50 PROGRESS OF VETERINARY SCIENCE AND ART. 
I have used the terms Acarus and Sarcoptes irrespectively 
during my remarks, just as authors have mentioned them; 
they are synonymous, British authors adhering to the former, 
whereas the Germans invariably use the second. 
The genus Acarus, in my revered preceptor, Dr. Grant’s 
classification, belongs to the order Tracheata, of the class 
Arachnida, in the Entomoid or Diplogangliated subkingdom. 
The generic characters, as given by Hering, are : 
6i Head retractile, snout double-valved, two or four thread- 
shaped palpi, no eyes. Body roundish, shield-like (vestudini- 
form, J. G.) Eight feet adapted for running, the four 
anterior ones springing from the circumference of the body, 
with tarsal discs ; the four posterior with or without tarsal 
discs, mostly ending in long filamentary organs, either spring- 
ing from the circumference or under surface of the body. 
Met with in the skin diseases of warm-blooded animals. 
The first sub-genus comprises those acari in which the 
legs spring from the sides of the bod} 7 ; they are — 
1st species: the third pair of feet each with two long 
hairy appendages and a tarsal disc; the fourth pair each 
terminating in two short hairs. Acarus equi ; see figs. 1, 2, 3. 
2d species : the third pair of feet, each with two long 
bristles without tarsal discs ; the fourth pair with a long 
filamentary organ and a tarsal disc. Acarus ovis. 
3d species : both hind feet with two filamentary organs 
each, without tarsal discs. Acarus cynotis ; figs. 4, 5. 
In the second sub-genus the fore-feet spring from the 
sides of the body, the hind ones from beneath the belly. 
4th species : the hind feet terminate in a bristle without 
tarsal disc. Acarus hominis . 
5th species : the fourth pair of feet each w ith a disc ; the 
third pair, in the male alone, has a long bristle and short 
pedicled disc ; in the female there are, on the contrary, two 
long bristles without disc; the processes from the hinder 
part of the body of the male are furnished with four bristles. 
Acarus lovis ; see figs. 6, 7. 
6th species : the hind feet terminate in a bristle w ithout 
tarsal disc ; the posterior part of the body nearly hairless. 
Sarcoptes rupicapra of Hering. The acarus of the chamois. 
7th species: the third pair of feet with a long filamentary 
organ ; the fourth pair furnished with a tarsal disc. Acarus 
cati — of the domestic cat; see figs. 10, 11. 
8th species : all eight pairs of feet furnished with long 
pedicled tarsal discs, without filamentary organs. Hind part 
of the body with eight feathered hairy appendages. Acarus 
hippopoclos ; fig. 8. The Acarus setosus probably belongs 
