Answer :
Answer: The embryonic period
Explanation:
The embryonic period is the period after implantation roughly starting from week 4 to week 11 , shows the development of the fertilized egg, In this early stage of development , due to the rapid cellular development the formation of body organs and structures like the heart, primitive brain, spinal cord are formed. Three stages occurs in the embryonic stage which include The pre-embryonic stage, the embryonic period, and the fetal period.
Therefore if Manish is studying development of fertilized egg, of which the spinal cord is about to form, then he is most likely observing the The embryonic period.