Cases of Haldane's Rule for inviability in toads.

��Unconfirmed cases�� are those crosses in which one sex is present while the other is absent, but sample sizes are too low to evaluate statistically. ��Quantitative cases�� are crosses that showed a statistical bias in the number of individuals for a particular sex. ��Complete cases�� are those crosses that resulted in zero offspring of one sex and more than six offspring of the opposite sex. The total number of crosses used to analyze the operation of Haldane's rule was 93 (65 cases in which females are the affected sex and 28 in which males are the affected sex).