THE THYSANURA. 423 



The third order of the Ametabola, that of the 



THYSANURA*, 



contains no parasitic species. Its members are fur- 

 nished, like those of the preceding group, with a re- 

 gular biting mouth, but they are distinguished from 

 these by the possession of bristle-like appendages at 

 the tail, by the agency of which they are enabled to 

 spring with considerable agility. Their bodies are 

 of a soft texture, and their skins are covered with 

 delicate hairs and minute scales. The latter exhibit a 

 beautiful metallic lustre, due to the presence of nume- 

 rous fine longitudinal lines upon their surface ; these 

 are clearly perceptible only under a high magnifying 

 power, and the scales of some species are amongst 

 the most delicate microscopic test-objects. 



The Podura plumbea, a very common species of this 

 group, may be found at almost all seasons, amongst 

 dead leaves in damp places in woods. It is about an 

 eighth of an inch in length, and covered with minute 

 lead-coloured scales ; the head bears a pair of four- 

 jointed antennae, of moderate length, and on each 

 side six or eight simple eyes ; the thorax is provided 

 with three pairs of legs, and the caudal extremity of 

 the abdomen with a long, forked appendage, which is 

 bent under the belly in repose. It is by the sudden 

 extension of the latter that these little creatures are 

 enabled to execute their vigorous leaps, which although 

 doubtless intended to facilitate their escape from 

 danger, only serve to betray their presence to the eyes 

 of the entomologist when he is rummaging about 

 amongst the leaves. Dead leaves and moss are not, 

 however, the only localities in which these curious 

 * Gr. thusanos, a fringe ; oura, a tail. 



