INTRODUCTION 21 



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

 one hundred and fifty-five times heavier than at its 

 birth. Some larva 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 them- 

 selves from injury, and in preparing for their change 

 by the construction of secure abodes, they manifest 

 great ingenuity and mechanical skill. The figures 

 on the preceding page, exemplify various forms of 

 insects in this stage of their existence. 



When larvce 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 Nymph; and when the inner 

 skin of the larva is converted into a membranous or 

 leathery coverinsj, which wraps the insect closely up 

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



Ptiocv, or Chrysalides. 

 blance to ail infant in swaddling bands. From the 

 pupa; of many of the butterflies appearing gilt as if 



