Is it the eye or heart that is first visible in fertile eggs?

[tatswell]

The dark spot, generally visible around day 3- eye or heart?
I didn't realize this was so controversial!

Some say eye, others say heart.

 

[Pyxis]

On Day Three they're still very tiny. This is an embryo on day 3:

Really not much to see, heart or eye.

But here's day 5:

And that black dot that you can see at one end of the embryo is the eye. You can see the heart too (not in this picture, it doesn't show up well), but it's toward the middle of the embryo. It doesn't show up as a dark dot, but rather a pulsing spot, because you can see it beating.

 

[tatswell]

Thanks! I see the heart beating. (Day 5) now where did the eye go?