SCLEROSTOMY TETRACANTHUM. 
565 
and the smaller ones a dirty white color. They are from one- 
fourth to three-fourths of an inch long, the females being a 
little larger than the males. The mouth is circular, with a 
salient rim that has a crown of triangular teeth, and outward¬ 
ly six papillae, two lateral, small, and on each side of them two 
others, conical and very prominent. The buccal capsule is 
cylindrical. The caudal pouch of the male is simply excised 
on the ventral surface. 
The posterior lines are trifurcated, the middle doubled and 
the anterior cleft. In the female the tail terminates in a point 
and the vulva is very near the anus. The digestive canal is 
complete. 
The sclerostomatetracanthum inhabits the caecum and colon 
of the horse often in company with the strongylus armatus, 
another troublesome equine parasite and one which formed 
the subject of an interesting and valuable paper at the last 
session of the United States Veterinary Medical Association, 
by Dr. J. F. Winchester. 
Round of Life. —The ova are segmented in the uterus. 
They are laid in the intestine of the host, passed out with the 
faeces, and if the proper conditions, warmth and moisture, are 
met with, will hatch out in a few days. The external phases 
in their development are, according to Bailliet, analogous to 
those of the strongylus armatus and are about as follows : If 
the conditions of warmth and moisture continue favorable 
after the ova are hatched out, they gradually grow, their in¬ 
tegument becomes folded and forms a kind of sheath in which 
the worm moults. It is at this period they enter the body of 
the host in the water the animal drinks, or perhaps on the green 
forage when on low, damp ground, pass into the intestines, 
and it is probable that thej^ encyst themselves directly into 
the mucous membrane of the colon and caecum without pen¬ 
etrating the circulatory apparatus. At least no wandering 
parasites of this kind have ever been observed. They remain 
imbedded beneath the mucous membrane until they attain sex¬ 
ual maturity, when they again enter the intestinal canal to pass 
the remainder of their lives. 
Effect on the host, —As the result of the association 
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