248 



ARTHllOPODA 



[CH. 



of the body are said to aid in the process. Many Insects however, 

 such as the Dragon-flies, Plant-lice, Butterflies, Moths, Flies, Bees 

 and numerous others, do not fold up their wings but either bear 

 them erect or lying depressed on the body In some cases the 

 wings are quite transparent, but in the Moths and Butterflies they 

 are covered with a dense fur of flattened scales which can readily 

 be brushed off as a. fine powder or dust (Fig. 104). It is these scales 

 which give rise to the beautiful and in some cases gorgeous colouring 

 of the Lepidoptera. 



Fia. 101. A Male Cockchafer, Melolontha vulgaris, seen from above and 

 slightly enlarged. After Vogt and Yung. 



1. Head, stretched forward. 2. Pro thorax. 3. Mesothorax, 



4. Metathorax. 5. Abdomen. 6. Anterior wing (elytron) of right 

 side, turned forward. 7. Posterior wing of right side, expanded. 



8. Maxillary palps. 9. Femur of third right leg. 10. Tibia of 



third right leg. 11. Tarsus of third right leg. 



Two pairs of wings are present as a rule, but the order Diptera 

 has only the anterior pair, the hind wings being replaced by certain 

 stalked structures called balancers or halteres. In the Hymeno- 

 ptera, the two wings of each side are clamped together by means of 

 hooks on the hind wing which fit into a ridge on- the hinder edge 

 of the front wing (Figs. 108, 109, and 110) The two wings of each 

 side thus move as one. It is not uncommon to find isolated 

 species in which the wings are not developed, for instance, the 

 females of many Plant-lice and some Moths ; while Fleas, which 

 used to be placed amongst or near the order Diptera, which now 

 are classed by themselves as Siphonaptera, never possess wings, 

 though their absence is compensated for by a special development 

 of the powers of jumping. 



