xxx Contents. 



IV. 



Why all Polygoneutic Species are not Seasonally Dimorphic, p. 63. 



Homochronic heredity, 63. Caterpillars, pupae and eggs of 

 summer and winter generations of seasonally dimorphic butterflies 

 alike, 64. The law of cyclical heredity, 65. Climatic variation of 

 Pararga sEgeria, 68. Continuous as distinguished from alternating 

 heredity, 68. Return from dimorphism to monomorphism, 70. 

 Seasonally dimorphic species hibernate as pupae, 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 modifi- 

 cation, 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 hetero- 

 genesis, 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, in. Specific constitu- 

 tion an important factor, 112. A "fixed direction of variation," 

 114. 



Appendix /., p. 117. 



Experiments with Araschnia Levana, 117. Experiments with 

 Picrintz, 122. 



Appendix II., p. 126. 



Experiments with Papilio Ajax, 126. Additional experiments 

 with Pap. Ajax, 131. Experiments with Phyciodes Tharos, 140: 

 with Grapta Interrogations , 149. Remarks on the latter, 152. 



Explanation of the Plates, p. 159. 



