ARACHNIDA. 267 
furnish so favorable a resort for the multiplication of the pests. On 
this account the history of the species is more particularly the history 
of this variety. 
Its distribution is at present practically over the entire world where 
sheep are bred, and while there may be practical immuuity in some 
States where vigilant attention has been in practice, no sheep breeder 
should neglect occasional examination for it nor, especially, the most 
careful scrutiny of all new animals introduced into his flock. 
Fia. 159..-Psoroptes communis var. equi. (Copied from Murray's figure after Furstenberg.) 
The effects of the parasite on the sheep and the appearances by 
which it may be detected are here quoted from Curtice’s Animal Para- 
Sites of Sheep: 
Attention to the disease is first attracted by the infected sheep scratching and bit- 
ing and rubbing themselves. The coats of the animals look rough, taggy, and felted. 
The itching is always most violent when the sheep have been heated by driving or 
warming in the stable. 
By separating the wool and examining a recently infected spot there can be seen 
some minute elevations which differ from the surrounding skin in being slightly 
whiter or yellower and which have been produced by the bites of the pests. The 
1h er Ro 
a 
a. 
