THYSANOURA. 357 



range of movable appendages, in the form of false feet; abdomen 

 terminated by articulated setae, three of which are the most remark- 

 able; body always covered with small shining scales. 

 It comprises but one genus, the 



Lepisma, Lin. 

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

 frequently silvery and brilliant, from which cii'cumstance 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 cox<e resembling scales. 



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

 windows, under damp boards, in wardi-obes, &c. Others retire under stones. 



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

 caudal appendages ai'e enabled to leap. They are divided into two sub- 

 genera, Maciiius, Lat. and Lepisma, Lin. 



FAMILY II. 



PODURELL-^, Lat. 



Antennae quadriarticulated; no distinct or salient palpi: abdomen 

 terminated by a forked tail folded under the venter when at rest, and 

 used for leaping. The Podurelte form but one genus in the Lin- 

 nasan system. 



PoDURA, Lin. 



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, movable 

 at base; to the extremity of which are articulated two appendages suscepti- 

 ble 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 rais- 

 ing 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 poste- 

 riorly. 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 



