1. The Mitzvah of Reishis ha'Gez does not apply to sheep that have hard wool.
2. A goat that is descended from another type of animal (even from its grandparent) such as a sheep cannot be used for the goat offered as a Korban on Rosh Chodesh.
3. The Gemara discusses many laws that apply to a sheep that is descended from another animal.
4. The Mishnah discusses the Halachah in a case in which a sheep seems to have given birth to two male offspring at once.
5. The Mishnah discusses the law in a case in which one of the sheep dies (in the previous case, #4) before any sheep is given to the Kohen.
A BIT MORE
1. This is derived from the verse, "And from the shearings of my sheep he will be made warm."
2. This is derived from the verse, "One [goat]," implying that this goat must be descended only from its species from the beginning of creation (to the extent that we can know).
3. Rebbi Acha says that its wool is not subject to the prohibition of Kil'ayim, and one who wears a mixture of its wool with linen does not receive lashes. Rav Papa says that its wool cannot be used for Techeles. Rav Nachman says that clothing made from its wool does not become Tamei with Tzara'as of garments.
4. Rebbi Yosi ha'Glili rules that both animals must be given to the Kohen. The Chachamim say that he gives only one to the Kohen. Rebbi Tarfon says that the Kohen chooses the one he wants. Rebbi Akiva maintains that the Kohen takes the weaker animal.
5. Rebbi Tarfon says that the Kohen and the owner should split the remaining animal. Rebbi Akiva maintains that the owner keeps the animal.