Hatch finished - failed eggs dissected - looking for reasons why

[envirobg]

This is a follow-on from my earlier thread "Problems and questions with first hatch"

In sumary I put nine eggs in.
I didnt candle - I don't know exactly how .. So not sure all were fertile

On day 20 one chick hatched ... I open bator and took him out. still alive and kicking
Same day second chick pipped and zipped his shell but never came out.
On day 21 I took out dead chick and could hear a third chirping
On day 23 no more activity ...I stopped bator , took out eggs and disected then.

4 eggs had yellow yokes ... No development ?
1 egg had black yoke
1 egg was bad and exploded when I broke it.
1 egg ( egg mentioned I heard on day 21 above) had a fully developed chick and had pipped
on the underside but did not zip. He seems fully developed and did not appear shrink wrapped.

I'm wondering if people might give me opinions on what cause these eggs to fail.

Also do infertile eggs loose weight in incubator ?
I forgot to weigh eggs at start but weighed the after week one and after week two.
Some of the yellow yoke eggs lost 6% in this period.

Many thanks

 

[ChickenCanoe]

All eggs will lose weight. Up till 18 days they should lose 12% so your humidity may have been too high.
It's a lot of info but this chart might help more than anyone's input.
http://www.natureform.com/kb/index.php?article=1011

 

[envirobg]

Thanks ChickenCanoe,
Remember this period was for one week (the seond week) not the full 21 days ... So I assumed they would loose maybe 6% on the first week as well and may be more on the 3rd week.

I suppose what I am saying is that as saw they had lost weight I assumed they were fertile and were growing.
Does a yellow yoke (after 21 days) mean it was infertile and do infertile eggs still loose weight ?