MIMICRY AND PROTECTIVE RESEMBLANCE. 717 



tiii<i,iiishetl except hy their generic characters." Bates himself was inclined 

 to look u|)()n tiiese not as cases of parastatic mimicry, but as due "to 

 the similar adaptation of all to the same local, prohahly inorganic, condi- 

 tions." 



But this vague explanation has not been satisfactory to others, and 

 Wallace and Meldola, and particularly Fritz Muller, have followed up the 

 matter and shown that, if the mimicked species ])Ossossed the slightest ad- 

 vantage in the mere point of numbers, over the mimicking, this advantage 

 is sufficient to produce the mimicry concerned. It is highly probable, from 

 the experiments of Fritz Muller and the observations of Belt, that the 

 Ileliconoid butterflies are simply distasteful, not poisonous, to insectivorous 

 animals. jMiiller has even figured a considerable number of examples of a 

 single species found by him (in this instance belonging to the Acraeinae, a 

 closely allied nauseous group) in which the wings had evidently been seized 

 by insectivonms birds, having great gaps in their wings, such as a l)ill 

 would make upon them. By such seizures many of the distasteful butter- 

 flies doubtless perish, and ^Nleldola shows very clearly by mathematical 

 analysis that a resemblance between two species so close that the experimen- 

 tal seizures would be divided between them in the ratio of their numbers, 

 gives an advantage decidedly in favor of the scarcer species. Or, as Wal- 

 lace puts it, " if two species, both equally distasteful, closely resemble 

 each other, then the number of individuals sacrificed is divided between 

 them in the proportion of the squares of their respective numbers." If 

 the rarer species is only one-tenth as numerous, it will benefit in the pro- 

 portion of one hundred to one. 



Exactly the same argument can be applied to mimicry between two 

 species neither of which is distasteful, which though less conspicuous are 

 probably more numerous than the other class ; for on the principles that we 

 have laid down, any advantage which one species has over another will be 

 attacked by that other in every possible way ; and if there be elements in 

 the structure or markings wdiich admit of a closer resemblance between the 

 two, and this resemblance will lessen the disadvantage under which the 

 weaker species labors, then in the very nature of things that resemblance must 

 follow, vmless other opposing elements intervene. For here at least the 

 relative abundance of the species concerned is an essential element. It has 

 been thought by some that it was also an essential element of all mimicry, 

 but not only is there no sufficient reason for holding such a view, except- 

 ing in cases like those last quoted, but it has been asserted by no less keen 

 an observer than Fritz Alliller himself, and agreed to by others, that the 

 mimicked species is not always more abundant than its counterfeit ; indeed, 

 the mimicking and the mimicked species have been found to vary in their 

 relative numbers in diflPerent localities, sometimes the one, sometimes the 

 other preponderating. But with regard to mimicry of one distasteful but- 



