Abstract
1. The observations of Hamling and Harris seemed to show that although the factor for melanism inHemerophila abruptaria is dominant to that for the type form, yet the ratio of type to melanic is not always a simple Mendelian phenomenon. 2. Nevertheless, a repetition of their work shows a ratio of type to melanic in the first broods, very closely approaching the equality expected. 3. In another set of matings, which produced the second broods, the mortality for various reasons was over 75%. In this case, as in the experiments of Hamling and Harris, the ratio was nearer 3 melanic to 1 type than equality. This suggests that there may have been a selective mortality in favour of the melanic insects, which disturbs the normal ratio. 4. That a certain constitutional strength seems to accompany many melanic forms has been pointed out by other authors, and attention is here drawn to the fact that this would account more easily than other hypothesis for the rapid replacement of type by melanic varieties.
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