ORDERS OF INSECTS. 57 



of fluid nourishment, they are hence called HAUS- 

 TELLATA or Sucking Insects. They form three prin- 

 cipal orders. 



The LEPIDOPTERA, forming the first of these, are 

 characterized by the possession of a spiral trunk 

 formed by a modification of the maxillae; they are 

 usually furnished with four large membranous wings, 

 the surface of which is more or less clothed with 

 delicate scales. Their metamorphosis is complete. 

 . In the DIPTERA, the mouth consists of a short and 

 usually fleshy proboscis (the labium), enclosing from 

 one to six bristles, the representatives of the other 

 parts of the mouth ; these insects are readily distin- 

 guished by the possession of only a single pair of 

 wings, behind the insertion of which we find a pair of 

 knobbed filaments (halteres) which are considered to 

 represent the hinder wings. Their metamorphosis is 

 also complete. 



Lastly, the series of Metabolous Insects is closed by 

 the B/HYNCHOTA, in which the labium forms a jointed 

 rostrum, enclosing four bristles representing the man- 

 dibles and maxillae ; the anterior wings are usually of 

 a firmer texture than the hinder ones, which in most 

 cases are folded up beneath them. The metamor- 

 phosis of the Rhynchota is incomplete. 



In addition to these, the Haustellate section of In- 

 sects includes a fourth small order, that of the APHA- 

 NIPTERA, including only the different kinds of Fleas ; 

 this group may be arranged close to the Dipt era. 



The Ametabolous insects are also divided into three 

 orders : of these, the ANOPLURA, or Lice, have a suc- 

 torial mouth ; the MALLOPHAGA, or Bird-lice, have a 

 biting mouth, and the extremity of the abdomen 

 destitute of any appendages ; whilst the THYSANURA, 



D5 



