MANGE OF THE HORSE. 65 
organ. The adult animal has eight legs, the young six. 
The roundish male has one fine claw on the first two pairs 
of legs, two larger ones on the third, and none on the fourth 
and last. The mites moult four times. 
This genus contains a single species, the Psoroptes com- 
mums Fuerst. Besides the characters already given for the 
genus it is only necessary to state that it also occurs in num- 
erous forms upon a number of domesticated animals, upon 
which'fit causes crusts by pricking their skins. The differ- 
ences between these forms or varieties are not great, but suf- 
ficiently so to give them each a name according to the host 
upon which they occur. 
THE COMMON MANGE OF THE HORSE. 
(Psoroptes communis var. equt). 
This disease caused by parasitic mites is the most 
common and longest known of all skin-diseases of the horse, 
ass and mule. It can appear upon 
any part of the body except the ex- 
tremities of the limbs, but it is most 
usually found upon the upper part of 
the neck, the root of the mane, the 
poll and the tail. The mites live in 
colonies on the surface of the skin, 
hiding under the shelter of hairs, and 
their presence is readily discovered. 
Fig. 37 shows the two sexes of this 
mite. If we take some scabs from the 
ee end eale Geom evaded ,parts and ‘put them upon 
ly enlarged. After Meguin. black paper, we can even with the un- 
aided eye see numerous mites moving about actively in all 
stages of growth. The mites, in feeding upon the surface 
of the skin, make punctures, and these soon form a crust, 
and as the parasites multiply rapidly they cause before long 
similar symptoms to those produced by the true burrowing 
itch-mites. The constant irritation caused by their presence 
forces the horse to the most energetic rubbings, which add 
to the inflammation of the skin, and the sores and ulcers 
thus produced are often impregnated with blood. 

