152 INVERTEBRATE ANIMALS. 



for itself a protective case of silken threads, which surrounds 

 the chrysalis, and is known as the " cocoon." Having re- 

 mained for a variable time in this inanimate, quiescent pupa- 

 stage, during which rapid changes have been going on in the 

 interior of the animal, the insect now frees itself from the en- 

 velope which obscured it, and appears as the perfect winged 

 adult or imago. 



