of these larger leaf -moths are hardly to be matched in any other branch of the 

 animal kingdom. (See Fig. 133, B, B and C.) 



In the disguisement of butterflies and moths alike there is one seeming 

 flaw, perhaps supported by insuperable organic limitations. That is, their 

 usually perfect dual symmetry in all details of pattern.* The markings of the 

 two wings on one side are as a rule almost exactly duplicated by those of the 

 opposite pair; and such duality and repetition tends to attract the notice of 

 the seeking eye. Of course it is only when the wings are outspread that this 

 duality becomes in any degree a defect. Upfolded, a butterfly, though still 

 dually symmetrical in fact, is not so in effect, any more than a bird or mammal 

 is, for only one side can be seen at a time. Indeed, even when a moth or 

 butterfly is outspread, its duality is usually frustrated in effect simply by the 

 irregularity of its position relative to the eye. Birds, on the other hand, which 

 tip and twist their heads, peeping and prying, with eyes in all sorts of irregular 

 positions, must often see moths and butterflies symmetrical where we should 

 not. Among moths this duality is often masked by sharp stripes which cross 

 continuously the whole extent of the expanded or triangularly part-folded 

 wings. Such a stripe, with its two sides unlike, 'cuts' the moth into two 

 very unequal parts, dividing it across the direction of its dual symmetry, while 

 the 'secant' itself pictures some landscape-detail — & stick or bark-ridge or 

 leaf -stem, with a shadow on one side of it. Sometimes a marking of this kind 

 cuts the fore-wings (or, more rarely, the hind wings) longitudinally, either 

 crossing or skipping the intervening body; but as a rule it is diagonal, forming 

 one clearly continuous (though not always straight) 'secant' stripe when the 

 wings are folded in the normal resting-posture. There are many wearers 

 and manifold variations of this marking, which, though often so very simple, 

 is one of the most potent of the fundamentally 'obliterative' details of lepidop- 

 terous pattern. 



It takes the eye of an artist, as we have said before, to recognize the wonder- 



* Of course, both sides of the insect need, in the long run, just the same pattern; while a score 

 of circumstances tend to rescue it from betraying its actual duality. — A. H. T. 



239 



