66 VETERINARY PARASITOLOGY 
full size, after which they again bore back into the 
intestinal wall, become encysted, and finally reach the 
lumen of the intestine as the perfect adult parasite. 
While in the aneurism, the parasite is spoken of as 
Sclerostomum armatum minor, while the adult is spoken 
of as Sclerostomum armatum major. 
Sclerostomum Tetracanthum.—This is a much smaller 
worm, normally white in colour, but almost invariably 
bright red, from the blood contained within its body, 
previously sucked from its host. It ranges from ro to 
15 millimetres in length. The mouth is circular, and 
the rim carries a series of teeth, together with six 
papille, four large and two small. A little behind these 
is another pair of long papille, placed laterally. The 
tail of the male terminates in a caudal pouch, while 
that of the female is pointed. 
This worm also inhabits the cecum and colon of the 
horse, usually in company with Sclevostomum armatum. 
They are probably taken into the body with the water, 
and then encyst themselves in the mucous membrane, 
finally returning to the lumen of the bowel. They do 
not enter the vessels and set up aneurisms. 
Symptoms.—Since both of these worms are usually 
found coexisting in the same horse, it is difficult to draw 
any marked distinction between the symptoms set up 
by either worm in particular. Since Sclerostomum tetra- 
canthum confines itself to the bowel, and seldom bores, 
it is less frequently the cause of the so-called vermi- 
nous colic than is Sclevostomum armatum, which does 
further damage in the vessels. Nevertheless, Sclero- 
stomum tetracanthum, when present in large numbers, is 
capable of causing marked anemia, emaciation, and 
death. 
The disease is commoner in the country, among horses 
that have been running at grass, than in town horses, ex- 
cept in those that have been recently introduced from the 
