This video shows identify the stages of the life cycle of a butterfly

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This video shows identify the stages of the life cycle of a housefly

An exoskeleton of an arthropod does not grow with the animal.  When the animal needs to increase in size it sheds its old skeleton. A new soft exoskeleton is underneath.  The animal puffs up its body with fluid and allows this new skeleton which is larger to harden.  This often needs to be repeated several times over the arthropod’s life.  An endo skeleton such as that found in vertebrates grows steadily throughout the vertebrate’s life or until it has reached full size.

Metamorphosis basically means to change from one thing into another. Many animals look completely different when they are young. A caterpillar looks nothing like the adult butterfly.  In the pupa it metamorphoses into its adult form. Other metamorphoses are more obvious such as a tadpole turning into a frog.