1. The Mishnah discusses the Taharah status of partially formed reptile eggs (from the Shemonah Sheratzim).
2. There is an argument regarding the Taharah status of a spontaneously generated mouse.
3. Tana Kama: One who touches the earth side of the mouse is Tahor, while one who touches the flesh side is Tamei.
4. The Gemara derives the law of the Mishnah (#1) from various verses regarding Tamei reptiles.
5. The sea mouse is not Tamei.
A BIT MORE
1. If there is a reptile inside an egg that is completely sealed, it is considered Tahor. If there is a hole in the egg, it is Tamei.
2. This mouse was believed by Chazal to be spontaneously generated from the ground. Even so, it is clear that the Mishnah considered it to have the status of a normal mouse.
3. Rebbi Yehudah: Even touching the earth side can make a person Tamei.
4. For example, it states that the extra word "ha’Temai’im" - "the Tamei ones," teaches us that even reptile eggs are Tamei.
5. From the verse, "On the land," the Gemara deduces that only the land mouse is Tamei, not the sea mouse.