242 MANUAL OF ZOOLOGY. 



phosis. The Insects which come under the first head (viz. 

 Ametabold] are not furnished with wings in the adult condition, 

 and the three orders which compose this section are com- 

 monly grouped together under the name Aptera. By some, 

 however, this division is entirely rejected, and the three orders 

 in question are placed amongst the Hemimctabola, or even 

 grouped with the Myriapoda. 



SUB-CLASS I. AMETABOLA. Young not passing through a 

 metamorphosis, and differing from the adult in size only. Imago 

 destitute of wings ; eyes simple, sometimes wanting. 



ORDER I. ANOPLURA. Minute Aptera, in which the mouth 

 is formed for suction ; and there are two simple eyes, or none. 

 This order comprises insects which are commonly parasitic 

 upon man and other animals, and are known as Lice (Pediculi]. 

 The common Louse is furnished with a simple eye, or ocellus, 

 on each side of a distinctly differentiated head, the under sur- 

 face of which bears a suctorial mouth. There is little distinc- 

 tion between the thorax and abdomen, but the segments of 

 the former carry three pairs of legs. The young pass through 

 no metamorphosis, and their multiplication is extremely rapid. 

 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 commonly 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 Podura, or 

 " Spring-tails," which are characterised by the possession of a 

 forked caudal appendage, by the extension of which consider- 

 able leaps can be effected. In the nearly allied Lepismce loco- 

 motion 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; 

 the larva differing from the imago chiefly in the absence of wings, 

 and in size; pupa usually active, or, if quiescent, capable of 

 movement* 



* The Coccidce, amongst the Hemiptera, undergo a complete metamor- 

 phosis. In certain of the Hemiptera and Orthoptera the adult is apterous, 



