I8S7.] VALUE OF COLOUR AND MARKINGS IN INSECTS. 265 



Just as it was considered to be probable that warning-colours 

 possess a sexual value for the species concerned, so it is pro- 

 bable that the most extreme cases of piotective resemblance also 

 have a similar significance. And in fact, when the most speci- 

 alized instances of the latter kind are detected and are looked at in 

 themselves, they are often seen to possess great beauty, which is 

 absent from the objects they protectively resemble. To take an ex- 

 treme case, the imago of Melanthia albicillata sits upon the upper- 

 side of a leaf in the usual attitude of the Geometers, with its wings 

 extended as if "set," and in such a position its creamy-white ground- 

 colour and dark lines and blotches are very conspicuous, but most 

 forcibly suggest the appearance of bird's excrement which has fallen 

 on to a leaf from a great height, and has therefore been spread out into 

 a large wide patch. But when the insect is detected and examined, it 

 is seen to possess the greatest beauty. Thus Mr. Beauchamp says of 

 it: — " The perfect insect, when bred, seems to me almost without a rival 

 for purity and exquisite delicacy of design. I should doubt whether 

 in the range of natural objects a more beautiful line is to be found 

 than that exquisite cool grey streak upon the rich creamy ground of the 

 fore wing" (Newman's ' British Moths,' p. 156). While entirely 

 agreeing with this description, we should all maintain that it is very 

 far from applying to the object suggested by the Moth, and which 

 it nevertheless resembles very faithfully. And it is probable that 

 in all cases the appearance of a sexually mature insect possesses this 

 among its other meanings. 



Thus I believe that the brightly-coloured underwings of the 

 genus Trypkcena have the same significance as those of Gatocala 

 and of Sphincc and Smerinthus, and the same significance as the 

 bright colours of the uppersides of both wing in most Butterflies, 

 which are also concealed during rest. But in Tryphcena alone 

 among these the bright sexually selected adornment has another 

 meaning as well, and has also come under the independent action of 

 natural selection. For the black and yellow colours of these 

 wings, together with the colours of the undersides of both wings. 

 Been during their rapid vibration in flight, greatly aid the protective 

 resemblance to a dead leaf whirled along by the wind. And yet the 

 very similar arrangement of red and black on the upper and under- 

 sides of the underwings in Gatocala are comparatively non-protective 

 and seem to have almost purely sexual significance. If, therefore, 

 these brilliant colours of Gatocala were modified by natural selection 

 as a response to some unusual activity on the part of its foes, if 

 they became yellow and black instead of red and black, and the 

 habits were correspondingly modified, we should have no reason to 

 conclude that they had in consequence lost their sexual significance, 

 and there is no reason for forming such a conclusion in the case of 

 the genus Trypliana. 



Jenner Weir has suggested that these brightly-coloured under- 

 wings have another protective meaning — that they are conspicuous, 

 and hence form the mark of an enemy, and yet when seized they 

 readily give way without doing harm to the insect. Again, he 



