PARASITOLOGY. 51 



Fourth Stage — Mature Male and Female. — The last 

 moulting in the nympha stage develops the distinct 

 sexes. 



Fifth 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. — Itch mite; mange mite. 



History. — In the United States it is found among 

 horses in the Northwest, especially upon the range. 



Animals hifested. — This is the common scab para- 

 site of the horse. 



Life 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 



