INTRODUCTION. 



21 



the maggot of the blow-fiy is, in twenty-four hours, 

 one hundred and fifty-five times heavier than at its 

 birth Some larva3 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 figures on the pre- 

 ceding page, exemplify various forms of insects in this 

 stage of their existence. 



When larvae are full grown, they cast their skins 

 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 JYijmjik; and when the inner 

 skin of the larva is converted into a membranous or 

 leathery covering, which wraps the insect closely up 

 like a mummy, it is termed Pupa^ from its resem- 



Pupce or Chrysalides. 



blance to an infant in swaddling bands. From the 

 pupa) of many of the butterflies appearing gilt as if 



