I can't figure out what I'm doing wrong! I've tried multiple incubations of my leopard geckos eggs and up until around the couple weeks that hatching should occur, the eggs shrivel up and just concave into themselves. They don't even stink or rot, and up until then they appear to be very healthy. I use perlite in an incubator with a thermostat and I keep the substrate moist. Could it be a problem with the geckos themselves being infertile?