INSECT METAMORPHOSIS 



is reduced to a few scattered cells, which build up the fat- 

 body of the adult. 



The internal adult organs undergo a continuous develop- 

 ment throughout the pupal period and are practically 

 complete when the latter terminates with the molt to the 

 adult. But the external parts, after quickly attaining a 

 halfway stage of development at the beginning of the 

 pupal metamorphosis are checked in their growth by the 

 hardening of the cuticular covering of the body wall, and 

 in their half-formed shape they must remain to the end 

 of the pupal period. It is only by a subsequent growth 

 of the cellular layer of the body wall beneath the loosened 

 cuticula of the pupa that the external adult parts are 

 finally perfected in structure; and it is only when the 

 pupal cuticula is then cast off and the organs cramped 

 within it are given freedom to expand that the adult 

 insect at last appears in its fully mature form. 



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