ALL DANAIDAS CLOSELY EELATED 159 



genus,' plexippus also must be included. I do not think you 

 need hesitate thus to simplify the classification of these 

 insects.' 



I have no hesitation in accepting this advice, 

 and in fusing all the four genera created by 

 Moore into the single genus Danaida. Within 

 this genus it has been made evident that the 

 group of forms ranged around Danaida plexippus 

 is the New World representative and close ally 

 of the group of D. genutia ; while that of D. 

 berenice is similarly representative of the group of 

 B. chrysippm. It is interesting to note that both 

 the American Danaidas have become much larger 

 than the corresponding Old World species, and 

 that the most northern forms are larger than the 

 southern in both hemispheres — the probable 

 result of a slower metamorphosis in a more 

 temperate climate. 



EVIDENCE THAT DANAIDA IS AN OLD WOELD 

 GENUS THAT HAS INVADED THE NEW 



The suggestion might perhaps be made that 

 the New World forms of Danaida are the more 

 ancestral, and that those of the Old World have 

 been- derived from them by migration westward. 

 There is no reason for concluding that the 

 Danaidas of either geographical area possess a 

 more primitive structure than those of the other ; 

 we are therefore driven to consult other lines of 



^ Drt Jordan's opinion that these three genera should be united 

 is quoted in Toxins. Ent. Soc. Land., 1908, 450. 



