PARASITES AND PARASITIC DISEASES OF HORSES PA 
maturity. On the contrary, the larve, after entering the body of 
the horse, undergo extensive migrations which bring them to various 
organs and tissues, such as the liver, pancreas, spleen, lungs, kidneys, 
and other organs and tissues, from which many of the larvee prob- 
ably fail to get back to the large gut. However, those larvee which 
return to this organ become attached to its wall and develop to 
fertile maturity. The eggs which are produced by the female worms 
and eliminated from the horse’s gut with the manure start the cycle 
of development once more. 
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Ficgurn 14.—Representation of the life history of one of the blood strongyles, 
S. equinus. The illustrations of the adult worms are about natural size and 
those of the eggs and larve are enlarged about 75 times. This iilustration is 
typical of the life cycle of horse strongyles generally 
From this account of the life cycle of these parasites it is evident 
that horses infested with blood strongyles contaminate the pastures 
on which they feed with the eggs produced by the worms, and that 
the larvee which issue from the eggs and develop to the infective 
stage may be swallowed by these and other horses. When horses 
are kept on the same pastures year after year the number of eggs 
and larvee gradually increases, and this contamination, accumulating 
from year to year on a given pasture, may be highly damaging to 
horses which are grazed there. Foals, in particular, suffer from 
the effects of gross parasitism acquired in this manner. 
