Head Capsule of a Gypsy Moth Caterpillar Showing the Tentorium (arrows)
Insects have an external skeleton consisting of a layer of cells and secreted cuticle. Unlike vertebrates that have muscles attached to internal structures (bones) insects have most skeletal muscles attached to the exoskeleton. In some cases, it would be adaptive for insects to have internal points of attachment for skeletal muscles? What is an insect to do?
Invaginate! In the head of an insect, the outer layer of cells…
Source: Living With Insects Blog