_The Origin and Significance of Seasonal Dimorphism_, p. 1.
Historical preliminaries, 1. Does not occur in other orders of insects,
4. Beginning of experimental investigation, 5. Lepidopterous foes, 7.
First experiments with _Araschnia Levana_, 10. Experiments with _Pieris
Napi_, 13. Discussion of results, 17. Origination of _Prorsa_ from
_Levana_, 19. Theoretical considerations, 23. The case of _Papilio
Ajax_, 30. Experiments with _Pieris Napi var. Bryoniæ_, 39. The summer
generations of seasonally dimorphic butterflies the more variable, 42.