On the Seasonal Dimorphism of Butterflies. 9 1 



Distinctly defined specific characters, are well 

 known not to occur generally, and it would 

 therefore be erroneous to attach but little value 

 to the differences in seasonal dimorphism because 

 these chiefly consist in the colouring and marking 

 of the wings. The question here under consider- 

 ation is not whether two animal forms have the 

 value of species or of mere varieties a question 

 which can never be decided, since the reply always 

 depends upon individual opinion of the value of 

 the distinctions in question, and the idea of both 

 species and varieties is moreover purely conven- 

 tional. The question is, rather, whether the distin- 

 guishing characters possess an equal constancy 

 that is, whether they are transmitted with the same 

 force and accuracy to all individuals ; and whether 

 they occur, therefore, in such a manner that they 

 can be practically employed as specific characters. 

 With respect to this, it cannot be doubtful for a 

 moment that the colouring and marking of a but- 

 terfly possess exactly the same value as the constant 

 characters in any other group of animals, such as 

 the palate-folds in mice, the structure of the 

 teeth in mammals, the number and form of the 

 wing and tail feathers in birds, &c. We have but 

 to remember with what wonderful constancy often 

 the most minute details of marking are trans- 

 mitted in butterflies. The systematist frequently 

 distinguishes between two nearly allied species, as 

 for instance in the Lyccenidce, chiefly by the posi- 



