TRACHEARIiE. 



469 



Fig. 37. 



vanced, in the form of a muzzle or beak. The majority have eight legs, the others six* This family 

 is composed of two tribes. 



The first tribe is that of the harvest-men, Phalangita, Latr., having the chelicers very apparent, 

 either projecting in front of the trunk or being inferior, but always terminating in a didactyle forceps, 

 preceded by one or two joints. They have two filiform palpi of five joints, the last terminated by a 

 small hook; two distinct eyes; two maxillae, formed by the prolongation of the basal joint of the palpi, 

 and often four others, composed merely of the dilated coxae of the two anterior pairs of feet. The body 

 is oval or rounded, covered, at least upon the thorax, by a more solid skin. The abdomen exhibits the 

 appearance of foldings. The legs are long, always eight in number, and divided distinctly, in the 

 manner of those of insects. Many {Phalangium) have, at the base of the two posterior feet, two spira- 

 cles, one on each side, but bidden by the coxae. The majority 

 live on the ground, upon plants, or at the roots of trees, and 

 they are very active ; others hide themselves beneath stones, or 

 ^ll/f lyf'li \\ in moss. 



Phalangium, Linn., has the chelicerae projecting-, much shorter than 



the body, and the eyes placed upon a common tubercle. The leg:s are 



very long- and slender, and, when detached from the body, they exhibit 



signs of irritability for a few moments. Ph. cornutum, Linn., male ; 



Ph. opiUo, Linn., female; and other native species. Consult, also, the 



monoa;raphs of this genus published by Latreille at the end of his Hist. 



Nat. des Fottrmis; Herbst. and Hermann, Mem. Apterolog. 



Gonyleptes, Kirby, has the palpi spined, with the two terminal joints nearly equal-sized ; 



and the coxa; of the hind pair of legs are very large, and soldered together, forming a plate 



beneath the body. The hind legs are wide apart from the others. G. horridus, Kirby. 



Brazil. 



filro, Latr., has the chelicer.-e projecting nearly as long as the body ; the eyes wide apart, 

 and each placed upon an isolated tubercle, or without support. S. ruhens, Latr. 



Macrocheles, Latr., has exposed and very long chelicerae, but the eyes are either sessile or 

 wanting. The two fore-legs are very long, and resemble antennje. The upper side of the 

 body is like a scale, without distinct articulations. Acarus marginatus, and A. testudi- 

 nariits, Hermann. 



Trogidus, Latr., has the anterior extremity of the body projecting like a clypeus, receiving, 

 in a cavity on its under-side, the chehceras and other parts of the mouth. The body is very 

 flat, and covered by a very firm skin. It is found beneath stones. T. nepaformis, Latr. 

 Phal. tricarinatum, Linn. South of France. 



fAL Dufour has described a genus allied to the last under the name of Cceculus, in the 

 Annales des Sci. M'at. for 1S32. Many other very curious Brazilian species are described and figured by Perty, in 

 the Delectus Animalium Bra-nlia, in which many new genera are proposed for their reception. Another very 

 singular species, with exceedingly long legs, is described by Mr. Hope, in the Linncean Transactions, vol. xvii., 

 under the name of Dolichoscelis Uaworthii.] 



The second tribe of the Arachnida holetra is that of the Acarides, which has occasionally chelicerae, 

 but they are simply composed of a single pincer, either didactyle or clawed, and hidden in a sternal 

 lip. Sometimes there is a sucker, formed of lancet-like plates united together ; or the mouth consists 

 merely of a cavity, without any other apparent pieces. This tribe is composed of the genus 



Acarus (Linn.), — 

 The majority of the species of which are very minute, or almost microscopical. They are universally dis- 

 tributed. Some are wanderers ; and, amongst tliese, some are found under stones, leaves, the bark of trees, 

 in the ground, the water, or upon provisions, such as flour, dried meat, old dry cheese, and upon putrid 

 animal matters. Others subsist as parasites upon the skin, and in the flesh of difl'erent animals, often 

 greatly weakening them by their excessive multiplication. The origin of certain diseases, especially the 

 itch, is attributed to them. It appears, from the experiments of Dr. Galet, that the Mites of the human 

 psora, placed upon the body of a perfectly healthy individual, will inoculate him with the serus of that 

 disorder. Other sorts of mites are also foimd upon insects ; and many beetles, which subsist upon 

 cadaverous substances or excrement, are often entirely covered with them. They have even been ob- 

 served in the brain and eyes of Man. The Mites are oviparous, and exceedingly prolific. Many of them 

 are born with only six feet, and the two others are developed a short time afterwards. The tarsi are 



• Tromhidium lutigipes, Herm., is 6gurcd with ten legs, the anterior being very long, but it li described an haviug only eight. 



