204 ELEMENTS OF COMPARATIVE ZOOLOGY. 



of no use to the animal. Of these forms there are hun- 

 dreds of species, including the milkweed-butterflies, the 



FIG. 88. A four-legged butterfly (A rgynnis aphrodite), under side shown 



on right. 



painted-beauty, the mourning-cloak (the first butterfly to 

 appear in the spring) , and numbers of others, the catalogue 

 of the names of which would prove 

 dry reading. Only one needs more 

 mention. This is the White Moun- 

 tain butterfly, found only on the tops 

 of the White Mountains, on the tops 

 of the higher peaks of Colorado, and 

 in Labrador. It is supposed that 

 this form is a remnant of an Arctic 

 fauna which extended over the North - 

 ern United States when the country 

 butterfly (CEnete semtdea) . was covered by the great ice-sheet (see 

 Geology), and on the retreat of the glacier these colonies 

 were left stranded upon these points as the only places cold 

 enough for them. 



