I watched a few vids of chickens developing in eggs without shells (see here for an example, somewhat graphic), and got to wonder.

You’d think that all the yolk is uniform and therefore it could develop anywhere, but is there an underlying mechanism that could cause the primitive streak and everything to develop near the centre? Maybe a sort of yolk density mechanism, that it starts where the yolk is densest? The furthest from oxygen exchange at the shell?

Or does such a mechanism not exist?

  • birdwing@lemmy.blahaj.zoneOPEnglish
    3·
    9 days ago

    I’m aware that the egg has more than the yolk, however my question concerned specifically the initial development of the embryo in the yolk itself. Does the yolk then have internal structures preceding embryonic formation?

    • BlackJerseyGiant@lemmy.worldEnglish
      3·
      8 days ago

      As best I understand it, the chick to be doesn’t grow in the yolk, but on it. What is left of the yolk is still attached to the chick when it hatches, and acts as a food supply for the chick for about 3 days. This is one of the reasons newly hatched chicks can be shipped through the mail. I would posit that eggs have evolved to grow chicks in the middle for the same reason hens turn their eggs regularly, to prevent long term blood flow loss to whatever part of the body the chick’s weight would be on. Growing closer to the middle of the eggs will let the Lil chicks to float for as long as possible before starting to rest weight on the “down” side of the shell.

      Edit: I dont think the yolk has internal structures.