207 



ORDER XL MALLOPHAGA. 



802. BESIDES the true Lice belonging to the preceding Order, 

 in which the mouth is adapted for suction, there is a consider- 

 able number of parasitic Insects which principally live upon the 

 bodies of Birds, in which the oral organs retain a mandibulate 

 and biting structure. Like the Anoplura, these Insects, which 

 are commonly known as Bird-lice, usually infest only a single 

 species of Bird ; and as the number of the latter is much greater 

 than that of the Mammalia, and most of them are subject to be 

 attacked by these creatures, the numbers of these parasites are 

 very considerable. They do not, however, feed upon the blood 

 of their hosts, but devour the most delicate parts of the feathers. 

 The species which are parasitic upon Mammalia feed upon the 

 finest parts of the hairy covering of these animals^ 



ORDER XII.-THYSANOURA. 



803. 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 LKPISMID^E, the abdomen is fur- 

 nished on each side with a row of moveable appendages, like 



