434 PACKARD— ORIGIX OF MARKINGS OF ORGANISMS. [Dec. 2, 



Mr. Pocock has clearly shown that the stripes and bars of zebras 

 and antelopes are in close relation to the environment of these 

 animals, and that the stripes and spots are the result of light and 

 shade. In Nature for August 13, 1903, p. 356, he states that 

 Grant's quagga, which inhabits northeastern Africa, is one of the 

 most completely striped of existing horses. It is, he says, a mass of 

 Stripes from head to tail, from hoof to spine. Intermediate forms 

 connect it with Gray's quagga of Cape Colony, which has pale 

 stripeless limbs, under sides and hind quarters. Now a series of 

 three local races lead from Grant's to Gray's quagga. The tendency 

 of these modifications is to convert a striped and conspicuously 

 parti-colored animal into one which, even at a short distance, must 

 have appeared to be an almost uniform brown, paling into cream 

 on the under side, limbs and back of the haunches. 



A zebra, he says, has such a coloration as to render it invisible 

 under three conditions, i.e., at a distance in the open plain in mid- 

 day, at close quarters in the dusk and on moonlit nights, and in 

 the cover afforded by thickets. The white stripes blend with the 

 shafts of light sifted through the foliage and branches and reflected 

 by the leaves of the trees, and in an uncertain light or at long range 

 they mutually counteract each other and fuse to a uniform gray. 

 Also the alternate arrangement of the black and white bars contri- 

 butes something to the effect produced, by imparting a blurred 

 appearance to the body. 



The asses of northeastern Africa are perfectly adapted to their 

 surroundings in color, and so with the kiang and with Prjevalsky's 

 horse of Central Asia. Their coloration and the resulting protec- 

 tion is explained by Thayer's theory or law of the counteraction of 

 light and shade. Pocock gives a good example. When the Asiatic 

 kiang or the quagga of Cape Colony lies on the ground in the atti- 

 tude characteristic of ungulates, the white on the back of the thighs 

 is brought into line with that of the belly, and a continuous expanse 

 of white, obliterating the shadow, extends all along the under side 

 from the knee to the root of the tail. **In correlation with the 

 adoption of a life in the open, a new method of concealment by 

 means of shadow counteraction was required, and was gradually 

 perfected by the toning down of the stripes on the upper side and 

 the suppression of those on the hind quarters, belly and legs." 

 The same style of markings occurs in many antelopes, gazelles and 

 in the bonte-bok. They need to be thus concealed when lying 



