Yevamot

in order to avert danger!  — Here  we are dealing with one whose marks  have not  been developed.  For it was taught: Who is an eight-month child? He whose months [of conception] have not been completed. Rabbi said: The marks, his hair and nails which were not developed, would indicate it.  The reason then is because they were not developed, but had they been developed it would have been assumed that the child was a seven-month one  only his [birth] was somewhat delayed. With reference, however, to the practical decision which Raba Tosfa'ah gave in the case of a woman whose husband had gone to a country beyond the sea and remained there for a full year of twelve months, where he declared the child legitimate,  in accordance with whose [view did he act]? [Was it] in accordance with that of Rabbi who maintains that [birth] may be delayed!  — Since R. Simeon b. Gamaliel also maintains that [birth may] be delayed. he acted in agreement with a majority. For it was taught: R. Simeon b. Gamaliel said: Any human  child that lingers for thirty days can not be regarded as a miscarriage. Our Rabbis taught: Who is a congenital saris?  Any person who is twenty years of age and has not produced two pubic hairs.  And even if he produced them afterwards he is deemed to be a saris in all respects. And these are his characteristics: He has no beard, his hair is lank, and his skin is smooth. R. Simeon b. Gamaliel said in the name of R. Judah b. Jair:  Any person whose urine produces no froth; some say: He who urinates without forming an arch; some say: He whose semen is watery; and some say: He whose urine does not ferment. Others say: He whose body does not steam after bathing in the winter season. R. Simeon b. Eleazar said:  He whose voice is abnormal so that one cannot distinguish whether it is that of a man or of a woman. What woman is deemed to be incapable of procreation? — Any woman who is twenty years of age and has not produced two pubic hairs.  And even if she produces them afterwards she is deemed to be a woman incapable of procreation in all respects. And these are her characteristics: She has no breasts and suffers pain during copulation. R. Simeon b. Gamaliel said:  One who has no mons veneris like other women. R. Simeon b. Eleazar said: One whose voice is deep so that one cannot distinguish whether it is that of a man or of a woman. It was stated: As to the characteristics of a saris, R. Huna stated, [Impotency cannot be established] unless they are all present. R. Johanan, however, stated: Even if only one of them is present.  Where two hairs were produced  all agree that impotency cannot be established unless all characteristics  are displayed. They only differ in the case where these were not produced. With reference, however, to what Rabbah b. Abbuha said to the Rabbis, 'Examine R. Nahman. and if his body steams I will allow him to marry my daughter'; in accordance with whose view [was he acting]? [Was it] according to R. Huna!  — No; R. Nahman had some stray hairs. THE SARIS NEITHER SUBMITS TO HALIZAH NOR CONTRACTS THE LEVIRATE MARRIAGE, AND SO ALSO A WOMAN WHO IS INCAPABLE OF PROCREATION etc. The saris was mentioned in the same way as the woman who is incapable of procreation; as the woman's incapacity is due to an act of  heaven so must that of the saris be an act  of heaven; and this anonymous [Mishnah] is in agreement with R. Akiba who stated [that halizah applies] only to a man-made [saris but] not [to one afflicted] by the hand of heaven. IF A SARIS SUBMITTED TO HALIZAH FROM HIS SISTER-IN-LAW, HE DOES NOT THEREBY CAUSE HER TO BE DISQUALIFIED etc. The reason then [why when HE COHABITED WITH HER HE CAUSES HER TO BE DISQUALIFIED] is because he  cohabited with her; another man, however, does not;