EVIDENCES— GEOLOGY 



139 



formed of the labium fin bugs 

 and flies) or a more or less com- 

 plete tube formed of the maxillae 

 (butterflies and moths ; the honey- 

 bee) in which other modified parts 

 may slide back and forth. The 

 long, slender, bristle-like mandi- 

 bles and maxillae operate in this 

 way in the bugs (Fig. 78). In the 

 flies a similar modification occurs. 



In both 

 orders the 



Labrum 



_.Mandlble 



f „ , Glossae or lleula 

 f Galea : , , , , 



SLuclnia i labial palp 



Stipes. •• 



Maxillary 



palp 



Paraglossa 



Cardo A V ^""^^ maxilla 



MentumVT' V/"Submentum 

 Second maxUlffi 



slender Fig. 77.- 



parts may 



roach. 



-The mouthparts of a cock- 

 (From Hegner, after Kerr.) 



be developed into sharp piercing organs. 

 The maxillae of butterflies form a closed 

 tube through which liquids are drawn by 

 muscular suction. In the honey-bee they 

 form a partial sheath for the hairy ligula, 

 a slender part of the labium, which slides 

 back and forth between them and raises 

 liquids to the mouth. 



The Wings. Some of the primitive an- 

 cestors of the insects had two pairs of 

 well developed wings on the second and 

 third thoracic segments and a pair of broad 

 lobes on the prothorax which appear to 

 have been rudimentary or vestigial wings 

 (Fig. 79A). In the existing species the pro- 

 thorax has no trace of wings but the persist- 

 ing wings of the remaining divisions supply 

 some of the finest evidences of evolution. 

 They vary in texture from thin membranous 

 structures with heavier supporting veins to 

 heavy chitinous shields, in some cases so 

 hard that they must be drilled before a 

 stock's Introduction to pin oan be passed through the insect. In 

 Entomology, with per- gome insects they are reduced to two, usu- 

 ITpubLhin'gS™: S'lly *c anterior pair (Fig. 80). Otlier 

 pany.) 



Fig. 78. — Last segment 

 of the beak of Letho- 

 cerus, a bug. md, man- 

 dibular setae; mx, max- 

 illary setae; t, tactile 

 hairs. (From Com 



insects have lost them entirely. 



