egg problem

[Sheldon & Tori]

ok, well about a week ago now one of our females laid her third clutch of eggs......now the clutch before that has been incubating for about 4-5 weeks, and we finally tossed one egg as there didn't appear to be anything inside it when we candled it.....the other one does have the red veins and a small dark spot inside the egg which would be the embryo.......my concern comes from comparing this egg to the first two that hatched as well as the one week old eggs.......in comparison this egg, for the amount of time it's been incubating, contains a very slow growing embryo.......also, the egg is firm but not hard like the first two were.......could this cause the slow development??? nothing has changed with our incubator since the first two have hatched.......if anyone has any info as to why this egg is developing much much slower than the other four that info would be greatly appreciated.

thnx,
sheldon and tori