INSECTA 69 



after each moult, until the adult form is finally attained. 

 Holometabolous insects have a " complete " metamorphosis. 

 They hatch from the egg as a worm-like larva, which feeds 

 for a time; then goes into a resting, or pupal, stage during 

 which no food is taken. The larval structures are com- 

 pletely lost as the pupa is formed. When the pupa moults, 

 an adult insect, or imago, comes out. 



According to recent usage, insects are classified into 

 nineteen orders. These will now be taken up in more or 

 less detail. 



Order 1. Aptera (Fig. 37). These are little ametabol- 

 ous, wingless insects with biting mouth parts. Wingless- 



Fio. 37. Insects belonging to the order Aptera. A, a collembolan; B, a- slicker, 

 or silver-fish; C, a spring-tail. 



ness in this case represents a primitive condition. The 

 little slickers, silver-fish, or fish moths ; the spring-tails ; and 

 the snow-fleas are examples. Slickers eat the glazing on 

 paper and starch from clothes. They are frequently seen 

 in dwellings or factories. Spring-tails are expert jumpers, 

 being able to hop many times their own length. The snow- 

 fleas are sometimes so abundant as to give the snow a 

 characteristic color. 



Order 2. Ephemerida (Fig. 38). The may-flies live 

 near water. They are heterometabolous insects with biting 

 mouth parts. Both the larval and adult may-fly are easily 

 recognized by the long setae which project from the end of 

 the abdomen. There are three of these on the larva, and 

 two or three on the adult. Eggs laid in the water hatch into 

 nymphs which live for about a year, feeding on aquatic life. 



