STRONGYLID^ OR PALISADE-WOKMS. 



63 



enters the large posterior arteries, especially one known as the 

 " anterior mesenteric artery," where it produces a swelling in 

 the wall of the artery (fig. 21). This growth checks the cir- 

 culation, and may lead to vascular disturbances of some im- 

 portance. Whilst in this abode the worm is immature ; but 

 just before maturity is reached the worm escapes, makee its way 

 through the gut wall, matures, and copulates. The ova are 

 carried out in tlie dung. The embryos are seen to develop in 



FiQ. 20.— Armed PAusArr-woRM of Horse (SderostoTmtm arTiiatum). Female. 

 a, Male bursa. 1 



damp mud and in water, and are thus taken by the horse. 

 Another form, the Giant Palisade-worm (S. gigas), is a red 

 worm nearly a foot in length in the female, and lives in the 

 pelvis of the kidney in both horse and man. Sometimes severe 

 epizootics of these Palisade-worms break out. 



Sderodomum tetracarifhum (fig. 22) and <S'. rubrum (fig. 23) 

 are usually the most injurious Strongyles in the horse. The for- 



' The female is often as big again as the line representing the natural 

 size in the figure. 



