THREAD-WORMS 171 



OXYURIS 



Oxyuris (Oxyurias). The three labial prominences are 

 slightly marked. The oesophagus has a marked double 

 dilatation. There is a single spicule in the male and two 

 pairs of pre-anal papillae. The opening of the vagina is 

 anterior, and the end of the female is drawn out to a 

 sharp point. 



Oxyuris vermicularis (" Thread-worm ") is the only repre- 

 sentative in man. It occurs in temperate and tropical 

 climates, and causes more trouble in children than in 

 adults. Probably it is more common in adults in the 

 Tropics than in temperate climates. 



The female is a white worm, about 10 mm. in length 

 and 0*6 mm. in breadth. The male is shorter, only 5 mm., 

 and can readily be distinguished as the tail is not pointed 

 and is curved on itself (fig. 68). 



The life-history is interesting. The worms, male and 

 female, are found in the small intestine, where copulation 

 occurs. The females only travel downwards and accu- 

 mulate in large numbers in the caecum, vermiform appen- 

 dix, and ascending colon. When the eggs are nearly 

 mature the females again travel downwards towards the 

 rectum. They rarely pass any eggs in the large intestine, 

 but pass out at the anus, and stimulated by the cold air 

 the uterine tubes contract and the eggs are expelled and 

 deposited round the anus and on the skin in the perineum. 

 Mature females containing eggs are often passed with 

 the faeces. Eggs are only found in the faeces exceptionally. 



A considerable, sometimes intolerable, itching of the 

 perineum is set up by the wanderings of the worms or 

 from irritation caused by the eggs, or possibly by larvae 

 which escape from them. , 



The eggs, when passed, contain a fully developed 

 embryo. The egg-capsule, though thin, is a little thicker 

 and much tougher than in the ankylostome egg, which 

 it resembles in size, though in shape, as well as in the 

 development of the egg contents, it differs, as the eggs are 

 flattened on one side. 



