Tosefta for Bava Batra 283:4

ואי סלקא דעתך עובר לא קני למה להו אחזוקי בשניה הא אחזיקו להו חדא זימנא

need to take possession a second time? They have, surely. already taken possession once!<span class="x" onmousemove="('comment',' The existence of the embryo if it could not acquire possession, should not have made any difference to their right of ownership. Consequently it follows, as R. Shesheth had stated, that an embryo does acquire possession. ');">¹³</span> Abaye [however] said: An inheritance which comes [to one] under the ordinary laws of succession<span class="x" onmousemove="('comment',' Lit., 'of itself'. ');">¹⁴</span> is different<span class="x" onmousemove="('comment',' Though an embryo may acquire ownership of an estate which is due to him as the legal heir, it does not follow that it can also acquire the ownership of a gift or any other assignment. ');">¹⁵</span> Raba said: There<span class="x" onmousemove="('comment',' n the case of the estate of a proselyte. ');">¹⁶</span> it is different,<span class="x" onmousemove="('comment',' From other cases of acquisition. ');">¹⁷</span>

Tosefta Peah