140 



INSECTS OR HEXAPOUA. 



insects are distinctly beneficial by destroying other noxious 

 insects (Chalcididaj, Coccinellidse), and a few are of no incon- 

 siderable commercial value (silkworms, cochineal, honey-bee, 

 lac insects). 



Insects commence their life in most cases as eggs or ova 

 produced by a female. Sonje have the power of bringing forth 

 living young (viviparous), as we shall see takes place in the 

 Plant Lice (Aphididse, &c.) In insects the ovum gives rise 

 to a larva : this state is the period during which the insect 

 grows. Larvae of insects are known also as maggots, grubs, 

 caterpillars, and false-caterpillars. CaterpiUar is a term applied 



A, Geometer larva ; 



Fl(i. 64. — Laev.'E 'IF Insects. 

 SawHy larva ; o, typical Lepidopterous larva ; 



larva of 



to coloured, often hairy larvae, provided with six true legs and 

 generally with four pairs of prolegs or sucker feet, in addition 

 to the anal proleg (fig. 64, c). The number of these mid 

 prolegs is .sometimes reduced to two or four (Geometridae and 

 Plusiadae), (a and d). These fleshy prolegs enable the cater- 

 pillars to hold on to the vegetation they are feeding upon. 

 False-caterpillars are the larvse of the Sawflies {Tentliredinidiv) ; 

 they have more than four pairs of central sucker feet — usually 

 the legs number twenty-two in all (b). Magyofs are legless, 

 fleshy larvse of the Diptera or Two-wiiigod Mies ; often dirty- 

 white in colour, and tapering to a point in front, blunt at the 

 tail end. Some have a distinct head (Tipulid larva?), others 



