BUTTERFLIES AND MOTHS 151 



"Two kinds of eyes are peculiar to insects viz. compound 

 eyes and simple eyes or ocelli. The compound eye is generally 

 large and conspicuous, divided up into numerous six-sided prisms 

 closely united together. Each six-sided prism is called a facet, 

 and is a perfectly transparent bi-convex lens. What the true 

 function of the simple eyes may be is doubtful, but from their 

 position and structure they probably are useful in judging the 

 intensity and direction of the light, and possibly for close vision. 



"There are three distinctive forms of mouth to be met with 

 amongst insects : the sucking mouth, the piercing mouth, and the 

 biting mouth. The parts of the mouth are divided into six articu- 

 lated pieces, called respectively the upper-lip or labrum ; the two 

 pairs of jaws, called the mandibles and maxilla; and the lower 

 lip or labium. Both the maxillae and labium have attached to 

 them jointed appendages called palpi. 



" The true legs of an insect consist of six to nine joints. The 

 first joint, which attaches the leg to the ventral surface of the 

 thorax, is called the coxa ; the second joint, which is short, is the 

 trochanter ; this is followed by a large and frequently stoutly 

 built joint, the femur ; the next joint, often long and thin, is the 

 tibia ; and lastly, a series of short joints, one to five in number, 

 called the tarsus, the terminal joint bearing a pair of claws or 

 ungues." 



The facts that all insects are capable of movement in a definite 

 direction, and that they are conscious of pain, heat, cold, light, 

 and darkness, prove the presence of a well-developed nervous 

 system. This more or less elaborate nervous system consists of 

 a double chain of nervous matter on the ventral surface of the 

 body, joined together by intervening double swellings, and corre- 

 sponding in function to the spinal cord and brain of the verte- 

 brate animals. A pair of these closely united, swollen nerve 

 masses are present in each segment of the insect's body from the 

 head to the tail, and are called the ganglia. From these large 

 nerve centres go forth branching nerves to supply the jaws, 

 eyes, antennae, wings, legs, feet, stings, and ovipositors with 

 consciousness. 



All true insects are incapable of breathing through their 

 mouths, the act of respiration being accomplished by means of 

 specially adapted apertures along the sides of the body. These 



