Fi<;. 1. Two bird-models, just 

 alike except that the one on the left 

 is counter-shaded, the other not. 

 though covered uniformly with the 

 very' material of its background. 

 This right-hand model, therefore, 

 is ad 'unity as light below* as above. 



Fro. :'!. Bird-models as in Fig. 1, 

 hut with the top-light cot oft' from 

 the oblitorati velv-shaded one. A. 



Via. 2. Ohhteratively-shaded bird-model, 

 is in Fig. 1A, but inverted. (Somewhat 

 <ide-lightod. i 



Fig. 4. Two bird-models as in Fig. 1, but out of doors against 

 bare ground. The one on the right is obliteratively-shaded, the 

 other not. 



Fig. 5. Two bh'd-models precisely as above save that the 

 right hand one is still hetter 'obliterated.' The reader will 

 have to take it on faith that this is a geuuine photograph, and 

 that there is a right-hand model of the same size as the other, 

 unless he can detect its position by its faint visibility in Fig. 4. 



