty-fifth to one-twelfth of an inch thick; reddish brown. Taken into the gut of the horse with the drinking water as a young, minute worm, it bores through the walls of this organ into the blood-vessels branching there. Later on it bores into the walls of the larger arteries of the hinder part of the body, especially into those which carry blood to the wall of the gut (particularly anterior mesenteric artery). At those parts of the arterial walls where it collects in large numbers, swellings (aneurisms) are produced, varying from the size of a pea to that of a hen’s egg. A constriction is often developed quite close to this swelling, and a plug of fibrin may also be formed within the artery, so that the circulation in the wall of the gut is greatly hindered. As a result of this the glands and muscles in the wall of the digestive tube refuse their office, so that regular digestion and onward movement of the food do not take place. This leads to colic. As soon as the strongyloid larvæ have become adult, they pass from the walls of the arteries into their cavities, and are carried by the blood-stream to the walls of the gut, which they penetrate in order to reach its cavity, where (cæcum and large intestine) they pair, after which the female lays eggs, which are carried to the exterior in the dung. The quickly hatched young seek water, mud, or damp earth, where they live until, by some means (_e.g._ with the drinking water) they manage to enter the gut of a horse or (more often) ass. _Preventive Measure_: Horses and asses must not be allowed to drink stagnant water. The =Stomach Palisade Worm=, or =Strongyle of the Sheep= (_Strongylus contortus_). Male one-half to two-thirds of an inch, female three-quarters to four-fifths of an inch long; whitish or reddish, somewhat coiled at both ends. The disease of the stomach, and diarrhœa, which affect lambs, usually in spring, and result from the presence of these worms in large numbers in the true or fourth stomach, lead to emaciation, weakness, and poverty of blood. Development unknown. Nutritious food will cure lambs which are not very badly infested, but hastens the death of those which are.