144 CLASS INSECTA. 



antennae are in the form of bristles, and usually very long. 

 The mouth is composed of a lip (labrum), of two mandibles, 

 almost membranous, of two jaws with two divisions, with a 

 palpus of from five to six articulations, and a lip with four 

 sections, and bearing two palpi with four articulations. The 

 thorax is of three pieces ; the abdomen, which is contracted 

 by little and little towards its posterior extremity, has, 

 along each side of the belly, a range of small appendages 

 supported on a short articulation, and terminating in silken 

 points. The last are the longest. From the anus issues a 

 sort of scaly stylet, compressed, and consisting of two pieces. 

 Then come the three articulated bristles, which are prolonged 

 beyond the body. The feet are short, and often have very 

 large haunches, strongly compressed, and in the form of 

 scales. 



Many species conceal themselves in the clefts of window- 

 frames which are seldom opened, or always closed ; under 

 planks which are somewhat moist ; in presses, &c. Others 

 live retired under stones. 



These insects run very fast : some of them leap by means 

 of the threads of their tail. 



Two subgenera have been formed of them — 



Machilts, Lat., Petrobius, Leach, 



whose eyes are very much composed, almost contiguous, and 

 occupy the major portion of the head. They have the body 

 convex, and arched above, and the abdomen terminated by 

 small threads, proper for leaping, and of which the middle 

 one, placed above the other two, is by far the longest. 



The maxillary palpi are very large, and in the form of 

 small feet ; the thorax is contracted centrally, and its first 

 segment is smaller than the second, and vaulted. 



These insects leap remarkably well, and frequent stony 



