122 ZOOLOGY. 
condition of other genera. Dugés divides the order into seven families, the 
succession of which is here followed in reversed order. The genera are 
numerous. 
Fam. 1. Oribatide. These have a remarkably hard exterior, the back 
being formed like a’ carapace, whence Hermann’s generic name WVotaspis. 
This carapace sometimes has a transverse division, and Dugés mentions a 
species in which the feet can be hidden by its lateral borders. The palpi 
have five articulations, of which the second is the thickest and longer than 
the rest conjointly. The mandibles are cheliform or didactyle, and the eyes 
are usually absent. 
fam.2. Bdellide. Body oblong and tumid posteriorly, contracted behind 
the eyes; rostrum in the form of a head, and elongated ; palpi resembling 
antennee, mandibles with a claw, or cheliform; feet cursorial. 
Fam.3. Acaride. In this family the feet are carunculated, the mandibles 
cheliform, and the palpi indistinct, on account of their adherence along the 
inside margin of the labium. ‘These animals increase rapidly, and various 
species infest provisions and living animals, including man. Others roam 
at large upon the ground, or on plants and other objects. Acarus siro (pl. 
TT, jig. 70) is the cheese-mite, which is mentioned by Aristotle. In Sar- 
coptes, the body is soft and tumid, the four posterior feet are rudimentary 
and provided with long bristles, the collar below and the base of the feet 
are armed with hooks, and the anterior feet terminate in vesicles. This 
genus is parasitic under the skin of various animals, including man, causing 
the disease named itch, and although this fact has been often doubted, it 
seems now to be established beyond dispute. The species which infests 
man has been known to the Arabs, and is mentioned by an Arabic author, 
Abenzoar, of the twelfth century. It has been known from time immemorial 
in Southern Europe, where it has been considered to be the cause of the 
itch, under names which are,diminutives of the terms used for lice, with 
which they were naturally confounded in the absence of microscopic 
examination. Linnzus confounded this species with Acarus siro, consider- 
ing the two to be varieties of a single species, a view which has been 
contended for in later times. It seems probable that Acarus siro is 
occasionally found about the itch pustules, but the Sarcoptes must be 
searched for at the bottom of the tortuous galleries which it forms under the 
skin, extending from one to six lines. The common Sarcoptes scabied (pl. 
77, fig. 68) is marked with curved lines above, the middle has small eleva- 
tions, and there is a small bristle on each side, and two large ones 
posteriorly. 
The itch, caused probably by different species of Sarcoptes, is spread 
over a great portion of the earth, and is endemic in some localities, and 
although it is readily destroyed, there are those who consider the irritation 
in the light of a luxury, and refuse to have it removed. 
Various species of Sarcoptes infest man, monkeys, horses, and drome- 
daries. That of the last-named animal (S. dromedari) is larger and better 
armed than the ordinary species, and in several instances it has been com- 
municated to man. 
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