Extended metaphor

Definition: it is a type of metaphor, and it cotinuing to develop a metaphor.

Ex: Hope is the thing with feathers
  That perches in the soul,
  And sings the tune--without the words,
  And never stops at all,

"And sweetest in the gale is heard;
  And sore must be the storm
  That could abash the little bird
Signification: it develop the metarphor and make the poem more interesting.
  That kept so many warm