INTRODUCTION TO ENTOMOLOGY. 15 



flow of sap of their food-plant, and in this point of their 

 constitutions we have a principle that may help much 

 towards getting rid of them. When the larva has reached 

 its full growth it ceases feeding, and (in the forms known 

 as caterpillar, grub, or maggot) it either goes down into 

 the ground and forms a cell in the earth, or spins a 

 "cocoon" (that is a web) round itself of threads drawn 

 from the lower lip (as in the well-known silkworm 

 cocoon), or in some way it makes or seeks a shelter in 

 which it changes from the state of larva to that of pupa. 



PUPA. Chrysalis. 



It is much to be regretted that we have no generally- 

 adopted word, excepting " Chrysalis" (which is com- 

 monly used in the case of butterflies or moths), to 

 describe the second stage of insect life in which it is 

 changing from the state of larva to that of the com- 

 plete insect. Whilst in this condition it is for the most 

 part without power of feeding, and perfectly inactive, lying 

 (in the instance of beetles, bees, and wasps, and some 

 others) with the limbs in sheaths folded beneath the breast 

 and body, or (as with butterflies and moths) protected by 

 a hardened coating secreted from the pores of the creature 

 within, when it casts its last larval skin. The method of 

 this change may be easily observed in the case of the 

 caterpillar of the peacock butterfly, which fastens itself 

 by the tail, and then (after its black and silver-spotted 

 skin has cracked) by infinite wriggling and struggling 

 passes this cast-off skin backward, till it is pressed together 

 at the tip of the tail ; and the creature from within appears 

 in its new form as a bright green chrysalis, or pupa. It 

 is covered with a moist gummy exudation, which quickly 

 hardens and forms a protecting coat, and in due time (if 

 left unharmed) the butterfly inside would crack through 

 this and appear from within the case ; but if it is wished to 

 observe that the beginning of the change to the butterfly 

 form has taken place already, one of these chrysalids may 

 be dropped into a little warm turpentine or turpentine and 

 Canada-balsam, directly the caterpillar skin has been cast ; 



