16 PROTECTIVE COLORATION 



on the grounds of economical design, that the colouring 

 pigment should not be supplied where protective 

 colour was of no use. Mr. Thayer attempts to prove 

 by some simple experiments that the whiteness of 

 breasts and bellies in these animals has a far deeper 

 significance. At a meeting of the American Ornitho- 

 logists' Union at Cambridge, Mass., on November 10th, 

 1897, he took three sweet potatoes, smeared with a 

 sticky material, and fixed them horizontally on a wire 

 stretched a few inches above a dusty road. Dust from 

 the road was then sprinkled over them, so that they 

 harmonised closely with the background, and the 

 undersides of the two end ones were painted pure 

 white, the paint being blended gradually into the 

 brown on the sides. Viewed at a distance of several 

 yards, the painted potatoes disappeared from, sight, 

 while the unpainted one in the middle was plainly 

 visible in strong relief, appearing many shades darker 

 than the road, which it had been prepared to match. 

 Mr. Thayer next explained that the white paint on the 

 undersides of the potatoes, corresponding to the white 

 underparts of terrestrial birds and mammals, was 

 essential to concealment, though, when viewed close, 

 it made them more conspicuous. The effect of it was 

 to neutralise the shadow, which, unless counteracted 

 in this way, renders the whole object far darker and 

 more conspicuous than it would be if laid close to the 

 ground. To prove this, he proceeded to paint with 

 white the underside of the middle potato, whereupon 

 it immediately disappeared from view of the spectators. 



