502 
CLASS ARACHNIPA. 
Macrocheles, Lat ., 
Have also the forceps very projecting, and long ; but the eyes 
are non-existent, or sessile. The two anterior feet are very 
long and antenniform. The upper part of the body forms a 
plate, or scale, without distinct rings. 
I refer to this genus, the Acarus marginatus , and testudi- 
narius , of Hermann the younger, (Memoire, apterol. p. 76, 
pi. vi. fig. 6, and pag. 80, pi. ix. fig. 1.) 
Trogulus, Latr. 
The anterior extremity of the body is advanced in the form 
of a hood, and receives, in a lower cavity, the forcep, and the 
other parts of the mouth. 
Their body is very flatted, and covered with a very firm 
skin. Under stones. 
The second tribe of Ho LETR A, that of ACARIDES, some- 
times has forceps, but simply composed of a single pincer, 
either didactylous, or talon-like, and concealed in a sternal 
labium; sometimes a sucker, formed of laminse, like lancets, 
and united ; or even but a mere cavity for a mouth, without 
any other apparent pieces. 
This tribe is formed of the genus of the 
Mites. Acarus, Lin . 
Most of these animals are very small, or almost micro- 
scopic. They are dispersed every where : some are erratic, 
and we find them under stones, leaves, the barks of trees, 
in the earth, the water, or in household provisions, such as 
flour, dried meat, old cheese, or animal substance in a state 
of putrefaction ; others live, parasitic ally, on the skin, or in 
the flesh of various animals, and often greatly enfeeble them 
from their excessive multiplication. To some species the 
origin of certain maladies is even attributed, and especially 
