THYSANOURA. 487 



THE FIRST FAMILY OF THE THYSANOURA,— 

 Lepismen^, Latr., 

 Has the antennae like threads, and divided, from the base, into a great number of minute joints; palpi 

 very distinct and exposed ; the abdomen furnished on eacli side, beneath, with a row of moveable 

 appendages, like false legs, and terminated by articulated seta;, of which three are more remarkable ; 

 and the body is clothed with minute, shining scales. It composes the single genus 



Lepisma, Linn., — 

 Which has the body elongated, and covered with small scales, silvery and shining, whence the most 

 common species has been compared to a small fish. The antennae are setaceous, and often very long. 

 The mouth is composed of a labrum, two nearly membranous mandibles, two maxillje, with two divi- 

 sions, having a 5 or 6-jointed palpus, and a labium with four divisions, bearing two 4-jointed palpi. 

 The thorax is composed of three segments. The abdomen, which is gradually narrowed towards its 

 posterior extremity, has, at the sides, a row of small appendages arising from a short joint, and termi- 

 nated in setose ])oints : the posterior are the longest. A kind of scaly style, compressed, and formed sf 

 two pieces, arises from the anus ; then follow three articulated seta;, which extend beyond the body. 

 The legs are short, ^N-ith the coxae often very large, and strongly compressed and scale- like. 



Many species hide themselves in the crevices of sashes which remain closed, or are but rarely opened, 

 under damp boards, in wardrobes, &c. Others lie hidden under stones. 



Machilis, Latr. (Petrobhts, Leach), has the eyes very much facetted, 

 nearly contig-uous, and occupying- nearly all the head ; the body convex, 

 ^tejB^^^Eir arched above ; the abdomen terminated by small threads fitted for leaping, 



the middle one placed above the other two, being much longer than 

 them. They leap very well, and frequent stony places. The species 

 are entirely European. Lepisma polypoda, Linn., &c. ; Petvobius mari- 



tijj. 47.— Machilis polj-poda. j. t , 



timus, Leach. 

 Lepisma, Linn. (Forbicina,GeoS.), has the eyes very small, wide apart, composed of a small number of grains ; 

 the body flat, and terminated by three threads of equal length, inserted in the same line, and not fitted for leaping; 

 the coxa; very large. The majority of the species are found in the interior of houses. Lep. saccharina, Linn., 

 four lines long, of a leaden, silvery colour, without spots, said to be a native of America, and other species. 



THE SECOND FAMILY OF THE THYSANOURA,- 



PoDUREiiL^, Latr., — 



Have the antennae composed of four joints ; the mouth not exhibiting distinct and exserted palpi, and 



of whicli the abdomen is terminated by a furcate tail, applied; in inaction, against the belly, and used 



in leaping. These, also, only form the single genus 



PoDURA, Linn. 



These insects are very small, soft, elongated, with the liead oval, and two eyes, each formed of eight 

 minute tubercles. The legs have only four distinct joints. The tail is soft, flexible, and composed of 

 a basal piece, moveable at its insertion, and terminated by two branches forming the prongs of the fork, 

 which are capable of opening and shutting. They can unfold their tail, striking it with force against 

 the plane of position, and thus raising themselves into the air, and leaping like the Fleas, but to a more 

 moderate height. 



Some species are found upon trees and plants, or beneath bark or stones, and sometimes upon the 

 snow itself, at the time of a thaw. Many species unite into numerous societies, upon the earth, in 

 sandy paths, and resemble, at a distance, a small quantity of gunpowder. The propagation of some 

 species appears to take place in the winter. 



Podtira, Linn., has the antenna; of equal thickness throughout, without minute 

 joints at the tip ; the body is linear or cylindrical, with the thorax distinctly articu- 

 lated, and the abdomen narrow and oblong. Podura arborea, Linn.; P. aquatica, 

 Linn., &c. 



Smi/nthurus, Latr., has the antenna; slenderer at the tip, and terminated by an 

 annulated joint ; the thorax and abdomen form a globular or oval mass. Podura 

 atra, Linn., &c. ■■'« '•'*-'''""• 



