224 HORTICULTURE FOR SCHOOLS 



The insect structure is peculiar. The body is divided into 

 three parts, head, thorax, and abdomen. The skeleton, in- 

 stead of being a bony framework within the body as is the 

 case with the higher animals, is a shell-like covering outside 

 of the body; this is known as an exo-skeleton, from the Greek 

 exo, out. Each insect is provided with two pairs of wings 1 

 and a mouth modified either for biting or sucking. The 

 internal structure is highly complex. There is a circulatory 

 and a digestive system, and an arrangement for breathing 

 that is wholly unique and very interesting. This breathing 

 system consists of ducts situated behind and below the wings, 

 and connected by small tubes with the outside of the body. 

 As the wings move, air is introduced into and expelled from 

 these openings, thus supplying the insect with the oxygen 

 necessary. One peculiar fact is that some insects may keep 

 these openings closed for a long period; and this adds to the 

 difficulty of their control. Beetles left for days in an atmos- 

 phere containing deadly cyanide gas will seem dead when 

 taken out, but frequently, after a period of hours, will revive 

 and crawl away uninjured. 



334. Insect groups. Flies are distinguished by having 

 apparently one pair of wings only. From this fact they 

 derive their technical name, Diptera, from two Greek words, 

 di meaning double, and ptera, wings. If the fly is examined 

 closely, a pair of stubs one-fourth inch or less in length will 

 be found beneath the wings and attached to the back. These 

 stubs are really rudimentary wings; so that while the fly 

 appears to have one pair of wings only, it really has two. 

 The butterfly and moth group is distinguished from others 

 by the scale-like covering on the wings; hence the name, 

 Lepidoptera, from lepido, a scale. The group is subdivided 

 into two smaller divisions, butterflies and moths. The former 

 have three distinguishing characteristics; when at rest their 

 wings remain poised in the air, the antennae or "feelers" are 



There are some exceptions to the rule. 



