( Hi ) 



it becurae almost absolutely invisible ; the fore wings being 

 coloured exactly as the stones among which it dropped, and 

 from which it was not easily disturbed. 



In our own country we have conspicuous instances in the 

 genera Catocala, TripJuEua, Heliodcf!, and others. Who has 

 not noticed the deceptive effect of the bright yellow under 

 wings displayed in the short flights of Triplmna pronubd., and 

 the extreme difficulty of following its movements at the 

 moment when these are no longer visible, as it darts down 

 among the grass-roots, where it is often extremely difficult to 

 detect or to dislodge ? If this protective effect of the partial 

 and intermittent display of brilliant colouring is so obvious in 

 relation to the human eye, must it not be at least equally so 

 in relation to the eyes of its more natural enemies, such as 

 birds, and have we not here indicated a new and distinct 

 line of investigation as regards the use and advantage of 

 brilliant colours in many cases which cannot be accounted 

 for by the theory that they are developed for the purpose of 

 warning, or through their aesthetic relation to courtship ? 

 Mr. Poulton has attempted to account for some of these 

 appearances by the idea that birds in pursuit of insects would 

 strike with their beaks at the most conspicuous part, and 

 that the body or more vital part would be thus protected at 

 the expense of a few chips out of the hind wings ; but in some 

 instances, especially in exotic Arctiadm, the body itself is the 

 more conspicuous and ornamented part of the insect. For 

 such cases this theory, however partially true it may be, 

 would fail to account ; moreover, it can scarcely be denied 

 that the insect, if less conspicuous in its flight, would be less 

 likely to attract the attention of the bird, and therefore le?3 

 liable to attack. 



Now in the same way it may possibly be shown, and I 

 merely indicate it for what it is worth as an interesting line 

 of enquiry, that insects with bright metallic markings or 

 colours may derive some advantage from a power of rendering 

 themselves suddenly inconspicuous by altering the angle at 

 "which the light strikes their scales. That tliey are aware of 

 the effect of such changes of position is suggested l)y Mr. 

 Poulton himself when observing that the angle at which the 



