full side-contour against an unfavorable background, especially if its mark- 

 ings do not clearly show. For, we repeat, these markings, though pictures 

 of comparatively near details, are still pictures, in the sense of representations 

 of patterns beyond the animal, and not exact facsimiles of the surface-mark- 

 ings of any object. It must be remembered that a large class of the enemies 

 of such a bird, namely, the terrestrial carnivorous quadrupeds, which ap- 

 proach it on its own level, usually see it against a more distant background 

 than do we tall bipeds who look down upon it. In accordance with this fact, 

 it will be found that there is more than one would at first suppose of the ele- 

 ment of distant background picturing in the side-markings of most terrestrial 

 birds. But even if it is merely the thickness of an animal's counter-shaded 

 body which habitually intervenes between its exposed side and the seeming 

 background pictured by its markings, the principle is not mimetic, according 

 to our nomenclature. To complete the statement, we must add that no ani- 

 mal bearing a full obliterative shading can, under normal conditions, pass for 

 some other kind of solid object, but must appear either as a flat plane, or as 

 merged into the scene behind it, whether near or far, — the smallest possible 

 extent of its apparent retrocession being a distance corresponding to the thick- 

 ness of its own body; but in order that it may completely undergo such 'ob- 

 literation' the pattern which it wears must always be smaller than the actual 

 pattern of its background. 



Figs. 27-30 need no explaining in the text. 



37 



