Confusion with The Panther

In "The Panther" I couldn't really find any meaning in the poet's words. The diction used is all diction of confinement. The image of a panther behind bars, sort of like a zoo, is able to easily be imagined. However, I don't understand what the panther stands for, if it stands for anything at all. Also, the point that the poet makes in the last stanza is referring to the closing and opening of the panther's eyes. Only at times does the panther open his eyes and he sees an image. The image has to stand for something. It seems as if the "image" is entering into the heart of the panther, but I'm not sure what exactly this means. Maybe the image is a sense of hope or desire of the panther. Even though the panther is captive, it still has hope for something more, even if that hope goes away quickly.