182 [J»iy. 



might perhaps be made that the New World forms of Banaida are the 

 more ancestral, and that those of the Old World have been derived 

 from them by migration westward. There is no reason for believing 

 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 evidence. The following comparisons clearly indicate 

 that Banaida is an Old World genus which has invaded America at no 

 very remote period : — (1) the far larger number of the Old World 

 forms and the greater degree of specialization by which some of them 

 are distinguished; (2) the place of Banaida as one out of a number 

 of nearly related genera making up the Banaini, a large and dominant- 

 Old World group, per contra its isolated position in the New World ; 

 (3) the highly developed and complex mimetic relationships of the 

 Old World Danaidas." Again (I.e., p. 162), " There can be little doubt 

 that B. plesrippus invaded America by way of the north, probably 

 following the line of the Aleutian Islands. In North America it 

 possesses an astonishing distribution for a member of so tropical a 

 group, ranging immensely further north than any Danaine in the world. 

 Furthermore B. genutia, the probable representative of its Old Woild 

 ancestor, extends far beyond the tropics into Western and Central 

 China. A study of the distribution of the Asclepiad food-plants on 

 the eastern coast of "Asia might perhaps throw light[on the problem." 

 Further (I.e., p. 163), " It is probable that both the American Danaidas 

 as they pressed southwards were ' held up ' for a considerable time at 

 the northern borders of the Neotropical Region, unable at first to 

 penetrate that crowded area. Finally they burst their way through, 

 and are now abundant throughout all the warmer parts of the region, 

 the forms of ylexippus extending further into the temperate south, 

 just as in the Northern Hemisphere they range further north than 

 those of be re nice. We are made to realize the recent date of the 

 invasion of South America when we remember that nowhere else in 

 the world do Danaine butterflies of equal abundance range through 

 a crowded area without producing any effect on any member of the 

 Lepidopterous fauna, or without themselves being affected thereby," 



That the wandering instinct which in all probability carried the 

 ancestor of B. plexippus in past ages from the Old World to the New 

 still survives in full strength in its present-day descendant, is evident 

 from its well-known migratory habits in North America, well summar- 

 ized by the late Mr. J. W. Tutt in his admirable series of papers 

 " Migration and Dispersal of Insects " (Ent. Record, 1900, pp. 182-6, 



