2i6 Annals Entomological Society of America [Vol. II, 



the most conspicuous feature of arthemis, the broad white band 

 crossing both wings. Save for the traces mentioned below, this 

 marking has disappeared from both surfaces of the hind wing of 

 archippiis, but its black outer border is retained, and, cutting 

 across the radiate pattern formed by the strongly blackened veins, 

 detracts considerably from the mimetic resemblance.^^ On the 

 under surface distinct traces of the white band may commonly be 

 seen along the inner edge of the persistent black border. So far 

 as my experience goes, these traces are only to be found on the 

 upper surface in the form hulsii (Edw.) . The modification of the 

 same marking in the fore wing is more interesting. Here towards 

 the costal margin the black outer border is much expanded, in- 

 vading the white band and cutting off from two to four white 

 spots from its outer part. While the rest of the band disappears 

 except on the costa itself, these black-surrounded white spots now 

 represent the sub-apical pale-spotted black bar of the model. The 

 new marking is larger and more conspicuous on the under surface, 

 corresponding with the strong development of white on this 

 surface of the model. The costal margin of the fore wing of the 

 latter is streaked with long narrow white markings. In corres- 

 pondence with this we find, commonly on the under surface, more 

 rarely on the upper, that the extreme costal end of the white 

 band is retained, often for the full breadth of the marking, form- 

 ing a linear streak. 



'"'In the course of the address on December 31, 1908, I remarked that if we 

 could revisit the earth in a few hundred years, we might expect to find that this 

 black line had disappeared from the hind wing, and the mimetic resemblance 

 correspondingly heightened. At the conclusion, Mr. John H. Cook, of Albany, 

 N. Y., informed me that he had discovered near his home many indviudals in 

 which the black line was wanting from the upper surface. A few daj's later he 

 very kindly sent ine a record of his observations, of which an abstract is printed 

 as a note at the end of this address (see pp. 241—12). The study of Mr. Cook's 

 facts shows that near the city of Albany not only did the stripeless variety occur 

 commonly (1 in 14), during the three seasons in which the observations were 

 conducted, but also transitional forms with more or less broken stripes were far 

 commoner than the normal archippus (18 to 1). The fact that entirely stripe- 

 less individuals were invariably males is contrary to the rule that mimetic 

 resemblance tends to develop more rapidly and fully in the other sex. But in 

 this species I have observed another point in which the female tends to be more 

 ancestral than the male, viz., the more frequent and complete development of 

 the white spot in the cell of the fore-wing upper surface (a common feature of 

 Limcnitis, although now generally absent from L. arthemis). 



Mr. Cook's observations show that a single marking — and one so simple 

 that we might have expected it to act as a unit, so small a traction of the pattern 

 that we could hardly speak of its sudden disappearance as an example of "dis- 

 continuous" evolution — that even this behaves differently on the tAvo surfaces 

 of the wing, while the individuals from which it has disappeared are immensely 

 outnumbered bv those in which it is transitional. 



