I 



WHAT AN INSECT IS LIKE 



Outside 



Let us begin our study by inquiring how an insect is 

 built. How it lives will be better understood when we know 

 something of how it is organized. What is its plan of struc- 

 ture? 



A stonefly is a primitive sort of insect that will show us 

 this plan very plainly. Let us get one of the larger stone- 

 flies from a stream and examine it. Taking a fresh specimen 

 in hand we first note that the body has some conspicuous 

 appendages. There are two long antennae in front and two 

 tails behind and six legs at the sides. We see that the body 

 is divided into segments encased in rings of armor with 

 flexible membranous joinings, and that the appendages are 

 similarly encased. There are no bones as in us. There are 

 big horny rings about the body, and little ones about the 

 appendages. These rings, together with some internal pro- 

 cesses from them, constitute the skeleton of the insect, 

 which is worn on the outside, and has the muscles attached 

 to its inner surface. 



If we bend the body and appendages at their joinings 

 and note how the parts move on one another, we will see 

 that some of them move freely in any direction on the in- 

 folded membrane, while others, like the knee joint in the 

 legs for example, bend freely in one plane only, two pivotal 

 points being developed in the membrane on opposite sides. 



