_Oxyuris_ is Meromyarian (see p. 137), and is characterised by the long capillary tail of the female. It includes another human parasite, _O. vermicularis_, and it is one which it is difficult to get rid of. The female has the characteristic tail and is about 10 mm. long. The male is smaller. They are found in the caecum and rectum of man, and cause great irritation and sometimes serious functional disturbance. The eggs are laid in immense numbers but perish in water. If whilst still in the egg-shell the larvae are swallowed on fruit or raw vegetables, etc., they are set free in the stomach and small intestine by the action of the digestive secretions. The distribution of this parasite is universal. Besides numerous species that inhabit the alimentary canal of Vertebrates, such as _O. ambigua_ Rud., found in hares and rabbits; _O. curvula_ Rud., in {142}the caecum of horses; _O. megatyphlon_ Rud., in iguanas; several species inhabit the rectum of insects, such as _O. blattae_, _O. diesingi_, _O. blatticola_, found in the cockroach; _O. spirotheca_, and _O. hydrophili_ in the water beetle _Hydrophilus_.[180] The genus _Nematoxys_ has the most complex arrangement of muscles of any Meromyarian, and forms a transition to the Polymyarian type. The whole body of both sexes is covered with numerous irregularly scattered papillae. The members of this genus have hitherto been found in snakes, Amphibia, and eels; there are but few species. _Oxysoma_ is another small genus with but three species, found in the intestines of opossums, frogs, and turtles respectively. II. FAMILY STRONGYLIDAE. Mouth surrounded by papillae; an armature of teeth or spines often present. The chitinous lining of the intestine projects into the interior as ridges. No oesophageal bulb. The male orifice at the posterior end of the body is surrounded by a bell-shaped bursa. Genera: _Eustrongylus_, _Strongylus_, _Dochmius_, _Sclerostomum_, _Cucullanus_, _Syngamus_, _Pseudalius_, _Ollulanus_, and others.