The Oxyuris Vermicularis, Thread or Seat worm, is commonly found in children.

Is white in color; the female is from 10 to 12 mm., the male 2.5 to 5 mm. long. The tail of the female is long and tapering, that of the male blunt and curved upon itself. The mouth lies between three lips. The genital pore is anterior in the female, posterior in the male. The eggs are oval, about 0.005 mm. long, and contain embryos with sharp posterior ends.

Fig. 118. - Ascaris Lumbricoides (Female) (Mosler and Peiper).

Fig. 119. - Eggs of Ascaris Lumbricoides (Mosler and Peiper).

The parasites live in the large intestine, usually in great numbers. May leave the rectum and enter the vagina and urethra in girls, causing much irritation and itching. The eggs are swallowed, hatch in the upper intestine, and the female worms becoming fecundated form more eggs.