LOUSE-TRIBE. THYSANOTJRA. LEPISMID^E. 



207 



The number of species is very considerable ; for it would appear 

 that almost every quadruped and bird has a kind almost peculiar 

 to itself, the same Louse not being found upon different animals, 

 except upon such as have analogous characters and habits ; 

 whilst one animal frequently supports two or more species of 

 these parasites. 



ORDER XI. THYSANOURA. 



737. IN the Insects of this Order, which resembles the 

 preceding in neither having wings, nor undergoing metamor- 

 phosis, there is a remarkable diversity of structure, especially 

 in regard to the mouth. Some of them possess as complex a 

 buccal apparatus as the Mandibulate Insects ; whilst in others 

 there is scarcely a perceptible opening. The same is the case 

 with regard to the eyes; these organs 

 being fully developed in some, and almost 

 rudimentary in others. The Order 

 contains two families. In the first, the 

 LEPISMID^E, the abdomen is furnished 

 on each side with a row of moveable 

 appendages, like false legs ; and is termi- 

 nated by long pointed bristles, of which 

 three are usually most remarkable. 

 The Machilis has long antennas, consist- 

 ing of a great number of joints ; its palpi 

 also are very large; and its eyes are 

 composed of numerous facets, and occupy 

 nearly the whole head. It frequents 

 stony places, and leaps well with the aid 

 of the appendages to the tail. The 

 Lepisma, of which one species is known 

 under the name of the Sugar Louse, from 

 its aspect and habits, has the eyes very 

 small, composed of few facets, and wide 

 apart ; its body is flat, and is terminated 

 by three threads of equal length, not fitted to assist in leaping. 



FIG; 433. MACHILIS. 



