70 STRONGYLID^ OR PALISADE- WORMS 



It is widely spread over Europe, Africa, Asia, Australia, and 

 America. In colour they are white to creamy white ; a few may 

 be tinged with pink. Adult females reach from 20 to 30 mm. 

 in length, the males from 10 to 20 mm. They are cylindrical,' 

 bluntly attenuated towards the head end, pointed at the tail 

 end in the female ; at the head end are two backwardly pro- 

 jecting papillae. The male has a trilobed bursa and no spiculae. 

 In the female the ovaries, &c., are spirally wound around the 

 intestine, giving the worm a very marked appearance. 



Eggs and young are passed out on to the ground in the faeces. 

 Whether development is direct or not has at present not been 

 demonstrated. The other abundant species are Ost&iagia 

 odertagi, found in the fourth stomach of cattle in Europe, 

 United States, and New Zealand. 0. cirmmcinda, found in 

 the fourth stomach and intestine of sheep and goats in Europe, 

 America, and Australia. 



The genus Trichostrongylus is represented by T. extenuatiis, 

 causing verminous gastro-enteritis in cattle and sheep, also found 

 in the fourth stomach. The life-cycle of these nematodes, which 

 often occur in countless numbers, is not known. 



The Armed Strongyles of the Horse. 



Another large Palisade-worm, known as the Armed Palisade- 

 worm (Srlerostomu7n annafum) (fig. 23), is found in the lower 

 parts of the horse's gut, chiefly in the ctecum and colon. It is 

 taken in by the horse in polluted drinking-water as a very min- 

 ute immature worm. This embryo bores into the blood-vessels, 

 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. 24). 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, makes its way 

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



