Page:Insects - Their Ways and Means of Living.djvu/317

 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 m 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 gien freedom to expand that the adult insect at last appears in its fully mature form.

[a6 ]