Nazir, Chapter 6, Mishnah 2. The Mishnah establishes that a nazir is liable for each of the products of the vine separately:
"V'chayav al hayayin bifnei atzmo" - "And he is liable for the wine on its own"
"V'al ha'anavim bifnei atzman" - "And for the grapes on their own"
"V'al hachartzanim bifnei atzman" - "And for the chartzanim on their own"
"V'al hazagim bifnei atzman" - "And for the zagim on their own"
The meaning is this: a nazir receives lashes for violating his nezirus with each one of these items separately. Wine on its own, grapes on their own, chartzanim on their own, and zagim on their own. According to this opinion in the Mishnah, the chartzanim are the grape seeds and the zagim are the grape skins.
The opinion of Rabbi Elazar ben Azaryah:
Rabbi Elazar ben Azaryah disagrees and says: "Eino chayav ad sheyochal shnei chartzanim v'zag" - a nazir is not liable for eating or drinking from the products of the vine until he eats two chartzanim, that is, two grape seeds, and a zag, the skin that surrounds them. He derives this from the wording of the verse: "Michartzanim v'ad zag" - "michartzanim" in the plural, "v'ad zag" up to and including the skin. From here he understands that this amount is the minimum required for liability.
Which are chartzanim and which are zagim:
Until now we have defined the chartzanim as the seeds and the zagim as the skin of the grape, but the Mishnah presents a dissenting opinion on this matter and asks: "Eilu hen chartzanim v'eilu hen zagim" - which are the chartzanim and which are the zagim?
The opinion of Rabbi Yehudah: "Hachartzanim eilu hachitzonim, v'hazagim eilu hapenimim, divrei Yehudah" - the chartzanim are the outer part, the skins, and the zagim are the inner part, that is, the seeds. This definition is the reverse of what we have seen until now, and certainly the reverse of what emerged from the words of Rabbi Elazar ben Azaryah.
The opinion of Rabbi Yosei: the zagim are the outer part, the skins, and the chartzanim are the inner seeds. The first part of the Mishnah follows his approach.
Rabbi Yosei adds a way to remember which is which: "Shelo tit'eh, k'zog shel behemah: hachitzon zog v'hapenimi inbal" - like the bell that an animal wears around its neck, whose outer part is called a zog and whose inner part is called an inbal. From this sign it emerges that the zog is the outer part, and therefore the zagim are the outer skins, while the chartzanim are the inner seeds.
In summary: in this Mishnah we learned that a nazir is liable for each of the products of the vine on its own - wine, grapes, chartzanim and zagim; that according to Rabbi Elazar ben Azaryah there is no liability until he eats two chartzanim and a zag, as derived from the verse "Michartzanim v'ad zag"; and we examined the dispute over the definition of the terms - according to Rabbi Yehudah the chartzanim are the outer part and the zagim the inner, while according to Rabbi Yosei, whose approach the beginning of the Mishnah follows, the zagim are the outer skins and the chartzanim are the seeds, as indicated by the sign of the zog and the inbal.