-ANNULOSA : INSECTA. 217 



ORDER II. MALLOPHAGA. Minute Aptera, in which the 

 mouth is formed for biting, and is furnished with mandibles and 

 maxillae. 



The members of this order are cemmonly known as * Bird- 

 lice,' being parasitic, sometimes upon Mammals, but mostly 

 upon Birds. They strongly resemble the Pediculi, but the 

 mouth is formed for biting, to suit their mode of life ; since 

 they do not live upon the juices of their hosts, but upon the 

 more delicate tegumentary appendages. 



ORDER III. THYSANURA. Apterous insects, usually with a 

 masticatory mouth, and having the extremity of the abdomen 

 furnished with locomotive appendages. 



The most familiar members of this order are the Podurce, or 



Fig. 63. Thysanura. Podura, without scales, enlarged. 



' Spring-tails ' (fig. 63), which are characterised by the pos- 

 session of a forked caudal appendage, by the extension of 

 which considerable leaps can be effected. In the nearly allied 

 Lepismcp, locomotion is assisted by caudal bristles. In both, 

 the body is covered with hairs or scales, the structure of the 

 latter being often very beautiful. 



SUB-CLASS II. HEMIMETABOLA. Metamorphosis incomplete; 



