Part I On the Seasonal Dimorphism of Butterflies
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.
II.
Seasonal Dimorphism and Climatic Variation, p. 45.
Distinction between climatic and local varieties, 45. The case of Euchloe Belia and its varieties, 47. The case of Polyommatus Phlæas, 49. The case of Plebeius Agestis, 50.
III.
Nature of the Causes producing Climatic Varieties, p. 52.
Seasonal dimorphism of the same nature as climatic variation, 52. How does climatic change influence the markings of a butterfly? 52. The cause of this to be found in temperature, 54. Part played by the organism itself, 58. Analogous seasonal dimorphism in Pierinæ, 60. The part played by sexual selection, 62.
IV.
Why all Polygoneutic Species are not Seasonally Dimorphic, p. 63.
Homochronic heredity, 63. Caterpillars, pupæ and eggs of summer and winter generations of seasonally dimorphic butterflies alike, 64. The law of cyclical heredity, 65. Climatic variation of Pararga Ægeria, 68. Continuous as distinguished from alternating heredity, 68. Return from dimorphism to monomorphism, 70. Seasonally dimorphic species hibernate as pupæ, 71. Retrogressive disturbance of winter generations, 72. The case of Plebeius Amyntas, 75.
V.
On Alternation of Generations, p. 80.
Haeckel’s classification of the phenomena, 80. Proposed modification, 81. Derivation of metagenesis from metamorphosis, 82. Primary and secondary metagenesis, 84. Seasonal dimorphism related to heterogenesis, 86. Heterogenesis and adaptation, 89. Differences between seasonal dimorphism and other cases of heterogenesis, 89. The case of Leptodora Hyalina, 93.
VI.
General Conclusions, p. 100.
Species produced by direct action of environment, 100. The transforming influences of climate, 103. The origin of variability, 107. The influence of isolation, 109. Cyclically acting causes of change produce cyclically recurring changes, 111. Specific constitution an important factor, 112. A “fixed direction of variation,” 114.
Appendix I., p. 117.
Experiments with Araschnia Levana, 117. Experiments with Pierinæ, 122.
Appendix II., p. 126.
Experiments with Papilio Ajax, 126. Additional experiments with Pap. Ajax, 131. Experiments with Phyciodes Tharos, 140: with Grapta Interrogationis, 149. Remarks on the latter, 152.
Explanation of the Plates, p. 159.