Reference for Niddah 53:14

אחד נגמרה צורתו לסוף שבעה ואחד נגמרה צורתו לתחלת תשעה

since in such circumstances it is possible that the features of one embryo were completed at the end<span class="x" onmousemove="('comment',' Within a day or two. ');">¹³</span>

Jastrow

Jastrow