136 BOARD OP AGRICULTURE. 



head is round, nearly globular, supported by a cliitinous bulb 

 or capsule, truncated at the end, where the large, round 

 mouth is situated. The mouth is surrounded by one to sev- 

 eral circles of fine denticles, or converging hooks. The oesc- 

 phagus is muscular and thick, club-shaped, separated from 

 the intestine by a strong constriction. 



The male is an inch or an inch and a quarter long, with a 

 large, membranous, caudal bursa, divided into two lateral 

 lobes, which are strengthened by numerous rays ; there arc 

 two long and slender spicules. The female grows to the length 

 of one and a half to two inches, with a long, tapering, caudal 

 portion, the anus not terminal ; the ovaries long and con- 

 voluted around the intestines, and showing through the integu- 

 ments ; the uterine tubes are double and contain great num- 

 bers of eggs, in which embryos are developed. 



Habits. 



This parasite is very common in the horse, generally living 

 attached by the hooks of its head to the lining membrane of 

 the intestine, particularly in the coecum and colon, but some- 

 times in the small intestine and duodenum, and even in the 

 pancreas. At the points where it adheres it Figure 83. 

 causes small, dark-colored, raised spots. They 

 sometimes occur in vast numbers in the large 

 intestine, completely covering the surface ; 

 the number sometimes amounting, it is said, 

 to a million or more. Ordinarily, however, 

 these parasites, when lodged in the intestines, 

 do not appear to produce any marked dis- 

 ease or notable symptoms, although when in 

 great numbers, there can be no doubt but 

 that they must cause some inflammation and 

 pain. More serious results, sometimes prov- 

 ing fatal, happen when the worms enter the 

 blood-vessels. They produce large aneurisms or dilations of 

 the arteries, chiefly in the anterior mesenteric artery, but 



Figure 83. Sclerostoma equinum, female, natural size ; and anterior portion en- 

 larged ; a, mouth ; b, circle of hooks ; c, oesophagus ; d, intestine ; e, reproductive 

 organs. From Cuvier. 



