When a baby is being developed inside the womb,
1) how does the baby's body know a finger, or any other part of the body, has been fully developed?
2) following question, how does it "stop" the development of that part? What kind of signals are being communicated here?
3) I have hairy arms. The length of the hair is almost the same length if i don't cut it. If it breaks, it grows back almost the same length. How does the body know the current length and how to stop when it reaches the "target length"? Is it the same "procedure" as the development of parts inside the womb?