ADAPTIVE COLORATION 



205 



The female of Papilio cenea, indeed, occurs (as was just mentioned) 

 under three varieties, which mimic respectively three entirely dis- 

 similar species of Danais, and none of the females are anything like their 

 male in coloration. 



The generally accepted explanation for these remarkable but numer- 

 ous cases in which the female alone is mimetic, is that the female,- bur- 

 dened with eggs and consequently sluggish in flight and much exposed 

 to attack, is benefited by imitating a species which is immune; while 

 the male has had no such incentive so to speak to become mimetic. 

 Of course, there has been no conscious evolution of mimicry. 



Wallace's fifth stipulation is important, but should read this way: 

 "The imitation, however minute, is but external and visible usually, 

 and never extends to internal characters which do not affect the exter- 

 nal appearance." For, as Poulton points out, the alertness of a beetle 

 which mimics a wasp, implies appropriate changes in the nervous and 

 muscular systems. In its intent, however, Wallace's rule holds good, 

 and by disregarding it some writers strain the theory of mimicry be- 

 yond reasonable limits. Some have said, for example, 

 that the resemblance between caddis flies and moths 

 is mimicry; when the fact is that this resemblance 

 is not merely superficial but is deep-seated; the entire 

 organization of Trichoptera shows that they are 

 closely related to Lepidoptera. This likeness 

 expresses, then, not mimicry, but affinity and 

 parallel development. The same objection applies 

 to the assumed cases of mimicry within the limits 

 of a single family, as between two genera of Heli- 

 coniidae or between the chrysomelid genera Lema 

 and Diabrotica. The more nearly two species are related to each other, 

 the more probable it becomes that their similarity is due not to mimi- 

 cry but to their common ancestry. 



On the other hand, the resemblance frequently occurs between 

 species of such different orders that it cannot be attributed to affinity. 

 Illustrations of this are the mimicry of the honey bee by the drone fly, 

 and the many other instances in which, stinging Hymenoptera are 

 counterfeited by harmless flies or beetles. A tettigoniid of the Sudan 

 resembles an ant (Fig. 249), and the resemblance, by the way, is ob- 

 tained in a most remarkable manner. Upon the stout body of this 

 orthopteron the abdomen of an ant is delineated in black, the rest of 

 the body being light in color and inconspicuous by contrast with the 



FIG. 24 9. A 

 tettigoniid, Myrme- 

 cophana fa II ax, 

 which resembles an 

 ant. Twice natural 

 length. From 

 B RUNNER VON 

 WATTENWYL. 



