ward, the bold transverse bars, being extended across the line of motion, make 

 the movement of the tail conspicuous, relatively to that of the longitudinally 

 streaked or finely speckled body ahead of it. By this device the bird's chances 

 of escape from an enemy are decidedly increased. For the predator's eye is 

 drawn to marks back of the vital part of his intended victim, which is at the 

 same time rapidly moving forward, hence there is likelihood that he will miss 

 his aim by striking behind, perhaps capturing a tail from which the bird tears 

 itself free and escapes. 



The practical force of this law of the comparative conspicuousness of 

 transverse and inconspicuousness of lengthwise marks in motion can easily 

 be demonstrated. One should take a ribbon of cloth, or a slender board, 

 and mark half of it (one end) straightly and evenly with lengthwise stripes of 

 several colors (or simple black and white), and the other half with the same 

 colors in transverse bars. Then if the stick or ribbon is drawn smoothly 

 across an opening, through which alone it is seen, its motion will be grossly 

 visible while the banded part is passing, and almost invisible during the passage 

 of the striped half. Motion merely tends to convert lengthwise marks into 

 lines, which have little or no visible activity, and may often seem to be passive 

 streaks on the background of the thing that bears them. Hence the elusive- 

 ness of gliding striped snakes among sticks and grasses, in remarkable contrast 

 to the conspicuous movements of banded snakes. (Of this the reader is to 

 hear more in a later chapter.) A practical artificial test of this effect even 

 simpler than that above described, and almost equally effective, can be made 

 with a white string, part of which has been marked with dark spots, and part 

 left blank. The alternate light and dark spots are equivalent to the bands, 

 and the unspotted part is equivalent to the streaks (being, in fact, a single, 

 perfect streak). But the whole proposition is pretty much self-evident, and 

 scarcely calls for demonstration. As a factor in the protection of birds and 

 other animals the principle is of decided importance, and it very likely plays 

 a much larger part than we yet know. Among snakes and long-tailed birds, 

 particularly pheasants, its use is certainly both general and pronounced. On 



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