Midrash for Chullin 177:21

The 32 Principles of Aggadah is a Beraita attributed to Rabbi Eliezer ben Rabbi Yossi Haglili and composed in similar fashion to the 13 principles of Halacha authored by Rabbi Yishmael. Rabbi Eliezer adapted the 13 principles of Rabbi Yishmael for use in Aggadah and began adding more principles until he reached a total of 32. And so he would teach these principles and associated teachings, in addition to his standard teachings. Concerning him the Talmud states: "Any place where you find the statements of Rabbi Eliezer, son of Rabbi Yosei HaGelili, make your ears like a funnel." (Chulin 89a)