52 Adaptive Mimicry. 



ON ADAPTIVE MIMICRY. 



Among the curious insects in the case before you are two to which 

 I wish briefly to draw your attention. One of them is the Pliyllium 

 Scythe or Walking Leaf insect; the other is one of the genus 

 Phasmidse or Walking Stick insect. The slightest glance at these 

 two creatures will shew you their very startling resemblance to the 

 vegetable structures from which they derive their popular names. 

 The Phyllium is not only of the exact colour of a leaf, and its 

 wings of an exact leaf shape, but the markings upon the wings 

 resemble in the minutest particulars the midrib and reticulate 

 venation of leaves, and even the legs and antenna; have a sort of 

 foliated appendage, which gives to them the exact appearance of 

 bracts and stipules. The Phasma is in a similar manner elabo- 

 rated into a ludicrously minute imitation of dead twigs ; it is 

 exactly of their colour, and it is dotted, corrugated, articulated, 

 and armed with spines in a way too minute and elaborate to be 

 regarded as accidental ; and further than this its legs which when 

 as in the specimen before us, they are spread out symmetrically, 

 might still pass for the decayed twigs of an endogen with opposite 

 leaves, have a strange power, when the creature is living, of dis- 

 torting themselves in all kinds of unsymmetrical shapes, so as to 

 mimic that irregular disposition of shoots, which Mr. Ruskin has 

 called " The Dryad's wildness ;" and further than this, they are 

 sometimes covered over with foliaceous excrescences so exactly 

 like moss, that nothing short of close observation would convince 

 the spectator that moss was not growing upon them. 



Now the question to which these creatures lead us is one of 

 the most curious, and one of the most suggestive in Natural His- 

 tory ; and it is one which may very likely lead us to the discovery 

 of certain laws. 



It is only recently that the problem, or even the facts which 

 give rise to the problem, have received any special attention. 

 Whenever, among the countless generations which have passed 

 through this world with their eyes closed, any one condescended 

 to notice the curious fact that there is often an astonishingly close 

 physical resemblance between animate and inanimate objects, or 

 of unallied genera of animal objects between themselves, the fact 

 was discussed with the mystical and oracular remark that there 

 was an " analogy" in nature, and that was all which could be said. 

 But within the last twenty years these resemblances have been 

 carefully examined, and are now classed together under the 

 convenient name of " Adaptive Mimicry." 



Although the two insects which I here exhibit are perhaps 



