The fact that there is an entry for fireflies in Kitamaru Kigin's manual for poetry suggest numerous things <span>about the roles of animals in Japanese poetry. It represents nature as well as a season for different things. They are actually representing the cultural life of the Japanese and it does not carry much biological significance.</span>
The pronoun is "it" and the antecedent is "a miniature glass hippopotamus".
Extra information:
The word antecedent is composed out of two Latin words: ante and cedere, and it literally means: the "preceding", meaning it refers to the word that precedes the pronoun, that the pronoun refers to. This is not important for the question, but it is important to remember that the antecedent is always in front of the pronoun!
