Re: Is there anyway to tell a fertilized eggs by looking at the opened egg

Dear Ann, 
I could say it depends on the egg!
However, I think your question is regarding chicken eggs: in this case, it 
depends from the time of examination of the opened egg. 
I could say to you that just a couple of days after fertilization it is 
possible to see on the surface of the yolk a thin white line which is the 
growing embryo. If you have the capabilities (I mean a good 
stereomicroscope) you can gently break open the shell of the egg, cut with a 
scissor the area of the membrane surrounding the yolk on which this white 
line (the embryo) is present and put it on a slide. Now, put the slide 
under the microscope and it will possible to see the growing chicken!
I made the experiment during my course at the university, and it is not to 
difficult to repeat.(oops, remember to put the yolk in a couple drops of saline 
solution when you take it from the inside of the shell and during the 
cutting; this prevents the yolk membrane from breaking).

I hope this answers to your question, but if you need more 
information do not hesitate to contact MadSci again.

Best regards 
Luca

ps: in different kind of eggs (amphiubia or fishes), the process of 
fertilization is more evident. For instance, the egg rotates so that the darker 
side is on top, and you could see that an egg is fertilized 
just a few  minutes after fertilization.