130 ACAKINA OR MITES. 



nearly to maturity. When about two months old the acarus 

 commences to lay. Some authorities say they mature much 

 sooner. The larvfe become eight-legged when the mi/m^;^ stage 

 is assumed. They remain attached to the leg-bristles of the 

 ovigerous female for some little time after birth. The adult 

 mites live for three or four weeks. Psoroptes may be found 

 amoDgst the wool and under the scabs, but never tunnel in the 

 time sliin. One can watch a young mite burrow into the outer 

 skin or cutis : in about ten days a small nodule will arise over 

 the point of entry ; from this vesicle a yellowish exudate 

 appears, which hardens over the skin, forms a scab, beneath 

 which the mites breed, being especially prevalent at the edges 

 of the psora. The scabs usually commence to be noticeable 

 about the sixteenth day after entry. This psoroptic mite, the 

 true scab acarus, is found chiefly affecting the woolly regions of 

 the sheep ; it is seldom found on the head or legs, or on the 

 abdomen beneath or breast region. The disease seems to die 

 out spontaneously, especially after dipping and shearing. The 

 acari often become detached on the wool the sheep rub off, when 

 trying to relieve the pruritus set up by them. Other sheep 

 rubbing against the wattles, pens, hedges, itc, where this 

 diseased wool is, will soon contract the malady, and so the 

 disease is spread from one flock to another. 



The Suivoj/t known as >S'. scabiei v. o;v> produces the head- 

 scab. This mite attacks those regions devoid of wool, or at 

 least where it is scanty. It is particularly plentiful around the 

 eyes, ears, nostrils, and lips. Youatt speaks of it as " black 

 muzzle." It may spread to the belly and legs, especially the 

 hocks and pasterns. The mite is round and white, with 

 numerous spines of two sizes on the dorsal surface, and with 

 two pairs of anal bristles. Logs short ; the two firet pairs have 

 the curious suclvcrs before referred to in the male, the fourth 

 pair also having tliem ; the third pair in the male, and tliird 

 and fourth in the female, are armed witli a long spine. 

 Tliis head-scal) is very like the itch-mite in man — in fact 



