INTRODUCTION. 



21 



^\it maggot of the blow-fly is, in twenty-four hours, 

 one hundred and fifty-five times heavier than at its 

 birth Some larvoe have feet, others are without: 

 none have wings. They cannot propagate. They feed 

 voraciously on coarse substances; and as they increase 

 in size, which they do very rapidly, they cast their skins 

 three or four times. In defending themselves from 

 injury, and in preparing for their change by the con- 

 struction of secure abodes, they manifest great inge- 

 nuity and mechanical skill. The figines on the pre- 

 ceding page, exemplify various forms of insects in this 

 stage of their existence. 



When larvse are full grown, they cast their sldns 

 for the last time, undergo a complete change of form, 

 and, with a few exceptions, cease to eat, and remain 

 nearly motionless. When an insect, after this change, 

 does not lose its legs, or continues to eat and move, 

 it is popularly called a JYijmph; and when the inner 

 skin of the larva is converted into a membranous or 

 leathery covering, which wraps the insect closely up 

 hke a mummy, it is termed Pupa, from its resem- 



blance to an infant in swaddling bands. From the 

 pupae of many of the butterflies appearing gilt as if 



