The bladder.
Bladder
The urinary bladder
Amniotic sac
Amniotic sac
The bladder.
Bladder
gallbladder
Pancreas.
The Stomach
The urinary bladder
Marsupial sac.
It's an Air Sac.
the stomach
Amniotic sac
Amniotic sac
I Think You Thinking Of The Alveoli/Alveoli's