1864.] 219 



In some few of the above cases it is demonstrable that distinc- 

 tions, such as are generally considered to be of specific value, ex- 

 ist between the forms found in the New and in the Old World. There 

 can also be little doubt that some of the above species have been 

 introduced into North America, but how many and which and where 

 and when, it is generally impossible to say. In regard to the three 

 butterflies asserted by Agassiz to have been introduced, it seems diffi- 

 cult to understand how Vanessa Atalanta, the larva of which feeds on 

 the nettle, or V. cardui, the larva of which feeds on the thistle, could 

 have been imported by human agency into North America. Do men 

 import nettles and thistles ? Even supposing that by some strange 

 chance the eggs of these butterflies reached North America in a livino; 

 state, by what unaccountable concatenation of events did it happen, 

 that they were glued to a growing and living nettle or to a growing 

 and living thistle ? For every breeder of Lepidoptera knows, that it 

 is necessary for the young larvae to have at hand, immediately that 

 they are hatched, a supply of their appropriate food, and that their 

 senses do not enable them to discover that food, even if it lies only a 

 few inches removed from them. Besides, in the case of cardtii, it is 

 necessary to account not only for its introduction by human agency 

 into North America, but for its dispersion by the same agency nearly 

 over the whole globe. As to Antiopa^ the larva of which feeds on 

 poplar-leaves, it may possibly have been introduced in the egg state 

 along with young poplars ; but there is a remarkable fact, not gene- 

 rally known, which makes against such a hypothesis. The chief foreign 

 commerce of the United States even at the present day, and more espe- 

 cially so in former times, is and was wich Kngland. If imported at 

 all, therefore, Antiopa was in all probability imported from England. 

 Now British specimens of this butterfly belong to a distinct variety, 

 with the border of the wings always white and not cream-colored ; and 

 specimens found iu North America and on the Continent of Europe 

 belong to another variety, with the border of the wings always cream- 

 colored and not white. Whence it follows that, if imported at all, 

 Antlnjm in all probability must have been imported, not from Eng- 

 land, but from the Continent of Europe, with which in colonial times 

 this country held no commercial intercourse at all, and in later times 

 comparatively but little. 



