2 14 Annals Entomological Society of America [Vol.11, 



phaline butterfly, rendering it an admirable mimic; whereas 

 D. Berenice, and probably its form strigosa also, have only effected 

 comparatively slight modifications in the mimetic pattern already 

 produced under the influence of plexippus (see pp. 217-18). It is 

 impossible to feel equal confidence in suggesting the line by which 

 the later invasion of the more tropical D. herenice took place; but 

 it is on the whole probable that it too came by way of the north 

 during some temporary period of warmth. It is tolerably certain 

 that it did not invade North America from the south. For 

 although D. herenice and strigosa have produced — as is shown 

 above — far less change in the indigenous N. American fauna 

 than plexippus they have still caused distinct and perfectly effect- 

 ive modifications in a single species; whereas in South America 

 their representatives have not been shown to have had any effect 

 at all.. It is probable that both the American Danaidas as they 

 pressed southward 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 plexippus extending further into the 

 temperate south, just as in the Northern Hemisphere they range 

 further north than those of herenice. We are made to realize 

 the recent date of the invasion of South America when we remem- 

 ber that nowhere else in the world do Danaine butterflies of equal 

 abundance "range through a crow^ded area without producing 

 any effect on any member of the Lepidopterous fauna, or without 

 themselves being affected thereby. "^^ Abundant wide-ranging 

 Danaines in the Old World, even when much smaller and with a 

 less marked appearance, invariably produce some effect, and often 

 themselves exhibit Miillerian resemblances. 



The Evolution of Limenitis (Basilarchia) archippus 

 AS A Mimic of the Invading Danaida plexippus. 



It has already been mentioned that a single species, under- 

 going corresponding modifications, provides a mimic for each of 

 the three Danaine models (including strigosa). We will first 

 consider the well-known beautiful mimic of D. plexippus; for it 

 undoubtedly arose earlier than the others. 



The abundant Limenitis or Basilarchia archippus is closely 

 related to the Palaearctic species of Limenitis, a group which 



" Trans. Ent. Soc. Land., (1908), 452. 



