2 LIFE STORIES OF AUSTRALIAN INSECTS. 



head, (b) the thorax, (c) the abdomen. To the 

 thorax are attached the three pairs of legs and the 

 two pairs of wings, (Plate i. Fig. i.) (Note that 

 some insects have but one pair of wings and others 

 are wingless.) The abdomen may carry the sting, 

 and in the case of females an ovipositor (egg pla- 

 cer), or a saw (example, sawflies). 



External Structure. — The outer skin of an insect 

 is somewhat hardened by the deposition in its cells 

 of a horny substance called chitin. This hardness 

 of the integument affords the insect a protection 

 as there is no internal skeletal structure. 



The Head. — This is usually more or less rounded 

 and made of a number of segments welded together. 

 To the head are attached the following: (i) The 

 Antennae or feelers (Plate i. Fig. i. d). These are 

 jointed structures situated on the front of 

 the head and usually between the eyes. In some 

 insects they are very short, ex. : cicada. Their 

 length varies, however ; some tree grasshoppers 

 have antennae from 4 to 6 inches long. The antennas 

 may be organs of feeling, smelling, or even hearing. 

 (2) Eyes: Most insects have one pair of compound 

 eyes (Plate i. Fig 4) which are immovable and 

 each eye is made up of a number of small structures 

 or eyes called facets (Plate i. Fig. 5). Each of 

 these facets is a centre of vision. The number of 

 facets varies from a few in some insects, to several 

 thousands in others. In addition to the com- 

 pound eyes are simple eyes, or Ocelli (Plate 

 I, Fig. 3a), varying in number from i to 5, 

 though 3 is the usual number; these are 



