134 INSECTS. 



or maxillae, and two lip-feelers, or labial palpi (c). 

 The eyes consist of a group of ocelli on each side (e) . 

 The body is protected by alternately larger and smaller 

 dorsal plates, which are fifteen in number; and there are 

 fifteen pairs of legs, which are terminated by a single 

 claw. On the sides of the body will be found some 

 oval dark-looking bodies, fringed with hairs; these 

 are the spir'acles (spirac'ulum, a breathing-hole) or 

 breathing-pores. They form the orifices of certain 

 branched and transversely striated tubes, which are 

 distributed throughout the body ; the tubes are called 

 tracheae (trachea, the windpipe), and their walls con- 

 tain an elastic spiral fibre which keeps them open. 

 These parts of the insect can only be distinctly seen 

 when the body has been slit up on the under side ; 

 and, after washing away the animal matter with water 

 by the aid of a hair pencil, pressed between two slides 

 with a clip, dried, soaked in turpentine, and mounted 

 in balsam. 



THYSAN^JRA (Ovaavoi,, fringe, ovpa, tail). The in- 

 sects belonging to the genus Podura, of this Order, are 

 very minute and difficult to examine ; but they are 

 specially interesting, on account of the structure of 

 their scales. They are common in gardens and 

 cellars, under flower-pots, &c., and are about one-tenth 

 of an inch long. They are of a brownish or silvery- 

 leaden colour, wingless, with six legs, and when 

 touched they leap like a flea. The leaping motion is 

 produced by the action of the tail, which is forked 

 and bent under the body. 



The body is usually covered with minute scales 

 (PI. X. fig. 19, #, c), and these are used as test-objects. 

 The structure of the scales varies in the different 

 genera and species; those usually used (fig. 19 #) are 

 stated to belong to Podura plum'bea- it appears, 

 however, that this is not correct. The scales sold as 

 test-objects under this name are covered with minute 

 and short raised lines (fig. 190), arranged in irregular 



