8 ttfSUCTS: THEIR STRtfCTlM AND 



The bodies of insects are made up of muscles, nerves, organs and 

 other parts just as other animals are, and they live in a very similar way. 

 The food taken in at the mouth passes into the stomach, and is digested ; 

 the remains are excreted. The stomach and intestine form a plain long 

 tube which passes from the mouth to the tail. The digested food passes 

 into the space between the skin and the intestine, in which all the muscles 

 and nerves lie ; above the stomach and intestine there is a small heart, 

 consisting of a long slender tube which pulsates and pumps the dissolved 

 food forward over the head and all round the body ; this can be seen in 

 many caterpillars, if the upper part of the body is intently watched for 

 some minutes. In the body there are numerous muscles, which enable 

 the insect to move. In the head there is a small brain, and running down 

 the lower side of the body there is a double cord of nerve tissue, with little 

 swellings in each ring. This cord is like our own spinal cord, and from it 

 nerves go to all the parts of the body. Insects have nerves similar to our 

 own though on a simpler scale. Besides these organs, the perfect insect has 

 reproductive organs, male or female. These open at the hind end of the body, 

 just below the opening of the intestine. In many insects the female has 

 attached to the hind end of the body a special instrument for laying eggs ; 

 the sting of the bee is really the egg-laying instrument : in some insects 

 this structure, called an ovipositor, is very large and conspicuous (fig. 52). 



Insects have senses and sense organs which we may compare with 

 those of other animals, though we cannot pretend to understand them. 



Eyes take the form either of a pair of large conspicuous structures 

 on the side of the head or of several small points on the upper surface or 

 side of the head. The former, known as compound eyes, we may consider 

 as hundreds or thousands of small eyes united to form a single complex 

 structure ; we can see these separate small eyes which give the whole eye 

 a honey-comb appearance. The latter, known as simple eyes, are found 

 in caterpillars and other immature insects, which do not have compound 

 eyes, and also in many mature insects in conjunction with compound 

 eyes. The caterpillar has five or six such eyes on each side of the head ; 

 the grasshopper has three only, some bugs have two, and many insects 

 have none. The function of eyes is not clearly understood, but it is 

 believed that the compound eyes are as efficient as our own eyes, and that 

 simple eyes perhaps serve to distinguish light and shade or act in some 

 such simple manner. 



Organs of hearing are present probably in many insects, but definite 

 organs similar to our ears are known only in the grasshoppers and their 

 allies. Many other insects probably hear sounds, since many of them 

 also make sounds, but it is not certain what is the organ of hearing. 



