When the iridescent-costumed animal is still, the slightest change of light upon 

 him will cause a bewildering play and movement of his colors; and when he 

 moves, his colors' varied dancings are far more apt to belie and perhaps con- 

 ceal his motions, than to accentuate them. For instance, the gleaming high- 

 light, the central point of shine on the back or side of an iridescent bird, say 

 a turkey gobbler or a peacock, may move backward on the bird's surface while 

 the bird himself moves forward, so that to the observer's eye it seems to be 

 standing still, and since by virtue of its very brightness this spot will hold the 

 attention, it must often happen that the bird seems to be motionless when 

 he is in fact slipping away. It may be objected, and truly, that such decep- 

 tions as this are of only momentary effect. But the reader should realize, 

 in this case and in all kindred ones, that it is just these tiny, trivial seeming 

 moments that often tip the balance toward escape or capture, toward life or 

 death, in an animal's career. The predatory animals and the animals they 

 prey upon have been developed together, and their powers of capture and 

 escape interadjusted to a nicety. The business of the one kind is to hunt 

 and kill, of the other to evade their clutches; both are Nature's children, both 

 are favored by her, and both' grow up and survive as races in the same woods 

 and fields. On the one hand, Nature fits the hunters to kill enough of the 

 weaker animals to keep themselves alive as a race, on the other she fits the 

 weaker ones to escape so often that their race too shall not succumb, that 

 the hunting race cannot overstep its boundaries ; that, in short, the even bal- ■ 

 ance between hunters and hunted shall in the long run be maintained. On 

 the hypothesis of Natural Selection, we must suppose that there is the closest 

 rivalry between the two opposed developments ; like the continual competition 

 which has long been going on in man's domain, between the development of 

 armor and the development of explosives and projectiles. To their rivalry 

 alone is due the wonderful and ever-increasing excellence of both develop- 

 ments, in the case of the human instruments of destruction and defense; and 

 just such, if we believe in Natural Selection — or, in fact, on any hj^othesis 

 that recognizes adaptation as something more than accidental — must we sup- 



