How to tell if you have a fertilized egg

[EmmaKnight]

I have chicken eggs on day 16. One of them looks like it is on point on day 16. The other egg, however, looks a little bit behind (around day 12 or 14). I checked on it today and it looks alright (black embryo black sprockets around it). When I was turning it to see how it was on the other side, it "swished" with it. So basically the egg is fertilized but seems to be either behind or dead (hoping behind) Any advice on what to think about it? The pictures below are from day 15:

 

[PD-Riverman]

I have chicken eggs on day 16. One of them looks like it is on point on day 16. The other egg, however, looks a little bit behind (around day 12 or 14). I checked on it today and it looks alright (black embryo black sprockets around it). When I was turning it to see how it was on the other side, it "swished" with it. So basically the egg is fertilized but seems to be either behind or dead (hoping behind) Any advice on what to think about it? The pictures below are from day 15:

Your pics are to dark---you really need a brighter light, but from what I can see these 2 pics are showing a bad egg.

 

[ChickAsThieves]

I had an egg that was clearly developed, much like yours, but had obvious dark fluid movement when turned. It was no longer living. When I performed the "eggtopsy" after I was sure it wasn't going to hatch, I saw that the "swishy fluid" was yolk that had turned brown.

I'm sorry.