bryos, in what is known as the rhabitform stage, escape. These 

 begin feeding and growing, the skin being molted in the process at 

 least once. The embryo is then in the sheathed stage, its former 

 cuticle completely encasing it. Embryos attain this stage in about 

 ten to fourteen days. The embryo is now sealed up and no longer 

 feeds. Previous to this time the eggs and embryos are easily killed by 

 drying and exposure to low temperatures. After becoming ensheath- 

 ed, the embryos are very resistant to these conditions. During wet 

 weather and while the dew is on the grass, the embryos crawl up the 

 blades of grass, and sheep or cattle eating the grass take the embryos 

 into the stomach where they develop into adult worms." 33 



Irritation of the mucous membrane is produced by the worms, 

 causing irregular digestion, resulting in scouring. These worms are 

 blood-sucking, and cause an anaemic condition of the animal. Infec- 

 tion is most serious in lambs which, apparently healthy, become low 

 in condition during July and August, and often die. Lambs affected 

 have diarrhoea, are unthrifty, w r eak and emaciated. Mature sheep 

 are able to resist stomach worms, but when heavily infested become 

 weak and are unable to stand the extra strain of lambing. 



Nodular Disease. 



"The adult worms live in the upper part of the large intestine in 

 sheep." "The female worm attains a length of about five-eighths of 

 an inch (15 millimeters), the male being a little shorter. The worms 

 have a characteristic solid-white color which differentiates them from 

 most of the other sheep parasites, which are somewhat translucent, 

 yellowish, or in the case of stomach worm, red. The head is bent 

 over and forms a hook with the body. The parasite appears to be a 

 native of this country, which has adapted itself to our sheep. 



The life history of this worm is not completely known. The 

 eggs produced by the female are passed with the feces of the host_ 

 \Yhen the resulting embryos again come to light they are found in* 

 tumors in the mucous lining of the intestine." Here they form cysts 

 which become surrounded by a green necrotic material due to the 

 resulting inflammation. "The cysts break down and the embryos live 

 in the necrotic mass. After a time they break from the tumors, and 

 attain maturity in the lumen of the intestines. It appears that the 

 formation of tumors may not be essential to the development of the 



'"Twenty-seventh Annual Report, United States Bureau of An. Industry* 

 page 443. 



27 



