236 HEMIPTERA-HOMOPTERA. 



there being little difference between the larva, pupa, and imago 

 in many genera. The pupse are always active except in the 

 Scales and Snow-flies. The larva, which also resembles to a 

 certain extent the adult, moults its skin several times, and then, 

 if it is destined to become a winged form, it develops rudiments 

 of wings as small bud-like lateral outgTowths on each side of 

 the thorax, the pupal stage, which after a time casts its skin 

 and becomes the adult (vide fig. 126). The ova of the Hemiptera 

 are often beautifully sculptured bodies. Many of this order are 

 extremely injurious, such as the Aphides or Plant-lice, many 

 of the " Bugs " {Heteroptera) and Scale insects (Coccidce). There 

 are generally considered to be three groups of Hemiptera, as 

 follows : — 



1. Homoptera (fig. 121), wings always clear and membranous 



when present, and the rostrum attached to frontal 

 region of 'heiaA = Aphididce, Coccidce, and Cieadidce. 



2. Hetefivptera (fig. 126), wings half leathery at the base, 



membranous at the tips, and the rostrum springing 

 from beneath the head = the Bugs (Meduviidce, 

 Lygceidm, Oimicidce, &c.) 



3. Anoplura, which are all devoid of wings and parasitic = 



Pedieulidce or Lice. 



The Homoptera contain the most injurious species of this 

 order. They are best exemplified by the Plant -lice and the 

 Scale Insects. 



Plant-lice (Aphimd*). 



Plant-lice are amongst the worst enemies the farmer and 

 gardener has to contend with. They live entirely upon the 

 sap of plants, which they draw from the leaves, stem, and 

 even roots. The structure of an Aphis is very simple. The 

 body is usually plump, and has two tubes called " honey-tubes " 

 or " cornicles " on the back towards the tail. Out of these is 

 passed a gummy liquid, the " honey dew," which falls upon the 



