A Tripartite body plan
This success, diversity and variation is all achieved with a tripartite body plan consisting of a head bearing a mouth, mouthparts (modified jointed appendages) and most of the sense organs; a thorax filled with muscles which operate three pairs of legs, and usually one or two pairs of wings and an abdomen which contains the organs for digestion and reproduction. All three sections are enclosed within an external skeleton made principally of chitin, a substance that is chemically similar to cellulose but has both flexibility and permeability.
Tripartite Body Plan
