Final answer:
The allantois is a finger-like outpocketing that forms from the yolk sac during embryonic development and becomes the primitive excretory duct of the embryo. It eventually develops into part of the urinary bladder.
Step-by-step explanation:
The allantois is a finger-like outpocketing that forms from the yolk sac during embryonic development.
Once it involutes, it becomes the primitive excretory duct of the embryo and eventually develops into part of the urinary bladder.
The allantois is important for supplying nutrients and blood circulation to the developing embryo in the early stages of development.