TUACHEARIyE. 215 



diseases, such as the itch, is attributed to particular species. The 

 experiments of Dr Galet prove that if the Acari of the human psora 

 be placed on the body of a perfectly healthy person, they will inocu- 

 late him with the virus of that disorder. Various species of Acari 

 are also found on Insects, and some of the Coleoptera that feed on ca- 

 daverous or excrementitious substances are frequently covered with 

 them. They have even been observed in the brain and eye of Man. 



The Acari, or Mites as they are vulgarly termed, are oviparous, 

 and excessively prolific. Several of them at first have but six legs, 

 the remaining two being developed shortly after. Their tarsi ter- 

 minate in various ways according to their habits. 



Some — AcARiDEs, Lat. — or the Acari proper, have eight legs, 

 solely destined for walking, and chelicerse. 



Trombidium, Fab. 



The chelicerse monodactyle, or terminated by a movable hook; 

 salient palpi, pointed at the end, with a movable appendage or spe- 

 cies of finger under their extremity; two eyes, each placed on a lit- 

 tle immovable pedicle. The body is divided into two parts, the first 

 of which, or the anterior, is very small, and bears the two first pair 

 of legs, together with the eyes and mouth. 



Tromh. holosericeum, Fab.; Herm., Mem. Apter., pi. I, 2, and 

 II, 1. Very common in gardens in the spring; blood-red; ab- 

 domen nearly square, posteriorly narrowed, with an emargina- 

 tion; the back loaded with papillse, hairy at base, and globular 

 at the extremity. 



Tromb. tinctorium, Fab.; Herm. Apter., I, 1. Three or four 

 times the size of the preceding; it furnishes a red dye. The 

 East Indies(l). 



Erythr^us, Lat. 



The chelicerse and palpi of Trombidium; but the eyes are not 

 placed on pedicles, neither is the body divided(2). 



Gamasus, Lat. Fab. 



Didactyle chelicerse; very distinct or projecting filiform palpi. 

 The superior surface of the body, in some, is either wholly or 

 partially invested with a scaly skin(3^. 



(1) T. fuliginosum, Herm. Mem. Apt. I, 3; — T. bicolor, lb. II, 2;' — T. assimik, 

 lb., 3; T. curtipes, lb., 4; — T. irigmium, lb., 5; — T. trimaculatum, lb., 6. 



(2) Eryihrxus jjlialangioides, Lat.; JVombidium j)halangioides, Herm., lb., I, 

 10; — Trombidium quisqutliarum, lb., 9; — Tromb. pariclinum, lb., 12; — T. pusil- 

 lum, lb., II, 4; — T. mururum, lb., 5. 



(3) Gamasus marginatus, Lat.; Icarus marginatusy Herm., Mem. Apter., VI, 6, 



