On the Seasonal Dimorphism of Butterflies, 3 i 



emerging in the following spring, and then always 

 in the winter form. Thus, Edwards states that 

 out of fifty chrysalides of the second generation, 

 which had pupated at the end of June, forty-five 

 Marcellus butterflies appeared after fourteen days, 

 whilst five pupae emerged in April of the fol- 

 lowing year, and then as Telamonides. 



The explanation of these facts is easily afforded 

 by the foregoing theory. According to this, both 

 the winter forms must be regarded as primary, 

 and the Marcellus form as secondary. But this 

 last is not yet so firmly established as Prorsa, in 

 which reversion of the summer generations to the 

 Levana form only occurs through special external 

 influences ; whilst in the case of Ajax some in- 

 dividuals are to be found in every generation, the 

 tendency of which to revert is still so strong that 

 even the greatest summer heat is unable to cause 

 them to diverge from their original inherited 

 direction of development, or to accelerate their 

 emergence and compel them to assume the Mar- 

 cellus form. It is here beyond a doubt that it is 

 not different external influences, but internal 

 causes only, which maintain the old hereditary 

 tendency, for all the larvae and pupse of many 

 different broods were simultaneously exposed to 

 the same external influences. But, at the same 

 time, it is evident that these facts are not opposed 

 to the present theory ; on the contrary, they con- 

 firm it, inasmuch as they are readily explained on 



