Caterpillarlarvae undergo one final development before becoming adults (metamorphosis). The larvae sheds its skin and develops a hard shell around itself and is now called a pupa. The pupa has spiracles for breathing, and its tip may twitch sporadically. When the larva first developed from the egg cells it was segregated into two groups. Some of these cells divided after a few hours but remained generalized in form, whereas other cells continued to build the caterpillar body. After the larva hatch these cells enlarge with no further cell division. Within the pupa the original giant cells of the caterpillar are used to feed cell division of those other group of cells which are re-organizing the new body of the butterfly.