On the Seasonal Dimorphism of Butterflies, 63 



IV. 



WHY ALL POLYGONEUTIC SPECIES ARE NOT 



SEASONALLY DIMORPHIC. 



IF we may consider it to be established that 

 seasonal dimorphism is nothing else than the 

 splitting up of a species into two climatic varie- 

 ties in one and the same locality, the further ques- 

 tion at once arises why all polygoneutic species 

 (those which produce more than one annual gene- 

 ration) are not seasonally dimorphic. 



To answer this, it will be necessary to go more 

 deeply into the development of seasonal dimor- 

 phism. This evidently depends upon a peculiar 

 kind of periodic, alternating heredity, which we 

 might be tempted to identify with Darwin's 

 " inheritance at corresponding periods of life." 

 It does not, however, in any way completely 

 agree with this principle, although it presents a 

 great analogy to it and must depend ultimately 

 upon the same cause. The Darwinian " inheri- 

 tance at corresponding periods of life" or, as it 

 is termed by Haeckel, " homochronic heredity" 

 is characterized by the fact that new characters 

 always appear in the individuals at the same stage 



