278 



OTHER INTESTINAL ROUNDWORMS 



fifths of an inch in length, and have about the diameter of an 

 ordinary pin. The males (Fig. 111,?) are only about half as 

 large and have the posterior end of the body rolled ventrally. 

 The adult females filled with eggs leave 

 the small intestine and coecum and wander 

 back to the rectum whence they are 

 passed out with the faeces or creep out 

 of the anus, lespecially in the evening 

 or at night, causing intense itching. 

 These egg-filled females, or the free eggs 

 which already contain coiled embryos, 

 live in the moist groove between the 

 buttocks, in girls sometimes creeping for- 

 ward to the vagina. From the scratching 

 and rubbing which results from the itch- 

 ing in the vicinity of the anus the fingers 

 and fingernails become infected with the 

 eggs. The eggs may then be transferred 

 to the mouth directly or indirectly, thus 

 causing reinfection, or they may be trans- 

 mitted from person to person by unclean 

 hands. Infection may also occur by 

 swallowing the mature egg-filled female 

 worms, or by the eating of raw vegetables 

 or other foods which have been polluted 

 by the eggs. As in the case of other 

 parasite eggs, those of the pinworm may 

 also be scattered by flies which have 

 visited infected fseces. 

 When first deposited, the eggs, often hanging together like 

 short strings of beads, contain larvae which resemble tadpoles 

 (Fig. 112A). In the faeces or in the moist groove between the 

 buttocks the larvae, still in the eggs, transform within a few hours 

 into worms of typical nematode form (Fig. 112B). Later stages 

 are shown in Figs. 112C and D. 



After infection, which probably nearly always occurs by way 

 of the mouth, about two or three weeks elapse before sexual 

 maturity is again attained and the eggs and females reappear 

 in the faeces. 



While usually no inconvenience is felt from the presence of 



Fig. 111. Pinworm, 

 Oxyuris vermicularis ; 9 , 

 female; $, male; ph., 

 pharynx; int., intestine; 

 ov., ovary; ut., uterus; an., 

 anus; v., vulva; t., testis; 

 sp. d., sperm duct, x 8. 

 (After Claus, from Braun.) 



