ON TRACHEAN ARACHNIDA. 
529 
deposits in the earth, at a certain distance from its surface, 
some eggs, of the size of a grain of sand, of a whitish colour, 
heaped one upon the other. 
Although these animals are akin to the spiders, neverthe- 
less they do not live, like them, for many years. Almost all 
of them perish at the end of autumn. One of their enemies, 
which fixes on their bodies to suck them, is a species of mite 
of the subgenus Leptus, This insect sometimes holds to the 
phalangium only by its bill ; the rest of its body appears sus- 
pended in the air. A gordius , similar to that which is often 
found in the interior of locusts, being found in the abdomen 
of the Phalangium cornutum , would lead us to believe that 
these araclinida are subject to be infested by these worms. 
That which was observed was very smooth, a little transpa- 
rent, and filled with a milky matter. It was about seven 
inches four lines in length, and two-tenths of a line in 
breadth. 
We are now come to the Acarijdes, or last family of the 
Arachnida, and our general observations upon them will be 
comprized in what we have to say respecting the genus 
Acarus, or the Mites. 
The name of Acarus in the method of Linnasus designates 
a genus of apterous insects very numerous in species. The 
acarus (proper) of M. Latreille comprehends the species of 
this tribe which have eight feet : simply ambulatory mandi- 
bles like forceps, palpi very short or concealed, and the body 
very soft, with the tarsi usually terminated by a vesicular pellet. 
The Acarus domesticus } or common mite , is of all the species 
the best known. It is found in great abundance upon old 
cheese, on dry or smoked meat, on birds and insects, in col- 
lections of natural history, on old bread, and dried up confec- 
tionary, which have been kept too long. It is for this reason 
that Degeer has named this species domestic. He also 
observed some of these mites in the flower-pots which he had 
VOL. XIII. 
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