IN BUTTERFLIES 247 



placed among monogoneutic insects, and the latter 

 certainly lias only a single brood in England 

 (where it is the onl}^ one of the two found) ; 

 Meyer Diir is in fact almost the only author who 

 claims these species as digoneutic ; both of them 

 occur in southern Europe ; our Pearl-studded 

 Violet (Rusticus scudderii), closely allied to these 

 and an insect hardly known south of the Canadian 

 border, is double brooded. Our Chequered White 

 (Pontia protodice) is triple brooded, and the Eu- 

 ropean Bath White (P. daplidice) only double 

 brooded, while our common Clouded and Orange 

 Sulphurs (Eurymus philodice and E. eury theme) 

 are triple brooded in the north, perhaps polygoneu- 

 tic farther south, and the closely allied European 

 species only single or double brooded. 



But the most striking example of all will be 

 found in the species of the genus Iphiclides. The 

 European I. podalirius is confined to the Mediter- 

 ranean region, while our Zebra Swallow-tail (I. 

 ajax) belongs to the southern half of the United 

 States ; the regions are therefore fairly compara- 

 ble ; yet we find no mention of more than two 

 broods of I. podalirius, while Mr. Edwards believes 

 that, even as far north as the Appalachian valleys 

 of West Virginia, I. ajax has four and sometimes 

 five generations during the year. 



