THE COMMON SHEEP-SCAB. 69 



great care should now be taken to stamp it out, and prevent 

 other flocks from becoming infested. Our farmers, and 

 chiefly those that are still unfamiliar with the details of 

 sheep husbandry, can not be too careful in regard to this 

 disease. Wherever sheep husbandry has been well estab- 

 lished for some time, and where farmers have learned to cure 

 the disease, the losses caused by scab are gradually reduced 

 by the proper use of remedies, and by the exercise of good 

 judgment in furnishing their animals sanitary surroundings. 

 This scab-mite can be more completely and readily extermi- 

 nated than many of the other parasites of sheep. 



The mite is very small, barely visible to the unaided eye; 

 it has an elongated oval body, resembling in shape a turtle. 

 Its skin shows numerous small wrinkles, and is covered with 

 spines, hairs, scales and wart-like projections. The mature 

 mite has eight legs, each composed of five joints. The illus- 

 trations (fig. 38, 39 and 26) show the male, female, and the 

 mouth parts. The male (fig. 38) upper side, is quite diff'erent 

 from the female (fig. 39), as can be readily seen by comparing 

 the illustrations. The young larval mite possesses but six 

 legs. Both males and females make burrows or tunnels in 

 the skin of their host, but those of the former are always 

 very short. 



Neither sex lives longer than from three to six weeks, but 

 during this time the female is almost constantly engaged in 

 laying eggs. These are smooth objects, of an elongated oval 

 shape, and are deposited in small patches, each containing 

 from twenty to twenty-four eggs, which hatch in the course 

 of four to seven days. The six-legged larvae undergo three 

 moults in the tunnels, and reach maturity in about fourteen 

 days, when they leave their old quarters and start tunnels 

 for their own use. Gerlach computed that a single female 

 could produce in three months a progeny of 1,500,000, He 

 gives the result in a tabular form : 



First generation after 15 days produces 10 females and 5 males. 

 Second " " 30 " " 100 " 50 



Third " " 45 " " 1,000 " 500 



Fourth " " 60 " " 10,000 " 5,000 



Fifth '♦ " 75 " ■ " 100,000 " 50,000 



Sixth " " 90 " " 3,000,000 " 500,000 



