Reference for Bava Batra 284:7
אמר ליה שמואל לרב חנא בגדתאה פוק אייתי לי בי עשרה ואימר לך באפייהו המזכה לעובר קנה והלכתא המזכה לעובר לא קנה
R. Isaac said in the name of R. Johanan: If possession was given to an embryo [through the agency of a third party]. it does not acquire ownership. And if objection should be raised from<span class="x" onmousemove="('comment',' Lit., 'and if you will say'. ');"><sup>17</sup></span> our Mishnah,<span class="x" onmousemove="('comment',' From which it might be inferred, as R. Nahman suggested supran that an embryo does acquire ownership. ');"><sup>18</sup></span> [it may be replied that there it is different] because a person is favourably disposed towards his son.<span class="x" onmousemove="('comment',' Hence he wholeheartedly transfers ownership to the embryo. In the case of a stranger however, this principle is inapplicable. ');"><sup>19</sup></span>