'God did it with magic, end of story' is probably not the right answer.<quoted text>
Who laid the egg? and at what point did the holes end up in the shell for the oxygen?
It would perhaps be a bit more instructive to compare the genes responsible for permeable amphibian egg sacks to those for impermeable egg shells with holes. I am not equipped for this level of reseach and neither are you. How much Calcium is in an amphibian egg sack anyway?