PATTERX-BLENDIXG. 



689 



whether the pattern does or does not imitate some part of the 

 animal's surroundings, does not come in : pattern can only be 

 eftective in concealing form by means of mimicry or protective 

 coloi'ation, within its blending distance ; nevertheless, beyond 

 blending distance, as has been seen, pattern still has powei'S of 

 concealing form. It is possible tliat a given pattern may com- 

 bine both these uses. Suppose AE (text-fig. 5, 3) be the extreme 



Text-fififure 5. 



li Ground plan of apparatus for experiments with artificial patterns. 

 2. The same, modified for measuring the blending distance of the patterns of 

 insects' wings. 



'Notes referring to 1 and 2. 

 B=backgrounds made of ' Velox ' paper exposed for varying lengths of time. 

 C & C' = standard candles. 



S & S' = screens of "Bristol" board painted black. 

 obj.=object to be examined. 

 G=glass plate on which is glued a small bead of cork to which the insect 

 is pinned. 

 obs.=observer along the dotted line. 



Using the following distances, au illumination is obtained not unlike that under 

 a hedge on a dull day : — 



C-8 and C'-S'= 6 cm. 



C-obj. and C'-obj. = 40 cm. 



C-C'=40 cm. 



G-B = 20cm. 



distance at which animal A is visible, and AF be the distance at. 

 which the pattern blends, then within the circle FGH the animal 



