CONTENTS. 



lact I. 



ON THE SEASONAL DIMORPHISM OF 

 BUTTERFLIES. 



I. 



The Origin and Significance of Seasonal Dimorphism, p. i. 



Historical preliminaries, i. Does not occur in other orders of 

 insects, 4. Beginning of experimental investigation, 5. Lepidop- 

 terous 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. Bryonice, 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 

 Phlaas, 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 dimor- 

 phism in Pierina, 60. The part played by sexual selection, 62. 



