During this stage the cuticle draws away from the imaginal cuticle which is forming beneath, ultimately becoming separated as a thin transparent pellicle through which the form of the adult can be seen.
These centres of renovation are called imaginal disks or folds.
In other insects the imaginal disks are less completely disconnected from the superficies of the larval hypodermis, and may indeed be merely patches thereof.
The number of imaginal disks in an individual is large, upwards of sixty having been discovered to take part in the formation of the outer body of a fly.
The imaginal disks for the outer wall of the body, some of them, at any rate, include mesodermal rudiments (from which the muscles are developed) as well as hypodermis.