Cad99C^21-9 mutant females lay ~50% fewer eggs than wild-type females, with <2% of those eggs producing larvae. These larvae develop into flies that only display defects if they are homozygous mutants. The majority of eggs from Cad99C^21-9 mutant females collapse soon after deposition and even non-collapsed eggs are penetrable to vital dyes (e.g. trypan blue), which do not stain wild-type eggs. These defects suggest that eggshells, which normally restrict permeability and prevent desiccation, are compromised. Eggs from mutant females are also highly intolerant to sodium hydrochlorite. Hydrochlorite treatment of wild-type eggs removes the outer eggshell, the chorion, but leaves the inner eggshell, the vitelline membrane, intact. Disintegration of eggs from Cad99C^21-9 mutant females in hydrochlorite suggests that the vitelline membrane is non-functional.

The vitelline membrane of Cad99C^21-9 mutant follicles varies in thickness and contains numerous holes. This variability in eggshell defects may explain why mutant females are not fully sterile, allow a few embryos to develop.