Structural lipids in the insect cuticle and the function of the oenocytes.

Stabilized lipid (cuticulin), combined with protein, serves to stiffen the cuticle before sclerotization occurs. It is always present in large amounts in exocuticle that will later be tanned to form sclerotin. It is plentiful also in the untanned mesocuticle, including the tracheal taenidia, as well as pore canals, egg shell and spermatophore sheath. Stabilized lipid present in small amounts between the laminae of the endocuticle may perhaps be concerned in reversible stiffening and plasticisation. The oenocytes appear to be the source of the precursors for cuticulin formation in both larva and reproducing adult.