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 Leptiis. 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 wdiich is often 

 found in the interior of locusts, being found in the abdomen 

 of the Phalangium cornutum, would lead us to believe that 

 these arachnida 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 AcARiDES, 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 Linnaeus 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, w4iich 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. M m 



