236 PARASITES OF THE DOMESTIC ANIMALS 



Occurrence. — Oxyuris equi is a common inhabitant of the large intes- 

 tine of the horse. The condition produced by these worms is usually 

 referred to as oxyuriasis, and they are commonly known as seat-worms 

 or pin-worms. Often they are observed projecting from the margin of 

 the anus to which they adhere while depositing their eggs. By means 

 of a sticky substance the eggs attach about the skin of the anus and 

 perineum and develop embryos within two to three days. Later the 

 substance by which they are fixed to the skin dries and the eggs drop 



Fig. 122. — Oxyuris equi, showing varying lengths of posterior 

 attenuated portion. 



to the ground where, through scattered manure, they contaminate the 

 pasturage, or, if the animal is in the stable, the feed may be contam- 

 inated in the same manner. 



The eggs are provided at one end with a sort of operculum which, on 

 reaching the stomach, is digested away. The released embryos are then 

 carried with the alimentary material to the large intestine where they 

 reach maturity. 



Effect. — The offense of the oxyurids is mainly one of unsightliness. 

 They produce itching about the anus which may become intense, causing 

 the animal to rub the parts and thus bring about a denudation of the 



