PARASITOLOGY. 51 
Fourth Siage—Mature Male and Female.—The last 
moulting in the nympha stage develops the distinct 
sexes. 
Fitth Stage.—The Ovigerous Female.—The impreg- 
nated female moults, which causes changes in the 
genital apparatus. 
_ It is estimated that each ovigerous female Sarcopt 
lays fifteen eggs, of which ten may be females and 
five males. Under favorable conditions it will pass 
its life cycle in fifteen days.’ At this rate, one ovig- 
erous female would cause the production of 1,500,000 
scab parasites in 90 days. 
THE SCAB PARASITES. 
SARCOPTES SCABEI, variety Equi (Equus—horse.) 
Synonym.—lItch mite; mange mite. 
History.—In the United States it is found among 
horses in the Northwest, especially upon the range. 
Animals Intested.—This is the common scab para- 
site of the horse. 
Lite Cycle-—The following may be added to what 
has been given as to the stages acari pass through: 
The ovigerous female burrows into the skin, form- 
ing galleries. In these galleries may be found fe- 
males, ova and larvae. As soon as the eggs are 
hatched the larvae leave the gallery. In the serum 
under the scab may be found the larvae, nymphae, 
adult males and females. 
Condition Produced.—The parasite is equipped with 
a piercing stylet with which it pierces the skin, the 
puncture causing a minute red spot, followed by a 
small vesicle, which ruptures. The serum dries and 
forms a minute scab. In this way the myriads of 
