Distribution.—Europe, America, Africa, Asia, Australia, New Zealand. Once in man in South America by de Magalhães.
Pathology.—Produces anæmia, emaciation, dropsy in sheep; and in the human case the symptoms were mistaken for those of ancylostomiasis.
Life-history.—Rhabditic embryos easily hatch in water, then moult several times, becoming eventually “filariform” larvæ enclosed in the moulted skin. These crawl up blades of grass and are swallowed by sheep, etc.
Genus. Nematodirus, Ransom, 1907, emend. Railliet, 1912.
Head over 50 µ in diameter. Cuticle may be slightly inflated and often transversely striated. Cuticle with eighteen distinct longitudinal ridges. Cervical papillæ absent (?). Posterior lobe of bursa reduced to short lobules each with a dorsal ray. Antero-anterior + latero-anterior (= anterior double) rays close together, parallel; antero-external ray diverges widely from antero- and postero-median, which are close together and parallel. Postero-external ray slender. Spicules more than 0·5 mm. long, at most one-twelfth of body, united by a membrane throughout their length or only distally. Gubernaculum absent. Vulva behind middle of body. Eggs ellipsoidal, shell rather thick.
Habitat.—Duodenum of ruminants.
Sub-genus. Mecistocirrus, Railliet, 1912.
Head slightly inflated, with transverse striations. Skin with eighteen longitudinal ridges, but little apparent; cervical papillæ distinct. Bursa bilobed; median ray double (= postero-median + antero-median); very large antero-external at the edge, close to the anterior. Spicules very long, slender, one-sixth length of body (3·5 mm.); tail pointed. Vulva immediately in front of anus.
Habitat.—Stomach of ruminants.
Mecistocirrus fordi, Daniels, 1908.