ADAPTIVE COLORATION 2 29 



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 external appearance." For, as Poulton 

 points out, the alertness of a beetle which mimics a wasp, 

 implies appropriate changes in the nervous and muscular sys- 

 tems. In its intent, however, Wallace's rule holds good, and 

 by disregarding it some writers strain the theory of mimicry 

 beyond 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 like- 

 ness 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 be- 

 tween two genera of Heliconiidse or between the chrysomelid 

 genera Leina and Diabrotica. The nearer two species are 

 related to each other, the more probable 

 it becomes that their similarity is due 

 not to mimicry but to their common 

 ancestry. 



On the other hand, the resemblance 

 frequently occurs between species of such 



. cr . A locustid, Myrme- 



different orders that it cannot be attnb- co ph ana faiiax, which 



uted to affinity. Illustrations of this are resembles f ant - Twice 



J natural length. From 



the mimicry of the honey bee by the BRUNNER VON WAT- 

 drone fly, and the many other instances in 

 which stinging Hymenoptera are counterfeited by harmless 

 flies or beetles. A locustid of the Soudan resembles an ant 

 (Fig. 245), and the resemblance, by the way, is obtained in a 

 most remarkable manner. Upon the stout body of this or- 

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



