ORDERS OF INSECTS. 55 



the first place to have recourse to the presence or 

 absence of a metamorphosis in order to separate those 

 small orders of Insects the members of which never 

 undergo any change^ from those in which the occur- 

 rence of a metamorphosis is a rule^ although liable to 

 a few exceptions. We thus get two very unequal 

 groups of Insects, — the Metabola, or Insects with a 

 metamorphosis of some kind, and the Ametabola, or 

 Insects without a metamorphosis. The former are 

 then divided into two primary groups, according to 

 the structure of the mouth. 



In the first of these groups, called the Mandi- 

 BULATA, the organs of the mouth, or some of them, 

 present the regular biting form, although in some 

 cases a portion of the organs is adapted for sucking 

 up fluid nourishment. The Mandibulata form four 

 principal orders, the characters of which are briefly 

 as follows : — 



In the CoLEOPTERA, or Beetles, the anterior wings 

 are converted into horny cases (elytra) which meet in 

 a straight line along the back of the insect, and serve 

 to cover and protect the delicate membranous poste- 

 rior wings, the true organs of flight, when these are 

 not in use. The wings are folded up on the back of 

 the insect, and as they are usually a good deal longer 

 than the elytra, they are folded back upon themselves 

 at the extremity so as to get them into the smallest 

 possible compass. The Beetles undergo a complete 

 metamorphosis. 



In the Orthoptera, the anterior wings still form 

 sheaths for the protection of the more delicate hinder 

 pair, but their texture, instead of being horny, is 

 usually leathery ; the posterior wings, as in the Beetles, 

 are much larger than the anterior, but their nervures 



