THE HIDDEN TYPE OF WING-GROWTH 99 



(Coleoptera) indicates the transformation of the forewings 

 into firm, hard sheaths (elytra, Fig. 56 g) beneath which the 

 delicate, membranous hindwings can be folded and protected 

 when not in use for flight ; in many beetles indeed the hind- 

 wings are so poorly developed as to be useless ; such never 

 fly at all and their strong, horny forewings (elytra) have 

 become a kind of armoured deck, roofing over the hind-body. 

 Beetles have jaws adapted for biting ; the mandibles and 

 maxillae are essentially like those of a grasshopper, but the 

 appendages which form the labium (Fig. 54) are much more 

 intimately joined together than in the latter, so that the two 

 inner lobes (laciniae) form a median process (ligula} while the 

 outer lobes (galeae) are small and inconspicuous. Beetles are 

 remarkable for the elaboration of their exoskeleton, the various 



FIG. 54- LABIUM OF A GROUND BEETLE 



m, mentum ; /, ligula (united laciniae) ; g, galea ; p, palp, x 8. 



sclerites of which, generally firm and rigid, are precisely fitted 

 together, so that the whole insect may be described as parti- 

 cularly well-armoured. 



When describing in the preceding chapter (pp. 91-7) the life- 

 history of mayflies, the likeness of the mayfly larva to a 

 thysanuran or bristle-tail was pointed out. From the name 

 (Campodea) of a common bristle-tail has been derived the 

 term campodeiform 1 often applied to such elongate, well- 

 armoured larvae, with comparatively long feelers and legs, 

 often provided with a pair of tail-feelers (cerci) at the hinder 

 end of the body. Examples of campodeiform larvae are 

 afforded by several families of beetles. We may take in the 

 first place the grub of a ground-beetle (Carabid). This larva 

 (Fig. 55) which, like its parent-beetle, usually feeds on small 



1 F. Brauer : " Betrachtung iiber die Verwandlung der Insekten ". 

 Verhandl. K. K. Zool-bot. Gesellsch. Wien., XIX. 1869. J. Lubbock : " The 

 Origin and Metamorphosis of Insects ". London, 1874. 



