18 



INSECTS AFFECTING VEGETATION 



At the present time we use the term insect only for those articu- 

 lates that possess six legs, and that have their external skeleton appar- 

 ently composed of thirteen joints or rings, which are grouped into 

 three regions, viz : the head, thorax and abdomen. The true insects, 

 or hexapoda, (six-feet) undergo a more or less complete meta- 

 morphosis, possess in the adult stage wings, and breathe through a 

 peculiar respiratory system with external openings termed spiracles. 

 All insects are developed from eggs, with a few apparent exceptions ; 

 plant lice, for instance, reproduce both by eggs and by budding. 

 The body of an adult insect is divided into three regions, each with 

 peculiar functions. The head contains the organs of vision (com- 

 pound eyes and simple eyes), the jointed antenna3 or feelers, which 

 are the principal organs of touch, smell and hearing, and the mouth- 

 parts, organs of taste and feeding. The thorax contains the organs 

 of locomotion the three pairs of legs and two pairs of wings. The 

 abdomen contains the organs of digestion, reproduction and often of 

 defense. All insects pass through a number of transformations or 

 metamorphoses before reaching the adult or winged and sexual 

 The first of the four principal stages is the egg. In most 



Head, 



TbSft* 



Antenne 

 Kyt 



tot pair of legs 



tat jmir OS \Sftngt 

 Sad pair of Leg* '~ 



tnd pair of Wing* 

 Jrd p*lr ol Les 



TibU 



Tartu* - . . 



A Locust or "grasshopper" dissected to show divisions of body. 



cases this is deposited by the female upon the proper food, and is 

 there left to hatch without any further maternal care. In social 

 insects, such as bees, ants, etc., the eggs are taken care of by various 

 methods. In exceptional cases the egg is retained in the oviduct 

 until ready to hatch, or even until it has hatched. The larva (cater- 

 pillar, worm, maggot, slug, grub, etc.), hatches from the egg, and it 

 is in this stage of the life of an insect that most growth is made. 

 But as the external skeleton of an insect does not grow the space 



