PARASITES OF THE ALIMENTARY TRACT 65 
sionally specimens are found which greatly exceed this 
length. 
In its adult form Sclerostomum armatum inhabits the 
large intestine of the horse, particularly the cecum, 
hanging on to the mucous membrane. It may even be 
found in the duodenum in some cases. 
Life-History.—Sclerostomum armatum appears in three 
different positions : 
xr. Attached to the mucous membrane, or free in the 
lumen of the intestine. 
2. Coiled up in nodules in the submucous tissue. 
These tumours range from the size of a millet-seed to 
that of a hazel-nut. They contain the worm, blood, 
and a quantity of soft, cheesy material. 
3. In the arteries (anterior mesenteric or branches of 
aorta). 
The eggs are laid either on or in the mucous mem- 
brane. In the former case the embryo burrows into the 
mucous membrane. After a while they bore their way 
out into the lumen of the gut. It is supposed that some, 
still in an agamous condition, again return and burrow 
into a vessel. They then work against the blood-stream 
to the root of the anterior mesenteric artery, and form 
an aneurism there, or else get into the aorta, and are 
transported by the blood-stream to other organs. 
Another theory, which makes the aneurism an essential 
part of the life-history of the worm, supposes that the 
ova are deposited in the bowel, and are passed out into 
damp ground or into water. Some consider that they 
develop into free Nematodes (rhabditide), and pass this 
stage of their existence in water or on damp ground. 
However this may be, the majority agree that after 
certain moults the embryo gets back into the intestine 
by ingestion of water or food. Those which bore into 
the vessels produce an aneurism in which it is believed 
further development takes place, and they reach their 
5 
