Vlll INTRODUCTION. 



the perfect insect is covered by an integument, which is finally 

 shed. This condition is called the pupa, during which the animal 

 is sometimes active, and sometimes inactive. The three thoracic 

 segments are in the perfect insect either similar (except that the 

 middle and posterior ones bear the wings) or agglutinated, or the 

 anterior one, or prothorax, is freely movable, and the other two 

 closely connected with each other and with the abdomen. The 

 parts of the mouth are also modified in form, so that the mandi- 

 bles and maxilla? are either free moving lateral organs fitted for 

 mastication and prehension, or are elongated, forming a sucking 

 tube. In the former case the mouth is said to be mandibulate, 

 in the latter haustellate. The wings are also of various structure. 



The embryological studies of insects are as yet not sufficiently 

 progressed to enable us to subordinate these complications of 

 structure, in such manner as to determine which 'forms are higher 

 and which lower. We can merely state in general terms that 

 those having a perfect metamorphosis are the highest ; and those 

 having the thoracic segments agglutinated, or the prothorax 

 separate, are to be considered above those in which the larval 

 character of similarity among the thoracic segments is preserved. 



By a parity of reasoning, those orders in which the appendages 

 of the thoracic organs (the wings) are remarkably different in 

 form must be considered as higher than the most nearly allied 

 forms in which they are similar. 



The sub-class therefore divides into orders as follows : — 



§ Metamorphosis distinct ; wings usually present ; 

 Pupa inactive ; 



Mouth mandibulate ; 



Prothorax free ; anterior wings corneous. I. Coleoptera. 



Thorax agglutinate ; wings 4, membranous ; posterior ones smaller. 



II. Hymenoptera. 

 Mouth haustellate ; thorax agglutinate ; 



Anterior wings membranous, posterior abortive. III. Diptera. 



Wings 4, membranous, usually covered with scales. 



IV. Lepidoptera. 

 Pupa variable, sometimes active,* sometimes inactive ; thorax variable ; 

 mouth mandibulate ; wings 4, membranous, nearly equal. 



V. Neuroptera. 



#~ 

 * Those having an active pupa (Biomorphotica, Westwood) are now 



called Pseudoneuroptera, and are united by some authors with Orthoptera, 



with which, however, they appear to have but little affinity. The habits. 



as observed to me by Baron 11. Osten Sacken, are quite different, the 



