THYSANOURA. 337 



LEPISMA, Linnceus. 



The body of these animals is elongated and covered with small scales, 

 frequently silvery and brilliant, from which circum- 

 stance the most common species has been compared 

 to a little fish. The antennae are setaceous and usually 

 very long. The feet are short, and frequently have 

 very large and strongly compressed coxae resembling 

 scales. 



Several species conceal themselves in the cracks and in the frame work of 

 windows, under damp boards, in wardrobes, &c. Others retire under stones. 



These insects run with great velocity; some of them by means of their 

 caudal appendages are enabled to leap. They are divided into two subgenera, 

 MACHIMS, Lat., and LEPISMA, Lin. 



FAMILY II. 



PODURELL^;, Lalreille. 



ANTENNAE quadriarticulated ; no distinct or salient palpi ; abdomen termi- 

 nated by a forked tail folded under the venter when at rest, and used for 

 leaping. The Podurellae form but one genus in the Linnaean system. 



PODUBA, Linnaeus. 



These insects are very small, soft, and elongated, with an oval head and two 

 eyes, each composed of eight granules. Their legs have but four distinct 

 joints. The tail is soft, flexible, and formed of an inferior piece, moveable at 

 base ; to the extremity of which are articulated two appendages susceptible of 

 being approximated, separated, or crossed they are the teeth of the fork. 

 They have the faculty of elevating their tail, and then forcing it suddenly 

 against the plane of position, as if they let go a spring, thus raising themselves 

 into the air, and even leaping like the Pulices, but to a less height. They 

 usually fall on their back, with their tail extended posteriorly. The middle 

 of the venter exhibits a raised oval portion divided by a slit 



Some keep on trees and plants, under old pieces of bark, or stones; others 

 on the surface of stagnant waters, and sometimes on that of snow during a 

 thaw. Several unite in numerous societies on the ground, and at a distance 

 resemble little heaps of gunpowder. We divide them into PODUBA and 

 SMYNTHUBUS, Lat.: the former having the antennae equal, and without 

 annuli or little joints to the last segment, embracing the P. arborea, P. nivalis, 

 &c.; the latter having the antennae more slender near the extremity, and 

 terminated by an annulated piece composed of little joints, to which belongs 

 the P. atra P. viridis, &c. 



