DRiONKUTISiM IN BUTTKRFLIKS. 925 



ami therefore is most niiiiilar to that of New Engl;iiul, and ctrtaiiily 

 more "continental" than that of Xantneket, this butterfly is single 

 brooded. We have exceedingly tew identical butterflies in Europe and 

 tlie United States, and this apparently is the only one of them that differs 

 in its broods in the two countries ; but there are several of our butterflies 

 which are represented by very closely allied species in Europe, and in half 

 a dozen or more of these we Hnd (|iiit<' similar disparities, all of which are 

 in the same direction. 



The Kuropean tortoise-shell (Aglais nrticae), for example, is generally 

 double brooded; occasionally a triph' brood is mentioned; it is one 

 of the commonest of European butterflies, and reaches from the North 

 Cape to the Mediterranean ; our congeneric species, the American 

 tortoise-shell, is rarely found south of the northernmost parts of the 

 United States, and yet it is triple brooded in all parts of Canada. 

 Even Rrenthis montinus of tlie White jVfonntains is probably double 

 brooded, while all the mountain species of Europe are single brooded. 

 Everes amyntas, again, occurs throughout Europe, with the excep- 

 tion of certain northern and northwestern portions, and is double 

 brooded ; our tailed blue, named for the resemblance to its European con- 

 gener, and by some careless authors considered identical with it, is also a 

 wide-spread insect ; but even in New Elngland, which is at the northern 

 limit of its eastern range, it is triple brooded. The wide-spread Ein'opean 

 blues, Kusticus argus and R. aegon, the silver-studded blue, are usually 

 placed among monogoneutic insects, and the latter certainly has only a 

 single brood in England (where it is the only one of the two found) ; 

 Mever 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 d()ul)le brooded. Our chequered 

 white (Pontia protodice) is triple brooded, and the Ein-opean Bath white 

 (P. daplidice) only double brooded, while our common clouded and 

 orange sulphurs (Eurymus philodiee and E. eurytheme) are triple brooded 

 in the north, perhaps polygoneutic 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 belongs to the southern half 

 of the United States ; the regions are therefore fairly comparable ; yet we 

 find no mention of more than two broods of I. podalirius, while IVIr. 

 Edwards has shown that, even as far north as the Appalachian valleys of 

 AVest Virginia, I. ajax has four and sometimes five generations during the 

 year. 



These cases might perhaps be multiplied, and it should be added that 



