Question #1 (R. Efrayim): He should ask from the Reisha of this Mishnah! The Reisha (Nidah 43b) says that a one day old feeds Terumah and disqualifies from Terumah;

Inference: Only a one day old [feeds and disqualifies], but not a fetus. This shows that one who is Mezakeh for a fetus did not acquire. This is difficult for Rav Sheshes, and now we could not answer like we answer about the Seifa (that a born baby inherits his mother to bequeath to his paternal brothers, but a fetus does not, because it dies before the mother)!

Question #2 (Ri): It asks there (Nidah 44a) "why does it teach a one day old? Even a fetus disqualifies! Rav Sheshes answered that the Mishnah discusses a Kohen with two wives - a divorcee and one who was not divorced;

He has sons from the non-divorcee, and one son from the divorcee, who disqualifies his father's slave from eating Terumah. This teaches unlike R. Yosi, who says that even a fetus disqualifies. It teaches that this is not so. A one day old disqualifies, but a fetus does not.

Why must he mention two wives? He should establish when he has one wife, a divorcee, and he has a son from her. Only a one day old disqualifies, but a fetus does not, and the slaves eat due to the entire family, according to Rabanan of R. Yosi, like we say in Yevamos (67a)!

Answer (Ri): Rav Sheshes holds that also according to Rabanan of R. Yosi, a fetus has Zechiyah (can acquire). The reason a fetus does not disqualify is because we join the minority [of women] who miscarry to the half that are females, so males (that will be born) are the minority, and [Rabanan] are not concerned for the minority, [un]like R. Yosi is concerned.

Therefore [Rav Sheshes] establishes it to discuss a Kohen with two wives, and he has sons from the non-divorcee. Since he has sons, the fetus does not disqualify. Even though [a fetus] has Zechiyah, we are not concerned for the minority of males, like I explained.

However, if he does not have sons, the fetus disqualifies also according to Rabanan, for he has Zechiyah. Whether [the fetus] is a male or female, the slaves belong to it;

Rav Sheshes argues with Shmuel, who says in Yevamos (67a) that according to Rabanan, [the slaves] eat due to the entire family. Shmuel holds that according to Rabanan, a fetus has no Zechiyah.

Support: Now it is fine that above, Rav Sheshes said "what is my source? A Beraisa teaches 'if a convert died...'", and we do not reject that the Beraisa is like R. Yosi, because Rabanan do not argue [about Zechiyah], just they are not concerned for the minority, like I explained.

Question: Above, it taught that one who acquired the second time (after the miscarriage) acquired, but one who acquired the first time did not acquire. Why didn't one who acquired the first time acquire, since in the end she miscarried?

In Yevamos (67a) we say that males are the minority, due to the minority who miscarry [and half are females], and a fetus that will later be miscarried has no share in the slaves. (Also here, since the fetus was miscarried, it never had a share in the convert's property!)

Answer: There, we attribute that perhaps already at the time the slaves eat Terumah, the fetus already died inside the womb, and it has no Zechiyah. (Even a small Safek causes males to be the minority. However, if we knew that it is alive now, it would have Zechiyah, even if it will be miscarried later. Regarding one who took the convert's property, we do not assume that the fetus already died at the time.)

Question: What was the Makshan's Havah Amina? You are forced to say like Rav Sheshes answered, that he inherits his mother's property. If not, it is difficult for him, that if the brothers want, they can inherit from him, or from their father! We infer like this in Nidah (44a).

Answer #1: Surely, the Makshan knew that he inherits his mother's property. However, he thought that the mother dies first. (If so, at the moment she dies, the fetus is considered born and alive, just it is in a "box" of dead flesh. If so, even a fetus inherits!) Rav Sheshes answered that the fetus dies first.

Implied question: [If also the Makshan knew this,] why did Rav Sheshes need to say that he inherits his mother's property?

Answer: Because the Makshan did not specify, Rav Sheshes clarified this.

Observation: In Erchin (7a), we challenge Shmuel from Rav Sheshes, who says that the fetus dies first. We could have answered that Shmuel holds like the Makshan here, that the mother dies first.

