Answer
The trophoblast is the first extraembryonic membrane to form in mammals. Trophoblastic cells begin the process of implantation by secreting proteolytic enzymes and burrowing into the endometrium.
Work Step by Step
The trophoblast is the first extraembryonic membrane to form in mammals. Trophoblastic cells begin the process of implantation by secreting proteolytic enzymes and burrowing into the endometrium.