Herbert H. Ross,
How to Collect and Preserve Insects
“ When the insect resumes its normal activities immediately after a molt, the soft parts of the cuticle fall into a large number of pleats or folds between the hard parts. As the insect grows larger following a molt, the body can lengthen by the unfolding of these pleated areas.The stages of the insect between molts are called instars. Among the different orders of insects the number of instars in the life history may vary, and various instars may have different forms. These characteristics of molting and instars are therefore important items in the classification of insects. ”
