14:60 THE STORY OF THE UNIVERSE 



stage of existence, may present a very great increase 

 in size, as compared with the dimensions it presented 

 at the beginning of its life. 



But, sooner or later, the caterpillar appears to 

 sicken, and to become quiescent. Its former state of 

 activity is exchanged for one of lethargy, from which 

 it awakes to begin an operation of a novel and differ- 

 ent nature from that in which it has been previously 

 engaged. It begins. to spin a delicate silky thread by 

 means of a special apparatus, situated in the head, 

 and which consists of silk-glands and of an organ 

 named the "spinneret." Within the silken case or 

 "cocoon" which it thus constructs with the thread 

 of the spinneret, the caterpillar-body is soon inclosed ; 

 the first stage of its existence comes to an end ; and the 

 second or cocoon stage, marked by outward quies- 

 cence and apparent rest, becomes known to us as that 

 of the "pupa," "chrysalis," or "nymph." 



Although outwardly still, and although all the 

 former activity appears to have been exchanged for 

 a state of dull repose, changes of active kind, and of 

 marvelous extent, are meanwhile proceeding within 

 the cocoon or pupa-case. The elements of the cater- 

 pillar's form are being gradually disintegrated or 

 broken down, and built up anew in the form and 

 image of the adult butterfly. Old textures and gar- 

 ments are being exchanged for new ones; particle by 

 particle the outward and inward structures of the 

 larva are being replaced by others proper to the ma- 

 ture being; and in due course, and after a longer or 

 shorter period, the cocoon is ruptured, and the per- 

 fect form emerges a bright and beautiful creature, 



