the practical aspect it is very important to recognise the 

 difference in feeding habits which must correspond with the 

 difference in the mouth parts, since species with jaws can 

 eat solid matter, while those with trunks merely suck up 

 juices through a minute hole. 



(b) The second section of the body, the thorax, is essentially 

 the part connected with movement. It usually carries three 

 pairs of legs and it may also be provided with one or two pairs. 

 of wings. 



(c) The third section of the body, the abdomen (often called 

 the " tail "), corresponds more or less with the lower part 

 of the body in man, and contains the organs of reproduction 

 and the gut, in passing through which food is digested. 

 Extending down the whole length of the insect, just under 

 the upper surface, is a long tube which pumps the blood, 

 beating like the heart, to which it may be compared. 



It will be noticed that no reference has yet been made as 

 to how insects breathe. This is because they have 

 entirely different " machinery " from that in man. In 

 the latter case the air is taken into the lungs and 

 the oxygen is absorbed by the blood and carried to wherever 

 it is needed. In insects the same result is obtained but by 

 a " short cut " since they have a series of holes (spiracles) 

 along the sides of the body (usually thorax and abdomen) 

 which lead into tubes passing to every part, so enabling air 

 to flow freely in and out. Every organ has therefore a 

 direct air supply and there is no need for lungs. In con- 

 trolling insect pests the special method of breathing is an 

 important point to remember. 



Finally, as regards the structure, the statement may be 

 recalled that insects have no bones, but depend for their 

 support on their " skin," which in consequence may be 

 regarded as .their skeleton, being either hard or tough and in 

 many cases forming almost an armour plate. This armoured 

 character of the skin makes many insects difficult to kill. 



Life History. In addition to a knowledge of the structure of 

 insects, it is helpful, or even necessary, to have some idea 

 of their life history their methods of breeding and develop- 

 ment. The usual method of starting life is from an egg 

 laid by the mother, but the young which are hatched from 

 these eggs often at first have little likeness to their 

 parents. In course of time they grow to resemble the latter, 

 but in so doing pass through stages so unlike in shape or 

 form that it seems hardly credible they can be the same 

 creature. This great change of form is perhaps explained 

 by the fact that insects at the different stages of their lives 

 concentrate strictly on " the business in hand," definite 

 periods of their existence being devoted very largely to one 

 object. This is clearly shown in the case of the White 

 Butterfly, the egg of which gives rise to a caterpillar 



