300 THE PLACE OF MIMICRY 



logical antithesis, and show how solid objects may be 

 made to fade away and become ghost-like, or even 

 invisible, by painting out the shadows. 



Twenty years ago the present writer recognized the 

 importance of the neutralization of shadow by a com- 

 pensating lightness of tint, for the purpose of conceal- 

 ment. But this was only in particular examples, — 

 a certain Geometrid larva, 1 and a chrysalis 2 — and the 

 far-reaching significance of the principle was unseen until 

 A. H. Thayer's great discovery in 1896. 



2. Adjustable Neutralization of Shadow. — An adjust- 

 able form of Thayer's principle was discovered in the 

 chameleon in 1905, when Dr. G. B. Longstaff, Pro- 

 fessor C. V. Boys, and the present writer observed that 

 the illuminated side of the South African Chamaeleo 

 pumilus is darkened, the side in shadow brightened in tint. 



These pigmentary changes neutralize the effects of 

 differing illumination on the two sides, and thus remove 

 the appearance of solidity. 3 



3. The Reduction of Shadow by Attitude. — It has 

 been shown, especially by Dr. G. B. Longstaff, 4 that 

 many butterflies, when they come to rest, turn the axis of 

 the body so that the head is away from the sun. In 

 this position, when the wings are raised, the shadow cast 

 is a mere line and inconspicuous. In other positions the 

 broad wings of a butterfly cast a shadow which, when 

 the axis of the body approaches a right angle to the sun, 

 may be far more conspicuous than the insect itself. 

 Many Satyrine butterflies, when they come to rest, have 

 a pronounced tilt to one side or 'list'. 6 It is probable 

 that this attitude also is valuable in reducing the 



1 Trans. Ent. Soc, Lond., 1887, pp. 292-4. 



1 Trans. Ent. Soc, Lond., 1888, pp. 595-7. 



* An account of the observations was read before The Linnean Society 

 of London, March, 1907. See Zool.Journ. Linn. Soc, vol. xxx, p. 45. 



4 Trans. Ent. Soc, Lond., 1905, p. 135; 1906, p. 97. 



6 See Dr. Longstaffs papers referred to in the above note : also 

 Colonel Bingham's observations on Melanitis quoted on p. 289 of the 

 present volume. Confirmatory observations on the same genus have 

 been made by Mr. E. E. Green (Spolia Zeylanica, vol. ii, Pt. vi, August 

 1904, p. 76), and Mr. T. R. Bell {Ent. Mo. Mag., 1906, p. 126). 



