502 CLASS ARACHNIDA. 



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.) 



Tkogulus, 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 Holetra, 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 laminss, 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, parasitically, on the skin, or in 

 the flesh of various animals, and often greatly enfeeble theiu 

 from their excessive multiplication. To some species the 

 origin of certain maladies is even attributed, and especially 



