Reference for Bekhorot 33:29

חוששין לזרע האב ורבנן סברי

R'Ahi said: We suppose it possesses certain marks [resembling the mother].<span class="x" onmousemove="('comment',' R. Meir holding that it is liable to the law of the firstling as the Mishnah states anonymously, whereas the Rabbis maintain that he is not liable.');">¹⁷</span>

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