1914.] NATURAL SCIENCES OF PHILADELPHIA. 193* 



than the hypothesis of mimicry." He does not venture to suggest 

 this interpretation for the resemblance of L. (B.) archippus to Danaida 

 plezippus; for the great environmental changes endured by both 

 model and mimic in their extensive north and south range make any 

 such suggestion untenable. With regard to the detailed likeness of 

 three forms of Limenitis to three Danaine butterflies in North America, 

 I_ may fairly retaliate on my friend and point out in his own words, 

 mutatis mutandis, that "it seems logical to consider that they are 

 governed by a general law rather than that two of them, but not the 

 third, are caused by similar environmental conditions." I have 

 already many years ago dealt with this supposed interpretation of 

 mimetic resemblance by an appeal to the forces of the environment, 

 and the arguments then brought forward (l5) have, so far as I am 

 aware, never been met. Dr. Skinner does not attempt to meet 

 them, nor does he even allude to the peculiarly strong evidence 

 furnished by these very North American mimics against the hypothe- 

 sis of environmental conditions. Although this evidence is clearly 

 set forth in the paper which Dr. Skinner was discussing (33) , as well 

 as in earlier publications of mine (16, 21), I will repeat the substance 

 of it on the present occasion. 



The three Danaines of North America are modern invaders from 

 the Old World, quite isolated and out of place in the New, while the 

 genus Limenitis is an ancestral element in the North American 

 fauna. My own experience of insect systematics is very limited, 

 and I could not with any confidence or authority attempt to weigh 

 the value of characters which have been described as generic. Know- 

 • ing these limitations only too well, I applied to my friend Dr. K. Jordan, 

 and he, after making fresh investigations into the male genitalia 

 and carefully studying Moore's generic characters, came to the 

 conclusion that the Old World Limnas and Salatura and the New 

 World Anosia and Tasitia could not be sustained as separate genera, 

 but that all four were to be properly included in the single genus 

 Danaida. This genus is nearly related to several much-mimicked 

 groups of Danaince in the Old World, but the two species from which 

 the few American geographical forms have been derived are aliens 

 in the New World. 



Dr. G. B. Longstaff has recently shown that in the gregarious 

 instinct, as manifested by hanging in festoons and clusters from trees, 

 the Old World Danaida gemitia (plexippus) resembles its New World 

 representative D. plexippus (37, pp. 75, 76), in which the same habit 

 has often been observed (6, pp. 730, 734-7) 

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