Implied question: Below (142b), Shmuel holds like Rav Sheshes, that one who is Mezakeh for a fetus acquires! (If so, he must answer the Mishnah like Rav Sheshes, that the fetus dies first!)

Answer: Even so, he need not answer like Rav Sheshes. He could answer like Mar brei d'Rav Yosef, that [only a born son is counted] for determining the Bechor's portion, [but a fetus] does not diminish it;

However, the Gemara prefers to establish Shmuel like Rav Sheshes.

Answer #2 (to Question (a)): Initially, the Makshan thought that he inherits the father's property, e.g. the father had no other children, and he was Makneh his property to others if (i.e. on condition that) this fetus will not inherit him; (Maharsha - the same applies if he had other children and stipulated like this, just it is not common for one with children to be Makneh his property to others.)

[The Mishnah] teaches that only a one-day old inherits from his father to bequeath to heirs from his father, but a fetus does not.

Remark: Likewise, we could have answered so in Nidah (44a).

Answer #3: The Makshan thought like Mar brei d'Rav Yosef, that it teaches about diminishing the Bechor's portion, without the Drashah "v'Yaldu Lo." Only a one day old son diminishes Bechorah, but a fetus does not.

Explanation: The reason is like it says in Erchin (7a). Since it has meager life, the drop from the Mal'ach ha'Maves enters it and cuts the Simanim.

Implied question: It says in Chulin (74a) that one who slaughters an animal and finds inside a live nine-month (i.e. viable) fetus... (This shows that the mother dies first!)

Answer: That is only when he slaughtered or killed [the mother]. Then she dies first, like it says in Erchin (7a).

Implied question: It says in Chulin (38b) "if the mother died, and then gave birth..."!

Answer #1: It means that it died through a person.

Answer #2: Or, [it died] through the Mal'ach ha'Maves, in a case that the fetus uprooted to leave [the womb]. Then, the fetus does not die, like it connotes in Erchin (7a. If a woman died during birth, we cut her open to remove the child, even on Shabbos.)

Question: Since if it was killed or the fetus uprooted to leave, the mother dies first and not the fetus, if so, why does it say that a one-day old [inherits...]? Also a fetus inherits and bequeaths!

Answer: For a one-day old, the law is uniform (it always inherits and bequeaths). It could not teach uniformly that a fetus [always] inherits and bequeaths.

Alternative text: Some texts say "until three Parsei", i.e. the distance of three Parsa'os (about 12 kilometers).

Question (Ri): Why doesn't he learn from "v'Yaldu Lo" [like] above? (We expounded it to teach that a son born after the father died does not diminish the Bechor's extra portion. This very Drashah should teach that a Bechor born after the father died does not get a double portion!)

Also in Bechoros (47b) we expound it regarding Bechor. We expound from it that a Bechor Yotzei Dofen (born through Caesarian section) does not receive the extra portion of a Bechor!

Answer: If we did not know about Bechor from another verse (Yakir), we would not establish this verse (v'Yaldu Lo) to discuss a Pashut (regular son, to teach about when he was born after the father died), rather, a Bechor!

Support #1: Also above (127a), we learn from "v'Yaldu Lo Banim" that a Tumtum does not diminish the Bechor's portion, and from "v'Hayah ha'Ben ha'Bechor" we learn that a Bechor Tumtum does not receive a double portion;

Also there, if we did not know about Bechor from another verse, we would not establish v'Yaldu Lo Banim to discuss a Pashut (regular son), rather, a Bechor!

Support #2 - Implied question: Why don't we say that a Yotzei Dofen does not diminish the Bechor's portion due to v'Yaldu Lo, like we expound from this verse in Bechoros that a Bechor Yotzei Dofen does not receive a double portion?

Answer: This is because if there are not two verses, we establish [v'Yaldu Lo] only to discuss a Bechor, but not a Pashut.

Observation (Rivam): Regarding an inheritance that comes automatically, it is possible that the Halachah follows R. Yosi;

We say in Yevamos (67a) that Chachamim agreed to R. Yosi, for his reason is logical.

Pesak: Even though [Chachamim] did not retract, it seems that the Halachah follows R. Yosi, since his reason is logical.