OF THE AMAZON VALLEY. 



77 



tions being of uncertain character, it seems evident that when the 

 mimicry is complete the indeterminate and intermediate grades of 

 variation have been eliminated by insectivorous animals. The 

 Leptalides have proba bly been subjected to this untiring persecu- 

 tion, even to the verge^of exterffltn lUion, in each ~sTTccessive gene- 

 ratnnr> thrrmfrfrftuj: a ti immense l apse oi' time. By living ill the 

 vicinity of other species free from the same persecution, and being 

 already similar to them in g eneral appearance, this latier Deing 

 inherited through a long line oi ancestors whicn nave been more 

 or ltfdal mil) | Billed to similar conditions, such of their varieties as 



nearest resembled the protected species would escape destruction 

 and thus alone propagate their kind" (jrene yal resem blances 

 between forms may be owing in som e cases to similar habits, or 

 to such general causes as have produced what are called recurrent 

 animal forms ; this general resemblance must exist before the 

 causes which produce "mimetic analogies c an come into play . It 

 must be remarked" that some" of the exact resemblances already 

 alluded to between species of HeJiconince seem not to be owing to 

 the adaptation of one to the other, but rather (as they have a real 

 affimty, the genera to which they belong being throughout very 

 similar in colours and all equally nourishing) to the similar adap- 

 tation of all to the same external local conditions: The check 

 which acts by destroying the indeterminate variations in these 

 cases would not be the same as in Leptalis • . in other respects, 

 however, the same law of nature appears, namely, the selection of 

 one or more distinct varieties by the elimination of mterme^iate 

 gradations. It maybe remarked also that a mimetic species need 

 not al ways be a rare one, although that is very generally the case : 

 it may be prolific, or its persecution may be intermitted, wlien 

 the disguise is complete. The operation of checks successively 

 eliminating variations unfavourable to a species, as thus explained, 

 produces the impression of a stimulus impelling an advance of 

 organization in a special direction. This apparent direct advance 

 suggests the only other scientific explanation that could be sug- 

 gested, viz. the operation of volition or an innate tendency in the 

 creatures themselves to become gradually assimilated to other 

 forms, and thus acquire a disguise favourable to the species. On 

 examination, however, this explanation is found to be untenable, 

 and the appearances which suggest it illusory. Those who earnestly 

 desire a rational explanation must arrive at the conclusion that 

 these apparently miraculous but always beautiful and wonderful 

 mimetic resemblances, like every other kind of adaptation in beings, 

 are brought about by causes similar to those here discussed. 



