204 HUXLEY AND NATURAL SELECTION 



of the leaf, light may pass through a curved and often 

 a semi-circular slit-like window. Such curved cracks are 

 extremely common in old weather-beaten dead leaves. 

 They are probably produced by drying and shrinkage 

 after much wetting and some decay. 



On April 23, 1903, I had the opportunity of testing 

 how far the whole attitude of Polygouia C-album, during 

 profound repose, is consistent with the interpretation 

 suggested above. By a curious coincidence, I had been 

 speaking of the differences between temporary and pro- 

 longed resting attitudes in butterflies, at the meeting of 

 the Entomological Society of France on the evening 

 of April 22, and the very next morning saw for the first 

 time in my life the position of this species during complete 

 repose. The day was excessively cold for this time of the 

 year, and the butterfly was hanging perfectly torpid from 

 the horizontal rail of a wood fence in a street at Passy. 

 Several excellent but very small photographs were taken 

 with my daughter's camera : enlargements have been 

 made, and from these the actual specimen has been set 

 and photographs taken of the natural size. 1 These show 

 that the two anterior wings are held so far forward that 

 a deep wedge-shaped notch appears between them and 

 the hind-wings. On each side of this notch the well- 

 known ragged outline of the wings is extremely distinct. 

 The two posterior pairs of legs by which the butterfly 

 clings to the supporting surface are light-brown in colour 

 and unexpectedly conspicuous. The antennae are con- 

 cealed, and the contour of the head does not break that 

 of the costal margin of the anterior wings so as to interfere 

 in any way with the general effect. The whole appearance 

 is consistent with a single interpretation — concealment 

 effected by resemblance to a weather-beaten fragment 

 of dead leaf, deeply notched and ragged, and hanging by 

 two denuded fibro-vascular ' veins ' standing out far beyond 

 one of the edges. The kind of injury suggested by the 

 ' comma ' only adds another convincing detail to a perfectly 

 harmonious cryptic effect. 



It is interesting to compare this mode of concealment 

 1 Exhibited upon the screen. 



