HIGH SCHOOL ZOOLOGY. 215 



with adaptation to habits of life chai'acteristic for each species. 

 Thus we have the carnivorous Carabidce, running forms often 

 destitute of the hind wings, the allied aquatic water-beetles, 

 Dytiscidce, and scavenger forms like the Sylphidce and Stajjhy- 

 linidce, several of the latter being always found in ants' nests, 

 and presenting curious instances of dependence upon their hosts. 

 Destructive household-pests like the Dermestidce (which attack 

 furniture, carpets, museum specimens, etc.), are amongst the 

 smallest of the order, while the Scarahceidce, along with a number 

 of familiar phytophagous forms like the May-beetle {Lachno- 

 sterna), include some tropical giants — Dynastes — which may 

 attain a length of 5 or 6 inches. The fire-flies {Lavipyridce) are 

 sufficiently marked by the luminous organs on the abdomen, 

 the weevils (Ctirculionidce) by the prolongation of the head into a 

 sort of proboscis, the bark-Vjeetles (^Bostrychidce) by the character- 

 istic channels which they hollow out in trees. Several of the 

 leaf-eating forms (^Chrysomelidte), like the potato-beetle {Dory- 

 fliwa decemlineata), are familiar, and the lady-birds {Coccinel- 

 lidce), which feed on plant-lice, attract attention as well by their 

 form as by their colouration. 



33. In the two next orders of insects, Diptera and Lepido- 

 ptera, the mouth-j^arts are formed for sucking, but this conver- 

 sion is carried out in different ways in the two gi"oups. In the 

 former the labrum and the labium form an unjointed double 

 tube, in which stylets formed of the mandibles, maxillae, and 

 hypopharynx are contained (Fig, 146, i ). In the Lepidoptera on 

 the other hand, it is the maxillae which by their apposition 

 form the sucking proboscis (Fig. 146, s) ; the maxillaiy palps 

 are rarely well developed, while the labial palps are. The 

 Diptera receive their name on account of the apparent absence 

 of the postex'ior wings, which are converted into balancei's — 

 halteres ; the Lepidoptera, theirs, from the presence of scales 

 (which are generally coloured) on the wings. 



