2o6 The Orders of Insects 



ORDER II.— COLEOPTERA. 



Structure. — The Beetles make up a very natural 

 and distinct order of insects, characterised by the 

 horny or leathery texture of their forewings which 

 serve as cases (elytra) for the folding membranous 

 hindwings alone used in flight. (The recently proposed 

 identification of the elytra of beetles with the tegulae 

 of Hymenoptera (15) rests on insufficient evidence.) 

 The head is usually extended from behind forwards, 

 having therefore a large crown and a small face ; the 

 feelers are very inconstant in form ; the number of seg- 

 ments may vary from thirteen to one. The mandibles 

 are always developed as strong biting jaws ; the first 

 maxillae are of the typical form displaying the parts 

 recognisable in the Orthoptera and lower orders ; the 

 second maxillae are reduced and fused together basally 

 in a very complete way to form the lower lip. In the 

 fore-body the prothorax is free and movable ; it& 

 tergite (pronotum) is a very prominent feature in all 

 beetles, reaching back to the origin of the elytra. 

 The scutellum of the mesothorax is sometimes visible 

 as a triangular plate between the bases of the elytra. 

 The parts of the ventral exoskeleton are well developed, 

 sternum, and paired episterna and epimera being usually 

 recognisable in all three segments. The legs vary 

 greatly in form according to the insects' manner of 

 life ; the number of segments in the foot may be 

 two, three, four or five. The hard forewings, when 

 closed, usually cover the whole hind-body. They 

 are strengthened with ridges around their edges, and 

 marked with a series of longitudinal furrows (stria) 

 and often also with impressed dots (punctures). The 

 hindwings are sometimes very small or wanting ; in 

 such cases the elytra are often fused together along 

 their middle edges (suture). The hindwings when 



